As opposed to conventional electrochemical sensors, nanomaterials-based sensors are active and effective in their action
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N A N O M AT E R I A L S BASED ELECTROCHEMICAL SENSORS: PROPERTIES, A P P L I C AT I O N S , A N D R E C E N T A D VA N C E S
N A N O M AT E R I A L S BASED ELECTROCHEMICAL SENSORS: PROPERTIES, A P P L I C AT I O N S , A N D R E C E N T A D VA N C E S Edited by AWAIS AHMAD Department of Chemistry, The University of Lahore, Lahore, Pakistan
FRANCIS VERPOORT State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan, P.R. China; National Research Tomsk Polytechnic University, Tomsk, Russian Federation
ANISH KHAN Chemistry Department, Center of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah, Saudi Arabia; Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia
SHAFAQAT ALI Department of Environmental Sciences and Engineering, Government College University Faisalabad, Faisalabad, Pakistan
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Contents List of contributors .......................................................................................xi
1 Introduction: nanomaterials and electrochemical sensors.......................1 Naqeebullah, Awais Ahmad, Hina Tabassum, Talha Mumtaz, Muhammad Pervaiz, Zohaib Saeed, Umer Younas, Asma Zaidi, Rana Rashad Mahmood Khan, Ayoub Rashid and Ahmad Adnan 1.1 Introduction .......................................................................................... 1 1.2 Voltammetric methods ........................................................................ 7 1.3 Cyclic voltammetry .............................................................................. 8 1.4 Differential pulse voltammetry............................................................ 9 1.5 Square wave voltammetry ................................................................ 10 1.6 Electrochemical impedance spectroscopy ....................................... 10 1.7 Electronic tongue: concepts, principles, and applications .............. 11 1.8 Future prospects................................................................................. 15 1.9 Conclusion .......................................................................................... 15 References ................................................................................................. 16
2 Nanomaterial properties and applications..................................................19 Areeba Saifullah, Arsh E Noor, Shoaib Hasnain, Farwa Batool Shamsi, Sadia Aslam, Shamim Ramzan and Abdur Rahim 2.1 Nanomaterials .................................................................................... 19 2.2 History ................................................................................................. 21 2.3 Nanomaterial type.............................................................................. 22 2.4 Metal nanomaterials .......................................................................... 25 2.5 Metal oxide nanomaterials ................................................................ 26 2.6 Properties of nanomaterials .............................................................. 27 2.7 Application.......................................................................................... 29 2.8 Conclusion .......................................................................................... 31 References ................................................................................................. 31
3 Analytical techniques for nanomaterials.....................................................37 Muhammad Yahya Tahir and Shafaqat Ali 3.1 Introduction ........................................................................................ 37 v
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3.2 Different analytical techniques for nanomaterials........................... 39 3.3 Conclusion .......................................................................................... 50 References ................................................................................................. 50
4 Toxicity of nanomaterials.................................................................................53 Kumar Rajendran, Latha Pujari, Madhuri Krishnamoorthy, Divya Dharmaraj, Kannan Karuppiah and Kannapiran Ethiraj 4.1 Introduction ........................................................................................ 53 4.2 Toxic effects of nanomaterials on humans and animals ................ 54 4.3 Toxic effects of nanomaterials on microorganisms ........................ 58 4.4 Toxic effects of nanoparticles on plants........................................... 59 4.5 Assessment of toxicity of nanomaterials ......................................... 61 4.6 Conclusion and future prospects ...................................................... 67 Acknowledgements .................................................................................. 67 References ................................................................................................. 68
5 Electrochemical sensors and their types.....................................................77 Arsh E Noor, Ikram Ahmad, Athar Rasheed, Shamim Ramzan, Abdur Rahim, Anish Khan and Muhammad Yahya Tahir 5.1 Introduction ........................................................................................ 77 5.2 Conclusion .......................................................................................... 85 References ................................................................................................. 85
6 Electrochemical sensors and nanotechnology...........................................89 Safia Khan, Mariam Khan, Naveed Kausar Janjua and Syed Sakhawat Shah Objectives .................................................................................................. 89 6.1 Introduction ........................................................................................ 89 6.2 Nanotechnology ................................................................................. 91 6.3 Electrochemical sensors .................................................................... 94 6.4 Nanosensing technology ................................................................... 95 6.5 Challenges .......................................................................................... 96 6.6 Future perspective.............................................................................. 97 6.7 Conclusion .......................................................................................... 98 References ................................................................................................. 98
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7 Sensing methodology ......................................................................................103 P. Shenbaga Velu, N.J. Vignesh, J. Senthil Kumar and Rajesh Jesudoss Hynes Navasingh 7.1 Introduction ...................................................................................... 103 7.2 Sensing methodology...................................................................... 106 7.3 Nanomaterial-based electrochemical biosensors for biomedical applications ................................................................... 107 7.4 Nanomaterials-based electrochemical biosensors for tumor cell diagnosis .................................................................................... 111 7.5 Nanomaterial-based electrochemical sensors for environmental applications ............................................................. 114 7.6 Conclusions ...................................................................................... 118 Acknowledgements ................................................................................ 119 References ............................................................................................... 119
8 Fabrication of biosensors...............................................................................123 R. Ruban, H. Mohit, M.R. Sanjay, G. Hemath Kumar, Suchart Siengchin and N.S. Suresh 8.1 Introduction to biosensors .............................................................. 123 8.2 Components of biosensors ............................................................. 125 8.3 Biosensor transducers ..................................................................... 125 8.4 Electrochemical biosensor............................................................... 129 8.5 Electrode fabrication technologies ................................................. 133 8.6 Direct growth .................................................................................... 145 8.7 Self-powered implantable biosensor.............................................. 146 8.8 Conclusion and outlook ................................................................... 148 References ............................................................................................... 149
9 Metal oxide and their sensing applications .............................................155 Shamim Ramzan, Abdur Rahim, Awais Ahmad and Mabkhoot Alsaiari 9.1 Introduction ...................................................................................... 155 9.2 Overview of metal oxides for different applications ..................... 157 9.3 Different sensing techniques for sensing applications ................. 164 9.4 Electrochemical sensing based on metal oxides........................... 167 9.5 Colorimetric and fluorometric sensing based on metal oxides ................................................................................................ 168
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9.6 Fluorescent and chemiluminescent sensing based on metal oxides ................................................................................................ 169 9.7 Issues and drawbacks ...................................................................... 170 9.8 Conclusion and Future prospective ................................................ 171 References ............................................................................................... 171
10 RFID sensors based on nanomaterials .....................................................177 J. Senthil Kumar, Rajesh Jesudoss Hynes Navasingh, P. Shenbaga Velu and J. Angela Jennifa Sujana 10.1 Introduction ...................................................................................177 10.2 Nanomaterials for RFID sensors ..................................................181 10.3 Inkjet printing of nanomaterial-based RFID sensors ..................183 10.4 Applications of RFID nanosensors ...............................................185 10.5 Conclusion .....................................................................................187 Acknowledgment .................................................................................. 188 References ............................................................................................. 188
11 Biological and biomedical applications of electrochemical sensors ..............................................................................................................191 Mushkbar Zahara, Soumaila Shaheen, Zohaib Saeed, Awais Ahmad, Anish Khan, Muhammad Pervaiz, Umer Younas, Syed Majid Bukhari, Rana Rashad Mahmood Khan, Ayoub Rashid, Ahmad Adnan, Abdur Rahim and Shamim Ramzan 11.1 Introduction ...................................................................................191 11.2 Components of electrochemical sensors ....................................193 11.3 Working principle of electrochemical sensors ............................195 11.4 Fabrication of nanomaterial-based electrochemical sensor ......197 11.5 Biological and biomedical applications of electrochemical sensors ...........................................................................................201 11.6 Conclusion .....................................................................................207 References ............................................................................................. 208
12 Nanomaterial-based electrochemical sensing of histamine..............211 Safia Khan, Mariam Khan, Arsh E Noor, Anish Khan and Awais Ahmad Objectives.............................................................................................. 211 12.1 Introduction ...................................................................................211
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12.2 Identification of histamine ............................................................214 12.3 Materials utilized in histamine electrochemical sensing ...........................................................................................218 12.4 Nanomaterials for histamine sensing..........................................220 12.5 Conclusion .....................................................................................223 References ............................................................................................. 223
13 Nanostructured complexes of gold(I) in sensing...................................227 Safia Khan, Mariam Khan, Awais Ahmad, Ifzan Arshad, Hu Li and Shern-long Lee Objectives.............................................................................................. 227 13.1 Introduction ...................................................................................227 13.2 Synthesis of AuNPs.......................................................................228 13.3 Gold nanoparticles with different morphologies........................230 13.4 Applications ...................................................................................236 13.5 Future perspectives .......................................................................239 13.6 Conclusion .....................................................................................239 References ............................................................................................. 240
14 Analyte sensing by self-healing materials..............................................245 M. Ramesh, L. Rajeshkumar, D. Balaji and S. Sivalingam 14.1 Introduction ...................................................................................245 14.2 Self-healing materials for analyte sensing ..................................248 14.3 Conclusion .....................................................................................261 References ............................................................................................. 262
15 Graphene-based electrochemical sensors ..............................................269 Kiran Aftab and Ayesha Riaz 15.1 Prefaces..........................................................................................269 15.2 Synthesis of graphene oxide metal oxide electrochemical sensors ...........................................................................................270 15.3 Properties of GO MO nanocomposite........................................281 15.4 Applications ...................................................................................285 15.5 Conclusions ...................................................................................292 References ............................................................................................. 292
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16 Polymer-based self-healable materials for energy storage................295 M. Ramesh and A. Saravanakumar 16.1 Introduction ...................................................................................295 16.2 Conductive polymeric materials ..................................................296 16.3 Self-healing material .....................................................................300 16.4 Self-healing materials for energy storage ...................................301 16.5 Conclusion .....................................................................................305 References ............................................................................................. 306 Index........................................................................................................... 311
List of contributors Ahmad Adnan Department of Chemistry, Government College University Lahore, Lahore, Pakistan Kiran Aftab Department of Chemistry, Government College University Faisalabad, Faisalabad, Pakistan Awais Ahmad Department of Chemistry, The University of Lahore, Lahore, Pakistan Ikram Ahmad Department of Chemistry, University of Sahiwal, Sahiwal, Pakistan Shafaqat Ali Department of Environmental Sciences and Engineering, Government College University Faisalabad, Faisalabad, Pakistan Mabkhoot Alsaiari Department of Chemistry, Faculty of Science and Arts at Sharurah, Najran University, Sharurah, Saudi Arabia Ifzan Arshad Institute for Advanced Study, University, Shenzhen, Guangdong, P.R. China
Shenzhen
Sadia Aslam Department of Botany, Government College University Faisalabad, Faisalabad, Pakistan D. Balaji Department of Mechanical Engineering, KPR Institute of Engineering and Technology, Coimbatore, Tamil Nadu, India Syed Majid Bukhari Department of Chemistry, COMSATS University Islamabad Abbottabad Campus, Abbottabad, Pakistan Divya Dharmaraj Aquatic Microbiology Lab, Department of Animal Health and Management, Alagappa University, Karaikudi, Tamil Nadu, India Kannapiran Ethiraj Department of Fisheries Science, Alagappa University, Karaikudi, Tamil Nadu, India Shoaib Hasnain Department of Chemistry, Government College University Faisalabad, Faisalabad, Pakistan G. Hemath Kumar Composite Research Center, Chennai, Tamil Nadu, India
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Naveed Kausar Janjua School of Applied Sciences and Humanity, National University of Technology, Islamabad, Pakistan J. Angela Jennifa Sujana Department of Artificial Intelligence and Data Science, Mepco Schlenk Engineering College, Sivakasi, Tamil Nadu, India Kannan Karuppiah Department of Zoology, Kongunadu Arts and Science College, Coimbatore, Tamil Nadu, India Anish Khan Chemistry Department, Center of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah, Saudi Arabia; Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia Mariam Khan School of Applied Sciences and Humanity, NUSASH, National University of Technology, Islamabad, Pakistan Rana Rashad Mahmood Khan Department of Chemistry, Government College University Lahore, Lahore, Pakistan Safia Khan Shandong Technology Centre of Nanodevices and Integration, School of Microelectronics, Shandong University, Jinan, P.R. China; Department of Chemistry, Quaid-i-Azam University Islamabad, Islamabad, Pakistan Madhuri Krishnamoorthy Aquatic Microbiology Lab, Department of Animal Health and Management, Alagappa University, Karaikudi, Tamil Nadu, India Shern-long Lee Institute for Advanced Study, University, Shenzhen, Guangdong, P.R. China
Shenzhen
Hu Li Technology Centre of Nanodevices and Integration, School of Microelectronics, Shandong University, Jinan, P.R. China H. Mohit Department of Mechanical Engineering, Alliance College of Engineering and Design, Alliance University, Bengaluru, Karnataka, India Talha Mumtaz Department of Chemistry, Government College University Lahore, Lahore, Pakistan Naqeebullah Department of Chemistry, Government College University Lahore, Lahore, Pakistan Rajesh Jesudoss Hynes Navasingh Faculty of Mechanical Engineering, Opole University of Technology, Opole, Poland; Department of Mechanical Engineering, Mepco Schlenk Engineering College, Sivakasi, Tamil Nadu, India
List of contributors
Arsh E Noor Department of Environmental Sciences and Engineering, Government College University Faisalabad, Faisalabad, Pakistan; Department of Chemistry, The University of Lahore, Lahore, Pakistan Muhammad Pervaiz Department of Chemistry, Government College University Lahore, Lahore, Pakistan Latha Pujari Department of Pharmacology, Institute of Pharmaceutical Technology, Sri Padmavati Mahila Visvavidyalayam, Tirupati, Andhra Pradesh, India Abdur Rahim Interdisciplinary Research Centre in Biomedical Materials (IRCBM), COMSATS University Islamabad, Lahore Campus, Lahore, Pakistan; Department of Chemistry, COMSATS University Islamabad, Lahore Campus, Lahore, Pakistan Kumar Rajendran Aquatic Microbiology Lab, Department of Animal Health and Management, Alagappa University, Karaikudi, Tamil Nadu, India; Department of Fisheries Science, Alagappa University, Karaikudi, Tamil Nadu, India L. Rajeshkumar Department of Mechanical Engineering, KPR Institute of Engineering and Technology, Coimbatore, Tamil Nadu, India M. Ramesh Department of Mechanical Engineering, KITKalaignarkarunanidhi Institute of Technology, Coimbatore, Tamil Nadu, India Shamim Ramzan Department of Chemistry, COMSATS University Islamabad, Lahore Campus, Lahore, Pakistan Athar Rasheed Department of Chemistry, Government College University Faisalabad, Faisalabad, Pakistan Ayoub Rashid Department of Chemistry, Government College University Lahore, Lahore, Pakistan Ayesha Riaz Department of Chemistry, Government College University Faisalabad, Faisalabad, Pakistan R. Ruban Department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli, Tamil Nadu, India Zohaib Saeed Department of Chemistry, Government College University Lahore, Lahore, Pakistan Areeba Saifullah Department of Chemistry, The University of Lahore, Lahore, Pakistan
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M.R. Sanjay Natural Composite Research Group Lab, Department of Materials and Production Engineering, The Siridhorn International Thai-German Graduate School of Engineering, King Mongkut’s University of Technology, North Bangkok, Thailand A. Saravanakumar Department of Mechanical Engineering, Dhanalakshmi Srinivasan College of Engineering, Coimbatore, Tamil Nadu, India J. Senthil Kumar Department of Electronics & Communication Engineering, Mepco Schlenk Engineering College, Sivakasi, Tamil Nadu, India Syed Sakhawat Shah School of Applied Sciences and Humanity, National University of Technology, Islamabad, Pakistan Soumaila Shaheen Department of Chemistry, Government College University Lahore, Lahore, Pakistan Farwa Batool Shamsi Department of Pathology, Faisalabad Medical University, Faisalabad, Pakistan P. Shenbaga Velu School of Mechanical Engineering, Vellore Institute of Technology, Chennai, Tamil Nadu, India Suchart Siengchin Natural Composite Research Group Lab, Department of Materials and Production Engineering, The Siridhorn International Thai-German Graduate School of Engineering, King Mongkut’s University of Technology, North Bangkok, Thailand S. Sivalingam Department of Mechanical Engineering, Coimbatore Institute of Technology, Coimbatore, Tamil Nadu, India N.S. Suresh Department of Electrical and Electronics Engineering, Saveetha School of Engineering, Saveetha University, Chennai, Tamil Nadu, India Hina Tabassum Department of Chemistry, University of Science and Technology of China, Anhui Province, P.R. China Muhammad Yahya Tahir Department of Environmental Sciences and Engineering, Government College University Faisalabad, Faisalabad, Pakistan N.J. Vignesh Department of Mechanical Engineering, Mepco Schlenk Engineering College, Sivakasi, Tamil Nadu, India
List of contributors
Umer Younas Department of Chemistry, The University of Lahore, Lahore, Pakistan Mushkbar Zahara Department of Chemistry, Government College University Lahore, Lahore, Pakistan Asma Zaidi Department of Chemistry, COMSATS University Islamabad, Abbottabad Campus, Abbottabad, Pakistan
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1 Introduction: nanomaterials and electrochemical sensors Naqeebullah1, Awais Ahmad2, Hina Tabassum3, Talha Mumtaz1, Muhammad Pervaiz1, Zohaib Saeed1, Umer Younas2, Asma Zaidi4, Rana Rashad Mahmood Khan1, Ayoub Rashid1 and Ahmad Adnan1 1
Department of Chemistry, Government College University Lahore, Lahore, Pakistan 2Department of Chemistry, The University of Lahore, Lahore, Pakistan 3Department of Chemistry, University of Science and Technology of China, Anhui Province, P.R. China 4Department of Chemistry, COMSATS University Islamabad, Abbottabad Campus, Abbottabad, Pakistan
1.1
Introduction
A sensor can be defined as any substance that is capable of detecting any change due to an external stimuli. Mostly, sensors respond to physical stimuli. A stimulus can be defined as any change that may initiate a reaction. For example, light is an external stimulus and so is heat. Basically, to detect stimuli, various sensors are utilized. Our skin is also called a sensor (receptor), as it detects various stimuli occurring externally or internally. In chemistry, scope is limited to external stimuli. The most easy to understand example of a sensor in chemistry is pH meter Fig. 1.1 [1]. It detects pH of any solution by using its electrode: the electrode acts as a sensor and it is attached to a digital meter; that digital meter shows us the reading of the analyte (solution whose pH is to be measured). The research on sensors dates back to the 1950s, but it caught pace in 1990s. In 1950s Professor Leland Clark worked on to establish an oxygen biosensor but unfortunately he could not succeed; nonetheless, research did not halt, and after some time, researchers came up with idea of an oxygen sensor. It was named as Clark’s electrode (1962) [2]. It was used as a sensor to detect an ambient amount of oxygen given inside a sample
Nanomaterials-Based Electrochemical Sensors: Properties, Applications, and Recent Advances. DOI: https://doi.org/10.1016/B978-0-12-822512-7.00017-X. © 2024 Elsevier Inc. All rights reserved.
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Chapter 1 Introduction: nanomaterials and electrochemical sensors
Figure 1.1 Working of the Clark electrode.
of water. It used a platinum surface. The platinum surface was catalyzed. The reaction is as follows [3]: O2 1 4e2 1 4H1 -2H2 O This became the basis of the formation of glucose biosensors. As Clark’s electrode was the basis for the genesis of glucose biosensors, Clark is known as the father of biosensor applications [4]. The bug did not stop here; in fact in 1981, a scanning tunneling microscope was invented based upon this technology. In 1986, an atomic force microscope was invented. An
Chapter 1 Introduction: nanomaterials and electrochemical sensors
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interesting fact about both these microscopes is the use of electrons in these microscopes, which creates less debris and makes them environment-friendly. In chemistry, chemical sensors have been majorly divided into five types: 1. Electrochemical sensors 2. Mass sensors 3. Optical sensors 4. Magnetic sensors 5. Thermal sensors Fig. 1.2 Here, the scope is entirely based upon electrochemical sensors. Based on working principles and a coupling relationship between analyte and featured electrode, these sensors are classified [5]. Electrochemical sensors can be defined as devices that work by mutually coupling an analyte with electrochemical transducers. A transducer basically turns an electrochemical reaction into a signal (electric) easily read by signal detectors [6]. Fig. 1.3 The electrochemical methods that are used in electrochemical sensors are (Table 1.1) 1. Potentiometry 2. Conductometry 3. Amperometry, voltammetry 4. Coulometry (Q) 5. Capacitance (C) Receptor (Enzyme, carbon nanotube, graphene...)
Transducer
Amplify
(Electrode, thermistor...)
Electrochemical signals
Analyte (H2O2, glucose, urea, ethanol...)
Figure 1.2 Detection of glucose, urea, ethanol, and so forth by using a sensitive carbon nanotube, graphene, and enzyme electrodes.
e
Recognition of molecules
hv m T
Transduction of signal Figure 1.3 Detection of signals and reorganization of molecules.
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Chapter 1 Introduction: nanomaterials and electrochemical sensors
Table 1.1 List of different electrochemical methods with the irrelative sensitive properties used to calculate. Electrochemical methods
Monitored electrical properties
Units
Potentiometry Conductometry Amperometry and voltammetry Coulometry (Q) Capacitance (C)
Potential difference (volts) Resistance (ohms) Current (amps) as a function of applied potential Current as a function of time (coulombs) Potential load (farads)
V Ω I C5Is F 5 C V21
Potentiometry monitors the electric signal as a function of potential difference, whereas conductometry monitors the electric signal as a function of resistance. Similarly, amperometry and voltammetry monitor the electric signal as a function of applied potential. Coulometry monitors the electric signal as a function of current as a function of time (coulombs), and capacitance monitors the electric signal as a function of potential load (in farads). These analysis methods can be divided into two types: 1. Non-interfacial methods 2. Interfacial methods Non-interfacial methods provide solutions as a whole such as various factors that are taken into account while dealing with this particular method: a cell whose size is known, electrodes are placed equidistantly in order to measure resistance, and in this case, an alternating current is applied resistance then depends upon the cell constant. The cell constant is dependent upon surface area, spacing of electrodes, and solution volume. Conductometry is an example of it. Interfacial methods make use of analytes (directly or indirectly) present on the sensory unit (electrode). Analytes can be defined as any sample that is to be tested. Interfacial methods are further divided into two types: 1. Static methods 2. Dynamic methods Those methods in which current displays zero value (i 5 0) or in other words there is no disturbance recorded are called static methods, and those methods in which current is not zero are called dynamic methods. The dynamic methods make use of redox reaction as flow of electrons between analyte and electrode, which is the main reason why current is not zero in this case. Basically, dynamic methods became the basis for the formation of
Chapter 1 Introduction: nanomaterials and electrochemical sensors
nanostructured sensors. Therefore, nanobased electrochemical sensors follow interfacial methods. In these types of methods, electrode’s (working) surface and sensor receive some amount of signals that are in electric form such as in amperometry. Actually, the principle is that the active layer must recognize analytes and then further transduction takes place following the recording process. The main parts of an electrochemical sensors are as follows: 1. Sensory unit 2. Analyte 3. Reaction medium 4. Electrodes So, this makes it like an electrochemical cell having a cathode and anode, resulting in the process of polarization that initiates a reaction (electrochemical). In convention, an electrochemical cell has the following: 1. Cathode 2. Anode 3. Voltmeter 4. Power source The most used method among the aforementioned techniques is potentiometry. It is an interfacial method and is static. The very familiar example is the pH meter used to measure H1 ions’ activity by using a glass electrode. The glass electrode compares activity (H1) of ions via a glass electrode. Two types of activities are prevalent: one is called internal activity (concentration inside the electrode that is fixed) and the other is external activity (concentration of solution that needs to be measured). Both these internal and external concentrations are compared using the Nernst equation, after which it is turned to an electric signal. The equation is as follows: E 5 Eo
RT RED ln nF OXI
E, cell potential, Eo , standard potential, R, universal gas constant, T, temperature, n, eq. molar no. of electrons, F, Faraday’s constant, RED, reduced species activity, OXI, oxidized species activity (Table 1.2). In order to have the maximum output, reference electrodes are used. A reference electrode is defined as any electrode whose potential is constant and follows the Nernst equation but does not get affected by temperature. The most used reference electrodes are 1. Normal hydrogen electrode (NHE) 2. Saturated calomel electrode (SCE) 3. Saturated silver/silver chloride electrode (E Ag ) AgCl Fig. 1.4
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Chapter 1 Introduction: nanomaterials and electrochemical sensors
Table 1.2 List of different reference electrodes with their respective standard potential at 25˚C. Reference electrode NHE SCE EAg/AgCI
Reversible reaction 1
2
2H 1 2e $H2 Hg2 CI2ðSÞ 1 2e2 $HgðIÞ 1 2CI2 AGCIðSÞ 1 e2 $AgðSÞ 1 CI2
Standard potential at 25˚C E0 5 0.0 V (by definition) E0 5 10.244 V (vs NHE) 0 EAgCI 5 2 0:199 Vðvs NHEÞ
NHE, normal hydrogen electrode; SCE, saturated calomel electrode.
Figure 1.4 Working of a voltammeter with sample and reference solution to detect molecules with sensitive electrodes.
The chronoamperometry technique was used in the 1960s for explaining crystals’ nucleation. In this method, along with the reference electrode, an auxiliary/counter electrode is used. As the name suggests, the auxiliary electrode helps in the completion of the electrochemical process along with the working electrode and reference electrode. All of the working is governed by the Cottrell equation: It 5
nFAcoDo1=2 bt1 ii 5 π1 2 2 t1=2
It, current recorded with respect to time (ts ); n, eq mol21 number of electrons; F, Faraday’s constant; A 5 electrode area in cm2; Co, oxidized species concentration (molcm23 ); and Do, diffusion coefficient (oxidized species) (cm2 s21 ). Two types of major processes occur during this technique • Mass transfer (species transfer to electrodesolution interface in the solution)
Chapter 1 Introduction: nanomaterials and electrochemical sensors
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Figure 1.5 Digital graphical explanation of strength of unknown molecules present in the solution.
•
• • • • •
Charge transfer (electrons transfer on the electrode surface [working electrode]) Further processes associated with this are as follows: Protonation Polymerization Adsorption Desorption Crystallization Fig. 1.5
1.2
Voltammetric methods
Jaroslav Heyrovsky, a Czech chemist, established polarography in 1922, which led to the creation of voltammetry technologies. Mercury oxidation or reduction, as well as reference electrodes, is studied in polarography. Current flow is measured as the potential difference between electrodes. A polarograph (I*E) [7] is created by plotting potential variation and current flow. The voltammetry field developed methodologies, theories, and instruments during the 1960s and 1970s [8]. Through electrochemical cells, all voltammetry procedures consider the resultant current (I) and potential on an electrode [9] range of inorganic and organic species concentrations, a large selection of solvents and electrolytes, a wide range of temperatures, fast analysis in seconds, simultaneous determination of analytes, kinetic parameters, unknown parameters, and measurements of very small current values [7]. Potential sweep methods are sometimes known as voltammetric methods. These methods are often used for cyclic sweep, linear pulse, and cyclic voltammetry, which is the study of processes occurring on the working electrode.
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Chapter 1 Introduction: nanomaterials and electrochemical sensors
Emax E1 Ei t1
Figure 1.6 Cyclic voltammetry parameters explanation [10].
t
Emin
1. 2. 3. 4. 5. 6. 7. 8. 9.
The following are some of the most common applications [8]: Electrochemical reaction mechanisms diagnostic The presence of various species identification in the solution Reaction speed analysis (semi-quantitative) Constant and kinetic rates are measured The adsorption mechanisms on various surfaces are investigated Research into the mechanism of reactions and electron transfer Calculation of solvated species’ thermodynamic characteristics Research into the mechanisms of oxidation and reduction The completed values and coordination are determined. Fig. 1.6
1.3
Cyclic voltammetry
Linear sweep voltammetry is done in only one direction and stops at a given value of Ef , such as t 5 t1 [11]. The direction of the sweep might be either negative or positive. The following parameters are generally examined in this voltammetry approach. Sweeping speed is one of the most important factors to consider. 1. Potential minimum and maximum 2. Potential in the end 3. Potential at the start 4. Direction of the initial sweep Potential (E) on the x-axis and current (I) on the y-axis together gives a cyclic voltammogram for reversible systems. Fig. 1.7 The most common example is the determination of nitrate and nitrite utilizing zeolite, graphite epoxy, and a silver electrode.
Chapter 1 Introduction: nanomaterials and electrochemical sensors
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Figure 1.7 Cyclic voltammogram drawn for the reversible systems [11].
0.00015
11
0.00010 1
/ (A)
0.00005 0.00000
–0.00005
1
–0.00010 –0.00015
11 –1.5
–1.0
–0.5
0.0 E (V) versus SCE
0.5
1.0
All of the aforementioned variables are calculated using the results and voltammogram generated by these lists [12]. Fig. 1.8
1.4
Differential pulse voltammetry
Differential pulse voltammetry (DPV) is an amplitude potential pulse on a real ramp potential technique. The potential value (base value) is chosen in this procedure. After that, current is measured both before and after the pulse. The difference is then recorded. It is a differential approach that is similar to a
Figure 1.8 Cyclic voltammogram for AgZEGE with a scan rate of 50 mVS2 [12].
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Chapter 1 Introduction: nanomaterials and electrochemical sensors
linear voltammogram’s derivative. A redox reaction pulse can be seen here. The voltammogram is like a wave in linear sweep, and the derivative peak is formed afterward. For organic molecules, DPV has the best reaction [11]. Because capacitive current is minimized, DPV is more sensitive than linear sweep. For example, a glass electrode of carbon was used to build and develop DPV for the detection of methyl parathion. This electrode is a multiwalled carbon nanotube and polyacrylamide nanocomposite film. Experiments reveal that microperoxidase (MP) has a high affinity and exhibits significant adsorption in environmental samples [13].
1.5
Square wave voltammetry
This is the most sensitive and fastest pulse voltammetry technique available. Its limits are also compared to those obtained using spectroscopic and chromatographic methods. The kinetics and mechanism of the electrode can also be studied using this method. The potential current curve shape in square wave voltammetry (SWV) is derived by applying the height of potential, which varies depending on the potential step E and the duration of the period (τ) [14]. Curves of current and potential are often symmetrical and have well-defined properties. This is because all currents are only recorded at the end of each semi-period, and variations in the height and width of the potential pulse are always constant within a certain potential range. Fig. 1.9 Because of its excellent sensitivity and selectivity, the SWV approach has been used in the construction of sensors and biosensors [14]. Fig. 1.10
1.6
Electrochemical impedance spectroscopy
Electrochemical impedance spectroscopy is a technique for studying electrochemical processes at the electrode/electrolyte solution interface. This is a technique for identifying and determining parameters from a model based on the frequency response of the electrochemical system under investigation. In such experiments, a frequency response analyzer with an electrochemical interface is used to measure the current response of the system, as it changes the frequency of an input sinusoidal signal [11,15,16], E 5 Eo sinðw 5 2πf Þ, applied to an unknown sample;
Chapter 1 Introduction: nanomaterials and electrochemical sensors
I1
'E
E
τ
11
Estep
I2 t1
Figure 1.9 Square wave voltammetry typical application representation [14].
t
(B)
(A)
l
l
∆l = l1–l2 l1 0
0 l2 E
∆l = l1–l2 l1 l2 E
the response is analyzed through a correlation with the resulting currentI 5 Io sinðwt 1 ΦÞ, where phi is the phase angle displacement. The vector sum given by [11] is the impedance (Z). Z 5 R 2 jXc pffiffiffi where j 5 1 (Fourier) R is resistance, XC is capacitive reactance equal to al=wC (measured in ohms) with w 5 2πf , and C is the capacitance of the electric double layer. As a result, R represents the real component (Z0 ) of the impedance, while 2jXC represents the imaginary part (Z00 ).
1.7
Electronic tongue: concepts, principles, and applications
Chemical sensors, as previously stated, are commonly utilized analytical equipment. The pH meter [17] was the first
Figure 1.10 Square wave voltammetry in a systemic way where (A) represents redox reaction in the reversible system, while (B) represents that in the non-reversible system [14].
12
Chapter 1 Introduction: nanomaterials and electrochemical sensors
ion-selective electrode based on potentiometric measures, which was introduced in 1909. One way to improve the analytical application of sensors is to use a combined matrix of sensors and more advanced data manipulation techniques so that the combination of responses forms a “fingerprint,” not only of an analyte but also of the combined form between analytes and their matrices, such as a pesticide in a specific soilwater matrix [18]. The concept of integrating responses from several sensors to create this “fingerprint” was first used in gas sensors, which are today known as electronic noses [18]. The electronic tongue (ET), like the biological tongue, works in a liquid media, but with far higher sensitivity and selectivity. These advantages allow the ET to perform more like the olfactory system than the gustatory system. The artificial neural network [19], whose algorithms are based on the learning and recognition processes of the human brain, is the most often used data processing system. Statistical methods, such as principal component analysis, multivariate regression techniques, and factorial analysis, are the most commonly utilized methodologies [20,21]. Mineral water, coconut water, coffee and tea [22], wine [23,24], and sugarcane juice have all been tested with the ET based on conductive polymers. Taste qualities determined with the ET in mineral waters could be linked to their physicochemical makeup. Heavy metals and pesticides could be detected in these beverages using this method [25]. The ET is currently a commercial product. The “ASTREE electronic tongue” gadget, developed by Alpha MOS, uses chemically modified field effect transistor technology and potentiometric measurements with seven specific liquid sensors for ionic, neutral, and chemical substances responsible for flavor. All these methods became the basis for formation of nanobased electrochemical sensors. Electrochemical sensors (nanobased) are highly sensitive and selective, which is why their usage in a number of sensing techniques is quite vivid. Nanotubes or nanobased electrodes have been made, which have proved very promising. Nanomaterials are those materials occupying any dimension associated with 1 nanometer. Carbon-based nanomaterials (two-dimensional graphene) [26], tubes, and electrodes have been brought into light, as they show immense potential for use as sensors. It was a very great success for humankind that many biosensing techniques were made, which are helpful in detection of early diseases that helps to cure different ailments including detection of neurochemicals (chemicals whose increased or decreased ratio can
Chapter 1 Introduction: nanomaterials and electrochemical sensors
13
affect brain’s normal functioning). Not only have the electrochemical sensors proved to be a great asset for biosensors but they have also been excellent toward sensing pollution and food security. Increased amount of arsenic in food or any matter is always alarming. Nanoparticle-modified electrodes have been made, which detect arsenic, as it is highly toxic and affects biologically and environmentally [27]. Sensitive, sensible, and selective nanomaterials and nanotubes are designed to control spread of arsenic openly. All this is due to the electrochemical sensing techniques. It does not stop here on the basis of electrochemical sensing active biological molecules such as H2O2, glucose, enzymes, proteins, and so forth. Fabricating carbonbased nanomaterials with biosensors holds a promising future, as biosensors are extremely important, as they provide accurate and precise results by detecting an increased or decreased amount of a particular chemical inside the body. Fig. 1.11 Enzymes are also used for this purpose, but as enzymes get denatured, carbon-based nanoelectrodes till now have proven to be an excellent remedy for biosensing [28]. Nanomaterials
Current
Uric acid
Glucose Vitamin C
H2O2
Time
Biosensor CNTS Graphene
Protein
Other analytes
DNA
Micro RNA
Dopamine
Figure 1.11 Working of graphene and CNTS biosensors for the detection of different biological molecules.
14
Chapter 1 Introduction: nanomaterials and electrochemical sensors
and nanotechnology have extended their scope beyond anyone’s imagination. Nanobased materials are being used to detect the normal functioning in the brain. The brain consists of neurotransmitters (chemicals that help in the process of normal messaging by the brain) such as dopamine. These chemicals increase or decrease normal brain functioning, thanks to nanobased electrochemical sensors; so detection of neurochemicals is easy now due to robustness, sensitivity, and selectivity of nanomaterials [29]. Apart from that, electrochemical sensors have extended their radar to food security. Food mostly gets contaminated by the chemicals used in them such as • Hydrazine (N2H4) • Malachite green • Biphenyl A • Ascorbic acid • Caffeine • Caffeic acid • Sulfite (SO22 3 ) • Nitrate (NO2 2) Fig. 1.12 All these are present in the form of additives either in foods or beverages. Electrochemical sensors help in detecting the increased values of these chemicals, thus adding another application to their chart. The problem of food can be a great threat to the world because as the environment is getting more polluted [30], food safety is also being affected. If it is unchecked, in the future, food safety can become a great problem [31].
Nitrite
Na no co m Ca po ffe sit es ic
ac
id
Malachite Green
mical Se che ro
Ele ct
on rb Ca
ls ia er at m
ph
en Go ol ld na A no m at er ial s
ors ns
Hydrazine
e lfit Su
Bis
s rial ic ate ll m rb o r y o p y c l d Po As ci
a
Caffeine Figure 1.12 Schematic explanation of different sensors used for detection of different materials.
Chapter 1 Introduction: nanomaterials and electrochemical sensors
1.8
Future prospects
Electrochemical sensors are going to be widely used in the future, even though they are not in common use nowadays; they shall dominate the market in the future. Glucose sensors have proven to be much helpful for diabetics; miniature-sized sensors are being used in hospitals to check the amount of electrolytes in a human body [32]. In chemistry labs, potentiometers are being used. All of this is due in large part to the use of nanotechnology in electrochemical sensors. In 2019, over 500 review articles were published about electrochemical sensors; nevertheless, scientific challenges must be overcome in order to use these sensors in everyday life [33]. Nanobased technology has a lot of advantages but is also very complex. Immense research has been carried out to overcome this complexity. For example, a glucose sensor might work excellently at 0.1 M NaOH, but it might not fit under different physiological conditions; robust technology is required and work is being done. Moreover, disposable sensors are being used nowadays for a single detection. Nonetheless, these must be cheap and easily available. An example is paper-based microfluidic analytical devices. In this case, the gap between electrochemical sensors’ ideas and analytical applications being done in real world is shortened; then in the future, sensors may be used for personal use and in technology (in situ). However, a lot of time is required [34].
1.9
Conclusion
The use of electrochemical sensors based on electrochemical analytical techniques has a lot of advantages in sensing techniques; biosensors and sensors can be used in food safety and for environmental purification. Although factors like chemical composition, size, and various processes occurring on surface-based nanocomponents are yet to be overcome, electrochemical techniques have become prevalent due to their applications. The sensitivity, sensibility, and calibration of electrochemical sensors make them different and they are leaving their mark. The growing use of these sensors in food safety, environment, and bioscience is highly commendable and stage is all set for further research.
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Chapter 1 Introduction: nanomaterials and electrochemical sensors
References [1] C. Zhu, et al., Electrochemical sensors and biosensors based on nanomaterials and nanostructures. 87 (1) (2015) 230249. [2] S. Su, et al., Recent advances in two-dimensional nanomaterials-based electrochemical sensors for environmental analysis. 3 (2) (2018) 97106. [3] J. Wang, Electrochemical glucose biosensors. 108 (2) (2008) 814825. [4] L.C. Clark Jr, C. Lyons, Electrode systems for continuous monitoring in cardiovascular surgery, Ann. N. Y. Acad. Sci. 102 (1) (1962) 2945. [5] M. Mittal, S. Sardar, A. Jana, Chapter 7 - Nanofabrication techniques for semiconductor chemical sensors, in: C.M. Hussain, S.K. Kailasa (Eds.), Handbook of Nanomaterials for Sensing Applications, Elsevier, 2021, pp. 119137. [6] F.R. Simo˜es, M.G. Xavier, 6 - Electrochemical sensors, in: A.L. Da Ro´z, et al. (Eds.), Nanoscience and Its Applications, William Andrew Publishing, 2017, pp. 155178. [7] D.A. Skoog, F.J. Holler, S.R. Crouch, Principles of Instrumental Analysis, Cengage Learning, 2017. [8] O.Pd Amarante Ju´nior, et al., Breve revisa˜o de me´todos de determinac¸a˜o de resı´duos do herbicida a´cido 2, 4-diclorofenoxiace´tico (2, 4-D). 26 (2) (2003) 223229. [9] S.P. Kounaves, Voltammetric Techniques, Prentice Hall, Upper Saddle River, NJ, 1997, pp. 709726. [10] G.J. Hills, D.J. Schiffrin, J. Thompson, Electrochemical nucleation from molten salts—I. Diffusion controlled electrodeposition of silver from alkali molten nitrates, Electrochim. Acta 19 (11) (1974) 657670. [11] C. Brett, A.M. Oliveira Brett, Electrochemistry: Principles, Methods, and Applications, 1993. [12] F. Manea, et al., Simultaneous electrochemical determination of nitrate and nitrite in aqueous solution using Ag-doped zeolite-expanded graphiteepoxy electrode, Talanta 83 (1) (2010) 6671. [13] Y. Zeng, et al., Differential pulse voltammetric determination of methyl parathion based on multiwalled carbon nanotubespoly(acrylamide) nanocomposite film modified electrode, J. Hazard. Mater. 217218 (2012) 315322. [14] Dd Souza, S.A. Machado, L.A. Avaca, Square wave voltammetry. Part I: theoretical aspects. 26 (1) (2003) 8189. [15] D.D. Macdonald, E. Sikora, G. Engelhardt, Characterizing electrochemical systems in the frequency domain, Electrochim. Acta 43 (1) (1998) 87107. [16] P. Agarwal, et al., Application of measurement models to impedance spectroscopy: II. Determination of the stochastic contribution to the error structure. 142 (12) (1995) 4149. [17] F.R. Simo˜es, M. Xavier, I. Applications, Electrochemical Sensors (2017) 155178. [18] J.W. Gardner, P.N. Bartlett, Sensors and Sensory Systems for an Electronic Nose, Springer, 1992. [19] N. Ware, Neural Computing, Neural Works Professional II/Plus and Neural Works Explorer, 1991. [20] K. Esbensen, S. Schon€ kopf, T. Midtgaard, Multivariate Analysis in Practice: Training Package, Computer-Aided Modelling, 1995. [21] H. Martens, T. Naes, Multivariate Calibration, John Wiley & Sons, 1992. [22] A. Riul, et al., An electronic tongue using polypyrrole and polyaniline, Synth. Met. 132 (2) (2003) 109116.
Chapter 1 Introduction: nanomaterials and electrochemical sensors
[23] A. Riul, et al., An artificial taste sensor based on conducting polymers, Biosens. Bioelectron. 18 (11) (2003) 13651369. [24] A. Riul, et al., Wine classification by taste sensors made from ultra-thin films and using neural networks, Sens. Actuators B: Chem. 98 (1) (2004) 7782. [25] P.A. Antunes, et al., The use of LangmuirBlodgett films of a perylene derivative and polypyrrole in the detection of trace levels of Cu21 ions, Synth. Met. 148 (1) (2005) 2124. [26] V. Dhinakaran, et al., Chapter Ten - Point-of-care applications with graphene in human life, in: C.M. Hussain (Ed.), Comprehensive Analytical Chemistry, Elsevier, 2020, pp. 235262. [27] S. Kempahanumakkagari, et al., Nanomaterial-based electrochemical sensors for arsenic - a review, Biosens. Bioelectron. 95 (2017) 106116. [28] J.N. Tiwari, et al., Engineered carbon-nanomaterial-based electrochemical sensors for biomolecules. 10 (1) (2016) 4680. [29] A. Azzouz, et al., Nanomaterial-based electrochemical sensors for the detection of neurochemicals in biological matrices, TrAC. Trends Anal. Chem. 110 (2019) 1534. [30] C.M. Hussain, R. Kec¸ili, Chapter 8 - Electrochemical techniques for environmental analysis, in: C.M. Hussain, R. Kec¸ili (Eds.), Modern Environmental Analysis Techniques for Pollutants, Elsevier, 2020, pp. 199222. [31] C.M.A. Brett, Deep eutectic solvents and applications in electrochemical sensing, Curr. Opin. Electrochem. 10, 2018, pp. 143148. [32] T. Yang, et al., A review of ratiometric electrochemical sensors: From design schemes to future prospects, 274 (2018) 501516. [33] R. Gui, et al., Recent advances and future prospects in molecularly imprinted polymers-based electrochemical biosensors, 100 (2018) 5670. [34] S. Harshavardhan, et al., Electrochemical Immunosensors: Working Principle, Types, Scope, Applications, and Future Prospects, 2019: p. 343369.
17
2 Nanomaterial properties and applications Areeba Saifullah1, Arsh E Noor1,2, Shoaib Hasnain3, Farwa Batool Shamsi 4, Sadia Aslam5, Shamim Ramzan6 and Abdur Rahim 7 1
Department of Chemistry, The University of Lahore, Lahore, Pakistan Department of Environmental Science and Engineering, Government College University Faisalabad, Faisalabad, Pakistan 3Department of Chemistry, Government College University Faisalabad, Faisalabad, Pakistan 4Department of Pathology, Faisalabad Medical University, Faisalabad, Pakistan 5 Department of Botany, Government College University Faisalabad, Faisalabad, Pakistan 6Department of Chemistry, COMSATS University Islamabad, Lahore Campus, Lahore, Pakistan 7Interdisciplinary Research Centre in Biomedical Materials (IRCBM), COMSATS University Islamabad, Lahore Campus, Lahore, Pakistan 2
2.1
Nanomaterials
Nanomaterials are particulate materials that have the structure in the nanometer (1029) range in one dimension at least [1]. The prefix nano determines the size 1 100 nm range approximately according to the International Organization for Standardization (ISO) [2]. A nanomaterial is larger than an atom that is single, which can be proved by comparing the distance and diameter of carbon, which are 0.15 and 0.25 nm, respectively. We found nanomaterials in nature like protein that are 10 nm long, DNA with a diameter of 25 nm, and parvovirus, the smallest virus, that is 25 nm wide [3]. The nanomaterial is a complicated compound; it consists of three layers of core, shell layer, and surface layer. The core is the nanoparticle itself and the central portion. The shell layer is different chemically in all aspects with a core. The surface layer is the outer layer and functionalized one that interacts with the surfactant, metal ion, polymers, and so forth [4]. European commissions in 2011 recommended a different definition for nanomaterial: “a natural, manufactured, or incidental material that contains particles, as aggregate or in the unbound state and agglomerate state, where, for 50% or more Nanomaterials-Based Electrochemical Sensors: Properties, Applications, and Recent Advances. DOI: https://doi.org/10.1016/B978-0-12-822512-7.00011-9. © 2024 Elsevier Inc. All rights reserved.
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Chapter 2 Nanomaterial properties and applications
particles in the number size distribution, one or more external dimensions is in the 1 100 nm size range” [5]. Any material surface and internal structure in the nanoscale range (1029) and any external dimension in the range of nanoscale are referred to as nanomaterials according to the ISO. According to the Canadians, the nanomaterial is “any manufactured product or substance and any component, ingredient, material, structure, material and device surface, or internal and external dimension structure at least in nanoscale or larger and smaller than nanoscale with all dimensions and having one and more phenomena and properties of nanoscale” [6,7]. The importance of nanomaterial emerges during the optical study when the researcher observes that by changing their size, these materials change the physiochemical properties and become new materials. This behavior can be understood in Fig. 2.1, where Au in different concentrations and sizes gives different materials with different properties [8]. This absorption behavior is observed in different metals like platinum (Pt), gold (Au), palladium (Pd), and silver (Ag) and can be used in the bioimaging application [4].
CLASSIFICATION Dimension
Origin
0D (quantum dots)
Natural (ferrin protein )
1D (nanotubes)
Anthropogenic (metal fumes)
Composion Carbon based(fullerene)
Metal (Au)
Bi-metallic (Fe-Cu) 2D(nanoplates) Metal -oxide(ZnO) 3D(aerogels) MOF (Fe-BTC)
Silicates(zeolite)
Figure 2.1 Schematic illustrations of the classification of nanomaterials.
Chapter 2 Nanomaterial properties and applications
2.2
History
Richard Feynman, in 1959, first talked about nanotechnology at the American Physical Society’s annual meeting, although the term was not coined at that time [9]. However, nanomaterials have been used from the Bronze Age, such as in dyes used for fabrics and filter color impartation in 2600 BC [10]. Cementite nanowires in the carbon nanotubes were used by metal smiths of the Middle Eastern countries in the 12th to 18th centuries for the production of Damascus steel [11]. Silver and gold nanoparticles were used on window panels to impart deep yellow and ruby red color in churches in the middle age [12]. Without knowing the properties like imparting strength, hardness, tear resistance, and abrasion, carbon black has been used since 1910 for the tires. Before what they created they don’t how to observe them [13]. 40 years ago, Richard Feynman challenged his colleague to produce a working electrical motor that is 1/64-cubic inch and offered a prize of $1000 price, which was given to William McLellan who used the watchmaking conventional design [14]. The term “Nano” is a Greek word, which means dwarf and billionth of a unit [3]; in 1974, the term “nanotechnology” was used for the first time by Norio Taniguchi for the semiconductor process of finishing and machining dimensional tolerance [13]. For nanoscale observation of materials like semiconductors and conductors, a quantum phenomenon, in 1981, a scanning tunneling microscope was developed by Heinrich Rohrer and Gerd Binning, who were IBM researchers. For this development, in 1986, they were awarded the Nobel Prize in physics [15]. In 1991, carbon nanotubes’ controlled growth was first observed by Sumio Iijima and his colleagues [16]; after that, nanomaterial growth largely increased, which in 2014 and 2019 was 19.8%, and their market in 2013 was estimated at US$22.9 billion and in 2019 at US$64.2 billion. No nanomaterial increased day by day and introduced commercial products 1628 last update from 2014 according to the international center of the Woodrow Wilson from the inventory of nanotechnology consumer product [3] exceptional properties and potential of different nanomaterials discovered over the years like electrical, optical, mechanical, physiochemical, chemical, magnetic, thermal, and their potential toxicity. Human discoveries of nanomaterials are used in different fields like automobile, oil refineries, aerospace, chemicals, cosmetics, petrochemical industries, construction, electronics, engineering, catalytic processes, energy, environment, household, food, medicine, drug delivery, security,
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Chapter 2 Nanomaterial properties and applications
military, textiles, and sports. Although they are widely modified and used in many fields, there is a need for precaution because of their toxicity to the environment and health, directly and indirectly [1,3].
2.3
Nanomaterial type
Although different definitions are given, all nanomaterials can be classified according to their dimensions, origin, and compositions, as explained in Schematic Fig. 2.1 [3].
2.3.1
According to their dimension
Nanomaterials, according to their dimensions, are categorized into OD, 1D, 2D, and 3D. OD nanomaterial has all external dimensions found at the nanoscale. Quantum dots, which are an example of the OD, are semiconductor crystals with ,10 nm dimension, which is used in electronics and as a potential well to confine holes and electrons [17]. Different types of nanoparticles are found in the OD, such as hollow sphere made like gold, sodium, tungsten, and carbon (fullerenes); full spheres like titanium dioxide anatase; those that constitute a palladium cube; dendrimers that are branched macromolecules and highly symmetrical; zinc oxide rings; tree or flower-like structure, for example, with magnesium oxide, silicon carbide, and molybdenum disulfide; and vanadium oxide star-shaped structure [3]. These can also be used individually like as emulsifiers in solution [18], as a cell marker [19] and as a reinforcement filler in a solid matrix [20]. When there are two external dimensions in the nanomaterial at the nanoscale and another one at the microscale, then these are referred to as one-dimensional (1D). Nanotubes, nanofibers, nanorods, and nanowires are examples of 1D. Nanotubes show the shape of the hollow cylindrical crystalline with atoms arranged as hexagons, pentagons, and heptagons. Nanotubes can be fabricated with molybdenum, copper sulfides, tungsten, and boron nitride and also with different halides like cadmium chloride, nickel chloride, and cadmium iodine but carbon is mostly known [21]. Nanofibers have been fabricated with inorganic materials like titanium dioxide, carbon, silicon dioxide, aluminum oxide, zirconium dioxide, platinum or titanium nitride, and polymers of different varieties such as polyurethane, nylon, polyolefin, polycarbonate, polyethylene terephthalate, polyvinyl alcohol, polyamide, polystyrene, and polylactic acid. They can be produced for the yarn from spinning and for filtration application as web [22].
Chapter 2 Nanomaterial properties and applications
According to the aspect ratio, nanorods are found at OD and 1D nanomaterials (NMs). The aspect ratio is generally found to be between 3 and 20 [23,24]. Electric field modification in orientation changes their reflectivity; this capability is shown by the nanorods. By absorption of infrared, radiation heat is generated in nanorods [3]. Nanowires have a length to width ratio of 1000 or more, and 1D nanomaterials have the largest aspect ratio [25]. Because they have the largest aspect ratio, they are used to confine electrons. Semiconductors are used for the production of nanowires like indium phosphide, silicon, and gallium nitride; electrical insulators like titanium dioxide and silicon dioxide; and metals like lead, nickel, gold, cobalt, and silver [3]. At nanoscale, if there is only one dimension, then these nanomaterials are referred to as two-dimensional (2D) nanomaterials. 2D NMs consist of nanocoatings, thin films, and nanoplates. Different metals are used to fabricate the nanocoating, which includes composites and polymers [26]. This is used for resistance to corrosion or abrasion, improvement to hardness, and supply of the insulating layer [3]. Thin films can be thin layers and can be atom layers and comprise metal and ceramic coating [27]. They are mainly used in electronics and physics so as to change the surface optical reflectivity with conductive and insulating surface properties to produce the electronic components [3]. Generally, nanoplates’ thickness is a few nanometers; for graphene nanoribbons, the width and length are up to 600 nm [28], and for nanoclay, they are 70 to 150 nm [29]. The natural origin of the nanoplates is smectic clay and manufactured like silver, graphene, gold, bismuth telluride, and bismuth selenide. It is used in electronics as components and for composites as reinforcement filler for improvement in their thermal, mechanical, and diffusion barrier properties [3]. At nanoscale, no external dimension is present in threedimensional (3D) nanomaterials, only the feature of the internal nanoscale is present. 3D nanomaterials are comprised of nanostructured materials and nanocomposites. Nanostructured materials consist of nanoporous structures like block copolymers [30], aerogels [31], and nanostructured metals and alloys [3]. Multiphase solid materials are nanocomposites with one external dimension at the nanoscale and at least one phase [32]. A natural example of the nanocomposite is a bone that has the nanocrystal of the calcium hydroxyapatite dispersed in a matrix of collagen. The surface to volume ratio is the difference between composites and nanocomposites. Structured materials used for the packaging material with increased modulus and strength are an example of the polymatrix nanocomposite [3].
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2.3.2
According to origin
According to the origin classification of nanomaterials, they are categorized into anthropogenic and natural, which is further categorized into the engineered and intentional nanomaterials that depend on the intention of formation. Nowadays, manufactured nanomaterials use different chemical compositions like metal oxides, metals, carbon, semiconductors, and polymers. These NMs show specific functionalities according to their design and can be coated and surface-treated. It can be fabricated in different forms like wires, spheres, fibers, rods, needles, tubes, rings, shells, plates, coating, and exotic flower-like, and so forth, and its shape, dimension, and composition can be controlled [33]. NPs that have incidental and natural sources are generally considered ultrafine particles. Inorganic nanomaterials from natural sources include breaking sea waves, erupting volcanoes, sand storms, forest fires, and soil [34]. They are also found in space like fullerene [35] and in living organisms like calcium hydroxyapatite that is found in bones as nanocrystals and ferritin that is protein for iron storage [36]. Human activity also unintentionally produced nanomaterials in the form of byproducts such as from power plants, internal combustion engines, incinerators, polymer fumes, metal fumes, jet engines, heated surfaces, and food transformation processes [33]. Smoke from the cigarette [37] and kitchen appliances also produced nanomaterials [38].
2.3.3
According to chemical composition
Nanomaterials are classified according to chemical constituents as follows.
2.3.4
Carbon-based nanomaterials
Nanomaterials based on carbon display unique properties and play key roles in interdisciplinary fields. Carbon has different forms like amorphous carbon, diamond, and graphite because of the solid-state allotrope form of carbon [39]. sp2 hybridization is displayed by the carbon-based nanomaterials in various dimensions [40,41]. Different physical and chemical properties are shown by the carbon nanomaterials at nanoscale dimensions such as mechanical properties, conductivity, thermal properties, and chemical stability, and so forth; because of these properties, carbon-based nanomaterials have a variety of applications in
Chapter 2 Nanomaterial properties and applications
different fields. Carbon-based nanomaterials are classified according to their forms like nanodiamonds and graphite, graphene sheets, carbon nanotubes, and fullerene. Nanodiamonds and graphite are 3D nanomaterials. Nanodiamonds have a sphere of layer-like shape, and graphite has a hexagonal shape with sp2 carbon atoms. These materials are used as a semiconductor, coating, and abrasives materials because of the unique characteristics of the nanodiamonds like magnetic and optical properties [42,43]. Graphene sheets form the honeycomb and hexagonal lattice with sp2 carbon and are known as a 2D nanomaterial. They have unique characteristics like high electrical conductivity, large surface area, chemical reactivity, and good stability. By using the chemical exfoliation and mechanical methods, graphite is isolated into the graphene [44]. Carbon nanotubes are 1D nanomaterials, and their structure is hexagonal and hollow by linkage of carbon. Different properties are explored by the modification of the physical and chemical properties [45]. When 60 carbon atoms are arranged and form the buckyball structure, they give the 1D fullerene. They neutralize the oxygen and nitrogen like reactive species with their derivatives [46].
2.4
Metal nanomaterials
Nanoparticles with a different metal show many properties that are different from bulk materials such as electrical, optical, and chemical properties. These different metals are silver, iron, gold, and other metallic nanoparticles [47]. The designed procedure determines the metallic nanoparticle size such as electronic structure bandgap, which is converted into the electronic level by changing the particle size into the nano range with atoms in large numbers on the surface. Surface atoms become active by reduction in size due to the distance increase between unsaturated sites and atomic coordinates. For the adsorption and catalysis process, the crucial property is the metal NPactivated surface area. In Ag, Al, Cu, and Au NPs, light is absorbed through intraband transition, and in Pd, Pt, Ru, and Ni, light is absorbed through an interband transition. Metallic NPs’ catalytic activity improved with the irradiation of light, as reported by previous studies [48].
2.4.1
Bimetallic nanomaterials
When nanoparticles comprise two different metals, they are considered as bimetallic nanoparticles. These NPs have unique
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Chapter 2 Nanomaterial properties and applications
properties like optical and size-dependent electrical properties, along with reactivity and chemical stability. Size distribution, shape, and composition affected these properties. The method of preparation significantly affects the NP size distribution and catalyst material recyclability. Stability and dispersion of NPs with magnetic and optical properties due to surface activity change in different combinations of metals in bimetallic NPs like Fe Cu [49], Ag Cu [50], Ag Au [51], Au Pd@SiO2 [52], Au/Pd [53], and Al TiO2 Ag [54]. The preparation condition and two metals’ miscibility influenced the bimetallic nanostructure according to previous studies.
2.5
Metal oxide nanomaterials
Metal oxides such as Al2O3, Fe2O3, ZnO, and TiO2 show advantages in different applications like chemical sensors, catalysis, and semiconductors because of the surface property changes, which influence the materials’ bandgap energy [55]. Metal oxides provide a large surface area with high activity and biocompatibility. Modification of the surface of NP properties can also alter precipitation in the solution of water due to the modifier hydrophobicity on the Al2O3 surface with fatty acid. The modifier is not only fatty acid but also amines [56], epoxides [57], thiols [58], and so forth. It has unique chemical and physical properties such as high density and targets specific analyte if the surface modifier is organic compounds [1].
2.5.1
Composite nanomaterials
Composite nanomaterials are many-phase solid materials in which at least one phase is in the nano range (1029) [51,59]. They also increased the surface area from 0.156 to 2.75 m2/g, which is revealed by the combination of different materials. It also improves the material adsorption capacity by different interactions like Yoshida H-bonding, electrostatic interaction, dipole-dipole H bonding, and π orbital delocalized lone pair n- π interaction [60]. Different properties like water sorption, wear, optical properties, gloss retention, and flexural strength are attained through forming composites by combining different materials [61,62].
2.5.2
Metal-Organic Frameworks
Organic ligands and inorganic ions of metals give hybrids the metal-organic frameworks (MOFs). High porosity, surface
Chapter 2 Nanomaterial properties and applications
modification ease, well-organized configuration and structure, and high surface area are the properties shown by the MOFs. Because of these, they can be widely used in different fields for increasing high reactivity such as Fe-BTC MOFs as enzyme support for good reactivity [63].
2.5.3
Silicates
Nanomaterials’ another category is silicates. Clay is a nanosilicate, which is mostly used and known as magnesium aluminum silicate. In the composite, nanoclay plays a part as a filler for enhancing the electrical conductivity, mechanical performance, flame and heat resistance, and barrier properties. For improving the adhesion and dispersion with a matrix of organics, it can be organic functionalized. Zeolite is also the type of silicate with an organic linker, which has a variety of applications, for example, as a molecular sieve and catalyst for hydrocarbons [3].
2.6 2.6.1
Properties of nanomaterials Optical properties
In the case of semiconductor nanomaterials, they show a special property, optical property, which is used in photovoltaics and photocatalysis. This property followed the Beer Lambert law and principle of basic light. Size, shape, size distribution, and type of the modifier are the factors that influenced the increase in the wavelength absorption. Size and composition of the NMS influence the optical properties [64]. The size of the NMs influences the scattering and reflectance optical property. By increasing size reflectance also increases and decreases if the refractive index decrease. In this way, they show different spectral reflectance underexposed light by scattering particles [65]. Nd-doped NiO shows optical properties by utilizing UV-Vis spectroscopy [66].
2.6.2
Electronics properties
NMs’ electronic properties are based on the surface area, size, modification, and composition [67]. Electronic properties like dielectric constant and electrical conductivity are enhanced by different modifications such as organic and inorganic linker introduction [68,69]. Barium titanate enhances the electronic
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properties because of its piezoelectric properties and perovskite nanostructure [3].
2.6.3
Mechanical Properties
NMs, in comparison to the bulk and microparticles, show different mechanical properties like adhesion, hardness, strain, stress, and elastic strain properties, which are enhanced due to the ease of modification and high surface area property of the NMs. NMs that contain the organic group show low mechanical properties as compared to the inorganic group containing NMs. An organic group exhibiting NMs’ mechanical properties, which are enhanced by the addition of the inorganic groups like SnO2 to the acrylic polyurethane. Abrasion and impact resistance, hardness, and adhesion property improvisation are reported [70]. The size of the NMs also influences the mechanical properties [71].
2.6.4
Magnetic properties
Magnetic properties of the NMs are influenced by the size, and 35 nm less size shows the best magnetic properties [72]. It can also be influenced by the synthetic method and composition. The magnetic moment value in the case of the single NMs is represented by the number of the magnetic atoms, but in the case of the multicomponent, it is represented by the lone pair that is explained by the VSEPR theory. Super-magnetism is displayed by the transition metals and their alloys at the nanoscale [73]. It is used for environmental and medical applications [59,72]. In the biomedical field, it can be used as a separation agent, contrasting agent, and low-risk thrombosis drug carrier. In electronics, it can be used as sensors with high sensitivity, and in the recording of a data system, it can be used in speakers for heat transfer. With rust nanoparticles, it is used for the decontamination of the carbon tetrachloride and arsenic [74].
2.6.5
Thermal properties
NMs’ thermal properties show advantages in comparison with their fluids due to the high surface area. In this way, the surface of a material is used for direct heat transfer. With the addition of SiO2 into polycarbonates, it can enhance the thermal properties. SiO2 restricts the formation of the polymer chain and enhances the polymer and NP interaction [75]. NMs’ thermal properties depend on the mass concentration, high
Chapter 2 Nanomaterial properties and applications
surface area, dispersed NP volume fraction, and NP energetic atom ratio [1].
2.6.6
Physiochemical properties
NMs also show a physiochemical property, namely, superhydrophobicity. This is a very interesting property because only with a contact angle .150, they show this property. This property shows a lotus effect, which does not allow the water to stick to the surface [76]. For this state, two criteria must be followed: preventing water from touching its base, so its nanostructure must be tall; the other criterion is that contact force must not be less than gravity. Due to this property, they are used in the textiles for easy decontamination, rapid drying, stain resistance, and hydrodynamic performance; decontamination floors, walls, and counters; and self-cleaning windows, screens, and glass to make them fog-free [3].
2.7 2.7.1
Application As a chemical catalyst
Different metal NMs such as lead, silver, nickel, and platinum in chemical reaction have been used as a catalyst. However, on the gold surface, oxygen and hydrogen dissociative adsorption is not carried out below 200 C [77]. Gold NMs in the oxidation and hydrogenation process are used as a catalyst due to low reactivity of the gold, which is so effective. Gold NMs’ activity increases with decrease in size in the reaction of catalyzed oxidation, and its cluster is stable [78].
2.7.2
In food and agriculture
Nanotechnology introduces new economical techniques of desalination and water filtration. It also introduces the techniques for the food industry. For biosecurity and food preservation, functional materials are introduced by nanotechnology, such as air-tight plastic packing by Bayer Company for food preservation. It also introduces genetic modification of crop plants [79].
2.7.3
In energy harvesting
NMs nowadays utilize low-cost renewable resources of energy due to their high surface area, optical behavior, and
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Chapter 2 Nanomaterial properties and applications
photocatalytic behavior. Photoelectrochemical and water splitting is carried out by using NMs [80]. Other than reduction, electrochemical CO2 [81], water splitting [82], nanofuels [83], piezoelectric generator, and solar cells [84] are also the latest options for energy production. They are also used for energy storage in different forms [85]. Recently energy converts into electrical from mechanical energy through using piezoelectric [86] which are nanogenerators that are an unconventional approach [79].
2.7.4
In medication and drug
The unique chemical and physical properties of either complex or simple inorganic nanosized particles show advantages in the nanodevice development, which plays a role in biomedical, physical, biological, and pharmaceutical applications [4,87]. They are used in gene delivery [88]; protein findings [89]; drugs [90]; pathogen biological detection [91]; DNA structure probing [92]; process of hypothermia, where destruction of tumor occurs through heating [93]; cell and tissue engineering [94]; for improvement in MRI [95]; in purification and separation of the biological molecules and cells [93]; as biosensors for the disease detection [96]; cellular imagining [97]; biological labeling through fluorescence [98]; and in phagokinetics studies [96].
2.7.5
Applications in electronics
In the last few years, the use of printed electronics has increased compared to silicon traditional printed techniques due to their low cost and high potential. Recently, printed electronics devices ink has been found to have the nanoparticles of the organic, carbon nanotubes, and ceramics [99]. Having a distinctive structure and optical [100] and electrical properties [101], the 1D semiconductors are utilized for the production of photonic and electric materials and sensors and behave as key structural blocks for manufacturing of these devices [102]. Production of new semiconducting electronic devices has been increasing day by day. Lately, miniature chips, transistors, and diodes have been utilized more than vacuum tubes [103].
2.7.6
In mechanical industries
NMs are used in the mechanical industry due to their mechanical properties such as Young’s modulus, strain, and stress properties. They are used as lubricants in coating and
Chapter 2 Nanomaterial properties and applications
adhesive applications. Stronger nanodevices can be obtained by using this property. The coating used for wear resistance and increasing toughness [104] is a strong mechanical characteristic. Titania, alumina, and carbon-based NMs are used for coating [105].
2.7.7
In the environment
Engineered NMs in household and industrial applications are increasing and lead to the environment. NMs are used for their mass ratio with a high surface in the environment for the adsorption of the contaminants from soil and water on the NM surface. This property depends on morphology, size, porosity, composition, aggregation, and disaggregation for the interaction with contaminants. Heavy metals such as lead, mercury, arsenic, cadmium, and thallium cause harmful effects on health and the environment, especially in natural water. For this purpose, many NMs are reported for degradation and removal like iron oxide. Superparamagnetic NPs are effective as sorbent materials [106]. The common practice is photodegradation with NMs [107].
2.8
Conclusion
Due to different types of nanomaterials, they have a promising impact on our scientific world in terms of biomedical, energy, as well as environmental research. In every field of science, these NMs play interesting roles such as in bioimaging, have fuel cell efficiency, and act as nanocatalysts, which are used mostly for environmental remediation. NMs’ diverse properties make them well-suited in terms of specificity, selectivity, and cost-effectiveness. These materials can help in all scientific era in the future due to their various shapes and properties.
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3 Analytical techniques for nanomaterials Muhammad Yahya Tahir and Shafaqat Ali Department of Environmental Sciences and Engineering, Government College University Faisalabad, Faisalabad, Pakistan
3.1
Introduction
Nanomaterials have been established for a variety of environmental applications such as the treatment of wastewater, elimination of hazardous pollutants, emission control-related technologies, corrosion fortification from the automotive industry, environmental sensors, pollution controller technologies, and biomedical submissions, such as drug delivery, biosensors, medical devices, and therapeutic agents. The chemical and physical chattels of nanoparticles are tremendously imperative to their presentation and collaboration with living systems. Consequently, a variety of analytical methods are compulsory to describe and characterize the possession of nanoparticles. The magnitude, form, shallow, and structure are key constraints of a nanocomposite’s physical characterization. For instance, the magnitude is one of the major properties of a nanocomposite, which is connected to the surface-to-volume proportion and its toxicity to human living systems. Furthermore, zeta potential is a significant physical property connected to the longstanding stability of the nanocomposite in solution. The chemical configuration and the inherent toxic properties of a chemical are well known. There are many analytical practices to estimate both physical and chemical categorizations of a nanocomposite. Nanotechnology is well-thought-out as a science that handles matter in nano range, and its painstakingly a pouring force behindhand factorial rebellion as it bids possible preparations for numerous difficulties. Due to the unique properties of a nanocomposite, these composites are used in many segments. Classification of nanocomposites plays many roles in defining the physicochemical, thermal, and optical characteristics. Many devices are used to determine these characteristics, such as Nanomaterials-Based Electrochemical Sensors: Properties, Applications, and Recent Advances. DOI: https://doi.org/10.1016/B978-0-12-822512-7.00003-X. © 2024 Elsevier Inc. All rights reserved.
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Chapter 3 Analytical techniques for nanomaterials
scanning and transmission electron microscopes (TEM). The analytical techniques, which are based on properties and instruments as well, are discussed in this chapter. Most of the techniques are briefly discussed with their advantages and flaws. Moreover, the characterization methodology that is used in nanomaterial science is also reported. Nanocomposites are used in various segments of science and technology, which include nanobiotechnology, energy, drugs, medicines, optical engineering, nanodevices, nanofabrics, and bioengineering, cosmetics, and in the security sector, as they possess a large surface area to volume ratio. Nanocomposites attract attention as they have unique chemical, mechanical, and physical properties from the bulk molecules and solids. Nanocomposites’ classification is based on their structure and origin. Based on arrangements, which depend on their origin, they are classified as zero-dimensional, one-dimensional, natural nanomaterial, artificial nanomaterial, and two- and threedimensional [1]. Physical classification nanocomposites are classified into major three types, for example, metal-based, carbon-based, and dendrimers. Size dispersal is the most important information to know while dealing with nanocomposites. There is increase in the percentage of an atom’s surface, which occurs with the reduction in size. Nanoparticles have a connection with atomic structure and bulk materials [2]. In comparison to a majority of materials, nanocomposites, which are measured as a low dimensional composite, have exceptional thermophysical properties [3]. High surface area, small size, deep access to cells, easy blending with liquids, strong point, and ductileness are the benefits of nanocomposites. There are some drawbacks, such as protection-related problems in relation to concocted nanocomposites, mostly in water and air, forfeiture of works in farming, and synthesis and easy accessibility of mechanical weaponries. The practice of using nanocomposites has amplified in numerous sectors. Before classification of a nanomaterial, analytical techniques of the materials are required. Here, we will deal with the analytical performances that are presently in work within the sector of nanocomposites [4]. Nanocomposites have an enormous exterior area to volume ratio, which is higher in the macroscopical composites. The structure and size of the nanocomposites are dependent on some factors like reactant concentrations, solvent conditions, surfactant additives during the time of synthesis, temperature, and salt. For advancing reproductive amalgamation of nanocomposites, the analytical technique of nanocomposites is found to be effective.
Chapter 3 Analytical techniques for nanomaterials
Analytical techniques refer to the learning of structure, arrangement, and some other properties like chemical, physiological, magnetic, and electrical. Most of the analytical methods are accessible for the classification of nanocomposites, but there is uncertainty in every method [5].
3.2
Different analytical techniques for nanomaterials
(Fig. 3.1)
Figure 3.1 Different analytical techniques for nanomaterials.
3.2.1
Electron Microscopy
A much higher tenacity cannot be attained by a light microscope; now we can achieve a beam of enhanced electrons produced by an electron microscope. Nowadays, most popular microscopes are TEM and scanning electron microscope (SEM). Transmission electron microscopy uses a high voltage electron beam to illumine the sample and produce its image. A beam of electron is instigated from an electron gun, which is augmented and transmitted through the sample upon a conducting grid. A communicated electron carries information regarding the edifice of the sample, and this information is recorded by a fluorescence or image detector (charge-coupled device camera). Transmission electron microscopy usually requires a thin part of the sample, characteristically less than 100 nm. The living
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Chapter 3 Analytical techniques for nanomaterials
organism’s samples, similar materials, and organic polymers may give special treatment with the heavy atoms, which are expected to get maximum image contrast. A TEM is a flawless apparatus for structural and chemical depiction at the nanoscale. Diffraction, imaging, and microanalytical information are easily obtained and give comprehensive insights into the belongings and behavior of nanostructured constituents. This chapter starts with an overview of imaging modes and numerous other vital features of high-resolution tomography, counting the expansion of deviation improvement for electron microscopy, scanning electron microscopy, and other analytical techniques for nanomaterials. A diverse assortment of applications of the TEM to perusing nanomaterials is described. Finally, the emergent trends and concerns that continue to affect the success of electron microscopy studies are briefly described.
3.2.1.1 Transmission electron microscope The TEM has progressed over the years into an extremely erudite apparatus that exhibits prevalent submission crosswise in many sectors of science. As the TEM has a matchless capability to deliver chemical information and structural view upon an array of length scales down to the atomic dimensions, it has advanced into a crucial means for researchers who are involved in understanding the properties of nanocomposites and their operating behavior. The optical microscope has limitations with respect to the wavelength of visible light, and its determination prevents atomic scale imaging. In contrast, a fast moving or an energetic ˚ (where 1 A ˚ 5 10210 m), so a e2 has a wavelength less than 1 A massive improvement can be obtained in resolution, and also by exploiting the electron sunbeam for imaging. An appropriate amalgamation of magnetic electron lenses is compulsory, both for large imaging and for covering the electron sunbeam onto the entity. Extreme magnification of the fixed-beam and conventional TEM is characteristically are nearly or beyond one million times, so significant structural aspects of nanoscale items are easily imagined on the final observing fluorescence screen or on the medium of video recording. Furthermore, the current scanning TEM can provide much greater magnifications, up to 50 million areas or more, and creation feature visibility is easy. Formation of an image in the TEM is more difficult in practice than in other optical microscopes. For fixing the electron
Chapter 3 Analytical techniques for nanomaterials
sunbeam, a solid magnetic field is required, and it causes the electrons to take a spiral path over the lens field. In addition, inevitable aberrations of electron lenses occurred in a major restriction on the definitive microscope presentation. Mostly due to the need for a negotiation between wide angle spherical aberration limits and small angle diffraction effects, the resolution denoted by d can be roughly stated by this equation d 5 ACS 1=4 λ3=4
ð3:1Þ
where CS is the objective lens’ globular aberration coefficient, A is a constant, with its value extending from 0.43 to 0.7 depending on the type of the image, regardless of whether it is coherent, incoherent, or phase contrast, and λ is the wavelength of the elec˚ and to 1 A ˚ , as tron. The value of d typically ranges between 3 A the energies of electrons are increased from 100 to 1250 keV. The modern-day TEM operates at 200 or 300 keV having resolution ˚ , which is analogous to the spacing among restrictions below 2 A atoms. The crystalline constituents of atoms can be determined by individual columns, which must be oriented so that the incident e2 beam is aligned along the crystallographic zone axis of the sample. In some situations, such as along the edges of catalyst particles or in two-dimensional sheets, single-layered, isolated single atoms can even be imaged [6].
3.2.1.2
Scanning electron microscope
The SEM is built on the interface of the beam of electrons with a specimen surface. What a SEM is, what can be done with it, and how it functions will be described here. Because of the high depth of the field in scanning electron microscopy, it shows three-dimensional occurrence. The specimen should be coated with a thin layer of conductive materials, that is, graphite or platinum and gold to get a clear image of the sample. Where the sample is apprehended, the substrate is a conducting grid or a simple filter membrane. Scanning electron microscopy is a significant electron microscopic analytical method which is capable of attaining a comprehensive pictorial image of a sample with high resolution and spatial resolution. A SEM is a multipurpose high-tech device that is mainly used to determine the surface spectacles of substances. A specimen is displayed in scanning electron microscopy to a high-octane electron beam and it gives information about composition, topography, chemistry, morphology, crystallographic information, and the orientation of grains.
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Hence scanning electron microscopy is a beneficial technique to be used for the description of composites and other materials. The morphology designates the size and shape, as topography designates the surface landscapes of the item and “how it looks,” its roughness, smoothness, and texture. Similarly, the composition means basics of the compounds that create the composite, while crystallography means the prearrangement of all the atoms present in the composite. Here, we discuss shortly the scanning electron microscopy method and its principle, utilization, operation, major advancement, sample applications, and preparation. The SEM is a multipurpose progressive device. It is largely used for the detection of surface phenomena of composites. By using high-energy electrons, the sample is observed in the SEM, and by using X-rays and outcoming electrons, the sample is analyzed. These outcoming electrons and X-rays deliver information regarding a composite’s composition, morphology, alignment of grains, crystallographic information, and so forth. The structure and morphology specify the shape and appearance. Scanning electron microscopy is a leading method used to obtain a comprehensive image of a material with high resolution and spatial resolution of 1 nm [7]. Intensifications of this device can extend up to 3 lakhs times. Even though scanning electron microscopy is used to imagine the surface image of a composite and it never gives any interior info, it is well-thought-out as a strong and powerful device that can castoff also in measuring electrical, magnetic, and crystallographic aspects of the material and in defining and in defining if any structural variations of the material has happened after amending the material surface further atoms and molecules [7]. Scanning electron microscopy is capable of delivering a lot of qualitative information of the composite, which includes its crystallographic and composition nature. It also gives information regarding surface texture, arrangements, and features of the composite on the model’s upper surface; different kinds of complexes and elements that the composite has; its qualified ratio; prearrangement of all the atoms in solo crystalline particles; and its degree of command [8]. Hence, the SEM is a versatile device which is capable of measuring and analyzing the sample with high resolution.
3.2.2
Dynamic light scattering
Particle magnitude and size can also be determined using the dynamic light scattering analytical technique. Dynamic light
Chapter 3 Analytical techniques for nanomaterials
scattering is also called photon correlation spectroscopy or quasielliptical light scattering. Typically, the Brownian motion of atoms causes the variations and the adjacent particles may have constructive or destructive interference of the dispersed light intensity in the convinced direction. This atom diffusion can cause variations in the scattered light and, consequently, the particle scope, which can be measured. Dynamic light scattering is one of the best methods that are currently being used to determine the size of nanoparticles. During the dynamic light scattering measurement, the nanoparticle suspension is uncovered to a light beam that may be an electromagnetic wave, and as the light is incident on the nanoparticles, the intensity and direction of the light beam are both changed due to a method called scattering [9]. Meanwhile, the nanoparticles are in continuous random motion owing to the kinetic energy and the change of the intensity with time; consequently, the random motion can also be used to measure the diffusion coefficient of the nanoparticles [10]. For spherical particles, by using the StokesEinstein equation, the hydrodynamic radius of the particles, RH, can be calculated from its diffusion coefficient Df 5 kB T =6πηRH ;
ð3:2Þ
where kB is the Boltzmann constant, T is temperature, and η is the viscosity of the surrounding media. Image analysis on the TEM graphs give the true radius of the nanoparticles, though determined on the statistically small sample, and dynamic light scattering gives the hydrodynamic radius on a collective average [11]. The hydrodynamic radius of the sphere has the same diffusion coefficient in the same viscous environment of the nanoparticles being calculated. Diffusive motion of the particles is directly related to this. Dynamic light scattering is used for determining the size of the nanoparticles and measuring the hydrodynamic size of different nanoparticles. It is practically automated and its measuring time is rapid, so less labor is required for this analysis, and for measurement, a widespread experience is not mandatory. After the measurement, the sample can be used for other determinations, so this analytical technique is noninvasive. For the recycling of nanoparticles having an expensive surface functional group like enzymes and molecular ligands, this aspect is particularly important. Furthermore, dynamic light scattering is extremely subtle for the existence of small aggregates since the intensity of scattering is directly proportional to the sixth power of the particle radius. Hereafter, with the incidence of limited
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aggregation events, specious measurement can be prohibited quite effectively. The most exclusive feature, colloidal stability monitoring, makes the dynamic light scattering technique an influential analytical technique compared to other techniques. The interaction of very small particles with light can be determined by this technique; for example, the fundamental question of why the sky is blue can be answered with this technique. This interaction is also the underlying principle of this technique, and it has another technical point of view. The basic purpose of this discussion is to analyze the mathematical and statistical analysis carried out to extract size relation information from this analytical technique.
3.2.2.1 Correlation function Dynamic light scattering deals with that intensity which is scattered over a range of scattering angles for a given time in time steps. The intensity which is time-dependent oscillates around the average intensity due to the Brownian motion of particles [11]: ð X ½IðqÞ 5 limtk-N1tk= tk0Iðq; tÞUdt limk-N1k ki ð 5 1Iðq; iUΔtÞIq 5 limtk-N1tk 0tkIq; tUdt limk-N1k
X
i 5 1kIq; iUΔt
ð3:3Þ
where the signification of [I(q)] is the time average of I(q). Here, t.k is time step measurement’s total period. I(q) is the average of nanoparticles. During the experiment of dynamic light scattering, usually, θdls is articulated just like the scattering magnitude wave vector q as q 5 ð4πn=λÞ sinðθdls=2Þq 5 4πn=λsinθdls=2 where n is the solution’s refractive index and λ denotes the incident light’s wavelength in vacuum. The intensity fluctuation rises from small particle dispersions with large particles. The fluctuation of intensity of small particles is very rapid compared to large particles, and the vulnerability of random forces of small particles is more than that of large particles. In dynamic light scattering, the intensity extension and the corresponding auto correlation are functional and intensity of scattered light is varied with time and also the auto-correlation function is varied with delayed time.
Chapter 3 Analytical techniques for nanomaterials
3.2.3
Atomic force microscope
Three-dimensional picturing or imaging and material detection to quantify morphology, height, size, surface texture, and roughness of nanoparticles can be done using the atomic force microscope. It exploits the cantilever by using a nanoscale lean tip, which can vacillate over the surface of a specimen. At the outside of both axes, X-axis and Y-axis, the piezoelectric actuators show regulations and vacillating movement over the Z-axis. Quantitative as well as qualitative information can be obtained using the atomic force microscope’s appropriate statistical analysis.
3.2.4
X-ray diffraction
The most common technique used to analyze the molecular structure and atomic structure of a composite is X-ray diffraction (XRD). The crystal-like particles lead the incident X-ray beam’s diffraction into various directions. The conforming intensity and diffraction angles can be measured and recorded, and it shows three-dimensional electron density in the crystal X-ray. This analytical technique is widely used in a large number of crystalline sample characterizations, which include inorganic and organic compounds and other biological molecules. For XRD, the physical condition of composites is elastic and it may be polycrystalline molecules or bulk materials and loose powder and may also be thin films. The advantages of using the XRD analytical technique are the minimum quantity of the composite required, easy interpretation, and nondestructive measurement. This is an authoritative and nondestructive analytical technique for the determination of crystalline composites. XRD gives information regarding crystal orientation, texture and structural parameters, phases, crystallinity, crystal defects, strain, and average grain size. When carrying out XRD, a monochromatic beam of X-rays can be scattered on specific angles, and the XRD peaks are formed by the productive interference of every set of lattice planes. The peaks of intensity can be determined by distribution of atoms within lattice. That is why the XRD pattern of a given composite is the fingerprint of periodic atomic arrangement. This chapter describes the developmental trends of the XRD technique in the scientific research. XRD has pertained to the field of pharmaceuticals, forensic science, geological application, glass application, as well as geological application in the past five years [12].
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When a ray is incident on the interface of the samples, it initiates a constructive interference and then the ray is diffracted when the condition becomes satisfactory, according to Bragg’s law nλ 5 2dsinθ
ð3:4Þ
where θ is the diffraction angle, λ is the wavelength of X-rays, d is interplanar spacing that produces the diffraction, and n is an integer. This law determines the wavelength of electromagnetic radiation to the diffraction angle and lattice spacing in a crystalline sample. When X-rays are diffracted, these are noted, processed, and counted. By perusing the sample via a range of 2θ, the diffracted orders of the lattice should be attained due to the random alignment of grinded or powdered samples. As each material has a set of unique d-spacing, the identification can be done by conversion of diffraction peaks to d-spacing, and characteristically, it can also be attained by comparison of standard reference patterns with the d-spacing. XRD is a high tech analytical and nondestructive technique involved in the examination of different materials like fluids, minerals, polymers, metals, plastics, pharmaceuticals, catalysts, thin filmed coatings, ceramics, solar cells, and semiconductors. XRD is also involved in numerous practical applications in different sectors, including aerospace, powder generation, microelectronics, and so forth. This analytical technique can effortlessly sense the presence of defects in crystals, its resistance level to stress, texture, degree and virtuality of crystallinity, size, and all the other variables, which are connected to the specimen’s structure. There are many advances on the reading of XRD instrumentation principally with respect to the peak resolution permitting the usage of data, which was obtained from the conventional laboratory diffractometers. The XRD peaks, shape, width, and patterners are precisely defined by the expansion of directspace approaches for structure solutions [13]. The application of XRD in the pharmaceutical sector is extraordinary, as it is involved in getting the crystal structure for three out of five polymers of m-aminobenzoic acid [4]. Applied and fundamental perspectives are involved in reputation of polymorphism’s spectacle. Nowadays, there is substantial interest in the discovery of unique schemes that parade a lot of polymorphisms. The direct space genetic algorithm analytical technique for structure resolution can determine directly crystal edifices of the three new polymers by powder XRD statistics. When crystals of sufficient quality and size for a single crystal
Chapter 3 Analytical techniques for nanomaterials
in XRD are unavailable, the Rietveld refinement method can be used to determine the crystal structure. The X-ray photoelectron spectroscopy establishes the task of the tautomeric form in the respective polymorph.
3.2.5
Zeta potential instrument
Electric charge on nanoparticle’s surface is measured by a zeta potential instrument. Particles disseminated in suspension or solution have electric charge just because of dipolar properties and intrinsic ionic characteristics. The degree of electrostatic repulsion between all the head to head is obtained by the zeta potential technique, and it leads to the basic stability of sufficient colloidal dispersions. Nanoparticles having a high value of absolute zeta potential possess better stability, although nanoparticles having the zeta potential value near 0 may lead to dispersion, aggregation, and flocculation problem in solution or suspension. Data for the zeta potential value can be obtained by a zeta potential device, and this value may vary from company to company.
3.2.6
Emmett, Brunauer, and Teller or surface area
Powder form nanomaterial’s surface area can affect its behavior in several submissions, which include scientific and pharmaceutical applications. The main physical sources of adsorption include moderately weak forces, for example, van der Waals forces between adsorbate gas molecules and adsorbent surface area of solid. The surface of testing powder from nanomaterials is dependent on this physical adsorption of a gas. Adsorbate gas quantity on the surface will be measured using this analytical technique. This calculation is usually conducted in liquid nitrogen at a specific temperature.
3.2.7
Fourier transform infrared spectroscopy
Functional groups and chemical information of nanocomposites can be measured by this analytical technique. In this technology, most molecules of the sample can absorb infrared light and it shows how the sample absorbs light at each wavelength and absorption will generate molecular fingerprints. It is very important for the identification of side chains, cross links, and functional groups present in nanocomposites. There is another fact that all the nanocomposites have distinctive vibrational frequencies in the range of infrared radiation.
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Optical chattels of chemically assembled nanocomposites include self-assembled functionalized monolayers, chemically stabilized monolayer-protected clusters, and some other metal base nanoparticles, which were deposited either on colloidal solutions or on different optically transparent glass substrates [5,14]. These all are monitored by Fourier transform infrared spectroscopy (FTIR), which is also used to determine the complex microemulsion behavior [15]; modification of geopolymer gel synthesis can be done using metal base nanoparticle seeding, which alters the structure and growth of a geopolymer [16], and alteration occurred in the chemical composition of iron oxide nanoparticles during their synthesis, which is observed using FTIR, for example, composition of upper shell dispersion was observed in magnetic coreshell complexes in the solution, which is liquid in nature, as iron oxide spines and silica produce this core [17]. Polyvinylidene fluoride as a nanocomposite can be altered by montmorillonite nanoparticles and BaSO4 to expand its UV protection characters and thermal stability [18] and can be also monitored by FTIR, which can lead to quantification of individual components. Another use of FTIR is to monitor complex dendrimer functional groups with metal nanoparticles or different metal species and to characterize dendrimers. Characterization of band shift in the IR spectrum and disappearance can be observed upon adsorption on the surface of nanoparticles or complex processes. FTIR is practical and has a good advantage in such enthusiastic areas as micro-level analysis, where high sensitivity is essential, in the analysis of solid-state samples and aqueous solutions or dark, which involved the use of special reflectance analytical techniques, in soundings, placing stress on quantitative assessment, and in trials where analysis time is a limiting factor, for example, in process or quality control measurements. When we apply Fourier transform to a specific function, it is very impressive to know that all the critical changes which occurred are due to the inversion of units of X-axis of that particular function. There is a example of an interferogram, which is a plot between infrared intensity and optical path difference, which we can calculate in centimeters. When we apply Fourier transform to that interferogram, an occupation is gained, which is a plot of infrared intensity versus cm21. Wavenumber unit is per centimeter; consequently, FTIR spectra are the plot of wavenumber versus infrared intensity. Any interferogram’s Fourier transform makes a single beam spectrum that is a plot of wavenumber versus arbitrary infrared intensity. In FTIR, the term “single beam” means that there is
Chapter 3 Analytical techniques for nanomaterials
only one infrared beam cast-off. Nevertheless, two beam infrared spectrometers are also used in research sectors. A single beam spectrum, which was deprived of a sample, is also called “background spectrum,” which is distinctive of the device and the measuring environment. Consequently, background spectra must always be gone when examining samples using FTIR. The Fourier transformation of interferogram when formed gave us a single beam spectrum of a specimen and it also looks similar to the background spectrum and excludes all the peaks of specimen that are placed upon the atmospheric bands and influential bands. To eradicate these characteristics, the bands contributed from atmosphere and device, and the spectrum of the specimen must be regularized versus background spectrum. A transmission spectrum is gained by this equation %T 5 I=I0
ð3:5Þ
where %T is transmittance, I is the intensity of the measuring specimen in the single beam spectrum, and I0 is the intensity of the background spectrum. The following equation is used for the measurement of the absorbance spectrum from the transmittance spectrum A 5 2 log 10T
ð3:6Þ
where A is the absorbance. So, the absorbance spectrum of transmittance should be lacking all environmental and instrumental contributions and it displays absorption bands of a specimen.
3.2.8
Thermogravimetric analysis
Coated nanocomposites have now become progressively significant in many applications. The relation to surface area and quantitative information, for example, quantity of coating molecules, is essential and is a main parameter to be assessed. Thermogravimetric analysis can be considered as the best analytic technique to give information regarding surface coating, compositional data, and purity of nanocomposites. Thermogravimetric analysis is used for the calculations of mass or weight; it changes the rate in the weight due to change in time, atmosphere, and temperature. Numerous research works have been carried out to measure the grafting density, ligand binding, and surface coating for various nanocomposites, for example, SiO2, CNTs, and Ag nanoparticles.
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3.3
Conclusion
Advancement in the analytical techniques, specifically characterization of nanomaterials, is now steadily progressing and is well known. The ability of the analytical technique to characterize biological and chemical base nanocomposites is exponentially increasing. In this chapter, we have provided details about analytical techniques for nanomaterials. Basic principles, introduction, and instrumentation have been discussed here. Fundamental techniques regarding specimen analysis and sample preparation of nanomaterials have been discussed. Finally, many analytical techniques’ applications in different scientific fields have been explored. This chapter will help the scientific community and also other readers gain advanced and detailed knowledge of analytical techniques of nanomaterials. In the future, we will further address the addition of new fixtures to these analytical techniques and mechanistically explain the role of further advancement in analytical techniques of nanomaterials and biological specimens.
References [1] S. Henning, R. Ashikari, Scanning Electron Microscopy and X-ray Diffraction, vol. 1, Elsevier, 2017. [2] C.J.C. Rayil, J. Abraham, R.K. Mishra, S.C. Georgeand, S. Thomas, Instrumental Techniques for the Characterization of Nanoparticles, vol. 3, Elsevier, 2017. [3] P. Alessio, P.H.B. Aoki, L.N. Furini, A.E. Aliaga, C.J.L. Constantino, Spectroscopic techniques for characterization of nanomaterials, Nanocharacterization Tech. 3 (2017) 6598. [4] P.A. Williams, C.E. Hughes, G.K. Lim, B.M. Kariuki, K.D.M. Harris, Discovery of a new system exhibiting abundant polymorphism: m-Aminobenzoic acid, Cryst. Growth Des. 12 (2012) 31043113. ˇ ´ , S. Rimpelova, J. Malinˇc´ık, M. Kohout, [5] K. Dobrovolny´, P. Ulbrich, M. Svecova et al., Copper nanoparticles in glycerol-polyvinyl alcohol matrix: in situ preparation, stabilisation and antimicrobial activity, J. Alloy. Compd. 697 (2017) 147155. [6] D.J. Smith, Characterization of nanomaterials using transmission electron microscopy, 2015. [7] J.I. Goldstein, D.E. Newbury, J.R. Michael, N.W. Ritchie, J.H.J. Scott, D.C. Joy, Scanning Electron Microscopy and X-ray Microanalysis, Springer, 2017. [8] D. Brabazon, A. Raffer, 3 advanced characterization techniques for nanostructures, in: W. Ahmed, M.J. Jackson (Eds.), Emerging Nanotechnologies for Manufacturing, William Andrew Publishing, Boston, 2010, pp. 5991. [9] H.C. Hulst, H.C. van de Hulst, Light scattering by small particles, Cour. Corp (1981). [10] P.C. Hiemenz, R. Rajagopalan (Eds.), Principles of Colloid and Surface Chemistry, Revised and Expanded, CRC Press, 2016.
Chapter 3 Analytical techniques for nanomaterials
[11] B.J. Berne, R. Pecora, Dynamic light scattering: with applications to chemistry, biology, and physics, Cour. Corp (2000). [12] A.A. Bunaciu, E.G. Udri¸STioiu, H.Y. Aboul-Enein, X-ray diffraction: instrumentation and applications, Crit. Rev. Anal. Chem. 45 (4) (2015) 289299. [13] K.D.M. Harris, Powder diffraction crystallography of molecular solids, Top. Curr. Chem. 315 (2012) 133178. [14] P. Pandey, R. Kurchania, F.Z. Haque, 2015. [15] D.P. Acharya, P.G. Hartley, Progress in microemulsion characterization, Curr. Opin. Colloid Interface Sci. 17 (5) (2012) 274280. [16] A. Hajimohammadi, J.L. Provis, J.S. Van Deventer, Time-resolved and spatially-resolved infrared spectroscopic observation of seeded nucleation controlling geopolymer gel formation, J. Colloid Interface Sci. 357 (2) (2011) 384392. [17] A.L. Andrade, J.D. Fabris, M.C. Pereira, R.Z. Domingues, J.D. Ardisson, Preparation of composite with silica-coated nanoparticles of iron oxide spinels for applications based on magnetically induced hyperthermia, Hyperfine Interact. 218 (1) (2013) 7182. [18] H. Agarwal, S. Yadav, G. Jaiswar, Effect of nanoclay and barium sulfate nanoparticles on the thermal and morphological properties of polyvinylidene fluoride nanocomposites, J. Therm. Anal. Calorim. 129 (3) (2017) 14711479.
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4 Toxicity of nanomaterials Kumar Rajendran1,2, Latha Pujari3, Madhuri Krishnamoorthy1, Divya Dharmaraj1, Kannan Karuppiah4 and Kannapiran Ethiraj2 1
Aquatic Microbiology Lab, Department of Animal Health and Management, Alagappa University, Karaikudi, Tamil Nadu, India 2Department of Fisheries Science, Alagappa University, Karaikudi, Tamil Nadu, India 3Department of Pharmacology, Institute of Pharmaceutical Technology, Sri Padmavati Mahila Visvavidyalayam, Tirupati, Andhra Pradesh, India 4Department of Zoology, Kongunadu Arts and Science College, Coimbatore, Tamil Nadu, India
4.1 4.1.1
Introduction Nanomaterials
Nanomaterials are the particles of organic or inorganic materials having defined sizes usually in the range of 1100 nm. The source of nanomaterials may be natural, such as volcanoes and mineral springs, biogenic from living organisms [1], and manmade processes using plants [2,3] and microorganisms [4,5] and mining. Due to their light weight, smaller size, increased surface area, high conductivity, and high strength, they have gained wide application in areas such as optical, magnetic, electrical, pharmaceutical, environmental, medicine, energy production, mining, textile, automobiles, and so forth. These nanomaterials are inevitably released in the environment during the manufacturing process, use, and disposal process. Their unique properties and high penetration ability make them not only attractive for industrial and medical technologies, but also potentially harmful for the environment and living organisms. Several studies have revealed that upon entry into biological systems, the nanoparticles translocate and easily diffuse into the cell membrane and interact with the metabolic process in the cytoplasm, resulting in the generation of reactive oxygen species (ROS) [6]. The excess ROS production leads to oxidative stress that causes DNA damage, cytotoxicity, apoptosis, interruption in cell signaling, development of cancer, and other disorders [7,8]. Hence, there is a need to understand their toxicities and interaction with the biological system. Nanomaterials-Based Electrochemical Sensors: Properties, Applications, and Recent Advances. DOI: https://doi.org/10.1016/B978-0-12-822512-7.00001-6. © 2024 Elsevier Inc. All rights reserved.
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4.1.2
Effect of physicochemical properties of nanomaterials on toxicity
The toxicity of nanomaterials depends on various factors [9]. The effect of nanomaterials in the biological systems is mainly dependent on their size, surface chemistry, dose, and so forth [10]. Several toxicological studies reported that smaller nanoparticles cause more negative effects than the large particles of the same chemistry, composition, and crystalline structure [1114]. Large particles cannot pass the biological barriers and cell membranes and are easily removed from the circulation. Further, smaller metallic nanomaterials tend to move rapidly through the systemic circulation, whereas non-metallic nanomaterials cannot translocate easily [1517]. Anatase titanium dioxide (TiO2) nanoparticles are more cytotoxic or cause oxidative DNA damage compared to rutile phase [18]. Aggregation of metallic nanomaterials seems to reduce their toxicity, as it lowers the reactive surface area and limits their translocation [19]. Usually, nanomaterials aggregate in sea water and are influenced by the organic matter in the fresh water, thus altering their toxicity. Coating the nanoparticle surface with stabilizing agents will prevent the nanoparticle aggregation. Positively charged nanomaterials interact efficiently with the negatively charged cell membranes and accumulate inside the cells.
4.2
Toxic effects of nanomaterials on humans and animals
Toxicity of nanomaterials has been studied in human/animal cell lines, small invertebrates, mice, and fish. The toxicity of nanomaterials in humans is mostly observed on medically important cell lines, especially cancer cells. Nanoplastics showed a clathrin-mediated endocytosis pathway and an energy-dependent mechanism of internalization. Small-sized polystyrene nanoparticles strongly induced upregulation of IL-6 and IL-8 genes affecting the cell viability of gastric adenocarcinoma (AGS) cells [20]. Mahler et al. reported that acute oral exposure to polystyrene nanoparticles may disrupt iron transport due to nanoparticle disruption of the cell membrane of intestinal cells and chronic exposure can cause remodeling of the intestinal villi [21]. Biosynthesized silver nanoparticles showed significant cytotoxic activity in dose-dependent cancerous cells [22]. Zinc oxide (ZnO) nanoparticles induced the expression of activating transcription factor 3 in human
Chapter 4 Toxicity of nanomaterials
55
bronchial epithelial cells leading to apoptosis [23]. Platinum nanoparticles enhance ROS production, resulting in induction of cytotoxicity and apoptosis in CHANG and HuH-7 human liver cells by modifying the cell morphology and density, increasing cell apoptosis, and causing chromosome condensation [24]. Human lung epithelial cells (BEAS-2B) on exposure to cerium oxide nanoparticles led to cell death, ROS increase, reduced glutathione, and the induction of oxidative stressrelated genes [25]. A brief summary of the toxic effect of various nanomaterials in human and animal cell lines is shown in Table 4.1. In an aquatic environment, nanoplastic materials can affect organisms from various trophic levels, including bacteria [35], algae [36], arthropods [37], echinoderms [38], bivalves [39], rotifers [40], and fish [41]. Polystyrene nanoparticles accumulated in the yolk sac and migrated to the gastrointestinal tract, pancreas, liver, gallbladder, heart, and brain as early as 24 h and 120 h post-fertilization in developing zebra fish (Danio rerio)
Table 4.1 Toxic effects of nanomaterials on human and animal cell lines. Nanomaterials
Effects
References
Polystyrene nanoparticles
Affect cell viability, inflammatory gene expression, and cell morphology in AGS cells Toxic to mammalian cells Induce apoptosis in human neural progenitor cells and rat brain tissue Induced apoptosis in human bronchial epithelial cells Cytotoxic to rat and human intestinal cells (IEC-6) in a doseand time-dependent manner Induced genotoxicity and apoptotic activity in human normal and cancer hepatic cells through oxidative stress-mediated Bax/Bcl-2 and caspase-3 expression Induction of oxidative DNA damage in human SH-SY5Y neuronal and A172 glial cells. Cytotoxic to MCF-7, A549, and HepG2 cancer cells Cytotoxic to 16HBE human bronchial epithelial cells Induce proteostasis disruption and autophagy in human trophoblast HTR-8/SVneo cells; mitochondrial dysfunctions and oxidative stress in murine microglial cells (BV-2) Cytotoxicity by an apoptotic process in human lung epithelial cells (BEAS-2B)
[20]
Silver nanoparticles Gold nanoparticles ZnO nanoparticles Cupric oxide nanoparticles Platinum nanoparticles
Iron oxide nanoparticles Hematite nanoparticles Silica nanoparticles Titanium dioxide nanoparticles
Cerium oxide nanoparticles
[22,26] [27] [23] [28] [24]
[29] [30,31] [32] [33,34]
[25]
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lead to swimming hypoactivity of the larvae [42]. Polystyrene nanoplastics of 20 nm diameter can reach and bioaccumulate in the brain of zebra fish embryo, leading to excessive ROS, oxidative DNA damage in the brain regions, increasing mortality, and prevailing abnormalities [43]. Chronic exposure to nanoplastics did not affect the survival or body length of Daphnia pulex. Nanoplastics influence the growth rate and reproduction in the F2 generation, indicating their potent multigenerational and long-term toxic effects on D. pulex [44]. Polystyrene nanoparticles with different surface charges affect the immune cells’ (coelomocytes) ability in the Antarctic sea urchin Sterechinus neumayeri [45]. Polymethylmethacrylate nanoplastics (B45 nm) were reported to interfere with the lipid metabolism and the proper functioning of the immune response in marine fish Dicentrarchus labrax after a short-term exposure [46]. Recent studies showed that nanoplastics adversely affect fish at different stages of development. Nanoplatics have the potential to penetrate different biological barriers and accumulate in many important organ tissues, affecting growth and the immune system, decreased locomotor and foraging activities, and alterations on metabolism of lipid and neurotoxicity [47,48]. The nematode Caenorhabditis elegans (C. elegans) is widely used for evaluating toxicity of pollutants and nanomaterials. Several metal nanoparticles showed toxicity to larvae and adults of mosquitos, ticks, lice, and mites (LC50 values 5 1 to 35 μg mL21) [49]. The toxic effect of nanomaterials in humans and animals is shown in Table 4.2. Silver nanoparticles disrupt the mammalian cell membrane through oxidative damage. Silver nanoparticles were reported to accumulate in reproductive organs, thereby affecting reproductive and development processes [50,51]. TiO2 nanoparticles of size less than 100 nm are transported and retained in the liver, kidneys, spleen, and lung tissues after uptake by the gastrointestinal tract in adult mice [52]. Copper nanoparticles mainly accumulate and damage the kidney, liver, and spleen and also exhibit genderdependent features of nanotoxicity in mice [53]. Nanoscale zinc powder causes lethargy, vomiting, and diarrhea in mice [54]. Manganese dioxide nanoparticles reduce the sperm count and motility as well as decrease the number of spermatogonia, spermatocytes, and diameter of seminiferous tubes [55]. Humans and animals have evolved and devloped a series of biological barriers including the airblood barrier, the bloodbrain barrier, and the placental barrier to defend against foreign particles. Respiration is one of the important routes of entry of nanomaterials into the human/animal body. After inhalation, TiO2 and CeO2
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Table 4.2 Toxic effects of nanomaterials to humans and animals. Nanomaterials
Effects
References
Nanoplastics
Affect growth and the immune system, decreased locomotor and foraging activities, and alterations on metabolism of lipid and neurotoxicity in marine organisms Oxidative stress-mediated DNA damage, inhibition on the reproduction and growth, and reduced life span in Nematode Caenorhabditis elegans Avoidance behavior, reduced reproduction and growth, and gut disruption in earthworm Oxidative stress due to upregulation of metallothionein-containing protein mRNA or alterations in the level of steady-state glutathione S-transferase mRNA in springtails Folsomia candida Development of Artemia salina Neurotoxicity to zebra fish Granuloma, fibrosis, or inflammation in the lungs Neurotoxicity to zebra fish embryo development Inflammation in rat lung tissue Hepatic injury, nephrotoxicity, and myocardial damage in mice; delaying the development of fetal mice and inducing skeletal malformation Kidney, liver, and spleen injury in mice Anemia, liver damage, and lesions in renal and heart tissue in mice Reproductive toxicity in adult male rats Slight liver, spleen, and kidney damage in mice. Abnormal embryonic development and abortion in early pregnant mice Inflammatory responses, oxidative stress and enhanced microvascular permeability in the rat lung Larvicidal activity against Aedes aegypti Sorb to wax layer of Sitophilus oryzae resulting in insect dehydration Trypsin inhibition in larvae of Aedes aegypti, Helicoverpa armigera, Callosobruchus maculatus, Callosobruchus chinensis, and Maconellicoccus hirsutu Severe midgut epithelial injury in bumblebees, Bombus terrestris L.
[47,48]
Silver nanoparticles
Silver nanoparticles Silver nanoparticles
Single-walled carbon nanotubes Carbon nanotubes Graphene Fullerene TiO2 nanoparticles Copper nanoparticles Zinc powder MnO2 nanoparticles Gold nanoparticles Ferric oxide nanoparticles ZnO nanoparticles Al2O3 nanoparticles Gold nanoparticles
Silica nanomaterials
nanoparticles can cross the airblood barrier and translocate via systemic circulation and accumulate in the extrapulmonary organs [80,81]. Nanomaterials gain entry to the central nervous system by blood circulation through injection, inhalation, and gavage [71,82]. TiO2 nanoparticles significantly damaged the neurons in the cerebral cortex and affect the secretion of various hormones and neurotransmitters (norepinephrine, dopamine, 5-hydroxytryptamine,
[5658]
[59,60] [61,62]
[63,64] [65,66] [67] [68] [52,69] [53,70] [54] [55] [7173] [74,75] [76] [77] [78]
[79]
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and monoamine) in mice. Fe2O3 nanoparticles cause pathological changes in hippocampus, striatum, and olfactory bulb [83]. Certain nanoparticles can cross the placental barrier depending on the size and surface of the nanoparticles and the developmental stages of the fetuses. Tian et al. reported that intrauterine inflammation is capable of enhancing the materno-fetal transfer of gold nanoparticles that are less than 15 nm in mice, especially in the late gestation stage of pregnancy [84]. Gold nanoparticles transfer into embryonic tissues and inhibit the ectodermal differentiation of embryonic stem cells, resulting in a lower fetal survival rate, high abortion rate, and abnormal decidualization [72]. However, exposure to gold nanoparticles during late pregnancy had little or no impact on fetuses. Maternal exposure of TiO2 nanoparticles inhibited development of the fetal skeleton, which may be associated with reductions in both calcium and zinc in maternal serum and the fetus [69].
4.3
Toxic effects of nanomaterials on microorganisms
The toxicity of various nanomaterials has been studied in medically important microorganisms. Generally, toxic property of nanoparticles varies between the types of microorganism and also depends on the membrane structure. It was mainly found that gram-negative bacteria are less sensitive than grampositive bacteria. Metal nanoparticles inhibit microorganisms through several possible mechanisms by metal ions such as (1) disruption of the cell membrane, (2) denaturation of the thiol group of critical enzymes, (3) creation of highly ROS, (4) inactivation through the respiratory burst mechanism, (5) disruption of the cellular transport system, and (6) interaction of the metal ions with the microbial DNA. The toxic effect of nanomaterials to microorganisms is shown in Table 4.3. Silver nanoparticles exhibit toxicity on microorganisms through reactive oxygen damage, ROS generation, membrane damage, protein oxidation, DNA damage, and so forth [98]. Silver nanoparticles penetrate the cell membrane and accumulate in the cytoplasm, where it interacts with the sulfur containing macromolecules leading to the cell lysis [99]. ZnO nanoparticles showed antimicrobial activity against Candida albicans with the concentration of 9.31 μg mL21 [100]. Bayrami et al. reported that the MIC values of ZnO nanoparticles against E. coli and S. aureus were 0.8 and 0.4 mg mL21, respectively [101]. Antibacterial property of TiO2 nanoparticles is based on
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Table 4.3 Toxic effects of nanomaterials to microorganisms. Nanomaterials
Effects
References
Silver
Antibacterial Antifungal Antifungal Antibacterial Antibacterial Antibacterial Antibacterial Inhibit the growth of certain bacteria and fungi; alter microbial community composition High concentrations repress most enzyme activities and lower the microbial activity and biomass in soils Inhibited the growth of Rhizoctonia solani Cell membrane disruption and protein leakage in bacteria Antibacterial
[85,86]
Silver oxide Gold Copper TiO2 nanoparticles Carbon nanomaterials Multiwalled carbon nanotubes Nitrogen-doped carbon nanohorns ZnO Platinum nanoparticles
the ROS production, which damage the bacterial cell membrane [102]. Antibacterial activity of TiO2 nanoparticles will be enhanced in the presence of light [103]. Subhapriya and Gomathipriya reported that the green synthesized TiO2 nanoparticles showed antifungal activity against C. albicans at 10 mg mL21 concentration [104]. Magnetite (Fe3O4) nanoparticles were reported to show antibacterial activity [105], whereas hematite (α-Fe2O3) nanoparticles had no negative effect on the growth of bacterial cells [30]. Nidhin et al. observed that 0.5 mM concentration of gold nanoparticles was sufficient to inhibit the growth of C. albicans [106].
4.4
Toxic effects of nanoparticles on plants
Plants typically absorb both essential and nonessential elements. Nanomaterials can enter plants through accidental release, contaminated soil/sediments, or direct application, resulting in notable negative impacts on food chains. Nanomaterials of less than 20 nm can pass through the plant cell wall pores, and larger particles can cause enlargement of pores or induce new pores in the cell wall [107]. Nanomaterials may also enter the plant through the stomatal openings on the leaf surface or through the base of trichomes and then
[87,88] [89] [90] [91] [92,93] [94] [95] [96] [97]
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transported to other tissues of the plant [108]. Larger nanomaterials accumulate in the cytoplasm, while smaller ones (less than 30 nm) may even enter the nucleus causing genotoxicity (micronuclei and cytogenetic anomalies) [109,110]. Plant response to nanomaterials was reported to vary depending on the type of nanomaterial, the plant species, and their growth stages (Table 4.4). There are contradictory effects of the same nanomaterial in different plants. For example, carbon nanotubes were found to show a negative effect in tomatoes and lettuce, whereas carrots and cabbage were unaffected by the nanotubes [111]. Multiwalled carbon nanotubes induced phytotoxicity (cell death and electrolyte leakage) at the seedling stage at above 1000 mg L21 in red spinach, lettuce, rice, and cucumber [112]. Ghosh et al. reported that multiwalled carbon nanotubes might cause chromosomal aberrations, DNA fragmentation, and apoptosis in root cells of Allium cepa [113]. Aluminum oxide (Al2O3) nanoparticles cause root length inhibition, root cell damage, DNA fragmentation, and induction of programmed cell death in an agronomic plant, Triticuma aestivum L. [122,123]. Aluminum nanoparticles were found to reduce the root elongation in corn, carrot, soybean, cucumber, and cabbage [114]. However, surface coating of the aluminum nanoparticles will
Table 4.4 Toxic effects of nanomaterials to plants. Nanomaterials
Effects
References
Single-walled carbon nanotubes functionalized with poly-3aminobenzenesulfonic acid Multiwalled carbon nanotubes
Root length reduction in tomato and lettuce
[111]
Significant reduction of root and shoot lengths of red spinach, lettuce, and cucumber Reduce the root elongation Inhibition of seed germination of corn and rye grass Reduce the length of emerging roots of zucchini plants Genotoxicity in Allium cepa Reduced root and shoot weight, carotenoid, and chlorophyll a and b and increased proline content in wheat seedlings Delay in germination, root length reduction, and reduced mitotic index in Zea mays and Vicia narbonensis Oxidative DNA damage in soybean plants
[112]
Aluminum nanoparticles ZnO nanoparticles Copper nanoparticles Silver nanoparticles SiO2 nanoparticles
TiO2 nanoparticles
CeO2 nanoparticles
[114] [115] [116] [117] [118]
[119,120]
[121]
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reduce their phytotoxicity. Nanoparticles of Zn or ZnO terminated root elongation and seed germination of corn and rye grass at 2000 mg L21 concentration [115]. ZnO nanoparticles exhibited dose-dependent root length inhibition with complete block of root growth with 50 mg L21 and mitotic aberrations in garlic (Allium sativum L.) plants [124]. Copper nanoparticles crossed the cell membrane and accumulated inside the plant cells. Copper nanoparticles inhibit the growth of seedling of Triticum aestivum (wheat) and Phaseolus radiatus (mung bean) [125]. Copper oxide nanoparticles cause inhibition of germination, reduction of root and shoot length and biomass, alteration of photosynthesis and respiration rates, changes in enzymatic activities, and oxidative damage to DNA [126,127]. Silver nanoparticles induce cytotoxic and genotoxic effects as evidenced by the increased number of chromosomal aberrations (chromatid and isochromatid types of gaps, breaks, and fragments), micronuclei, and decreased mitotic index in root tip cells of Vicia faba [128]. Silver nanoparticles penetrate root tip cells of A. cepa (onion) and impair stages of cell division producing numerous chromosomal breaks and cell disintegration [117]. Negatively charged silica nanoparticles were reported to cause reduced development and chlorosis in Arabidopsis thaliana, whereas uncharged silica nanoparticles did not show any phytotoxicity despite significant uptake [129]. Silva and Monterio reported that silica nanoparticles reduced the germination rate and root growth as well as chromosomal aberrations in root tip cells of A. cepa [130]. High concentrations of SiO2 nanoparticles (200 mg L21) reduced root and shoot weight, carotenoids, and chlorophyll a and b content and increased catalase activity and lipid peroxidation in leaves of T. aestivum L. seedlings, but showed some positive effects at lower concentrations [118]. Several studies confirmed the cytotoxic and genotoxic potential of TiO2 nanoparticles in plants. The toxic effect of TiO2 nanoparticles depends on several variables including the size, concentration, crystalline form, plant species, and time of exposure. TiO2 nanoparticles induced oxidative stress-dependent phytotoxic effects and DNA fragmentation in Vicia narbonensis [119]. In A. cepa, TiO2 nanoparticles induce micronuclei and chromosomal aberrations, resulting in reduction of root growth [131].
4.5
Assessment of toxicity of nanomaterials
Organization for Economic Co-operation and Development (OECD) implemented some national policies that mainly focus on the safety evaluation and assessment of manufactured
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nanomaterials (MNMs) to ensure human health and environmental safety [132]. The work is endorsed to OECD’s Working Party on Manufactured Nanomaterials (WPMN) established in 2006. The WPMN promotes the safety assessment of nanomaterials on environment and human health. There are several in vitro and in vivo methods for determining the toxicity of nanomaterials. The nanomaterials alter the gene expression, reproductive function, and growth and induce behavioral changes. The in vitro evaluation of toxicity of nanomaterials in one of the robust methods widely accepted for its advantages that include ease of conduction, small sample size, low cost, reduced use of animals, and being fast. These assessments are based on oxidative stress, DNA damage, apoptosis, necrosis, and alteration in gene expression induced by nanomaterials. These are assay procedures recommended by OECDENV/JM/MONO (2018)4 as follows.
4.5.1
Cytotoxic assays
4.5.1.1 5-Diphenyltetrazolium bromide assay 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay is widely used in the evaluation of nanotoxicity. This test is widely accepted due to its reproducibility, fastness, and ease of conduction. The principle involved in this test is the formation of formazan that is detected spectrophotometrically at 570 nm. It quantifies the viability of cells, cell proliferation, and cytotoxicity in culture media [133]. Though MTT assay is a traditional cell proliferation assay, it has a drawback that the formazan crystal formed is water-insoluble and requires further solubilizing steps for detection. To minimize the alteration in measurements, utmost care must be taken for cell additives and media pH. Modified tetrazolium derivatives like water-soluble tetrazolium salt (WST-1), XTT, WST-8, and so forth are synthesized to produce water-soluble formazan. Hence, these assays are more preferred nowadays.
4.5.1.2 Reactive oxygen species/oxidative assays It is the most commonly used method for detecting ROS generation, 20 , 70 -dichlorofluorescein diacetate (DCFDA), a nonfluorescent probe assay. This assay helps in measuring different types of ROS like HO, RO, ROO, ONOO-, and H2O2 in the presence of cellular peroxidases. The principle behind this assay is that DCFDA undergoes oxidation by ROS in the cell and is converted into 2,7dichlorofluorescein, a highly fluorescent compound detected by
Chapter 4 Toxicity of nanomaterials
fluorescent spectroscopy [134]. The other tests used for detecting oxidative stress were thiobarbituric acid assay and lipid peroxidation [135].
4.5.1.3
Neutral red uptake assay
Neutral red (2-amino-3-methyl-7-dimethylaminophenazoniumchloride) is a weakly cationic dye. It is widely used to assess the integrity of a cell membrane and cell viability. The dye easily diffuses into the cell membrane and bound to the lysosomes by electrostatic hydrophobic bonds to anionic and/ or phosphate groups of the lysosomal matrix. Alterations in cell integrity induced by nanomaterials reduce the uptake of neutral red into lysosomes [136]. OECD guidelines (OECD 432-TG) for testing chemicals accepted the in vitro 3T3 neutral red uptake phototoxicity test to assess the xenobiotics that induce photocarcinogenicity, photoallergic, and photogenotoxicity [137].
4.5.1.4
Apoptosis assay
Programmed cell death is known as apoptosis. It was characterized by blebbing in the cytoplasm, pyknosis, karyorrhexis, and karyolysis, where finally the DNA fragmentation takes place. Generation of free radicals is one of the major contributors for the damage of DNA and induction of apoptosis. Several studies revealed that nanomaterials are potent inducers of ROS [138]. There are several assays for detecting apoptosis, and the most used assays are terminal deoxynucleotidyl transferase (TdT) deoxyuridine triphosphate (dUTP) nick end labeling (TUNEL) and Comet assays. TUNEL assay detects the DNA fragments. In this assay, TdT-mediated addition of a labeled dUTP to 30 -OH ends of DNA fragments induced by apoptosis takes place. The fluorescent dUTP is further estimated by using fluorescent microscopy or immunohistochemical stains. It is also used to detect necrotic cell death induced by toxic substances [139]. Comet assay is widely used for detecting DNA single strand breaks (strand breaks and incomplete excision repair sites) because of its flexibility, low cost, small sample size, and single data collection with good statistical interpretation. The DNA bases with oxidative damage are detected by adding specific endonucleases, such as formamidopyrimidineDNA glycosylase and endonuclease III [140].
4.5.2
Genotoxicity/mutagenicity assays
Bacterial reverse mutation test or Ames test was first developed by Bruce Ames in 1970. This test helps to assess the
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mutagenic potential of nanomaterials and was conducted as per OECD-471 TG [141]. The principle behind the test is that it detects mutations which revert in the different strains of Salmonella like S. typhimurium TA1535, S. typhimurium TA1537 or TA97 or TA97a, S. typhimurium TA98, S. typhimurium TA100, and S. typhimurium TA102, and E. coli strains WP2 uvrA or E. coli WP2 uvrA (pKM101) and restore the function of bacteria to synthesize its own essential amino acid histidine. The reverent bacteria that grow in the histidine or tryptophandeficient media indicate mutations are occurred in them due to test chemicals/nanomaterials. Though it is not a perfect model for humans and not recommended for testing of MNM, it is widely acceptable, as it is less expensive, rapid and costeffective. Several nanomaterials like gold nanoparticles, silver nanoparticles, ZnO nanoparticles, SiO2 nanoparticles, TiO2 nanoparticles, carbon nanotubes, and fullerenes are tested as per OECD-471 TG.
4.5.2.1 In vitro mammalian chromosomal aberration test In this assay, the nanomaterials/test chemical is exposed to the mammalian or human cell cultures with and without an exogenous source of metabolic activation and incubated (OECD 473-TG). Later, they are treated with colchicine, a metaphase arresting substance, harvested, and examined for chromatid or chromosomal aberrations.
4.5.2.2 In vitro mammalian cell gene mutation tests using the Hprt and xprt Genes It helps to assess the genetic mutations at hypoxanthineguanine phosphoribosyl transferase, xanthine guanine phosphoribosyl transferase, and thymidine kinase end points. It detects the cell type, gene locus, and phenotype expression in mammalian cell lines. The mammalian cell cultures were exposed to test chemicals with and without metabolic activation and incubated as per OECD 476-TG and evaluated for cytotoxicity and phenotype expression. It detects the forward mutations, and toxicity of TiO2, ZnO, SiO2, and MWCNTs nanomaterials was detected by this method.
4.5.2.3 In vitro mammalian micronucleus test It detects the micronuclei that are originated during anaphase of cell division in whole chromosome that fails to migrate to the poles and from acentric chromosome fragments
Chapter 4 Toxicity of nanomaterials
(i.e., lacking a centromere). It was performed as per OECD 487-TG, where mammalian cells treated with nanomaterials both with and without the liver extract are allowed to grow till the formation of micronuclei in the interphase of cells. The addition of cytochalasin B prior to mitosis helps in identifying and analyzing micronuclei. This test also provides information of the mechanism of action of micronuclei formation and chromosomal damage when treated with immunochemical labeling of kinetochores, or hybridization with centromeric/telomeric probes (fluorescence in situ hybridization techniques). Nanomaterials like SiO2 and TiO2 nanoparticles were assessed as per these guidelines.
4.5.3
In vivo assessment of nanomaterials
Though several effective in vitro tests which are robust, reliable, reproducible, and low-cost and can be conducted in short duration, are available for testing MNM, for long-term toxicity studies, the best model is in vivo studies. In vivo studies are conducted in animal species like rats, mice, rabbits, and so forth, and they have their own limitations like high cost, requirement of skilled personnel, high time consumption, being laborious, and having ethical concerns, but they still gained significant importance in providing information on absorption, distribution, metabolism, excretion, and toxicity, organ toxicity, and accumulation of xenobiotics in the body. The data obtained is more reliable and safer. The lethal dose LD50 of the nanomaterials was determined as per OECD 425, 423 guidelines in different doses such as 5, 50, 300, and 2000 mg Kg21. Acute toxicity studies of several nanomaterials are conducted as per OECD guidelines [142]. All the studies proven to be safe in in vitro are not the same in in vivo. It was proven on ZnO nanomaterials, which were safe in the in vitro toxicity test but produced pulmonary toxicity in rats [143]. Repeated dose inhalation toxicity studies are performed as per OECD 412-TG, which was revised in 2009 and 2018 to incorporate the testing of particle aerosols, including nanomaterials. The study was conducted in rats and guinea pigs in both sex to obtain information on broncho-alveolar lavage fluid analysis and lung burden to poorly soluble nanoparticles. Chronic toxicity studies (OECD 452-TG) are conducted preferably in rodents in routes intended for humans to assess the long-term toxicity of nanoparticles on organs, accumulation in tissues, alteration in hormones, and neurological and behavioral changes. The challenges with in vivo studies are preparation of nanoparticle
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suspension by using suitable solvents. Utmost care must be taken in selection of solvents based on physicochemical properties of nanoparticles to avoid solvent-induced toxicity and aggregation.
4.5.3.1 Mammalian bone marrow chromosome aberration test The test is usually conducted in rats, mice, and Chinese hamsters. The animals that are exposed to the nanoparticles in the routes commonly intended by humans, and animals are periodically sacrificed to detect the structural chromosome aberrations. Prior to sacrifice, the animals were treated with colchicine, a metaphase-arresting compound. Later, the bone marrow cells were collected from the animals, stained and tested for chromosome aberrations. The study was conducted for a period of 14 days as per OECD 475-TG.
4.5.3.2 Mammalian erythrocyte micronucleus test (OECD 474-TG) The test is conducted usually to assess the damage induced by nanoparticle/xenobiotics to the chromosomes or the mitotic apparatus of erythroblasts. The bone marrow cells or peripheral blood cells of rodents were collected and evaluated for micronuclei formation. Increased formation of micronuclei indicates the cytogenetic damage induced by nanomaterials. The number of mature and immature erythrocytes in each animal was determined, and it should be at least 500 erythrocytes for bone marrow and 2000 erythrocytes for peripheral blood cells. At least 4000 immature erythrocytes per animal should be scored for the incidence of micronucleated immature erythrocytes [144]. Other models used for the assessment of acute toxicity of silver nanoparticles as per ENV/JM/MONO (2017) 31 include different species of fish like Cyprinus carpio and D. rerio and invertebrates like Daphnia magna, Daphnia galeata, and D. pulex. Chronic toxicity is evaluated in fishes like Oryzias latipes and D. rerio. Some of the studies are also conducted in algae and cyanobacteria such as Desmodesmus subspicatus, Anabaena flosaquae, and Pseudokirchnerella subcapitata. Microorganisms like Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, Arthrobacter globiformis, and Vibrio fisheri are used for detection of nanotoxicity. Soil invertebrates except arthropods are also used to evaluate the genotoxicity of nanomaterials and xenobiotics. The commonly used soil invertebrates are C. elegans, Eisenia Andrei, and Perionyx excavates.
Chapter 4 Toxicity of nanomaterials
4.5.4
In silico models
It is the emerging assay model for assessing toxicity of nanomaterials. This model has advantages like being less time-consuming and cost-effective and having no ethical issues since animals were not used. The approach of this model is that it uses physicochemical properties of the molecules (Quantitative StructureActivity Relationships) and quantum chemistry. Though the approach is effective, it has its own challenges since it is a theoretical model [145].
4.6
Conclusion and future prospects
Nanoparticles are one of the candidates with the effective applications in medical, industrial, and agricultural areas. Different types of mechanisms are involved in the toxicity of various nanomaterials and are dependent mainly on size and surface characteristics. The extent of toxicity of nanomaterials depends on the dose and duration of exposure. The exact mechanism of toxicity of several nanomaterials is still not clear and is contradictory. Several studies reported that the toxicity is mainly due to the generation of ROS or oxidative stress. However, several nanoparticles were reported to possess excellent free radical scavenging property and be very good antioxidants. In vitro and animal model studies used nanomaterial concentrations often exceeding a realistic relevant dose. Compared with laboratory conditions, the behavior of nanomaterials in terrestrial and aquatic ecosystems is more complex due to the heterogeneity of the environmental conditions. Hence, more field studies are endorsed to improve our understanding of the toxicity of nanomaterials. Further nanomaterials were also found to accumulate in plants and fish tissues, indicating possible threat to higher trophic levels along the food chain. Several studies showed the toxic effect of almost all types of nanomaterials on biological cells. Long exposure to these toxic nanomaterials is hazardous to any living organism, including microorganisms, and therefore the usage of metallic nanoparticles should be restricted and proper care should be taken to minimize their entry into the environment.
Acknowledgements This work has been sponsored under RUSA 2.0 Post-doctoral fellowship by Alagappa University, Karaikudi, Tamil Nadu, India. Authors are thankful for the RUSA Scheme Phase 2.0 grant [F-24-51/2014-U, Policy (TNMulti-Gen), Department of Education, Govt. of India. Dt. 09.10.2018].
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5 Electrochemical sensors and their types Arsh E Noor 1, Ikram Ahmad 2, Athar Rasheed 3, Shamim Ramzan 4, Abdur Rahim 4, Anish Khan 5,6 and Muhammad Yahya Tahir1 1
Department of Environmental Sciences and Engineering, Government College University Faisalabad, Faisalabad, Pakistan 2Department of Chemistry, University of Sahiwal, Sahiwal, Pakistan 3Department of Chemistry, Government College University Faisalabad, Faisalabad, Pakistan 4 Department of Chemistry, COMSATS University Islamabad, Lahore Campus, Lahore, Pakistan 5Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia 6Chemistry Department, Center of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah, Saudi Arabia
5.1 5.1.1
Introduction Electroanalytical chemistry
Electroanalytical chemistry is branch of electrochemistry that focuses on developing new chemically modified electrodes (CMEs), techniques, and methods for qualitative and quantitative analytical investigations. In this, the branch electrode is used as a probe for the measurement of concentration of analyte in a water sample [1].
5.1.1.1
Electroanalytical techniques
These techniques are a collection of analytical methods based upon electrical characteristics of analyte solution through constructing an electrochemical cell. These techniques are very selective and have a very low detection limit [2].
5.1.1.2
Recent developments in detection techniques
Keeping in mind the disadvantages of classical spectroscopic techniques for the detection of pollutants present in sample wastewater, it is very important to develop fast, reagent-less, cheap, facile, and efficient techniques that are fit for on-spot and on-time detection and measurement of water pollutants, Nanomaterials-Based Electrochemical Sensors: Properties, Applications, and Recent Advances. DOI: https://doi.org/10.1016/B978-0-12-822512-7.00012-0. © 2024 Elsevier Inc. All rights reserved.
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especially heavy metal ions (HMIs). There is much work development going on in this area [3].
5.1.1.3 Advantages These techniques are comparatively more convenient and easier to work with for real-time monitoring. These techniques adapt easy and facile methods and are fit for miniaturization, as they can be integrated on very small circuits devices that are portable and can be used to monitor polluted wastewater samples in real time. Consequently, sample contamination, degradation, and loss due to adsorption or shifting is also reduced. One of the biggest advantages of these techniques is that they are quick and need very short time for analysis of a sample, normally only a few minutes, and can be used for online analysis of wastewater samples [4].
5.1.1.4 Improvements needed Nevertheless, a lot of specific development is still needed in order to improve the sensitivity, selectivity, limit of detection (LOD), and automation of these techniques. For this purpose, different electrochemical techniques are combined with sensing electrodes by chemically modifying them with a wide range of interface materials for the improvement of sensitivity, selectivity, and LOD [5]. Improving the selectivity of these techniques is of utmost importance in order to detect HMIs because heavy metals present in the sample cause interference. Scientists are working to improve the selectivity of these electrochemical sensing devices.
5.1.2
Sensors
From the reviews of developments taking place in electroanalytical techniques, it is interesting to know that among all other chemical sensors, electrochemical sensors have become the fastest emerging class of sensors. Any device, system, or module which detects and measures the changes taking place in a certain environment in the form of signals which are interpreted into valuable information by the computing devices is called a sensor [6].
5.1.2.1 Ideal sensor According to IUPAC, any device which converts chemical information received from chemical reaction involving analytes present in a sample into a useful signal is termed as an ideal sensor. Chemical sensors have two main components: receptor and transformer. The receptor converts the data received during
Chapter 5 Electrochemical sensors and their types
chemical reactions into measurable energy, and the transformer changes this data into useful electrical signals [7]. An ideal sensor must have the following features: 1. Selectivity and specificity for the target analyte in a sample 2. Sensitivity with respect to target analyte concentration 3. Rapidness in response time 4. Reproducibility 5. Robustness 6. Miniaturization 7. Inexpensiveness 8. Being facile and inexpensive (nanoparticles as electrochemical sensors)
5.1.2.2
Chemical sensors
Chemical sensors are the devices that provide a definite response, which is directly related to the concentration of a particular chemical species that is present in a certain environment. These chemical sensors have some kind of transducer whose function is to convert the instrumental response in the form of signals [8].
5.1.2.3
Types of chemical sensors
Chemical sensors are categorized with respect to the characteristics or property that is needed to be determined, such as thermal, mass, optical, or electrical sensors. These sensors have the capability to detect and provide signals of the analyte about its types and concentration present in all states of matter. Among these sensors, electrochemical sensors are substantially appealing due to their excellent selectivity, sensitivity, LOD, low cost, rapidness, and easy workability. They are at the forefront of the devices currently accessible that have reached the business phase and have a wide range of significant applications in clinical, environmental, agricultural, and industrial analysis [9,10].
5.1.3
Electrochemical sensors
Electrochemical sensors are the devices that convert information received during electrochemical reactions between electrodes and analyte present in sample solution into useful quantitative and qualitative electrical signals. Electrochemical sensors display these output signals into the digital form for further analysis of the sample. For environmental monitoring, a variety of electrochemical sensors are developed depending
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upon the selectivity, sensitivity, LOD, and analyte nature in the sample and sample matrix [11,12].
5.1.3.1 Construction of electrochemical sensors An ordinary electrochemical sensor consists of four main parts, namely, sensing electrode having transduction material, reference electrode (RE), a diffusion barrier, and sample solution, which serves as the electrolyte. During chemical reaction, electrical signals originating due to redox reaction taking place between target analyte and transduction material present at the sensing electrode are converted into useful analytical information [13].
5.1.3.2 Advantages of electrochemical sensors Electrochemical sensors are emerging devices for the onsite monitoring of the environment. They provide important and useful information about the current status of an ecological system, which is helpful in developing strategies to control the environmental degradation. Electrochemical sensors are superior to many classic analytical techniques due to their many characteristics including their selectivity, sensitivity, portability, rapidness, flexibility, specificity, compactness, easy workability, and low cost [14].
5.1.3.3 Types of electrochemical sensors On the basis of electrochemical measurement techniques, electrochemical sensors are divided into these major types depending upon different types of electrical signals and principles of workability [15]: 1. Potentiometric sensors 2. Conductometric sensors 3. Impedometric sensors 4. Coulometric sensors 5. Electrochemiluminescent sensors 6. Voltammetric sensors In potentiometric electrochemical sensing techniques, important information regarding the chemical composition of the samples is determined by measuring the potential difference among electrodes. In this type of sensing technique, equilibrium is established at the interface of the sensor and change in potential is measured at the membrane or the electrode [16]. In the conductometric sensing technique, change in conductivity is measured at different frequency ranges. The RE is not
Chapter 5 Electrochemical sensors and their types
needed in these types of sensors. Conductometric measurement techniques is nonselective [17]. The impedance measurement technique measures the change in capacitance, resistance of solution, and charge transfer due to the analyte present in solution, especially HMIs. Most common techniques that are used to measure the analyte concentration present in the sample solution are ac voltammetry and electrochemical impedance spectroscopy [18]. Coulometry measurement techniques measure adsorption of electroactive species at the electrode interface by calculating the amount of charge that is passed when controlled potential is provided. Electrochemiluminescence is a broadly used measurement technique to determine the HMI concentration with respect to the luminescence effect, which takes place during the reactions involving electron transfer caused by radical ions in sample solution [19]. The voltammetric electrochemical sensing technique measures the resulting current caused by oxidation reduction reactions taking place at the electrode interface and electrolyte having electroactive species when potential is applied from an external source to the working electrode (WE) and RE. Electrical signals are directly related to target analyte’s concentration present in solution [20].
5.1.4
Cyclic voltammetry
Cyclic voltammetry (CV) investigates the system for its electrochemical behavior. Randles was the first scientist to report and describe it theoretically in 1938. In order to acquire useful qualitative data of electrochemical reactions, CV is the key technique that is used extensively. CV has the potential to quickly give significant data about the heat exchange taking place as a result of redox reactions, kinetics of reactions involving electron transfer, and adsorption reactions. For electroanalytical research, CV is the main experimental technique because it gives fast location of electroactive species involving redox potentials and gives appropriate analysis of redox reactions affected by the sample media [21].
5.1.4.1
Basic principle of cyclic voltammetry
During an electrochemical analysis, linear potential applied to the WE as a result of a cyclic voltammogram is generated. The analyte present in a sample gets oxidized or reduced due to the flow of current coming from the electrode when potential is
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varied from the formal potential Eo. The increase in current flow is directly related to analyte concentration present in sample solution. That is why CV is used for determination of the concentration of the analyte. An experimental setup to perform CV includes a three-electrode potentiostat, which is connected with working, reference, and counter electrodes (CEs) dipped in sample solution. The potentiostat measures the current at the WE, while applying and maintaining the potential at the WE and RE. The electrical charge keeps flowing between the WE and CE, and recording devices record the cyclic voltammograms in the form of a graph between current and potential [22].
5.1.5
Applications of electrochemical sensors
Electrochemical sensors are being used for environmental monitoring for many years, especially for monitoring the water quality of different water bodies, including natural and wastewater for conductivity, pH, dissolved oxygen, pathogens, HMIs, and carcinogenic pollutants of organic and inorganic nature.
5.1.6
Electrochemical sensing of heavy metal ions
An electrochemical cell is established for the detection of HMIs present in a water sample. The water sample serves as the electrolyte because of the presence of HMIs. Three electrodes are used: WE, which can be modified using different interface materials for selectivity and sensitivity, CE, and RE, which acts as a reference for the measurement of cell potential [23].
5.1.6.1 General experimental setup An electrochemical cell consisting of three electrodes normally has a CE. Normally, the passage of current takes place between the CE and WE. Current is passed through the sample solution from an external electrical source and cell potential at the interface of sample solution and electrode is measured. Different reactions occur in an electrochemical cell. Reactions taking place at the WE is important because changes in the current signals are measured, which are directly related to HMIs present in the sample [24] (Fig. 5.1). The WE can be modified using a variety of transducing nanomaterials, which serve as the interaction platform for HMIs. The WE and CE are kept separately using separators usually made up of glass. Very high input impedance instruments are used to avoid drawing of current by the RE. All the electrodes are electrically connected with laboratory instruments that serve as an electrochemical workstation or with portable
Chapter 5 Electrochemical sensors and their types
Figure 5.1 Working principal of an electrochemical sensor.
devices. These devices and instruments provide excitation electrical signals to electrodes and measure the response signals. These signals are further analyzed and interpreted by the preinstalled computer programs. Detection of HMIs using these techniques is more useful and effective because of miniaturization, small instrumentation setup, portability, and flexibility in modification of electrodes [25].
5.1.7
Carbon-based electrode materials
Presently, carbon-based electrodes are commonly used for electrochemical analysis of water due to wide potential range, small background current, great surface chemistry, affordability, low cost, and inertness to chemicals and for being sustainable to different kinds of application for the detection of analyte present in the sample. The biggest drawback of carbon-based electrodes is the reduction of electron transfer by their surface when compared to the metal electrodes. The carbon surface is purely dependent upon its origin, and as a result, it sharply reduces electron transfer [26]. These days, special focus is being given to establish more environment-friendly electrodes. Few alternative materials are being studied for their use as electrode material, which include boron-doped diamond and diamondlike carbon [27].
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5.1.7.1 Glassy carbon electrodes Glassy carbon is being remarkably used to make electrode material owing to its exceptional electrical and mechanical characteristics, broad potential range, resistance to chemicals, and its reproducibility. The resin body of phenol formaldehyde is carefully heated in a normally inert atmosphere to prepare the material used for GC [28]. Gases like hydrogen, nitrogen, and oxygen are removed by the carbonization of the material from 300 C to 1200 C. Glassy carbons have elevated density, very narrow size of pores, and very low electrical resistance [29]. To increase electrochemical activity and reproducibility of the glassy electrode, its surface is polished with alumina particles of size less than 0.05 µm [30]. Before using these glassy electrodes, it is very important to wash them using deionized water. There are many other steps that are used to increase their performance, including heating and electrochemical and laser treatments [31]. These steps remove the contaminants present at the surface of the electrode, and fresh edges of glassy carbon are exposed, increasing the density of groups having surface oxygen [32].
5.1.7.2 Chemically modified electrodes The growth of electrodes created by chemical modification of multiple conductive materials is an effective part of electrochemical studies. CMEs are being extensively used to serve a wide range of electrochemical analysis. In order to chemically modify electrodes, the WE is coated with synthesized nanomaterial having enhanced properties and functionalities. These CMEs efficiently increase the redox reaction taking place involving analytes, resulting in the amplification of signals and thus detection of the analytes without any interference [33]. These CMEs have a wide range of applications, including corrosion protection, molecular electronics, conversion and storage or solar energy, and biological and environmental matrices, electrochromic display devices, and electrochemical analysis of water samples. Electrodes are modified to enhance their stability and durability. Selectivity and sensitivity can be easily improved by chemically modifying the electrode with a wide range of nanomaterials. These CMEs have increased repeatability and reproducibility. These CMEs are primarily used in electrochemical sensors [34].
Chapter 5 Electrochemical sensors and their types
5.1.7.3
Material used for chemical modification of a glassy carbon electrode
For the improvement in the selectivity, stability, reproducibility, and selectivity of electrochemical sensors, different materials including nanoparticles, nanocomposites, metal oxides, carbon nanotubes, silicon nanowires, and graphene are being used to chemically modify the glassy carbon electrode in electrochemical sensing of pollutants in a water sample [35]. Using nanomaterials in sensing devices has decreased the LOD of many pollutants from the nano to pico level. Electrochemical sensors possessing CMEs by nanomaterials are an emerging class of electrochemical sensors because of their excellent selectivity and accessibility. Experimentation is facile and cheap, which is why these sensors are being extensively used. Nanoscaled materials have found increased application in electroanalytical techniques because of their enhanced physiochemical characteristics [36].
5.2
Conclusion
Electrochemical analysis has been improved by the use of nanomaterials because they enhance the diffusion, increase the effective surface area, enhance electrocatalytic and conductive characteristics, have excellent selectivity, and increase the signal/noise ratio. Gold nanoparticles are commonly used in electrochemical sensors.
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[7] M. Herrmann, Sensor models for the development and validation of automated driving functions, ATZ Electron. Worldw. 14 (6) (2019) 50 53. [8] T.M. Swager, J.H. Wosnick, Self-amplifying semiconducting polymers for chemical sensors, MRS Bull. 27 (6) (2002) 446 450. [9] N. Katta, M. Hira, C. Kim, A. Sivaraman, J. Rexford, Hula: scalable load balancing using programmable data planes, Proc. Symp. SDN Res. 56 (6) (2016) 85 89. [10] J.D. Fowler, M.J. Allen, V.C. Tung, Y. Yang, R.B. Kaner, B.H. Weiller, Practical chemical sensors from chemically derived graphene, ACS Nano 3 (2) (2009) 301 306. [11] Y. Fu, N. Wang, A. Yang, H.K.W. Law, L. Li, F. Yan, Highly sensitive detection of protein biomarkers with organic electrochemical transistors, Adv. Mater. 29 (41) (2017) 1703787. [12] J. Zhang, Z. Qin, D. Zeng, C. Xie, Metal-oxide-semiconductor based gas sensors: screening, preparation, and integration, Phys. Chem. Chem. Phys. 19 (9) (2017) 6313 6329. [13] Z. Chen, Z. Wang, X. Li, Y. Lin, N. Luo, M. Long, et al., Flexible piezoelectric-induced pressure sensors for static measurements based on nanowires/graphene heterostructures, ACS Nano 11 (5) (2017) 4507 4513. [14] N.P. Shetti, S.D. Bukkitgar, R.R. Kakarla, C. Reddy, T.M. Aminabhavi, ZnObased nanostructured electrodes for electrochemical sensors and biosensors in biomedical applications, Biosens. Bioelectron. 65 (43) (2019) 111417 111422. [15] P. Fabry, E. Siebert, Electrochemical sensors, Handb. Solid. State Electrochem. 76 (2) (2019) 329 369. [16] K.Y. Chumbimuni-Torres, N. Rubinova, A. Radu, L.T. Kubota, E. Bakker, Solid contact potentiometric sensors for trace level measurements, Anal. Chem. 78 (4) (2006) 1318 1322. [17] J. Qi, X. Xu, X. Liu, K.T. Lau, Fabrication of textile based conductometric polyaniline gas sensor, Sens. Actuators B: Chem. 202 (2014) 732 740. [18] J. Wang, Electrochemical sensing of explosives, Electroanalysis 19 (4) (2007) 415 423. [19] X. Li, H. Xu, Z.S. Chen, G. Chen, Biosynthesis of nanoparticles by microorganisms and their applications, J. Nanomater. 2011 (2011) 34 39. [20] M. Pumera, S. Sanchez, I. Ichinose, J. Tang, Electrochemical nanobiosensors, Sens. Actuators B: Chem. 123 (2) (2007) 1195 1205. [21] C.R. Raj, T. Okajima, T. Ohsaka, Gold nanoparticle arrays for the voltammetric sensing of dopamine, J. Electroanal. Chem. 543 (2) (2003) 127 133. [22] D. Semenova, A. Zubov, Y.E. Silina, L. Micheli, M. Koch, A.C. Fernandes, et al., Mechanistic modeling of cyclic voltammetry: a helpful tool for understanding biosensor principles and supporting design optimization, Sens. Actuators B: Chem. 259 (2018) 945 955. [23] Y. Lu, X. Liang, C. Niyungeko, J. Zhou, J. Xu, G. Tian, A review of the identification and detection of heavy metal ions in the environment by voltammetry, Talanta 178 (2018) 324 338. [24] B. Bansod, T. Kumar, R. Thakur, S. Rana, I. Singh, A review on various electrochemical techniques for heavy metal ions detection with different sensing platforms, Biosens. Bioelectron. 94 (2017) 443 455. [25] M.B. Gumpu, S. Sethuraman, U.M. Krishnan, J.B.B. Rayappan, A review on detection of heavy metal ions in water an electrochemical approach, Sens. Actuators B: Chem. 213 (2015) 515 533.
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[26] J. Wang, Carbon-nanotube based electrochemical biosensors: a review, Electroanalysis 17 (1) (2005) 7 14. [27] M.J. Lobo-Castanon, A.J. Miranda-Ordieres, P. Tunon-Blanco, A bienzymepoly-(o-phenylenediamine)-modified carbon paste electrode for the amperometric detection of L-lactate, Anal. Chim. Acta 346 (2) (1997) 165 174. [28] A. Afkhami, A. Bahiraei, T. Madrakian, Gold nanoparticle/multi-walled carbon nanotube modified glassy carbon electrode as a sensitive voltammetric sensor for the determination of diclofenac sodium, Mater. Sci. Eng.: C. 59 (2016) 168 176. [29] D. Nardiello, C. Palermo, A. Natale, M. Quinto, D. Centonze, Pulsed amperometric detection at glassy carbon electrodes: a new waveform for sensitive and reproducible determination of electroactive compounds, Anal. Chim. Acta 894 (2015) 1 6. [30] B. Thirumalraj, S. Palanisamy, S.M. Chen, K. Thangavelu, P. Periakaruppan, X.H. Liu, A simple electrochemical platform for detection of nitrobenzene in water samples using an alumina polished glassy carbon electrode, J. Colloid Interface Sci. 475 (2016) 154 160. [31] O.M. Filipe, C.M. Brett, Characterization of carbon film electrodes for electroanalysis by electrochemical impedance, Electroanalysis 16 (12) (2004) 994 1001. [32] W.E. Van der Linden, J.W. Dieker, Glassy carbon as electrode material in electro-analytical chemistry, Anal. Chim. Acta 119 (1) (1980) 1 24. ˇ Nikoli´c, V.M. Jovanovi´c, [33] A. Dekanski, J. Stevanovi´c, R. Stevanovi´c, B.Z. Glassy carbon electrodes: I. Characterization and electrochemical activation, Carbon 39 (8) (2001) 1195 1205. [34] J.J. Gooding, Nanostructuring electrodes with carbon nanotubes: a review on electrochemistry and applications for sensing, Electrochim. Acta 50 (15) (2005) 3049 3060. [35] Y. Zhang, Y. Liu, J. He, P. Pang, Y. Gao, Q. Hu, Electrochemical behavior of graphene/Nafion/Azure I/Au nanoparticles composites modified glass carbon electrode and its application as nonenzymatic hydrogen peroxide sensor, Electrochim. Acta 90 (2013) 550 555. [36] R.C. Engstrom, Electrochemical pretreatment of glassy carbon electrodes, Anal. Chem. 54 (13) (1982) 2310 2314.
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6 Electrochemical sensors and nanotechnology Safia Khan1, Mariam Khan2, Naveed Kausar Janjua3 and Syed Sakhawat Shah3 1
Department of Chemistry, Quaid-i-Azam University Islamabad, Islamabad, Pakistan 2School of Applied Sciences and Humanity, NUSASH, National University of Technology, Islamabad, Pakistan 3School of Applied Sciences and Humanity, National University of Technology, Islamabad, Pakistan
Objectives 1. To understand the significance of advanced nanotechnology with respect to its multifunctioning properties. 2. To address the multiple strategies that are currently being applied for successful application of nanotechnology in various fields. 3. To discuss the importance of electrochemical sensors and various types of electrode materials used. 4. To comprehend the application of multiple types of electrochemical sensors in nanotechnology advancement. 5. To highlight the consequences of electrochemical sensors used in nanotechnology and their synergistic impact on current scientific advancements. 6. To provide the major improvements, challenges, and future impacts of recent nanosensors based on research.
6.1
Introduction
Nanotechnology is the science of big things originating from a tiny world [1,2]. It works on the nano level of arrangement of atoms and molecules where the basic and instinctive nature of all systems are built. By origin, nanotechnology assures the development of precise and reliable devices composed of molecular sizes utilizing the tools and techniques exhibiting higher performances [3]. Besides, it is also associated with the creation of new materials at nanoscale, ranging from 1 to 100 nm, using advanced-scale analytical manipulations [4]. Nanomaterials-Based Electrochemical Sensors: Properties, Applications, and Recent Advances. DOI: https://doi.org/10.1016/B978-0-12-822512-7.00008-9. © 2024 Elsevier Inc. All rights reserved.
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As per National Science Foundation of USA, nanotechnology is the approach to apprehend, monitor, and deploy the matter at the nano level of discrete atoms and molecules [5]. It is often described as an all-purpose technology, as in its improved versions, it can exert a significant influence on a multitude of industries and be applied in all fields of science, where applied science and engineering, mainly dependent upon nanotechnology, are considered as prime accelerators of global scientific technology race. Combining the conventional science knowledge and emerging nanoscale science lays a new foundation for innovation and integration of technology. A longitudinal process based on 2000 years occurred in major scientific fields to reach the science of nanoworld and at last, every field converged to advance nanoparticles [6]. In the last few decades, global scientists have been trying to investigate the complexities of nanoscale materials, and recently, the researchers have acquired a clear picture and enough knowledge of manufacturing, manipulation, and modification of nanomaterials with the desired properties [7,8]. A multitude of products, synthesized and fabricated at nanoscale, have been introduced recently [9,10]. Wound dressings with antibacterial action contain nanoscale silver particulates [11]. Nanopowders, which can neutralize gases, are available [12]. Power-generating batteries are being manufactured by utilizing nanoscale materials, which deliver energy with a much higher efficiency and low heat loss. Moreover, transparent sunscreens are composed of nanoscaled titanium dioxide and zinc oxide, which prevents sunburns by reflecting ultraviolet (UV) radiations admirably [13]. Nanotechnology is seen as a promptly emerging field of research owing to the amazing physiognomies of nanomaterials. In comparison to bulk materials, nanomaterials are established to exhibit enhanced physical and chemical features with thermal, magnetic, plasmonics, optical, and catalytic properties. Such enriched structures have paved a path for the assimilation of these nanomaterials into modern electrochemical sensing systems as an advanced tool of emerging sensor technologies [14,15]. Noble metal-based materials and carbon-derived materials have usually been preferred in such Electrochemical (EC) sensing applications due to their chemically nonreactive nature and biocompatibility [16,17]. Silicon, nickel, palladium, cadmium telluride, gallium nitride, and several sorts of metal oxides are some materials of interest [18]. However, the more frequent applications of nanoscale materials deal with the modification of electrodes. Multiple illustrations of single nanoparticles or highly
Chapter 6 Electrochemical sensors and nanotechnology
well-ordered arrays and compositions of nanoparticles are being used as electrodes. EC sensors-based nanotechnology, including nanoelectromechanical systems, nanophotonics, and a combination of multiple nanotechnologies with microtechnology, have a wide range of chemical, biochemical, biomedical, and biological applications, which encompasses healthcare, environment monitoring, defence and security, biosensing, and light sensing [19,20]. Similarly, nanosensors have also been introduced for estimation of physical parameters and detection of electromagnetic radiations [21]. One of the frequently used detectors is based upon zinc oxide (ZnO), which can efficiently sense the UV radiations [22]. Superconducting nanowire single-photon detectors (SNSPDs) play a substantial part in various applications for visible and near-IR photon detection [23,24]. Likewise, high performance SNSPDs were developed for the infrared visible wavelength range by an Italian group at the University of Salerno [25]. These unique sensors are made up of nanowires of superconducting niobium nitride. Moreover, hard silicon detectors of various kinds have also been discovered so far [26]. In this way, nanomaterials displayed a strong interrelationship between biology, chemistry, physics, and engineering with respect to sensing applications.
6.2
Nanotechnology
Nanotechnology has been designated as a ground-breaking tool considering its potential influence on commercial applications, as it offers possible solutions to a number of hurdles experienced with emerging techniques. Owing to such a strong inter- and multidisciplinary significance of nanotechnology, a huge number of research disciplines and prospective applications involve nanotechnology.
6.2.1
Drug delivery
Dendrimers, one sort of nanostructure, are specifically designed and produced for an extensive use, mainly in curing cancer and several other diseases. Dendrimers, composed of different composite materials and their branches, are able to perform multiple functions simultaneously, like diagnosing diseased cells, drug delivery, recognizing diseased states together with cell death, location reporting, and recording outcomes of therapies [27 29].
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6.2.2
Nanofilms
A variety of nanoscale materials have been applied in thinfilm applications to make these films potentially water-repellent, self-cleaning, anti-reflective, scratch-resistant, UV- or infraredresistant, anti-fog, anti-microbial, and electrically conductive. Nanofilms are used in eye glasses, computer screens, and cameras to shield and treat their surfaces.
6.2.3
Water filtration
Scientists are working with carbon-derived membranes for water distillation and nanosensors to detect contaminants in water bodies. Many other nanoscale materials also exhibit enough potential for filtration and purification of water, for example, nanoscale titanium dioxide is used in sunscreens and sun blocks, which have been shown to neutralize bacteria [30,31].
6.2.4
Nanotubes
Carbon nanotubes (CNTs) are allotropic forms of carbon having a nanostructure of cylindrical shapes. Nanotubes are typically synthesized with a length-to-width ratio of about 28,000,000:1 [32], which seems to be significantly larger than several other materials. These cylindrical CNTs have unique properties, which enable them to be much useful in various nanotechnological applications like electronics, optics, materials science, and architecture. Nanotubes demonstrate amazing strength and distinct electrical assets and are competent conductors of heat. However, the commercialization of such nanotubes is still hindered by their toxicity [33,34].
6.2.5
Nanoscale transistors
Transistors are seen as electronic switching devices, in which a little quantity of electricity is applied as a gate to regulate the flow of a huge amount of electricity. Talking about the computers, more electronic transistors result in higher power generation. Miniaturization of transistors is leading to more efficient and powerful computers [35]. Till now, the best produced commercially available computer chips with transistors have a size of 45 nm. Researchers and industrialists are working on developing 32 nm chips [36,37].
Chapter 6 Electrochemical sensors and nanotechnology
6.2.6
Nanorobots
The innovation and introduction of nanorobots with actuators and entrenched nanobiosensors are considered as an opportunity to offer advanced medical approaches to doctors. At microscopic environments, integrated mechanisms are different from conventional techniques. It is obvious from the approaches using feed forward control, which are considered to facilitate advancements in emerging medical science. Therefore, the research and development of such microelectronic devices have led to the growth of novel biomedical instrumentations and nanoelectronics manufacturing. Such miniaturization further permits the evolution of nanorobots, promoting efficient procedures for prognosis of pathological diseases [38,39].
6.2.7
Nanotechnology and space
Nanotechnology is a fundamental tool to make the space flight applications more practical by introducing lightweight solar sails and faster cable for space elevators. These advances can lower the traveling cost in space by significantly minimizing the requirement of rocket fuels. Consequently, these new nanomaterials, in combination with nanorobots and nanosensors, could enhance the functioning of spaceships, space kits, and space equipment for making nanotechnology more useful to explore moons and other planetary bodies [40,41].
6.2.8
Nanotechnology in electronics: nanoelectronics
Nanoelectronics is responsible for increasing the performance of electronic devices with the advantage of reduced weight and decreased power consumption. Such development in nanoelectronics is due to the upgradation of display screens of electronic instruments. Increase in memory chip density could lead to reduced power inputs and decreased weight and thickness of electronic screens. Scientists are currently developing a memory chip with an anticipated density of 1 TB per square inch and even more. Hence, minimizing the size of electronic transistors up to the nanoscale could be more effective in future integrated circuits [42 44].
6.2.9
Nanotechnology in medicine
Nanotechnology is influencing the currently developing medicinal fields owing to the applications of nanoparticles.
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These nanoparticles are used for transporting and delivering drugs, heat, light, and several substances to specific target cells inside the human body. Engineered nanoparticles allow for reliable detection, efficient treatment, and increased prognosis of diseases and injuries within the target cells and therefore reduce the damage of healthy cells of the body [45,46].
6.3
Electrochemical sensors
EC sensors are being broadly accepted as a cheap and simple tool for sensitive detection of various biological and biomedical samples. The most necessary and unavoidable features of any chemical sensor include selectivity, reversibility, limit of detection, and surface structure, which are responsible for successful implementation of EC sensors. The more appropriate and acceptable sizes of nanomaterials range between 1 and 100 nm owing to their enhanced surface area. The most frequently used materials for sensing applications are discussed here.
6.3.1
Carbonaceous materials-based electrochemical sensors
Carbon-derived EC sensors are generally used due to their affordability, commendable electron transfer kinetics, chemical stability, and superb biocompatibility [47,48]. Methacrylic acrylic copolymers offer a feasible platform to ionophores to get immobilized, as revealed by the integration of multiple acrylic crown ethers. Although this novel sensor resembles conventional plasticized polyvinyl chloride comprising dissolved ionophores, it offers a significantly increased lifetime of polymeric sensors [49,50]. Sol gel membranes-modified ion-selective electrodes also indicated that this sol gel could be functionalized chemically with alkoxysilylated bis (crown ether sensors) and its derivatives as immobilized ionophores possess covalent bonding [51]. Moreover, one of the most widely used stable solid materials is conducting polymeric material, for example, poly(pyrrole) (P49) or poly(thiophene) (P50), which works as ion-to-electron transducers [52,53].
6.3.2
Metal-derived materials-based electrochemical sensors
Metal and metal oxide nanostructures have played a significant role as a sensing material because of their high activity and selectivity. Semiconducting materials like InSb, InAs, and
Chapter 6 Electrochemical sensors and nanotechnology
GaAs could be applied as indicator electrodes in the detection and estimation of chloride and sulfate ions using a potentiometric titration technique. Multiple EC sensors and biosensors based on metals and metal oxides act as protein sensors, photochromic sensors, immunosensors, hydrogen peroxide sensors, cholesterol and glucose biosensors, nicotinamide adenine dinucleotide sensors, and so forth [54,55].
6.3.3
Nanomaterials-based electrochemical sensors
In nanotechnological applications, the state-of-art application of nanomaterials is perceived for sensing multiple analytical samples for EC analysis. A single nanotube offering a steady current response obtained from ion transfer across the nanotube, termed as single channel current record, assimilated with a nonpermeable membrane is used as a stochastic sensor. Also, the incorporation of gold nanotubules within polycarbonate membrane pores by the conventional chemisorption method makes this template membrane more permeable and selective [56]. Streptavidin-coated gold nanoparticles lead to a sensitivity that approaches the very low nanomolar range to magnify DNA hybridization [57]. The growth of palladium mesowire nanoarrays embedded on a graphite surface and then their transfer on to cyanoacrylate film are another efficient nanotechnological approach for EC sensing applications [58,59]. Furthermore, there are various types of CNTs used for sensing purposes, like single-walled, double-walled, and multiwalled [60,61]. All these types have specific varying thicknesses and conducting properties. Consequently, a broader range of EC sensors fulfilling the requirement of being user-friendly and environment-friendly are now commercially accessible.
6.4
Nanosensing technology
Highlighting concerns about the dissemination and the impact of sensing materials in analytical methodologies has paved the way for novel and more reliable field methods intended to avoid the use of toxic compounds in analytical pretreatment and measurement. The highest reliable output in terms of sensitivity and selectivity of a system depends upon two main features, that is, the nature of the electrode material used and the efficiency of the analytical technique being applied. EC methods of sensing analysis could be particularly sensitive, selective, affordable, and portable even in remote sites [62,63].
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Conventional EC sensors comprise a sensing electrode, which acts as a transduction component, a diffusion barrier, a counter electrode, a reference electrode, and an electronconducting electrolyte. The sensing electrode can be modified with different types of nanomaterials, which are divided into several groups based on their chemical nature. The major groups of nanomaterials include metals, metal oxides, carbon nanomaterials, polymers, and dendrimeric and composite materials. A system’s analytical information is attained from electrical or EC output obtained from the interaction of the analyte and diffusion layer at the working electrode surface. With respect to displaying and interpretation of the electrical signal to be measured, EC measurement techniques are classified into potentiometric, amperometric, conductometric, coulimetric, and voltammetric methods [64]. Moreover, EC devices of multiple kinds are still being developed for environmental monitoring owing to specificity of analyte, sensitivity, and selectivity. Nanotechnology, in combination with nanomaterials, is preferred for sensing applications owing to their rapid response, specificity of target species, high sensitivity to detect real-time changes in target, low limit of detection, low manufacturing cost, small size, and extended life time [65]. Additionally, some nanotechnological methods are used for specific modification of nanowires and nanotubes such as UV lithography specifically utilized for semiconductor fabrication, focused ion beam machining, nanoimprint lithography, atomic layer deposition, and molecular vapor deposition. Also, di-block copolymers are employed for molecular self-assembly techniques. The precursors of such technological advancements led to an nanotechnological era and are considered as extension leading toward modern scientific achievements. Subsequently, the assimilation of nanotechnology with emerging EC techniques led to the development of more reliable and powerful sensing devices for efficient processing and effective monitoring of several industrial, biological, medical, and environmental applications.
6.5
Challenges
The prefix “nano” for multiple applications and products is frequently used these days for being trendy and incredible. The development and manufacturing of nanotechnological products must be handled and administered with proper precautions and care. Careless use of molecular synthesis and manufacturing could bring about black markets and massive destruction
Chapter 6 Electrochemical sensors and nanotechnology
due to arms races. Moreover, a more critical issue is that most of the nanomaterials possess an enhanced surface area and small particle size, which on the one hand dramatically alter the conductive properties and on the other hand may lead to aggressive chemical activity, if handled irresponsibly [66]. Moreover, in free form, nanoparticles could be released in air and water in their production as a byproduct of manufacturing and could eventually accumulate in soil reservoirs, water bodies, and plants. In compound or fixed forms, where nanoparticles appear as a manufactured product, they ultimately need to be reused or disposed of as a waste. Such nanoparticles may produce a new type of nonbiodegradable pollutants. Also, such pollutants must be removed from air and water bodies. In this way, nanotechnology may exert a negative influence upon the environment. Moreover, there are health issues associated with work places in manufacturing companies and laboratories involved in nanomaterials and nanotechnological research. The current work place exposure standards cannot be implicated perfectly to nanoparticle dusts. Purposely, the health hazards linked with engineered nanoparticles need to be monitored and therefore such nanoparticles require the evaluation of storage, distribution, abuses, and disposal of such dangerous byproducts. Some nanomachines can cause immense destruction upon unprotected population. Certain nanoparticle products like microscopic antipersonnel systems and prevailing aerospace weaponries could raise a critical concern. Besides, unrestricted exposure of nanotechnology must be planned with effective management systems [67,68].
6.6
Future perspective
Scientists are working toward applying nanotechnology in various fields. Improvement in the cable of a space elevator could reduce the cost of the sending vehicle in the orbit. Novel carbon materials are being designed to reduce the spaceship and interplanetary ship weight and increase structural strength. It will tackle the hurdle of lifting enough fuel into space during interplanetary missions. A complex system of nanosensors is deployed to detect and estimate the traces of useful compounds like water on Mars and other planets. However, many nanotechnological applications still require a lot of development. Quantum dots are being designed for identification of cancer cells in the body [69]. Nanotubes are under innovation for bone repairing to provide materials to bones for growth [70]. Many
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researchers are developing nanoparticles that could attach to infected cells and aid doctors in identification of blood samples. Moreover, thinner and flatter electrodes are being made of nanowires, that is, a nanoemissive display panel that could perform efficiently is being developed [71]. Integrated circuits are under production; it can measure in nanometer scale up to 45 nm or more specially in transistors [72]. Subsequently, molecular-sized transistors are being designed to introduce high-density transistors in integrated circuits. It is worth noting that nanosized magnetic rings are used to develop magnetoresistive random access memory that will allow for memory density up to 400 GB per square inch [73,74]. In the future, the development of such efficient, sensitive, and selective EC nanosensors will be a great gift to nanotechnological applications.
6.7
Conclusion
This chapter discussed the background and need of nanotechnology and EC sensors, recent trends, current challenges, and future impacts regarding the combined applications of EC sensors and nanotechnology. Today, many of the most innovative scientists and engineers have been searching new trends to utilize nanotechnology to upgrade the global life standards. These scientists envisaged a domain in which novel materials, manufactured at the atomic or molecular levels, offer realistic, affordable techniques to harness renewable energy sources and environment protection. Disease diagnosis at earlier stages and treatment of lethal illnesses like cancer and diabetes can be effectively performed with the aid of nanotechnology. Even though there are still many research challenges, nanotechnology is generating an extensive range of valuable materials and hence indicating a major breakthrough in various fields. Nanotechnology has led many researchers to the world of emerging opportunities. However, it is nowhere near mature yet, and a lot of development is leading to a point where its commercialization is imminent.
References [1] T. Singh, et al., Application of nanotechnology in food science: perception and overview, Front. Microbiol. 8 (2017) 1501. [2] D. Bhattacharyya, et al., Nanotechnology, big things from a tiny world: a review, Int. J. u-e-Serv. Sci. Technol. 2 (3) (2009) 29 38.
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[3] A. Ahmad, D. Jini, M. Aravind, C. Parvathiraja, R. Ali, M.Z. Kiyani, et al., A novel study on synthesis of egg shell based activated carbon for degradation of methylene blue via photocatalysis, Arab. J. Chem. 13 (12) (2020) 8717 8722. [4] S.E. McNeil, Nanotechnology for the biologist, J. Leukoc. Biol. 78 (3) (2005) 585 594. [5] M.C. Roco, The Long View of Nanotechnology Development: The National Nanotechnology Initiative at 10 years, in Nanotechnology Research Directions for Societal Needs in 2020, Springer, 2011, pp. 1 28. [6] J.H. Phan, et al., Convergence of biomarkers, bioinformatics and nanotechnology for individualized cancer treatment, Trends Biotechnol. 27 (6) (2009) 350 358. [7] M. Aravind, A. Ahmad, I. Ahmad, M. Amalanathan, K. Naseem, S.M.M. Mary, et al., Critical green routing synthesis of silver NPs using jasmine flower extract for biological activities and photocatalytical degradation of methylene blue, J. Environ. Chem. Eng. 9 (1) (2021) 104877. [8] W. Yaling, et al., Nanomaterial-biological System Interaction Studied by X-ray Imaging Techniques. [9] A.V. Chaves, et al., Novel Nano Biocomposite Based TiO2 Covered with Hydroxyapatite Coating for Orthopedic and Dental Implants. [10] M.J.A. Jassani, et al., A minireview: nanomaterial as antimicrobial agents. Eur. J. Mol. Clin. Med. 7 (11) 4190 4202. [11] G. Andrade, Pine nanocellulose and bacterial nanocellulose dressings are similar in the treatment of second-degree burn? Exp. Study Rats. [12] O. Kudryashova, et al., Atomization of nanopowders for adsorption of toxic substances, J. Eng. Phys. Thermophys. 88 (4) (2015) 833 838. ¨ ller-Goymann, Sun protection enhancement [13] J. Villalobos-Hernandez, C. Mu of titanium dioxide crystals by the use of carnauba wax nanoparticles: the synergistic interaction between organic and inorganic sunscreens at nanoscale, Int. J. Pharm. 322 (1 2) (2006) 161 170. [14] A. Tuantranont, Applications of nanomaterials in sensors and diagnostics. 2014 Springer Series on Chemical Sensors and Biosensors, Springer, Berlin Heidelberg, 2013. [15] M.E. Harb, et al., Fabrication of organic transistors using nanomaterials for sensing applications, J. Electron. Mater. 47 (1) (2018) 353 358. [16] S. Guo, E. Wang, Noble metal nanomaterials: controllable synthesis and application in fuel cells and analytical sensors, Nano Today 6 (3) (2011) 240 264. [17] J. Li, et al., Engineering noble metal nanomaterials for environmental applications, Nanoscale 7 (17) (2015) 7502 7519. [18] A. Mirzaei, et al., Metal-core@ metal oxide-shell nanomaterials for gassensing applications: a review, J. Nanopart. Res. 17 (9) (2015) 1 36. [19] S. Marı´n, A. Merkoc¸i, Nanomaterials based electrochemical sensing applications for safety and security, Electroanalysis 24 (3) (2012) 459 469. [20] M.Z.M. Nasir, M. Pumera, Emerging mono-elemental 2D nanomaterials for electrochemical sensing applications: from borophene to bismuthene, TrAC. Trends Anal. Chem. 121 (2019) 115696. [21] L. La Spada, L. Vegni, Electromagnetic nanoparticles for sensing and medical diagnostic applications, Materials 11 (4) (2018) 603. [22] A.W. Skinner, et al., Factorial design of experiments for optimization of photocatalytic degradation of tartrazine by zinc oxide (ZnO) nanorods with different aspect ratios, J. Environ. Chem. Eng. 8 (5) (2020) 104235.
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[46] A. Aleksandrova, J. Kuye Adesegun, Principles of application of nanotechnology in delivery of pharmaceuticals: review and prospects. Aleksandrova AV. Princ. Appl. Nanotechnol. Deliv.. . .. [47] M. Jian, et al., Advanced carbon materials for flexible and wearable sensors, Sci. China Mater. 60 (11) (2017) 1026 1062. [48] V.S. Bhat, S. Supriya, G. Hegde, Biomass derived carbon materials for electrochemical sensors, J. Electrochem. Soc. 167 (3) (2019) 037526. [49] V.K. Gupta, R.N. Goyal, R.A. Sharma, Comparative studies of neodymium (III)-selective PVC membrane sensors, Anal. Chim. Acta 647 (1) (2009) 66 71. [50] V.K. Gupta, et al., Porphyrins as carrier in PVC based membrane potentiometric sensors for nickel (II), Anal. Chim. Acta 355 (1) (1997) 33 41. [51] J.L. Unangst, Salophen Sol-Gel Hybrid Sorbent Material for the Sensing and Sequestration of Actinyl Ions, UC Irvine, 2019. [52] E. Bakker, M. Telting-Diaz, Electrochemical sensors, Anal. Chem. 74 (12) (2002) 2781 2800. [53] A. Facchetti, π-Conjugated polymers for organic electronics and photovoltaic cell applications, Chem. Mater. 23 (3) (2011) 733 758. [54] W.-T. Koo, J.-S. Jang, I.-D. Kim, Metal-organic frameworks for chemiresistive sensors, Chem 5 (8) (2019) 1938 1963. [55] A. Walcarius, Mesoporous materials-based electrochemical sensors, Electroanalysis 27 (6) (2015) 1303 1340. [56] Y.B. Mollamahalle, M. Ghorbani, A. Dolati, Electrodeposition of long gold nanotubes in polycarbonate templates as highly sensitive 3D nanoelectrode ensembles, Electrochim. Acta 75 (2012) 157 163. [57] S.R. Torati, et al., Electrochemical biosensor for Mycobacterium tuberculosis DNA detection based on gold nanotubes array electrode platform, Biosens. Bioelectron. 78 (2016) 483 488. [58] S. Cherevko, et al., Hydrogen sensing performance of electrodeposited conoidal palladium nanowire and nanotube arrays, Sens. Actuators B: Chem. 136 (2) (2009) 388 391. [59] J. Zou, Synthesis and Application of Palladium Nanomaterials for Sensing and Catalysis, University of Western Australia, 2011. [60] J.A. Robinson, et al., Role of defects in single-walled carbon nanotube chemical sensors, Nano Lett. 6 (8) (2006) 1747 1751. [61] S. Yun, J. Kim, Multi-walled carbon nanotubes cellulose paper for a chemical vapor sensor, Sens. Actuators B: Chem. 150 (1) (2010) 308 313. [62] F.J. Iftikhar, et al., Introduction to Nanosensors, New Developments in Nanosensors for Pharmaceutical Analysis, Elsevier, 2019, pp. 1 46. [63] V.K. Khanna, Nanosensors: Physical, Chemical, and Biological, CRC Press, 2011. [64] S.-M. Lu, et al., Electrochemical sensing at a confined space, Anal. Chem. 92 (8) (2020) 5621 5644. [65] G. Maduraiveeran, M. Sasidharan, V. Ganesan, Electrochemical sensor and biosensor platforms based on advanced nanomaterials for biological and biomedical applications, Biosens. Bioelectron. 103 (2018) 113 129. [66] X. Ma, et al., A strategy for construction of highly sensitive glycosyl imprinted electrochemical sensor based on sandwich-like multiple signal enhancement and determination of neural cell adhesion molecule, Biosens. Bioelectron. 156 (2020) 112150. [67] G. Tatishvili, et al., Theoretical aspects of nanosensors for radiation hazards detecting, Advanced Nanomaterials for Detection of CBRN, Springer, 2020, pp. 123 132.
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[68] R. Kaur, S.K. Sharma, S. Tripathy, Advantages and limitations of environmental nanosensors, Advances in Nanosensors for Biological and Environmental Analysis, Elsevier, 2019, pp. 119 132. [69] M. Ganesan, P. Nagaraaj, Quantum dots as nanosensors for detection of toxics: a literature review, Anal. Methods 12 (35) (2020) 4254 4275. [70] R. Eivazzadeh-Keihan, et al., Carbon based nanomaterials for tissue engineering of bone: building new bone on small black scaffolds: a review, J. Adv. Res. 18 (2019) 185 201. [71] H. Zhao, et al., Recent advances in designing and fabricating self-supported nanoelectrodes for supercapacitors, Adv. Sci. 4 (10) (2017) 1700188. [72] Y. Zhan, et al., Synthetic plasmonic nanocircuits and the evolution of their correlated spatial arrangement and resonance spectrum, ACS Photonics (2020). [73] S. Yuasa, et al., Materials for spin-transfer-torque magnetoresistive randomaccess memory, MRS Bull. 43 (5) (2018) 352 357. [74] S.-O. Jung, et al., Offset-canceling (OC) write operation sensing circuits for sensing switching in a magneto-resistive random access memory (MRAM) bit cell in an MRAM for a write operation, Google Patents, 2019.
7 Sensing methodology P. Shenbaga Velu1, N.J. Vignesh2, J. Senthil Kumar3 and Rajesh Jesudoss Hynes Navasingh2,4 1
School of Mechanical Engineering, Vellore Institute of Technology, Chennai, Tamil Nadu, India 2Department of Mechanical Engineering, Mepco Schlenk Engineering College, Sivakasi, Tamil Nadu, India 3Department of Electronics & Communication Engineering, Mepco Schlenk Engineering College, Sivakasi, Tamil Nadu, India 4Faculty of Mechanical Engineering, Opole University of Technology, Opole, Poland
7.1 7.1.1
Introduction Advancements in nanotechnology
Nanotechnology-enabled sensors and analysis can distinguish and expose chemical agents in the air and soil or biological sensing elements for medical implementations. They can also be used as identifiers for sensing virulent chemicals or biological components like temperature, coercion, humidity, depiction signals, and vibrations. Advanced nanosensors are expanded on the basis of nanotechnology as sensing devices that are executed using nanomaterials, nanosized composition, or compounds [1], as given in Table 7.1.
Table 7.1 Types of nanomaterials used. Applications of nanotechnology
Nanomaterials used
Pharmaceuticals and medicine Environmental and water remediation Electronics, ICT, and photonics Catalysts and lubricants Food packaging Composite materials Agrochemicals
Nanomedicines and carriers (nanobiotechnology) Iron, polyurethane, carbon nanotubes, and graphene Carbon nanotubes, fullerenes, and graphene Cerium oxide, platinum, and molybdenum trioxide Gold, nanoclays, titanium dioxide, and silver Graphene and carbon nanotubes Silica as a carrier
Nanomaterials-Based Electrochemical Sensors: Properties, Applications, and Recent Advances. DOI: https://doi.org/10.1016/B978-0-12-822512-7.00006-5. © 2024 Elsevier Inc. All rights reserved.
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7.1.2
Development of nanomaterials
Advancements in materials metrology and developments in the discipline of material science describe the principles of medium with single isolated unit of small-sized materials lies between 1 and 100 nm (nanoscale). These nanoscale materials or nanomaterials have an eccentric optical, electronic, or mechanical effects [2]. Nanomaterials are arranged and implemented to fulfill the industrial and nonindustrial needs. Legacy nanomaterials are used before the development and advancements in nanotechnology. It also includes carbon black and titanium dioxide [3]. Nanoparticles and nanomaterials include both the nanoobjects and nanostructured materials, which have interior or exterior plane composition on nanoscale. The European commission expounds the nanomaterials as “a natural, incidental, or manufactured material containing particles, in an unbound state or as an aggregate or as an agglomerate and where, for 50% or more of the particles in the number size distribution, one or more external dimensions is in the nanoscale.” To alleviate health, environmental, and safety concerns, the size distribution threshold can be taken between 1% and 50% [4], as given in Table 7.2.
7.1.3
2-Dimensional nanomaterials
2D materials have ultrafine units of dimensions and scaled in nanometers, corresponding to large, but exact thin layers or sheet (sheet of canvas). It is feasible to abridge the extent depth of the medium to a isolated atom and chances in properties also occur (2D material nanosheet). Graphene, initially known as the “modern” 2D material, was discovered in 2004. The introductory MXene was found in 2011 at Drexel University. The primary post-graphene materials silicene, germanene, stanine, and plumbene were found in 2012, 2014, 2015, and 2018, respectively [5]. 2D nanomaterials are highly different in terms of form, structure, Table 7.2 Various nanoscopic dimensions. Number of nanoscopic dimensions
Classification
Example
0 1 2 3
Bulk 2D (nanosheet) 1D (nanotube and nanowire) 0D (nanoparticle)
Visible to eyes Graphene Carbon nanotubes Quantum dot
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105
porosity, biocompatibility, and degradability. These different properties make them appropriate for a broad range of applications. 2D nanomaterials are known to be the thinnest and finest materials, exhibiting an elevated particular surface area. Table 7.3 shows nanotechnology used in diagnosis in sensor technology. Graphene: It refers to the covalently affixed hexagonal grids of carbon atoms of 0.14 nm thickness. Due to graphene, peculiar band formation electrons budge through it at incredibly high speeds of about 1/300 the speed of light, which results in unparalleled thermal conductivity. Optically clearly visible, graphene preoccupies only 2% of incident visible light and has the highest tensile strength of any substance. It is a semimetal and an excellent electrical conductor [6]. Hexagonal boron nitride: Isomorph of graphene has a crystallographic appearance with a lattice of boron and nitrogen atoms. Being a single atom-thick and having an alternating atom (boron and nitrogen) in its atomic structure, it acts as an insulator with a wide bandgap of B5.9 eV [7]. Transition metal dichalcogenides (MX_2): It has the chemical composition of transition metal (molybdenum or tungsten)-combined chalcogen (sulfur, selenium, or tellurium). In bulk TMDCs, the metal layer is placed between the two chalcogenide layers which are known to be van der Waals materials. This medium shows extraordinary thinness. For example, WTe2 exhibits anomalous giant magnetoresistance and superconductivity [8]. Transition metal oxides: They are similar in appearance with higher surface to volume proportion and surface charge. Transition metal oxides are used as gene delivery conveyors for
Table 7.3 Nanotechnology use in diagnosis. Term
Definition
Nanomaterial Material with an external dimension and internal structure or surface structure in the nanoscale Nanoparticle Nanoobject with all the three dimensions in the nanoscale Nanoscale Length range approximately from 1 10 nm Nanostructure Composition of an interrelated constituent with one or more parts in the nanoscale region Nanotube Hollow nanofiber Nanowire Electrically conducting or semiconducting nanofiber
Source ISO/TS 80004-1:2015 ISO/TS 80004-3:2010 ISO/TS 80004-1:2015 ISO/TC 80004-1:2015 ISO/TC 80004-3:2010 ISO/TC 80004-2:2015
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various gene delivery applications. MnO2 and TiO2 have encouraging distinctive features for efficient gene silencing [9]. Silicate clays or nanoclays: They are nanoparticles of coated or heaped mineral silicates. On the basis of chemical configuration and architecture, patterning nanoclays are arranged into several classes such as montmorillonite, bentonite, kaolinite, hectorite, and halloysite. MMT nanoclays are formerly known to be in the ratio 2:1 phyllosilicate that possesses a single layer of octahedral alumina and two combined tetrahedral silicate layers [10].
7.2 7.2.1
Sensing methodology Electrochemical biosensors
Evolution of wearable electrochemical sensors has been made possible by the adaptability of new materials like transmittable polymers and carbon nanomaterials. They provide good electrical and chemical properties and are also widely used for the realization of biosensors [11]. Electrochemical biosensor functions take place with the help of electrochemical transducers and expose the biological materials such as enzymes, whole cells, specific ligands, and tissues. Biosensors facilitate the catalysis reaction on enzymes that create or destroy electrons. The target analyte complex helps the reaction toward the active electrode surface to take place. This reaction may either give rise to the transfer of electrons over the double layer (produces the flow of electrons) or provide the double layer potential (produces a electromotive force). By measuring the electron flow at a stable potential or potential at the range of zero electron flow, it is possible to monitor the analytes or the biological activity [12]. A biosensor consists of three electrodes: a reference electrode, a working electrode, and a counter electrode. The possibility of employed or active electrode is space charge subtle.
7.2.2
Electrochemical sensors
Electrochemical sensors are employed for the detection of toxic gases such as H2S, Cl2, and SO2 and also the variations of oxygen in the air. They operate on the principle that electrical current is allowed to pass through a sensing electrode generated by an electrochemical response on the surface of the electrode coated with a catalyst when the metallic anode and metallic cathode are immersed on an electrolytic solution (a form of a gel) isolated by a membrane. An electromotive force in terms of
Chapter 7 Sensing methodology
volts is applied between two electrodes placed; when the gas contacts the chamber through the membrane, it reacts with gel. Due to this reaction, oxidation or reduction takes place, and in turn, there arises a small amount of current to flow, linear to path of gas concentration [13].
7.3
Nanomaterial-based electrochemical biosensors for biomedical applications
The introduction of new and rare functional nanomaterials modified by analytical technology indicates the best possibility for the advancement of biosensors for extensive applications in the medical field. It includes the biological, biomedical, biotechnological, clinical diagnostics, medical diagnostics, and health monitoring, as shown in Fig. 7.1. Microfabrication techniques enable new surface modifications to design electrochemical sensors with sensitivity and selectivity. This technique helps to obtain diverse nanomaterials with individuality in properties. Biosensors have probable applications such as in early-stage observation of irregularities and tunable diagnostic and therapeutic systems. High sensitivity and selectivity, rapid response, and magnificent
Figure 7.1 Nanomaterial-based electrochemical biosensors for biomedical applications.
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durability are some of their facets. The design of the electrochemiluminescence (ECL) biological nanomaterial is used for manufacturing a sensitive ECL immunosensor to capture cyst or cancer markers. ECL nanomaterial was embellished and assembled by a number of single and dual luminophores [14]. These luminophores include the perylene tetracarboxylic acid and carbon quantum dots and graphene as a nanocarrier. The nanomaterial helps to classify the peripheral antibody and construct the sequenced carcinoembryonic antigen (CAE) immunosensor. The CAE immunosensor depicts high sensitivity, and its linear semi logarithmical scale is noted from 0.001 fg mL21 to ng mL21 with a moderate identification limit of 0.00026 fg mL21. CAE is appropriate for many cancers’ model detection and diagnostics.
7.3.1
Types of nanotechnologies used in the medical field
7.3.1.1 Carbon nanotubes CNTs are attained in the form of cylindrical huge molecules that consist of a hexagonal positioning of blended or combined carbon atoms, which are formed by a monolayer sheet of graphene. CNTs exhibit outstanding heat conductivity, electrical conductivity, and mechanical properties, and they are widely preferred for biomedical applications. They are polymers of carbon, made and manipulated by an extremely rich chemistry of carbon. Various types of carbon nanotubes are single-walled and multiwalled nanotubes. CNTs can be used for Raman or photoacoustic imaging. CNTs are implemented in nanotechnology, which includes high aspect ratio resonator circuits and detectors [15]. CNTs have 4 to 5 range of magnitude rapid water variability (7-nm diameter) compared to a conventional medium of liquid [16]. Single-walled carbon nanotubes: SWCNTs are composed of a single cylindrical surface of atoms, which includes a single molecule imposed with the diameter in the range of nanometer and large aspect ratio. It is a regular hexagonal lattice whose vertices are the positions of the carbon atoms and also known as onedimensional materials. During chemical vapor deposition synthesis, members of the fullerene family have a tube-like appearance and single-walled carbon nanotubes are processed into oneatom-thick nanocarbon sheets. It is an allotrope of sp2-hybridized carbon and a diameter of approximately 1.0 nm. SWCNTs are inert and also used to increase mechanical and conductive properties in other materials. Applications of SWCNTs include
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biomedical applications [17], sensor applications, wearable electronics, advanced electrodes, catalyst supports, and transparent conductive coatings. Multiwalled carbon nanotubes (MWCNTs) consist of two or more packed single-wall CNTs joined by inner-molecular forces or a single sheet of graphene rolled up several times to form a hollow cylindrical structure. MWCNTs are made of sp2 carbon and have a diameter of 3 30 nm [18]. The external walls of MWCNTs can be influenced by the functional groups such as hydroxides, carboxylic acids, or amides to attain extraordinary functionality, for example, modified dispersibility and the ability to bind to the target for use in biomedical applications. MWCNTs are most commonly used in biomedical implementations due to their inflated compatibility of nanotubes and capacity to fix individual proteins and to functional groups. Carbon Bucky paper: Bucky paper is developed with new materials that are highly resistant and light in weight and is constructed by using deflated CNTs. It is a cylindrical and extended structure that consists of hexagonal graphite components attached at the corners and also has remarkable low optical reflectivity and thermal conductivity. It can dissipate heat like brass or steel and allow for electricity flow like copper or silicon [19]. Bucky paper is also used in the field of medicines, as it is a good material to be used in artificial implants. Nerve cells can also be grown with Bucky paper. Bucky paper acts as a filter film to absorb microparticles in air or medium fluid. These nanotubes in the bucky paper are insoluble and add additional features for various functional groups to separate the selective compounds. It can also act as a sensor [20].
7.3.1.2
Metal nanoparticles
Platinum nanoparticles: Platinum nanoparticles are present in the formation of colloidal or suspension of platinum nanoparticles in a liquefied medium (liquid or gas). The size of the nanoparticles ranges between 2 and 100 nm in brownish-red or black color [21]. Platinum nanoparticles are processed and attained by depletion of platinum ion predecessors in a mixture of balancing medium or by using a capping factor like sodium polyacrylic acid or sodium citrate. This incorporating agent like sodium polyacrylic acid or sodium citrate can be employed as a capping or stabilizing agent to prevent the cluster and collision of nanoparticles. Gold nanoparticles: Gold nanoparticles are identified as wine-red compounds with an antioxidant nature or effect. The
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size of gold nanoparticles is about 2 nm, and they have distinct structures like suboctahedral, spherical, octahedral, icosahedral multiple twined, tetrahedral, nanotriangles, hexagonal platelets, nanorods, and nanoprisms. Gold nanoparticles as signal amplifiers are used to detect C-reactive protein and are also used in QCM (Quartz Crystal Microbalance) immune sensor systems. Gold nanoparticles irradiated with laser generate heat due to the excitation of electrons and can be used as an anticancer or antibacterial agent [22]. Silver nanoparticles: Silver nanoparticles in a spherical form are widely used, and they are a collection of a huge amount of silver oxide due to large proportions of plane to expand silver atoms. Their huge surface area allows for the coordination of a vast integral of ligands [23]. Silver nanoparticles molded from the ions detach from silver compounds and obtain an electron in redox reaction with a diminishing agent. These nanoparticles are used for antimicrobial coatings, wound dressings, and in biomedical devices to protect against the bacteria.
7.3.1.3 Nanotubes Titanium dioxide nanotubes (TNTs) are one-dimensional structures that exist as bundled tubes with a diameter between 30 and 80 nm, and tube length ranges from 10 to 220 µm, as given in Table 7.4. Titanium dioxide is a new group of biocompatible broadened nanocarriers. Individual TNTs are extremely flexible drug transportation systems due to their stacking ability and direct forward functionalization. They provide refined control on the therapeutic stacking and release in contrast to solid nanocarriers and also improve margination in the microenvironment of solid tumors when subjected to hemodynamic forces [24]. Table 7.4 Properties of TiO2. Compound formula
TiO2
Molecular weight Appearance Melting point Exact mass Monoisotopic mass
79.9378 g mol21 Solid 1843- C (3349- F) 79.9378 g mol21 79.937776 Da
Chapter 7 Sensing methodology
7.4
Nanomaterials-based electrochemical biosensors for tumor cell diagnosis
Cancer is the major diminishing factor in the world. Cancer biomarkers are widely used in oncology for the prognosis and ascertainment of diseases by their symptoms. Modern cultivation (elaboration) of functional nanomaterials provides novel possibilities for developing the action of electrochemical sensors. Electrochemical nanobiosensors are portable and versatile devices used for the fast detection and diagnosis of cancer biomarkers and also for cancer diagnosis and management and cancer screening. Applications of a wide variety of nanomaterials are due to their magnificent electrical conductivity and enhanced surface extent connecting to its volume.
7.4.1
Nanoshells and quantum dots
Nanoshells are circular in shape, and nanoparticles are correlated by using tercopolymorpholy, with the pH-sensitive doxorubicin-enclosed shell glazed with fine metallic shells. It improves the biocompatibility and optical immersion. The plane of nanoshells can be simply organized for the assigned targeting applications [25]. Quantum dots are semiconductors, and their size ranges between 2 and 10 nm in diameter. These quantum dots are made up of the 10 50 atoms, comprising of electron hole sets of distinct quantized energy. Quantum dots were interfused with folate, which is beneficial for fast extension and cell splitting, to execute the assays where the folate-specific receptor was selected [26].
7.4.2
Electrochemical biosensor in cancer cell detection
The functional module of the electrochemical biosensor has an identification matrix and transducer system. The identification system communicates with the selective analyte and transforms the attained variables into a signal. The obtained output signal is received and transmitted by the transduction system using the electronic approach, which shows these variables in the configuration of electrochemical signals. The electronic approach develops the obtained signal and provides the output. Cell impedance sensing is carried out on the basis of electrode impedance variation that occurs due to growth of cells on the electrode layer or plane at the interface. Therefore, it is used to
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measure the changes in the cell stratum resistance that occurs due to the cell structure, cell drift, and cell contact. The folic acid receptor is also a cell surface receptor used for antitumor drugs.
7.4.3
Electrochemical immunosensors in cancer cell detection
Electrochemical immunosensors are outcome products built on the correlation antigen antibody particulate enzymatic response and electrochemical mechanisms. The fundamental theory of antigen antibody in direct contact is achieved between the sensing element and molecular recognition element, which includes the antigen and antibody molecules. The kind of chemical concentration that is obtained is detected and converted into the signal through the sensing element. Biosensors are created on the basis that individual reaction takes place between the antigen and antibodies. Glycosyls on top of the cell play a essential role in cell acceptance, bonding, response, occurrence, and the movement of the cancer cells. Due to their inflated sensitivity and linear deviation, cancer cells are used for the diagnosis of hepatocellular carcinoma HepG2, invasive ductal carcinoma MCF-7, small cell lung cancer, metastatic breast cancer, basal cell carcinoma, skin cancer, prostate cancer, and breast cancer [27], as shown in Fig. 7.2.
7.4.4
Electrochemical nucleic acid biosensors in cancer cell detection
The basic principle of the recognition element in the electrochemical nuclei acid biosensor uses the molecules of nucleic acid to fix the single fibril of oligonucleotides to the target material of the electrode and blend it to the assigned DNA to detect the targeted substances. The tumor is monitored and recognized by measuring the electrochemical elements before and after blending with the targeted material, which can be DNA, miRNA, or biological molecules. Nucleic acid adapters are highly specific in binding the targeted tumor cells, so they are mainly used for the implementation of cell sensors. The diagnosis methodology of identification of cancer cells is based on the aptamer and electrochemical probe. The aptamer is a simulated or fabricated nucleic acid with elevated specificity, exhibits biological and chemical diversification, and is concealed by screening techniques (systematic evolution of ligands by exponential enrichment in vitro) [28]. Aptamer-based electrochemical cytosensors are used for tumor diagnosis, as shown in Fig. 7.3.
Chapter 7 Sensing methodology
Figure 7.2 Electrochemical immunosensors in tumor cell detection.
Figure 7.3 Electrochemical nucleic acid biosensors in tumor cell detection.
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7.5
Nanomaterial-based electrochemical sensors for environmental applications
Across the globe, these direct or indirect control break of containments, for example, toxic massive elements, antibiotics, and pesticides to the living domain or habitat, is a severe concern [29], as shown in Fig. 7.4. Nanotechnology provides numerous benefits to develop the existing environmental technologies and fabricate new technology. Nanomaterials are portable and the surface area to volume proportion is high, so they can be utilized to find various extremely sensitive contaminants. Nanotechnology has three important capabilities that are appealing with respect to the environment: • Remediation (clean-up) and purification • Detection of contaminants • Prevention of pollution There is an intersection element present in many of the anthropogenically sourced chemicals that humans are exposed to, and there are health consequences to the use of a particular, secluded compound [30].
Figure 7.4 Electrochemical sensors for environmental applications.
Chapter 7 Sensing methodology
7.5.1
Sensor applications for pollution detection and environmental contaminants
7.5.1.1
Emerging contaminants and toxic gases
Emerging contaminants (ECs) refer to a heterogeneity of synthetic chemicals employed for industrial and nonindustrial operations, which include the use of herbicide, pesticides, brominated compounds, phthalates, and additives to plastics [31]. On the basis of environmental impact and high solubility, ECs are divided into groups of toxicity, for example, pesticides cypermethrin. Excessive quantities of harmful and polluting gases like ammonia, carbon monoxide, nitrous oxides, methane, and chlorofluorocarbons introduced into the environment cause several health- related ailments. The Environmental Protection Agency has recorded 12 contaminants for the upcoming situation at federal provisions with fluctuating origins and health outcomes due to exposed contaminants [32].
7.5.1.2
Screen-printed electrodes
The development of biosensors depends on sensitivity, specificity, and parallelism. One of the developed mechanisms involves screen-printed sensors. They work on the basis of electrochemical reaction and are used for the identification of heavy metal ions, pesticides/herbicides, and phenolic compounds. Screen-printed electrodes (SPEs) are used as a tool to design degradable and portable electrochemical sensor units for environmental monitoring, which include quality checks, analyses of organic or inorganic compounds, and detection of heavy metals and gas pollutants [31]. Disposable and replaceable biosensors are constructed on SPEs that include the microelectrodes and modified electrodes, which guide to a new prospect in capturing and quantitation assay of biomolecules, pesticides, antigens, DNA, microorganisms, and enzymes. SPE-formulated sensors are regulated for executing quick and precise error-free in-situ analyses and used for the implementation of feasible and portable devices [33].
7.5.1.3
Nanowires
Nanowires are defined as structures that have lateral constrained or unconstrained longitudinal size and dimensions in the range of the nanometer scale (10 9). Nanowires can also be made from carbon nanotubes. Ion track technology enables the development of homogeneous and segmented nanowires that
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are lower than 8 nm in diameter, and thermal oxidation procedures are applied to attune their morphology [34]. Nanowires are made up of potassium manganese oxides that can muck out oil and many other types of biotic pollutants and make oil recuperation practical. The nanowires mold a network that assimilates up to 20 times its influence on hydrophobic liquids by eliminating water with a water-repulsing layer of covering. It is stable even when it exposed to higher temperatures, and both oil and nanowires are restated [35].
7.5.2
Electrochemical sensors for toxic gas detection
7.5.2.1 Components and working of electrochemical sensors The basic elements of electrochemical sensors include the working (or sensing) electrode, a counter electrode, and a reference electrode. The electrodes to be included in the sensors placed in exposure to the fluid medium electrolyte in the form of a gel are shown in Fig. 7.5. The working electrode faced the interior side of the membrane. The membrane is made of teflon, as it is permeable to gas and cannot penetrate the electrolyte. When the gas starts scattering into the sensor, it reaches
Figure 7.5 Electrochemical sensors for toxic gas detection.
Chapter 7 Sensing methodology
the working electrode through the layer of the membrane. Depending on the type of gas chemical reaction, oxidation or reduction occurs [12]. Due to the oxidation reaction, current proceeds from the working electrode to the counter electrode, and due to the reduction reaction current proceeds from the counter electrode to the working electrode. The internal drift of the electrode produces an electric current proportionate to the level of gas concentration. The electronic part of the apparatus amplifies and scales the output according to the calibration. The instrument also displays the gas accumulation in parts per million and percent volume for harmful gas detection and oxygen sensors [36]. The electrochemical sensors are also formed on the basis of cell impedance sensing methodology. Cyclic voltammetry is widely used to identify the type of reaction that takes place on that electrode layer to determine the impedance variation or microcurrent. Differential pulse voltammetry is a procedure carried out using the graphical data observations made from the linear sweep voltammetry and staircase voltammetry with a low framework of electron flow and perception sensitivity at an excessive rate. It displays a highly stable output. Due to redox reactions appearing at the modified electrodes, electrochemical sensors compute the swap in current, potential, conductance, or impedance [37].
7.5.2.2
Configurations of electrochemical sensors
The basic arrangement of the electrochemical sensors consists of a working (or sensing) electrode, an auxiliary electrode, and a reference electrode, as shown in Fig. 7.6. Configurations of electrochemical sensors include amperometric and potentiometric sensors. Amperometric sensors have a constant value of applied voltage, and the sensor signal is a current. The rate of the reaction is determined by the rate of gas transport, and it is limited by a diffusion barrier made of porous ceramic or small holes. Amperometric sensors compute the electron flow reaction to identify the application or attentiveness of an analyte at stable potential. An elementary model of amperometric computation is single-potential amperometry or DC amperometry. The measured current is proportional to the concentration of gases, and it is monitored as a sensor signal. By this amperometric principle, the detection of oxygen, HC, or nitric oxides is possible [38]. Potentiometric sensors operate when the electron flow is at the zero level and the sensor signal has varying voltages
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Figure 7.6 Configurations of electrochemical sensors.
between the sensing electrode and a reference electrode at different concentrations of the analyte in the gas or solution phase. Potentiometric sensors are developed for pathogen detection and also for the pollutant indication of bisphenol A (BPA) in water [39]. It follows a “symmetrical arrangement” that results in stable potential at both the inner boundary of the membrane and the interface of the inner reference electrode. This makes sensors stable [40].
7.6
Conclusions
Nanotechnology has achieved great progress in the past several decades. It enables objects to harvest energy from the environment and current products of nanotechnology like reinforced plastics, stain-resistant clothes, better cosmetics, and healthcare products with carbon nanotubes. It is easy to detect the movement of nanoparticles inside the living systems, the effects that nanoparticles cause at the cellular level, and the dosage of nanoparticles to the targeted organs. It is expected to change the diagnosis methodology in the field of dentistry, healthcare, and human life. By monitoring the outcomes and results of nanoparticles routinely, one can better assess the potential hazards of the environment which causes pollution. Increasing interest in the future medical implementation of nanotechnology is the main objective behind the exposure of new fields of nanomedicines, which are used to overcome the
Chapter 7 Sensing methodology
challenges, analyze the basis of diseases, provide sophisticated diagnosis opportunities, and yield preventive and more effective properties. The improvement in the miniaturization, modification, and microfabrication technology leads to the development of highly selective and sensitive devices for complete fieldbased monitoring of human cells and also for environmental applications. This chapter addresses the sensing methodology, sensor design, and modifications associated with the sensing module.
Acknowledgements Author Rajesh Jesudoss Hynes Navasingh acknowledges the support from Ulam NAWA Postdoctoral Fellowship of Polish National Agency for Academic Exchange programme, Contract Agreement No. BPN/ULM/2022/1/00133/U/ 00001. All the authors gratefully acknowledge the Management, the Principal, Dr. S. Arivazhagan; the Head of Mechanical Engineering, Dr. P. Nagaraj; and the Head of Electronics and Communications, Dr. R. Shantha Selvakumari of Mepco Schlenk Engineering College, Sivakasi, Tamil Nadu, India, for extending the necessary support toward this work.
References [1] M. Debia, B. Bakhiyi, C. Ostiguy, J.H. Verbeek, D.H. Brouwer, V. Murashov, A systematic review of reported exposure to engineered nanomaterials, Ann. Occup. Hyg. 60 (8) (2016) 916 935. [2] A. Hubler, O. Osuagwu, Digital quantum batteries: energy and electrical information storage in Nano vacuum tube arrays, Complexity 15 (2010) 48 55. [3] “A new integrated approach for risk assessment and management of nanotechnologies” (PDF). EU Sustainable Nanotechnologies Project, 2017, pp. 109 112. [4] Nanomaterials, European Commission, 2011. [5] M. Naguib, M. Kurtoglu, V. Presser, J. Lu, M. Heon, L. Hultman, et al., Twodimensional nanocrystals produced by exfoliation Ti3AlC2, Adv. Mater. (Deerfield Beach, Fla.) 23 (37) (2011) 4248 4253. [6] C. Lee, X. Wei, J.W. Kysar, J. Hone, Measurement of the elastic properties and intrinsic strength of monolayer, Graphene, C. Sci. 321 (2008) 385 388. [7] G.R. Bhimanapati, J.A. Robinson, Semiconductors and Semimetals, 2016. [8] A. Eftekhari, Tungsten dichalogenides (WTe2, WS2 and WSe2): materials chemistry and applications, J. Mater. Chem. A. 5 (35) (2017) 18299 18325. [9] M.N. Hasan, Y.-K. Lee, Biomedical Applications of Graphene and 2D Nanomaterials, 2019. [10] H. Salam, I. Davies, Fillers and Reinforcements for Advanced Nanocomposites, 2015. [11] Shirley C., Dermot Diamond, Wearable Sensors, 2014. [12] S.Q. Lud, M.G. Nikolaides, I. Haase, M. Fischer, A.R. Bausch, Field effect of screened charges: electrical detection of peptides and proteins by a thin film resistor, ChemPhysChem 7 (2) (2006) 379 384.
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[13] B.R. Mehta, Y.J. Reddy, Industrial Process Automation Systems, 2015. [14] P. Skladal, Advances in electrochemical immunosensors, Electroanalysis. 9 (1997) 737 745. [15] V. Harik, Mechanics of Carbon Nanotubes, 2018. [16] J. Lee, Nanoscale Materials in Water Purification, 2019. [17] A. Chen, S. Chatterjee, The royal society of chemistry, Chem. Sov. Rev., 42, 2013, pp. 5425 5438. [18] S. Lijima, Helical microtubules of graphitic carbon, Nature. 354 (6348) (1991) 56 58. [19] Bucku paper-14, Future planes, cars may be made of buckypaper. Yahoo! Tech News, 2008-10-17. Retrieved 2008-10-18. [20] M. in het Panhuis, C. Salvador-Morales, E. Franklin, G. Chambers, A. Fonseca, J.B. Nagy, Characterization of an interaction between functionalized carbon nanotubes and an enzyme, J. Nanosci. Nanotechnol. 3 (3) (2003) 209 213. [21] E. Ramirez, L. Erades, K. Philippot, P. Lecante, B. Chaudret, Shape control of platinum nanoparticles, Adv. Funct. Mater. 17 (13) (2007) 2219 2228. [22] M.A. Mokammel, S. Hashmi, Reference Module in Material Science and Materials Engineering, 2019. [23] C. Graf, Vossen, L.J. Dirk, A. Imhof, A. van Blaaderen, A general method to coat colloidal particles with silica, Langmuir. 19 (17) (2003) 6693 6700. [24] N.P. Truong, M.R. Whittaker, C.W. Mak, T.P. Davis, The importance of nanoparticle shape in cancer drug delivery, Expert. Opin. Drug. Deliv. 12 (2015) 129 142. [25] L.R. Hirsch, A.M. Gobin, A.R. Lowery, et al., Metal nanoshells, Ann. Biomed. Eng. 34 (2006) 15 22. [26] J.E. Schroeder, I. Shweky, H. Shmeeda, U. Banin, A. Gabizon, Folatemediated tumor cell uptake of quantum dots entrapped in lipid nanoparticles, J. Control. Rel. 124 (2007) 2834. [27] Y. Yang, Y. Fu, H. Su, L. Mao, M. Chen, Sensitive detection of MCF-7 human breast cancer cells by using a novel DNA-labelled sandwich electrochemical biosensor, Biosens. Bioelectron. 122 (2018) 175 182. [28] D. Sun, J. Lu, Y. Zhong, et al., Sensitive electrochemical aptamer cytosensor for highly specific detection of cancer cells based on the hybrid nanoelectrocatalysts and enzyme for signal amplification, Biosens. Bioelectron. 75 (2016) 301 307. [29] M. Bilal, T. Rasheed, J.E. Sosa-Hernandez, A. Raza, F. Nabeel, H.M.N. Iqbal, Biosorption: an interplay between Marine Algae and potentially toxic elements- a review, 16 2018 65. [30] Basic Information on the CCL and Regulatory Determination. EPA, 201907-19. [31] I. Ahmed, H.M.N. Iqbal, K. Dhama, Enzyme-based biodegradation of hazardous pollutants -an overview, J. Exp. Biol. Agri. Sci. 5 (2017) 402. 411. [32] One example of a listed chemical is RDX, an explosive. Technical Fact Sheet- Hexahydro-1,3,5- trinitro-1,3,5-triazine (RDX). EPA. EPA 505-F-17008, 2017. [33] Z. Taleat, A. Khoshroo, M. Mazloum-Ardakani, Screen-printed electrodes for biosensing: a review, 2008 2013. [34] M. Liu, J. Peng, et al., Two-dimension modelling of the self-limiting oxidation in silicon and tungsten nanowires, Theor. Appl. Mech. Letters. 6 (5) (2016) 195 199. [35] J. Yuan, et al., Nat. Nanotechnol. 3 (2008) 332 336.
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[36] D. Pletcher, J. Evans, P.R. Warburton, T.K. Gibbs, Acidic gas sensors and method of using the same, US Patent 5,071,526, Dec. 10, 1991. [37] R. Sharma, K.S.M.S. Raghavarao, Nanomaterials for Food Applications, 2019. [38] U. Guth, H.-D. Wienhofer, Gas Sensors Based on Conducting Metal Oxides, 2019. [39] H. Bi, X. Han, Chemical, Gas and Biosensors for IOT and Related Applications, 2019. [40] D. Antuna-Jimenez, P. Tunon-Blanco, Molecularly Imprinted Sensors, 2012.
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8 Fabrication of biosensors R. Ruban1, H. Mohit2, M.R. Sanjay3, G. Hemath Kumar4, Suchart Siengchin3 and N.S. Suresh5 1
Department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli, Tamil Nadu, India 2Department of Mechanical Engineering, Alliance College of Engineering and Design, Alliance University, Bengaluru, Karnataka, India 3Natural Composite Research Group Lab, Department of Materials and Production Engineering, The Siridhorn International ThaiGerman Graduate School of Engineering, King Mongkut’s University of Technology, North Bangkok, Thailand 4Composite Research Center, Chennai, Tamil Nadu, India 5Department of Electrical and Electronics Engineering, Saveetha School of Engineering, Saveetha University, Chennai, Tamil Nadu, India
8.1
Introduction to biosensors
Biosensors are analytical instruments that use enzymes, antibodies, tissues, organelles, or whole cells that turn biological reactions into electrical, thermal, or optical signals [1 3]. Biosensors should be deceptive and reusable independent of physical parameters such as pH and temperature. Biosensors must have excellent sensitivity, speed, reproducibility of signal response, quick response and recovery time, stability, availability, selectivity, versatility, low cost, good operating life, and ease of use [4,5]. A biosensor consists of two components. The first is the sensing element, and the second is the transducers. Biosensors are commonly used to analyze foodstuff, study biomolecules and their interaction, and produce drugs and in crime departments, medical applications, delivery of medicines, wastewater management, soil quality monitoring, defense applications, and environmental monitoring applications [6]. The biosensor response depends on geometry, manufacturing process, type of transducer used, biological reaction, and operating conditions. The production of biosensors, their components, transducing tools, and immobilization encompasses multidisciplinary work in chemistry, biology, and engineering. The materials used in biosensors are based on the different mechanisms: enzymedependent biocatalytic group, affinity group like antibodies and Nanomaterials-Based Electrochemical Sensors: Properties, Applications, and Recent Advances. DOI: https://doi.org/10.1016/B978-0-12-822512-7.00014-4. © 2024 Elsevier Inc. All rights reserved.
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nucleic acids, and microbe-related microorganisms. A biosensor’s principle includes the bioreceptor, which is used for recognition, and a transducer for converting the biological and chemical reaction into an electrical signal, which is sent to processing, and the digital display is shown in Fig. 8.1. Biosensors usually contain a chemical (molecular) for identification (receptor), whereas a physicochemical transducer provides biochemical mechanisms interfaced with the optoelectronic system. The sensor categories used are enzyme-based, tissue-based,
Figure 8.1 Modules of a biosensor [7]. Source: Reproduced by permission of The Royal Society of Chemistry, S. Shrivastava, et al., Recent progress, challenges, and prospects of fully integrated mobile and wearable point-of-care testing systems for selftesting. Chem. Soc. Rev. 49 (6) (2020) 812 1866.
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immunosensors, biosensors to DNA, and thermal and piezoelectric biosensors. The fabrication of biosensors involves multidisciplinary fields such as biology, chemistry, electronics, instrumentation, physics, optics, and market.
8.2
Components of biosensors
Biosensors are composed of three major elements: a bioreceptor, a transducer, and a signal processing device [8]. A biosensor’s classification is based on the bioreceptor and sensor. Biosensors are developed using biomarkers to test drug therapies. Biomarkers are molecules such as glucose, protein, and DNA, which are used to detect the disease’s progress. Some examples of biomarkers for the respective conditions are shown in Table 8.1.
8.3
Biosensor transducers
A biosensor transducer detects biologically identifiable electric signals. Biosensor technology’s biological portion is divided into two distinct groups: catalytic (enzymes, microorganisms, and tissues) and noncatalytic (antibodies, receptors, and nucleic acids). The transformation of analytes of particular interest has a significant impact on the development of a biosensor. The transducer’s various types are electrochemical, optical, calorimetric, and acoustic transducers, as shown in Fig. 8.2. The principles of multiple biosensors are as follows: 1. The electrochemical sensor detects natural elements, such as enzymes. Table 8.1 Biomarkers of various diseases. Diseases
Biomarkers
Diabetes mellitus Hypertension Heart failure Asthma Cardiac ischemia Cancer biomarkers Oxidative biomarkers
Hemoglobin A1c, fasting blood glucose, and post-prandial blood glucose Plasma renin and aldosterone Amino-terminal pro-peptide counterpart (NT-proNP) Leukotrienes Troponins and myoglobins Prostrate-specific antigen and epidermal growth factor receptor Hydrogen peroxide and glutathione peroxidase
Biosensors
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Optical
Piezoelectric
Biosensors
Electrochemical
Calorimetric
Figure 8.2 Biosensor transducers.
2. An optical biosensor is devised based on the measurement of change in optical properties, which helps in detecting microorganisms 3. A calorimetric biosensor is designed based on accompanying heat absorption or heat addition involving a change in temperature, which detects antibodies, receptors, and nucleic acids 4. Acoustic biosensors measure the biological element based on measurement of improvements in sensor’s acoustic properties. 5. Piezoelectric biosensors are focused on mass change calculation. A detailed description of various transducers is discussed in the following subsections.
8.3.1
Optical biosensors
The light beam is allowed to travel inside a transparent optically denser medium, and when it strikes the interface of the lighter medium, total internal reflection occurs. This total internal reflection occurs when the incident angle is more significant than a critical aspect. The reflected light creates an evanescent electromagnetic wave that excites fluorescent molecules at the wave guidance surface. It helps to remove the bond from unbound labels, as in enzyme-linked immunosorbent assay. If a
Chapter 8 Fabrication of biosensors
thin layer of metal is coated on the interface between two mediums of the various indices of the refractive effect, evanescent wave couples with electron plasma, leading to electron oscillation and generating a surface plasmon wave. The reduction of reflected light intensity occurs when plasma resonance occurs on the surface. There are various types of detection methods for optical biosensing, such as using fluorescence-based biosensors, surface plasmon resonance (SPR)-based biosensors, and chemiluminescence-based biosensors. In the case of fluorescent detection, target molecules or components of biorecognition are labeled with fluorescent labels, which emit light during biorecognition events due to fluorescence. For instance, nucleic acids or antibodies are tagged with the fluorochrome agent, which converts the interaction of the hybridization of two complementary DNA strands into optical signals. Fluorescence-based biosensors are incredibly prone to the detection limit of single molecules. However, they face difficulty in labeling biorecognition elements and are not suitable for real-time monitoring. Using an SPR-based biosensor (SPIR) is a label-free detection method of light matter interaction with biorecognition elements without radioactivity and fluorescence. It is easy to use and allows for the measurement of molecular interaction for qualitative and kinetic analyses. It is highly attractive for rapid detection, has fewer reagents, and does not require any pretreatment of samples before measurement. SPIR was first demonstrated [9] for biosensing applications and proposed as the first commercial biosensor. When the target analyte interacts on the substratum surface with immobilized biomolecules, the refractive index changes. The differences in refractive indices and solution molecules can be optically sensed, which can be used to determine the sensing performance. In SPIR, the gold film is coated on the glass substratum, and the item of the biorecognition element is immobilized on the film. The biological factors present in the buffer solution are made to flow across the gold film through the fuel cell. A stream of a light wave is allowed to interrogate the glass’s surface at a mere equivalent wavelength of SPIR through the glass substratum surface. The reflectivity of gold changes shifts after the binding of target molecules on the surface of gold with higher sensitive performance. There are four different ways of coupling needed to excite surface plasma waves in SPIR to get transduction signals that were obtained from binding refractive index changes. The various methods of coupling are prism coupling, waveguide coupling, and fiber optic and grating coupling.
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Prism base coupling is the most efficient SPIR configuration, where total light is reflected at the interface in connection with prism metal, which produces an evanescent field where it penetrates inside the metal and excites the surface plasma waves. However, it is difficult to interrogate and miniaturize, and it is bulky in nature. In the case of waveguide coupling, the light wave propagates through total internal reflection and generates an evanescent field at the waveguide metal interface. It is easy to interrogate with the components that are robust in nature. Both fluorescence and label-free detection methods provide complete information on the matter particle interaction, which makes the optical-based biosensor versatile in nature.
8.3.2
Piezoelectric biosensors
Piezoelectric biosensors are based on the principle of the piezoelectric effect. The potential difference is developed across the material when the material is subjected to applied mechanical stresses, which is called the piezoelectric effect. Piezoelectric sensors have been used in sensing applications since the 1950s. They have been used extensively in applications such as medical, aerospace, and nuclear devices. In piezoelectric biosensors, a transducer is made of a quartz crystal, a piezoelectric material, and the coating is done on biosensing material. Piezoelectric elements can produce and transmit frequency-dependent acoustic waves [10]. The optical frequency response for transmission of acoustic waves depends significantly on the physical dimensions and properties of the piezoelectric material. The crystal vibrates at a specific frequency when pressure is applied to them. There is a linear correlation between the crystal resonant frequency and the mass adsorbed on to the surface during its binding interactions, which help measure the weight of the analyte with a greater accuracy [11]. Piezoelectric biosensors have numerous advantages like compactness, low detection limits to picogram, labelfree detection, and real-time tracking. There are two modes of wave propagation: bulk acoustic wave (BAW) and surface acoustic wave (SAW), where the acoustic wave passes through the substrate in the former, and the acoustic wave passes over the surface of the substrate in the latter. The most common types of BAW devices are thickness-shear mode (TSM) resonator and shear-horizontal acoustic plate mode (SH-APM) sensor. A TSM resonator or quartz crystal microbalance utilizes piezoelectric crystal oscillating shear, and a SAW resonator uses wave propagation mode. The SH-APM sensor incorporates the
Chapter 8 Fabrication of biosensors
advantages of both BAW and SAW devices. In BAW, the piezoelectric material is sandwiched between the electrodes. As electric fields are applied, potential differences are developed across the electrodes, resulting in shear deformation of the crystal, creating a mechanical wave of standing oscillations traversing the majority of the bulk. The parameters, such as natural frequency and thickness of the material, are used to achieve the desired rate. In SAW, Rayleigh waves propagate over the surface of the piezoelectric element. A piezoelectric biosensor finds its application in a chemical sensing device to detect organic species of specific interest.
8.3.3
Calorimetric biosensors
All biological and chemical reactions involve exothermic reaction [12]. They lead to the development of calorimetric instruments. This theory is based on the estimation of temperature change in the reaction between the biorecognition element and the desired analyte of specific interest. The change in temperature is proportional to the reactants produced or consumed. The heat fluctuations were calculated by either thermistor (typically metal oxide) or thermopile (ceramic semiconductor). The advantages of this biosensor are stability, sensitivity, label-free detection, being unlike optical biosensors, and the possibility of miniaturization. It is being used in clinical diagnostics, environmental monitoring, and the food sector industries [13,14]. It also finds applications in the detection of pesticides and other enzymatic reactions.
8.4
Electrochemical biosensor
Among the different transducer types, electrochemical transducers are perhaps the most widely used since they are portable, have low instrumentation cost, and are easy to handle, especially for clinical or home applications [15]. In an electrochemical biosensor, the electrode is being used as a transducer. Many chemical reactions generate or consume ions from solutions that induce some changes in the electrical properties of the solution, which are used as parameters of measurement. An electrochemical response is based on the analyte’s activity, not on the concentration of the analyte. The electrical response for reading is correlated with the level of analytes. The electrochemical cell is composed of a working electrode, a reference electrode, and counter electrode. The working electrode acts as
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a cathode or anode based on the reaction, regardless of whether it is oxidation or reduction. The commonly used working electrodes are glass carbon electrode, Pt electrode, gold electrode, screen-printed electrode, and electrodes coated with indium tin oxide and carbon paste. The electrochemical biosensor application is based on detecting analytes such as urea, oligonucleotides, and activated cells. Several enzymatic reactions, such as those of urease and several biological membrane receptors, can be controlled using integrated microelectrodes by ion conductometric or impedimetric devices. The measurement’s responsiveness is slowed down by the buffer’s parallel conductance using a differential measurement between an enzyme sensor and an equivalent enzyme-free one. The typically used electrochemical biosensor is the glucose biosensor, where the working electrode is coated or immobilized with glucose oxidase enzyme. In 1962, Clark and Lyons invented the first glucose biosensor. The work is based on the conversion of glucose into gluconic acid and hydrogen peroxide with GO enzyme in the presence of oxygen. An increase in the amount of hydrogen peroxide results in current generation due to redox reaction. Glucose 1 O2 .Gluconicacid 1 H2 O2 The glucose level is monitored indirectly by measuring the decrease in the oxygen level using the Clark-type electrode or measuring the change in pH due to the gluconic acid formation. Some examples of hydrogen peroxide-measuring biosensors are alcohol as an analyte, where the enzyme is alcohol oxidase, and D-Glucose as an analyte, where the enzyme is GO. Similarly, in the case of a cholesterol biosensor, the cholesterol reduction in the presence of oxygen into cholest-4en-3one with cholesterol oxidase enzyme is shown in Fig. 8.3. Current is increased due to the increased amount of hydrogen peroxide and a change in impedance, enabling the detection of the amount of cholesterol present in the body. The application of real and exact determination of biological molecules at the point of interest is still a significant challenge in biosensors’ growth [17]. Mahnaz [18] developed a new enzymatic biosensor based on immobilization of cholesterol oxidase enzyme on the polyaniline/crystalline nanocellulose/ ionic liquid-modified screen-printed electrode. Another example of an electrochemical biosensor is the DNA biosensor, based on the principle where fluorescence is correlated to the concentration of target DNA. It uses an electrochemical transducer to detect the hybridization of DNA. The sample molecules of DNA
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Figure 8.3 Cholesterol biosensor [16]. Source: Reproduced from Elsevier, V. Narwal, et al., Cholesterol biosensors review. Steroids 143 2019 6 17.
are placed on an electrically active surface and are recognized by measuring the variation of current or resistance changes based on the DNA’s hybridization, which is used to identify cancer gene mutation. Electrochemical biosensors are classified based on the nature of detection in electrochemical changes: amperometric, voltammetric, impedimetric, and conductometric, as discussed in the following subsection.
8.4.1
Potentiometric biosensors
It is based on the principle of measuring the potential difference between the working electrode, where the biorecognition element is an immobilized and second reference under the conditions of zero current. This technique is nondestructive since there is no consumption of analytes. Three types of potentiometric devices are commonly used as transducers in biosensors: (1) ion-selective electrodes, (2) gas sensing electrodes, and (3) field-effect transistors (FETs). All three types of sensors followed the logarithmic relationship between the potential produced at the surface of the electrode and the ion of specific interest. Ionselective electrodes find their application in water monitoring [18]. They have a broader range of sensing applications. It is based upon thin films or selective membranes as an aspect of recognition. The most common potentiometric devices are pH electrodes and other ions (F2, I2, CN2, Na1, K1, Ca2 1 , and NH4 1 )- or gas (CO2 and NH3)-selective electrodes. The reference electrode should be stable for proper sensing applications. Among the ion-selective electrodes, the FET is most widely used due to its advantages of higher sensitivity, portability, and
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ease of use. The FET, commonly used in semiconductor devices, could help miniaturized devices be employed in the microelectronics industry. The FET applies the electric field at the gate to control the conduction channel, that is, modifying form and scale, between the source and drain. Biosensors are simply a combination of FET and biological material with conductivity. They are configured by modifying the gate terminal of FET with molecular receptors or ion-selective membrane of the analyte of interest. Applying the voltage to the gate is equivalent to binding a charged molecule to the gate, which suits the FET well for electrical biosensors. An ion-selective FET, a promising technique of FET, provides higher sensitivity and label-free detection and can be used as core components [19,20]. Biomolecules functionalized on the substrate surface are exposed to electrolyte solution containing a complete analysis of desired interest through the circuit through gate voltage bias. The electrical properties are enhanced by using 1D and 2D nanomaterials such as silicon nanowire, polymer-based nanowire, metal oxide (zinc oxide) nanowires, carbon nanotubes (CNTs), and graphene nanosheets on the surface due to a higher proportion of surface area to volume. However, it envisages future generations but complicates the process of integration in incorporating natural elements and packaging into the sensing devices. The major limitation is that it cannot be used for real monitoring of commercial purposes for clinical diagnostic applications.
8.4.2
Amperometric biosensors
It is based on the concept of measuring the current stemming from biorecognition, such as electrochemical oxidation or reduction of an electroactive material on the surface [21]. The oxidoreductase enzymes are well suited as biorecognition elements due to their biocatalytic activity for sensing blood glucose levels. It works on the principle of maintaining a constant potential concerning a reference electrode at Pt, Au, or C electrodes that can also act as an auxiliary electrode, where currents are small in the order of 10 6 A. The current produced within the adjacent biocatalytic layer is interrelated with the bulk concentration of the electroactive species or its production or consumption rates. The rates of biocatalytic reactions have an advantage, in that they are a first-order dependency of the level of an analyte. The analytes such as alcohol, oligonucleotides, phenols, sugar, and oxygen can be measured using
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amperometric transduction techniques. Biosensors incorporate an acetylcholinesterase or butyrylcholinesterase single enzyme as a biorecognition element. The production of thiocholine is controlled amperometrically, and the development of acid production is potentiometrically supervised. It also finds its application in drug characterization studies.
8.5
Electrode fabrication technologies
The fabrication of an electrode plays a crucial role in sensing applications of biosensors. It should be fabricated at a lower cost with a reliability feature for the analyte’s various desirable analysis. Biosensors are fabricated in a smaller size with sophisticated techniques, and handling of analytical reagents in this microchip is a very tedious process. Typically, several biosensors were produced using coating, screen printing, and the process of direct deposition. Among those, screen printing is one of the most commonly used fabrication methods for base transducers since the 1990s, adapted from the microelectronics industry at a lower cost. It is created by printing various inks on different types of plastic or ceramic substrates. It uses a stencil with transparent areas on which ink passes, and solid areas serve as a mask to prevent ink from passing. The selection of inks used to print on the electrodes defines the selectivity and sensitivity needed for each analyte [22]. The polyester screen is typically used for printing the analyst of design concern and is immobilized with essential enzymes. PVC, polycarbonate, polystyrene, and alumina are also used as base transducers in screen printing. The screen printing technologies are advantageous for smaller volumes—less than 1 billion sensors per annum and film thickness up to 40 µm. Advancement in transducer design in measuring 1 million measurement points on a 1 cm2 chip is possible with liquid handling biosensor devices. Biosensors are fabricated in a smaller size, and with sophisticated techniques, handling of analytical reagents in this microchip is a very tedious process. The biosensors which comprise handling liquid allow for detection of biomolecular interaction in liquids [23]. Photolithographic techniques are widely used in the manufacture of microfluidic cells and lab-on-a-chip. It enables the fabrication of biosensors in bulk production. The FET-based biosensors have been developed to study biomolecular interactions, one of the key drivers of biological responses in in vitro or in vivo systems. They have many advantages such as portable instrumentation, small sample requirements, low cost
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with mass production, and high speeds. Organic thin-film transistors help in sensing the analyte for both gas- and liquidphase applications [24], and the detection limit of a biosensor is enhanced by the specific surface area of nanomaterials. Biosensors made from nanomaterials are widely used to detect molecular biomarkers associated with the diagnosis of a disease [25]. The nanomaterial-based biosensor is very useful in biomedical applications and the detection of food pathogens in recent decades. The fabrication of nanomaterial-based biosensors is discussed in the following subsection.
8.5.1
Fabrication of nanomaterial-based biosensors
Several conductive electrodes (i.e., Ag, Au, and Pt) and metal oxide electrodes such as fluorine-doped tin oxide and indium tin oxide have been used as electrodes in biosensors, since the invention of a glucose biosensor by Clark and Lyons in 1962. The electrodes are modified by coating with nanomaterials, which provides a higher surface area of the electrode with exposed catalytic sites to enhance efficiency in sensing performance. Nanomaterials, because of their nanoscale, offer good electrical conductivity and mechanical, optical, and magnetic properties. The nanomaterials are deposited onto surfaces of the electrode surfaces using various methods [26 28]. The details of various fabrication methods of nanomaterial-based biosensors are shown in Fig. 8.4, and their pros and cons are discussed in the following subsection.
8.5.1.1 Coating-based methods The electrodes are modified by coating with nanomaterials. The coating method does not require any sophisticated instruments, which results in low-cost sensor fabrication. The limitation of this method is that only soluble or processible solution nanomaterials can be deposited on the electrode surface. Four coating methods for the fabrication of nanomaterial deposition onto the electrode surfaces are as follows: 1. Drop casting: In this fabrication method, nanomaterials are mixed with suitable binders or solutions in suspension or slurry medium through either sonification or physical-based methods of combining pestle and mortar. The suspension is collected and coated onto a cleaned surface of the electrode, followed by binders and solvent evaporation. Optimized parameters include mixing process, homogeneity of slurry, and
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Figure 8.4 Coating-based methods for fabrication of biosensors [29]. Source: Reproduced from Elsevier, A. Rafiq, et al., Deposition of nanomaterials: a crucial step in biosensor fabrication - a review. Mater. Today. Comm. 17 2018 289 321.
additives (binders or solvents), which are necessary to achieve consistent and maintained morphology of the deposited nanomaterials [30]. Researchers developed various biosensing devices to detect a wide range of analytes such as biomolecules (lactate, proteins, DNA and RNA, and hydrogen peroxide [H2O2]), biological agents (viruses, bacteria, and other pathogenic organisms, toxins, and minerals) using the drop-casting method [31 33]. Almost every type of nanomaterial (metal oxides, carbon-based nanomaterials, metal/oxide nanocomposites, polymers, and their derivatives) can be deposited
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using this drop-casting method for fabrication [34,35]. Glucose sensing biosensors are manufactured using this dropcasting method. The properties of high conductivity, high enzyme loading efficiency, and mass transport of nanomaterials are the main factors for the precision of glucose detection. Multiwalled CNTs [36], herringbone CNTs [37], CoWO4 nanospheres [38], and carbon nanodots [39] were used for fabricating glucose biosensors. Nanomaterials tend to coagulate during synthesis onto the method of drop-casting. It can be eradicated by using suitable supporting metal/metal oxide nanoparticles such as graphene [40], which improves the structure, electrical conductivity, and electrocatalysis activities. The constraints in the case of the drop-casting method are viscosity, and stability of slurry is optimized for coating nanomaterials onto the surface of the electrode, resulting in poor reproducibility, low confidence, and decreased electrical analytical activity [41,42]. The crack formation upon drying, which can be eliminated upon drying at lower temperatures and its chief restraint, is the use of organic additives, which are environmentally toxic and unsafe. The deposition of enzymes on the electrode surfaces from one aqueous solution has detrimental effects on reaction with another aqueous solution, resulting in the disappearance of the enzyme on the substrate and its properties. 2. Dip coating: The electrode is immersed in sol-gel/ polymer nanomaterials for a certain period and drawn out at a higher speed. The balancing of forces at the liquid electrode surfaces controls the uniformity of the film formed over the surface. This method involves a time-consuming process and wastage of materials. It has the advantage of superior controllability of film formation. Several researchers have fabricated biosensors using this dip-coated method, such as fluorine (F) doped on a silicon oxide (SiO2) glass working electrode coated with Fe3O4@SiO2 nanocomposite dispersion [43]. A cholesterol biosensor was developed by transferring Ag nanowires on to graphene oxide (GO) and a chitosanbased indium tin oxide (ITO) electrode [44] and a lactate biosensor was developed by dipping the electrode in a biosynthetic blend of oxidase lactate [Lox] and oxygen-rich Pt-doped ceria nanoparticles [45]. This method is critical in creating multilayer nanomaterial-based biosensors [46]. Dip coating is preferred for the fabrication of nanomaterialbased biosensors. 3. Spin coating: In this method, nanomaterials soluble in solgel is dropped over the electrode substrate and spanned at a
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higher speed through centrifugal action, resulting in the spread of the solution over the substrate surface. The thickness of film formation over the substrate surface depends on spin speed, resolution’s viscosity, and the concentration of nanomaterials. The coating of polymer films on electrode substrates is widely done using this spin-coating method, which provides good quality film-forming uniqueness with functionalization [47]. Spinning speed significantly impacted film’s physical properties such as film thickness, electrical resistance, and mechanical properties, observed when the urea biosensor is fabricated by coating ZnO-carbon on the FTO electrode, active porous media [48]. Used ink contains photoreactive conducting polymer poly (3,4-ethylene dioxythiophene) situated on the polydimethylsiloxane substrate; the drying and patterning process is carried out with ultraviolet light exposure. Similarly, Kucherenk et al. fabricated a biosensor utilizing nanosized zeolites using spin coating, which is used as the first matrix for various enzyme immobilizations. Applications of spin coating methods are solar panels, gas sensors, and diodes emitting light. This process is suitable for polymer as well as thin films. 4. Blade coating: This method is a simple roll-to-roll coating technique that produces 3D highly ordered colloidal polymer nanocomposites and polymer biosensor membranes [49]. This method creates uniform films over a large surface area. Yet, it is inadequate for making thin films. The blade spreads the colloidal solution over the substrate’s surface from one side of the surface wall of the substrate. This blade coating method has the advantage of controlling film thickness, no waste of materials, excellent uniformity, and fast film deposition. The film thickness variations depend on the surface tension, viscosity, coating speed, and form of sol-gel based on the colloidal solution. This coating method is used for printing, paper and textile, fuel cells, and ceramic industries.
8.5.1.2
Deposition-based methods of biosensor fabrication
Direct deposition methods of fabrication require fewer steps of manufacturing compared to coating-based methods. The various deposition methods are electrochemical, electrospinning, electrospray, sputtering, and vapor deposition, as shown in Fig. 8.5. Electrochemical deposition is an effortless and economical process conducted at room temperature and does not require high vacuum. In this method, three working electrodes (working, counter, and reference) are dipped into the solution,
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Figure 8.5 Direct deposition methods of biosensors. Source: Reproduced from Elsevier, A. Rafiq, et al., Deposition of nanomaterials: a crucial step in Biosensor Fabrication - a review. Mater. Today. Comm. 17 2018 289 321.
and sufficient current is applied, which helps in reducing metal ions and polymerizing the polymers depositing on the working electrode surface. The different modes of deposition are cyclic voltammetric, potentiostatic, pulse potentiostatic, and chronoamperometric deposition methods. The morphology and thickness of coated films are controlled by selecting electrochemical parameters (i.e., potential, additive, current, temperature, and pH). The fabricated electrodes are binder-free, disposable, costeffective, and environment-friendly. Several researchers have shown considerable interest in the fabrication of biosensors using the electrochemical deposition approach. Electrochemical codeposited cytochrome-c and vertically aligned rGO onto GCE were used for H2O2 and superoxide anion detection [50]. 3D chitosan-Au NPS/hollow form like PPy on a stainless electrode was used for sialic acid detection [40]. Au-NP-rGO deposited onto the GCE was used to determine methylmercury (CH3Hg 1 ) in fish [51]. However, the electrochemical deposition method of biosensors requires an electrically conducting
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surface on the substrate. Therefore, this technique cannot be used for paper-based or nonconductive substrates. Electrospinning deposition is one of the simple, low-cost, one-step, and straightforward method for the fabrication of nanomaterials. It consists of three components: (1) high voltage power supply, (2) a syringe with a metallic needle, and (3) electrode substrate surface. High voltage is provided to the solution, which leads to the formation of a pendant droplet in the form of a conical shape at the tip of the needle, and it ejects a polymer jet from the tip of the needle. The interaction of the electric field with the surface tension of the liquid jet stretches the jet, and whipping motion leads to evaporation and formation of a uniform film of nanofibers. This method is deployed in the production of distinct nanomaterials such as carbon nanomaterials (graphene and CNTs), inorganic nanomaterials (Ag, Au, ZnO, Fe2O3, and TiO2), and conjugated polymers (i.e., PPy, PANI, PPV, PtH, and their derivatives) [52 54]. Nanofibers fabricated using this method are found to have adequate properties like larger surface areas and high porosity on the conductive electrode substrate surface for enzyme immobilization. These electrospun nanofibers are used to produce various electrochemical biosensors [55]. A carbon nanofiber film consisting of 3D PAN fibers was presented by electrospinning subsequently, followed by oxidation and carbonization, as shown in Fig. 8.6.
Figure 8.6 Fabrication of a nonenzymatic glucose biosensor (NiCO2O4/carbon nanofibers) [55]. Source: Reproduced from Elsevier, L. Liu, et al., NiCo2O4 nanoneedle-decorated electrospun carbon nanofiber nanohybrids for sensitive non-enzymatic glucose sensors. Sens. Actuators. B. 258 2018 920 928.
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The carbon nanofibers were adorned further with NiCO2O4 needles to fabricate nonenzymatic glucose biosensors. The direct blending of nanomaterials in nanofibers was more efficient in causing instability in storage before the initiation of electrospinning fabrication [56]. More attempts were carried out to study the fabrication of biosensors by various researchers [57 59]. An electrode was tailored by blending with 4-aminothiopheno (4-ATP) and Au nanoparticles, improving the electrode’s adhesion and conductive properties. An electrode was fabricated using electrospun polycaprolactone fibers on the ITO electrode using CuO nanoparticles. This approach has certain drawbacks: toxic solvents are used, pores are controlled in 3D structures, and calcination is required before putting into it use. Electrospray deposition is one of the biosensor fabrication processes carried out by spraying natural polymers, synthetic polymers, and solutions of composites. It uses the principle of electrostatic force for the deposition of fibers/particles on the substrate surface. The working high voltage is applied between the target and tip of the capillary needle, which leads to the exit of the spray of fibers/solution when electrostatic force overcomes the surface tension in the form of the Taylor cone. Several attempts have also been made in the fabrication of biosensors using the electrospray technique [57,58]. The limitations of this method are unacceptable for depositing nanomaterials in quite a small region. The parameters such as viscosity of the solution, tip geometry, and gap between nozzle and substratum must be regulated properly. This method is suitable for the materials that have ink stability. Other similar deposition methods, including physical vapor deposition and chemical vapor deposition, create thin films of nanomaterials on the electrode’s surface.
8.5.1.3 Printing-based methods Printing-based methods received substantial interest in deposited nanomaterials onto the surface of the electrode substrate. This approach is commonly utilized in applications for sensors, photonics, energy storage, and sensing. It allows for direct deposition of nanomaterials onto the substrate surface, which is not possible with the coating techniques, where it uses some other form of approaches to deposit on to the substrates. The various methods of fabrication deploying printing techniques are screen printing, inkjet printing, nozzle jet printing, and laser scribing, as shown in Fig. 8.7. The screen printing technique prints the nanomaterials onto the substrate surface through stencils and mesh-covered
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Figure 8.7 Inkjet methods of fabrication. Source: Reproduced from Elsevier, A. Rafiq, et al., Deposition of nanomaterials: a crucial step in biosensor fabrication - a review. Mater. Today. Comm. 17 2018 289 321.
frames/screens. Here, ink is made to pass through the mesh onto the substrates/electrodes. Ink flows into the printed area where the photopolymerized resin is not allowed to pass through. Inks used for printing may be polymeric binders and metal/metal oxide dispersions. Printing with inks/pastes provides a larger surface area, which strengthens the performance of the device. The function of the synthesis of nanomaterial and preparation of inks is one of the critical concerns in this screen printing method. Only a few nanomaterials are suitable for the development of ink. The proper dissolution of nanomaterials in solution, syntheses, and additives is essential for the preparation of ink, and aggregation of nanomaterials in solution results in the uneven printing of materials. Degradation of printed ink substrate occurs due to exposed aggregated enzymes. It results in decreasing the sensing performance of sensors. The electrodes printed on-screen are written using different inks of nanomaterials. The sensing performance of six carbon-based nanomaterials (i.e., graphene, graphene oxide, carbon, single-walled CNT, multiwalled CNT, and carbon
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nanofiber [CNF]) printed on to working electrodes was studied [60]. The CNF-based biosensor exhibits superior sensitivity, selectivity, and a lower limit of detection of 0.75 pg mL21. Screen-printed rGO carbon black nanocomposites were placed on a polythene terephthalate (PET) substrate to create dopamine-, epinephrine-, and paracetamol-based electrochemical biosensors [61]. Screen printing methods are not suitable for flexible sensing applications since due to the viscosity of ink, resulting in the formation of thick film over the substrates. During printing, the loss of materials and contamination is difficult to monitor and is dependent entirely on contact where the blade is used to disperse the ink across the glass surface mesh. Inkjet printing is a noncontact and demand-based process commonly used for printing electronic devices due to its ability to create spatial fidelity and electrically conductive patterns on the surface of the electrode. Inkjet printing has gained popularity in the fabrication of disposable and flexible electronics due to diverse advantages. This system provides a smaller nozzle size, regulates the mode of jetting, and reduces the drop size. The smaller jet size in the range of 5 10 nm of printed patterns was reported [62]. This printing can create mass production of electrodes with less deviation in the reproducibility of electrodes. It can also save materials and avoid contamination on any premade patterns/substrates during printing. Nanomaterial-based inks are produced using metals, metalbased inks, carbon-based materials such as CNT and GO, and conductive polymers (e.g., PANI, PPy, and PEDOT) [36,63]. Electrochemical sensors made of paper are disposable because of the low cost. A paper-based biosensor uses a graphene-PANItailored electrode to detect human papillomavirus [64,65]. Inkjet printing is a fast, effective, and low-cost technology for nanomaterial deposition onto electrode surfaces. A biosensor which undergoes aptamer functionalization and detects antibiotics within a few minutes at 10 µg mL21 in milk, and this presents the simplest and cheapest method of producing microelectrodes on flexible substrates of paper and plastics. The major concern in inkjet printing is that rheological behavior of the ink should be optimized for good sensing device fabrication. Nozzle jet printing is another method of fabrication that is cheaper and straightforward compared to the inkjet printing method. High viscosity resins at higher pressure are applied over the substrate using a large nozzle tip. The parameters to be optimized are speed of motion of the nozzle, the pressure of the nozzle, the diameter of the tip of the nozzle, the temperature of the plate, and height between the substrate and the tip of the
Chapter 8 Fabrication of biosensors
nozzle. This approach is ubiquitous in building hydrogen scaffolds, and currently, it is put to use in fabricating enzymatic or nonenzymatic biosensors. Nozzle jet printing was used to produce a versatile FET-based glucose biosensor [10,66,67]. They have taken a precleaned substratum, and two different Ag lines are printed using a jet printer nozzle. Such lines function as an electrode (S-D) of source drain with a channel length of 0.4 cm. ZnO QDs’ ink has been printed between S-D electrodes, and the area has been used as a seed layer to produce ZnO nanorods (NRs) and to immobilize the enzymes. It provided a large surface area for GOx immobilization, which enhances the performance of glucose. Another research work developed a nonenzymatic glucose biosensor by nozzle jet printing of nanomaterials onto a flexible substrate [68], and its fabrication procedure is shown in Fig. 8.8. They took a PET substrate, and Ag was printed on the substrate using nozzle jet printer; subsequently, CuO NPs were published over the Ag/PET substrate to toil as a catalyst for oxidizing glucose reaction. It results in the improvement of sensor performance for enzyme immobilization. Laser scribing is another fabrication technique that is an efficient, cost-effective, and one-step fabrication process of biosensors. Lasers were scribed initially to reduce graphite oxide into graphene and formed into laser scribed
Figure 8.8 Fabrication process of a field-effect transistor-based biosensor. Source: Reproduced from Elsevier.
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Figure 8.9 Electrode fabrication using laser scribed graphene on the polythene terephthalate substrate. Source: Reproduced from Elsevier.
graphene (LSG) films, resulting in characteristics offering a large surface area, good conductivity, and electrocatalytic activity. The PET substrate was taken, and graphite oxide was drop-cast on the substrate subsequently with laser printing of electrodes at predefined locations and PET layer, which was pre-printed, was removed, as shown in Fig. 8.9 [69].
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8.6
Direct growth
The sensibility of biosensor performance during sensing application is improved by direct nanomaterial growth on the substrate’s surface, which provides a high region surface with accessible catalytic sites, an environment for immobilization of enzymes, and accessibility of electrolytes and target analytes. The method of direct nanomaterial growth on the electrode surface is hydrothermal, thermal decomposition, template, anodization, and chemical decomposition. This approach allows for nanomaterial growth on electrode surfaces ranging from 1D (NRs, nanowires, and NTs), 2D (nanosheets and nanoflakes), and 3D (nanoflowers and nanorods) for the fabrication of biosensors [70,71]. The merits of direct nanomaterial growth on the substrate’s surface are improved mechanical interaction between the grown nanomaterial and the substrate, movement of electrons, and sufficient strength. The specific synthesis of ZnO NRs on the Ag electrode by a hydrothermal low-temperature process [71] enhances the immobilization efficiency, enabling us to detect the glucose in urine. Similarly, by growing ZnO NRs on Au and Pt electrodes, the electrode surface was tailored to detect glucose [52,72]. The linear growth of ZnO NRs on substrates also finds application in the development of a cholesterol biosensor [73,74]. An electrochemical biosensor was fabricated, on which ZnO NRs were grown on Ag wire using a chemical approach [73]. A biosensor was developed for cholesterol detection on a substratum of Ag-coated Si [75]. Here, ZnO is made to sputter on the Ag electrode surface’s surface, which grows with different aspect ratios of ZnO. It was observed that a higher aspect ratio (60) possesses a higher surface area, shows enzyme immobilization, and has excellent contact between the ZnO NRs and the electrode surface. The structure of ZnO NRs was tailored using thiol, and phosphonic acid enhances the sensing performance [76]. ZnO NRs were grown hydrothermally on reduced graphene film to fabricate a glucose biosensor, which has the advantages of directly enhancing transfer motion of electrons [77]. The surface modification of ZnO NRs with metal/metal oxide enhances sensing and catalytic properties by providing a higher surface area. Thus, it was concluded that a nanomaterialbased biosensor provides enhanced sensible performance and more surface area for immobilization of enzymes. An implantable biosensor with a self-powering feature is discussed in the following section.
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8.7
Self-powered implantable biosensor
Diseases such as cancer or diabetes cause considerable changes to the affected tissues inside the body. The continuous monitoring of the target analyzed would help detect the changes in the concentration of disease-affected tissues without any need for intervention from the patient or clinician for point-of-care diagnostics applications. It necessitates developing implantable biosensors. However, an implantable biosensor faces a crucial problem in replacing or recharging the battery (i.e., primarily in the present glucometers or continuous glucose monitoring systems) and hence is not suitable for constant long-term in vivo monitoring. Therefore, innovative design involving immobilization strategies and bioelectrode plans is essential and is being developed for the implantable biosensors with self-powered features. Biosensors with self-powered features came into existence in 2001. Self-powered biosensors have been developed utilizing biofuel cells as a simultaneous power source with a simple mechanism. Unlike in the electrochemical biosensor, it does not require any potentiostat, which maintains the flow of current between the working and reference electrodes and helps in the conversion of biochemical energy from body fluids. Implantable biosensor devices rely on enzymatic reactions occurring inside the body, and the detection signal was an electric output related to an analyte such as glucose or lactate. Biofuel cells are of mainly two types: Enzymatic biofuel cells (EFCs) and microbial fuel cells (MFCs). EFCs harnessed the biochemical energy (biocatalyst enzymes) present inside the body and converted it into bioelectricity with no toxic byproducts. Enzymes as biocatalysts present in the living organisms oxidize the fuel and transfer the electrons to the anode. The enzymes which possess the advantage of specificity eliminate the need for a membrane separator, unlike microbebased fuel cells; however, they have certain limitations such as low power output, high cost, little fuel versatility, and need for improved enzyme immobilization methods, and they are covalently bonded by immobilizing the enzymes in a matrix conducive to three dimensions such as CNTs. This EFC requires the mediator to establish electrical contact and tends to have much higher current densities than a MFC. The power produced by a single EFC is not sufficient to power implantable devices. Hence, stacked multiple glucose biofuel cells are used to enhance the power output, making the component bulky [78]. To overcome this limitation, charge pump circuits coupled
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with DC converters are used to amplify nearly 3 V for an implantable device like a pacemaker. Genetic engineering is required to improve enzyme properties and the development of stable abundant scale sources of enzymes. MFCs also use the principle of conversion of a biocatalyst (i.e., bacteria) into bioelectricity. MFCs consist of two chambers, where microorganisms are placed in the anode chamber, which act as biorecognition elements, and proton exchange membranes and electrodes act as a transducer. The bacteria give their response in the form of electric current according to the proportion of an analyte. The generation of current depends on microbial respiration, which is equally proportional to the fuel concentration. The hydrogen ions formed from microbes’ reaction with enzymes on the substrate (anode) pass through the semipermeable membrane and combine with the oxygen in the aerobic chamber (cathode) to get treated water. Thus, the MFC finds its application effectively in wastewater management [79]. However, the MFC’s efficiency has to be improved in terms of stability, sensitivity, repeatability, and selectivity at poor infrastructure.
8.7.1
Glucose detection
Diabetes mellitus, is a severe problem among humans nowadays; it may be hypoglycemia or hyperglycemia depending on blood glucose levels, which leads to even serious complications, which are the root cause for heart diseases, kidney failure, and ultimately death. The World Health Organization estimates that by 2025, there will be 300 million people affected by diabetes and that continuous monitoring of blood glucose is critically essential. Significant efforts were taken to build self-powered glucose biosensors. The self-powered biosensors were built based on a connection between changes in peak power density or voltage drop overload with glucose concentration [80 82]. A self-powered biosensor was developed using a load pump circuit coupled with a condenser to induce biochemical reaction occurring at the bioelectrodes and sensing of glucose [83]. The system continuously generated electricity and measured the analyte of interest. The anode was first treated with heterobiofunctional cross-link polymer 1 pyrenebutanoic succinimidyl ester (1 mM), and selective enzyme of glucose such as pyrroloquine quinone glucose dehydrogenase soluble in phosphate buffer saline was deposited onto the buckypaper multiwalled CNTs for specific binding of glucose. This procedure was
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repeated for the oxygen enzyme bilirubin oxidase (BOD) immobilization biocathode. It is the first direct electron transfer-based self-powered glucose biosensor, and it has good selectivity. The system develops very few microvolts, which is amplified to 1.4 V using a charge pump circuit and stepped up to 3 V using the DC converter circuit, and the system exhibits an open circuit voltage of 552 mV and density of 0.225 mWcm22 at 285 mV and a current density of 1.285 mAcm22 in 20 mM glucose. The system can execute its steady operation for nearly 53 days of 20 3 mM glucose. Two types of self-acting featured biosensors were compared, that is, one with the bioanode and biocathode as POQ-GDH and Lacasse and another with BOD as the cathode [84], and it was observed that the latter shows higher current density and peak power, that is, 0.64 mAcm22 and 0.089 mWcm22. A biosensor (ZnO nanowire arrays on a Ti substrate) was built for in vivo applications [85]. The system utilizes a piezo enzymatic reaction involving the mutual coupling of the substratum GO@ZnO to detect glucose concentration without batteries. The fabrication of a biosensor is as follows: a Ti substrate was initially cleaned with alcohol and deionized water and subsequently dried in an oven at 60 C; 10 mM ethanol was dropped onto the substrate, nitrogen gas was exposed over it, it was annealed at 350 C for 20 min, and the reaction beaker was enclosed and held to 90 C for 24 h. ZnO wire arrays on the Ti substrate are transferred to the Kapton substrate for biasing the device and subsequently photolithographed using a photoresist mask. Finally, the GOx aqueous solution is dropped on the ZnO wires, where the fabrication of the device is completed. The experiments are carried out on rats by implanting the equipment inside the mouse’s abdomen and injecting 0.045 gL21 into the mouse for about 5 s. Biosensors’ development and design is still an emerging area and needs to be improved for various analytes of concern.
8.8
Conclusion and outlook
Biosensors play a vital role in today’ market, especially in the food industry, drug processing, defence, and biomedical applications. They consist of components such as biorecognition element, transducer, and signal conditioning equipment. The sensibility of biosensor performance is a main concern with respect to the production of their parts and accessories. The method of fabrication depends upon the analysis of the
Chapter 8 Fabrication of biosensors
analyte of interest. The manufacture of biosensors mainly concerns with the types of the transducer. The electrochemical sensor is the most commonly used transducer among several biosensor transducers due to its portable and higher sensing performance. The increase of the surface area enhances the sensing performance of biosensors, which are done by depositing nanomaterials. Four methods are used to carry out the deposition of nanomaterials on the electrode surfaces: coating-based methods, direct testimony-based methods, and uninterrupted growthbased methods. The conventional biosensor fabrication techniques such as spin coating, dip coating, blade coating, and spin coating are required for separately synthesizing nanomaterials deposited on the substrate. However, it limits the sensing performance of the biosensor during its application. Hence, more attempts are needed to improve the sensing efficiency and stability of the biosensors. In the present generation, wearable biosensors have become common among the people avoiding the necessity of going to the clinic for health monitoring of diseases such as diabetes mellitus or heart diseases (pacemaker). The self-powered characteristic features of biosensors are essential for the continuous online monitoring of patients. The self-powered biosensor utilizes biofuel cells for simultaneous power generation and sensing of biological elements. The biofuels typically used are MFCs and EFCs. MFCs utilize microbes, and EFCs use enzymes as biocatalysts; the former use membranes specifically for the application of wastewater management. The generated power by a single EFC is in terms of microwatt, further amplified by coupling many EFCs in series, which makes the system bulky. The problem of the significant component is eliminated by using a charge pump circuit with a DC convertor, which miniaturizes the part that is useful for implantable biosensor applications. More attempts are still being made in the design and processing of biosensors for various applications with excellent sensitivity and reproducible features.
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9 Metal oxide and their sensing applications Shamim Ramzan1, Abdur Rahim1,2, Awais Ahmad3 and Mabkhoot Alsaiari4 1
Department of Chemistry, COMSATS University Islamabad, Lahore Campus, Lahore, Pakistan 2Interdisciplinary Research Centre in Biomedical Materials (IRCBM), COMSATS University Islamabad, Lahore Campus, Lahore, Pakistan 3 Department of Chemistry, The University of Lahore, Lahore, Pakistan 4 Department of Chemistry, Faculty of Science and Arts at Sharurah, Najran University, Sharurah, Saudi Arabia
9.1
Introduction
Metal oxides (MOs) are chemical compounds produced between metal cations such as Na, K, Li, and so forth and oxygen. Such layers appear to be solid, basic, and more compact than their nonmetallic oxide equivalents. MOs typically contain oxygen anions in the oxidation state of 22. MOs are common in nature. MOs are materials recognized for their sensing applications owing to many advantages. First, they have extraordinary electric, optic, and chemical properties. Furthermore, additional functional groups for the immobilization of other biological catalysts may also be added on the surface. Third, due to the retention of increased oxidation rates of transition metals, MOs have greater alkaline corrosion resistance compared to other products in the electrochemical setting. Ultimately, with their retained thickness, their unique crystalline architectures benefit from the prevention of MO agglomeration [1,2]. A MO surface is a key factor for efficient interaction with target molecules, and therefore, MO particles have also been favored as enhanced detection signal carriers and biosensing interfaces. Sensors are devices based on integrated sensor materials that transfer the signals as a result of chemical reaction, thus generating an analog signal for further processing [3]. Various MOs such as ZnO2, Fe2O3 [4,5], CeO2 [6,7], CdO2 [810], ZrO2 [11,12], magnesium oxide [1315], titanium oxide TiO2 [16,17], RuO2 [18] SnO/SnO2 [19], WO3 [20], CuO/Cu2O Nanomaterials-Based Electrochemical Sensors: Properties, Applications, and Recent Advances. DOI: https://doi.org/10.1016/B978-0-12-822512-7.00013-2. © 2024 Elsevier Inc. All rights reserved.
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[21,22], and V2O5 [23] were achieved through various methods and have been widely studied for their sensing applications (Table 9.1). Besides, it was reported that the incorporation of conductive or semiconductive nanoparticles (NPs), for example, Au, Ag, carbon nanotubes (CNTs), graphene, has been reported to increase the physical and chemical properties of MOs, thus consequentially enhancing the sensing efficiency. Therefore, ideal design and innovations in MO’s applications will pave the way for the modern generation of sensing devices that will be able to exhibit improved signal amplification and doping strategies that may compensate with commercial and societal needs in the future [24].
9.1.1
Metal-oxides-based chemical sensors
A chemical sensor is a tool that converts the chemical signal into an analytically valuable signal, varying from the concentration of a particular sample item to the overall composition analysis. MOs have been extensively studied as chemical sensing Table 9.1 Different metal oxides, synthesis method, and applications. Sr# Metal oxide 1. 2. 3. 4. 5. 6. 7. 8. 9. 10 11. 12. 13. 14.
rGO/SnO2, ZnO Fe2O3NPs ZnCO2O4
Morphology Synthesis method
Conjugated Template-assisted method nanowires Nanocomposite Pyrophoric technique Nanoparticles Cascade toehold-mediated strand displacement reaction Nickel oxide Nanodonut Low temperature hydrothermal (NiO) reaction MoS2/ZnO Nanospheres Wet chemical Pd/ZnO-SnO2 Nanoparticles Thermal evaporation and sol gel CuO-Zn/rGO Nanoparticles Wet chemical and refluxing Au-ZnO Nanowires Hydrothermal ZnO/rGO Nanoparticles Thermal annealing SnO2/MoO3 Nanofibers Wet chemical WO3/RuO2 Nanofibers Wet reduction CuO on AL-C Nanostructure Negative potential-induced substrate growth SnO2@ZnO Nanotubes Facile 2-stephydrothermal CDs-Cu2O/ Nanotube Hydrothermal method using reed CuO
Sensing application References Gas sensing
[25]
Dopamine sensing Dopamine sensing
[26] [27]
Glucose detection
[28]
NO2 sensing NO2 gas sensing NO2 gas sensing NO2 gas sensing NO2 gas sensing CO sensing Urea sensing Biomarkers of diabetes and oxidative stress NO2 gas sensing Detection of hydrazine
[29] [30] [31] [32] [33] [34] [35] [36] [37] [38]
Chapter 9 Metal oxide and their sensing applications
material owing to their attractive properties. They are also used as substrates, regulators, structure modifiers, connectors, electrodes, and filters for the efficient sensor designs. In addition, chemical sensors based on MOs can be generated in arrays to allow for simultaneous detection of multiple species with great sensitivity and low detection limits.
9.1.2
Metal oxides-based biosensors
A biosensor is a ruggedized analytic device constructed on an analyte substrate and a natural receiver, combined with a transducer for the measurement of signals. This receptor layer is a biocatalytic sensing component that is accomplished by identifying its particular analysis and controlling the biosensor’s specificity and response. MOs have various captivating features and therefore considered as auspicious materials for biosensing applications. There are many types of biosensors, immunosensors, calorimetric DNAbased sensors, enzyme-based, tissue-based, cholesterol-based, lipase-immobilized, nucleic acid-immobilized, cytochrome complex (cyt c)-immobilized, antibody-immobilized immunosensors, and urease- and glutamate dehydrogenase-based sensors [39,40]. The amperometric glucose sensor is considered as a commercially most successful biosensor that can help diabetic patients to control blood glucose periodically [39].
9.2 9.2.1
Overview of metal oxides for different applications ZnO-based sensors
Since 1935, zinc oxide (ZnO) has been studied extensively owing to its application to several technologies. Over the past few years, numerous publications have documented the development of various ZnO nanostructures [41]. Hahn et al., for the first time, demonstrated a hydrazine electrochemical sensor based on ZnO nanonails. This showed high sensitivity with a response time of less than 5 s, with a 0.2 mM detection limit. They also reported the effective fabrication of hydrazine sensors retaining ZnO nanorods (NRs) [42]. ZnO is adept at sensing a range of gases, such as CO2, H2S, NO2, NO, NH3, C3H8, and CH4 [43,44]. ZnO has become an extensively studied MO material and has been used in UV sensing applications. Initially, researchers have paid attention to the advancement of ZnO thin film sensors, but these films posed several inherent disadvantages, such
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as poor response time and recovery rate. So in the last decade, several authors recorded that photoresponse could be improved by increasing the surface area of ZnO nanostructures [45]. Many studies have shown the use of ZnO in biosensing applications, that is, in DNA immobilization, glucose sensing [46], and cardiac biomarker sensing [47]. Balram et al. synthesized flower-shaped ZnO NPs without using the aqueous solution method. This work provided excellent catalytic activity of the flower-shaped composite ZnO@GCE in the determination of dopamine, with modified features like good anti-interference potential, broad linear range, fast response, and so forth [48]. Fabrication of a sensitive and label-free electrochemical sensing platform based on multiwalled CNT (MWCNT)-embedded ZnO nanofibers for atrazine detection was reported by Patta Supraja. The binding of atrazine to the anti-atrazine antibody, by immobilization on the nanofiber-modified electrode, was examined with electrochemical impedance spectroscopy (EIS), which showed sensitivity, and the limit of detection (LOD) of the sensor was 21.61 for a broad detection range of 10zM1 μM [49]. Active ZnO/Fe2O3 (ZF2) heterojunction synthesis has been documented for dual application in electrochemical sensing and photocatalytic pollutant removal. All electrodes showed a higher value of Ip (peak current) when scanned in [Fe (CN) 6]3 solutions and showed higher peak currents for the modified glassy carbon electrode (GCE) ZnO/Fe2O3. Both Ip and RCT values confirm the suitability of the modified ZF2 GCEs in biological fluids for dopamine detection. Additionally, the LOD was 0.27 μM for the modified electrode ZF2. Studies of interference and reproducibility confirm the significance of the modified ZF2 electrodes for dopamine (DA) detection [50]. In 2018, Tian et al. introduced a method to integrate multilayered black phosphorus (m-BP) into ZnO to form ZnO-BP that results in excellent carrier mobility and ultrahigh sensing cap, that is, 1 part per billion of NO2 gas relative to sensors based on black phosphorus graphene and ZnO [51].
9.2.2
Indium oxide-based sensors
Indium oxide NRs were effectively incorporated by altered amounts of m-BP to form the BP-In2O3 composite. Fascinatingly, the strength of BP significantly increased by the incorporation of In2O3. BP-In2O3 composites displayed greater response, poor LOD, and exceptional selectivity at 250 C, which is attributed to a large surface area and excellent carrier mobility of BP-In2O3 in the presence of black phosphorous resulting from the fast transfer of
Chapter 9 Metal oxide and their sensing applications
electrons from black phosphorous to In2O3 [52]. Z Tian et al. prepared rGO-In2O3 hybrid nanocube materials through a simple self-assembly technique for the electrostatic. The findings of the characterization revealed close interfacial interaction between the In2O3 nanocubes and the reduced graphene oxide (rGO) surfaces. The as-prepared rGO/In2O3 nanocomposites display rapid comeback and tremendous selectivity of ammonia (NH3) at 250 C, which showed the value of design and coherent assimilation with rGO sheets. The greater gas sensing performance of the rGO/In2O3 nanocomposites was ascribed to the synergetic effects of rGO sheets and In2O3 nanocubes. The detailed synthesis of composites based on rGO/MOs provides a general approach to a semiconductor for applications for gas sensing at room temperature [53]. In2O3/SnO2 composite NPs were synthesized by B Nam et al. The X-ray diffraction (XRD) pattern showed that this composite sensor is composed of three phases: In2O3, SnO2, and In2Sn2O7 (ITO). The energy-dispersive X-ray spectrum of the NP composite showed that the atomic ratio of In2O3 to SnO2 was close to 9:1. The ITO NPbased gas sensor was selective toward CO against other reducing gases such as toluene, acetone, and benzene [54].
9.2.3
Nickel oxide-based sensors
Rafiq Ahmad et al. synthesized nanodonut-molded nickel oxide nanostructures for developing glucose sensors through the hydrothermal method at low temperatures. The developed sensor displayed excellent linearity of reaction within a concentration spectrum of 0.059.5 mM at the compassion of 904.6 l AmM21 cm22 and 1.4 lM LOD. A nanodonut-shaped NiO nanostructure was believed to be used as an excellent electroactive sensing medium in reduced microelectronic detecting systems [55]. Minggang Zhao et al. synthesized Ni foam decorated with p-n junction NRs of ZnO/BiOI core-shell and used it as an enzyme-filling matrix for the detection of glucose. Metalsemiconductor froth has provided the porous surface for enzyme loading and multiple catalyses, and using p-n junction designs was considered as an effective strategy to improve efficiency for biosensing [56] (Fig. 9.1).
9.2.4
Titanium oxide-based sensors
Graphene/TiO2 NPs were created by Giampiccolo et al. through the sol-gel technique. Before starting the sol-gel reaction and toughening, the addition of graphene to the reaction container resulted in an intimately mixed composite
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Figure 9.1 Engineering of Ni/ZnO/BiOI froth for enhanced performance of electrochemical biosensing to glucose. Copyright r 2019 Elsevier [56].
Figure 9.2 Schematic illustration of G/TiO2 NPs for photocatalytically supported detection and NO2 elimination. Copyright r 2019, Elsevier [57]
(GTiO 2S). The as-prepared samples for the monitoring of NO2 gas at low air concentrations were evaluated as sensing materials. The GTiO2S sensor was the most sensitive under UVVisible excitation. The physical processes, that is, free carrier photogeneration and subsequent reactions between oxygen and NO2 and semiconductor surface, were possible when subjected to LED excitation. Furthermore, the photochemical properties, a consequence of NOx reduction, have the same NOx sensing pattern, with GTiO2S being the most active substance relative to both GTiO2 M and pure TiO2, rendering it the most desirable for multipurpose applications [57] (Fig. 9.2). K Montoya-Villegas et al. reported the advancement of a novel, portable, selective, and fast response sensor based on a Au-TiO2 electrode for quantification of 3-mercaptopropionic
Chapter 9 Metal oxide and their sensing applications
161
acid (3MPA). 3MPA plays a vital role in sulfur biogeochemistry (S). The concentration level of 3MPA in aquatic environments ranges from nanomolar to micromolar. 3MPA is harmful at certain doses and is used in studies to induce epilepsy seizures in mice. Cyclic voltammetry (CV) was employed to analyze the calibration curve of the sensor, with an LOD of 50 nM within a linear range of 080 μM [58]. N Khaliq et al. proposed a nonenzymatic amperometric biosensor centered on Cu2O-TiO2. TiO2 nanotubes (TNTs) were created by anodizing titanium foils and subsequently decorated them with Cu2O NPs via the chemical bath deposition method. CV and the amperometric response of the engineered sensor showed a strong catalytic response for cholesterol oxidation. This fabricated electrode showed a five times increased sensitivity to pristine with a low LOD and faster response (3 s). Besides, the immediate cholesterol measurement in the serum of human blood provided desirable precision concerning the commercially available biosensors of cholesterol. These results showed the impending application of Cu2O NPdecorated TNTs for the development of durable, reproducible, and discerning biosensors [59].
9.2.5
Copper oxides-based sensors
Copper oxides are copious, eco-friendly, nontoxic materials which are well-suited with wet chemical synthesis methods (Fig. 9.3) [60,61]. For the detection of ascorbic acid (AA), the hydrothermal MW-assisted method based on Cu2O/CuO/rGO was
Figure 9.3 Graphene sensor allowing for enzyme-free detection of glucose through conformal attaching of CuO NPs. Copyright. r 2020, American Chemical Society [60].
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proposed. A combination of Cu2O and graphene permitted more active sites and increased electrical conductivity, and the presence of Cu2O prevented the graphene oxide sheet from being restocked. The experiments were executed within the linear range of 1001000 mM, and the detection limit was recorded as 0.301 mM [62]. H Zhang et al. successfully developed robust, free-standing, enzyme-free electrochemical sensors for the detection of glucose via the electrochemical installation of Cu2O/Cu on carbon cloth. Owing to its low cost and easy implementation, this composite has attracted vast attention and expands the prospects of glucose sensors and other applications [63].
9.2.6
Tin oxide-based sensors
Tin oxide (SnO2), a highly penetrating and profligately responding MO, has been extensively researched in the production of chemical sensors targeting different gases. Specific nano-SnO2 morphologies have been used for limited or multiple chemical identification. Wang et al. have shown that SnO2 NW-based sensors can detect concentrations of hydrogen (H2) between 10 and 1000 ppm. SnO2 NPs were attached consistently on both sides of 35 nM graphene oxide sheets. In the meantime, a series of gas sensors based on a SnO2/rGO composite and SnO2 were invented, and the results revealed that the composite had enhanced gas sensing properties [64].
9.2.7
Cerium oxide-based sensors
Cerium oxide NPs, based on certain remarkable properties, are favorable in nanotechnology. Yeni Wahyuni et al. successfully synthesized and combined nanostructures of cerium oxide to antiHER2 in order to form the bioconjugate CeO2-anti HER2 for the detection of HER2. A voltametric immunosensor was versatile and prone to identify HER2 using the bioconjugate CeO2-anti-HER2. It was believed that the experimental immunosensor had strong sensitivity to quantify HER2 and could be active in the creation of alternate therapeutic bioanalysis. The modified electrode of the CeO2 NPs, however, showed an immediate response, superior sensitivity, and enhanced selectivity. Furthermore, the designed electrode was tested in numerous water samples to evaluate nitrite [7]. Tamizhdurai P. et al. succesfully synthesized crystalline CeO2 NPs for oxidation into C6H5CHO and nitrite detection via efficient MW combustion and sol-gel methods (Fig. 9.4). The as-synthesized NPs demonstrated good optoelectronic properties and increased electrocatalytic activity toward nitrite detection [65].
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163
Figure 9.4 Schematic illustration of cerium oxide nanoparticles via MW combustion and sol-gel method. Copyright r 2017, Springer Nature [65].
9.2.8
Iron oxide-based sensors
Butmee et al. designed the electrochemical immunosensor for the detection of carcino-embryonic antigen (CEA) based on Fe3O4@Au NPs. Fe3O4@Au was able to serve as a platform for the detection of antibody immobilization and active immunosensor signal amplification. The probability of the immunosensor to sense CEA in human serum was confirmed by a good match between immunosensor-restrained values and immunoassay electrochemiluminescence-measured values. The suggested immunosensor was, therefore, able to offer the cancer biomarker a new diagnostic platform with high sensitivity and low-cost portability [66]. Alizadeh et al. demonstrated a carbon paste electrode (CPE) modified by sulfate-doped α-Fe2O3 as an appropriate indicator for the determination of iodide concentration. Sulfate-doped α-Fe2O3-incorporated CPE showed better I2 oxidation and I2 reduction relative to bare CPE. However, a sulfate-doped α-Fe2O3-CP electrode has
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contributed to the maximum efficiency for I2 oxidation, indicating that hematite alteration by sulfate increases the catalytic capacity of iodide ions. A linear relation was obtained between the concentration of iodide and the CV response [67].
9.3 9.3.1
Different sensing techniques for sensing applications Electrochemical sensing technique
Electrochemical sensors are the most recommended sensors for the detection of MOs. They operate by reacting with chemical solutions and generating an electric signal that is related to the concentration of the analyte. They are classified as follows:
9.3.1.1 Cyclic voltammetry Voltammetry comprises all the methods that quantify currentpotential curves at small indicator electrodes other than the dropping mercury electrode (DME). It is convenient for electrochemical characterization, which provides mechanistic information based on optimization of operating conditions. In the CV approach, the potential is scanned linearly forward from E1 to E2 in the forward direction and then backward from E2 to E1, providing a theoretically triangular cycle. CV results are generally reflected as a guide for all electrochemical techniques used in detection procedure, in particular for chronoamperometry and pulsed amperometry.
9.3.1.2 Linear sweep voltammetry In this method, a static indicator electrode is used, and potential is scanned either in the positive or negative direction at a constant rate. There is no new restricting area, as opposed to DC polarography. The current decreases again once it reaches a peak. For LSV, the electrolyte bath comprises three electrodes: a quantitatively coated RDE or RRDE, a reference electrode, and an auxiliary electrode Pt wire [68].
9.3.1.3 Amperometry The amperometric technique is very important for the application of electrocatalytic detection. For amperometric sensors, the current is produced substantially to the analyte concentration to be identified. A biosensor based on amperometry is an autonomous device based on the amount of the current as a
Chapter 9 Metal oxide and their sensing applications
result of oxidation and thus provides quantitative as well as analytical information about any specie. There is a possibility to combine CV and amperometry for electrochemical detection. For example, the point of specific redox peaks is resolute by CV. Then, amperometry extents are performed at the fixed potential based on information determined by CV [69].
9.3.1.4
Electrochemical impedance spectroscopy
In recent decades, EIS has become a prevalent and active technique for evaluating double-layer capacitance Cdl, characterizing electrode developments, and defining multifaceted interfaces. EIS records the system’s response by stimulating an imposed, periodic, small amplitude AC signal. EIS calculations are usually conducted at specific AC frequencies, and then, EIS can be calculated with the same sinusoidal frequencies by adjusting the ratio between AC potential and the actual signal [18].
9.3.2
Colorimetric technique
The colorimeter’s working principle is based on BeerLambert’s law, which states that the amount of light in which a colored solution absorbs is directly proportional to the solution concentration and the duration of a light path through the solution. Calorimetric analyses are used to evaluate the concentration of the analyte by analyzing the color changes of a solution. In 1977, Hunt recognized three stages of the colorimetric technique: 1. Development color matching. 2. Color difference appraisal. 3. Prediction of color appearance. Colorimetric sensors are widely accepted owing to their highly penetrating and selective reaction to a specific analyte.
9.3.3
Fluorescence technique
Fluorescent probes allow researchers to detect specific, complex bimolecular components with excellent sensitivity and selectivity. It is conceivable to categorize the fluorescence detection systems into the following elements: 1. Excitation source 2. Fluorophore 3. Wavelength filters 4. Detector
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Owing to most effective analytical techniques in bioanalysis, several fluorescent samples have been produced for the identification of H2O2 and dopamine sensing, such as europium coordination complexes [70], dichlorofluorescine [71], quantum dots [72], gold nanoclusters, and cationic conjugated polymers [73].
9.3.4
Quartz crystal microbalance technique
Quartz crystal microbalance (QCM) is a piezoelectric, pressure-sensitive device built on a dynamical quartz crystal, capable of detecting nanogram pressure shifts. QCM is a highly sensitive instrument that can quantify nanogram changes in mass. The QCM sensors are based on changes in resonance frequency on a QCM after changes on the surface of the probe/ transducer. When a piezoelectric sensor surface coated with MOs is positioned in a solution comprising the analyte, the association of the agent and the surface covered with MOs causes an increase in the crystal mass and results in a subsequent frequency shift. The resonant frequency of QCM depends upon the amount of substance being loaded. Permitted to make the best use of QCM, a superb design on the chip is desired to functionalize the electrode with a multiplicity of surface attractions and alterations for molecular recognition.
9.3.5
Surface-enhanced Raman scattering technique
A surface-enhanced Raman scattering effect is a substratedependent technique, well-defined by improvement in Raman frequency for molecules lysed on different surfaces. Nie’s group has described the sensing of a single molecule by SERS, which indicated enhanced sensitivity of SERS for ultrasensitive biological sensing. Owing to very narrow bandwidth, SERS is also well adapted for the detection of multicomponent-based samples. Two mechanisms/processes are generally accepted for the understanding of this phenomenon.
9.3.5.1 Electromagnetic process In this, the electrical field will be intensified when excitation occurs within the local surface plasmon resonances of substrate objects, resulting in factors of enhancement (EFs) up to 106. The mediated local field enhancement by plasmonic pairing is named as electromagnetic “hot spots”.
Chapter 9 Metal oxide and their sensing applications
9.3.5.2
167
Chemical process
It suggests the production of charge transfer complexes between the substrate and chemisorbed species; thus an enhancement in frequency is observed when the excitation level is in equilibrium with the change of charge transfer with EFs about 10 to 100. TiO2 provides biocompatibility, as well as superior chemical and mechanical resilience against variability in pH or ambient temperature. As shown by Tereschenko et al., these sensors based on SERS can sense lower concentrations but still suffer from inadequate selectivity. So improving selectivity for SERS MO-based biosensors seems to be a current challenge.
9.4
Electrochemical sensing based on metal oxides
The most flexible and exceedingly developed chemical sensors are electrochemical sensors. They are divided into several types: potentiometric, amperometric, and conductometric. Sometimes the distinction between these types can be blurred (Table 9.2). Electrocatalytic oxidation and identification of famotidine in pharmaceutical forms were effectively Table 9.2 Metal oxides-based electrochemical sensors. Sr# Target molecule
Sensor type
Transducer
Sensitivity range
References
1. 2.
Dopamine Bisphenol-A
Voltammetry Voltammetry
0.02800 μM 0.87.20 μM
[75] [28]
3. 4. 5.
Glucose Uric acid MCF-7 & T47D (breast cancer cells) Nucleic acids biosensor Carcino-embryonic antigen (CEA) Glucose H2O2 Acetone
Voltammetry EIS Electrochemical impedance spectroscopy Electrochemical impedance spectroscopy Amperometric
ZnO-polypyrrole Zn-St-Ni multioxide system Au/Cu2O ZnO/TiO2 Titanium oxide/Au
6. 7. 8. 9. 10.
0.052.0 mM [76] 5205 mg dL21 [77] 10106 cells mL21 [40]
Zinc oxide/ 102111026M graphene Mn2O3 Titanium oxide/Mo N/A
Amperometric Fe2O3 Amperometric ZnFe2O4/chitosan Conductometric technique MgNi2O3
0.028 mM 0.01850 μM 0.5 ppm
[78] [25] [79] [80] [81]
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determined by using the electrochemical sensor. CV and steadystate polarization measurements were used to study the electrochemical oxidation process and its kinetics, and the analytical measurements were performed by chronoamperometry for the analysis of famotidine with a 5.91 mol L21 LOD. The developed sensor displayed enhanced sensitivity and selectivity, compared to some other reported methods [74]. Omolola E Fayemi et al. identified the transportation of electrons and catalytic properties of MOs (NiO, ZnO, and Fe3O4) on MWCNTs. A GCE was used to provide electrochemical characterization. GCEMWCNTMO provided better transportation of electrons and enhanced response to DA as compared to all other electrodes studied. The MWCNT-NiO-modified GCE proved as an ideal electrode for DA oxidation with a detection limit in the range of nanomolar. Dopamine and AA signals have been clarified through square wave voltammetry and differential pulse voltammetry (DPV) relative to CV, with DPV offering the highest peak separation of 400, 300, and 600 mV, respectively, for GCEMWCNT-NiO, GCE-MWCNT-ZnO, and GCE-MWCNT-Fe3O4 electrodes. Electrocatalysis of dopamine on the GCE was achieved by diffusion and a sequence of electrode processes. This analysis revealed that the GCE-containing MWCNT/NiO composite can be used effectively for dopamine assay in DA samples [39].
9.5
Colorimetric and fluorometric sensing based on metal oxides
Because of their collective photosensitive and oxidative/ reductive potential, MOs are used as colorimetric displays for the replacement of traditional sensors [82]. Zhen Lin et al. combined the oxidase-mimicking property of the MO NPs and the ACP-catalyzed hydrolysis of AAP to reveal an unpretentious colorimetric method for the detection of ACP [83]. Huiyuan Sun et al. described an IrO2 and GO-based peroxidase-imitating enzyme. The resulting composite showed peroxidase-like activity that was estimated by catalytic oxidation of 3,30 ,5,50 -tetramethyl-benzidine in the presence of H2O2. In view of this study, a colorimetric assay was established to determine amino acids which showed a linear relation between absorbance and the concentration of amino acid with a 324 nM LOD [84]. Colorimetric sensing of glucose based on the redox reaction between MnO2 nano-oxidizers and the glucose was described by J Zhang et al. He argued that in the presence of
Chapter 9 Metal oxide and their sensing applications
169
suitable conditions, glucose could reduce the manganese oxide nano-oxidizers to manganese ions (Mn21), which resulted in decolonization and intense decrease in absorbance of MnO2 solution. This system presented great sensitivity and superior selectivity for glucose [85]. Zhang X. et al. fabricated granular CO2V2O7 particles by using a quick and easy hydrothermal process and examined the triple-enzyme activities and catalytic processes of the prepared particles. Oxidase and peroxidase-like activities of CO2V2O7 particles were used to fabricate a colorimetric biosensor to detect glutathione in health products and a fluorescent sensor to detect glucose in human serum (Fig. 9.5). The fluorescence-revealing system, in particular, showed extremely high sensitivity for H2O2, with an LOD of 0.002 μM, which is far superior to most of the values reported in the literature [86].
9.6
Fluorescent and chemiluminescent sensing based on metal oxides
Interferences in some colorimetric sensors are limited by selectivity problems due to coexisting redox molecules other than the analyte, for example, DA and AA [87]. Fluorescent sensors have been investigated to address those limits. A fluorescent sensor for glucose was reported in which adsorption of
Figure 9.5 Colorimetric responses of CO2V2O7. Copyright r 2020, American Chemical Society [86].
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DNA resulted in a subsequent loss in fluorescence, while contact to H2O2 enhanced fluorescence [88]. Tian X. et al. investigated the imitative action of CeO-NP (nanoceria) via CDP-star as a chemiluminescent substrate. CDP-star is a substrate of alkaline phosphatase (Fig. 9.6). Phosphatase imitative action of nanoceria is remarkably inhibited by the addition of Al31. A highly sensitive and selective Al31 detection CL method has been proposed, which is based on these outcomes. The CL intensity of the nanoceria/CDP-star system decreased with increasing concentrations of Al31 [89].
9.7
Issues and drawbacks
The use of MOs is also associated with certain disadvantages such as poor selectivity, tedious characterization of these electrodes, uncertainty in the electrode process mechanism, stability, toxicity, low sensitivity, and instability; also, sometimes chemicals with communal features may react at altered levels and be sensed, creating wrong alarms, leading to the unnecessary shutdown of apparatus and departure. Sensor performance is also influenced by temperature, O2 concentration, and humidity. Furthermore, some other factors like advancement in
Figure 9.6 Schematic design of nanoceria’s phosphatase imitative action, and its use for Al31 chemiluminescence detection. Copyright r 2020, Elsevier [89].
Chapter 9 Metal oxide and their sensing applications
protein structure, biochemical stabilization, tuning, and reproducibility are also affecting the performance of the sensor, particularly in biological sensors, which is why the nonenzymatic detection of H2O2 is still highly needed. New strategies for sensor growth, including doping of MOs with different groups, have proven more beneficial than conventional sensors. Therefore, each sensor should be monitored consistently over a sufficient period before being launched into the market.
9.8
Conclusion and Future prospective
Addressing the critical challenges in the fabrication of innovative and reliable electrodes is increasing progressively with the advancement in nanotechnology and a wide range of MOs. However, complete integration of MOs in sensors is still questionable owing to maintenance and toxicity of their operation over extended periods. Highlighting human health and clinical use, there is a great need to develop a hybrid biosensor that can detect different biomolecules simultaneously. Furthermore, wearable and implantable biosensors must be built to resolve all the constraints of ambulatory technology. There is a great need to design sensors with particular strategies and a wide range of features to target specific applications and physical properties that will be able to mitigate all the challenges faced by currently available materials. Another hybrid, an integrated theoretical sensor, is based on both biological and chemical sensors having the ability to detect multiple gases at a time. This innovative sensor can be used at different places such as hospitals and in the area of protection or war zones. All these unique strategies need to be highly sensitive, consistent, and intuitive, as well as it should be able to transmit in real or near-real time securely and wirelessly.
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10 RFID sensors based on nanomaterials J. Senthil Kumar1, Rajesh Jesudoss Hynes Navasingh2,3, P. Shenbaga Velu4 and J. Angela Jennifa Sujana5 1
Department of Electronics & Communication Engineering, Mepco Schlenk Engineering College, Sivakasi, Tamil Nadu, India 2Faculty of Mechanical Engineering, Opole University of Technology, Opole, Poland 3Department of Mechanical Engineering, Mepco Schlenk Engineering College, Sivakasi, Tamil Nadu, India 4School of Mechanical Engineering, Vellore Institute of Technology, Chennai, Tamil Nadu, India 5Department of Artificial Intelligence and Data Science, Mepco Schlenk Engineering College, Sivakasi, Tamil Nadu, India
10.1
Introduction
Nanosensors are in the nanoscale size within the range of 10 to 100 nm. They can detect the presence of nanomaterials or molecules in that size range or smaller. The usage of nanomaterials for the fabrication of nanosensors improves the sensitivity and increases the speed of detection, and they are capable of detecting multiple targets due to their unique properties. Their sensitivity can range down to a few molecules of inorganic, organic, or biological materials. There are two types of nanosensors: active and passive. Active nanosensors would have the ability to send a signal that could be received from a remote place. A passive nanosensor, on the other hand, relies on the observation of the environmental parameters. Three types of communication exist between the nanodevices and the physical macroworld, nano to nano communication, nano to macro communication, and macro to nano communication, depending on the application of nanodevices and nanosensors. Certain novel solutions using nanostructured materials are employed for sensor fabrication with improved efficiency and flexibility [1]. RFID is a technology, which works on radio frequency of the radio waves. This technology is primarily used for identifying objects or tracking the objects. The RFID tag is attached to the objects that need to be tracked. The objects could be inventory Nanomaterials-Based Electrochemical Sensors: Properties, Applications, and Recent Advances. DOI: https://doi.org/10.1016/B978-0-12-822512-7.00009-0. © 2024 Elsevier Inc. All rights reserved.
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goods and products in warehouses. An RFID system is composed of an RFID reader and an RFID tag. Also, the tags could be active, passive, or semipassive tags. When the objects are in the range of the reader, then these RFID tags are used to transmit the feedback signal to the reader. Based on the material used and the employed applications, the RFID readers can sense various physical parameters such as gas, temperature, pressure, and many more. Fig. 10.1 shows the RFID sensor antenna coated with a nanosensing film along with a memory chip. Those sensing films fabricated using nanomaterials are capable of measuring various physical parameters. Fig. 10.2 shows the various physical
Figure 10.1 RFID tag sensor antenna coated with the chemically sensitive thin film. Redrawn from (R. A. Potyrailo, C. Surman, A passive radio-frequency identification (RFID) gas sensor with self-correction against fluctuations of ambient temperature. Sens. Actuators. B Chem. 185 2013 587 593 [2].
Figure 10.2 Physical variables that can be sensed with RFID sensors.
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parameters that can be measured using RFID sensors. The RFID reader continuously sends radio waves of a particular frequency, and it induces enough power into the tag as well as acts as a carrier for return data and synchronizes its clock with the tag. RFID tags are operated mainly at three different frequencies such as low (125 or 134 kHz), high (13.56 MHz), and ultrahigh frequencies (860 960 MHz). The low-frequency signals can travel a very short distance, and the RFID tags using this lowfrequency range are up to 10 cm. The high-frequency RFID tags can detect distance up to 1 m, while the ultrahigh frequency RFID tags can detect objects in the range of 10 to 15 m. The RFID tags used for low and high frequency use the principle of inductive or near-field coupling, while the ultrahigh frequency RFID tags operate based on the electromagnetic or far-field coupling. The vast growth of RFID applications is also extended to the nanoscale level across the diversified domain. When the RFID sensors are fabricated in the nanoscale level, their flexibility and reachability across the healthcare sector, environmental applications, food safety, and other domains are huge. Pavaser et al. [3] reviewed different categories of nanocomposite materials used for the fabrication of nanosensors for a large class of applications. Singh et al. [4] reviewed the nanomaterial composites based on graphene, gold, carbon nanotubes, copper, and silver materials used for fabricating RFID tags which can be inkjetprinted on flexible materials. McGee et al. [5] reported the design aspects of chipless RFID sensors, which are used for identifying the tag and determining sensing and impedance characteristics of the nanomaterials when they are stimulated. Fig. 10.3 shows the broad category of domains that utilize nanoscale RFID sensors. The RFID sensors can observe the environmental parameters through the chemical sensors fabricated using nanomaterials. The nanosensors are interfaced with the RFID processors through a proper analog to digital interface. Wireless transmission from the RFID sensors is enabled through an antenna. The transmitted radio signals are read using either an RFID reader or a near-field communication-enabled smartphone. The schematic representation of the RFID sensors with the environment and the reader is shown in Fig. 10.4. The rest of this chapter will discuss the following issues related to nanomaterial-based RFID nanosensors. In Section 10.2, nanomaterials for sensor fabrication are briefly discussed. Section 10.3 elaborates on the inkjet printing methodology for RFID sensor development using nanomaterials.
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Figure 10.3 Functions of RFID sensors for the common category of applications.
Figure 10.4 RFID sensor interfaced with the environment and the reader through a wireless interface.
Chapter 10 RFID sensors based on nanomaterials
Section 10.4 discusses various applications of using RFID nanosensors including energy applications, food industry, biomedical applications, and structural health monitoring applications. Finally, future research scopes are outlined.
10.2
Nanomaterials for RFID sensors
The development of nanotechnology has forced the electronics and computing industries to evolve sensor fabrication techniques. The major category of nanomaterials used for the fabrication of sensors falls under the category of inorganic, organic, and hybrid materials. A more detailed classification of the materials involved under each category is shown in Fig. 10.1. Sensors made of graphene oxide belong to the organic category of nanomaterials, which are highly sensitive to humidity variations, and they can be capable of measuring physical environmental parameters with the change in the resistance of the graphene oxide [6]. These graphene-based circuits are capable of chemical sensing at the nano level, and their characteristics are utilized for realizing a flexible RFID sensor [7]. Also, the graphene nanoflake antenna for RFID is fabricated for achieving better conductivity using screen printing [8]. The category of carbon nanomaterials also possesses electrically insulating properties and widely used as conductive polymers for sensor fabrication [9]. Graphene-based nanomaterials are also used for food packing as an active component [10]. Fig. 10.5 shows the major categories of nanomaterials used for the fabrication of RFID nanosensors. Among the inorganic category, the nanomaterials are categorized under metals, metal oxides, and quantum dots. The semiconductor nanomaterials ranging between the sizes of 1 to 100 nm are known as quantum dots. In the organic category, the nanomaterials are categorized under nanotubes, fullerene, and electrospun nanofibers. The nanomaterials of two dimensions between 1 to 100 nm are known as nanotube or nanowire. Fullerene is the nanomaterials with molecules comprising of carbon atoms with strong covalent bonds. Electrospun nanofibers are highly porous mesh form of nanofibers with excellent nanoscale physical and chemical properties. Aluminum tensile-based nanomaterials possess characteristics of strain measurement and are used for designing RFID sensors for strain measurement applications [11]. For operating at an ultrahigh frequency, the RFID sensor tag coated with functionalized polypyrrole nanoparticles was designed for
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Figure 10.5 Categories of nanomaterials used for fabrication of RFID nanosensors.
Chapter 10 RFID sensors based on nanomaterials
commercial usage [12]. Cellulose nanofibrils are used as responsive materials for displays and flexible electronics, triggered by the magnetic fields [13]. Ammonia gas sensors are made of nanocomposites based on graphene oxide for sensing dimethylamine and ammonia gases [14]. RFID sensors operating between frequency ranges of 2.4 and 2.5 GHz are designed using 3D printing technology [15]. Data from RFID transducers used as chemical nanosensors are analyzed using a machine learning approach to predict their smartness and selectivity characteristics [16]. Humidity sensors are made using Van Atta retrodictive materials in the array form that can be operated for long-range wireless and low-power applications [17]. Such reflect array structures are also used for implementing a chipless RFID sensor, capable of operating in millimeter-wave frequencies with improved performance [18]. Unmanned aerial vehicles (UAVs) deploy a large number of nanosensors for performing routing that supports the mobility and navigation of UAVs [19]. A low-power temperature sensor that changes its impedance based on the environmental conditions operating at ultrahigh frequency is realized [20].
10.3
Inkjet printing of nanomaterial-based RFID sensors
Life science application demands customized flexible sensors for clinical analysis, environmental testing, food control, and many more. Low-cost printed sensors are printed on polished materials with layers of pastes, electrodes, and other subsequent layers that are perfectly aligned using highresolution cameras. RFID tag sensors fabricated using inkjet-printed nanomaterials enable flexible characteristics. They are commonly utilized in the Internet of Things applications and wearable electronics and for distinguishing harmful gases and chemicals in various applications. The commonly used nanomaterials for inkjet-printing are gold, silver, copper, graphene, carbon nanotubes, conductive polymers, and composites based on them. RFID tag sensors based on inkjet-printed nanomaterials can be effectively imprinted on paper, cloths, glasses, plastic, and flexible metallic surfaces [4]. A 3D-printed dual-port slot antenna for RFID sensors operating at 2.4 GHz exhibits satisfactory performance at the nanoscale [15]. A complete inkjet-printed flexible RFID sensor was implemented based on Van Atta reflect array materials for ultrahigh frequency ranges of RFID operation [18]. Also, wearable
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Figure 10.6 Resistivity variation of the drawn Cu line for the RFID sensor concerning various sintering times processed at 160˚C. Redrawn from (W. Li, M. Chen, Synthesis of stable ultra-small Cu nanoparticles for direct writing flexible electronics. Appl. Surf. Sci. 290 2014 240 245 [22].
body area networks use RFID tags for sensing body parameters using flexible devices made using inkjet printing [21]. The electrical conductivity of single-walled carbon nanotube composites is most commonly suitable for fabricating chipless RFIDenabled wireless sensor nodes that are capable of the detection of toxic gases and other gas content estimation. Copper is quite a good material for the distribution of nanoparticles for inkjet printing of sensors. Copper nanoparticle solution is used to draw the lines for the sensors on the printable materials. Rather than bulk copper, the drawn copper shows better resistivity characteristics concerning the sintering time. From Fig. 10.6, it is evident that the resistivity of the drawn copper material decreases gradually with a change in the sintering time [22]. Bulk copper materials maintain constant resistance with variation in sintering time. The conductive patterns of the copper ink after inkjet printing on a photo-paper were determined, and an RFID antenna was prepared using the conductive patterns of copper material. This supports an excellent solution for developing flexible and foldable electronics on a photo-paper from inkjet printing using carbon nano ink. Similar to copper nanomaterials, silver nanomaterials possess excellent characteristics for inkjet printing of RFID sensors. Field emission scanning electron microscopy (FESEM) is commonly used for the magnification of microstructures.
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Figure 10.7 Comparison of silver- and copper-coated RFID antenna tags as a function of the resonant frequency.
Inkjet-printed RFID antennas can be inspected using FESEM. From the characteristics of the nanoparticle-coated RFID antenna, the performances of silver and copper materials are compared [23]. The observations are made with copper-etched materials as reference. Fig. 10.7 shows the comparison of silverand copper-coated RFID antenna tags as a function of the resonant frequency. The copper ink-printed RFID sensor antenna resonates at 14 MHz, and the silver ink-printed RFID sensor antenna resonates at 13.7 MHz.
10.4 10.4.1
Applications of RFID nanosensors Energy
Nanopower applications can best make use of energy harvesting as their power source. Nanodevices can benefit from energy harvesting for environmental awareness, such as when the sensor measures physical parameters such as temperature, pressure, and so forth to make decisions on reliability, process variations, and many more. With the aid of nanomaterials, separator membranes for lithium-ion batteries actuated using magnetic fields are made for flexible electronics [13]. Using electromagnetic and solar energy, an energy harvesting system is designed to operate the RFID tag in the frequency range of 2.4 to 2.5 GHz [15]. Reliable energy characteristics are observed from a chipless version of RFID sensors [24]. Wearable RFID
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tags are used for a body sensing network with the support of DC power through energy harvesting [21].
10.4.2
Food industry
Managing food safety along the entire food chain is achieved using nanosensor-based strategies to ensure vigilance and quality food materials. Specificity and sensitivity characteristics of RFID nanosensors are used to measure food matrices [25]. Nanobiosensors with appropriate electrochemical and optical properties play a major role in maintaining safety in food supply [26]. The movement of agro-food between producers and consumers can be traced using RFID nanosensors to reduce the risk of unhealthy food intake [27]. Nanomaterials are also used for intelligent food packaging for enhancing food safety and quality all along the supply chain [28 30]. Also, more intelligent, smart, and active packaging of food materials was proposed [10] using electrochemical methods and graphene nanomaterials. The detection of food materials’ freshness is gaining importance in food industries for delivering high-quality food materials to consumers. Nanomaterials have started playing a crucial role in maintaining the freshness in the food materials [31]. Particularly, the freshness of various kinds of seafood gets deteriorated quickly, and consumption of such decayed food leads to bad health. Nanomaterials with conjugated polymers used for sensor fabrication act as an active technique for predicting the spoilage of seafood [3].
10.4.3
Biomedical applications
Applications of nanoparticles are growing, and they are having a significant impact, particularly in the healthcare sector, such as in cancer therapy, medical implants, tissue engineering, and many more. Nanotechnology has incredibly improved the exhibition of biosensors by consideration of nanomaterials like nanowires, carbon nanotubes, and other nanoparticles such as graphene, which enhances the adaptability characteristics of sensors for medical applications with reliable and multidimensional qualities. Nanotube-based nanosensors can help prevent progression of cancer by detecting it at an earlier stage. Nanosensors are prominently used for smart drug delivery, implantable devices, body area networks, Internet of Nano Things, and other healthcare applications for the treatment of injuries and other medical complications. Carbon nanotubes
Chapter 10 RFID sensors based on nanomaterials
are a certain category of nanoparticles that possess special luminescent and electrical properties, which enable them to determine certain proteins through emitted light. They can also be used to make implantable devices to monitor proteins in the affected locations whenever required. The developments in this field are expected to flourish and lead to several life-saving medical technologies and treatment methods. Nano-RFID sensors are used in wearable electronics for monitoring body parameters [21] and health aspects of intake food materials [32] and as facemask using graphene oxide [6].
10.4.4
Structural health
With recent advancements in nanomaterials and sensor innovation, structural health observation systems are being used in various civil architectures such as dams, bridges, and buildings. Structural health monitoring is the regular observation of a structure over a period of time to better understand its behavior. Structural monitoring is used to confirm whether a structure or component is safe in its everyday usage. Various categories of sensors, ranging from wired to remote sensors, are being used for continuous real-time health monitoring of structures. They can be used to spot potential problems before they result in damage to a structure, even in out of sight areas. Architects may be interested in monitoring displacement, subsidence, tilt, vibrations, stress, or strain. Apart from RFID sensors, fiber optic sensors, vibrating transducers, load cells, and tiltmeters can also be used for monitoring the health of the buildings and structures. Piezoelectric arrangements in RFID sensors are also playing a major role in monitoring the state of the structures. Nanomaterial-based improved sensors are developed for assisting the structural health for monitoring acceleration, corrosion, and strain [33]. Passive RFID antenna wireless sensor systems are used for structural health inspection [34,35].
10.5
Conclusion
This chapter deals with the usage of nanomaterials as RFID sensors for various applications. First, the unique properties and features of RFID sensors are presented along with the physical parameters sensed by RFID sensors. Then, the functions of RFID nanosensors are introduced. Afterward, the nanomaterials used for the fabrication of RFID sensors are categorized based
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on the materials used for the design. Finally, elaborate discussion on the applications of the RFID nanosensors is summarized with key observations from various research articles. There are issues in the nanoscale level in terms of size and physical, chemical, and thermal properties of materials, particularly in the fabrication of RFIDs, and other nanosensors that are used in mission-critical applications are facing a huge range of challenges, which can be studied in the future researches.
Acknowledgment The authors gratefully acknowledge the Management, the Principal, Dr. S. Arivazhagan; the Head of Mechanical Engineering, Dr. P. Nagaraj; and the Head of Electronics and Communications, Dr. R. Shantha Selvakumari of Mepco Schlenk Engineering College, Sivakasi, Tamil Nadu, India, for extending the necessary support toward this work. Author Rajesh Jesudoss Hynes Navasingh acknowledges the support from Ulam NAWA Postdoctoral Fellowship of Polish National Agency for Academic Exchange programme, Contract Agreement No. BPN/ULM/2022/1/00133/U/00001.
References [1] F. Gaspari, S. Quaranta, Nanostructured materials for RFID sensors, Nanomaterials Design for Sensing Applications, Elsevier, 2019. [2] R.A. Potyrailo, C. Surman, A passive radio-frequency identification (rfid) gas sensor with self-correction against fluctuations of ambient temperature, Sens. Actuators. B, Chem. 185 (2013) 587 593. Available from: https://doi. org/10.1016/j.snb.2013.04.107. [3] T.R. Pavase, H. Lin, S. Hussain, Z. Li, I. Ahmed, L. Lv, et al., Recent advances of conjugated polymer (CP) nanocomposite-based chemical sensors and their applications in food spoilage detection: a comprehensive review [Publisher: Elsevier] Sens. Actuators B: Chem. 273 (2018) 1113 1138. [4] R. Singh, E. Singh, H.S. Nalwa, Inkjet printed nanomaterial based flexible radio frequency identification (RFID) tag sensors for the internet of nano things [Publisher: Royal Society of Chemistry] RSC Adv. 7 (77) (2017) 48597 48630. [5] K. Mc Gee, P. Anandarajah, D. Collins, A review of chipless remote sensing solutions based on RFID technology [Publisher: Multidisciplinary Digital Publishing Institute] Sensors 19 (22) (2019) 4829. [6] M.C. Caccami, M.Y.S. Mulla, C. Di Natale, G. Marrocco, Wireless monitoring of breath by means of a graphene oxide-based radiofrequency identification wearable sensor, in: 2017 11th European Conference on Antennas and Propagation (EUCAP), IEEE, 2017. [7] M. Hajizadegan, M. Sakhdari, L. Zhu, Q. Cui, H. Huang, M.M. Cheng, et al., Graphene sensing modulator: toward low-noise, self-powered wireless microsensors [Publisher: IEEE] IEEE Sens. J. 17 (22) (2017) 7239 7247. [8] T. Leng, X. Huang, K. Chang, J. Chen, M.A. Abdalla, Z. Hu, Graphene nanoflakes printed flexible meandered-line dipole antenna on paper substrate for low-cost RFID and sensing applications [Publisher: IEEE] IEEE Antennas Wirel. Propag. Lett. 15 (2016) 1565 1568.
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[9] N.R. Tanguy, Wireless Sensors Using Radio-Frequency Identification Technology: Developing Carbon Nanocomposites for Improved Sensing and Detection of Ammonia Gas and Volatile Amine Vapors (Doctoral dissertation), 2019. [10] A.K. Sundramoorthy, T.H.V. Kumar, S. Gunasekaran, Graphene-based nanosensors and smart food packaging systems for food safety and quality monitoring, Graphene Bioelectronics, Elsevier, 2018. [11] G. Chakaravarthi, K.P. Logakannan, J. Philip, J. Rengaswamy, V. Ramachandran, K. Arunachalam, Reusable passive wireless RFID sensor for strain measurement on metals [Publisher: IEEE] IEEE Sens. J. 18 (12) (2018) 5143 5150. [12] J. Jun, J. Oh, D.H. Shin, S.G. Kim, J.S. Lee, W. Kim, et al., Wireless, room temperature volatile organic compound sensor based on polypyrrole nanoparticle immobilized ultrahigh frequency radio frequency identification tag [Publisher: ACS Publications] ACS Appl. Mater. Interfaces 8 (48) (2016) 33139 33147. [13] R. Sabo, A. Yermakov, C.T. Law, R. Elhajjar, Nanocellulose-enabled electronics, energy harvesting devices, smart materials and sensors: a review [Publisher: Tech Science Press] J. Renew. Mater. 4 (5) (2016) 297 312. [14] N.R. Tanguy, B. Wiltshire, M. Arjmand, M.H. Zarifi, N. Yan, Highly sensitive and contactless ammonia detection based on nanocomposites of phosphate-functionalized reduced graphene oxide/polyaniline immobilized on microstrip resonators, ACS Appl. Mater. Interfaces 12 (8) (2020) 9746 9754. Available from: https://doi.org/10.1021/acsami.9b21063. [15] J. Bito, R. Bahr, J.G. Hester, S.A. Nauroze, A. Georgiadis, M.M. Tentzeris, A novel solar and electromagnetic energy harvesting system with a 3-d printed package for energy efficient internet-of-things wireless sensors [Publisher: IEEE] IEEE Trans. Microw. Theory Tech. 65 (5) (2017) 1831 1842. [16] H. Hallil, C. Dejous, Microwave chemical sensors, in: H. Hallil, H. Heidari (Eds.), Smart Sensors for Environmental and Medical Applications, 1st ed, Wiley, 2020H. Hallil & H. Heidari (Eds.). Available from: https://doi.org/ 10.1002/9781119587422.ch10. [17] D. Henry, J.G. Hester, H. Aubert, P. Pons, M.M. Tentzeris, Long-range wireless interrogation of passive humidity sensors using van-atta crosspolarization effect and different beam scanning techniques [Publisher: IEEE] IEEE Trans. Microw. Theory Tech. 65 (12) (2017) 5345 5354. [18] J.G. Hester, M.M. Tentzeris, Inkjet-printed flexible mm-wave van-atta reflectarrays: a solution for ultralong-range dense multitag and multisensing chipless RFID implementations for IoT smart skins [Publisher: IEEE] IEEE Trans. Microw. Theory Tech. 64 (12) (2016) 4763 4773. [19] R. Pirmagomedov, R. Kirichek, M. Blinnikov, A. Koucheryavy, UAV-based gateways for wireless nanosensor networks deployed over large areas [Publisher: Elsevier] Comput. Commun. 146 (2019) 55 62. [20] K. Zannas, H. El Matbouly, Y. Duroc, S. Tedjini, Self-tuning RFID tag: a new approach for temperature sensing [Publisher: IEEE] IEEE Trans. Microw. Theory Tech. 66 (12) (2018) 5885 5893. [21] T.-H. Lin, J. Bito, J.G.D. Hester, J. Kimionis, R.A. Bahr, M.M. Tentzeris, On-body long-range wireless backscattering sensing system using inkjet-/3d-printed flexible ambient RF energy harvesters capable of simultaneous DC and harmonics generation, IEEE Trans. Microw. Theory Tech. 65 (12) (2017) 5389 5400. Available from: https://doi.org/10.1109/ TMTT.2017.2768033. [22] W. Li, M. Chen, Synthesis of stable ultra-small cu nanoparticles for direct writing flexible electronics, Appl. Surf. Sci. 290 (2014) 240 245.
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[23] Y. Kim, B. Lee, S. Yang, I. Byun, I. Jeong, S.M. Cho, Use of copper ink for fabricating conductive electrodes and rfid antenna tags by screen printing, Curr. Appl. Phys. 12 (2) (2012) 473 478. [24] F. Costa, E. Perret, S. Genovesi, S. Tedjini, A. Lazaro, D. Girbau, et al., Progress in green chipless RFID sensors, in: 2017 11th European Conference on Antennas and Propagation (EUCAP), IEEE, 2017. [25] T. Caon, S.M. Martelli, F.M. Fakhouri, New trends in the food industry: application of nanosensors in food packaging, Nanobiosensors, Elsevier, 2017. [26] Y. Wang, T.V. Duncan, Nanoscale sensors for assuring the safety of food products [Publisher: Elsevier] Curr. Opin. Biotechnol. 44 (2017) 74 86. [27] P. Di Sia, Agri-food sector, biological systems and nanomaterials, Food Applications of Nanotechnology, CRC Press (Taylor & Francis Group), Boca Raton, 2019. [28] G. Fuertes, I. Soto, R. Carrasco, M. Vargas, J. Sabattin, C. Lagos, Intelligent packaging systems: sensors and nanosensors to monitor food quality and safety [Publisher: Hindawi] J. Sens. (2016) 2016. [29] B. Kuswandi, M. Moradi, Sensor trends in beverages packaging, Trends in Beverage Packaging, Elsevier, 2019. Available from: https://doi.org/10.1016/ B978-0-12 816683-3.00010 4. [30] N. Mlalila, D.M. Kadam, H. Swai, A. Hilonga, Transformation of food packaging from passive to innovative via nanotechnology: concepts and critiques [Publisher: Springer] J. Food Sci. Technol. 53 (9) (2016) 3395 3407. [31] B. Kuswandi, Freshness sensors for food packaging, Ref. Module Food Sci. (2017). [32] A. Grumezescu, Nanobiosensors, Academic Press, 2016. [33] S. Das, P. Saha, A review of some advanced sensors used for health diagnosis of civil engineering structures [Publisher: Elsevier] Measurement 129 (2018) 68 90. [34] R.F. Wright, P. Lu, J. Devkota, F. Lu, M. Ziomek-Moroz, P.R. Ohodnicki, Corrosion sensors for structural health monitoring of oil and natural gas infrastructure: a review [Publisher: Multidisciplinary Digital Publishing Institute] Sensors 19 (18) (2019) 3964. [35] J. Zhang, G.Y. Tian, A.M. Marindra, A.I. Sunny, A.B. Zhao, A review of passive RFID tag antenna-based sensors and systems for structural health monitoring applications [Publisher: Multidisciplinary Digital Publishing Institute] Sensors 17 (2) (2017) 265.
11 Biological and biomedical applications of electrochemical sensors Mushkbar Zahara1, Soumaila Shaheen1, Zohaib Saeed1, Awais Ahmad2, Anish Khan3,4, Muhammad Pervaiz1, Umer Younas2, Syed Majid Bukhari5, Rana Rashad Mahmood Khan1, Ayoub Rashid1, Ahmad Adnan1, Abdur Rahim6 and Shamim Ramzan7 1
Department of Chemistry, Government College University Lahore, Lahore, Pakistan 2Department of Chemistry, The University of Lahore, Lahore, Pakistan 3Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia 4Chemistry Department, Center of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah, Saudi Arabia 5Department of Chemistry, COMSATS University Islamabad Abbottabad Campus, Abbottabad, Pakistan 6Interdisciplinary Research Centre in Biomedical Materials (IRCBM), COMSATS University Islamabad, Lahore Campus, Lahore, Pakistan 7Department of Chemistry, COMSATS University Islamabad, Lahore Campus, Lahore, Pakistan
11.1
Introduction
There is a high demand for rapid diagnostic approaches and clinical monitoring that couple selectivity, quick performance, and high sensitivity with sample resolution. Current progress in bioanalytical methods has assisted in consolidating ordinary biological conceptions with electronic instrumentation to organize an easy-to-handle system. Biosensors are a notable development in scientific analysis, which could be elucidated as the instrument that depends on particular biology reactions involving immune systems, isolated enzymes, organelles, or tissues during the thermal, optical, and electrical signal observation of chemical compounds. They allow for the observation of biologically linked substances through signal transduction and biorecognition. Several researchers have taken efforts to establishing a sensor device that can root out
Nanomaterials-Based Electrochemical Sensors: Properties, Applications, and Recent Advances. DOI: https://doi.org/10.1016/B978-0-12-822512-7.00005-3. © 2024 Elsevier Inc. All rights reserved.
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antigens, proteins, DNA, and enzymes in complex samples. Following those revolutions, biosensors have gained significant attention for converting the medical standard from treatment to precaution and diagnosis because of potential biological molecules as biomarkers [1]. Electrochemical sensors are powerful analytical tools because of their captivating properties such as being self-contained, low cost, and portability. Therefore, a zillion electrochemical sensors with a range of sensing methods, such as potentiometric, electrochemical impedance, and amperometric, have been fabricated for practical applications. By the integration of electrochemical approaches, advanced nanomaterials have opened a gateway for researchers to fabricate very sensitive tools, which are selected in pharmaceutical and biomedical applications [2]. Electrochemical sensors speedily modify the chemical signal into the electrical signal [3]. Electrochemical sensors constitute the emerging class of chemical sensors. An applicable definition for the electrochemical sensor is “a small tool that, as a consequence of a chemical process or interaction between the sensor device and the analyte, transforms biochemical information of a qualitative type into an analytical signal.” Chemical sensors consist of a chemically sensitive layer and physical transducer, which directs out an optical, thermal, or electrical signal and interprets the change in the property, helped by the interfering chemical. In contrast to the other known sensors, electrochemical sensors are captivating due to their exceptional experimental simplicity, low cost, and detection capacity. They have a guiding position among the currently accessible sensors that have extended the commercial level and which have initiated a wide range of versatile applications in the fields of industrial, biomedical, and clinical analyses. Advanced developments in microelectrodes, chemically modified electrodes, and electrochemical methods (such as potentiometric and adsorptive voltammetry) have cleared the way for electrochemical applications for the survey of many chemical species. Electrochemical sensors countered the trend in the current research work, which is to promote device dimensions; microtechnological and nanoelectrode approaches to constructing sensors exhibit the link between engineering, physics, and chemistry in this field. Finally, integration into microfluidic platforms is the logical step in clinical applications [4]. The fabrication of nanomaterials has had an extensive impact on biosensors, catalysis energy storage, and energy conversion devices in the past decade. A range of nanoparticles with well-regulated physiochemical characteristics, shape, dimension, and surface charge are produced by remarkable
Chapter 11 Biological and biomedical applications of electrochemical sensors
development in synthetic approaches. Owing to the small particle size and high surface area, nanoparticle-based sensors provide noteworthy advantages and upgraded chemical, biological, and physical properties. A higher surface area to volume proportion permits higher sensing response, in addition to superior magnetic, electrical, and optical properties, showing important interest over macroscale resources for biomedical and biological applications. The fabrication of nanomaterials that are capable of interconnecting with discrete polymers and biological compounds has been challenging recently [5]. Carbon nanoparticles (e.g., graphene, fullerenes, and carbon nanotubes [CNTs]) are extensively used in electrolytic and electroanalytical sensing applications. A crucial aspect that has led to the splendid success of the usage of carbon nanomaterials for electrolytic applications indubitably correlates to their potential to excite electron transfer in redox reactions. Noble metals have previously been demonstrated to be among the most vital classes of nanoparticles for biosensing applications. The physical aspects of noble nanoparticles play an essential role in nanotechnology [6]. This chapter principally focuses on the recent advances in the progress of electrochemical sensors and their potential in biomedical and biological applications. In addition, it aims to elucidate how advanced nanoparticles could be engaged in the development of a high-ordered electrochemical sensor for the observation of innumerable diseases and promotion of suitable medical therapies. We expect that the observations outlined in this chapter will drive the modern nanoparticles and help in the integration and construction of the electrochemical sensor for sustaining human life. We will also highlight the advanced developments with regard to electrochemical sensors and the viewpoint related to biomedical and biological applications.
11.2
Components of electrochemical sensors
Like the human body, chemistry also contains sensors that transform the reactions into expedient data for further examination. To understand electrochemical sensors, the word “sensor” should be defined first: it is a tool that senses a signal from the surrounding environment and changes it into useful information [7]. The electrochemical sensors are the main type of chemical sensors used for identifying the composition of the system in real time, and they consist of three major components, that is, receptor, analyte, and transducer, as shown in Fig. 11.1. The function of the receptor is to bind the sample or
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Figure 11.1 Conventional setup of an electrochemical sensor [8].
analyte, whereas the analyte is an object, which is quantified and analyzed by the electrochemical sensor and the transducer is used to convert chemical reactions into quantifiable electrical signals. Other major components of electrochemical sensors are as follows:
11.2.1
Hydrophobic membrane
The gas-permeable membrane is also known as a hydrophobic membrane and is used to cover the electrode in the sensor. It also monitors the gas concentration of the electrode surface. In electrochemical sensors, some barriers are called membranecovered sensors, as they are made up of thin, low-sponginess Teflon membranes. On the other hand, the sensing electrodes are enclosed with highly permeable Teflon membranes, and the concentration of gas molecules coming toward the electrode is monitored by the capillary; hence, such sensors are called capillary sensors [9].
Chapter 11 Biological and biomedical applications of electrochemical sensors
11.2.2
Electrodes
The choice of the electrode is extremely important. It is a catalyzed object, which accomplishes the half-cell reaction over a stretched period. Usually, noble metals such as platinum and gold are used to make the electrodes, which are later catalyzed by gas molecules to show high efficiency. The composition of electrodes varies with the design of the sensors to complete the cell reaction [10,11].
11.2.3
Electrolyte
The electrolyte has an important role to play in electrochemical sensors. It is used to carry the ionic charge across the electrodes proficiently. It essentially also creates the stable reference potential with a standard electrode and is attuned with things present in the sensor. If the electrolytes are highly volatile, the signals will fade [12].
11.2.4
Filters
The filter is the most significant part of the sensor, which filters out the gases that are not required from the sensor. There is a restricted selection of strainers having different degrees of efficiency. Activated charcoal is the most famous and wanted filter medium (as shown in Fig. 11.2) used in sensors for filtering the nondesired gases. The activated carbon/charcoal filters out various gases with the exemption of carbon monooxide and hydrogen gas [13].
11.3
Working principle of electrochemical sensors
The electrochemical sensors activate by reacting with the required gas and creating an electrical signal, which directly depends upon the amount of the gas used in the cell reaction. A conventional electrochemical sensor has a working electrode and counter electrode, which is separated by sharp layers of electrolytes, as shown in Fig. 11.3. Gas before approaching the electrochemical sensor first goes through a small membranetype opening and then disperses through a permeable membrane and then approaches the electrode. This strategy is followed to permit a sufficient amount of gas to chemically react at the surface of the working electrode and create
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Figure 11.2 Number of publications of magnetic nanoparticles for biosensors from 2001 to 2020, with expected publications in the form of dotted lines [2].
Figure 11.3 Number of publication on graphene oxide per year [16].
sufficient electrical signals and stop the electrolytes from dripping out of the sensor. The gas which chemically reacts at the electrode surface goes through either a reduction or oxidation reaction mechanism. There are catalysts present to catalyze the gas reaction in the electrode. After the gas reaction, the
Chapter 11 Biological and biomedical applications of electrochemical sensors
electrical current is directly proportional to the number of gas streams between the anode and cathode. The gas concentration can be determined by measuring the current and vice versa. Because current is produced in the procedure, the electrochemical sensor is also known as a micro fuel cell or amperometric gas sensor [14]. To improve the efficiency of the sensor, the reference electrode is also introduced in electrolyte near the sensing electrode. Current does not flow through the reference electrode, but it maintains the fixed voltage of the sensing electrode. The gas molecules react at the sensing electrode, and the current drifts between the sensing and counter electrodes and is quantified and directly related to the gas concentration. The sensing electrode remains specific to the target gas when fixed voltage is applied on it [15].
11.4 11.4.1
Fabrication of nanomaterial-based electrochemical sensor Magnetic nanomaterials
The progress made in magnetic nanoparticles (MNPs) has had a huge impact on the biomedical and pharmaceutical applications. MNPs show unique electromagnetic performance such as quantum effects because of their large surface area, exhibiting superparamagnetic properties. They also exhibit evident magnetism, such as ferromagnetism, paramagnetism, ferrimagnetism, and diamagnetism. Typically in a sensor, analytes in the test disperse to the sensing surface to generate a response by a transducer. It applies to the extent of interaction between the surface and the analytes. MNPs have been used to accelerate mass transport to the surface of the sensor under magnetic power. Taking this into consideration, it should be mentioned that there are two benefits in using the MNPs: (1) the sample preconcentration allowing for the increase of reactivity and decrease of response time and (2) the temporal and special dissociation of the sample assortment from the cell signaling of the collected sample. Recent advances using MNPs for electrochemical sensors have been examined in 2001 and 2020 [2]. Kharat et al. explained biomedical applications of multifunctional MNPs. The working principle of this kind of sensor is that the magnetic inductions fabricated by the MNPs which modify the magnetizing field of the sensor give rise to an electric field inside the sensor. Compared with radioactive, colorimetric, or
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electrochemical properties, the magnetic sensors have indicated frequent focal points for biological marker capabilities, allowing for a high possibility of appliance miniaturization [9].
11.4.2
Polymer
Conducting polymers (CPs) have been extensively used in broad-spectrum applications such as biosensing, chemical sensing, supercapacitors, and gas sensing because of their distinctive electronic applications. The nanostructured polyaniline, polyethylene, polypropylene, and their derivatives have been employed for biosensing applications due to their natural conductivity. The recent progress of biochemical sensors has also prompted us to explore the linkage of these CPs with living tissues through in vitro methods to boost biocompatibility [17]. Runsewe et al. found considerable applications of CPs in the biomedical industry. This is because of alteration in their electrical effects when an electric impetus is applied, which makes them be used in diverse applications such as tissue engineering frames, drug delivery, energy storage, and electrochemical sensors. CPs show superiority, such as the prospect of pliable medical apparatus, this can be operated in living things [17].
11.4.3
Metal oxide
Shetti et al. fabricated zinc oxide (ZnO)-based nanoparticles for electrochemical sensors and biological applications. ZnO has many admirable properties such as wide bandgap, high abundance, and low cost. ZnO relates to wide and direct bandgap metal oxide. The compatibility and toxicity of ZnO with individual skin have exhibited the usage of ZnO as a supplement in textile industries [10]. Copper oxide (CuO) nanoparticles provide multipurpose properties such as high surface area, hierarchical nanostructure, electron transport interpretation, and versatile valence states. The survey of CuO nanoparticles has been successfully used in many biosensing applications. Yang et al. showed nonenzymatic glucose biosensing utilizing nana-needle-type CuO on a nitrogen-coupled (CuO/N-rGO) composite in 0.2M solution of NaOH. This composite showed a quick response to Aldo sugar with a broad linear range from 0.5 to 639 µM. This nanohybrid structure extends the interfacial interconnecting area by providing more reactive sites for glucose, which improved and fused the connectivity and diffusion length. Additionally, this sensor was successfully used for the observation of glucose in human serum fluid [18].
Chapter 11 Biological and biomedical applications of electrochemical sensors
11.4.4
Noble metals
11.4.4.1
Gold nanoparticles
Gold nanoparticles (AuNPs) have been realized as a prospective applicant in the region of biological research due to the following properties: (1) high chemical solidity; (2) facile integration process; (3) versatile solderability; and (4) great synergistic properties. Gold nanomaterials have been extensively utilized in the area of nanomedicines due to their excessive biocompatibility with the vast scope of biomarkers. It has been demonstrated that the relative mass of plasma S-nitrosothiol might be linked with several diseases. The precise sensing of S-nitrosothiol in an abiotic medium utilizing gold nanomaterial-based sensors has been carried out with an observation limit of B100 nM. The goldbased nanomaterials for the observation of RNPs were developed in the presence of free thiols by S-nitrosothiol degradation by gold nanomaterials with a microelectrode [5]. Yola et al. fabricated graphene oxide (GO)-based AuNPs for the determination of tyrosine in milk. Nanosized AuNPs can increase the electron transfer and electric conductivity of the invention of sensors [19].
11.4.4.2
Silver nanoparticles
Silver nanoparticles (Ag NPs)-based electrochemical sensors have had remarkable effects on biological applications as a consequence of their considerable biocompatibility, high conductivity, and improved electrochemical signals. Over the previous decades, extensive efforts have been taken to design novel methods for many samples such as infectious and biological agents in the advanced stage observations of disease. The fabrication of silver-based nanocomposites with substances such as polymer, fibers, graphene, and dendrimers enhanced biomedical sensing performance due to the multiskilled nature of the substances. The stability and sensitivity of the biomedical sensor are based on the prevention and dispersion of the accumulation of Ag NPs [18]. Xiao et al. categorized the synthetic path and properties of silver and silver-based nanoparticles that endowed them with great electrochemical properties [20].
11.4.5
Carbon nanotubes
Carbon nanomaterials provide distinctive benefits such as high electrical conductivity, high surface-to-volume ratio, mechanical strength, and biocompatibility. Carbon nanoparticlebased sensors commonly have a lower detection range and higher sensitivities than ordinary counterparts. The structures of carbon
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nanomaterials are a critical factor that allows for their stable and functional operation in the fabrication of operative electrochemical sensors; all of these affect their electron radiation kinetics. Carbon-based nanotubes are important for the determination of biological molecules for in vitro and in vivo applications. CNTs are newly investigated nanoparticles that have been examined as a biocompatible and novel matrix for the design of biomedical sensors [6]. CNTs have unique biomedical and pharmaceutical applications. The transfer of diverse pharmacological agents such as protein, drugs, peptides, immune modulators, and genes through the biomembrane has been obtained using the CNTs [5]. The electrochemical applications of CNT nanocomposites also include determination of methyl parathion [21].
11.4.5.1
Graphene
Extensive research works have been done using graphenebased composite materials for versatile applications. Graphene is an undefined expanded 2D dimensional carbon structure, which looks like a honeycomb lattice and shows great selectivity, high sensitivity, excellent stability, and superb catalytic activity [22 24]. It has many appealing properties such as high electrical conductivity, excellent transparency, great stability, good electrical and thermal conductivity, high specific area, and versatile electronic properties [25]. Different configurations of graphene such as rGO and GO are possible after liberating the CNTs. The operationalized graphene utilizing materials, counting enzymes, organic and biomedical molecules, metal oxide NPs, and polymers are operated for obtaining better sensing performance to biomedical applications. Recently, many workers have reviewed the electroanalytical properties of the GO-based composite with versatile biomedical, biological, environmental, and food safety applications [18]. The progress in graphene-based materials is depicted in Fig. 11.4. Detection of high absorption of alpha-fetoprotein (AFP) in serum of humans is favorable in the primeval investigation of testicular cancer, nasopharyngeal cancer, and hepatocellular carcinoma. Anti-AFP transfixed on the hybrid of AuNPs on porous graphene nanoribbon (PGNR), which can help us notice the concentration of AFP at a limit order of 1 ng mL21 anti-AFP inactivated on AuNPs/PGNR of the CNT electrode for the examination of AFP antigen. AuNPs improve the incorporation of electron transfer and anti-AFP, and PGNR enhances the electroactive surface area. Voltammetric and differential examination of this freelabel electrochemical sensor exhibited a broad physiological range of pH. High stability, repeatability, and high sensitivity are
Chapter 11 Biological and biomedical applications of electrochemical sensors
Figure 11.4 Fabrication of a nanomaterial-based electrochemical sensor.
properties of this electrochemical sensor. A very sensitive and rapid sensor was fabricated for the chemical testing of histamine. The sensor is designed from the Ag NPs organized on graphene nanoribbons adapted with pyrolytic graphite. This composite exhibited extraordinary catalysis on the oxidized histamine. Oxidation of this histamine on an electrochemical sensor involves a uniform number of protons and electrons. The reactivity of this composite is due to its large catalytic activity and surface area. The examination of histamine exhibits noble extract from the blood serum, which can be used for the detection of histamine from the blood sample [26]. Fig. 11.5 shows different materials for the synthesis of an electrochemical sensor.
11.5
Biological and biomedical applications of electrochemical sensors
The electrochemical sensors are modified with different materials, that is, nanocomposites, CNTs, platinum black, carbon paste [29], and so forth, and they have been used in multiple dimensions. Their biological and biomedical applications are shown in Fig. 11.6. The details of these applications has been given below.
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Noble metals
Magnec nano-
•
materials
Gold nanopart
Electrochemical sensors can be d
d
Polymers i.e.
Metal oxides
conducng ZnO: Zinc oxide Carbon nanotubes:
Figure 11.5 The concentration of an electrochemical sensor [27,28].
Figure 11.6 Image illustrating the biological and biomedical applications of electrochemical sensors.
11.5.1
In Metabolite
11.5.1.1
Glucose
In the human body, glucose maintenance is very important. The improper absorption of glucose results in diabetes, which may lead to renal and neural problems. Hence, recognition of glucose is medically significant for the detection of diabetes in
Chapter 11 Biological and biomedical applications of electrochemical sensors
the human body. For the analysis of glucose, the GO-based glucose sensors have been dynamically used as potential successors of analytical techniques.
11.5.2
Body fluid ketones
The incomplete metabolism of fatty acid in mitochondria of liver cells resulted in ketenes bodies, that is, betahydroxybutyrate, acetoacetic acid, and acetone. It has been indicated by recent research that before the amount of blood sugar increases, the ketone body’s amount deceptively increases. Hence, it helps in controlling the concentration of blood-ketone bodies for early diabetes diagnosis as well as for ketonemia identification. For investigating the blood-ketones, a disposable amperometric sensor was designed on the screenprinted electrodes. The ketone electrode has also been developed for the determination of the 3-D-hydroxybutyrate limit in the blood, which has good precision and accuracy [30].
11.5.3
Recognition of H2O2 from breast cancer cells
Hydrogen peroxide has a significant role in cancer. A low amount of it has a major role in signaling, whereas a higher amount can cause cell death. Modern H2O2 monitoring sensors are delicate and extensively used for footage within a few minutes. Composite electrodes of different compositions of multiwalled CNTs and platinum black have been prepared and studied through different analytical methods, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. In the electrochemical sensors, the composition of multiwalled CNTs is 15%, while that of platinum black is 20%, which is found to be most effective for the detection of hydrogen peroxide. The electrochemical sensors have a detection limit of 17 nM for chemicals. For the assessment of the sensors, different measurements in breast cancer cells were taken. It was found that the electrochemical sensor can stabilize where the pro-oxidant tertiary butyl-hydro peroxide increased the H2O2 limit. Researchers have found that multiwalled CNTs and platinum black composites have high sensitivity for hydrogen peroxide, hence giving excellent and accurate measurement. Hence, these sensitive sensors are highly significant in the biological environment to detect the different reactive species that can be harmful to living organisms [31].
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11.5.4
Quantitation of neurochemicals
For the treatment of various diseases, indicators for quantifying the disorders are of great importance. Dopamine, adenosine, glutamate, and serotonin are neurochemicals and are also known as competent indicators for brain disorders. Along with conventional tools, that is, biosensors, and capillary electrophoresis, nanocomposite-based electrochemical sensors have also been found to be powerful objects due to being sensitive, selective, and accurate for the quantitation of neurochemicals. The performance of electrochemical sensors varies with the variation of detecting competencies. Nanomaterial-based electrochemical sensors are known to have exciting areas for the detection of neurochemicals in different biotic samples such as urine, serum, and tissues. Nanomaterial-based electrodes such as CNTs can detect the neurochemicals in living body fluid, which are the indicators of various diseases. Hence, the detection of disease through different indicators leads toward the treatment [32].
11.5.5
Electrochemical detection of antibiotics in biological samples
Amoxicillin is considered one of the most popular antibiotics used for human medication. It is widely used against bacterial infection in humans and animals. However, spare use of it can be fatal for the health and environment due to perilous potential related to its pharmacological industry discharges. Moreover, its wide use in food animal production may lead to some non-required scum in food, for example, meat, eggs, and milk, and can be responsible for various diseases such as queasiness, vomiting, outbreaks, and antibiotic-related colitis. Hence, there is a dire need for recognition and quantization of amoxicillin in biotic fluids and environmental samples, which requires modern electroanalytical approaches with sensitive and rapid measurement capabilities. Electrochemical sensors used for this purpose are mostly chemically modified, that is, carbon material electrochemical sensors, nanoparticle electrochemical sensors, glassy carbon, and polymer-based electrochemicals are used for the determination of amoxicillin in the human body. The voltammetry behavior of amoxicillin shows its electrooxidation without modified electrodes. Another way to make amoxicillin less harmful is its electrochemical oxidation, which shows a signal that indicates the oxidation reaction of a phenolic substituent to the respective carbonyl group on the side chain [33] (Fig. 11.7).
Chapter 11 Biological and biomedical applications of electrochemical sensors
Figure 11.7 Mechanism for the electrochemical oxidation of amoxicillin.
11.5.6
Measurement of biomolecules
Electrochemical sensors have been found to monitor biotic molecules. Three-dimensional lithography has appeared to be an encouraging approach to design electrochemical sensors that can firmly measure in an abiotic environment. Threedimensional imaging has the ability to design such electrochemical sensors, which can detect different biomolecules in various areas of the body [34].
11.5.7
Electrochemical detection of nitrogen oxide in human beings
Nitrogen oxide has a significant role in the biological processes, and it has been found that some humanoid diseases are linked to its physiological functions. The electrochemical sensors can show the nitrogen oxide function in the human body. The electrochemical sensor consisted of polymeric porphyrin and Nafion film, was disinfected with ethylene oxide, for checking NO concentration, and injected in the shallow veins of healthy volunteers. The results showed that the higher pressure of nitrogen oxide was in acupuncture points as compared to the non-acupuncture points, which show the firm relationship between nitrogen oxide release and skin acupuncture points.
11.5.8
Electrochemical detection of nitrogen oxide in plants
Nitrogen oxide not only is present in the human body but also has a significant role in plants. Borisjuk et al. proposed that from nitrite, nitrogen oxide is produced in mitochondria in retort to hypoxia. Nitrogen oxide can modify the respiratory oxygen uptake as well as oxygen presence in the seed [35].
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11.5.9
Electrochemical sensors for detecting pathogens
The bacterial infection causes trillions of illnesses each year and excessively influences people in developing countries like Pakistan. There is an extreme need to monitor the pathogens to combat their infections and spread. Different technologies must be applied to detect the microorganisms at the point of contagion. Advanced technology introduced electrochemical sensors, as they are accurate, rapid, quantitative, and sensitive and do not require expensive equipment. The electrochemical sensor senses the analyte in samples and changes it into electrical peaks at an electrode. From the signal, the concentration of analyte can be measured from which the number of pathogens can also be inferred [36].
11.5.10
Analysis of antineoplastic drugs
Antineoplastic drugs have a high capability of poisoning human beings and the environment and can be used to cure cancer (to some extent), which is the foremost cause of death all over the world. Hence, investigation of antineoplastic drugs is extremely important. Among the other techniques, the electrochemical sensors are most useful, sensitive, and rapid for the analysis of antineoplastic drugs. The electrochemical sensor is linked to the transducer, which changes the analyte sensor attraction into a peak that carries the information about the analyte. Hence, this is the way the analyte (drug in this case) can be monitored and investigated for further details [37].
11.5.11
Detection of antiinflammatory drugs
Antiseditious drugs are the most used over-the-counter medicines to treat temperature, pain, and control swelling. However, their extra dose can also cause harmful effects on the human body. Electrochemistry presents the best devices such as electrochemical sensors which facilitate sensitive, rapid, and costeffective recognition of drugs in complicated media. Different electrochemical sensors, that is, nanocomposite, nanotubes, polymer, and electrode-modified sensors are used for the investigation of nonsteroidal and antiinflammatory drugs. These sensors were used to investigate and quantify the drugs, hence they can be controlled [38].
Chapter 11 Biological and biomedical applications of electrochemical sensors
11.5.12
Analysis of forensic drugs
The electrochemical sensors are potent analytical devices that can be used by the forensic sector specifically for the investigation of illegal substances from streets and biotic samples. These electrodes have been extensively used for the detection and investigation of drugs [39].
11.5.13
Pharmaceutical applications
With the rapid increase in the human population, the pharmaceutical industry has also been growing, which leads to new environmental and biomedical problems. Along with the quality control of pharmaceutical products and drugs, there is a dire need to develop accurate, rapid, sensitive, and less costly technology to control patients extra-dosing and to check the wastewater for pharmaceutical contaminants. The nanocomposite-based electrochemical sensors have attracted attention due to their high efficiency and accuracy. These sensors are known to have attributes of detection and quantification of different drugs, that is, antiinflammatory, antimicrobial, antifungal, and so forth [40].
11.5.14
For healthcare
The electrochemical and biosensors have been found to have different applications in the human body, plants, bacteria, pharmaceutical industries, drugs, and so forth; they are also used in healthcare applications. The drug’s effect is controlled by the electrochemical sensors, indicating the integration of the sensor in the central nervous system. The aspirin used as the antiinflammatory and antifever drug can also be detected in tablets and human fluids by chitosan-capped gold-modified electrochemical sensors. Hence, these new sensors can be used for the sensitive investigation of drugs [41].
11.6
Conclusion
The electrochemical method is a nondestructive, precise, and rapid tool to examine a wide range of target materials. Outmoded detection methods are time-consuming and demand intricate working conditions and exclusive instrumentation. Hence, electrochemical sensors, being highly sensitive, accurate, and having fast detection speed, have provoked extensive research interest. Each component of the electrochemical sensor plays an important role in enhancing its overall efficiency.
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In this chapter, we review the progress of electrochemical sensors based on nanomaterials, CNTs, graphene, polymers, noble metals, and metal oxides and their biological and biomedical applications.
References [1] I.R. Suhito, K.-M. Koo, T.-H. Kim, Recent advances in electrochemical sensors for the detection of biomolecules and whole cells, Biomedicines 9 (1) (2021) 15. [2] F. Mollarasouli, et al., Magnetic nanoparticles in developing electrochemical sensors for pharmaceutical and biomedical applications, Talanta 226 (2021) 122108. [3] S. Gu, et al., A droplet-based microfluidic electrochemical sensor using platinum-black microelectrode and its application in high sensitive glucose sensing, Biosens. Bioelectron. 55 (2014) 106 112. [4] S. Laschi, M. Mascini, Planar electrochemical sensors for biomedical applications, Med. Eng. Phys. 28 (10) (2006) 934 943. [5] G. Maduraiveeran, M. Sasidharan, V. Ganesan, Electrochemical sensor and biosensor platforms based on advanced nanomaterials for biological and biomedical applications, Biosens. Bioelectron. 103 (2018) 113 129. [6] A. Chen, S. Chatterjee, Nanomaterials based electrochemical sensors for biomedical applications, Chem. Soc. Rev. 42 (12) (2013) 5425 5438. [7] J.R. Stetter, W.R. Penrose, S. Yao, Sensors, chemical sensors, electrochemical sensors, and ECS, J. Electrochem. Soc. 150 (2) (2003) S11. [8] Z. Awang, Gas sensors: a review, Sens. Transducers 168 (4) (2014) 61 75. [9] P.B. Kharat, S.B. Somvanshi, K. Jadhav, Multifunctional magnetic nanoplatforms for advanced biomedical applications: a brief review, Journal of Physics: Conference Series, IOP Publishing, 2020. [10] N.P. Shetti, et al., ZnO-based nanostructured electrodes for electrochemical sensors and biosensors in biomedical applications, Biosens. Bioelectron. 141 (2019) 111417. [11] J. Hu, Z. Zhang, Application of electrochemical sensors based on carbon nanomaterials for detection of flavonoids, Nanomaterials 10 (10) (2020). [12] D. Wei, A. Ivaska, Applications of ionic liquids in electrochemical sensors, Anal. Chim. Acta 607 (2) (2008) 126 135. [13] R. Hanafi, et al., Electrochemical sensor for environmental monitoring system: a review, AIP Conference Proceedings, AIP Publishing LLC, 2019. [14] M. Pohanka, P. Skla´dal, Electrochemical biosensors principles and applications, J. Appl. Biomed. 6 (2) (2008). [15] W. Gao, et al., A Solid-State Reference Electrode Based on a SelfReferencing Pulstrode, Angew. Chem. Int. Ed. 59 (6) (2020) 2294 2298. [16] P.V. Nidheesh, Graphene-based materials supported advanced oxidation processes for water and wastewater treatment: a review, Environ. Sci. Pollut. Res. 24 (35) (2017) 27047 27069. [17] D. Runsewe, T. Betancourt, J.A. Irvin, Biomedical application of electroactive polymers in electrochemical sensors: a review, Materials 12 (16) (2019) 2629. [18] G. Maduraiveeran, W. Jin, Functional nanomaterial-derived electrochemical sensor and biosensor platforms for biomedical applications, Handbook of Nanomaterials in Analytical Chemistry, Elsevier, 2020, pp. 297 327.
Chapter 11 Biological and biomedical applications of electrochemical sensors
[19] M.L. Yola, T. Eren, N. Atar, A sensitive molecular imprinted electrochemical sensor based on gold nanoparticles decorated graphene oxide: application to selective determination of tyrosine in milk, Sens. Actuators B: Chem. 210 (2015) 149 157. [20] T. Xiao, et al., Au and Au-Based nanomaterials: synthesis and recent progress in electrochemical sensor applications, Talanta 206 (2020) 120210. [21] H. Zhao, et al., Nanocomposite of halloysite nanotubes/multi-walled carbon nanotubes for methyl parathion electrochemical sensor application, Appl. Clay Sci. 200 (2021) 105907. [22] M.E. Khan, M.M. Khan, M.H. Cho, CdS-graphene nanocomposite for efficient visible-light-driven photocatalytic and photoelectrochemical applications, J. Colloid Interface Sci. 482 (2016) 221 232. [23] D.T.T. Trinh, et al., New insight into the photocatalytic degradation of organic pollutant over BiVO4/SiO2/GO nanocomposite, Sci. Rep. 11 (1) (2021) 1 11. [24] W. Choi, et al., Synthesis of graphene and its applications: a review, Crit. Rev. Solid. State Mater. Sci. 35 (1) (2010) 52 71. ¨ , G. Zhao, X. Wang, A brief review of graphene-based material [25] K. Lu synthesis and its application in environmental pollution management, Chin. Sci. Bull. 57 (11) (2012) 1223 1234. [26] A.P. Johnson, H. Gangadharappa, K. Pramod, Graphene nanoribbons: a promising nanomaterial for biomedical applications, J. Contr. Rel. (2020). [27] N. Sharma, V. Mutreja, H. Kaur, Electrochemical sensors, Eur. J. Mol. Clin. Med. 7 (07) (2020) 2020. [28] C.-O. Park, S. Akbar, W. Weppner, Ceramic electrolytes and electrochemical sensors, J. Mater. Sci. 38 (23) (2003) 4639 4660. [29] B.J. Privett, J.H. Shin, M.H. Schoenfisch, Electrochemical sensors, Anal. Chem. 82 (12) (2010) 4723 4741. [30] Y. Wang, et al., Electrochemical sensors for clinic analysis, Sensors 8 (4) (2008) 2043 2081. [31] A. Abdalla, et al., Bicomponent composite electrochemical sensors for sustained monitoring of hydrogen peroxide in breast cancer cells, Electrochim. Acta 398 (2021) 139314. [32] A. Azzouz, et al., Nanomaterial-based electrochemical sensors for the detection of neurochemicals in biological matrices, TrAC. Trends Anal. Chem. 110 (2019) 15 34. [33] A. Hrioua, et al., Recent advances in electrochemical sensors for amoxicillin detection in biological and environmental samples, Bioelectrochemistry 137 (2021) 107687. [34] A. Abdalla, B.A. Patel, 3D-printed electrochemical sensors: a new horizon for measurement of biomolecules, Curr. Opin. Electrochem. 20 (2020) 78 81. [35] T. Xu, et al., Electrochemical sensors for nitric oxide detection in biological applications, Electroanalysis 26 (3) (2014) 449 468. [36] L.M. Castle, et al., Electrochemical sensors to detect bacterial foodborne pathogens, ACS Sens. 6 (5) (2021) 1717 1730. [37] H.R.S. Lima, et al., Electrochemical sensors and biosensors for the analysis of antineoplastic drugs, Biosens. Bioelectron. 108 (2018) 27 37. [38] P.K. Kalambate, et al., Nanomaterials-based electrochemical sensors and biosensors for the detection of non-steroidal anti-inflammatory drugs, TrAC. Trends Anal. Chem. 143 (2021) 116403. [39] L. Shaw, L. Dennany, Applications of electrochemical sensors: forensic drug analysis, Curr. Opin. Electrochem. 3 (1) (2017) 23 28.
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[40] L. Qian, et al., Nanomaterial-based electrochemical sensors and biosensors for the detection of pharmaceutical compounds, Biosens. Bioelectron. 175 (2021) 112836. [41] H. Lu, B. He, B. Gao, Emerging electrochemical sensors for life healthcare, Eng. Regen. (2022).
12 Nanomaterial-based electrochemical sensing of histamine Safia Khan1, Mariam Khan2, Arsh E Noor3, Anish Khan4 and Awais Ahmad5 1
Shandong Technology Centre of Nanodevices and Integration, School of Microelectronics, Shandong University, Jinan, P.R. China 2School of Applied Sciences and Humanity, NUSASH, National University of Technology, Islamabad, Pakistan 3Department of Environmental Sciences and Engineering, Government College University Faisalabad, Faisalabad, Pakistan 4Chemistry Department, Center of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah, Saudi Arabia 5Department of Chemistry, The University of Lahore, Lahore, Pakistan
Objectives • • • •
•
To study the significance of histamine with respect to food safety and scombroid poisoning. To concisely utilize the most common histamine sensing techniques. To recognize the significance of electrochemical approaches in the detection of histamine. To discuss and highlight the most effective nanomaterials used as sensors for histamine detection and quantification in actual samples. To hypothesize the future of histamine detection in terms of nanomaterial-based electrochemical sensing.
12.1
Introduction
Different molecular arrangements are exhibited by biogenic amines, which appeared as those nitrogen bases that are composed by microbial decarboxylation of amino acid. Cadaverine, histamine, and putrescine are Bas, which are the main cause of sprouting of food [1]. Histamine is a nitrogenous base produced Nanomaterials-Based Electrochemical Sensors: Properties, Applications, and Recent Advances. DOI: https://doi.org/10.1016/B978-0-12-822512-7.00004-1. © 2024 Elsevier Inc. All rights reserved.
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Figure 12.1 Molecular structure of histamine.
as a result of amino acid l-histidine decarboxylation [2]. This is a heterocyclic compound showing a C C linking among the imidazole ring and aliphatic amino groups, as shown in Fig. 12.1 [3]. It is a highly reactive entity in living organisms that is essential for the immune system and has physiological characteristics because it allows for restricted signal transmission between the cells [4]. Deterioration of food is the most trending issue, which occurs due to ingestion of infected food. Among all the causes of food poisoning, histamine poisoning is the most prominent. Almost all seafood contains histamine. A tolerable amount of histamine is also present in all healthy food items. Seafood containing toxic levels of histamine is responsible for allergic reactions in the body after ingestion. Histamine-containing food includes dry fruits, processed food, beverages, dairy products, bananas, avocados, shellfish, and some food additives. Likewise, tuna, a food rich in histamine, is a universally disbursed food item [5,6]. Hypersensitivity reaction in response to histamine shows the vital part in causing itching. The allergic response by histamine poisoning is likely to occur by scombroid fish infected by bacteria. Normally, histamine has no hazardous effect on health, but when the food is infected and its level approaches a toxic level (50/100 g of food), it results in poisoning. The common bacterial species that cause histamine toxicity are Morganella morganii, Proteus vulgaris, Klebsiella pneumoniae, and Morganella psychrotolerans in scombroid and decayed fish. Such hypersensitivity reactions and sensitivities are commonly instigated by histamine, as it is the main component of the immune system of the body. Histamine is produced in a large amount by mast cells, which are activated in rare disorders, such as Mastocytosis [7,8] (Fig. 12.2). For good health, metabolism of histamine is compulsory. An enzyme named diamine oxidase (DAO) is present in the human body and is responsible for histamine metabolism in food. Insufficiency of DAO is the main factor for less metabolic rate of histamine, so histamine toxicity will occur in the
Chapter 12 Nanomaterial-based electrochemical sensing of histamine
Figure 12.2 Nanomaterial-based electrochemical sensing of histamine [1].
human body [9,10]. A few allergic reactions in body caused by histamine toxicity are fatigue, nasal congestion, vomiting and digestion problems, sinus issues, headache, nausea, and irregular menstrual cycles. In severe hypersensitivity, reactions include high blood pressure, cramping in the abdomen, irregularity in heartbeat, anxiety, and tissue swelling. Moreover, histamine poisoning is triggered by increased bacterial growth. This occurs when food is not digested and the number of bacteria is increased. For this, a large amount of DAO is required for histamine metabolism. The foods which are responsible for insufficient generation of DAO are black tea, green tea, energy drinks, mate tea, and alcohols. To prevent from histamine intolerance, foods low in histamine levels should be taken in diet to minimize the indications of histamine poisoning [11,12]. To cease the possible risks prompted from histamine in eatables, especially seafood, the European community had reported that the typical quantity of histamine in seafood should be lower than 10 mg/100 g of food. Just like in treated tuna fish, the level of histamine is 3 mg/100 g [13].
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12.2
Identification of histamine
Histamine ingestion at higher levels than average is toxic, so identification of the right quantity is necessary in food safety. The food quality can be analyzed by quantifying the histamine in different products, which is the standard for identification of good manufacturing and preservation of food. Histamine identification in food industries is compulsory to avoid any hypersensitivity reaction [14,15]. Seafood processors performed tests for identification of histamine in a regulatory manner. The tolerable range of histamine in hale and better quality fish is 10 to 30 ppm [16,17]. The following are the methods conventionally used for identification of histamine specifically in food. • Thin-layer chromatography • Enzymatic detection • Gas chromatography • Ion-mobility spectrometry • Fluorimetric sensing • Enzyme-linked immune-sorbent assay • Capillary-zone electrophoresis • Calorimetry • High-performance liquid-chromatography These processes of histamine sensing and determination in food are solely based on conventional means. New methods such as biosensing-based strategies are attracting attention for histamine identification in food. The most advanced approach, which is currently evolving, is nanotechnology for the detection of histamine. The histamine detection instruments adopted molecular printing and nanotechnology, with which they have improved their outcome. It is not compulsory to use more timeconsuming conventional methods of identification, which require extensive preliminary formalities and expert analysts, if a nanotechnology-based process of identification is chosen [18,19]. For the exposure of histamine in different food items, currently, several advanced approaches have been developed. Some of them are mentioned below:
12.2.1
Surface-enhanced Raman scattering
The Surface-enhanced Raman scattering (SERS) technique is extensively implemented in food security for recognition of injurious substances. SERS is the most appropriate method for analysis that can identify even a single entity up to 1016-fold. Because of its higher accuracy, it has attracted attention in identification of
Chapter 12 Nanomaterial-based electrochemical sensing of histamine
histamine. For the identification of histamine, many procedures have been discussed by the SERS technique, such as a wellintegrated molecularly imprinted polymers (MIPs) SERS technique. MIPs-SERS involves the connection among polymers and histamine analyte in micro/nano scales, which are investigated to segregate as well as identify histamine in food concurrently [6,20]. Metal complexes, especially the Au and Ag suspensions, are extensively used to identify the histamine applying the SERS mechanism, as these colloids give accurate results at a low toxicity rate. An extensive collection of metal alloys and nanoclusters in bimetallic and trimetallic constitutions is consumed for histamine identification in food [21]. This process of identification has been utilized for detection of minute constituents in food. This constitutes a very easy preliminary process and can isolate a wide range of frequencies. Its harmful feature is a minor photo damage, which can be ignored, but a feature of food matrix in the SERS spectrum that interferes in analysis is a challenge to overcome in this method.
12.2.2
Fluorescence-grounded histamine sensing method
To detect the mediators in allergic reactions, the initial step is mostly conducted using an ex vivo strategy. The identification method using the fluorescence technique, for histamine, is illustrated in Fig. 12.3. The fluorescent investigation
Figure 12.3 Uncovering of histamine by using the fluorescence-based method [22].
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technique is broadly utilized to check numerous biological molecules. It is an appropriate identification process because it permits altering the intensity and strength of bombarded light radiations on the target entity under observations at moderate condition [22,23]. Recently, histamine identification is reported by harmonizing the fluorescence signals. Herein, the ligand exchange technique is implemented using metal ion chelates. A few examples of such a technique are mentioned here. 1. Histamine identification using mast cell degranulation established on the harmonization transposition technique [24]. 2. Histamine identification by altering the fluorescence signal through the harmonization transposition technique among imminodiacetic acid histamine and metal complexes [25,26]. 3. Detecting probes depend on nanofluids are produced for label-free identification of histamine; it is a cheaper and easy method of identification. However, the most widely used method of identification of histamine is the fluorescence-based method, but this method is deemed unsatisfactory with respect to viscidity, applicability, and accuracy.
12.2.3
Enzymatic detection
The electroanalysis process of histamine using enzymeamended biosensors has enhanced the interest of many investigators. Not long ago, enzymatic assay was produced to identify histamine in seafood by the process of aqueous extraction. Such a technique was utilized in canned tuna, fresh tuna, frozen mahi, and tuna. The identification of histamine via enzyme assay is beneficial with respect to ease of operation, less time-consuming, and easy extraction, but there is a problem with this detection method: some components in food may cause hindrance with the outcomes of the assay [27,28]. Histamine detection test kits are also available, in which colorimetric enzymatic assay is used. In these test kits, the detection principle involved is dehydrogenation reaction of histamine. This method of detection is less time-consuming, but the cost of the kits and instability of enzymes make it somewhat less fruitful. It is concluded that there is a need of production of such types of biosensors, which are selective in their enzymatic activity for detection purposes [29].
Chapter 12 Nanomaterial-based electrochemical sensing of histamine
12.2.4
Electrochemical methods
A big problem in the identification of histamine in natural food specimens is the obtrusion caused by other structurally similar amines and other biochemicals like tyramine, uric acid, and histidine. For this, the most effective method of identification of biological amines and many other compounds is electrochemical analysis. The electrochemical identification of histamines based on nanosensor technology is an emerging field in food safety. There are many identification methods for histamines, in which electrochemical analysis has been employed. The electrochemical analysis is an appropriate method with respect to low cost, simplicity of operating procedures, and rapid outcomes and is totally appropriate for such purposes owing to its simple operation, inexpensiveness, greater accuracy, and rapid response [19,30 32].
12.2.4.1
Amperometric detection
With respect to food and nutrition, amperometric determination of histamine is a burning question for researchers. For the direct detection of histamine, many investigations have suggested the use of electrodes modified via metal nanoparticles in amperometric analysis, such as Au nanomaterials, which are associated via pulse amperometry and nickel film-modified electrodes. In optimized environments, an amperometry-based sensor can sense the histamine very well at lower potential values of 10.55 V versus Ag/AgCl reference in oxygen evolution reaction. This amperometric sensing utilizes copper plating to directly sense the histamine in analytical samples [33,34]. Other than metal-derived sensors, the use of enzyme-based detectors in chronoamperometry for histamine sensing is also reported. DAO coupled with a screen-printed carbon electrode has been observed to detect histamine by chronoamperometry. DAO seemed immobilized on the carbon electrode surface because of cross-linkage. These types of sensors displayed a commendable response time of 60 s at 20.3 V in a sample with a concentration of 40 µL, as presented in Fig. 12.4. Enzymatic sensors have shown 103% recovery efficiency in histamine analysis [34].
12.2.4.2
Impedimetric detection
To characterize fabricating materials in sensing, the impedimetric methods have been used, which also serves as a tool to study diverse catalytic reactions. Multiple electrochemical sensors for histamine detection are conveyed having a 15 nM detection
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Figure 12.4 Histamine sensing by enzyme-based chronoamperometry [34].
limit. Magnetic and alumina-based sensors have been utilized in impedimetric sensing. In order to capture histamine from the surface, there is the coupling of antihistamine antibodies with the magnetic nanoparticle histamine, resulting in the signal amplification. Graphene-containing immunosensors are also introduced for histamine detection in the impedimetric sensing technique [35,36].
12.2.4.3
Voltammetric detection
Voltammetric analysis is attracting the attention of researchers since it is the most versatile technique in the study of sensors (Fig. 12.5). These sensors are specifically fabricated and used for histamine detection in food. Graphene and silver nanoparticle (AgNP)-composed sensors have fascinated researchers around the world since they are highly effective in sensing of histamine via cyclic voltammetry and square-wave voltammetry [38]. Correspondingly, the electrodes amended with MIPs/graphite epoxy are established for sensing histamine via stripping voltammetry. AuNPs doped on manganese oxide/screen-printed electrodes are used in direct histamine sensing and estimation via cyclic voltammetry [39]. In this way, histamine can be frequently quantified and detected by electrochemical techniques, especially voltammetric methods.
12.3
Materials utilized in histamine electrochemical sensing
Generally, electrochemical histamine detectors are frequently simpler, sensitive, defined, and discriminating with fast response and low cost. Electrochemical analysis based on nanomaterials is
Chapter 12 Nanomaterial-based electrochemical sensing of histamine
219
Figure 12.5 Scheme for fabrication and cyclic voltammetry response of the GCE/CeO2-PANI/DAO electrode for sensing of histamine [37].
significantly effective in detecting of histamine. The materials that are used for histamine detection on large-scale production are given below.
12.3.1
Quantum dots
Quantum dots (QDs) are used as a tool for detection of histamine electrochemically in food quality control. In 2017, QDs were reported for the first time as histamine detectors. In tuna fish, cadmium-tellurium QDs/thioglycolic acid was treated as a photoluminescent probe in this preliminary investigation. Then, for the same objective, numerous cadmium-based QDs with improved sensitivity, such as poly methyl methacrylate with the alteration of cadmium-selenium/Zn-sulfide QDs, were formed [40]. QDs were found to be a very efficient detecting material in recognition of histamine, with maximum signal intensity, improved photo stability, broader excitation spectrum, size tenability, and higher biocompatibility. For histamine analysis, the use of core-shell QDs has also been reported [41,42].
12.3.2
Molecular-imprinted polymers
MIPs are efficient detectors that can detect a variety of molecules. For instance, some of the outstanding benefits provided by the cross-linked polymers are as follows: • Capability to recognize the main molecules • Preparatory methods are less cost-effective • High stability.
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In electrochemical detection of histamine, MIPs are also used. The MIP electrodes have been shown to be a viable technique for evaluating the quantitative concentration of histamine by using electrochemical impedance and cyclic voltammetry. Use of sensors based on MIPs is strongly advised for detection of ultratraces of histamine in food. The gold-doped MIPs were found to have significant sensitivity and selectivity for histamine detection in real samples in analytical experiments [43,44].
12.3.3
Nanomaterials
Nanoparticle-based techniques have been developed for the highly sensitive detecting of histamine. There is no need for sophisticated equipment because the nanosensors, which have highly promising ranges for histamine analysis, can be used in moderate conditions. Significant innovations in nanomaterialbased histamine sensing have demonstrated great accuracy in terms of operational sensitivity, specificity, and ease. Nanoparticles are believed to have shown to be the finest electrochemical sensors with strong potential capabilities in the sensing platform for determining numerous biomolecules in the future. The researchers chose histamine sensing as the best field because of the features of nanomaterials such as high quantum yield, electrocatalysis, biocompatibility, and chromogenicity.
12.4
Nanomaterials for histamine sensing
Because of their unique catalytic capabilities, nanomaterialbased detectors have stimulated the interest of researchers in the field of sensing. Scientists and analysts are focusing on the application of recently modified electrochemical nanosensors to detect histamine via enzymatic or other schematic reactions. Some nanoparticles used in histamine sensing are discussed below.
12.4.1
Metal nanoparticles
There is requirement to consolidate a fast and precise pace for detection of histamine in food products. To achieve this goal, nanosensors based on metal/metal oxides have been employed, which was found to be the best ever path for sensing. The metallic nanosensors are in possession of the single metal, metal amalgams, or alloy composition. Nanocomposites of gold, platinum, and silver are used for the preparation of nanosensors because of the properties mentioned below:
Chapter 12 Nanomaterial-based electrochemical sensing of histamine
• • • •
Immobility of receptor substances Catalysis in a reaction Greater electron transferring nature Easy to label the analytes and receptors molecules. Metal-based histamine sensors have been used in a variety of cases. The determination of histamine on the surface of a glassy carbon electrode was conducted using amperometric sensors based on AgNPs [45]. For histamine determination, AgNPs exhibit promising sensitivity and catalytic capabilities [38]. Histamine detection has been reported using a variety of silver-based sensors, such as Ag-Ag2O/glassy carbon [46]. Histamine is also identified using silicon oxide/gold/silver alloy nanoparticles [21]. It is reported that a catalytic mediator based on ReO2 is used in histamine flow-injection analysis amperometric sensing [47]. That is why, the nanoparticles based on metal are extremely valuable and so are frequently applied in exposure and determination histamine using electrochemical analysis.
12.4.2
Core-shell nanoparticles
Because of their increased sensitivity and selectivity in electrochemical analysis, core-shell nanomaterials made of metals such as iron, cobalt, nickel, copper, and others have gained a lot of interest. One metal shell is generated in core-shell synthesis, which envelops the core of another metal. Noble metals are usually utilized to make core shells [48]. There have been numerous reports on histamine detection sensors based on core-shell innovation. Using cyclic voltammetric and amperometric approaches, CeO2 PANI core-shell nanoparticles may be manufactured as histamine sensors that are free of mediators [19]. Enzyme-free amperometric sensors for histamine with low potential and high sensitivity, similar to copper/palladium-based core-shell composites, have been reported [41]. For sensing histamine, graphite-based core-shell nanostructures with a high electrochemical surface area have been developed, which are more reactive than their basic bimetallic components. As a result, the core-shell nanomaterials have proven to be highly advantageous, as they are less expensive and more responsive to histamine detection.
12.4.3
Carbonaceous nanoparticles
Food analysts have been paying close attention to carbonaceous elements in order to detect and identify various biomolecules in food samples. CNTs, graphene-based metal nanoparticles,
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have been investigated for electrochemical detecting techniques to detect a variety of biomolecules. Histamine is electrochemically detected on graphene-based electrodes, as described [49]. Because of their strong electron transfer capabilities between the electrode surface and active species, CNTs are being explored for sensing. Using differential pulse voltammetry, single-walled CNTs are used to identify histamine. The nickel/ carbon sensors are used to monitor histamine ultrasensitivity that has proven to be active due to its huge surface area, strong conductivity with low potential, and enormous number of active sites, as well as its less cost-effective synthetic process. Functionalized Ru(bpy)32 1 hybrid material has been reported to increase the histamine detection limit [50]. For histamine detection, solution-gated graphene transistors have been developed with remarkable sensitivity and selectivity [51]. Similarly, gold nanoparticles based on carboxylate CNTs were synthesized for the electrochemical detection of histamine [52]. Along with this, glassy carbon modified with polystyrene graphene oxide was designed as a polymeric nanobased sensor for electrochemically detecting histamine in real food samples [53]. Table 12.1 summarizes some important electrochemical approaches for histamine sensing based on nanomaterials.
Table 12.1 Sensing techniques based on nanomaterials for histamine detection. Type of nanomaterial
Detection strategy
Sample type
CdSe/ZnS QDs TGA-CdTe QDs Nanoporous silica Nano-MIPs Magnetic nanoparticles Graphene CNTs Cu@Pd core-shell nanoparticles Magnetic nanomaterials Graphene and platinum Graphene nanoribbons and silver nanoparticles Gold nanoparticles Carbon nanotubes Ce-Polyaniline (CeO2-PANI) CeO2-PANI Rhenium oxide
Fluorescent method Fluorescent Fluorescence sensing Fluorescent Spectrophotometric sensing Voltammetry and amperometry Voltammetry Amperometry Impedimetric Amperometry Voltammetry Voltammetry Voltammetric sensing Voltammetry and amperometry Voltammetry Amperometric analysis
Tinned fish Rotted tuna fish Salmon and tuna fish Spiked milk Tuna fish Serum Beer and wine Preserved tuna fish Surrey fish Fishes in freshwater Plasma Seafood Muscle extract of fish Tiger prawn Fish Sauce of fish
Chapter 12 Nanomaterial-based electrochemical sensing of histamine
12.5
Conclusion
Poisoning of food components is a worldwide problem caused by the consumption of unsafe food. Toxic histamine is the leading source of health concerns in contaminated food. In some cases, histamine is caused by rotten or contaminated seafood. Inflammation and scombroid toxicity are triggered by a high intake of malformed histamine. To detect the poisoning materials on its origin, it is essential to develop highly responsive and effective tools. Histamine must be accurately detected in genuine samples, as this is required for food safety. Analysts are concentrating mainly on the development of active sensing materials and methodologies. The sensitivity and detection limit of histamine quantification using nanomaterial sensors and electrochemical sensing approaches have been described. For the detection of histamine, various sensing approaches such as electrochemical voltammetry, impedance, and chronoamperometry have been developed. Innovative electrochemical approaches using enzymatic and nonenzymatic sensors, as well as appropriate strategies, are being investigated. The research must be continued to evolve the nanoanalytical sensing technology for detection of histamine by utilizing nanomaterials that researchers may employ even in remote locations. Histamine diagnostic devices should be the focus of nanoparticle-based research.
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[10] E. Kovacova-Hanuskova, et al., Histamine, histamine intoxication and intolerance, Allergol Immunopathol 43 (5) (2015) 498 506. [11] P. Visciano, et al., Histamine poisoning and control measures in fish and fishery products, Front. Microbiol. 5 (2014) 500. [12] G. Velut, et al., Histamine food poisoning: a sudden, large outbreak linked to fresh yellowfin tuna from Reunion Island, France, April 2017, Eurosurveillance 24 (22) (2019) 1800405. [13] R. Adamou, et al., Fluorimetric determination of histamine in fish using micellar media and fluorescamine as labelling reagent, J. Fluoresc. 15 (5) (2005) 679 688. [14] A. Moyano, et al., Magnetic immunochromatographic test for histamine detection in wine, Anal. Bioanal. Chem. 411 (25) (2019) 6615 6624. [15] M. Gagic, et al., Fully automated process for histamine detection based on magnetic separation and fluorescence detection, Talanta 212 (2020) 120789. [16] B.-S. Hwang, J.-T. Wang, Y.-M. Choong, A rapid gas chromatographic method for the determination of histamine in fish and fish products, Food Chem. 82 (2) (2003) 329 334. [17] H. Takahashi, et al., Cloning and sequencing of the histidine decarboxylase genes of gram-negative, histamine-producing bacteria and their application in detection and identification of these organisms in fish, Appl. Environ. Microbiol. 69 (5) (2003) 2568 2579. [18] X.-X. Dong, et al., Portable amperometric immunosensor for histamine detection using Prussian blue-chitosan-gold nanoparticle nanocomposite films, Biosens. Bioelectron. 98 (2017) 305 309. [19] M.B. Gumpu, et al., Development of electrochemical biosensor with ceria PANI core shell nano-interface for the detection of histamine, Sens. Actuators B: Chem. 199 (2014) 330 338. [20] T. Zhou, et al., Fabrication of Fe3O4/Au@ ATP@ Ag Nanorod sandwich structure for sensitive SERS quantitative detection of histamine, Anal. Chim. Acta 1104 (2020) 199 206. [21] K.-H. Huynh, et al., Facile histamine detection by surface-enhanced raman scattering using SiO2@ Au@ Ag alloy nanoparticles, Int. J. Mol. Sci. 21 (11) (2020) 4048. [22] B.L. Neumeier, J.G. Heck, C. Feldmann, Fluorescence-based histamine sensing with inorganic organic hybrid nanoparticles, J. Mater. Chem. C. 7 (12) (2019) 3543 3552. [23] J. Bi, et al., Detection of histamine based on gold nanoparticles with dual sensor system of colorimetric and fluorescence, Foods 9 (3) (2020) 316. [24] Y. Oshikawa, et al., Cell surface-anchored fluorescent probe capable of realtime imaging of single mast cell degranulation based on histamine-induced coordination displacement, Anal. Chem. 88 (3) (2016) 1526 1529. [25] D. Seto, et al., Selective fluorescence detection of histamine based on ligand exchange mechanism and its application to biomonitoring, Anal. Biochem. 404 (2) (2010) 135 139. [26] D. Seto, et al., An amphiphilic fluorescent probe for the visualization of histamine in living cells, Bioorg. Med. Chem. Lett. 20 (22) (2010) 6708 6711. [27] W. Henao-Escobar, et al., Dual enzymatic biosensor for simultaneous amperometric determination of histamine and putrescine, Food Chem. 190 (2016) 818 823. [28] S. Gone, et al., Validation study of MaxSignals histamine enzymatic assay for the detection of histamine in fish/seafood, J. AOAC Int. 101 (3) (2018) 783 792.
Chapter 12 Nanomaterial-based electrochemical sensing of histamine
[29] M.A. Beaven, S. Jacobsen, Z. Hora´kova´, Modification of the enzymatic isotopic assay of histamine and its application to measurement of histamine in tissues, serum and urine, Clinica Chim. Acta 37 (1972) 91 103. [30] K. Pihel, et al., Electrochemical detection of histamine and 5-hydroxytryptamine at isolated mast cells, Anal. Chem. 67 (24) (1995) 4514 4521. [31] Y. Xu, et al., Synthesis of MOF-derived Ni@ C materials for the electrochemical detection of histamine, Talanta 219 (2020) 121360. ¨ ter, S. Shinde, Ultratrace detection of histamine using [32] M. Akhoundian, A. Ru a molecularly-imprinted polymer-based voltammetric sensor, Sensors 17 (3) (2017) 645. [33] K. Zeng, et al., Amperometric detection of histamine with a methylamine dehydrogenase polypyrrole-based sensor, Anal. Chem. 72 (10) (2000) 2211 2215. [34] R. Torre, et al., Amperometric enzyme sensor for the rapid determination of histamine, Anal. Methods 11 (9) (2019) 1264 1269. [35] E. Bongaers, et al., A MIP-based biomimetic sensor for the impedimetric detection of histamine in different pH environments, Phys. Status Solidi (a) 207 (4) (2010) 837 843. [36] G. Wackers, et al., Towards a catheter-based impedimetric sensor for the assessment of intestinal histamine levels in IBS patients, Biosens. Bioelectron. 158 (2020) 112152. [37] N. Nesakumar, et al., Theoretical investigation of surface coverage in the electrochemical behaviour of enzyme modified electrodes, Sens. Lett. 13 (4) (2015) 344 348. [38] N. Kumar, R.N. Goyal, Silver nanoparticles decorated graphene nanoribbon modified pyrolytic graphite sensor for determination of histamine, Sens. Actuators B: Chem. 268 (2018) 383 391. [39] S. Kneˇzevi´c, et al., A single drop histamine sensor based on AuNPs/MnO2 modified screen-printed electrode, Microchem. J. 155 (2020) 104778. [40] Q.-H. Wang, et al., Fluorescent sensing probe for the sensitive detection of histamine based on molecular imprinting ionic liquid-modified quantum dots, Food Anal. Methods 10 (7) (2017) 2585 2592. [41] R.K.R. Gajjala, S.K. Palathedath, Cu@ Pd core-shell nanostructures for highly sensitive and selective amperometric analysis of histamine, Biosens. Bioelectron. 102 (2018) 242 246. [42] T. Deng, et al., Water-solubilizing hydrophobic ZnAgInSe/ZnS QDs with tumor-targeted cRGD-sulfobetaine-PIMA-histamine ligands via a selfassembly strategy for bioimaging, ACS Appl. Mater. Interfaces 9 (13) (2017) 11405 11414. [43] F. Gao, E. Grant, X. Lu, Determination of histamine in canned tuna by molecularly imprinted polymers-surface enhanced Raman spectroscopy, Anal. Chim. Acta 901 (2015) 68 75. [44] F.A. Trikka, et al., Molecularly imprinted polymers for histamine recognition in aqueous environment, Amino Acids 43 (5) (2012) 2113 2124. [45] S. Yadav, et al., Nanomaterials based optical and electrochemical sensing of histamine: progress and perspectives, Food Res. Int. 119 (2019) 99 109. [46] N. Butwong, et al., Electrochemical sensing of histamine using a glassy carbon electrode modified with multiwalled carbon nanotubes decorated with Ag-Ag2O nanoparticles, Microchim. Acta 186 (11) (2019) 1 10. [47] A. Veseli, et al., Electrochemical determination of histamine in fish sauce using heterogeneous carbon electrodes modified with rhenium (IV) oxide, Sens. Actuators B: Chem. 228 (2016) 774 781.
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[48] T.K. Sau, et al., Properties and applications of colloidal nonspherical noble metal nanoparticles, Adv. Mater. 22 (16) (2010) 1805 1825. [49] M. Yang, J. Zhang, X. Chen, Competitive electrochemical immunosensor for the detection of histamine based on horseradish peroxidase initiated deposition of insulating film, J. Electroanal. Chem. 736 (2015) 88 92. [50] D. An, et al., Polyoxomatelate functionalized tris (2, 2-bipyridyl) dichlororuthenium (II) as the probe for electrochemiluminescence sensing of histamine, Food Chem. 194 (2016) 966 971. [51] R. Wang, et al., Solution-gated graphene transistor based sensor for histamine detection with gold nanoparticles decorated graphene and multi-walled carbon nanotube functionalized gate electrodes, Food Chem. (2021) 128980. [52] A.M. Mahmoud, et al., Dual-recognition molecularly imprinted aptasensor based on gold nanoparticles decorated carboxylated carbon nanotubes for highly selective and sensitive determination of histamine in different matrices, Anal. Chim. Acta 1133 (2020) 58 65. [53] L. Saghatforoush, M. Hasanzadeh, N. Shadjou, Polystyrene graphene oxide modified glassy carbon electrode as a new class of polymeric nanosensors for electrochemical determination of histamine, Chin. Chem. Lett. 25 (4) (2014) 655 658.
13 Nanostructured complexes of gold(I) in sensing Safia Khan1, Mariam Khan2, Awais Ahmad3, Ifzan Arshad4, Hu Li5 and Shern-long Lee4 1
Shandong Technology Centre of Nanodevices and Integration, School of Microelectronics, Shandong University, Jinan, P.R. China 2School of Applied Sciences and Humanity, NUSASH, National University of Technology, Islamabad, Pakistan 3Department of Chemistry, The University of Lahore, Lahore, Pakistan 4Institute for Advanced Study, Shenzhen University, Shenzhen, Guangdong, P.R. China 5Technology Centre of Nanodevices and Integration, School of Microelectronics, Shandong University, Jinan, P.R. China
Objectives • • • • • •
To briefly address the synthetic methodology of AuNPs. To study the different morphologies and sizes of AuNPs and their applications in various fields of sciences. To comprehend the usefulness of gold-based nanomaterials in sensing applications. To study the role of AuNPs in biomedical applications like therapeutic, cancer therapy, photothermal therapy, and so forth. To highlight the importance of AuNPs in metal detection for biological and environmental analyses. To propose the future perspective of histamine detection with respect to nanomaterial-based electrochemical sensing.
13.1
Introduction
Material science and technology is predominantly run by various kinds nanostructured atoms, molecules, and composites. Nanoparticles aroused from different metal origins, that is, platinum, palladium, ruthenium, silver, zinc, and gold, are under consistent research for development of efficient electrode materials used in a multitude of electrochemical applications. Gold (Au) is one of the best nanostructured materials utilized for multiple technological applications. It is a soft as well as a neutral metal Nanomaterials-Based Electrochemical Sensors: Properties, Applications, and Recent Advances. DOI: https://doi.org/10.1016/B978-0-12-822512-7.00007-7. © 2024 Elsevier Inc. All rights reserved.
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displaying a shiny yellow appearance having a melting point at 1068 C. Although gold has many favorable properties such as bulk-like reflectivity, corrosion resistance, and malleability, unique and more commendable properties emerge when it is converted to nanoscaled structures [1,2]. Gold nanoparticles (AuNPs) are structures of nanosize, maintaining a diameter ranging from 1 to 100 nm [3]. AuNPs are being widely studied in various applications owing to their attractive electrical, conducting, and optical properties. Besides the typical applications, AuNPs are currently being applied even in sensing, diagnosing, biomedical, and catalytic fields [4]. Likewise, modern touch screen systems can replace the conventional carbon nanotubes (CNTs) with more efficient gold nanowires [5]. Also, if the typical platinum and palladium nanoparticles get replaced with AuNPs, the catalytic application displays superior efficiency owing to minimum usage of metal up to thousand times. Moreover, the innovation in design and synthesis of AuNPs have a huge impact upon the prepared nanostructured gold species of different particle sizes, shapes, and orientations. Nanostructured gold films and gold electrodes can be developed by multiple modern techniques including sputtering, vacuum evaporation, electrodeposition, and monolayer formation by self-assembling colloidal nanoparticles. A combination of AuNPs with conventional CNTs have demonstrated superior electrocatalytic outputs, working as electrodes. In this way, a reliable and unceasing development of gold nanostructures of controlled morphologies and products of desired characteristic have offered new pathways for synthesis and growth approaches.
13.2
Synthesis of AuNPs
Synthesis of controlled size and morphology has been the concern of extensive research for decades as the catalytic output and conductive properties of gold nanostructures are decidedly dependent upon dimensions and shape [6]. Anisotropic forms of gold nanostructures frequently involving nanosheets, nanorods, nanowires, nanoplates, and so forth have attained much attention owing to their striking applicability in various science fields like photonics, electronics, catalysis, and biomedicines [7]. Generally, AuNPs are synthesized via two conventional methods, that is, “top up” and “top down” methods [8]. In the top down method, nanoparticles are produced via scattering of gold in bulk, while in the top up method,
Chapter 13 Nanostructured complexes of gold(I) in sensing
nanoparticles are synthesized from the atomic level. The production of AuNPs via the reduction method consists of two steps [9]. 1. Gold precursor reduction in which salt solution of a precursor is reduced by any reducing agent like citrate and BiH4. 2. The reduced AuNPs are stabilized by stabilizing agents. Stabilization of AuNPs is an important factor, as the base AuNPs are quite unstable because they aggregate and precipitate as metallic Au powder. The capping agents like citrates, polymers, surfactants, and thiols are used to stabilize the AuNPs, which cover them and reduce the aggregation [10,11]. The synthesis of AuNPs can be easily done by adopting different synthetic methods. It depends on the shape and size of nanoparticles required. The advantage of using AuNP is that their surface can easily be modified by any type of molecule like protein, lipids, carbohydrates, and antibodies. The spherical and rod-shaped AuNPs have been used in biomedical applications [12,13]. These are the most commonly used shapes of AuNPs in biomedical applications. The chemical reduction method is used to prepare spherical-shaped AuNPs, and the seed-mediated synthetic method is mostly used to prepare spherical shaped AuNPs. The electrochemical deposition method is adopted to prepare gold nanowires, in which anodic alumina films are used as templates [14]. The shape and size difference of AuNPs provides different and unique optical and cellular uptake properties that lead to the wide use of AuNPs in advanced biomedical applications, both ex vivo and in vivo, for example, AuNPs are used potentially to diagnose different diseases. In photothermal therapy, AuNPs play an important role; as these nanoparticles absorb light energy due to their excellent surface plasmon property, they convert that light energy into heat energy, which is used in photothermal therapy [15,16]. Hexagonal single-crystalline AuNPs like triangular nanoplates are prepared on a large scale by adopting a mild wet chemical method, in which gold chlorates in aqueous medium are reduced with ortho phenylenediamine at standard temperature and pressure. Hexagonal nanoplates can also be prepared by the etching of triangular nanoplates [17]. By adopting different ways of synthesis, different sizes and shapes of AuNPs can be obtained, which lead to modified optical, magnetic, and electronic properties, making the AuNPs attractive for researchers. By decreasing the size of gold structured particles to the nanorange, they can be used in advanced biomedical and electrical applications, as they enhance the surface area of nanoparticles. AuNPs have gained attention due to their unique optical and electrical properties, which depend on shape and size.
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The green synthesis of AuNPs using plant extractions is studied recently. This study revealed that the use of biomolecules as reducing agents is more advantageous than the chemical reducing agents [18,19]. Various studies showed the advanced use of AuNPs due to their antimicrobial properties. The synergistic effect of AuNPs with antibodies against different microorganism has been reported [20,21].
13.3
Gold nanoparticles with different morphologies
The unique properties of metals in nanosize have enhanced their importance in various nanotechnology applications [22,23]. AuNPs, owing to their fascinating properties, have been reported in numerous grounds of imaging such as surface enhance Raman spectroscopy, computed tomography, and photoacoustic. The precise controlled synthesis produces AuNPs of different shapes with different geometries like nanowires, nanocages, nanocubes, nanospheres, and nanorods, as shown in Fig. 13.1. The surface morphology of AuNPs affects the activity and physical properties, so this should be carefully studied. The best property of AuNPs is that they are biocompatible and do not cause any inflammatory reactions or allergy in the body and they are nontoxic and are best for optical imaging [25]. Modification of surface of AuNPs is usually done by the thiols as the nanoparticles have strong affinity for these groups. Different imaging agents are used during application of gold in imaging such as lanthanide chelates and fluorophores [26]. The fluorophores have a wide emission range, while lanthanides are prohibited to extravascular spaces in a nonselective way. For
Figure 13.1 Basic synthetic method for gold nanoparticles [24].
Chapter 13 Nanostructured complexes of gold(I) in sensing
sensing different types of cancerous cells, AuNPs connected with the quantum confinement and surface plasmon resonance are improved as contrasting agents in distinctive imaging [27]. By advanced developments in synthetic methodologies, AuNPs with different morphologies like nanocubes, nanoshells, nanospheres, nanoflowers, and so forth have been prepared [28,29]. The sensing and catalytic activity of AuNPs is attributed to the availability of atoms on the surface. The enhanced chemical activity can be seen in nanostructures having atoms on the surface at corners and edges with a low coordination number.
13.3.1
Gold nanowires
Au-nanowires are one-dimensional structures, which are mostly 30 μm in length and 30 nm in height; they are an alternative or complementary substance to CNTs. The unique properties of gold nanowires like high conductivity, transparency, and resistivity to oxidative or corrosive reactions as compared to silver nanowires make them fascinating nanomaterials [30,31]. In transparent electrode material displays of touch screen, Aunanowires are used as replacement for CNTs. In electronic biosensors, Au-wires have proved to be a highly sensitive promising material. Till now, various methods have been used to synthesize Au-nanowires, like seed-mediated method, template growth method, and oriented attachment method [32,33]. Nanoribbons/nanobelts are another one-dimensional gold nanomaterials which are mostly studied [34]. They could be prepared by self-assembly of triangular gold nanoplates. Gold nanowires vertically bonded with elastomers having configuration like enokitake with the head on one side (NPs) and the tail (nanowires) on the other side, as shown in, are used in stretchable electrochemical electrode materials [24]. Due to extensive tensile properties of the tail and head of these materials, they are used as potential materials for electrochemical sensing applications like amperometric sensing by using enzymeinduced reaction and fabrication of H2O2. To sense the glucose level in blood, nanosensors with high sensitivity are required. Single Au-nanowires such as electrochemical sensors are proved to be reliable and effective sensing material for detection of glucose low concentration quantitively ranging 10 μM to 1 mM. These sensors are shown as more selective toward detection of glucose with zero or less interferences, for example, salicylic acid, fructose, paracetamol, uric acid, and ascorbic acid [35] (Fig. 13.2).
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Figure 13.2 v-Au nanowires bonded with an elastomer [36].
13.3.2
Gold nanorods
Au nanorods are capsule-like particles ranging from few nm to 100 nm in size. They have strong optical properties as compared to spherical AuNPs because of the effect of their localized surface plasmon resonance. Au-nanorods have long axial directions and independent electronic vibrations [37,38]. In the past 2 decades, two-dimensional spherical AuNPs have found their applications in cancer therapies. However, the drawback of using spherical AuNPs is that these nanoparticles were not reported as optimized because they have limited absorption peaks of nearly 580 nm for the particle of 100 nm diameter, while the transmission range for biological substances like tissues and skin is 650 to 900 nm. Gold nanorods (AuNRs) are like Au nanoparticles in some respects, but they are elongated and can be optimized for peak absorption and scattering of light. The AuNRs have the ability to tune their absorption limit from 580 nm up to 1400 nm by using various manufacturing methods [39]. The tuning ability of nanorods helps them to scatter light across the visible and near IR region. The synthetic methods to prepare AuNRs reported are lithographic, template, catalytic, and seed-mediated synthesis [40]. AuNRs have a high electrochemical sensing ability due to their high sensitivity, conductivity, and selectivity. Au-nanorods
Chapter 13 Nanostructured complexes of gold(I) in sensing
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are utilized to improve in vivo imaging, and they are highly effective in nonlinear optics like four-wave mixing [41]. Rod-shaped AuNPs are reported as highly efficient in photothermal activity. The optical absorption window can be tuned across the IR region, which decreases the risk of damage of healthy tissues because of greater intensity of light [42,43] (Fig. 13.3). The AuNRs having high surface plasmon absorptive properties and light scattering capabilities are effective nanomaterials in diagnosis, therapeutics, and imaging. In sensing of different small molecules like H2O2 and HNO3, biomolecules like dopamine, NADH, glucose, DNA, enzymes, immunity-related substances, AuNRs showed improved electrical conductivity and sensitivity. In the near future, the AuNR-based electrode materials are considered for detection of biomolecules [45,46].
13.3.3
Nanoplates/nanosheets
The gold nanosheets in the 2D form are gaining attention in electrochemistry and production of various nanodevices. The gold nanosheets are mostly prepared in triangular and hexagonal shapes [47,48]. Gold-based nanoplates can be prepared by nanoprisms, for which surfactants are used. The concentration of surfactants is an important factor in the preparation of gold nanoprisms. The Au nanoplates in triangular and hexagonal shapes coexist in polymer- and surfactant-aided methods [49]. In organic electronic devices, the multilayered gold nanosheets are novel materials for fabrication of stretchable electrodes. The fcc and hcp domains are structurally present in gold nanosheets.
GBP-SpA
Antibody
CTAB-Capped Gold Nanorods
CTAB
Activated Carbon
Figure 13.3 Functionalization of AuNRs are useful for imaging and biological sensing [44].
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In sensing, these nanosheet-based sensors showed zero degradation and excellent properties. Au nanosheet-based sensors having high sensitivity, tuning capability, durability, and fabricating power have been reported as effective materials in detection of human activities [50] (Fig. 13.4).
13.3.4
Metal-coated gold nanostructures
The gold NPs could be synthesized as monodispersed, and this monodispersed nature of AuNPs make them an effective and supportive platform to coatings of noble metals palladium and platinum for catalytic activities [52]. The complete surface area of nanoparticles can be used if these are monodispersed, and this is helpful for catalysis. The reduced size and monodispersity of AuNPs create a surface area 10 times larger than the uncoated platinum and palladium nanomaterials and 1000 times larger than the materials in bulk [53] (Fig. 13.5). To prepare Pt/gold nanoporous film electrode material, the most easy and simple methodology is direct deposition of platinum on the gold nanoporous film electrochemically. The Pt/gold nanoporous film electrode exhibited the best catalytic activity and thus facilitated the electrochemical oxidation of methanol. In water splitting, gold-based electrodes are promising candidates in pholoelectrochemical catalytic reactions due to their mechanically stable surface and high hydrogen H2 evolution [54,55] (Fig. 13.6). For direct ethanol fuel cells, the palladium AuNPs prepared in mesophases showed high potential toward electrocatalytic oxidation of ethanol. They provided high stable reaction conditions. The core of the nanostructure consisted of gold materials, while the shell is made up of palladium metal [56] (Fig. 13.7). Au nanosheet multilayer film
Figure 13.4 The locomotion sensors based on Au nanosheets [51].
strain sensor
Chapter 13 Nanostructured complexes of gold(I) in sensing
Figure 13.5 Pt-coated gold nanostructure (left) and Pd-coated gold nanostructure (right).
Figure 13.6 Photoelectrochemical H2 evolution on the surface of a Pt(shell)/Au(core) electrocatalyst.
Figure 13.7 Transmission electron microscopy images of Pd(shell)/Au(core) nanostructures.
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13.3.5
Functionalized gold nanoparticles
To achieve the selectivity of the analyte, nanoparticles could be functionalized properly. The functionalized nanoparticles have been developed in past few decades, which were applied in various fields of physics, chemistry, pharmacy, and biology. Functionalized AuNPs have attracted attention as a potential candidate to deliver payloads into the targeted material to transport and release the drug material [57]. AuNPs proved to be effective owing to their fantastic chemical and physical properties. The important features of AuNPs are as follows: 1. The gold-based core is nontoxic and inert 2. Monodispersed AuNPs range from 1 to 150 nm and can easily be prepared by different methodologies 3. Multifunctional AuNPs are created by thiol linkages 4. Drug delivery at remote places due to greater photophysical properties The AuNPs having different core sizes can be easily prepared by the reduction methods of salts of gold. The stabilizing agent is used, which prevents agglomeration. Functionalized AuNPs having unique properties like controlled drug release, dimensions, and tunable surface are very attractive materials for use in drug delivery [58].
13.4
Applications
AuNPs’ magnetic, catalytic, electronic, biocompatibility, and optical properties make them extensively studied materials in the field of imaging, electronics, diagnosis, energy conversion, and storage and sensing among different materials, as shown in Fig. 13.8.
13.4.1
Gold nanoparticles in sensing
AuNPs have been used as sensing materials to detect and determine different types of analytes by adopting different sensing strategies. The substances like anions, biomolecules like proteins, nucleotides, toxins, and saccharides, and metal ions can be detected by using AuNPs. The use of AuNPs in in vivo DNA and photothermal therapies has been reported, where these particles uptake the drug cytosomally [60]. The ionic strength, hydrophobic/hydrophilic nature, and morphology of these particles are key factors of focus for sensing. The use of nanostructured gold electrodes for sensing
Chapter 13 Nanostructured complexes of gold(I) in sensing
237
Drug delivery
Targeting Toxic removal
Bacteria removal
Separation 3 2.5
2
2
Sensing
3 2.5
1.5 1
1.5 1 0.5
0.5
0
0 0
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Ketonazole drug analysis
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0
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Promazine drug analysis
Figure 13.8 Illustrated representation of gold nanoparticles applicable in sensing, targeting, drug delivery, and separation of various molecules [59].
purposes as compared to macrostructured electrodes has several advantages like • High surface area • Enhanced mass transport • Low solution resistance • Low detection limits • Improved signal-to-noise ratio • High selectivity and sensitivity • Larger biocompatibility The quantitative detection of the analyte can be achieved by developing gold-based multichannel assays and biosensors. As
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biosensors, the antigens and protein are detected by using AuNP-based sandwiched-type assay for immunosensing. By adopting Au-based sandwiched assay, the surface enhances on the immunocomplexes, which make them more sensitive toward electrochemical detection. In electrochemical sensing, the surface of the electrode can be modified by the AuNPs, which have proved to be very effective in sensing of a wide class of materials. To detect water vapors in volatile compounds, thiol-based functionalized AuNPs are reported. Recently, gold nanosheets based on patchable strains are used as sensors. The human activities can be monitored by the movement of muscles during the motion of humans due to AuNPs, which potentially measure strains on skin. This is a big step in science and technology. Further, AuNPs are used in colorimetric and fluorescent sensing of DNA [61].
13.4.2
Gold nanostructures in biomedical applications
The use of AuNP-based electrodes in biomedical applications for biomolecules has been studied, where AuNPs act as biosensors, bioassays, active drug carriers, and so forth [62 64]. The AuNPs having a very small size of about 2 nm exhibit outstanding antimicrobial activities. The AuNPs absorb light when exposed to radiations, and they undergo electronic excitations and generate heat energy, which make them antibacterial and anticancer agents. The tuning of size and shapes of colloidal AuNPs attracted a lot of attention in the field of cancer therapy. In tissue imaging, AuNPs are used at the nanoscale level. The healthy cancer cells can be characterized by using AuNPs because of their light scattering nature. The AuNPs capped with different biomolecules like 2-deoxy-D-glucose and citrates are used in theranostic applications [65]. Au-based lateral flow assay represented greater selectivity for the IgM antigen detection against COVID-19 having no interference from other viruses. The GNP-LF assay proved to be a very effective method for the diagnosis of COVID-19 in hospitals [66]. Thus, the AuNPs are a promising candidate for diagnosis, imaging, therapies, and drug delivery in the future.
13.4.3
Gold nanostructures in metal detection
The sensing of metals in various media by using AuNPs is an emerging field in research. The electrochemical detections of
Chapter 13 Nanostructured complexes of gold(I) in sensing
various substances like mercury, copper, arsenic, and lead on the surface of a gold-based electrode material have been reported. The human health and ecosystem are at great risk due to contaminations caused by the presence of heavy metals like cadmium, arsenic, mercury, and lead. In environmental analysis, the detection of metals at low concentration is a necessary task. Using the DNA-Au-based nanoparticles is a well-recognized approach, where the AuNP interface is used between the target metal and DNA via colorimetric signals [67] The toxic materials like H2O2 and pesticides can be detected by the AuNP electrodes.
13.5
Future perspectives
The electrochemical sensing can be improved in the aspects of stability, sensitivity, accuracy, and detection limits by using AuNP-based sensors. To design AuNPs electrochemical sensors, developmental and optimization methods are used. The biosynthesis must be adopted to prepare gold nanostructures in the coming years. It is implicated that the electrochemical sensors should be nanostructure-based, and the optimized combination of gold and other nanoparticles should be adopted to synthesize these sensors. The selectivity of nanostructures will be a main focus area for each type of analyte. The AuNP-based electrochemical sensors can be considered as an optimized and alternative approach for environmental analysis and biomedical applications in the future. These adoptions can be significant in qualifying the life and survival rate.
13.6
Conclusion
The AuNPs are being substantially studied in the fields of nanotechnology, electronics, biomedical, biological, and environmental analysis. There are various types of AuNPs, and their applications are expanded from bulk to atomic level. Now, the single AuNPs are utilized in industrial and laboratory levels for research purposes. The enhanced surface reactivity and photothermal characteristic properties of gold materials are actively applied and studied. The different sizes and shapes of AuNPs with enhanced surface properties have attracted the research scientists. The benefit of using AuNPs is that they can be used in pure and composite forms, where these are combined with other materials like CNTs, metals, biomolecules, and so forth. The gold-based sensors are used to detect different types of
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molecules because of their high sensitivity, biocompatibility, selectivity, and low detection limit. This chapter summarizes the characteristic properties of AuNPs, and recent studies reported their size and morphologies and their synthetic methodologies as well as their applications. An overview of different synthetic approaches to obtain AuNPs of different shapes, surfaces, and structures is provided. The optical properties for sensing and imaging applications showing these properties are reviewed here. The superstructure of AuNPs for various applications is described. The chemical and physical properties of AuNPs are related to their shape, nanosize, and surface, which can be tuned to get the desired parameters. To optimize the desired physiochemical properties of AuNPs selective for a defined application, the synthesis approach and stabilizing agents should be selected crucially. Various procedural methods have been designed for the synthesis of various types of AuNPs with different morphologies and structures. Although AuNPs have fascinating sizes, shapes, and surfaces, there is still growing research related to the best size and shape-controlled synthetic approach to get monodispersed and well-assembled AuNPs into suitable functional architectures, which is still an interesting challenge.
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Chapter 13 Nanostructured complexes of gold(I) in sensing
[10] J.-W. Park, J.S. Shumaker-Parry, Structural study of citrate layers on gold nanoparticles: role of intermolecular interactions in stabilizing nanoparticles, J. Am. Chem. Soc. 136 (5) (2014) 1907 1921. [11] M.K. Corbierre, et al., Polymer-stabilized gold nanoparticles and their incorporation into polymer matrices, J. Am. Chem. Soc. 123 (42) (2001) 10411 10412. [12] N. Elahi, M. Kamali, M.H.J.T. Baghersad, Recent biomedical applications of gold nanoparticles: a review. 2018, 184, pp. 537 556. [13] S.A. Bansal, et al., Role of gold nanoparticles in advanced biomedical applications. 2020, 2(9): pp. 3764 3787. [14] N. German, A. Ramanavicius, A. Ramanaviciene, Electrochemical deposition of gold nanoparticles on graphite rod for glucose biosensing, Sens. Actuators B: Chem. 203 (2014) 25 34. [15] X. Huang, M.A. El-Sayed, Gold nanoparticles: optical properties and implementations in cancer diagnosis and photothermal therapy, J. Adv. Res. 1 (1) (2010) 13 28. [16] B. Khlebtsov, et al., Optical amplification of photothermal therapy with gold nanoparticles and nanoclusters, Nanotechnology 17 (20) (2006) 5167. [17] S.I. Stoeva, et al., Face-centered cubic and hexagonal closed-packed nanocrystal superlattices of gold nanoparticles prepared by different methods, J. Phys. Chem. B 107 (30) (2003) 7441 7448. [18] S.A. Aromal, D. Philip, Green synthesis of gold nanoparticles using Trigonella foenum-graecum and its size-dependent catalytic activity, Spectrochim. Acta Part. A: Mol. Biomol. Spectrosc. 97 (2012) 1 5. [19] S.P. Dubey, M. Lahtinen, M. Sillanpa¨a¨, Green synthesis and characterizations of silver and gold nanoparticles using leaf extract of Rosa rugosa, Colloids Surf. A: Physicochem. Eng. Asp. 364 (1 3) (2010) 34 41. [20] P. Khashayar, et al., Fabrication and verification of conjugated AuNPantibody nanoprobe for sensitivity improvement in electrochemical biosensors, Sci. Rep. 7 (1) (2017) 1 8. [21] G. Ruiz, et al., Antibodies irreversibly adsorb to gold nanoparticles and resist displacement by common blood proteins, Langmuir 35 (32) (2019) 10601 10609. [22] M. Khan, et al., Electro-oxidation of ammonia at novel Ag2O 2 PrO2/γ-Al2O3, Catalysts. 11 (2) (2021) 257. [23] S. Khan, et al., Electro-oxidation of ammonia over copper oxide impregnated γ-Al2O3 Nanocatalysts. 2021, 11(3): p. 313. [24] S. Alex, A. Tiwari, Functionalized gold nanoparticles: synthesis, properties and applications—a review, J. Nanosci. Nanotechnol. 15 (3) (2015) 1869 1894. [25] R.K. Das, et al., The synthesis of gold nanoparticles using Amaranthus spinosus leaf extract and study of their optical properties. 2012. [26] Y. Zeng, et al., Lipid-AuNPs@ PDA nanohybrid for MRI/CT imaging and photothermal therapy of hepatocellular carcinoma, ACS Appl. Mater. Interfaces 6 (16) (2014) 14266 14277. [27] B. Aydogan, et al., AuNP-DG: deoxyglucose-labeled gold nanoparticles as X-ray computed tomography contrast agents for cancer imaging, Mol. Imaging Biol. 12 (5) (2010) 463 467. [28] M. Fa, et al., The effect of AuNP modification on the antioxidant activity of CeO2 nanomaterials with different morphologies, Appl. Surf. Sci. 457 (2018) 352 359. [29] R. Bleach, et al., In situ formation of polymer gold composite nanoparticles with tunable morphologies, ACS Macro Lett. 3 (7) (2014) 591 596.
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[30] M. Nakagawa, T. Kawai, Chirality-controlled syntheses of double-helical Au nanowires, J. Am. Chem. Soc. 140 (15) (2018) 4991 4994. [31] Z. Lin, et al., Ternary heterogeneous Pt Ni Au nanowires with enhanced activity and stability for PEMFCs, Chem. Commun. 56 (31) (2020) 4276 4279. [32] U. Gomes, et al., Controlling the diameter distribution and density of InAs nanowires grown by Au-assisted methods, Semicond. Sci. Technol. 30 (11) (2015) 115012. [33] Q. Xue, et al., Au nanowires@ Pd-polyethylenimine nanohybrids as highly active and methanol-tolerant electrocatalysts toward oxygen reduction reaction in alkaline media. ACS, Catalysis 8 (12) (2018) 11287 11295. [34] E. Carbonell-Sanroma, et al., Electronic properties of substitutionally boron-doped graphene nanoribbons on a Au (111) surface., J. Phys. Chem. C. 122 (28) (2018) 16092 16099. [35] K. Dawson, M. Baudequin, A. O’Riordan, Single on-chip gold nanowires for electrochemical biosensing of glucose, Analyst 136 (21) (2011) 4507 4513. [36] Q. Zhai, et al., Vertical gold nanowires stretchable electrochemical electrodes, Anal. Chem. 90 (22) (2018) 13498 13505. [37] L. Scarabelli, et al., A “Tips And Tricks” Practical Guide to the Synthesis of Gold Nanorods, ACS Publications, 2015. [38] Q. Zhang, et al., Facet control of gold nanorods, ACS Nano 10 (2) (2016) 2960 2974. [39] G. Zheng, et al., Tuning the morphology and chiroptical properties of discrete gold nanorods with amino acids, Angew. Chem. Int. Ed. 57 (50) (2018) 16452 16457. [40] C. Ferna´ndez-Lo´pez, et al., Gold nanorod pnipam hybrids with reversible plasmon coupling: synthesis, modeling, and sers properties, ACS Appl. Mater. Interfaces 7 (23) (2015) 12530 12538. [41] S. Zheng, et al., Gold nanorod integrated electrochemical sensing for hyperglycaemia on interdigitated electrode. BioMed Res. Int. 2019. [42] J.B. Vines, et al., Gold nanoparticles for photothermal cancer therapy, Front. Chem. 7 (2019) 167. [43] R.S. Riley, E.S. Day, Gold nanoparticle-mediated photothermal therapy: applications and opportunities for multimodal cancer treatment, Wiley Interdisciplinary Reviews: Nanomedicine and Nanobiotechnology 9 (4) (2017) e1449. [44] W.M. Park, et al., Facile functionalization of colloidal gold nanorods by the specific binding of an engineered protein that is preferred over CTAB bilayers. 2013, 78 (1): pp. 48 51. [45] E. Grueso, et al., Reversible cationic gemini surfactant-induced aggregation of anionic gold nanoparticles for sensing biomolecules, Colloids Surf. A: Physicochem. Eng. Asp. 610 (2021) 125893. [46] B. Thirumalraj, et al., Highly stable biomolecule supported by gold nanoparticles/graphene nanocomposite as a sensing platform for H2O2 biosensor application, J. Mater. Chem. B 4 (38) (2016) 6335 6343. [47] S. Ye, et al., Sub-nanometer thick gold nanosheets as highly efficient catalysts, Adv. Sci. 6 (21) (2019) 1900911. [48] Q.-L. Zhang, et al., A glassy carbon electrode modified with porous gold nanosheets for simultaneous determination of dopamine and acetaminophen, Microchim. Acta 182 (3 4) (2015) 589 595. [49] M.-M. Chen, et al., Spatiotemporal imaging of electrocatalytic activity on single 2D gold nanoplates via electrogenerated chemiluminescence microscopy, Chem. Sci. 10 (15) (2019) 4141 4147.
Chapter 13 Nanostructured complexes of gold(I) in sensing
[50] R. Ahmad, et al., One-step synthesis and decoration of nickel oxide nanosheets with gold nanoparticles by reduction method for hydrazine sensing application, Sens. Actuators B: Chem. 286 (2019) 139 147. [51] G.-H. Lim, N.-E. Lee, B. Lim, Highly sensitive, tunable, and durable gold nanosheet strain sensors for human motion detection, J. Mater. Chem. C. 4 (24) (2016) 5642 5647. [52] B. Qiao, et al., Preparation of highly effective ferric hydroxide supported noble metal catalysts for CO oxidations: from gold to palladium, J. Catal. 261 (2) (2009) 241 244. [53] X. Zhang, Gold nanoparticles: recent advances in the biomedical applications, Cell Biochem. Biophys. 72 (3) (2015) 771 775. [54] B. Tian, et al., UV-driven overall water splitting using unsupported gold nanoparticles as photocatalysts, Chem. Commun. 54 (15) (2018) 1845 1848. [55] R.-B. Wei, et al., Plasmon-enhanced photoelectrochemical water splitting on gold nanoparticle decorated ZnO/CdS nanotube arrays, ACS Sustain. Chem. Eng. 5 (5) (2017) 4249 4257. [56] R.S. Moakhar, et al., Enhancement in solar driven water splitting by Au Pd nanoparticle decoration of electrochemically grown ZnO nanorods, J. Appl. Electrochem. 46 (8) (2016) 819 827. [57] S. Thambiraj, S. Hema, D.R. Shankaran, Functionalized gold nanoparticles for drug delivery applications, Mater. Today: Proc. 5 (8) (2018) 16763 16773. [58] A. Umapathi, et al., Curcumin and isonicotinic acid hydrazide functionalized gold nanoparticles for selective anticancer action, Colloids Surf. A: Physicochem. Eng. Asp. 607 (2020) 125484. [59] K. Alaqad, T.A.J.J.E.A.T. Saleh, Gold and silver nanoparticles: synthesis methods, characterization routes and applications towards drugs. 2016, 6(4): pp.525 2161. [60] F.-Y. Kong, et al., Unique roles of gold nanoparticles in drug delivery, targeting and imaging applications, Molecules 22 (9) (2017) 1445. [61] P.-J.J. Huang, et al., Good’s buffers have various affinities to gold nanoparticles regulating fluorescent and colorimetric DNA sensing. 2020, 11(26): pp.6795 6804. [62] R.A. Barmin, et al., Air-filled bubbles stabilized by gold nanoparticle/ photodynamic dye hybrid structures for, theranostics. 11 (2) (2021) 415. [63] J. Wu, et al., Gold nanoparticle layer: a versatile nanostructured platform for biomedical applications. 2018, 2(12): pp. 2175 2190. [64] J. Liu, Q.J.Ab Peng, Protein-gold nanoparticle interactions and their possible impact on biomedical applications. 2017, 55: pp.13 27. [65] S. Suvarna, et al., Synthesis of a novel glucose capped gold nanoparticle as a better theranostic candidate. 2017, 12(6): p.e0178202. [66] C. Huang, et al., Rapid detection of IgM antibodies against the SARS-CoV-2 virus via colloidal gold nanoparticle-based lateral-flow assay. 2020, 5(21): pp.12550 12556. [67] Z. He, et al., Interfacing DNA with gold nanoparticles for heavy metal detection. 2020, 10(11): p.167.
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14 Analyte sensing by self-healing materials M. Ramesh1, L. Rajeshkumar 2, D. Balaji 2 and S. Sivalingam3 1
Department of Mechanical Engineering, KIT-Kalaignarkarunanidhi Institute of Technology, Coimbatore, Tamil Nadu, India 2Department of Mechanical Engineering, KPR Institute of Engineering and Technology, Coimbatore, Tamil Nadu, India 3Department of Mechanical Engineering, Coimbatore Institute of Technology, Coimbatore, Tamil Nadu, India
14.1
Introduction
A sensor requires the parallel revealing of more than one analytes which is considered to be one of its desirable feature. Recently, the volammetric analysis’ capability of detecting different compounds with sensitivity, selectivity, and rapidity has been explored. Recent development in biosensors proves the abovementioned fact. Current day researches can concurrently quantify various compounds such as catecholamines, uric acid, and ascorbic acid, which are chemically distinct and physiologically alike [1 3]. Many researchers reported the importance of manufacturing various ranges of sensors, which are capable of multiple analyte sensing and could explore many nanomaterials such as carbon nanotubes (CNTs) [4 6], metallic nanoparticles [7], and nanopolymer composites [8,9]. Electronic tongue is a measuring instrument known for its chemical sensor array which is cross-sensitive and partially specific upon detection of various compounds by the use of a suitable pattern of compound identification and multiple analyte sensing capability. These instruments are capable of segregating the composition of complex liquids and gases in a quantitative manner. Food and beverage industries and pharmaceuticals sector [10] have a lot of scope for the application of these sensors; they can be employed in determining the stability of medicines with respect to their taste, quantification of formulation for taste masking in foods [11], analysis in beverage flavor ageing, and quantification of dissolved bitterness in compounds.
Nanomaterials-Based Electrochemical Sensors: Properties, Applications, and Recent Advances. DOI: https://doi.org/10.1016/B978-0-12-822512-7.00015-6. © 2024 Elsevier Inc. All rights reserved.
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Researches in electronic noses have been very high recently due to their cheap and rapid processing in sensing as far as the industrial applications are concerned [12]. Few researchers developed an electrode made of poly (3, 4-ethylendioxythiophene) and infiltrated that in an electronic tongue. For classification of red wine originated in various regions and its calibration of purity, these sensors were employed. Data acquired from the voltammetric readings were utilized when comparing these data with conventional ones and also for categorizing the type of wine available by processing them according to the partial least squares technique, while the quantity of each parameter and the data about the type and origin were taken as the base. Based on the threshold limit data of total polyphenols, sulfur dioxide and color intensity were obtained at a rapid pace from the tongue, and it can also be used in quality checking of the red wine. Similar analysis was performed by various authors aimed at developing sensors for the categorization of white and red wines [13,14]. Such sensors comprised a microelectrode for capturing oxygen demand electrochemically, ion-sensitive field effect transistor sensor, gold microelectrode, amperometric electrodes, redox potential sensor, and conductivity-measuring sensor. Such an instrument has enough potential to categorize wines based on the type of grape used and even their origin based on geographical data. Multianalyte sensing capability of these sensors was also showcased by making them sense the distinction between mixed wines and monovariety wines. Such capability of the sensor can be effectively utilized in many industrial applications and has got a wider scope of other applications too. Few trials were conducted to unveil the application of a transdermal analyte sensing device. This device majorly comprises a cartridge contact to pass on the electric current, sensor cartridge with a porous membrane to receive an analyte transdermally from the liquid, an electrode to generate electric current with respect to the byproduct concentration, another fluid reservoir with a liquid to receive the target analyte, and an enzyme for converting the target analyte into a byproduct for further analysis. It also consists of a transmitter for transmitting the electric signals received to a monitor, a peripheral electrical device in electrical contact with the cartridge electrical contact, and a cartridge receptacle to receive the cartridge sensor and to place the membrane over the contact skin. Many studies on the analyte sensing devices for the measurement of pH and other analytes were performed in various categories, specifically in a hand compact device [15,16].
Chapter 14 Analyte sensing by self-healing materials
In a few researches, a photonic crystal fiber (PCF) sensor, which has the capability of rendering low confinement loss and high birefringence, was used for the analyte sensing of liquids. Two distinct types of PCF materials, with elliptical air holes in the core of the material, such as horizontal PCF and vertical PCF, are designed and used. These holed PCF sensors were measured for their confinement loss, modal birefringence, refractive index, and sensitivity by means of the full vectorial finite element method of simulation. From the results of these theoretical simulations, it was determined that the PCF materials exhibited enhanced birefringence and sensitivity along with less confinement loss when compared with other analyte sensors [17]. Self-healing is an inherent ability of various life forms such as vertebrates [18,19] and invertebrates [20 22], like sandcastle worm and mussels and plants [23 25]. In addition to the self-healing ability of life forms including humans and animals, sensing in various forms could be found in sense organs. For instance, animals and humans have skin for sensing temperature and pressure, tongue to sense the taste, and nose to sense odor [26]. The merits of coupled selfhealing ability with sensing in various organisms include the autonomy of working, reliability, longevity of use, repairing capability, durability, continuity, and safety of the life form. It was nearly 2000 years back when the first ever human-made self-healing material was produced [27]. The material comprises a cementite material as a matrix reinforced with stratlingite crystals, calcium-aluminum-silicate binder, and calcium-aluminosilicate mineral in different suitable proportions in the interface region. This material works because of the in-situ growth of stratlingite crystals by crystallization for healing of a crack. The working mechanism of self-healing is due to the reaction between the alkali-rich compounds and the lime present in the calcite. Several researchers performed various experiments after the abovementioned experiments for duplicating the self-healing material production for its usage in concretes and composites by means of various mechanisms such as hydration that forms mineral byproducts within the cracks [28 30], interaction between calcium lactate and bacterial spores [31,32], and release of polymeric elements from capsules for filling the formed cracks [33,34]. Yet, the concept of self-healing could not be applied, as it is for the metallic elements but with an external stimulus as the melting point of metals is high [35 38], and so, the metals are not inherently self-healing materials. Hence, materials can be classified into those that are self-healing without the necessity of an external stimulus but healing would be induced at ambient conditions and those that are healable by
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applying an external stimulus either by thermal or electrical energy. In spite of such classifications, self-healing materials are highly researched and used in various applications, as they avoid damage to the host material and can work autonomously with an external or internal stimulus. Moreover, polymers have a greater advantage than the inorganic or metallic elements, as they are delicate in nature and are soft. This is the major reason why the polymeric materials dominate the self-healing materials community [39,40] and could be broadly classified into intrinsic and extrinsic self-healing polymeric materials.
14.2
Self-healing materials for analyte sensing
An outline of various self-healing materials, both polymers and composites, along with a few specifications about the necessity of the material in the area of analyte sensing has been discussed in the earlier part of the chapter. Usually, the sensing materials have two major features: one is the ability of the material to detect the target analytes with the help of the functional groups present in them by differentiating whether the analyte is responsible for self-healing or not. The other feature is that analyte sensing self-healing materials may stick well onto the transducer surface. Adherence plays a major role in sensors used in flow and under liquid conditions, where the failure of a top active layer may frequently occur [41]. One more important feature of an analyte sensor is that it should possess the ability to convert the chemical signals from the transducer into physical signals, which in turn require few supplementary characteristics for the self-healing materials such as fluorescence, color, and electrical conductivity. Based on the abovementioned facts, analyte sensing self-healing materials are widely classified into two categories: analyte-responsive polymers and analyte-responsive composites.
14.2.1
Analyte-responsive polymers
The basic function of an analyte sensing self-healing material includes three actions: self-healing, analyte detection, and signal transduction. These functions often demand the polymerization function along with chemical elements at nanoscale, which develops the ability to undergo the abovementioned mechanisms. Some of the commonly used functional groups for inducing the polymerization of self-healing polymers includes
Chapter 14 Analyte sensing by self-healing materials
sulfonate group, pyridyl-dithiadiazole, and N-(4-picolyl)-1,8naphthalimide [42 44]. π π interaction facilitates self-healing of these materials through the aromatic rings of the first two functional groups [45,46]. Meanwhile, acidic analytes were majorly detected by an active proton acceptor called pyridine moiety, which is a capable chemical sensor for this task [47]. With the help of nonpolar solvents such as hexane, decane, or cyclohexane, the first two polymer functional groups can be converted into self-healing organogels as per the results of few experiments [42,43]. This becomes possible as the long alkyl chain affinity [42] or nonpolar solvents’ cholesterol formation [43] backed the self-healability to some extent, thereby decreasing the transition temperature (Tg) of the organogels. Normally, the self-healing gels undergo reversible reaction at a faster rate of less than 3 min, but they are naturally soft materials with lower strain during breakage. These materials possess fluorescence at various wavelengths and so the spectrum of fluorescence is tailorable according to the requirement. For example, N-(4- picolyl)-1,8-naphthalimide emits yellow light for alkanes and green light for cycloalkanes, which are material-specific, whereas pyridyl-dithiadiazole-functionalized organogels emit blue light for all materials [42,43]. Few elements exhibit the inherent applicability for a specific function, for example, for signal transduction, 2,4,6-trinitrophenol, HCl, or trifluoroacetic acid could be used when the mechanism between acid group of analytes and pyridyl group of self-healing materials may take place. Incidentally, the organogel-based analyte sensing becomes reversible when triethyl amine is used for the neutralization of proton-rich organogels back to its extremely fluorescent form. In spite of all the abovementioned points, the analyte limit of detection (LOD) is very low, and specifically, it took more than an hour for the analyte sensing of acidic gases owing to its bulk gel form. Few experiments focused on trying to manufacture a hydrogel and making the hydrophilic sulfonate group of poly (2-acrylamido2-methyl-1-propanesulfonic acid, PAMPSA) to behave as a self-healing material induced through the coordination of lanthanide ions [44]. The resulting hydrogel was found to be self-healing with luminescent characteristics and possessed low efficiency of self-healing. Fig. 14.1 depicts the PAMPSA hydrogel along with its luminescence property. It was also noted that the material could get only about 29% of its original ability of elongation at break after being healed, which was due to the poor reversibility of coordination between lanthanide-sulfonate ions at neutral pH values.
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Ammonia vapor
ON
(A) Eu(tta)3@PAMSPA- NH3
(B)
Treatment with ammonia vapor Tb(sal)3.2H2O Eu(tta)3.2H2O
Tb(sal)3@PAMSPA- NH3
OFF Adding n
O HO
O CH2
C CH
S
HO N n
N O H S
CH
CH2
C
O
Eu (III) / Tb (III) - complexes
Eu(tta)3 / Tb(sal)3@PAMPSA- NH3
OH
O
PAMPSA Figure 14.1 (A) Fabrication process and (B) luminescence of the NH3-doped self-healing lanthanide-PAMPSA hydrogels [43].
The same hydrogels, when required to be used for luminescent analyte sensing of HCl, need to be triggered with ammonia vapor in order to develop a complex coordination between the PAMPSA sulfonate groups and lanthanide ions, and in doing so, the hydrogel emits red and green light upon sensing, as shown in Fig. 14.1. Since the lanthanide ions of europium (Eu) and terbium (Tb) had many chemical similarities, they complement each other by acting as self-healing materials themselves. Yet, the hydrogels experienced reduced luminescence when made to sense the HCl gas rather than liquid. Those hydrogels were also characterized by few demerits like the necessity of a separate fluorescence detector, low sensitivity, high cost of practical application, requirement of a UV inducer, and so on. Hence, the need for sensors made of self-healing thin-film materials and sensors with better convenience are the order of the day. For instance, a self-healing material made of poly (2-hydroxypropyl methacrylate)/poly (ethyleneimine) (PHPMA/PEI) assortment was used as a dielectric insulating layer in an organic fieldeffect transistor (OFET), which is flexible and printable [48]. A low-cost and eco-friendly solution of ethanol is used for the preparation of the abovementioned dielectric layer by singlecomponent chemistry. This layer allows for a greater change in drain current because of the presence of the semiconductor poly(3-hexylthiophene) (P3HT), and it also works at low voltage, allowing for the diffusion of ammonia into it easily owing to the
Chapter 14 Analyte sensing by self-healing materials
high polarity of the layer. This results in the sensing of ammonia by the OFET sensor even up to a level of 0.5 ppm. Self-healing of PHPMA/PEI could be effectively induced by the formation of the hydrogen bond within the functional groups upon the polymer chains. This combination renders low Tg for the material blend, and the polymer chain turns dynamic so that the induction of hydrogen bond creation is enhanced at room temperatures for kindling the self-healing ability. The PHPMA/PEI polymer, at a ratio of 1:1, was tested for its scratch resistance through a thickness of 10 11 microns by heating the materials at a temperature of 50 C for 10 min, and it was found that they possess a better self-healing ability. After being healed at room temperature in air for about 10 h, the OFET sensor exhibited better recovery of drain current, mobility, and also enhanced behavior of a transistor even at lower gate voltages. Nevertheless, the P3HT layer of the semiconductor could not be considered as a self-healable material, while the dielectric layer of PHPMA/PEI layer could behave as self-healing material. Hence, the OFET sensor containing the abovementioned layers could be concluded as a partially self-healing analyte sensor. The gelatin gelatin pair functionalized by glucose-oxidase contains the self-healing ability of a material in a simple on-off function [49]. This pair experiences self-healing through breaking and reformation of physical and chemical bonds of triple helix and Schiff base, respectively, at 37 C and 23 C, respectively. This mechanism could control the on-off state sensing for a glucose biosensor through the abovementioned temperature-dependent process. When the GOx sensing of glucose in the analyte solution at an LOD of 0.2 mM is carried out between two electrodes, then it is stated as the on state. This sensing process possesses benefits like reversible self-healing process, autonomous sensing, and the occurrence of self-healing at a lower temperature in the order of 22 C and few limitations like high temperature operation, which is mostly uncommon in self-healing materials. In addition to the abovementioned capabilities, the gelbased materials can undergo reversible swelling and shrinkage and they could be apparently used for humidity sensing through a volume actuator [50,51]. Like the OFET sensor stated above, the GOx sensor is also a partially self-healable sensor, as it fails to behave as a healable material if the gel electrode undergoes damage instead of the GOx/gel interface. Many primeval researches state that the self-healing polymers, which could act as bulk sensors such as organogels or partial sensors such as dielectric layers, possess few demerits such as nonhealing sensing layer or less analyte sensitivity. Such shortcomings
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could be overcome by manufacturing the self-healing polymer sensors using functional fillers and converting them into selfhealing composites.
14.2.2
Analyte-responsive hydrogels
Sensing devices should be comprised of elements for signal detection and molecular identification. Particularly, when a communication, by any means, is established between the ligand and the receptor, it results in signal detection and hence an electrochemical or optical output is obtained. Epitomic sensors are characterized by low cost, environmental stability, low LOD, and high sensitivity. The following section deals with a few classical examples of analyte sensing hydrogels used in conventional applications.
14.2.2.1
Recognitive and molecularly imprinted polymers for sensing
Detection of molecules in synthetic hydrogels can be accomplished by adding inductive molecules or by molecular imprinting onto the substrate sensing materials. Such molecular imprints are easy to manufacture, sturdy, inexpensive, and readily incorporated into the sensors. Such imprints when used in analyte sensing may undergo deswelling or swelling, which is normally utilized for signal transduction. When such swelling or deswelling occurs, the volume and refractive index of the hydrogel undergoes changes. When these sensitive imprints are used in self-healing hydrogels for analyte sensing, signal transduction easily occurs by binding of analytes with the imprints. In photonic crystals, lattice spacing between the colloidal arrays governs the specious color and diffraction wavelength. Consequently, increase or decrease of lattice spacing of colloidal arrays is dependent upon the swelling or deswelling during the analyte binding, respectively, which in turn is responsible for the color change. Many researchers used the abovementioned fact for analyte sensing of various categories [52]. Many analytes such as metal cations [53] and small molecular structures such as glucose [54] and concanavalin proteins [55] were detected by means of functional hydrogels incorporated with the functional groups through polymerization reaction. Fig. 14.2 depicts the scanning electron microscopy (SEM) images of photonic polystyrene nanoparticles in a colloidal array in the deswelled (Fig. 14.2) and swelled (Fig. 14.2B) condition. Fig. 14.2C denotes the diffraction wavelength of the nanoparticles, while the inset
Chapter 14 Analyte sensing by self-healing materials
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Figure 14.2 SEM images of polystyrene nanoparticles: (A) a close-packed; (B) a non-close-packed; (C) diffraction spectra of 2D mannose hydrogel sensors [55].
photograph shows the color change due to the addition of concanavalin molecules. By the same way, hydrogels can be made in spherical arrays as said earlier and can then be used to extract spherical voids termed as inverse opal [56]. Such inverse opals can be readily employed for macromolecular detection since the analyte can flow into a sensor easily through large pores [57]. Few special analytes such as bovine serum albumin and tetracycline [58,59] can be sensed by coupling the molecular imprinting technology with the inverse opal concept. The refractive index of the hydrogel also changes because of the water absorption of release from the swelling or deswelling, induced by the analyte as stated above. Such a refractive index change can be detected by means of surface plasmon resonance (SPR) using the sensing methods. Specifically, a strong light absorption is experienced by gold nanoparticles at certain wavelengths, thus resulting in localized SPR. Such light absorption by the nanoparticles solely depends on their local refractive index, shape, and size. Few experimenters tried to develop a glucose sensor based on the refractive index sensitivity of the materials [60]. Trials were made to blend the phenyboronic acid hydrogel with gold nanoantennas that had undergone reversible swelling when it establishes a bond with the glucose. Decrease of the refractive index resulted in the blue shift of the wavelength as a result of swelling of hydrogel and binding of glucose. Such changes were used to identify the changes in glucose concentration physiologically. In some cases, recognitive polymers
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were employed not only for molecular recognition and signal transduction in sensors, but also for concentrating or segregating the analyte molecules before sensing them. Few cases were reported on segregating hemoglobin, a protein serum in human blood, by using molecular imprinted cryogels [61]. By segregating the surplus proteins from a target analyte, scarcely available biomarkers can be easily detected by the imprinted hydrogels. As an alternative means, few laboratory experiments tried to deploy a “nanotrap,” which segregated the outer surface of a biomarker for lymeborreliosis called borrelia. This method of preconcentration can be employed to improve the immunoassay sensitivity.
14.2.2.2
Biomolecule-containing hydrogels for sensing
When the target analytes do not have a binding partner and if the sensing application is of low cost, molecularly imprinted and recognitive polymers can be used as analyte sensors. In contrast, the biomolecule containing hydrogels are costly but can be used for accurate analyte sensing as they sense with engrained molecular recognition characteristics. These sensing materials primarily focus on enhancing the LOD of the sensor by properly approaching the signal transduction and exploring it deeply. One such attempt of visually detecting the target DNA was made by few researchers with the help of hydrogels containing DNA and colloidal gold. Particularly, the red color of the gold nanoparticle was sensitive to the target DNA when sensing even at a lowest concentration of 100 pM. The detection limit of the sensor can further be enhanced by increasing the ability of colloidal gold in silver reduction. This resulted in lowering the LOD of hydrogel to about 1 pM and ending up with black color of the hydrogel as a result of silver reduction [62]. A high affinity aptamer for detection of mercury was then fabricated by a few researchers with the hydrogel comprising of microparticles and used it with the approach of fluorescence-based sensing. Such aptamer-containing microparticle-incorporated hydrogels facilitated a rapid detection within 2 min, while the conventional hydrogels rendered a detection time of 60 min. The LOD of the sensors was also enhanced to 10 nM, while the classical aptamers had an LOD of 500 nM. Besides, experimenters found that a microarray for mercury detection can be engendered by spotting, drying, and rehydrating the hydrogel microparticles in a glass slide [63]. Many researchers prepared molecular imprints with the aid of methacrylated or acrylated aptamers combined with macromolecules. In order to have a low-cost imprint, instead of using a full
Chapter 14 Analyte sensing by self-healing materials
length costly aptamer, authors tried to use only two or three fragments of adenosine aptamers. These fragments of aptamers were restrained nearer to each other by polymerization of methacrylated aptamer fragments with adenosine as a catalyst, so that after some time, they would cause fluorescence quenching by reforming. Sensitivity toward the analyte could considerably be increased by the imprinting of aptamer fragments over the polymers when compared with the nonimprinted fragments. Biomolecules can render precise spacing in between the arrays of molecules during sensing and better self-healing apart from their default molecular detection properties. Few authors experimented with self-healing octopeptide for the accurate detection of an oligonucleotide as an idea. Such oligonucleotide-modified or -unmodified self-healing peptides caused an orderly array formation of peptide-gel surface molecules. Response of the detection was very rapid, with an increase in the fluorescence signal causing an LOD of 22 pM, which is due to the segregation of target DNA caused by the bonding induced by the fluorescence resonance energy transfer pair. By using this method, the analytes containing aptamers can easily be sensed [64].
14.2.2.3
Enzyme-containing and enzymatically responsive hydrogels for sensing
Analyte-responsive hydrogels that contain enzyme-responsive materials have a high scope of application in many fields of sensing. Interactions between substrates and enzymes usually produce a signal; detection of colors is the basic aspect of many analytesensing materials such as enzyme-linked immunosorbent assays. Such enzyme-responsive analyte-sensing materials may encompass or react with the enzymes in the target analytes and engender a detectable signal and adapt to changes when they come in contact with the analyte. Encompassing the enzymes within low hydrogel volumes may render sensitive detection and enable a large concentration of enzymes to be interacted with. Experimenters incorporated glucoamylase enzyme within an aptamer cross-linked hydrogel and found that the cross-linking of both the elements occurred instantly, avoiding the necessity of rough polymerization reactions that may change the nature of the enzyme [65]. When the abovementioned self-healing analyte sensor was introduced into the target analyte, the hydrogel disintegrated and the glucoamylase was released into the solution, which contains the amaylose substrate. When the amylase comes into contact with glucoamylase, glucose was produced, which could easily be detected with a conventional glucometer, as shown in Fig. 14.3. This reaction
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Figure 14.3 Aptamer-cross-linked hydrogel with trapped glucoamylase [65].
takes place between the hybridized aptamer containing a crosslinked hydrogel encompassing glucoamylase and the polymer strands of complementary DNA (PS A and PS B). Upon introduction of target analytes, the aptamers detect the target analytes to form aptamer target complex molecules and so the hydrogel disintegrated to release glucoamylase. This acts as a catalyst during the hydrolysis of amylose and glucose in larger quantity is rendered as a product, which is shown as physical reading in a glucometer. This method of analyte sensing can also be used for non-glucose-forming analytes by customizing the aptamer used, which in turn causes changes in the cross-linking aptamer to detect the analyte. Fibers containing nanoscale hydrophobic and hydrophilic self-healing synthetic materials were developed by an alternate enzymeencompassing methodology. Hydrocavities were present in those materials, which were used to hold the lysylendopeptidase (LEP) enzymes [66]. In the same sensor, a conjugate LEP for the hydrophilic peptide called dansyl, which is a hydrophobic fluorescent dye, was used. By such a strategy, when the peptide from LEP underwent cleavage and acted with hydrophobic dansyl hydrogel fibers, the intensity of fluorescence enhanced greatly and the light emission wavelength changed from 545 to 508 nm. Such adaptable changes occurring due to the bond between enzyme and substrate rendered the analyte responsiveness of the materials easy. A few researchers added adenylate kinase as a crosslinking agent to the hydrogel, and when introduced into the
Chapter 14 Analyte sensing by self-healing materials
analyte, the abovementioned adaptable change occurred in a nanometer scale when the adenylate kinase established a bond with its substrate adenosine triphosphate [67]. As many adenylate molecules experienced this nanoscale adaptable change at a time, it magnified into a macroscale change and became easier to detect those changes in a specific volume of hydrogel. Such enzyme-level adaptable change could bring out precise detection of analytes when it establishes a bond with its substrate molecules.
14.2.3
Analyte-responsive composites
As a means of expanding the scope of developing sensing materials from self-healing materials, polymeric structural modification could be done by incorporating nanostructured materials such as electroactive species, metal nanoparticles, or carbon-based nanoparticles, so that it results in novel composite materials, which possess self-healing capability [68 71]. Self-healing composite materials offer a wide range of signal transduction, as they are characterized with inherent electrochemical, electronic, and electrical properties. This paved way for developing self-healing composites with various sensing-capable devices. A basic organogel-based self-healing composite was prepared by blending dimethylformamide with N-isopropylacrylamide and dopamine methacrylate in the presence of reduced graphene oxide (rGO) [72,73]. In blending the abovementioned elements, a diverse chemical assortment is rendered by the catechol contained in dopamine and a reversible complexation by boron-dicatechol elements [74]. This chemical composition is responsible for the self-healing ability of the composite along with the hydrogen bonding present within the amides. The presence of rGO as a catalyst for the reaction enhanced the stiffness of the resulting organogels in humid conditions. The results of rheology reveal that the rGOorganogel combination withstands up to 300% strain with a time of recovery of 20 min. Complex formation in this composites occurs only at a pH value of greater than 7.5 because of the catechol chemistry and reversibility. Initially, this composite was used for the analyte sensing of HCl gas and when it was exposed to HCl, boron-dicatechol bonds disintegrated and the composite degelated. CNT-based composite materials are widely popular among the materialists owing to their established methods of functionalization with polymers, stand-alone characteristics, better electron conductivity, and its low percolation threshold limits [75 78].
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A humidity sensor can be fabricated from CNT-based composites, and they can be turned into self-healing composites by suitable functionalization of CNTs to render conductive composites by the bottom-up approach of construction techniques [79]. Fig. 14.4 depicts the step-by-step approach in manufacturing CNT-based conductive composite materials. It consists of four steps: First, the CNT surface is attached with pyrene-modified β-cyclodextrin (β-CD) through π π interaction [80,81]. Secondly, by means of inclusion chemistry, 2-hydroxyethyl methylacrylate was added to β-CD to form a self-healing conductive composite material. Inclusion chemistry is a process in which a complex formation takes place between the host compound cavity and the guest compound molecule, which is also feasible within water due to the hydrophobic nature of the host and the guest [82]. Third, in order to convert the self-healing composite into an analyte sensor, polymerization cross-linking of the composite with ethylene glycol dimethacrylate as a catalyst was carried out. This composite has few demerits such as high percolation threshold in the order of 7 11 wt.%, which increases the stabilization temperature of the composite. This makes the material stiffer and the polymer chains immovable and restricts the self-healing ability of the composites.
Py-β-CD
Step 1
Step 2 HEMA-SWCNT-β-CD
SWCNT-β-CD
SWCNT
Step 3 HEMA-SWCNT-β-CD Py-β-CD
PHEMA-SWCNT-β-CD
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Figure 14.4 Schematic preparation of the conductive self-healing composite [70].
Ad-HEMA
Chapter 14 Analyte sensing by self-healing materials
Methods of manufacturing self-healing CNT-polymer composites include distribution of CNTs into a polymer matrix and layer-by-layer (LBL) manufacturing technique. The LBL method is carried out by coating a thin film of CNTs over the surface of a self-healing polymer material substrate and the incorporated CNT self-heals by the induction of self-healing polymers [83]. After the occurrence of damage within the composite, they are reunited by means of hydrogen bonding between the two fibrous elements present in the self-healing polymer [84]. This happens between the CNT fibers by the action of van der Waals (VdW) forces along the cross section of the fibers at the time of self-healing of the CNT-reinforced polymeric composites [85]. Even though the VdW forces occurring in a single CNT fiber are of very less magnitude and weak, the accumulation of forces of all the CNT fibers would be of very high magnitude and adhesive in nature. Using such a phenomenon, the self-healing PEI and polyacrylic acid (PAA) polymers were deposited with a conductive CNT layer of thickness 150 nm and with a resistance of 175 kΩ21 [86]. The LBL film of CNTs turns self-healing mainly due to the action of hydrogen bonding in PEI and the reaction between amine groups of PEI and carboxylic groups of PAA. Nevertheless, this composite works better only in a humid environment as the self-healing nature is induced only by water molecules limiting its application range. A few studies reported that this LBL layer is used for the detection of ammonia gas by depositing CNTs over the chemiresistive layer of polyethylene terephthalate. This layer established the LOD of the composites over a fewer range of ppm of the analyte, and the chemiresistor was very selective in detecting various gases like dicholoromethane, toluene, ethanol, and water. Such a selective nature of the sensor is mainly because of the chemical interaction between p-type CNTs and ammonia, which is an electron donor [87,88]. Fig. 14.5 represents the self-healing chemiresistor array, optical micrographs of conductive polymers, and their time resistance plots. In Fig. 14.5A, the green layer represents the circuit board, yellow lines represent the electrical wiring connection, cyan represents the glass slide, brown represents the self-healing polymeric substrate, and pink and black represent the self-healing electrode and composite, respectively. The sensors discussed so far are selective in nature and are responsive and sensitive to only one analyte and cannot be used for multiple analytes. When the sensor has to be a multianalyte sensor, the self-healing ability of the material pose certain restrictions [90 93]. This forced the progress of array of self-healing sensors (as shown in Fig. 14.5A) for the multianalyte sensing of
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Figure 14.5 (A) Self-healing chemiresistor array; (B) optical images of conductive self-healing composites; and (C) time-resistance plot of three sensors [89].
pressure, temperature, strain, and volatile organic compound sensing [94]. The self-healing nature of the electrode and the substrate is driven by the reformation of disulfide and hydrogen bonds occurring between the functional polyurethane (PU) polymeric chains at both the sides. The density of hydrogen bonds and disulfide bonds developed between urea groups and the polymer chain flexibility governs the healing efficiency and healing time of PU material directly. PU material and microsized silver-reinforced composites are used as a self-healing substrate and electrode, respectively, in a chemiresistor [89,94]. Sometimes, the carbon-based self-healing composites or gold nanoparticles (AuNPs) could act as sensing layers in the abovementioned composite materials [95] and can render electrical resistance in the order of kΩ to MΩ. Such AuNPs have only half of the sensitivity when compared with the other sensors due to their induced self-healing nature. A few other studies focused in developing a biosensor for detection of heavy mercury (Hg21) metal ions by using a DNA hydrogel impedance biosensor [96]. Such detection is possible when the affinity of mercury toward thyamine-thyamine pairs in oligonucleotide is used properly and the chemical coordination between T-Hg21-T molecules is used as the detection approach. Preparation of a biosensor includes the activation of Hg21 by specific DNA chain reaction hybridization between polyacrylamide polymeric chains. This biosensor possessed a
Chapter 14 Analyte sensing by self-healing materials
Figure 14.6 (A) Schematic representation of the polymerization mechanism and (B) electron impedance spectroscopy of mercury detection [97].
very good LOD of 0.042 pM and a better selectivity and sensitivity for Hg21 heavy metal ions. Fig. 14.6A shows the polymeric chain reaction in the process of biosensor preparation for Hg21 detection, and Fig. 14.6B shows the Nyquist plot and electron impedance spectroscopy for the mercury sensing biosensor. From Fig. 14.6B, it could be seen that the proportional increase in impedance increases the LOD of the biosensor [97].
14.3
Conclusion
Research in the area of analyte sensing is very novel in the current scenario, as this topic had its first publication in the year 2013. However, the publications were sharply increasing
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Figure 14.7 Publication and citation trends in analytesensing materials research.
0
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year by year, as illustrated in Fig. 14.7, which shows the potentiality of this area for performing research. Meanwhile, the sensing applications are growing, including luminescent signals to electric, electrochemical, and magnetic signals, calorimetric sensing, dispersion of signals from single sensor to an array of sensors utilized exclusively for analyte sensing and so on. Usage of self-healing materials for analyte sensing is a very encouraging trend of research, and these materials act as proof-ofconcept ones for analyte sensing. Analyte sensing may be used safety-control devices, autonomous control, and self-repair mechanisms in the future.
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Chapter 14 Analyte sensing by self-healing materials
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[63] Y. Helwa, N. Dave, R. Froidevaux, A. Samadi, J. Liu, Aptamer functionalized hydrogel microparticles for fast visual detection of mercury(II) and adenosine, ACS Appl. Mater. Interfaces 4 (4) (2012) 2228 2233. [64] P.J.S. King, A. Saiani, E.V. Bichenkova, A.F.A. Miller, de Novo. Self-assembling peptide hydrogel biosensor with covalently immobilised DNA-recognising motifs, Chem. Commun. 52 (40) (2016) 6697 6700. [65] L. Yan, Z. Zhu, Y. Zou, Y. Huang, D. Liu, S. Jia, et al., Target-responsive sweet hydrogel with glucometer readout for portable and quantitative detection of non-glucose targets, J. Am. Chem. Soc. 135 (10) (2013) 3748 3751. [66] S. Kiyonaka, K. Sada, I. Yoshimura, S. Shinkai, N. Kato, I. Hamachi, Semiwet peptide/protein array using supramolecular hydrogel, Nat. Mater. 3 (1) (2004) 58 64. [67] W. Yuan, J. Yang, P. Kopeckova, J. Kopecek, Smart hydrogels containing adenylate kinase: translating substrate recognition into macroscopic motion, J. Am. Chem. Soc. 130 (47) (2008) 15760 15761. [68] N. Zhong, W. Post, Self-repair of structural and functional composites with intrinsically self- healing polymer matrices: a review. Compos, Part. A 69 (2015) 226. [69] S. Bauer, M. Kaltenbrunner, Materials science: semiconductors that stretch and heal, Nature 539 (2016) 365. [70] T.-P. Huynh, P. Sonar, H. Haick, Advanced materials for use in soft selfhealing devices, Adv. Mater (2017). Available from: https://doi.org/10.1002/ adma.201604973. [71] A. Ghavami Nejad, S. Hashmi, M. Vatankhah-Varnoosfaderani, F.J. Stadler, Effect of H2O and reduced graphene oxide on the structure and rheology of self-healing, stimuli responsive catecholic gels, Rheol. Acta 55 (2016) 163. [72] M. Vatankhah-Varnoosfaderani, A. Ghavami Nejad, S. Hashmiac, F.J. Stadler, Mussel-inspired ph-triggered reversible foamed multi-responsive gel—the surprising effect of water, Chem. Commun. 49 (2013) 4685. [73] M. Krogsgaard, V. Nue, H. Birkedal, Mussel-inspired materials: self-healing through coordination chemistry, Chem. Eur. J 22 (2016) 844. [74] P.R. Bandaru, Electrical properties and applications of carbon nanotube structures, J. Nanosci. Nano-technol 7 (2007) 1. [75] P.M. Ajayan, L.S. Schadler, C. Giannaris, A. Rubio, Single-walled carbon nanotube-polymer composites: strength and weakness, Adv. Mater. 12 (2000) 750. [76] Z. Spitalsky, D. Tasis, K. Papagelis, C. Galiotis, Carbon nanotube polymer composites: chemistry, processing, mechanical and electrical properties, Prog. Polym. Sci. 35 (2010) 357. [77] J.K.W. Sandler, J.E. Kirk, I.A. Kinloch, M.S.P. Shaffer, A.H. Windle, Ultra-low electrical percolation threshold in carbon-nanotube-epoxy composites, Polymer 44 (2003) 5893. [78] K. Guo, D.-L. Zhang, X.-M. Zhang, J. Zhang, L.-S. Ding, B.-J. Li, et al., Conductive elastomers with autonomic self-healing properties, Angew. Chem. Int. Ed. 54 (2015) 12127. [79] C. Ehli, G.M.A. Rahman, N. Jux, D. Balbinot, D.M. Guldi, F. Paolucci, et al., Interactions in single wall carbon nanotubes/pyrene/porphyrin nanohybrids, J. Am. Chem. Soc 128 (2006) 11222. [80] C. Ehli, D.M. Guldi, M.A. Herranz, N. Martın, S. Campidelli, M. Prato, Pyrene-tetrathiafulvalene supramolecular assembly with different types of carbon nanotubes, J. Mater. Chem 18 (2008) 1498. [81] J. Szejtli, Introduction and general overview of cyclodextrin chemistry, Chem. Rev. 98 (1998) 1743.
Chapter 14 Analyte sensing by self-healing materials
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15 Graphene-based electrochemical sensors Kiran Aftab and Ayesha Riaz Department of Chemistry, Government College University Faisalabad, Faisalabad, Pakistan
15.1 15.1.1
Prefaces Brief introduction
In this era, sensors have gained a lot of attention owing to their diverse applications in areas of research and development. Their application includes monitoring pollution in the environment, diagnosis of diseases that are life-threatening, examining food quality, and also monitoring terrorism. A trace number of gases and chemicals can be detected using chemical and electrochemical sensors to investigate and oversee the quality and toxicity of air in our ecosystem. The detection of gases (like nitric oxide [NO], nitrogen dioxide [NO2], ammonia [NH3], carbon monoxide [CO], carbon dioxide [CO2], sulfur dioxide [SO2], hydrogen sulfide [H2S], and volatile organic compounds [like acetone, ethanol, formaldehyde, and methanol]) is vital because they produce toxic effects, even if they are in small amounts [1]. Chemical sensors are also utilized in the nuclear research, space areas, and, majorly, energy sectors.
15.1.2
Graphene and graphene oxide metal oxide composites
Graphene, an allotrope of carbon, is simply a single thick sheet or layer of graphite having carbon atoms connected in a hexagonal and conjugated way. Some of its properties are • large surface area of 2630 m2g21 • high speed electron mobility of 200,000 cm2V21s21 • good tensile strength of 42 Nm21 • enormous electrical conductivity of 106 s cm21 • thermal conductivity of 5000 Wm21 K21 • optical transparency less than 2.3% against visible light • band gap, which is tunable [2]. Nanomaterials-Based Electrochemical Sensors: Properties, Applications, and Recent Advances. DOI: https://doi.org/10.1016/B978-0-12-822512-7.00002-8. © 2024 Elsevier Inc. All rights reserved.
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Graphene is an extremely suitable material for almost all types of chemical sensor applications due to its unique structural, electrical, and chemical properties as mentioned above [3]. Efforts are made to combine graphene with different kinds of nanomaterials, keeping in view the outstanding performance and low cost. The nanoparticles not only enhance the graphene’s properties but also act as a stabilizer for the assembly of each graphene sheet on individual basis, which is due to strong van der Waals interactions between the layers of graphene. MO nanostructures can be hybridized with 1. transition metals and noble elements 2. metal oxides (MOs, other) 3. carbon-based nanomaterials like carbon nanotubes 4. graphene and its derivatives like graphene oxide (GO) and reduced GO (rGO) [1].
15.1.2.1
Advantages of GO MO composites over Graphene
The unique catalytic, electronic, and magnetic features of graphene nanocomposites are based on hybridization of graphene with nanoparticles, and they have gained tremendous attention. • Unusual electrical, optical, and molecular properties. • For the immobilization of catalysts, usually biological, it can load more functional groups on its surface. • MOs have large alkaline corrosion resistance • Distinctive crystalline structures inhibit the clustering of MO nanostructures, and also their size is maintained • Cheap and simple process of preparation • Synergistic effects of graphene sheets • Electrochemical sensing • Energy storage ability Briefly speaking, graphene-based nanocomposites are recommended as one of the most promising hybrid materials. In addition to the fabrication of electrochemical and gas sensors, it can further help in the manufacture of more energy devices
15.2
Synthesis of graphene oxide metal oxide electrochemical sensors
GO MO composites can be manufactured in a number of ways. Few of the most common methods are discussed. 1. General synthesis 2. Hydrothermal and solvothermal methods
Chapter 15 Graphene-based electrochemical sensors
3. 4. 5. 6.
Chemical methods Electrochemical methods Thermal methods Microwave-assisted methods
15.2.1
General synthesis
A brief overview of GO MO and rGO MO synthesis is given below.
15.2.1.1
GO MO composite synthesis
To manufacture GO nanocomposites, oxide nanoparticles are recommended because these nanomaterials have the ability to improve gas response. GO MO composites have two components; one is the oxide of graphene, and the other is the metal composite. 15.2.1.1.1
Graphene oxide
Oxides of graphene can be obtained by “Hummer’s method.” Its preparation requires graphite flakes, concentrated acid (like H2SO4), nitrates (like NaNO3), KMnO4, and deionized water. These components are stirred in an ice bath. The mixture is treated with H2O2 for a specific interval of time. This mixture is then cleansed with deionized water. This cleansing is accomplished by repeated centrifugation, which is then followed by filtration. The wet GO powder obtained is dried. Commercial GO can also be used for the manufacture of nanocomposites [3]. 15.2.1.1.2 Metal oxide The second component is the MO, which is synthesized from the following: 1. Metal precursors are usually organic, which are taken in appropriate basic pH or acidic conditions 2. Metallic powders, for example, for zinc oxide synthesis, metallic zinc powder is used as a precursor [3]. GO serves as a magnificent precursor for a variety of graphene-based nanocomposite materials. Recent studies show that GO sheets have negative charges when dissolved in water due to dissociation of the carboxylic acid and phenolic hydroxyl groups. When the graphene sheets are immersed in the solution, the oxide nanoparticles become settled on the graphene to form the GO nanocomposite. Consequently, GO forms colloidal
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dispersions in water that are stable, which is devoted to the electrostatic repulsion and hydrophilicity of the GO sheets [4]. To complete the GO sonication the mixture is stirred (GO water) for a specified period to make aqueous suspensions of GO sheets. The hydrophilic nature of GO prevents direct oxidation of it in nonaqueous solvents. This is because of the strong internal H-bonding interactions between the layers of GO adjacent to each other [4] (Fig. 15.1). 15.2.1.1.3 Chemical functionalization Efforts are made to synthesize homogeneous suspensions of GO sheets in aqueous and in nonaqueous solvents by chemical functionalization of GO. Chemical functionalization actually decreases the density of the H-bonding groups (OH in GO) and hence reduces the strength of the H-bonding, consequently providing less hydrophilic GO sheets. The groups consisting of GO enhance the functionality by supplying reactive sites for chemical modification. This method also inhibits the stacking of individual sheets of GO in dispersion. Irresponsibility can cause agglomeration of graphene or GRO sheets; they can even restack. Modified GO can be used for water purification. In this regard, the hydrophilic character of GO is retained by linking thiol groups covalently to GO. The modified GO preparation
Figure 15.1 Graphene oxide sheets.
Chapter 15 Graphene-based electrochemical sensors
was enhanced by the working of carboxyl as amides and hydroxyl groups as carbamate esters [4].
15.2.1.2
Highly reduced GO MO composite synthesis
Besides graphene and GO, researchers worked on the manufacture of rGO, also denoted as HRG. rGO or HRG nanoparticles were prepared by GO reduction thermally, which is further obtained by Hummer’s method, as discussed above. Yet, vital quality of the graphene and its derivatives is dependent on its utilization. HRG is obtained from the reduction of GO. This reduction can be accomplished by chemical, photochemical, thermal, and electrochemical methods. The precursors used in hydrothermal methods were 0.4 mg of GO diffused in water, 0.1 M ammonia solution, and 0.35 g of SnCl4€ 5H2O dissolved in water. Tin dioxide is formed by the attachment of tin chloride on rGO’s surface. Heterogeneous nucleation sites are provided by rGO surfaces [3]. Despite structural differences between natural graphene and rGO, their similarities promote the reduction process as crucial reactions of GO or rGO. On a large scale, the most suitable methods for preparation of graphene-based composite materials are chemical or thermal methods. Both of these methods will be discussed in the upcoming sections. The properties of rGO strongly depends on the reduction processes. Therefore, efforts are made to improve the properties and materials for the development reduction process (Fig. 15.2). The binding MO nanoparticles on graphene for manufacture of graphene-based nanomaterials is accomplished in two ways: 1. Post-immobilization, also called “ex situ hybridization” In this method, graphene sheets are surface-functionalized in order to improve the final products. Then, separate solutions of graphene nanosheets are mixed. These sheets are called conjugated graphene sheets. Their functionality is enhanced further by covalent coupling (C C reactions). By this method, solubility can be increased, but on the other hand, low density and nonuniform coverage are drawbacks [4]. 2. In situ binding, also called “in situ crystallization” In situ chemical reduction methods are most commonly and widely used. Metal precursors like HAuCl4, AgNO3, K2PtCl4, and H2PdCl6 are chemically reduced with reductants like hydrazine hydrate, amines, and NaBH4 by the in situ method. Consider an example of rGO/Co3O4 nanocomposites that were synthesized by Kim et al. as anode materials. In deionized water, GO and cobalt acetate were reduced. In this case,
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Figure 15.2 Reduced graphene oxide.
ammonium hydroxide and hydrazine work as a reductant. The homogeneous rGO dispersion facilitates nucleation sites for Co3O4 nanoparticles, resulting in homogeneous Co3O4 nanoparticles’ growth on the conducting rGO sheet’s surface [4]. rGO SnO2 and ternary rGO SnO2 Au nanocomposites can also be synthesized by this method. These rGO MOs have applications in lithium-ion batteries as anode materials. The materials of this nanocomposite can be synthesized from an aqueous dispersion of GO and tin chloride. Tin chloride will act as a source of tin and reducing agent for GO and HAuCl4 in the sonication process. This further has the ability for manufacturing other multicomponent nanocomposites, starting from different varieties of metal salts [4].
15.2.2
Hydrothermal and solvothermal methods
Hydrothermal and solvothermal methods are the most convenient and emerging methods for synthesis of GO and its nanocomposites. This process is carried out in a closed system
Chapter 15 Graphene-based electrochemical sensors
in aqueous conditions and specific temperature. The method is that oxide nanoparticles and graphene are prepared individually and stored in aqueous solution in the form of dispersions. The aqueous dispersions are then sonicated and then mixed in the required proportions. The resulting product is then treated thermally in a closed environment. The heat treatment requires a long time and is accomplished slowly. After thermal treatment, the composite is washed with ethanol. Now, this washed composite is dried at temperatures for almost 12 h 24 h. Sometimes, before drying, the product is frozen and then dried, which is known as freezedrying. This single-pot process manufactures highly crystalline homogeneous nanocomposites of graphene [3]. If we use supercritical water, then it will also work as a reducing agent, giving an eco-friendly alternative for toxic chemical reductants. During GO reduction, when using supercritical water as a reductant, the supercritical water not only partly removes the oxygen containing functional groups but also restores the aromatic structure. The water actually acts as a source of hydrogen ions for protonation of hydroxyl group protonation. This further leads to dehydration of rGO, consequently facilitating reduction [4]. • GO CuO nanocomposite In the synthesis of GO CuO nanocomposite, cupric acetate and GO are used as precursors. The process is conducted for almost 10 h under diverse temperatures. The obtained product is washed through deionized water and finally dried. Now, this product can be used for electrochemical applications. This work was done by Dai et al. [2] (Fig. 15.3). Deoxygenation of GO was observed by solvothermal reduction too. The procedure was explained by Wang et al. The reduction of GO was carried out at a temperature of 180 C. The solvent used is N, N-dimethlyformamide (DMF). The reductant is hydrazine monohydrate. The rGO sheets were immersed in DMF. The disadvantage is that the rGO sheets exhibit bad conductivity because of the nitrogen doping that is caused by a hydrazine reductant [4]. Dubin et al. used N-methyl-2-pyrrolidinone (NMP) as a solvent. The container was not closed; the temperature of the reaction was less than 200 C. The oxygen-scavenging properties of NMP enhanced the GO reduction [4]. • GO SnO2 nanocomposite To synthesize the GO SnO2 composite, graphene is synthesized by mixing graphite oxide and aqueous sodium 1dodecanesulfonate at a temperature less than 100 C. The oxide component is accustomed by mixing tin chloride in
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Figure 15.3 Schematic description for synthesis of the CuO GO nanocomposite [5].
•
• •
•
HCl solution. Now, the solution is added into the already presynthesized graphene surfactant mixture. After that, urea and hydrogen peroxide are added. Water is also added to dilute the solution. The mixture is handled at 90 C for nearly 12 h 16 h. The resulting yield is then cleaned and then dried at 50 C 70 C [4]. A few advantages of the hydrothermal process are as follows: Under hydrothermal reaction conditions, water has a high diffusion coefficient as well as dielectric constant. This property helps remove oxygen-containing groups by the process of dehydration. It also increases bond cleavage (heterolytic). The reduction process does not add any impurities in the final nanocomposite. The extent of reduction and features of the nanohybrid material can also be modified by balancing temperature and pressure of reaction. The process is cheap and has a simple setup and thus could be easily incorporated at the industrial level.
15.2.3
Chemical methods
Chemical reduction is another common synthetic approach for different graphene-based nanohybrid composites. GO can be reduced chemically by a variety of reducing agents, for example, hydrazine monohydrate, sodium borohydride, hydrogen spillover, and so forth. Hydrazine monohydrate is used mostly because of its reactivity and stability in water media. Using hydrazine as a reductant will restore the pi-electron conjugation in the aromatic system of graphite. This consequently facilitates the electrical conductivity. The drawback of hydrazine is introduction of heteroatoms like
Chapter 15 Graphene-based electrochemical sensors
277
nitrogen as an impurity. Nitrogen covalently attaches to the surface of the graphene sheets in the form of amines or hydrazones. To overcome the limitations of hydrazones as a reducing agent, many other reducing agents are introduced that • allow for low temperature reduction • require a short period of time • are eco-friendlier than other reducing agents • produce homogeneous graphene suspensions [4] Feng et al. used a sodium-ammonia solution as a reducing agent for huge synthesis of high quality rGO. Here, solvated electrons enhanced the reduction of rGO and also restored the conjugated network of highly rGO [4]. Esfandiar et al. used melatonin as replacement of hydrazine. It is a biocompatible antioxidant which can reduce rGO suspension in a more stable way as compared to a reduced hydrazine suspension [4]. For the specific synthesis purposes, different reducing agents are used by different researchers (Table 15.1). A few of the reducing agents and methods are summarized in the table given below. One major benefit of this method is the extent of reduction, and other features can be modified by using specific reducing agents. One major drawback is the necessity of purifying the final product from different reducing agents.
15.2.3.1
Metal-mediated reduction of graphene oxide
In recent research, metal-mediated reduction of GO is considered eco-friendly and leads to faster reduction. Fan et al. demonstrated a route for graphene synthesis via reduction of rGO by aluminum powder. This reaction was accomplished in
Table 15.1 Reducing agents used to synthesize differnt nanocomposites. Researcher
Reducing agent
Nanocomposite
Qiao et al. Guo et al. Yang et al. Khezrian et al.
NaOH in CuCl2 and N-doped rGO mixture Diethylene glycol (DEG) Ammonia solution Ammonia solution
Wang et al. Ruoff et al.
Citric acid Hydrazine
CuO/N-rGO nanohybrid [2] Cu2O/RGO composite [2] PDDA-G/Fe3O4 nanohybrid material [2] Fe3O4 magnetic nanoparticles RGO hybrid nanosheets [2] MnO2/GO [2] RGO/tin oxide (TiO2) [2]
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an acidic medium in a short interval of time (nearly half an hour). The graphene sheets synthesized have a bulk electrical conductivity of 2.1 3 103 S m21 [4]. Mei and Ouyang used Zn in place of aluminum. Mild acidic conditions under ultrasonication at room temperature were applied to accomplish reduction. The reaction is completed within 1 min. Both the low reduction potential of Zn2 1 /Zn and the ultrasonication enhanced the reduction of rGO. Also, the rGO sheets obtained by this method have fine electrical conductivity and thermal stability [4].
15.2.3.2
Plant extracts as a reducing agent
Plant extracts are easy to handle readily available cheap biocompatible Because of them, they are used as a reducing agent. Khan et al. gives an systematic route for highly rGO synthesis by the reduction of rGO. He uses Pulicaria glutinosa as a reducing agent. The phytomolecules present in the P. glutinosa plant extract were actually responsible for the reduction of rGO, operationalization of the surface of the rGO nanosheets, stabilization in solvents, and limiting the use of external and toxic chemical reductants and surfactants [4]. Li et al. uses a technique in which gallic acid was employed. It acts as both reductant and stabilizer for reduction of rGO [4]. Microbial reduction of rGO has also been described. Kuila et al. used the root of carrot as a biocatalyst as well as reducing agent. In the carrot roots, the endophytic microorganisms present reduce exfoliated GO to rGO. The process is carried out at room temperature [4]. • • • •
15.2.4
Electrochemical method
Among the various reduction methods, electrochemical synthesis is a fast, uncomplicated, economic, measurable, and ecofriendly method. Using this method, one can obtain a pure nanohybrid material with less power consumption. On the other hand, this method usually yields solid nanocomposite materials, which are tricky to process further. Two pathways are generally observed for electrochemical reduction of GO.
Chapter 15 Graphene-based electrochemical sensors
•
•
279
The one-step path: In a colloidal solution, GO is directly reduced by the electrochemical method. The supporting electrolyte is used on the electrode. The two-step path: GO is predeposited on the electrode prior to reduction. For this purpose, conductive electrolyte is used on an electrode [6].
15.2.4.1
Synthesis of GO MO electrodes
Kong et al. prepared CuO-modified electrodes for nonenzymatic detection of glucose in saliva [2]. Duan et al. deposited MnO2 nanowires on graphene for sensing purposes. These nanowires were deposited electrically onto a graphene paper electrode by cyclic voltammetry. This deposition was anodic. The potential range of 1.4 to 1.5 V was obtained. Fig. 15.4 shows loading of MnO2 wires on graphene. It is a one-step path [2]. Reduction of GO may give proliferate structural defects and also improve exceptionally the electrochemical activity of uncovered GO-modified electrodes. Electrochemical reduction of GO can be observed in several electrolytes. The electrochemical response of reactants basically relies on electron transfer kinetics and available surface area. It is observed that edge plane sites (also called defects) on graphitic materials facilitate the electron transfer mechanism. Rapid electron kinetics at graphene edges will result in outstanding capacitive and electrocatalytic features like four times the specific capacitance and two times the density of current.
15.2.5
Thermal methods
Thermal reduction of graphene is a simply heating procedure obtained by slow heating of solid GO or dispersion of GO in solvents. To avoid loss of carbon content, atmosphere should
Figure 15.4 Loading of MnO2 nanowires on graphene [License#6] [7].
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be free from oxygen and reactive chemicals; otherwise, gases or volatile substances will be formed. rGO is prepared by thermal treatment of presynthesized GO. The resultant product is then accompanied by exfoliation. A ceramic crucible having GO is filled into a muffle furnace at around 500 C. Heat treatment is carried out in air for 4 min. After that, rGO was withdrawn from the furnace instantly and was allowed to cool till room temperature was reached [8]. Decrease in weight loss indicates conversion of GO into rGO. Besides this, decomposition of the oxygenated functional group is also indicated by weight loss. If GO is completely reduced by the heating process, then it is known as thermal annealing reduction. If GO is heated rapidly at a rate .2000 C per minute, then exfoliation of GO into graphite will occur [9]. The rapid heating in this case leads to the decomposition of the oxygencontaining functional groups that are linked to the carbon plane of GO and results in releasing gases like CO and CO2. These gases can easily diffuse into the spaces between GO sheets. Such thermal treatment exfoliates as well as causes the reduction of GO into graphene. This method is widely used to manufacture a large amount of graphene. The demerit of this method is that the release of gases causes enormous damage to the structure of platelets. Almost 30% of the mass of the GO is lost. Also, these methods consume a large amount of energy and are also difficult to handle. To overcome the difficulties, efforts are made to reduce GO at low temperatures. Vacuum conditions and temperature of 200 C are used nowadays to manufacture few-layered graphene sheets. However, the surface area of the sheets prepared by this process is much less.
15.2.5.1
Graphene oxide metal oxide hybrid
The columbic interaction between GO nanosheet (having negative charge) and chemical ingredients (having positive charge) including metal ions works to form such hybrids. In the beginning, a few primary metal ions react to a few of the partially charged oxygenated sites of graphene nanosheets and inhibit these sites to react further with other metal ions. GO nanosheet becomes heavy and precipitates in the form of GO metal hybrid. It is then transferred to a graphene metal hybrid by further processes. During reduction, the growth of a metal precursor occurs by progressive combination with O atoms, MO molecules, and free metal ions. Consequently, irregular-shaped MO nanoparticles attach to rGO matrices.
Chapter 15 Graphene-based electrochemical sensors
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These matrices behave as a hybrid of graphene with metal or MO [9].
15.2.6
Microwave-assisted method
Microwave-assisted synthesis is a simple and uniform heating technique for rapid synthesis of nanomaterials having small particle dimensions, uniform particle size distribution, and high purity (Table 15.2). Microwave can enhance the nucleation of nanoparticles and lessen the time for synthesis. In this method, microwave energy is converted into heat using a microwave absorbent. Although reactants and solvents have different dielectric constants, selective dielectric heating can also be accomplished by this process. This method transfers energy directly to reactants and increases the internal temperature. rGO is synthesized by exfoliation and reduction of GO without chemicals or solvents in 1 min [2] (Fig. 15.5). The merits for the microwave-assisted method include fast reaction time, chances of large-scale production, and pure final yield. However, this experimental setup is costly, which is a drawback. GO MO composites, their method of synthesis, and the precursors used for them are shown in Table 15.3.
15.3 15.3.1 • • • •
Properties of GO MO nanocomposite Mechanical properties
Graphene has the following distinctive properties [11] Break strength 5 42 N ml Young’s modulus 5 1.0 TPa Tensile strength 5 130.5 GPa Fracture toughness less than or equal to 4.0 6 0.6 MPa ml/2
Table 15.2 Nanomaterials synthesized by Microwave-assistance. Researcher
Precursor
Nanomaterial
Peng et al. Ruoff et al. Wang et al.
Graphene oxide and cupric acetate Ferric chloride and graphene oxide rGO in toluene and water system
CuO/SG [2] RGO/Fe2O3 [2] Titanium dioxide (TiO2) nanoclusters [2]
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Figure 15.5 Schematic representation of the microwave-assisted synthesis of copper oxide [License 8] [10].
Table 15.3 GO-MO composites, their method of synthesis, and the precursors. Metal oxide
Nanocomposite
Synthesis method
Precursors
Copper oxide
GO CuO Cu2O/RGO CuO RGO
Cobalt oxide
CoO/Rgo Co3O4/HRG
Iron oxide
RGO/Fe2O3 Fe3O4/rGO
Hydrothermal Chemical reduction Hydrothermal Chemical Microwave-assisted Hydrothermal Thermal Solvothermal Chemical Microwave-assisted Microwave-assisted Chemical reduction Hydrothermal
GO, cupric acetate, DMF [2] GO, cupric acetate, DEG [2] GO Cu (CH3COO)2 [4] GO Cu (OAc)2.H2O [4] GO (Cu (CH3COO)2 H2O) [4] GO, Co (Ac)20.4H2O, CO(NH2)2 [2] GO CoCl2. 6H2O(NaBH4) [4] GO CoSO40.7H2O [4] GO (C2H3O2)2Co.4H2O (NH2NH2) [4] GO Co (NO3)20.6H2O [4] GO, FeCl3, N2H2 [2] GO, FeCl3.6H2O, FeCl20.4H2O [4] GO FeCl30.6H2O, FeCl2 4H2O [4] (Continued )
Chapter 15 Graphene-based electrochemical sensors
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Table 15.3 (Continued) Metal oxide
Nanocomposite
Synthesis method
Precursors
Manganese oxide
GO/MnO2 MnO2 rGO Mn3O4/GO Mn3O4/HRG
Tin oxide
RGO/SnO2 SnO2 rGO V2O5/GO V2O5 rGO
Chemical reduction Thermal Hydrothermal Hydrothermal Solvothermal Thermal Chemical reduction Hydrothermal Chemical reduction Hydrothermal Solvothermal Electrochemical Hydrothermal Microwave-assisted Hydrothermal Hydrothermal Thermal Solvothermal Thermal Hydrothermal Hydrothermal Chemical Microwave-assisted
GO, KMnO4 [2] GO KxMnO2 [4] GO, N2H4, KMnO4 [2] GO MnAc20.4H2O [4] GO MnAc20.4H2O [4] GO MnO2 organosol [4] GO, SnCl40.6H2O [2] GO, SnCl40.6H2O [2] GO, HVO3 [2] GO V2O5 [4] GO Vanadium oxytriisopropoxide [4] GO V2O5•nH2O (H2O2) [4] GO NH4TiF6 [4] GO Tetra butyl titanate [4] GO ZrO (NO3)2.3H2O [4] GO RuCl3 [4] GO CoCl2. 6H2O (NaBH4) [4] GO CoSO40.7H2O [4] GO Ni (NO3)2 [4] GO Ni (NO3)2 6H2O [4] GO [4] GO ZnCl2(NaOH) [4] GO ZnSO4 7H2O (NaOH) [4]
Vanadium oxide
Titanium oxide
TiO2/HRG
Zirconium oxide Ruthenium oxide
ZrO2/HRG RuO2/HRG
Nickel oxide
NiO/HRG
Zinc oxide
ZnO/rGO
Blends of GO and rGO are produced in order to achieve the abovementioned properties. The values for these properties vary with surfaces, processes, and defects. Suk et al. synthesized GO with a Young’s modulus of 207.6 6 23.4 GPa [11] and Gomez-Navarro et al. prepared an rGO monolayer with a Young’s modulus of 250 6 150 TPa [11]. GO and its derivates are very good for polymer nanomaterials. Cheng-an et al. [11]. observed the effects of GO in polyvinyl alcohol (PVA) films prepared via solution casting. 20% GO filler content was able to increase the tensile strength of the nanocomposite to 59.6 MPa, which is more than five times the strength of the pure PVA film. The enormous enhancement in mechanical properties is not only due to the GO filler strength but also because of the strength of the matrix interface, the hydroxyl groups of PVA,
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and the oxygen functionalities of the GO. These features also lead to a high degree of H-bonding. Jiang et al. gave a distinctive combination of polyurethane (PU) with GO. With the insertion of 0.1 wt.% of GO nanosheets into PU, the tensile strength of PU elastomer rose by 16.4%, that is, from 42.4 to 49.3 MPa. With the insertion of 0.1 wt.% GO and 1% CFGO, the tensile strength further increased by 46.4%, that is, to 62.1 MPa. The carbon fibers have GO grafted by electrophoretic deposition on their surfaces at 3 V of applied voltage to enhance the interfacial adhesion between GO and PU.
15.3.2
Electrical properties
Graphene has high electron mobility of 25 m2 V21 s21 and electrical conductivity of 6500 Sm21 [11]. Using low contents of filler, electrical conductivity of graphene has improved much. The general fabrication process of GO results in distribution of the sp2bonding orbitals of graphene and the addition of more surface groups that prevents its electrical conductivity and makes making GO resistive (1.64 3 104 Ω m). Reduction improves the electrical conductivity of GO, and it also be tuned over many orders of magnitude. The conductivities range from B0.1 to 2.98 104 S m21 [11]. To reduce the use of GO, research is being done to introduce techniques that can enhance or improve the manufacturing of electrically conductive rGO. In this case, Stankovich et al. reduced colloidal suspension of GO in water using hydrazine hydrate. It exhibits an electrical conductivity of 2 3 102 S m21, which implies that conductivity of GO is improved by five times. Voiry et al. used microwave at 1000 W for 1 s 2 s to make rGO, which improves electron mobility of GO in field-effect transistors [11]. Kim et al. [11] synthesized polyaniline and rGO supercapacitor. It was highly flexible, having a capacitance of nearly 431 Fg21. This supercapacitor has an electrical conductivity of 9.06 3 104 S m21 at a 24 wt.% rGO.
15.3.3
Thermal properties
GO obtained from graphite has less and nonideal thermal conductivity of about 0.5 1 W m21K21. On the other hand, graphene has the highest thermal conductivity of B3000 5000 W m21 K21 of the known nanomaterials [11]. Renteria et al. demonstrated that annealing GO at temperature of 1000 C to make rGO film can facilitate the thermal
Chapter 15 Graphene-based electrochemical sensors
conductivity (in-plane). The improvement in values is from B3 to 61 W m21K21 [11]. The insertion of rGO in polymers has also improved the thermal conductivity to a great extent. Kumar et al. combined rGO with poly (vinylidene fluoride co-hexafluoropropylene). The nanomaterial exhibits a thermal conductivity of 19.5 W m21K21 at 27.2 wt.% rGO, which is greater than many other alloys. GO has proved to be an effective filler to increase flameretardant properties of several polymer nanocomposites. Wicklein et al. added GO and sepiolite clay nanorods to carbon nanofiber in order to develop a flame-retardant foam that is superinsulating. This film had a thermal conductivity of 15 mW m21K21, which is less than that of insulation materials used commonly [11].
15.4 1. 2. 3. 4. 5.
Applications
Chemical sensing Gas sensing Heavy metal ion sensing Inorganic sensing Organic sensing
15.4.1
Chemical sensing
For a long time, various graphene-based nanoparticles have been utilized as electrochemical sensors to detect several chemicals.
15.4.1.1
Agrochemicals
15.4.1.1.1
SnO2 rGO nanocomposite
Dipa Dutta et al. [12] demonstrated that the urea sensors utilize urease and are biosensors. Owing to their exceptional properties, they fabricated ultrasensitive urea sensor (enzyme free) using tin dioxide quantum dot-rGO nanocomposite (SnO2 rGO). SnO2 quantum dots are enriched onto the layer of rGO. Because of the combined effects of the elements, these composites are best for electrochemical sensing. Several electrochemical studies were carried out to assess sensor’s properties in the sensing toxic urea.
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15.4.1.1.2 CoO rGO nanocomposite Ming et al. [12] synthesized an electrochemical sensor made of cobalt (II) oxide rGO nanocomposite. The CoO was decked on rGO. In this nanocomposite, compounds of carbofuran and carbaryl were detected in fruits and vegetable samples.
15.4.1.2
Organophosphorus
Zirconia (ZrO2) is a thermally stable and nontoxic oxide. This inorganic chemical has strong attraction toward phosphoric components; hence, it is commonly utilized for detection of organophosphorus substances, phosphopeptide improvement, and phosphoprotein capture. To increase both the electrochemical and sensing properties of zirconia, Du et al. [4] synthesized HRG/ZrO2 nanocomposites. The nanocomposites are fabricated electrochemically, as it will have high kinetics and electrocatalytic activity. In this case, ZrO2 nanoparticles detect organophosphorus pesticides and nitroaromatic organophosphorus pesticides.
15.4.1.3
Glucose
15.4.1.3.1 rGO Ni (OH)2 nanocomposite rGO Ni (OH)2 is used as an electrochemical sensor because Ni-type materials possess an awesome catalytic activity for molecules like hydrogen peroxide, ethanol, glucose, and so forth. For the detection of glucose, Subramanian et al. [4] illustrated a nonenzymatic glucose sensor that was based on this composite. The Ni (OH)2 is a leaf-shaped nanoplate that is dispersed between graphene nanosheets. This dispersion can be put or settled onto a carbon electrode for sensing properties of glucose. Using this method, we obtained a low detection limit with a broad linear range. 15.4.1.3.2
CuO rGO nanocomposite
The CuO rGO nanocomposite is a stable and sensitive glucose biosensor that is synthesized to detect glucose. When CuO is modified, then there is a uniform distribution of these rodlike nanoparticles on the surface of rGO.
15.4.1.4
Dopamine
15.4.1.4.1 rGO TiO2 nanocomposite The modified rGO/TiO2 composite shows good electrochemical sensing against dopamine. The rGO-titanium dioxide nanocomposite has a highly exposed surface and is synthesized by a
Chapter 15 Graphene-based electrochemical sensors
simple solvothermal reaction of nanocomposite with diethylenediamine. This acts as the surface growth-manipulating agent. 15.4.1.4.2
Fe3O4 rGO nanocomposite
Teymourian et al. [13] prepared a graphene MO nanocomposite that uses the conductive and paramagnetic properties of Fe3O4 on rGO sheets (Fe3O4/rGO). Hydrazine hydrate is used to form Fe3O4-rGO by a simple chemical reduction method. Salamon et al. demonstrated that magnetite nanorods harbored over rGO (rGO/Fe3O4) via a simple one-pot technique. The lower detection limit for rGO/Fe3O4 is 7 nM against the detection of dopamine due to the large surface area of GO. The cubic spinel structure of the Fe3O4 nanorods also enhanced adsorption, therefore increasing electrocatalytic activity [13]. 15.4.1.4.3 SnO2 GO fabricated with sodium dodecyl sulfate A procedure to explain the fabrication of GO with sodium dodecyl sulfate to synthesize graphene nanosheet tin oxide SnO2 hybrid nanocomposite is reported. The employment of sodium dodecyl sulfate in the nanocomposite inhibits the restacking of graphene layers. It also improves the electrochemical features due to which the nanocomposite encounters a lower detection limit of 80 nM for dopamine [13]. 15.4.1.4.4
GO SiO2 nanocomposite
SiO2-coated GO nanomaterial is used as a surface to synthesize molecularly imprinted polymers of GO SiO2 composites. These composites are prepared through the sol gel method. Vinyl groups are introduced onto GO/SiO2 with the help of γ-methacryloxypropyltrimethoxysilane, also known as γ-MAPS and at last copolymerized. This fabrication shows electrochemical and selective properties of dopamine.
15.4.2
Gas sensing
Electrochemical sensing is one of the most promising applications of graphene and graphene-based composites. Fabrication of sensors has gained much importance in this era. Because of the excellent transport property of electron, high charge transfer, broad electrochemical potential, and catalytical activity, the electrochemical reactions are accomplished on the graphene layer and the voltametric response is facilitated.
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Besides electrochemical sensing, these nanocomposites have excellent applications in biosensing, gas sensing, toxins detection, and so on. A brief description of a few GO MO nanocomposites for detection of gases is given below.
15.4.2.1
rGO ZnO nanocomposite
These nanocomposites are utilized as highly efficient gas sensors. Zinc oxide nanoparticles were assimilated into graphene to fabricate HRG/ZnO composites. Zinc oxides act as UV-absorbing and charge carrier-generating materials, while graphene behaves as a conductive material. Tian et al. synthesized HRG/ZnO nanocomposites via ultrasonication of zinc plates in graphite oxide solution using NH3 at room temperature. This nanocomposite was also modified using zinc porphyrin (ZnP). Zinc porphyrin acts as a photosensor for production of photocurrent in the visible range. Ding et al. [4] revealed field emission and photoluminescence features of rGO ZnO nanocomposites, synthesized by the techniques of magnetron sputtering and electrophoretic deposition. This hybrid evinces great emission response, and its photoluminescence properties are explored for gas sensing. These nanocomposites also have semiconducting and electronic properties present near UV to blue photoluminescence. The luminescent ZnO nanoparticles can act as a sensing transducer for gases like carbon monooxide, ammonia, and nitrous oxide.
15.4.2.2
Silver-loaded rGO ZnO nanocomposite
A silver-loaded ZnO rGO hybrid was fabricated by a simple chemical route using an acetylene gas sensor. As a result of this combination, we obtained not only a well-structured crystalline nature but also mixed phases of silver, graphene, and zinc oxide. Morphological observation indicates that ZnO and Ag nanoparticles are distributed well closely on the surface of thinlayer rGO sheets.
15.4.2.3
GO SnO2 nanocomposite
A rGO tin dioxide-based sensor has good sensitivity for propanol, which has major volatile aldehyde utilized in chemical and medical industries. These nanocomposites were also utilized for the detection of gases like H2S, ammonia, and nitrogen dioxide.
Chapter 15 Graphene-based electrochemical sensors
15.4.3
Heavy metal ion sensing
Heavy metal ions like lead, mercury, silver, cadmium, arsenic, and so forth caused pollution in the ecosystem. The highly water-soluble compounds can easily get adsorbed and absorbed anywhere. Hence, development of selective and sensitive techniques is required to examine and control the effects of these toxins on the ecosystem.
15.4.3.1
rGO PbO2
The rGO-lead dioxide composite was described as an fantastic material for the detection of arsenic (limit of detection 5 10 nM) [14]. Possibly, the rGO PbO2 composite can also be used for detection of arsenic and lead simultaneously.
15.4.3.2
rGO SnO2 nanocomposite
Yan Wei et al. [12] isolated cadmium [Cd (II]), lead [Pb (II)], copper [Cu (II)], and mercury [Hg (II)] ions after many studies, utilizing a glassy electrode using SnO2 nanoparticles with graphene. The studies shows that SnO2/rGO nanocomposite has combined properties of both SnO2 and graphene composite, and electrochemically, it can detect heavy metal ions.
15.4.3.3
rGO ZnO nanocomposite
Wei Liu et al. [12] blended graphene with ZnO through reduction of GO to synthesize the rGO ZnO nanocomposite. He synthesized the graphene carbon electrodes using the hydrothermal method to prepare a new rGO ZnO nanocomposite. This composite is used for the detection of heavy metals, for instance, Cu (II), Cd (II), Hg (II), and Pb (II) in aqueous solutions. The limit of detection values are found to be extraordinarily lower than the values given by the World Health Organization. Hence, rGO ZnO has greater merits of ZnO and graphene to detect heavy metal ions.
15.4.4
Inorganic sensing
15.4.4.1
Hydrogen peroxide
Zhi-Liang et al. [12] synthesized the MnO2 rGO nanoribbons, denoted as MnO2/rGONRs by a single-step hydrothermal method. The hydrogen peroxide detection is accomplished by this composite electrode. The electrochemical properties of this composite can also be investigated by this sensor (Fig. 15.6).
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Mul-walled Carbon Nano tubes
KMNnO4,H2SO4,H3PO4
Oxidaonal/Longitudinal Unzipping
Graphene Oxide Nano Rods
Citric Acid
MnO2/rGONRS
Single step Hydrothermal Coreducon
KMnO4
Figure 15.6 The schematic presentation of the preparation of MnO2/rGO.
15.4.4.2
Cyanide
Cyanide is a toxic but widely used industrial chemical. Cyanide ions were determined amperometrically by Hallaj and Haghighi. They introduced an improved glassy carbon electrode. At first, aminopropyltriethoxysilane was coated on the TiO2 nanoparticle surface and then GO nanosheets were placed on the surface of the glassy carbon electrode. Reductive deposition of reduced 4-nitrophenol was done. The GO-tin dioxide-ASrNPh glassy carbon electrode was utilized to design a photoelectrochemical amperometric cyanide. This sensor can detect cyanide at such an extensive range of concentrations [12].
15.4.4.3
Hydrazine
15.4.4.3.1 Glassy carbon GO MnO2 Lei et al. [12] synthesized glassy carbon MnO2 GO. MnO2 GO was coated onto the glassy carbon surface by the sonication method, and then the nanocomposite was utilized for hydrazine detection. The transmission electron microscopy image of the GO nanocomposite shows that after the MnO2 nanoparticle was placed homogeneously on the graphene sheet, the GO gains a smooth surface area. It was also observed that the interaction between GO and nanoparticles was good. Hence, we can say that this nanomaterial is more stable and selective and has good electrocatalytic activity and detection limit against hydrazine. 15.4.4.3.2 Polypyrrole GO Fe3O4 Yang et al. [12] prepared an Fe3O4 nanoparticle made of polypyrrole and GO denoted as Fe3O4 PPy GO. This combination is accomplished by oxidative polymerization and coprecipitation. The Fe (III) ion works as both the oxidant for pyrrole as well as a precursor of Fe3O4. In this case, the transmission
Chapter 15 Graphene-based electrochemical sensors
electron microscopy indicates that Fe3O4 is distributed homogeneously and densely. The traces of hydrazine in wastewater can be detected by this electrode. It has high stability and can be vastly used as an electrochemical sensor.
15.4.5
Organic sensing
15.4.5.1
Phenolic compounds
15.4.5.1.1 GO ZnO nanocomposite Tanvir et al. [12] synthesized an electrode consisting of nanocomposite GO zinc oxide (GO ZnO) to oversee the electrochemical behavior of phenol. The nanocomposite is highly stable and precise and has an appropriate reproducibility. The detection limit was about 2.2 nM. 15.4.5.1.2 rGO-based MnO2 Nanocomposite Wire Yaling Tian et al. [12] made rGO nanocomposites based on manganese nanowire. Manganese oxide nanowire was fabricated on rGO or glassy carbon electrodes to determine bisphenol A (BPA). This nanocomposite was receptive and potentially consistent. Besides this, it has properties such as reproducibility, selectivity, sensitivity, and stability. By quantitative analysis on the basis of the augmented experimental conditions, it was observed that this composite has a better linear response with respect to BPA concentration within the range of 0.02 20 μM and 20 100 μM. The detection limit in this case was 6.0 nM. The merits of this method were sensitivity, good synthesis, fast response, and low cost. In this work, more electrochemical sensors were modified for sensing application of BPA.
15.4.5.2
Aromatic nitro compounds
15.4.5.2.1 GO TiO2 nanocomposite 4-nitrophenol is a compound which is vital for the environment and human health. It was detected by Raja Nehru et al. [12] who constructed an electrode made of the GO-titanium dioxide nanocomposite. This simple electrochemical sensor has great potential for toxins detection like 4-Nitrophenol. This nanohybrid is prepared by the ultrasound sonication method. The GO TiO2 nanocomposite displays excellent performance in detecting 4-nitrophenol with high sensitivity and low detection and quantification limit. This composite has a relative standard deviation value of 2.35% and storage stability of 91.5%. To detect 4-nitrophenol in river samples, the standard addition
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method is used. Owing to its good electrocatalytical activity, this composite shows good potential to detect 4-nitrophenol. 15.4.5.2.2 rGO ZnO nanocomposite Alam et al. [12] synthesized polyethylene glycol-mediated rGO ZnO nanocomposites by an uncomplicated and economical chemical reduction method. They utilized GO and zinc acetate as the precursors. The morphology and thermal decomposition of this nanocomposite were identified by different advanced techniques. The glassy carbon electrode sensor can also be fabricated with a thin layer of presynthesized rGO ZnO nanocomposite to detect selective 2-nitrophenol. The electrochemical responses indicate high sensitivity, large dynamic range, and good stability with respect to the selective 2-nitrophenol. The detection limit was 0.27 nM. Because of its good stability, this nanocomposite can also be applied for waste water samples. This electrochemical sensor can also detect 2-nitrophenol in the environmental samples in trace amounts.
15.5
Conclusions
The effective combination of GO and MO will pave the way to further design and explore several varieties to determine their applications in different sectors like medical, industrial, energy, and so forth. These nanohybrids are faster and efficient owing to their low cost and rapid response. They are reliable for gas sensing, biosensing, chemical sensing, and toxin sensing. They can be functionalized as well as modified to change their optical and electrochemical properties. Their stability and selectivity make their use on a large scale very easy. Each combination of GO with MO can be utilized for specific and selective sensing. Keeping the research updated for GO and MO will be very beneficial in security, pharmacology, environmental, and energy sectors. Introducing new techniques and new combinations may enable us to sense sophisticated materials that have not yet been characterized.
References [1] A. Hazra, N. Samane, S. Basu, A review on metal oxide-graphene derivative nano-composite thin film gas sensors, Multilayer Thin Films: Versatile Applications for Materials Engineering, IntechOpen, 2020, p. 1.
Chapter 15 Graphene-based electrochemical sensors
[2] A. Halder, M. Zhang, Q. Chi, Electrocatalytic Applications of Graphene Metal Oxide Nanohybrid Materials. Advanced Catalytic Materials: Photocatalysis and Other Current Trends, 2016, pp. 379 413. [3] S.K. Hazra, S. Basu, Graphene-oxide nano composites for chemical sensor applications, C—J. Carbon Res. 2 (2) (2016) 12. [4] M. Khan, et al., Graphene based metal and metal oxide nanocomposites: synthesis, properties and their applications, J. Mater. Chem. A 3 (37) (2015) 18753 18808. [5] K. Zhang, et al., Copper oxide graphene oxide nanocomposite: efficient catalyst for hydrogenation of nitroaromatics in water, Nano Convergence 6 (1) (2019) 1 7. [6] T. Tite, et al., Impact of nano-morphology, lattice defects and conductivity on the performance of graphene based electrochemical biosensors, J. Nanobiotechnol. 17 (1) (2019) 1 22. [7] S. Dong, et al., High loading MnO2 nanowires on graphene paper: facile electrochemical synthesis and use as flexible electrode for tracking hydrogen peroxide secretion in live cells, Anal. Chim. Acta. 853 (2015) 200 206. [8] B. Gurze˛da, et al., Graphene material prepared by thermal reduction of the electrochemically synthesized graphite oxide, RSC Adv. 6 (67) (2016) 63058 63063. [9] M.R. Karim, S. Hayami, Chemical, thermal, and light-driven reduction of graphene oxide: approach to obtain graphene and its functional hybrids, in: G.Z. Kyzas, A.C. Mitropoulos (Eds.), Graphene Materials- Advanced Applications, IntechOpen, 2017, pp. 89 103. [10] Y. Tian, et al., CuO nanoparticles on sulfur-doped graphene for nonenzymatic glucose sensing, Electrochim. Acta 156 (2015) 244 251. [11] A.T. Smith, et al., Synthesis, properties, and applications of graphene oxide/ reduced graphene oxide and their nanocomposites, Nano Mater. Sci. 1 (1) (2019) 31 47. [12] S. Vinodha, L. Vidhya, T. Ramya, Graphene-metal modified electrochemical sensors for toxic chemicals, Graphene-Based Electrochem. Sens. Toxic. Chem. 82 (2020) 91 124. [13] A. Pandikumar, et al., Graphene and its nanocomposite material based electrochemical sensor platform for dopamine, RSC Adv. 4 (108) (2014) 63296 63323. [14] N.F. Atta, A. Galal, E. El-Ads, Graphene—a platform for sensor and biosensor applications, Biosensors-Micro Nanoscale Appl. 9 (2015) 38 84.
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16 Polymer-based self-healable materials for energy storage M. Ramesh1 and A. Saravanakumar 2 1
Department of Mechanical Engineering, KIT-Kalaignarkarunanidhi Institute of Technology, Coimbatore, Tamil Nadu, India 2Department of Mechanical Engineering, Dhanalakshmi Srinivasan College of Engineering, Coimbatore, Tamil Nadu, India
16.1
Introduction
Worldwide energy utilization has been constantly growing in the past few decades as a result of high population growth. Devices that can store energy are suitable for transportable electronic devices and storage in grid scale for the effective utilization of resources from renewable energy. There is a strong requirement for superior energy storage devices to cater to the essential necessity of human life. Traditional energy storage materials and resources are supported either on porous carbon or on lithium-ion batteries. Even if the newgeneration lithium-ion batteries are proficient of powering electric vehicles to a restricted driving range while charging, they are still far from achieving the goal of 500 km [1]. Further, lithium-ion batteries have many downsides such as damage to batter life due to lithium metal electrodes’ reactivity leading to dendrite formation. By considering the drawbacks of lithium-ion batteries, solid polymer electrolyte systems are developed, which slow down the dendrite growth and enhance its energy density, power efficiency, and so forth [2]. Conductive polymers fall under the conventional type of pseudocapacitive materials, which may be used in electrochemical doping or redox reaction with anions and cations. Many conducting polymers such as polyaniline, polypyrrole, and derivatives of polythiophene have been widely applied in supercapacitors in light of their large capacitances, good flexibility, and high conductivity [3]. Conductive polymers are promising candidates as selfhealing materials because of low cost, high capacitance, light weight, excellent conductivity, and good flexibility, and they can store energy through redox reactions [4 7]. In this scenario, conducting polymer-based self-healable materials entered into the Nanomaterials-Based Electrochemical Sensors: Properties, Applications, and Recent Advances. DOI: https://doi.org/10.1016/B978-0-12-822512-7.00016-8. © 2024 Elsevier Inc. All rights reserved.
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storage system with the intention of developing the electrochemical performance of the energy storage system. So many types of energy storage systems are available, among which electrochemical storage system for energy (EES) expedients are predominantly chosen and entered into the limelight of significant scientific concern. Predominant parameters for assessing the performance of EES are energy and power density, specific capacity, life cycle, safety, and cost. Conducting polymers characteristics were discovered in 1977, and in particular, researchers found conducting properties of this new class of polymer material [8]. An essential feature of polymers is the tailorable and impending control of properties with the use of ingenious chemicals and artificial concepts discovered from the major investigations on carbon-based chemistry [9]. The progress of the conducting polymer synthesis technique can be classified into three generations [10]: the initial generations of conducting polymeric materials were prepared through adding conductive fillers or additive materials. The next generation of polymeric materials has the inherent potential of carrying electric current without the aid of additives. The third generations of conducting polymers are generally insulators or fair conductors that can be made conductive by incorporation of conductive fillers or additives. This type of polymer materials’ conductivity purely rests on the character of the dopants and the range of doping. Polymers played a major role in many insulator-based applications because of their insulating properties. Generally, electrical conduction takes place in polymers because of the inaccurately bound ions, whose action was taken into account seriously [11]. Polymers are the upcoming materials of the 20th century, which were earlier used in coatings or other inactive applications, and are now being involved in active applications like optical, mechanical, electrical, and energy storage and other diversified areas of technology.
16.2
Conductive polymeric materials
Polymeric materials prepared by inclusion of conductors, for example, metalized fibers, carbon black, or metal flakes, and by the electrochemical and chemical production technique are termed as conductive polymeric materials. Discovery of conducting polymers and their capability to dope them to their fullest capacity into metal from an insulator was mostly interesting since this formed an innovative research area in the interface connecting condensed-matter physics and chemistry [12]. Most
Chapter 16 Polymer-based self-healable materials for energy storage
importantly, conducting polymers presented the guarantee of attaining the current equivalents of polymers. These materials demonstrate the optical and electrical properties of metals or semiconductors and still have advantages of polymers with striking mechanical properties. Conducting polymers are classified as follows: 1. According to polymer and dopant material nature a. Conjugated polymeric materials b. Charge transfer polymers c. Ironically conducting polymers d. Conductively filled polymers 2. According to the conduction mechanism a. Conducting polymers b. Organometallic polymers c. Polymeric charge transfer complex d. Polymers with inherent conductance In the case of conjugated materials, carbon compounds in large chains hold alternating single and double bonds, which directs restricts the presence of one carbon atom per unpaired electron. In charge transfer polymer materials, continuous one-dimensional bands formed due to the overlapped orbital on adjacent molecules. The electron donor and acceptor molecules exchange the electrons between them, which is said to be the charge carriers in the structure. Ionically conducting polymers, because of exchange of ions within the coordination regions continually produced through the local motion of polymeric molecular chain segments, increase the conductivity [13]. These polymers be a symbol of a reasonably new category of solid ionics. Conductivity is bringing in the inclusion of the conducting materials in diverse polymeric chains counting crystalline and amorphous polymeric materials, which could be converted as conductors of electricity as far as the electrically conductive polymers are concerned. The polymer composites that are conductive undergo synthesis generally through the inclusion of filler materials, which are also conductive with the polymer matrix, which is insulating. When organometallic collections to molecules of polymer are added to conducting materials, organometallic polymeric conductors were obtained. The polymeric charge transfer complex is produced once acceptor molecules are included with the insulating polymers. Research on inherently conducting polymers was started almost four decades ago, and radical augmentation in conductivity of polyacetylene (PA) thin films was found when exposed in the open to iodine vapor [14].
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Polyethyne was the first polymer manufactured with considerable conductivity and was found to have electrical conductivity. In 1974, using a Ziegler-Natta catalyst, PA was first obtained as a silver-colored film from acetylene. The first trial did not give a very conductive polymer in spite of its metallic appearance. Later in 1977, it was noticed and found that when halogen vapor undergoes oxidation, it generates PA film with an enormous amount of conductivity [15]. This property was relatively and considerably greater when compared with the other recognized conductive polymers. This point of innovation initiated many new developments of the conductive organic polymers. The presence of a conducting band of conjugated polymers such as PA is the main reason for conductivity of nondoped material. On the other hand, nondoped polymers possess a moderately low conductivity when compared to doped materials. The definite conductivity was based on the structure and morphology of the polymer and also depends on its concentration and nature of the dopant. The conjugated polymers, as most organic polymers do not have intrinsic charge carriers, are considered to be electrical insulators and semiconductors. Such a type of polymeric materials can turn extremely conductive by incorporating or inserting electrons into their atomic field. This phenomenon of modification of the atomic structure is termed as doping. When an electron is detached by oxidation (p-doping) from the valence band or conducting band added with an electron by reducing it through n-doping, the polymer becomes extremely conductive. The different doping techniques are redox p-doping, redox n-doping, electrochemical p- and n-doping, and photoinduced doping. Polymer chains’ mechanical alignment is another technique to increase conductivity in the conductive polymer material. In PA, 105 S m21 conductivity is observed, which is still quite a few magnitudes inferior to that of silver and copper (108 S m21). However, for electronic applications like light-emitting diodes, lasers, and polymer-based transistors, this conductivity range is adequate. By adding conductive additives or fillers into the polymeric composite materials, their conductivity can be instigated. Classic conductive materials utilized to manufacture this type of conducting polymers comprise conducting solids like metal-coated fillers and particles, stainless steel fibers, aluminum flake carbon-fibers, and conjugated conducting polymers. Since the conductivity is initiated by inclusion of the conducting components with polymer materials containing both crystalline polymers and amorphous polymers, they can be electrically conducting. A variety of synthesis techniques, for
Chapter 16 Polymer-based self-healable materials for energy storage
299
Table 16.1 Electrical conductivity of some conductive polymers. Compound
Repeating unit
Trans-polyacetylene
103 105
Polythiophene
103
Polypyrrole
102 7.5 3 103
Poly(p-phenylene)
102 103
example, in situ polymerization, extrusion, and hot compression, were used to manufacture the polymers filled with conductivity. This kind of material was used for a variety of applications, like electromagnetic interference/radiofrequency interference and electrostatic discharge protection [16]. Conductive polymeric materials combine a few smart properties from the usual polymeric material and distinctive electronic characteristics of semiconductors [6]. In recent times, many researchers have shown considerable interest in nanostructured conductive polymers as a result of their exclusive properties over their bulk counterparts, for example, shortened pathways for charge and large surface areas, which endow them with wide applications in energy conversion and storage. The electrical conductivity of some conductive polymers is given in Table 16.1.
16.2.1
Conductivity (S cm21)
Band theory
While studying about conducting polymers, it is important to know about the band theory. The energy band gap distance decides the polymer properties whether it is insulator, metal, or semiconductor. The band theory explains that electrical properties of direct gap inorganic semiconductors are decided by their structure of electronics and movement of the electrons within discrete energy states called bands. The energy band diagram is given in Fig. 16.1.
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Chapter 16 Polymer-based self-healable materials for energy storage
Figure 16.1 Energy band diagram demonstrating energy gap (eV).
Conduction band
Conduction band
Conduction band
Eg = 0 eV
Eg = 1- 3 eV
Eg> 3 eV
Valence band
Valence band
Valence band
(A) Metal
(B) Semiconductor
(C) Insulator
The result of the energy band from the orbital bonding of a molecule is known as the valence band, where the antibonding orbital of the molecule is known as the conduction band. The individual movement of delocalized electrons through the range of energy levels is called bandwidth. The gap between the highest energy level that is filled and the lowest energy level that is unfilled is called band gap (Eg). This band gap characterizes a series of energies that cannot be used by the electrons, and this gap is known as the energy gap. The size of the gap of the energy band is based on extent of delocalization and the change of double and single bonds. The size of the energy band gap demonstrated in the figure shows that the conducting polymer is metal, semiconductor, or insulator [17].
16.3
Self-healing material
Self-healing materials are simulated or synthetic materials, which have the inherent ability to repair the impairment by themselves without human intervention or any peripheral analysis of the calamity. The massive requirement of polymer materials enforced to lengthen their reliability and long lifetime. A novel class of polymers capable of renovating their functionality after injury or damage was analyzed. A three-step process followed by self-healing polymers is similar to a biological response. If damage happens, the first kind of response is actuation or triggering, which occurs to maintain damage. The material supplied to the affected area is the second kind of selfhealing that also occurs immediately. This kind of polymers can be grouped into two diverse categories depending on the strategy of the self-healing mechanism: intrinsic or extrinsic [18]. Intrinsic self-healing polymers are materials proficient in revamping molecular and macroscale damages by means of enhancing the movement of polymeric molecules temporarily. Such behavior is commonly centered toward explicit polymeric molecular structures, which allow for important moves in
Chapter 16 Polymer-based self-healable materials for energy storage
interchain mobility upon the delivery of diffident measures of energy followed by a process of renovation of the chemical or physical bond strength after the removal of stimulus. Selfhealing needs the material enervation during manufacturing for the pre-embedded materials. Such a type of mechanism is called as extrinsic self-healing. The design approaches of the self-healing materials are mixed up in different categories like metals, concrete, ceramics, and paint coatings with suitable processing of its self-repairing setups. Discharging of healing materials into cracks that are well-established into the structure of polymers during the establishing phase was the other design strategies of selfhealing materials. Reversible cross-linking is specifically utilized to accomplish superlative mechanical characteristics such as high strength against fracture in self-healing materials, even though it holds the reproducing competence of the selfhealable polymers. Many researchers hoped that the storage devices and energy harvesting with self-healability can overhaul breakages, cracks, or other forms of mechanical damages, in order to refurbish the unique performances or diminish the failure of the devices [19 22]. This will considerably enlarge the lifetime and develop the durability of the devices and decrease the economic cost and electronic waste [23]. In its present form, these materials are foreseen to contribute significantly to the shelter and robustness of polymeric components without much costs of active monitoring or exterior repair. All the way through the growth of this new variant of smart materials, the replicating of biological systems is motivating the nextgeneration materials [24].
16.4
Self-healing materials for energy storage
Swift developments in electronic devices and energy storage devices with high safety and performance have attracted interest due to the growing demand for renewable energy [25 29]. According to the system of nature, some restoration of biological system functions is possible by healing the damages. Recently, nonnatural self-healable materials have been developed for storage of energy and its harvesting by using the basic principle of a biological system [30 33]. According to these materials, the two major areas of self-healing energy storage devices are supercapacitors and lithium batteries. Based on their functional aspects, they could be categorized as ionic conductors, electrical conductors, insulators, and semiconductors [34].
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Self-healing polymers are mostly insulating by nature. Because of this property, these polymeric materials can be used as supporting elements for electronic devices, dielectric layers, and encapsulating materials in their original form. The self-healing polymer exhibited very less creep when loaded and larger elongation after recovery in the order of 100%. It was also noticed that the healing cycles of these materials were very large, in such a way that they could heal themselves at room temperature without being induced by any external stimulus. Moreover, the self-healing insulator acts as barrier coatings for numerous electronic applications and devices. For example, in the fiber/yarn-shaped supercapacitors, the self-healing polyurethane polymer was utilized as an encapsulating material. Hence, it could be concluded from the abovementioned discussions that the demand for the development of self-healing multifunctional encapsulation materials is inevitable for various applications like energy storage, wearable electronics, portable devices, and energy harvesting. This could also enhance the reliability of such applications when these materials are used. When the conductive network within the polymer chains is rearranged and constructed, self-healing conductive materials arise. In the previous researches, the conductive materials were encompassed in microchannels or capsules and were placed inside the polymer matrix, turning them into self-healable conductive materials. Most of the early researchers focused on developing microcapsules with conductive liquids such as carbon material suspensions [35,36] and liquid metals [37,38] in order to fabricate self-healing conductive polymeric materials. Other researchers tried to coat the conductive materials over the selfhealing polymer substrates for converting them into potential self-healing conductive polymers. Nevertheless, the researchers faced many challenges in fabricating a self-healing electrically conductive polymeric material with better flexibility, enhanced conductivity, improved stretchability, better mechanical characteristics, and rapid self-healing ability. Recent researches have proved that incorporating the conductive filler materials into the self-healing polymeric material could result in an efficient selfhealing conductive polymer, and this could be done by properly selecting the conductive filler, self-healing polymer, and the ratio of both to obtain the final material. Polyelectrolytes are characterized with high ionic conductivity in the order of 1024 to 1023 S cm21 and are much better for energy storage applications when compared with solid-state electrolytes. Self-healing ionic conductors are currently made of reversible cross-linkers and abovementioned polyelectrolytes.
Chapter 16 Polymer-based self-healable materials for energy storage
The initial research on ionic conductors was carried out by a few researchers with the fabricated self-healing ionic conductors containing vinyl hybrid silica nanoparticles (VSNPs) as cross-linkers and a hydrogel electrolyte comprising polyacrylic acid (PAA) and proton ion content as self-healing materials [39]. H3PO4 proton ionic provider endowed enhanced ionic conductivity to the abovementioned self-healing conductive polymer. Hydrogel exhibited stretchable behavior by the hydrogen bond and VSNP dual cross-linking, which also resulted in faster self-healing. The rate of stretching of the polymers was about 3700% more than its original value and was due to the restoration of ionic conductivity and inherent mechanical properties of the PAA-VSNP polymer electrolytes at room temperature due to the reversible hydrogen intermolecular bonding. Novel self-healing conductive polymers are manufactured nowadays by incorporating ionic species inside the commonly used intrinsic self-healing polymeric materials. Few researchers tried to release the encapsulated precursor solution from microcapsules into the self-healing semiconductor materials for transferring the conductive charge salt, and the first ever semiconductor-based self-healing organometallic polymer was based on this approach [40]. Such organometallic polymers were characterized with the network structure, and their electrical conductivity was around 1023 S cm21. These organometallic elements were cross-linked with transition metals and carbene compounds with N-heterocyclic (NHC) reversible bonds, while both of these materials were dynamic in nature and electrically conductive. Electrical resistance of these compounds increased when microcracks were produced in the materials with conductive thin film and decreased in pathways for electron percolation. These conductive thin films induced self-healing of the materials by means of repairing the NHC-metal bondages when the fabricated materials were treated using solvent vapor and thermal treatment at 150 C. Few researches were carried out in producing an intrinsically self-healing and stretchable conductive polymer by means of noncovalent cross-linking based on hydrogen bonds, which were the first ever reported work in this area [41]. The nextgeneration energy storage and harvesting devices require a high electrical conductivity and unlimited self-healability, which are the major lacuna to be filled as far as the currently available selfhealing conductive semiconductors are concerned.
16.4.1
Supercapacitors
Electrochemical capacitors or supercapacitors are highly useful devices for the storage of energy since they possess many
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Chapter 16 Polymer-based self-healable materials for energy storage
merits like high power density, fast charging and discharging characteristics, long lifetimes, and so on [35 37,41]. Generally, the sold-state supercapacitors were made of two electrodes and a gel electrolyte with a conventional device structure, which indicates the necessity of understanding the self-healability of electrodes and gel electrolytes for the manufacturing of self-healing supercapacitors. Revamp of electrical conductivity in the electrodes and the ionic conductivity of gel-based electrolytes were the most important concepts to be understood when self-healing electrolytes were developed. Many researchers have thrown light over the manufacturing strategies of self-healing conductors, and many practical selfhealing supercapacitors were utilized in various applications as a forerunner. Few authors investigated the self-healing supercapacitors, which were electrically and mechanically conductive [42]. Single-walled carbon nanotubes were deposited over the selfhealing material substrates to form healable electrodes and were made of TiO2 nanoparticles with supramolecular networks. In solid-state hydrogel electrolytes of supercapacitors, polyvinyl alcohol (PVA) was the most commonly used substrate materials since it possesses better electrochemical and chemical solidity [43]. Few authors tried to fabricate the self-healing PVA hydrogel electrolyte by using PAA coupled with diol-borate dynamic ester bonding [44]. This gel-based electrolyte could reinstate ionic conductivity and mechanical characteristics of the materials to almost 100% at room temperature within a time of 20 min even when the cutting and healing cycles were about 15 in number. This was primarily due to the aforementioned dynamic bond between PVA and borax within diol-borate ester bonds.
16.4.2
Lithium batteries
Electric vehicles, medical implants, and portable electronic devices require next-generation lithium-ion batteries, as their power sources, with high energy storage capacity and long lifecycles [39,40,42 53]. In order to render high energy density during power storage, traditional graphite anodes were substituted with metallic alloys, composites, and silicon as electrode materials, which were considered to possess high theoretical energy storage capacities [51,54,55]. Yet, the life cycle of these novel electrodes could be extended further due to the initiation and propagation of microcracks in these materials, when they undergo a structural change, which hinders the availability of these electrodes for their utilization in lithium-ion batteries. When self-healing materials were considered for usage in lithium-ion batteries, such damages or mechanical cracks could be impetuously eradicated and the material might behave as
Chapter 16 Polymer-based self-healable materials for energy storage
self-healing lithium-ion batteries and the stability of the device could also be enhanced. Self-healing intrinsic active metallic alloys were used for the design and manufacture of self-healing electrodes, and attention was given highly toward this research [56,57]. Importance was also given toward incorporating the self-healing polymer materials into the electrodes in order to accomplish better self-healing lithium-ion batteries [58 61]. The performance of the energy storage and harvesting devices was tracked. Reducing their property loss can be done by the selfhealing materials, which possess the capacity to repair mechanical damages, cracks, or breakages as soon as they occur [21 23,62,63]. Conductive polymer-based self-healable energy storage materials are characterized with good mechanical durability, energy and power density, and high capacity and stability. Conductive polymers can be tailored as flexible supercapacitor electrode materials through electrochemical or chemical oxidation by layering them over a flexible substrate [64 70].
16.5
Conclusion
Recent developments in self-healing materials for storage and energy harvesting were discussed in this chapter. Almost all electronic devices require a self-healing electrical conductor as a salient component, which are specifically applied in contacts, current collectors of the devices, interconnects, and electrodes, and so these electrically conductive materials are the most investigated materials. The possibility of using the self-healing materials for fabricating numerous self-healing storage devices and energy harvesting systems was also discussed. From the perspective of material type, many self-healable materials were conveyed as conductors and insulators, while for developing semiconductors, a lot of efforts are required in the near future. Devices like selfhealing solar cells and self-healing triboelectric nanogenerators, under the category of energy harvesting devices, were described clearly for their self-healing concept applied to the key functions. In energy storage devices, self-healing lithium batteries and self-healing supercapacitors were materialized by employing self-healing electrolytes and designing self-healing electrodes, which derive the benefits from self-healing ionic and electrical conductors. Greater challenge lies ahead in developing appropriate self-healing electrical and ionic conductive materials for energy storage and harvesting. Convincingly, the field of selfhealing devices and materials are at the budding stage and thus have great research potential in the future.
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309
Index Note: Page numbers followed by “f” and “t” refer to figures and tables, respectively.
A AA. See Ascorbic acid (AA) Aberration coefficient, 4041 Acetone, 167t Acetylcholinesterase, 132133 Acoustic biosensors, 126 Active nanosensors, 177 Additive materials, 296 Adenocarcinoma (AGS) cells, 5455 Adenosine, 204 Adsorption, 7 Advanced nanosensors, 103 Aerogels, 23 AFP. See Alpha-fetoprotein (AFP) Agrochemicals, 285286 CoOrGO nanocomposite, 285 SnO2rGO nanocomposite, 285 Airblood barrier, 5658 Algae, 5556 Allium cepa, 5960 Alpha-fetoprotein (AFP), 200201 Aluminum oxide (Al2O3), 2223, 6061 Aluminum tensile-based nanomaterials, 181183 Ames test, 6364 Amino acid l-histidine decarboxylation, 211212 4-aminothiopheno (4-ATP), 140 Ammonia (NH3), 158159, 269 Ammonia gas sensors, 181183 Amorphous polymers, 297299 Amoxicillin, 204, 205f Amperometric biosensors, 132133
Amperometric detection, 217 Amperometric electrodes, 246 Amperometric sensors, 117 Amperometry, 3, 4t, 164165 Anabaena flosaquae, 66 Analyte detection, 248249 Analyte-responsive composites, 257261 Analyte-responsive hydrogels, 252257 biomolecule-containing hydrogels, 254255 enzyme-containing and enzymatically responsive hydrogels, 255257 recognitive and molecularly imprinted polymers, 252254 Analyte-responsive polymers, 248252 Analytical techniques, 3949, 39f atomic force microscope, 45 dynamic light scattering, 4244 electron microscopy, 3942 scanning electron microscope, 4142 transmission electron microscope, 4041 Fourier transform infrared spectroscopy, 4749 surface area, 47 thermogravimetric analysis, 49 X-ray diffraction, 4547 zeta potential instrument, 47 Antigens, 191193 Antiinflammatory drugs, 206 Antineoplastic drugs, 206
Antiseditious drugs, 206 Apoptosis, 5355 Apoptosis assay, 63 Aquatic ecosystems, 67 Aquatic environment, 5556 Arabidopsis thaliana, 6061 Aromatic nitro compounds, 291292 GOTiO2 nanocomposite, 291292 rGOZnO nanocomposite, 292 Arthrobacter globiformis, 66 Arthropods, 5556 Artificial neural network, 12 Ascorbic acid (AA), 14, 161162, 245 Aspirin, 207 ASTREE electronic tongue, 12 Atomic force microscope, 23, 45 Atomic layer deposition, 96 AuNPs. See Gold nanoparticles (AuNPs) Auto-correlation function, 44 Automotive industry, 37 Autonomous control, 261262
B Bacillus subtilis, 66 Background spectrum, 4849 Bacterial reverse mutation test, 6364 Band gap, 300 Bands, 299 Band theory, 299300 Bandwidth, 300 BeerLambert’s law, 27, 165 β-cyclodextrin (β-CD), 257258
311
312
Index
Bimetallic nanomaterials, 2526 Bioengineering, 38 Biofuel cells, 146 Biomedical applications of electrochemical sensors, 201207 gold nanostructures in, 238 RFID nanosensors for, 186187 Biomolecule-containing hydrogels, 254255 Biosensors, 15, 123125, 157, 191193 components of, 125 direct deposition methods of, 138f direct growth, 145 electrochemical biosensor, 129133 amperometric biosensors, 132133 potentiometric biosensors, 131132 electrode fabrication technologies, 133144 magnetic nanoparticles for, 196f modules of, 124f self-powered implantable biosensor, 146148 glucose detection, 147148 transducers, 125129 calorimetric biosensors, 129 optical biosensors, 126128 piezoelectric biosensors, 128129 Bisphenol A (BPA), 14, 117118, 167t Blade coating method, 137 Block copolymers, 23 Bloodbrain barrier, 5658 Body fluid ketones, 203 Boltzmann constant, 43 Borrelia, 253254
Bovine serum albumin, 252253 BPA. See Bisphenol A (BPA) Bragg’s law, 46 Bronze Age, 21 Bucky paper, 109 Bulk acoustic wave (BAW), 128129 Butyrylcholinesterase, 132133
C Cadaverine, 211212 CEA. See Carcino-embryonic antigen (CEA) Caenorhabditis elegans, 56 Caffeic acid, 14 Caffeine, 14 Calorimetric biosensor, 126, 129 Calorimetry, 214 Cancer cell detection electrochemical biosensor in, 111112 electrochemical immunosensors in, 112 electrochemical nucleic acid biosensors in, 112113 Cancer therapy, 186 Candida albicans, 5859 Capacitance (C), 3, 4t Capillary sensors, 194 Capillary-zone electrophoresis, 214 Carbon, 2223 Carbonaceous nanoparticles, 221222 Carbon-based nanomaterials, 1213, 2425 Carbon-based nanoparticles, 257 Carbon black, 296297 Carbon Bucky paper, 109 Carbon dioxide (CO2), 269 Carbon monoxide (CO), 269 Carbon nanodots, 134136 Carbon nanofibers, 140 Carbon nanomaterials, 139 Carbon nanoparticles, 191193 Carbon nanotubes (CNTs), 2122, 57t, 92, 108109, 132,
155156, 179, 183, 186187, 199201, 228, 245, 257258 graphene, 200201 Carbon paste electrode (CPE), 163164 Carcino-embryonic antigen (CEA), 107108, 163164, 167t Carotenoids, 6061 Catecholamines, 245 CEA. See Carcino-embryonic antigen (CEA) Cell contact, 111112 Cell death, 5960 Cell drift, 111112 Cell impedance sensing, 111112 Cell membrane, 58 Cell signaling, 197 Cell structure, 111112 Cellular imagining, 30 Cellular transport system, 58 Cellulose nanofibrils, 181183 Central nervous system, 207 Cerium oxide-based sensors, 162 Cerium oxide nanoparticles, 55t CEs. See Counter electrodes (CEs) Charge transfer, 7, 297 Chemical catalyst, 29 Chemical composition, 24 Chemical functionalization, 272273 Chemically modified electrodes (CMEs), 77, 84 Chemical methods, 271, 276278 metal-mediated reduction of graphene oxide, 277278 plant extracts as reducing agent, 278 Chemical process, 167 Chemical sensing, 285287 agrochemicals, 285286 CoOrGO nanocomposite, 285 SnO2rGO nanocomposite, 285
Index
dopamine, 286287 Fe3O4rGO nanocomposite, 287 GOSiO2 nanocomposite, 287 rGOTiO2 nanocomposite, 286287 SnO2GO fabricated with sodium dodecyl sulfate, 287 glucose, 286 CuOrGO nanocomposite, 286 rGONi (OH)2 nanocomposite, 286 organophosphorus, 286 Chemical sensors, 23, 1112, 79, 156157, 191193, 245, 269 types of, 79 Chemical vapor deposition, 140 Chemiluminescent sensing, 169170 Chemisorption method, 95 Chlorophyll, 6061 Cholesterol biosensor, 130, 131f Chronoamperometry technique, 6, 164 Clark’s electrode, 13, 2f, 130 Classic conductive materials, 298 CMEs. See Chemically modified electrodes (CMEs) CNTs. See Carbon nanotubes (CNTs) Coating, 133134 Coating-based methods, 134137 blade coating, 137 dip coating, 136 drop casting, 134136 spin coating, 136137 Colorimetric sensing, 168169 Colorimetric technique, 165 Competent indicators, 204 Composite nanomaterials, 26 Conducting polymers (CPs), 198, 297 Conduction band, 298, 300
Conductive fillers, 296 Conductively filled polymers, 297 Conductive organic polymers, 298 Conductive polymeric materials, 296300 band theory, 299300 Conductive polymers, 12, 142143, 183, 259, 295296 Conductivity, 297 Conductometric sensing technique, 8081 Conductometric sensors, 80 Conductometry, 3, 4t Conjugated polymeric materials, 297 Conjugated polymers, 298 Contradictory effects, 5960 Copper, 184 Copper nanoparticles, 57t, 60t Copper oxide (CuO), 198 Copper oxides-based sensors, 161162 Core-shell nanoparticles, 221 Correlation function, 44 Cottrell equation, 6 Coulometric sensors, 80 Coulometry (Q), 3, 4t Coulometry measurement techniques, 81 Counter electrodes (CEs), 8182, 96, 195197 CPE. See Carbon paste electrode (CPE) Crystalline polymers, 298299 Crystallization, 7 CuO. See Copper oxide (CuO) Cupric oxide nanoparticles, 55t CV. See Cyclic voltammetry (CV) Cyanide, 290 Cyclic voltammetry (CV), 89, 8182, 117, 160161, 164 basic principle of, 8182 Cyprinus carpio, 66 Cytoplasm, 5960, 63 Cytotoxic assays, 6263 5-diphenyltetrazolium bromide assay, 62
313
apoptosis assay, 63 neutral red uptake assay, 63 oxidative assays, 6263 reactive oxygen species, 6263 Cytotoxicity, 53
D Damascus steel, 21 Dansyl, 255256 Daphnia galeata, 66 Daphnia magna, 66 Daphnia pulex, 5556 Defects, 279 Dendrimers, 91 Deoxyuridine triphosphate (dUTP), 63 Deposition-based methods, 137140 Desmodesmus subspicatus, 66 Desorption, 7 Diabetes mellitus, 147148 Diamagnetism, 197 Diamine oxidase (DAO), 212213 Dicentrarchus labrax, 5556 Dicholoromethane, 259 20 , 70 -dichlorofluorescein diacetate (DCFDA), 6263 Differential pulse voltammetry (DPV), 910, 117, 167168, 222 Dip-coated method, 136 5-diphenyltetrazolium bromide assay, 62 Direct growth, 145 DNA, 191193 DNA damage, 53, 5859 Dopamine, 5658, 167168, 167t, 204, 286287 Fe3O4rGO nanocomposite, 287 GOSiO2 nanocomposite, 287 rGOTiO2 nanocomposite, 286287 SnO2GO fabricated with sodium dodecyl sulfate, 287 Dopamine methacrylate, 257
314
Index
Double-walled CNTs, 95 DPV. See Differential pulse voltammetry (DPV) Drop-casting method, 134136 Drug delivery, 91, 237f dUTP. See Deoxyuridine triphosphate (dUTP) Dynamic light scattering, 4244 correlation function, 44 Dynamic methods, 45
E Echinoderms, 5556 ECL. See Electrochemiluminescence (ECL) EFCs. See Enzymatic biofuel cells (EFCs) EIS. See Electrochemical impedance spectroscopy (EIS) Electrical conductivity, 27, 248, 298 Electric vehicles, 304305 Electroanalytical chemistry, 7778 advantages, 78 electroanalytical techniques, 77 improvements needed, 78 recent developments in detection techniques, 7778 Electrochemical and chemical production technique, 296297 Electrochemical biosensor, 111112, 129133 amperometric biosensors, 132133 potentiometric biosensors, 131132 Electrochemical capacitors, 303304 Electrochemical cell anode, 5 cathode, 5 power source, 5 voltmeter, 5
of antibiotics in biological samples, 204 of nitrogen oxide in human beings, 205 in plants, 205 Electrochemical doping, 295296 Electrochemical immunosensors, 112 Electrochemical impedance spectroscopy (EIS), 1011, 81, 158, 165 Electrochemical methods, 217218, 271, 278279 amperometric detection, 217 impedimetric detection, 217218 synthesis of GOMO electrodes, 279 voltammetric detection, 218 Electrochemical nanobiosensors, 111 Electrochemical nucleic acid biosensors, 112113 Electrochemical sensing technique, 164165, 167168, 238 amperometry, 164165 cyclic voltammetry, 164 electrochemical impedance spectroscopy, 165 linear sweep voltammetry, 164 Electrochemical sensors, 3, 7981, 9495, 125, 191193 advantages of, 80 analyte, 5 applications of, 82 biological and biomedical applications of, 201207, 202f antiinflammatory drugs, 206 antineoplastic drugs, 206 body fluid ketones, 203 for detecting pathogens, 206
electrochemical detection of antibiotics in biological samples, 204 electrochemical detection of nitrogen oxide in human beings, 205 electrochemical detection of nitrogen oxide in plants, 205 forensic drugs, 207 healthcare, 207 measurement of biomolecules, 205 metabolite, 202203 pharmaceutical applications, 207 quantitation of neurochemicals, 204 recognition of H2O2 from breast cancer cells, 203 carbonaceous materialsbased, 94 carbon-based electrode materials, 8385 chemically modified electrodes, 84 glassy carbon electrodes, 84 components and working of, 116117 components of, 193195 electrodes, 195 electrolyte, 195 filters, 195 hydrophobic membrane, 194 configurations of, 117118 construction of, 80 conventional setup of, 194f cyclic voltammetry, 89, 8182 basic principle of, 8182 differential pulse voltammetry, 910 electroanalytical chemistry, 7778 advantages, 78 electroanalytical techniques, 77 improvements needed, 78
Index
recent developments in detection techniques, 7778 electrochemical impedance spectroscopy, 1011 electrodes, 5 electronic tongue, 1114 fabrication of nanomaterialbased, 197201 carbon nanotubes, 199201 magnetic nanomaterials, 197198 metal oxide, 198 noble metals, 199 polymer, 198 of heavy metal ions, 8283 metal-derived materialsbased, 9495 nanomaterials-based, 95 reaction medium, 5 sensors, 7879 chemical sensors, 79 ideal sensor, 7879 sensory unit, 5 square wave voltammetry, 10, 11f types of, 8081 voltammetric methods, 78 working principle of, 83f, 195197 Electrochemical storage system for energy (EES), 295296 Electrochemiluminescence (ECL), 81, 107108, 163164 Electrochemiluminescent sensors, 80 Electrodes, 4, 9091, 195, 305 Electrolyte, 195 Electrolyte leakage, 5960 Electromagnetic interference/ radiofrequency interference, 298299 Electromagnetic process, 166 Electron-conducting electrolyte, 96 Electron donor, 297 Electronic noses, 1112
Electronic properties of NMs, 2728 Electronics nanomaterials in, 30 nanotechnology in, 93 Electronic tongue (ET), 1114, 245 Electron impedance spectroscopy, 260261, 261f Electron microscopy, 3942 scanning electron microscope, 4142 transmission electron microscope, 4041 Electrospinning deposition, 138139 Electrospray technique, 140 Electrospun nanofibers, 181 Electrostatic discharge protection, 298299 Embryonic stem cells, 5658 Emerging contaminants (ECs), 115 Energy, 185186 Energy band diagram, 299, 300f Energy-dispersive X-ray spectroscopy (EDX), 203 Energy gap, 300 Energy harvesting, 2930 Energy storage, 301305 lithium batteries, 304305 supercapacitors, 303304 Engineered nanoparticles, 9394 Engineered NMs, 31 Environment, nanomaterials application in, 31 Environmental Protection Agency (EPA), 115 Environmental sensor, 37 Environment monitoring, 91 Enzymatic biofuel cells (EFCs), 146, 149 Enzymatic detection, 214, 216 Enzyme-containing and enzymatically responsive hydrogels, 255257 Enzyme-free amperometric sensors, 221
315
Enzyme-linked immunosorbent assay, 126127, 214, 255 Enzymes, 1314, 191193 EPA. See Environmental Protection Agency (EPA) Escherichia coli, 66 Europium (Eu), 250251 Ex situ hybridization, 273 Extrinsic self-healing, 300301
F Factorial analysis, 12 Factors of enhancement (EFs), 166 Faraday’s constant, 57 Ferric oxide, 57t Ferrimagnetism, 197 Ferromagnetism, 197 FETs. See Field-effect transistors (FETs) Field-effect transistors (FETs), 131132 Field emission scanning electron microscopy (FESEM), 184185 Filters, 195 Fingerprint, 1112 Fluorescence-based biosensors, 127 Fluorescence-based sensing, 254 Fluorescence-grounded histamine sensing method, 215216 Fluorescence technique, 165166 Fluorescent sensing, 169170 Fluorometric sensing, 168169, 214 Food industry, RFID nanosensors in, 186 Forensic drugs, 207 Fourier transform infrared spectroscopy (FTIR), 4749 Fullerene, 57t, 181 Functionalized gold nanoparticles, 236
316
Index
G Gas chromatography, 214 Gas sensing, 287288 GOSnO2 nanocomposite, 288 rGOZnO nanocomposite, 288 silver-loaded rGOZnO nanocomposite, 288 Gas sensing electrodes, 131132 GCE. See Glassy carbon electrode (GCE) General experimental setup, 8283 General synthesis, 270274 Genotoxicity/mutagenicity assays, 6365 in vitro mammalian cell gene mutation tests, 64 in vitro mammalian chromosomal aberration test, 64 in vitro mammalian micronucleus test, 6465 Glass electrode, 5 Glassy carbon electrode (GCE), 84, 158 material used for chemical modification of, 85 Glucoamylase, 255256 Glucose, 167t CuOrGO nanocomposite, 286 rGONi (OH)2 nanocomposite, 286 sensors, 202203 Glucose detection, 147148 Glucose oxidase enzyme, 130 Glucose sensing biosensors, 134136 Glucose sensors, 15 Glutamate, 204 GO. See Graphene oxide (GO) Gold (Au), 1920 Gold microelectrode, 246
Gold nanoparticles (AuNPs), 55t, 5658, 57t, 109110, 199, 228, 260 applications, 236239 in biomedical applications, 238 in metal detection, 238239 in sensing, 236238 basic synthetic method for, 230f with different morphologies, 230236 functionalized gold nanoparticles, 236 gold nanorods, 232233 gold nanowires, 231 metal-coated gold nanostructures, 234235 nanoplates/nanosheets, 233234 functionalization of, 233f sensing and catalytic activity of, 231 synthesis of, 228230 Gold nanorods (AuNRs), 232233 Gold nanowires, 231 GOMO composite synthesis, 271273 chemical functionalization, 272273 graphene oxide, 271 metal oxide, 271272 Gram-negative bacteria, 58 Graphene, 57t, 105, 155156, 200201, 218 Graphene-based electrochemical sensors applications, 285292 chemical sensing, 285287 gas sensing, 287288 heavy metal ion sensing, 289 inorganic sensing, 289291 organic sensing, 291292 graphene oxidemetal oxide composites, 269270
properties of GOMO nanocomposite, 281285 electrical properties, 284 mechanical properties, 281284 thermal properties, 284285 synthesis of graphene oxidemetal oxide electrochemical sensors, 270281 chemical methods, 276278 electrochemical method, 278279 general synthesis, 271274 hydrothermal and solvothermal methods, 274276 microwave-assisted method, 281 thermal methods, 279281 Graphene-based nanomaterials, 181 Graphene oxide (GO), 186187, 196f, 199, 270271 Graphene sensor, 161f Graphite oxide, 143144
H Healthcare, 207 Heavy metal ions (HMIs), 7778 Heavy metal ion sensing, 289 rGOPbO2, 289 rGOSnO2 nanocomposite, 289 rGOZnO nanocomposite, 289 Heavy metals, 12, 31 Hematite nanoparticles, 55t Hepatocellular carcinoma, 200201 Hexagonal boron nitride, 105 Highly reduced GOMO composite synthesis, 273274 post-immobilization, 273 in situ binding, 273274
Index
High-performance liquidchromatography, 214 Histamine, 211212 electrochemical methods, 217218 amperometric detection, 217 impedimetric detection, 217218 voltammetric detection, 218 electrochemical sensing, 218220 molecular-imprinted polymers, 219220 nanomaterials, 220 quantum dots, 219 enzymatic detection, 216 fluorescence-grounded histamine sensing method, 215216 nanomaterial-based electrochemical sensing of, 213f nanomaterials for, 220222 carbonaceous nanoparticles, 221222 core-shell nanoparticles, 221 metal nanoparticles, 220221 sensing techniques based on, 222t surface-enhanced Raman scattering, 214215 HMIs. See Heavy metal ions (HMIs) Hprt genes, 64 Human lung epithelial cells (BEAS-2B), 5455 Humidity sensors, 183 Hybrid materials, 181 Hydrazine, 290291 glassy carbon GOMnO2, 290291 polypyrrole GOFe3O4, 290291 Hydrazine (N2H4), 14 Hydrocavities, 255256
Hydrogen peroxide (H2O2), 167t, 203, 289 Hydrogen sulfide (H2S), 269 Hydrophobic membrane, 194 Hydrothermal and solvothermal methods, 270, 274276 GOCuO nanocomposite, 275 GOSnO2 nanocomposite, 275276 2-hydroxyethyl methylacrylate, 257258 5-hydroxytryptamine, 5658 Hypersensitivity reaction, 212
I Ideal sensor, 7879 Immense research, 15 Impedance measurement technique, 81 Impedimetric detection, 217218 Impedometric sensors, 80 Indium oxide-based sensors, 158159 Indium tin oxide (ITO), 136 Inkjet printing method, 141f, 142143, 179181 Inorganic sensing, 289291 cyanide, 290 hydrazine, 290291 glassy carbon GOMnO2, 290291 polypyrrole GOFe3O4, 290291 hydrogen peroxide, 289 In silico models, 67 In situ crystallization, 273274 Integrated circuits, 9798 Interfacial methods, 4 dynamic methods, 4 static methods, 4 Internal activity, 5 International Organization for Standardization (ISO), 19 Intrinsic self-healing polymers, 300301 In vitro mammalian cell gene mutation tests, 64
317
In vitro mammalian chromosomal aberration test, 64 In vitro mammalian micronucleus test, 6465 In vivo assessment, 6566 mammalian bone marrow chromosome aberration test, 66 mammalian erythrocyte micronucleus test, 66 Ion-mobility spectrometry, 214 Ion-selective electrodes, 131132 Ironically conducting polymers, 297 Iron oxide-based sensors, 163164 Iron oxide nanoparticles, 55t
K Karyolysis, 63 Karyorrhexis, 63 Klebsiella pneumoniae, 212
L Laser scribed graphene (LSG), 143144 Layer-by-layer (LBL) method, 259 Light-emitting diodes, 298 Limit of detection (LOD), 78, 158, 249, 252 Linear sweep voltammetry (LSV), 8, 164 Lithium batteries, 304305 Lithium-ion batteries, 295, 304305 Lysylendopeptidase (LEP) enzymes, 255256
M Magnesium aluminum silicate, 27 Magnetic nanoparticles (MNPs), 197198 Magnetic properties of NMs, 28 Magnetic sensors, 3 Malachite green, 14
318
Index
Mammalian bone marrow chromosome aberration test, 66 Mammalian erythrocyte micronucleus test, 66 Manufactured nanomaterials (MNMs), 6162 Mass sensors, 3 Mass transfer, 6 Mastocytosis, 212 MCF-7, 167t Mechanical properties of NMs, 28 Medical implants, 186, 304305 Membrane-covered sensors, 194 Membrane damage, 5859 3-mercaptopropionic acid (3MPA), 160161 Metabolite, 202203 glucose, 202203 Metal-coated gold nanostructures, 234235 Metal complexes, 215 Metalized fibers, 296297 Metal nanomaterials, 2526 Metal nanoparticles, 109110, 220221 gold nanoparticles, 109110 platinum nanoparticles, 109 silver nanoparticles, 110 Metal-organic frameworks (MOFs), 2627 Metal oxide nanomaterials, 2627 composite nanomaterials, 26 metal-organic frameworks, 2627 silicates, 27 Metal oxide nanowires, 132 Metal oxides (MOs), 155, 181, 198, 271272 applications, 156t biosensors, 157 cerium oxide-based sensors, 162 chemical sensors, 156157 colorimetric and fluorometric sensing based on, 168169
copper oxides-based sensors, 161162 electrochemical sensing based on, 167168 fluorescent and chemiluminescent sensing based on, 169170 indium oxide-based sensors, 158159 iron oxide-based sensors, 163164 issues and drawbacks, 170171 nickel oxide-based sensors, 159 synthesis method, 156t tin oxide-based sensors, 162 titanium oxide-based sensors, 159161 ZnO-based sensors, 157158 Methacrylic acrylic copolymers, 94 MFCs. See Microbial fuel cells (MFCs) Microbial fuel cells (MFCs), 146147, 149 Microfabrication techniques, 107108 Micro fuel cell, 195197 Micro-level analysis, 48 Microorganisms, toxic effects of NMs on, 5859 Microwave-assisted method, 271, 281 MNMs. See Manufactured nanomaterials (MNMs) MOFs. See Metal-organic frameworks (MOFs) Molecularly imprinted polymers (MIPs), 214215, 219220 Monoamine, 5658 Morganella morganii, 212 Morganella psychrotolerans, 212 MOs. See Metal oxides (MOs) Multianalyte sensing, 246 Multilayered black phosphorus (m-BP), 158 Multiphase solid materials, 23
Multivariate regression techniques, 12 Multiwalled carbon nanotubes (MWCNTs), 5960, 60t, 95, 109, 134136, 158, 203 MWCNTs. See Multiwalled carbon nanotubes (MWCNTs)
N N-(4-picolyl)-1,8naphthalimide, 248249 Nanobased technology, 15 Nanoclays, 106 Nanocomposites, 3839 Nanodevices, 185186 Nanodiamonds, 2425 Nanoelectromechanical systems, 91 Nanoelectronics, 93 Nanofibers, 2223 Nanofilms, 92 Nanoimprint lithography, 96 Nanomaterial-based biosensors, 134144 coating-based methods, 134137 blade coating, 137 dip coating, 136 drop casting, 134136 spin coating, 136137 deposition-based methods, 137140 printing-based methods, 140144 Nanomaterial-based electrochemical biosensors for biomedical applications, 107110, 107f for tumor cell diagnosis, 111113 electrochemical biosensor in, 111112 electrochemical immunosensors in, 112, 113f electrochemical nucleic acid biosensors in, 112113, 113f nanoshells, 111
Index
quantum dots, 111 Nanomaterial-based electrochemical sensors for environmental applications, 114118, 114f pollution detection and environmental contaminants, 115116 for toxic gas detection, 116118 Nanomaterial-based inks, 142143 Nanomaterials, 1214, 1922, 37, 53, 220222 application, 2931 chemical catalyst, 29 in electronics, 30 energy harvesting, 2930 environment, 31 food and agriculture, 29 mechanical industries, 3031 medication and drug, 30 carbonaceous nanoparticles, 221222 carbon-based nanomaterials, 2425 chemical composition, 24 classification of, 20f core-shell nanoparticles, 221 development of, 104 dimension, 2223 electronic properties, 2728 history, 2122 magnetic properties, 28 mechanical properties, 28 metal nanomaterials, 2526 metal nanoparticles, 220221 metal oxide nanomaterials, 2627 composite nanomaterials, 26 metal-organic frameworks, 2627 silicates, 27 optical properties, 27 origin, 24 physiochemical properties, 29
sensing techniques based on, 222t thermal properties, 2829 toxic effects of on humans and animals, 5458, 55t on microorganisms, 5859, 59t physicochemical properties of, 54 on plants, 5961, 60t toxicity cytotoxic assays, 6263 genotoxicity/mutagenicity assays, 6365 in silico models, 67 in vivo assessment of, 6566 2-dimensional nanomaterials, 104106 types of, 103t Nanoparticles (NPs), 104, 155156 Nanophotonics, 91 Nanoplastics, 57t Nanoplates/nanosheets, 233234 Nanopowders, 90 Nanorobots, 93 Nanorods (NRs), 2223, 142143, 157 Nanoscale, 1920, 23 Nanoscale transistors, 92 Nanosensing technology, 9596 Nanosensors, 177, 185187 biomedical applications, 186187 energy, 185186 food industry, 186 structural health, 187 Nanoshells, 111 Nanotechnology, 1314, 21, 3738, 8991, 103, 118119, 181, 186 advancements in, 103 challenges, 9697 in diagnosis, 105t drug delivery, 91 in electronics, 93
319
in medical field, 108110 carbon nanotubes, 108109 metal nanoparticles, 109110 nanotubes, 110 in medicine, 9394 nanofilms, 92 nanorobots, 93 nanoscale transistors, 92 nanosensing technology, 9596 nanotubes, 92 and space, 93 water filtration, 92 Nanotrap, 253254 Nanotubes, 2223, 92, 110, 181 Nanowires, 2223, 115116, 181 n-doping, 298 Nernst equation, 5 Neutral red uptake assay, 63 N-heterocyclic (NHC) reversible bonds, 303 N-isopropylacrylamide, 257 Nitric oxide (NO), 269 Nitrogen dioxide (NO2), 269 Nitrogen oxide in human beings, 205 in plants, 205 N-methyl-2-pyrrolidinone (NMP), 275 NMP. See N-methyl-2pyrrolidinone (NMP) N,N-dimethlyformamide (DMF), 275 Noble metal-based materials, 9091 Noble metals, 191193, 199, 221 gold nanoparticles, 199 silver nanoparticles, 199 Nondestructive technique, 46 Non-interfacial methods, 4 Norepinephrine, 5658 Normal hydrogen electrode (NHE), 5 Novel self-healing conductive polymers, 302303
320
Index
Nozzle jet printing, 142143 Nucleic acids biosensor, 167t Nylon, 2223 Nyquist plot, 260261
O OECD. See Organization for Economic Co-operation and Development (OECD) OFET. See Organic field effect transistor (OFET) Oligonucleotides, 132133, 260261 One-dimensional materials, 108109 One-dimensional (1D) nanomaterials, 2223, 132 Optical biosensors, 126128 Optical engineering, 38 Optical microscope, 40 Optical properties of NMs, 27 Optical sensors, 3 Organic field effect transistor (OFET), 250251 Organic sensing, 291292 aromatic nitro compounds, 291292 GOTiO2 nanocomposite, 291292 rGOZnO nanocomposite, 292 phenolic compounds, 291 GOZnO nanocomposite, 291 rGO-based MnO2 nanocomposite wire, 291 Organization for Economic Cooperation and Development (OECD), 6162 Organometallic polymeric conductors, 297 Organometallic polymers, 297, 303 Organophosphorus, 286 Oryzias latipes, 66 Oxidative assays, 6263
P PAA. See Polyacrylic acid (PAA) Palladium (Pd), 1920
Paramagnetism, 197 PCF. See Photonic crystal fiber (PCF) p-doping, 298 PET. See Polythene terephthalate (PET) PGNR. See Porous graphene nanoribbon (PGNR) Pharmaceutical applications, 207 Phaseolus radiatus (mung bean), 6061 Phenolic compounds, 291 GOZnO nanocomposite, 291 rGO-based MnO2 nanocomposite wire, 291 Photolithographic techniques, 133134 Photon correlation spectroscopy, 4243 Photonic crystal fiber (PCF), 247 Photonic crystals, 252253 Physical vapor deposition, 140 Physiochemical properties of NMs, 29 Piezoelectric biosensors, 126, 128129 Piezoelectric effect, 128129 Platinum (Pt), 1920 Platinum nanoparticles, 55t, 109 Pollution controller technologies, 37 Poly (2-acrylamido-2-methyl-1propanesulfonic acid) (PAMPSA), 249 Poly(3-hexylthiophene) (P3HT), 250251 Poly (3, 4ethylendioxythiophene), 245246 Polyacetylene (PA), 297 Polyacrylic acid (PAA), 259, 302303 Polyamide, 2223 Polyaniline, 198, 295296 Polycarbonates, 2223, 133134
Polyelectrolytes, 302303 Polyethylene, 198 Polyethylene terephthalate, 2223, 259 Polyethyne, 298 Polylactic acid, 2223 Polymatrix nanocomposite, 23 Polymer-based nanowire, 132 Polymer-based self-healable materials conductive polymeric materials, 296300 band theory, 299300 self-healing material, 300301 Polymer chains, 298, 302 Polymeric charge transfer complex, 297 Polymeric composite materials, 298 Polymeric materials, 296297 Polymerization, 7 Polymer matrix, 259 Polymers, 198, 296 Polymers with inherent conductance, 297 Polymethylmethacrylate nanoplastics, 5556 Polyolefin, 2223 Poly (2-hydroxypropyl methacrylate)/poly (ethyleneimine) (PHPMA/ PEI), 250251 Polypropylene, 198 Polypyrrole, 295296 Polystyrene, 2223, 133134 Polystyrene nanoparticles, 55t Polythene terephthalate (PET), 140142 Polyurethane (PU), 2223, 259260 Polyvinyl alcohol (PVA), 2223, 303304 Polyvinylidene fluoride, 48 Porous graphene nanoribbon (PGNR), 200201 Potential sweep methods, 7 Potentiometric biosensors, 131132
Index
Potentiometric electrochemical sensing techniques, 80 Potentiometric sensors, 80, 117118 Potentiometric titration technique, 9495 Potentiometry, 3, 4t Principal component analysis, 12 Printing-based methods, 140144 Protein oxidation, 5859 Proteins, 191193 Proteus vulgaris, 212 Protonation, 7 Pseudomonas aeruginosa, 66 Pulsed amperometry, 164 Pyknosis, 63 Pyridine moiety, 248249 Pyridyl-dithiadiazole, 248249
Q Quantum dots (QDs), 22, 9798, 111, 181, 219 Quartz crystal microbalance (QCM) technique, 166 Quasielliptical light scattering, 4243
R Radio-frequency identification (RFID) sensors, 177179, 178f fabrication of, 187188 functions of, 180f inkjet printing of nanomaterial-based, 183185 nanomaterials for, 181183 nanosensors, 185187 biomedical applications, 186187 energy, 185186 food industry, 186 structural health, 187 3D-printed dual-port slot antenna for, 183184 Rayleigh waves, 128129 RE. See Reference electrode (RE)
Reactive oxygen species (ROS), 53, 6263 Recognitive and molecularly imprinted polymers, 252254 Redox potential sensor, 246 Redox reaction, 130, 295296 Reduced graphene oxide (rGO), 158159, 257, 270 Reference electrode (RE), 5, 6t, 7, 80, 96, 132133 Refractive index, 253254
S Safety-control devices, 261262 Saturated calomel electrode (SCE), 5 Scanning electron microscopes (SEM), 3742, 203, 252253, 253f Scattering, 43 Screen-printed electrodes (SPEs), 115 Screen printing technique, 133134, 140142 Seafood processors, 214 Self-healing, 247 Self-healing ionic conductors, 302303 Self-healing materials, 300301 for energy storage, 301305 lithium batteries, 304305 supercapacitors, 303304 Self-healing materials for analyte sensing, 248261 analyte-responsive composites, 257261 analyte-responsive hydrogels, 252257 biomolecule-containing hydrogels, 254255 enzyme-containing and enzymatically responsive hydrogels, 255257 recognitive and molecularly imprinted polymers, 252254 analyte-responsive polymers, 248252
321
Self-powered implantable biosensor, 146148 glucose detection, 147148 Semiconductors, 2223 Sensing electrode, 96 Sensing methodology, 106107 electrochemical biosensors, 106 electrochemical sensors, 106107 Sensing techniques, 164167 colorimetric technique, 165 electrochemical sensing technique, 164165 amperometry, 164165 cyclic voltammetry, 164 electrochemical impedance spectroscopy, 165 linear sweep voltammetry, 164 fluorescence technique, 165166 quartz crystal microbalance technique, 166 surface-enhanced Raman scattering technique, 166167 chemical process, 167 electromagnetic process, 166 Sensors, 12, 7879, 191193 chemical sensors, 79 ideal sensor, 7879 for pollution detection and environmental contaminants, 115116 emerging contaminants, 115 nanowires, 115116 screen-printed electrodes, 115 toxic gases, 115 Serotonin, 204 Shear-horizontal acoustic plate mode (SH-APM), 128129 Signal transduction, 248249 Silica nanomaterials, 57t Silica nanoparticles, 55t Silicates, 27
322
Index
Silicates (Continued) clays, 106 Silicon dioxide, 2223 Silicon nanowire, 132 Silver (Ag), 1920 Silver nanoparticle (AgNP), 55t, 57t, 5859, 60t, 110, 199, 218 Single-walled carbon nanotubes (SWCNTs), 57t, 60t, 95, 108109, 183184, 303304 S-nitrosothiol, 199 Soil quality monitoring, 123125 Sol-gel technique, 159160 sp2 hybridization, 2425 Spin-coating method, 136137 SPR-based biosensor (SPIR), 127 Square wave voltammetry (SWV), 10, 11f Stainless steel fibers, 298 Static methods, 45 Sterechinus neumayeri, 5556 StokesEinstein equation, 43 Structural health, RFID sensors for, 187 Sulfur dioxide (SO2), 269 Supercapacitors, 303304 Superconducting nanowire single-photon detectors (SNSPDs), 91 Super-magnetism, 28 Superparamagnetic NPs, 31 Surface acoustic wave (SAW), 128129 Surface-enhanced Raman scattering (SERS), 166167, 214215, 230 chemical process, 167 electromagnetic process, 166 Surface plasmon resonance (SPR), 127, 253254 SWCNTs. See Single-walled carbon nanotubes (SWCNTs) SWV. See Square wave voltammetry (SWV) Synthetic materials, 300
T T47D, 167t Target DNA, 254 Teflon membranes, 194 TEM. See Transmission electron microscopes (TEM) Terbium (Tb), 250251 Terminal deoxynucleotidyl transferase (TdT), 63 Tetracycline, 252253 Thermal methods, 271, 279281 graphene oxidemetal oxide hybrid, 280281 Thermal properties of NMs, 2829 Thermal sensors, 3 Thermogravimetric analysis, 49 Thickness-shear mode (TSM), 128129 Thin-layer chromatography, 214 Three-dimensional lithography, 205 Three-dimensional (3D) nanomaterials, 23 3D printing technology, 183 Tin oxide (SnO2), 162 Tissue engineering, 186 Titanium dioxide (TiO2), 2223, 54 Titanium dioxide nanoparticles, 55t Titanium dioxide nanotubes (TNTs), 110 Titanium nitride, 2223 Titanium oxide-based sensors, 159161 Top down methods, 228 Top up methods, 228 Toxic gases, 115 Transition metal dichalcogenides (MX_2), 105 Transition metal oxides, 105106 Transmission electron microscopes (TEM), 3741, 235f
Trifluoroacetic acid, 249 Triticum aestivum (wheat), 6061 2,4,6-trinitrophenol, 249 Tumor cell diagnosis, 111113 electrochemical biosensor in, 111112 electrochemical immunosensors in, 112, 113f electrochemical nucleic acid biosensors in, 112113, 113f nanoshells, 111 quantum dots, 111 Two-dimensional (2D) nanomaterials, 2325, 104106, 132
U Ultraviolet (UV) radiations, 90 Unmanned aerial vehicles (UAVs), 183 Uric acid, 167t, 245
V Valence band, 298, 300 van der Waals (VdW) forces, 259 van der Waals interactions, 270 Vibrio fisheri, 66 Vicia faba, 6061 Vicia narbonensis, 6061 Vinyl hybrid silica nanoparticles (VSNPs), 302303 Volatile organic compounds, 269 Voltammetric detection, 218 Voltammetric methods, 3, 4t, 78, 81 Voltammetric sensors, 80 VSEPR theory, 28
W Wastewater management, 123125 Water filtration, 92
Index
Water-soluble tetrazolium salt (WST-1), 62 Wavenumber unit, 48 Wireless transmission, 179 Working electrode, 7, 129132, 195197 Working electrode (WE), 81 Working Party on Manufactured Nanomaterials (WPMN), 6162 World Health Organization, 147148
X Xprt genes, 64 X-ray diffraction (XRD), 4547, 158159 X-rays, 42, 45
Y Young’s modulus, 3031
Z Zeolites, 27 Zeta potential, 37 instrument, 47
323
Ziegler-Natta catalyst, 298 Zinc oxide (ZnO), 5455, 91, 157158, 198 Zinc porphyrin (ZnP), 288 Zinc powder, 57t Zirconia (ZrO2), 286 Zirconium dioxide, 2223