nanobiosensors - download.e-bookshelf.de€¦ · vi contents 1.8 conclusion 17 acknowledgment 17...

Nanobiosensors

Nanobiosensors

From Design to Applications

Edited byAiguo WuWaheed S. Khan

Editors

Prof. Aiguo WuCixi Institute of Biomedical EngineeringCAS Key Laboratory of MagneticMaterials and Devices& Key Laboratory of AdditiveManufacturing Materials ofZhejiang ProvinceNingbo Institute of MaterialsTechnology and EngineeringChinese Academy of SciencesNingbo 315201PR China

Dr. Waheed S. KhanNational Institute for Biotechnology &Genetic Engineering (NIBGE)Nanobiotech Research GroupJhang Road38000 FaisalabadPakistan

Cover Image: © Billion Photos/Shutterstock

All books published by Wiley-VCHare carefully produced. Nevertheless,authors, editors, and publisher do notwarrant the information contained inthese books, including this book, tobe free of errors. Readers are advisedto keep in mind that statements, data,illustrations, procedural details or otheritems may inadvertently be inaccurate.

Library of Congress Card No.:applied for

British Library Cataloguing-in-PublicationDataA catalogue record for this book isavailable from the British Library.

Bibliographic information published bythe Deutsche NationalbibliothekThe Deutsche Nationalbibliothek liststhis publication in the DeutscheNationalbibliografie; detailedbibliographic data are available on theInternet at <http://dnb.d-nb.de>.

© 2020 Wiley-VCH Verlag GmbH &Co. KGaA, Boschstr. 12, 69469Weinheim, Germany

All rights reserved (including those oftranslation into other languages). Nopart of this book may be reproduced inany form – by photoprinting,microfilm, or any other means – nortransmitted or translated into amachine language without writtenpermission from the publishers.Registered names, trademarks, etc. usedin this book, even when not specificallymarked as such, are not to beconsidered unprotected by law.

Print ISBN: 978-3-527-34510-6ePDF ISBN: 978-3-527-34516-8ePub ISBN: 978-3-527-34514-4oBook ISBN: 978-3-527-34513-7

Typesetting SPi Global, Chennai, IndiaPrinting and Binding

Printed on acid-free paper

10 9 8 7 6 5 4 3 2 1

http://dnb.d-nb.de

http://dnb.d-nb.de

v

Contents

1 Basics of Biosensors and Nanobiosensors 1Pravin Bhattarai and Sadaf Hameed

1.1 Introduction 11.2 Biosensor and Its Working Principle 31.3 Characteristics of a Biosensor 41.3.1 Selectivity 41.3.2 Reproducibility 41.3.3 Stability 51.3.4 Sensitivity and Linearity 51.4 Biosensor Evolution: A Brief Outlook 61.5 Types of Biosensors 61.5.1 Electrochemical Biosensors (ECBs) 61.5.1.1 Potentiometric Biosensors 81.5.1.2 Voltammetric/Amperometric 81.5.1.3 Impedance (Electrical Impedance Spectroscopy, EIS) 81.5.1.4 Conductometric 91.5.2 Optical Biosensors 91.5.2.1 Surface Plasmon Resonance 101.5.2.2 Evanescent Wave Fluorescence Biosensors 101.5.3 Piezoelectric Biosensors 111.5.4 Electronic Biosensors: Based on Field-Effect Transistor 121.6 On the Basis of the Use of Biorecognition Elements: Catalytic Versus

Affinity Biosensors 131.6.1 Enzymatic Biosensors 131.6.2 Immunosensors 131.6.3 DNA Aptamer Biosensors 141.6.4 Peptide-Based Biosensors 141.6.5 Whole-Cell Biosensors 141.7 Application of Biosensors 151.7.1 Biosensors in Microbiology 151.7.2 Biosensors for Environmental Monitoring Applications 161.7.3 Biosensors for Cancer Biomarker Identification 161.7.4 Biosensor in the Detection of Infectious Diseases 16

vi Contents

1.8 Conclusion 17Acknowledgment 17References 17

2 Transduction Process-Based Classification of Biosensors 23Fang Yang, Yuanyuan Ma, Stefan G. Stanciu, and Aiguo Wu

2.1 Introduction 232.2 Electrochemical Biosensors 242.2.1 Potentiometric Biosensors 252.2.2 Impedimetric Biosensors 262.2.3 Conductometric Biosensors 282.3 Optical Biosensors 292.3.1 Biosensors Based on Surface Plasmon Resonance (SPR) 292.3.2 Raman and Fourier Transform Infrared Spectroscopy

(FT-IR) 302.3.3 Biosensors Based on Fluorescence Effect 312.4 Mass-Based Biosensors 322.4.1 Piezoelectric Biosensors 322.4.2 Quartz Crystal Microbalance (QCM) 332.4.3 Surface Acoustic Wave (SAW) 342.5 Thermal Biosensors 352.5.1 Thermometric Sensors 352.5.2 Terahertz Effect 362.5.3 Thermal Radiation 372.6 Energy Biosensors 382.6.1 Adenosine Triphosphate 392.6.2 Fluorescence Resonance Energy 392.7 Conclusion 40

Acknowledgments 40References 40

3 Novel Nanomaterials for Biosensor Development 45Sadaf Hameed and Pravin Bhattarai

3.1 Introduction 453.2 Graphene and Its Composites 463.2.1 Graphene and Their Composite-Based Biosensors 483.2.1.1 Graphene and Their Composite-Based Electrochemical

Biosensors 493.2.1.2 Graphene and Their Composite-Based Field-Effect Transistor

Biosensors 503.3 Carbon Nanotubes and Their Hybrids 513.3.1 Biosensors Based on Carbon Nanotubes and Their Hybrids 533.4 Nitride-Based Biosensors 573.4.1 Biosensing Application of Nitride-Based Nanomaterials 583.5 Metal and Metal Oxide Nanoparticles for Biosensors 603.5.1 Fundamental Characteristics of Metal and Metal Oxide Nanostructure

for the Development of a Biosensor 61

Contents vii

3.5.2 Performance of Nanostructured Metal and Metal Oxide-BasedBiosensors 61

3.6 Conclusion 64Acknowledgment 64References 64

4 Biomarkers and Their Role in Detection of Biomolecules 73Ayesha Taj, Abdul Rehman, and Sadia Z. Bajwa

4.1 Introduction 734.2 Types of Biomarkers 754.2.1 Predictive Biomarker 754.2.2 Prognosis Biomarker 754.2.3 Pharmacodynamic Biomarker 754.3 Cancer Biomarker 764.3.1 Role of Biomarkers in Cancer Medicine 774.3.2 Use of Biomarkers in Cancer Research 784.3.2.1 Risk Assessment 794.3.2.2 Screening 794.3.2.3 Diagnostic Test 794.3.2.4 Staging 804.3.2.5 Monitoring Tests 804.3.3 Types of Cancer Biomarkers 804.4 Cardiac Biomarkers 804.4.1 Measurement 814.4.2 Types of Cardiac Biomarkers 814.4.2.1 Troponin 814.4.2.2 Creatine Kinase (CK) 824.4.2.3 Myoglobin 824.4.2.4 Lactate Dehydrogenase (LDH) 824.4.2.5 C-Reactive Protein (CRP) 824.5 Biomarker of Aging 834.6 Alzheimer’s Biomarker 834.7 HIV Biomarker 854.8 Conclusion 87

Acknowledgment 88References 88

5 Detection of Cancer Cells by Using Biosensors 95Nuzhat Jamil and Waheed S. Khan

5.1 Introduction 955.2 Early Stage Detection of Cancer and Its Importance 965.3 Biosensor – A Good Option for Detecting Cancers 965.4 Cancers Commonly Observed in Females 975.4.1 Breast Cancer Detection 975.4.1.1 Electrochemical DNA Biosensor Based on Immobilized ZnO

Nanowires 97

viii Contents

5.4.1.2 Optical Biosensor of Breast Cancer Cells 985.4.1.3 Microfluidic Plasmonic Biosensor 1005.4.1.4 QCM Biosensor for Sensitive and Selective Detection 1005.4.2 Ovarian Cancer Detection 1025.4.2.1 ZnO–Au-Based Electrochemical Biosensor for Ovarian Cancer 1025.4.2.2 Magnetic Nanoparticle–Antibody Conjugates (MNP–ABS)-Based

Assay 1035.4.3 Cervical Cancer Detection 1035.4.3.1 Impedimetric Biosensor for Early Detection of Cervical Cancer 1045.4.3.2 Automated Cervical Cancer Detection Using Photonic Crystal-Based

Biosensor 1055.5 Cancers Commonly Observed in Males 1065.5.1 Lung Cancer Detection 1065.5.2 Gold Nanoparticle-Based Colorimetric Biosensor 1065.6 Prostate Cancer Detection 1075.6.1 Novel Label-Free Electrochemical Immunosensor for Ultrasensitive

Detection of Prostate-Specific Antigen Based on the EnhancedCatalytic Currents of Oxygen Reduction Catalyzed by Core–ShellAu@Pt Nanocrystals 107

5.6.2 Electrochemical Biosensor to Simultaneously Detect VEGF and PSAfor Early Prostate Cancer Diagnosis Based on GrapheneOxide/ssDNA/PLLA Nanoparticles 108

5.6.3 Detection of Early Stage Prostate Cancer by Using a Simple CarbonNanotube@Paper Biosensor 109

5.7 Oral Cancer 1105.7.1 Graphene Biosensor Based on Antigen Concentration in

Saliva 1105.8 Conclusions 111


6 Biosensor Applications for Viral and Bacterial DiseaseDiagnosis 117Ayesha Shaheen, Rabia Arshad, Ayesha Taj, Usman Latif, and Sadia Z. Bajwa

6.1 Introduction 1176.2 Dengue Fever Virus Detection 1186.2.1 Nanostructured Electrochemical Biosensor 1186.2.2 Plasmonic Biosensor for Early Detection of Dengue Virus 1206.2.3 Impedimetric Biosensor to Test Neat Serum for Dengue Virus 1206.3 Zika Virus Detection 1226.3.1 Electrochemical Biosensors for Early Stage Zika Diagnostics 1226.3.2 Novel Graphene-Based Biosensor for Early Detection of Zika

Virus 1246.3.3 Smartphone-Based Diagnostic Platform for Rapid Detection of Zika

Virus 1266.4 Yellow Fever 1266.4.1 Field-Effect Transistor Biosensor for Rapid Detection of Ebola

Antigen 127

Contents ix

6.5 Hepatitis B 1286.5.1 Carbon Nanotube-Based Biosensor for Detection of Hepatitis B 1286.5.2 Gold Nanorod-Based Localized Surface Plasmon Resonance (SPR)

Biosensor for Sensitive Detection of Hepatitis B Virus 1296.5.3 Amplified Detection of Hepatitis B Virus Using an Electrochemical

DNA Biosensor on a Nanoporous Gold Platform 1296.6 Hepatitis C 1306.6.1 Aggregation of Gold Nanoparticles: A Novel Nanoparticle Biosensor

Approach for the Direct Quantification of Hepatitis C 1316.6.2 Impedimetric Genosensor for Detection of Hepatitis C Virus (HCV1)

DNA Using the Viral Probe on Methylene Blue-Doped SilicaNanoparticles 132

6.6.3 Ultrasensitive Aptasensor Based on a GQD Nanocomposite forDetection of Hepatitis C Virus Core Antigen 133

6.7 Typhoid Fever 1346.7.1 Graphene Oxide–Chitosan Nanocomposite-Based Electrochemical

DNA Biosensor for Detection of Typhoid 1356.8 Mycobacterium tuberculosis 1376.8.1 Gold Nanotube Array Electrode Platform-Based Electrochemical

Biosensor for Detection of Mycobacterium tuberculosis DNA 1386.8.2 Label-Free Biosensor Based on Localized Surface Plasmon Resonance

for Diagnosis of Tuberculosis 1386.9 Conclusions 139


7 Detection of HIV Virus Using Biosensor 149Haq Nawaz, Muhammad Tahir, Shumaila Anwar, Muhammad Irfan Majeed,and Nosheen Rashid

7.1 Introduction 1497.1.1 Structure and Genomic Specifications of HIV 1507.1.2 Morphology 1507.2 Electrochemical Based Biosensors for HIV Detection 1557.2.1 DNA Electrochemical Biosensors for Detection of HIV 1557.2.1.1 Detection of HIV DNA Sequence 1557.2.2 Label-Free Electrochemical Biosensor for Detection of HIV 1567.2.3 Ultrasensitive Biosensors for HIV Gene 1577.2.4 Optical Biosensors for HIV Detection 1587.2.5 Nanostructured Optical Photonic Crystal Biosensor for HIV 1597.2.5.1 Virus Capture 1607.2.6 Surface Plasmon Resonance-Based Biosensors 1607.2.7 Sensitive Impedimetric DNA Biosensor for the Determination of the

HIV-1 Gene 1627.2.8 Improved Piezoelectric Biosensor for HIV Rapid Detection of

HIV 1637.2.8.1 Measurement Procedure 1637.3 Conclusions 164


x Contents

8 Use of Biosensors for Mycotoxins Analysis in Food Stuff 171Muhammad Rizwan Younis, Chen Wang, Muhammad Adnan Younis, andXing-Hua Xia

8.1 Introduction 1718.2 Types of Mycotoxins 1738.2.1 Aflatoxins 1738.2.2 Ochratoxins 1748.2.3 Citrinin 1748.2.4 Patulin 1748.2.5 Fusarium 1758.3 Biosensors for Aflatoxin Detection 1758.3.1 DNA-Based Biosensor for Aflatoxins 1768.3.2 Electrochemical Detection Systems 1798.3.3 Carbon Nanotube (CNT)-Based Aflatoxin Biosensor 1808.3.4 QCM Biosensor for Aflatoxin 1828.4 Biosensors for Ochratoxins 1858.4.1 Horseradish Peroxidase-Screen-Printed Biosensor for the

Determination of Ochratoxin 1858.4.2 Aptamer–DNAzyme Hairpin Biosensor for Ochratoxin 1868.4.3 Development of QCM-D Biosensor for Ochratoxin A 1898.5 Biosensors for Citrinin Determination 1928.5.1 Molecular Imprinted Surface Plasmon Resonance (SPR)

Biosensor 1928.6 Biosensors for Patulin Determination 1948.6.1 Cerium Oxide ISFET-Based Immune Biosensor 1948.6.2 Conductometric Enzyme Biosensor for Patulin Determination 1968.7 Biosensors for Fusarium Determination 1968.7.1 Rapid Biosensor for the Detection of Mycotoxin in Wheat

(MYCOHUNT) 1988.8 Conclusions 198


9 Development of Biosensors for Drug DetectionApplications 203Razium Ali Soomro

9.1 Introduction 2039.2 What Is the Need of Biosensors for Drug Detection? 2059.3 Biosensors for the Detection of Antibiotics 2069.3.1 Electrochemical Biosensor for Antibiotics 2079.3.2 Voltammetric Biosensor for Antibiotics 2079.3.3 Photoelectrochemical Biosensors for Antibiotics 2099.3.4 Amperometric Biosensor for Antibiotics 2119.4 Biosensors for the Detection of Therapeutic Drugs 2129.5 Biosensors for Neurotransmitter 2149.6 Conclusion and Perspective 219


Contents xi

10 Detecting the Presence of Illicit Drugs Using Biosensors 223Muhammad Irfan Majeed, Haq Nawaz, and Falaq Naz Arshad

10.1 Introduction 22310.1.1 Classification of Illicit Drugs 22410.1.2 Drug’s Effect on Brain and Body 22510.1.3 Signs of Illicit Drug Addiction 22510.1.4 Biosensors for Illicit Drugs 22610.1.5 Nanomaterials for Biosensors 22710.1.6 Molecular Receptors for the Nanobiosensors 22910.2 Cocaine Detection 23010.2.1 Quantum Dot-Based Optical Biosensors for Cocaine Detection 23010.2.2 Nanopore Biosensor for Rapid and Highly Sensitive Cocaine

Detection 23110.2.3 Colorimetric Cocaine Aptasensors 23210.2.4 Electrochemical Based Cocaine Aptasensors 23410.3 Methamphetamine Detection 23410.3.1 Nonaggregated Au@Ag Core–Shell Nanoparticle Based Colorimetric

Biosensor for Methamphetamine Detection 23510.4 Chlorpromazine Detection 23710.4.1 DNA Intercalation-Based Amperometric Biosensor for

Chlorpromazine Detection 23810.5 Codeine Detection 23910.6 Morphine Detection 24110.7 Alcohol Detection 24210.8 Conclusion 244


11 Biosensors for Determination of Pesticides and TheirResidues 255Asma Rehman, Lutfur Rahman, Bushra Tehseen, and Hafiza F. Khalid

11.1 Introduction 25511.2 Types of Pesticides and Their Benefits 25611.2.1 Insecticides 25611.2.2 Herbicides 25711.2.3 Fungicides 25711.2.4 Benefits of Pesticides 25811.2.5 Beneficiaries of Pesticides 25811.2.6 Controlling Agricultural Pests and Vectors of Plant Disease 25911.2.7 Benefits of Pesticides to Prevent Organisms that Harm Other

Activities or Damage Structures 26011.3 Detrimental Effects: Health and Environmental Effects 26111.3.1 Impact of Pesticides on Human Health: Topical or Systemic 26211.3.2 Short-Term Effects of Pesticides 26211.3.3 Long-Term Effects of Pesticides 26311.3.4 Effects of Pesticides on Pregnant Women 26311.3.5 Pesticides and Children 26311.3.6 Effects of Pesticides on the Environment 264

xii Contents

11.3.7 Safe Use of Pesticides 26411.4 AuNP/MPS/Au Electrode Sensing Layer-Based Electrochemical

Biosensor for Pesticide Monitoring 26511.5 Citrate-Stabilized AuNP-Based Optical Biosensor for Rapid Pesticide

Residue Detection of Terbuthylazine and Dimethoate 26611.6 Piezoelectric Biosensor for Rapid Detection of Pesticide Residue 26711.7 Amperometric Acetylcholinesterase Biosensor Based on Gold

Nanorods for Detection of Organophosphate Pesticides 27211.8 Conclusions 275


12 Detection of Avian Influenza Virus 289Waheed S. Khan, and Muhammad Zubair Iqbal

12.1 Introduction 28912.2 Surface-Enhanced Raman Spectroscopy (SERS)-Based

Nanosensor 29012.2.1 Design of Magnetic Immunoassay Based on SERS Strategy 29112.3 Carbon Nanotube-Based Chemiresistive Biosensors for Label-Free

Detection of DNA Sequences 29212.4 Influenza Virus Detection Using Electrochemical Biosensors 29712.5 Aptamer-Based Biosensors 30312.6 Conclusions 304


13 Biosensors for Swine Influenza Viruses 311Madiha Saeed and Aiguo Wu

13.1 Introduction 31113.2 Diagnostic Methods for Swine Influenza Virus and Their

Limitations 31213.3 Nanomaterial-Based Sensors 31313.3.1 Applications of Carbon-Based Nanomaterials 31313.3.2 Gold Nanoparticle-Based Biosensing 31513.3.3 Gold Nanoparticle-Based Localized Surface Plasmon Resonance

Sensors 31513.3.4 Magnetic Nanoparticle-Based Biosensing 31913.3.5 Others 32113.4 Conclusion 321


14 Biosensors for Detection of Marine Toxins 329Khizra Bano, Waheed S. Khan, Chuanbao Cao, Rao F.H. Khan, andThomas J. Webster

14.1 Introduction 32914.2 Algal Blooms and Marine Toxins 330

Contents xiii

14.3 Classification of Marine Toxins, also Known as Biotoxins 33014.4 Harmful Effect of Marine Toxins on Human Health 33514.5 Biosensing of Marine Toxins 33714.5.1 SPR-Based Biosensors for Marine Toxins with Special Reference to

Saxitoxin Sensing 33814.5.2 Detection of Marine Biotoxin in Shellfish 34414.5.3 Smartphone-Based Portable Detection System for Marine Toxins 34514.5.4 Superparamagnetic Nanobead-Based Immunochromatographic Assay

for Detection of Toxic Marine Algae 34714.5.5 Gold Nanorod Aggregation-Based Optical Biosensor for Rapid

Endotoxin Detection 34914.6 Conclusion 350


15 Smartphone-Based Biosensors 357Muhammad Rizwan Younis, Chen Wang, Muhammad Adnan Younis, andXing-Hua Xia

15.1 Introduction 35715.2 Smartphone-Based Devices and Their Applications 36015.3 Rapid GMR Biosensor Platform with Smartphone Interface 36315.4 Smartphone-Based Electrochemical Biosensor for Portable Detection

of Clenbuterol 36715.5 Biosensing of Metal Ions by a Novel 3D-Printable Smartphone 36915.6 Ambient Light-Based Optical Biosensing Platform with

Smartphone-Embedded Illumination Sensor 37215.7 Smartphone Optical Biosensor Point-of-Care Diagnostics 37415.8 Monitoring of Cardiovascular Diseases at the Point of Care by

Smartphone 37715.9 Smartphone-Based Sensing System Using ZnO- and

Graphene-Modified Electrodes for VOCs Detection 37915.10 Use of Smartphone Technology in Cardiology 38115.11 Smartphone-Based Enzymatic Biosensor for Oral Fluid l-Lactate

Detection 38315.12 Conclusions 385


Index 389

1

1

Basics of Biosensors and NanobiosensorsPravin Bhattarai and Sadaf Hameed

Peking University, Department of Biomedical Engineering, Beijing 100871, PR China

1.1 Introduction

The conventional analytical methods, both qualitative and quantitative, based onthe measurements of species in complex matrices dominated the era of chemicalsensing. These methods were based on the complete separation of sample com-ponents followed by the identification and quantitation of the target analytes.However, (i) expensive nature of the measurement techniques both financiallyand temporally, (ii) difficulty in the analysis of complex samples within a limitedsample concentration, and (iii) the employment of separation methods limitingreal-time analysis during in vivo applications subtly challenged its future devel-opment [1]. At present, an inexpensive and facile way of biosensor fabricationfor the real-time detection and/or quantification of biologically relevant analytesprovides an analytically powerful tool over conventional techniques [2]. Thesebiosensors can surpass the major limitations of traditional sensors such as sensi-tivity, speed, and sensibility. Such biosensors typically function by combining abiomolecular recognition unit that is capable to sense the biochemical reactionand a transducer that can convert the concentration of the target analytes into ameasurable signal. In 1977, Karl Camman first coined the term biosensor, but theIUPAC (International Union of Pure and Applied Chemistry) disagreement ledto the conception of a new standard definition in 1997 [3]. A standard definitionof biosensor now is as follows: “A biosensor is a self-contained integrated device,which is capable of providing specific quantitative or semi-quantitative analyticalinformation using a biological recognition element (biochemical receptor), whichis retained in direct spatial contact with a transduction element. Because oftheir ability to be repeatedly calibrated, we recommend that a biosensor shouldbe clearly distinguished from a bioanalytical system, which requires additionalprocessing steps, such as reagent addition. A device that is both disposable afterone measurement, i.e., single use, and unable to monitor the analyte concentrationcontinuously or after rapid and reproducible regeneration should be designated asa single-use biosensor.” Since the earliest enzymatic electrode-based biosensorsdeveloped by Clark, there has been a rapid development/improvement in thedesign and application of these biosensors (Figure 1.1). Recently, biosensors

Nanobiosensors: From Design to Applications, First Edition. Edited by Aiguo Wu and Waheed S. Khan.© 2020 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2020 by Wiley-VCH Verlag GmbH & Co. KGaA.

2 1 Basics of Biosensors and Nanobiosensors

1980

Publication year

No. of public

ations

1990 2000 2010 202019701960

0

1000

2000

3000

4000

Biosensors5000

Figure 1.1 Recent publication trend in biosensors.

(electrochemical, optical, electronic, and piezoelectric) comprising variousbiorecognition molecules such as enzymes [4], aptamers [5], whole cells [6],antibodies [7], and deoxyribonucleic acid (DNA) [8] are widely applied in healthcare, food quality management, forensics, pharmaceutical industries, and severalother areas (Figure 1.2). Improvised methods in the fabrication of biosensorshave greatly augmented the characteristics of a biosensor measured in termsof selectivity, reproducibility, stability, sensitivity, and linearity. Moreover,rapid advancement in the fabrication technology together with electroniccomponents has ushered miniaturization of such devices resulting a hugesurge in the biosensor market. Notably, the use of nano-sized materials (havingat least one dimension <100 nm) in the fabrication of biosensors leading tonanobiosensors have gained high momentum lately. The unique properties(mechanical, chemical, structural, and electrical) of these nanomaterials usedin nanobiosensors have not only helped to overcome challenges based on thesensitivity and detection limit of the devices but has also improved the interfacialreaction owing to the better immobilization of biorecognition molecules [9, 10].In addition, hybridization of nanomaterial-based strategies with a microscalesystem has allowed a new type of biomolecular analysis together with a high levelof sensitivity that can leverage nanoscale binding events to detect circulatingtumor cells (CTCs) or sense rare analytes [11]. In brief, this chapter compre-hends all the basic information about biosensors and also provides in-depthknowledge of the design, components, characteristics, and applications ofbiosensors.

1.2 Biosensor and Its Working Principle 3

30.62%

19.19%

(a) (b)

46.77%34.53%

16.53%

44.07%

3.42%4.88%

5-year publication trend

Electrochemical

Piezoelectric

OpticalElectronic

NanobiosensorsPyroelectric/gravimetric

Figure 1.2 Five-year publication trends of various types of biosensors. (a) 2017–2013 and(b) 2012–2008.

1.2 Biosensor and Its Working Principle

A simple design of any biosensors basically comprises four major components:(i) a bioreceptor, (ii) a transducer, (iii) electronic components, and (iv) a read-out/display unit (Figure 1.3). Briefly, a bioreceptor is an external component of abiosensor that comes in direct contact with the target analyte during operation.The major function of a bioreceptor is to capture the target analytes with highspecificity and selectivity [12]. Some examples of bioreceptors commonly usedin the construction of biosensors are enzymes [4], aptamers [5], whole cells[6], antibodies [7], and DNA [8]. Construction mechanism typically followsthe adsorption/immobilization of a biorecognition element on the surface of abiosensor. Therefore, techniques deployed for the adherence of such biorecogni-tion elements remain central to the sensitivity and selectivity of a biosensor.

A most common approach for the immobilization of biorecognition elementsincludes adsorption, microencapsulation, entrapment, covalent bonding, andcross-linking [13–15]. Immobilization serves one or more of the following

Bioreceptor TransducerSignal

conditioningDisplay

Figure 1.3 Schematic of biosensor components.


purposes: (i) continuous monitoring of analytes in flowing samples such asenvironmental samples, biological fluids having less amount of target moleculesor bioreactor fluids, (ii) the biosensor can be used repeatedly, (iii) enhances theperformance of biosensors in terms of reproducibility and sensitivity owing tothe advancement of the biorecognition unit, and (iv) simplicity and flexibility ofthe immobilization technique. Toward a closer look in the fabrication strategies,(nano)biosensors confer multivariate interfacial region ranging between 1 and10 nm, especially for the recognition of target analytes [11]. The detection of vari-ous biological molecules including protein–protein interactions can occur in thisregion. However, complexity during immobilization of such nanoscale compo-nents may be a challenging task. The chemical reaction at the site of bioreceptor,also termed as biorecognition, results in the generation of various signals such aslight, changes in pH, heat generation, or changes in mass, which can be perceivedby the physical component, transducer. The transducer can be defined as a devicethat can convert one form of energy to another. Therefore, depending on the typeof biochemical reactions, several types of transducers can be used during con-struction of a biosensor; for instance, if the biorecognition process yields outputin the form of light, then an optical transducer (e.g. photodetector) can perceivethe incoming light and convert into a measurable electrical form [16]. Notably,all of the conversion processes are directly proportional to the amount ofanalyte–bioreceptor interactions at the biorecognition unit. The signals gen-erated by the transducer (usually electrical) are in analogous form and cannotbe read directly. Therefore, a signal conditioning unit assimilating various highpass/low pass/notch filters, amplifiers, and analogs to digital converters usuallyquantifies the signal that can be displayed directly in a readable format [17].Biosensors may consist of different types of display units such as liquid crystaldisplay (LCD), computer, or directly to the printer that comprises a pictorialrepresentation of the measured signal. Depending on the user’s requirement,the format of output signals may vary, e.g. the final data can be either numeric,tabular, graphics, or an image.

1.3 Characteristics of a Biosensor

The design of a biosensor defines the intended purpose of the application; how-ever, other key factors are still central to manipulate the performance of thesebiosensors (Figure 1.4) [18].

1.3.1 Selectivity

Selectivity is the ability of a biosensor to detect a specific target analyte from apooled sample containing mixtures of unwanted contaminants. The best classicalexample to explain selectivity is the interaction between an immobilized antibodyand an antigen that is highly specific in nature.

1.3.2 Reproducibility

Reproducibility, on the other hand, is the ability of a biosensor to yield identi-cal end results regardless of the number of times experiment is repeated. This is

1.3 Characteristics of a Biosensor 5

Linearity

Sensitivity

Stability

Characteristics of a

biosensor

Precisionand

accuracy

Selectivity

Reproducibility

Figure 1.4 Biosensor characteristics.

mainly determined by the precision and accuracy of the transducer or electroniccomponents in a biosensor. The reliability of biosensor output is highly dependenton the reproducibility of the biosensor devices.

1.3.3 Stability

Although precision and accuracy regulate the ability of biosensors to yield highlyreproducible results, nevertheless, stability is another key aspect that may alsoundermine the performance of biosensors. In brief, stability refers to the ability ofbiosensors to circumvent ambient disturbances that are likely to alter the desiredoutput response during measurement. This is more critical in the fabrication ofbiosensors that may require longer time or continuous monitoring to give a finalresult. Several factors such as temperature, the affinity of the bioreceptor, andfouling of membranes can influence the stability of a biosensor.

1.3.4 Sensitivity and Linearity

Sensitivity and linearity are two major properties of biosensors that determinethe application and robustness of the device. Moreover, in a clinical setting, thesebasic characteristics of biosensors cannot be overlooked and should be dealt withutmost care. Sensitivity refers to the lowest detection limit of an analyte by abiosensor. This may range from nanogram per milliliter to even femtogram permilliliter. Basically, in case of biosensors designed for medical or environmentalmonitoring applications, sensitivity can be attained in the lowest possible valuesuch as nanogram per milliliter or even femtogram per milliliter. Alternatively,linearity represents the accuracy of the obtained output within a working rangewhere the concentration of the analyte in the sample is directly proportional tothe measured signal. The straight line in the form of y = mx+ c represents the lin-earity of a biosensor. Here, y = output signal, m = sensitivity of the biosensor, andc = concentration of the analyte. Generally, detection of high-substrate concen-tration is usually better if the dynamic range or the linearity of the sensor is higher.


1.4 Biosensor Evolution: A Brief Outlook

The biosensor has a long history of development and also experienced hugetransformation encompassing design strategies, working mechanisms, and mostimportantly reduction in the size of the biorecognition unit to a nanoscale. Untilnow, glucose biosensors are a role model to exemplify changes that took placesince the advent of the term “biosensor.” Herein, we present a brief snapshot onthe evolution of biosensors while considering glucose biosensors as a backboneof our discussion. The success story of glucose biosensors and their subsequentevolution with the passage of time have become a role model in the historyof biosensors [19]. Since past 50 years, a variety of transformations have beenattributed to the design and construction of these glucose biosensors [20]. Thefirst-generation glucose biosensors were based on the use of natural oxygensubstrate and relied mainly on the detection of the hydrogen peroxide [21]. How-ever, several limitations such as restricted solubility of oxygen in biological fluidsresulting in “oxygen deficit” and limited selectivity of hydrogen peroxide severelycompromised the accuracy of measurement. The limitations of first-generationglucose biosensors were overcome by replacing oxygen with nonphysiologicalelectron acceptors. These redox mediators were able to carry electrons fromthe enzyme to the surface of the working electrode [22]. A variety of electronmediators such as ferrocene, ferricyanide, quinines, tetrathiafulvalene (TTF),tetracyanoquinodimethane (TCNQ), thionine, methylene blue, and methylviologen were used to improve the sensor performance [19, 23]. In addition,the second generation of glucose biosensors experienced a huge paradigm shiftin the sensor performance and design strategies such as (i) introduction ofcommercial screen-printed strips for self-monitoring of blood glucose, (ii) useof modified electrodes and tailored membrane, and (iii) the first electrochem-ical pen-sized blood glucose monitor for self-monitoring of diabetic patient[22, 24, 25]. Various strategies to enable electron transfer were primarily adoptedfor enhancing the sensor performance: (i) enzyme wiring of GOx developed byHeller’s group, (ii) chemical modification of GOx with electron-relay groups,and (iii) application of nanomaterial as electrical connectors [19, 26, 27]. Thethird generation or the concurrent glucose biosensors are reagentless and basedon direct transfer (without mediators) between the enzyme and the electrode[28]. This has led to the development of an implantable, needle-type device forcontinuous in vivo monitoring of blood glucose [29, 30].

1.5 Types of Biosensors

Biosensors can be classified either based on the mechanism of transduction oron the biological signaling mechanism (Figure 1.5).

1.5.1 Electrochemical Biosensors (ECBs)

These biosensors are basically a subclass of chemical sensors that hybridizethe sensitivity of electrochemical transducers and high specificity of biological

1.5 Types of Biosensors 7

Immunosensors

Biosensors

On the basis oftransduction

Electrochemical Optical

On the basis ofbiological

mechanism

Amperometric

Potentiometric

Impedimetric

Conductometric

Piezoelectrical Electronic

Surfaceplasmon

resonance

Evanescentwave

fluorescence

Enzymatic

DNA aptamers

Whole-cell

Peptides

Figure 1.5 Biosensors classification.

recognition processes [31, 32]. Both of these features make electrochemical sen-sors as the best choice in a variety of clinical applications. The inherent selectivityof the biological components in electrochemical biosensors (ECBs) is mainlyachieved by the use of enzymes (most commonly used), antibodies, proteins,cells, nucleic acids, receptors, or tissues. In principle, ECBs can selectively reactwith the target analyte to produce an electrical signal proportional to the concen-tration of the target analyte. Over the past several decades, ECBs have receivedoverwhelming attention and are increasingly adopted in routine diagnosis ofdiseases or important areas, e.g. industrial, agricultural, and environmental anal-ysis [33]. Advantages of ECBs over conventional detection techniques are (i) lowdetection limits, (ii) a wide linear response range, (iii) good stability and repro-ducibility, (iv) experimental simplicity, (v) low cost, (vi) portability, and (vii) smallsample volumes [34, 35]. So far, various experts in this field have greatly reviewedsubsequent progress, improvised concepts, and future applications of ECBsand opined about multitude ways of ECB classification [31]. For example, ECBscan be classified based on biological signaling mechanism (e.g. enzyme-basedbiosensor, immunosensors, DNA/nucleic acid sensor, cell-based biosensor, andbiomimetic biosensor) or signal transduction mechanism (e.g. amperometric,potentiometric, conductometric, electrical impedance spectroscopy [EIS], andcalorimetric). Because the detailed concept of individual biosensors and theirtypes will be greatly discussed elsewhere in this chapter, we aim to briefly summa-rize the basic principles that can help readers to understand the most commonlyused ECBs.


1.5.1.1 Potentiometric BiosensorsPotentiometric biosensors characterized by simplicity, low cost, and familiarityhave been widely used since the early 1930s [36]. In general, potentiometricbiosensors can exist in three different types: ion-selective electrodes (ISEs),coated wire electrodes (CWES), and field-effect transistors (FETs) [37]. However,the most common examples of these classes are the glass pH electrode and ISEsfor detection of potassium, calcium, sodium, or chloride ions. In contrast to ISE,the CWES received attention lately around the 1970s after it was introducedby Freiser [38, 39]. The CWES responses are very much similar to those ofclassical ISE, but elimination for the need of an internal reference electrodeallowed flexibility in miniaturization of the device. A more advanced form ofpotentiometric sensors comprises an ion-selective field-effect transistor (ISFET),which is more like an upgraded version of CWES [40]. The advantage of thistype of biosensor is to easily fabricate smaller sized devices that are greatlyuseful for the in vivo testing of several ions. The fabrication of these biosensorsis similar to the one used in manufacturing microelectronic chips. In brief,potentiometric biosensors have been greatly successful in clinics, industries,and other major sectors. Since the advent of a glass electrode, an increasingnumber of potentiometric biosensors (ISEs) have come into existence, resultingin successful analysis of various inorganic ions that were initially thought asdifficult to analyze. Interestingly, commercialization trend has revealed themaximum use of potentiometric sensors in the clinics and industries whereaccuracy, speed, and simplicity are a primary focus.

1.5.1.2 Voltammetric/AmperometricThis type of ECB is mainly responsible for the continuous measurement ofcurrent resulting from the oxidation/reduction process during a biochemicalreaction [41]. The current produced at the working electrode as a result of electro-chemical reduction or oxidation proportional to the oxygen concentration that ismeasured at a constant potential is referred as an amperometry [42]. In contrast,voltammetry is the technique that measures current during controlled variationsof the potential or over a set potential range. Despite limited mass transport ofthe molecules to the electrodes, it is claimed that amperometric devices facilitatea wide dynamic range suitable for low-level quantitation and superior sensi-tivity compared to potentiometric devices. Examples of such sensors includeglucose biosensors, human chorionic gonadotropin β-subunit (β-HCG)-basedpregnancy testing, adenosine triphosphate (ATP) sensors, and so on [43, 44].

1.5.1.3 Impedance (Electrical Impedance Spectroscopy, EIS)EIS was first described by Lorenz and Schulze in 1975 where a sinusoidal poten-tial, U (2–10 mV), was applied to measure the resulting current response, I,representing both resistive and capacitive properties of materials [45]. To obtainthe impedance spectrum, the excitation frequency of the applied potential isvaried over a range of frequencies resulting in the sum of a real and an imaginaryimpedance component (complex impedance). This technique is more powerful interms of sampling electron transfer at a high frequency and mass transfer at a lowfrequency. An example of the impedimetric detection to monitor immunological


binding events of antibody (Ab)–antigen (Ag) on an electrode surface includesmeasurement of the small changes in impedance that are proportionalto the concentration of Ag in the specimen [46]. However, limitation of suchimmunosensors may constitute damage and release of the bound immunoreagentfrom the surface of transducer, resulting in a compromised efficiency of the sen-sor. Moreover, nonspecific binding of Ab–Ag should also be carefully minimized.

1.5.1.4 ConductometricThese are basically a subset of impedimetric devices that monitor changes inthe electrical conductivity of the sample solution with respect to the change inthe composition of solution/medium during the process of chemical reaction.Conductometric sensors have been used in chemical analysis, environmentalmonitoring, or detection of foodborne pathogens such as Escherichia coli orSalmonella spp. [47]. Some major limitations of enzyme-based conductometricbiosensing devices that limit their wide applications are the variable ionicbackground of clinical samples and the obligation to measure small differencesin the conductivity of high ionic strength media. However, the rapid advent ofelectronic-based technologies such as semiconductors and integration of sensorsto microelectronic devices (e.g. FETs) have greatly surpassed these limitations[48]. The most successful examples in this category highlights detection ofdrugs in human urine and pollutant detection in the testing of environmentalspecimen [49].

1.5.2 Optical Biosensors

Optical biosensors are the most preferred type because of the ease of real-time,direct, and label-free detection of various chemical and biological substances[50]. In comparison to conventional measurement techniques, optical measure-ment strategies are mainly preferred because of higher sensitivity, specificity,low cost, and portability [51]. In the recent trend, optical measurement tech-nologies have received profound attention for the development of new opticalbiosensors that integrates microelectronics or micro-electro-mechanical system(MEMS)-based technologies together with molecular biology, chemistry, andbiotechnology [16, 52, 53]. An exponential growth in the design and fabrica-tion of optical sensors over the past decade has paved its way for worldwideapplication in the field of health care systems, biotechnology industry, andother environment-related applications. Optical biosensors following an opticaldetection technique mostly exploit the interaction of the optical field witha biorecognition element, which can be either labeled or label-free. In brief,label-free optical detection technique follows interaction of analyzed sample oranalytes with the transducer; however, labeled detection technique involves theinteraction of the label and analytes to generate signals such as colorimetric,fluorescence, or luminescence, followed by the detection with the transducerof a specific type. The design of the latter one comprises a sensing element(biorecognition unit) that is integrated with an optical transducer systemcapable to generate signal proportionate to the concentration of the measuredanalyte. The biorecognition unit of optical biosensors may also include biological


materials similar to the other types of sensors. The interaction of biorecognitionunit and the target analytes results in the generation of an optical signal thatcan be further deployed for measurements via surface plasmon resonance (SPR)[54], optical waveguide interferometry [55], and evanescent wave fluorescenceimaging [56]. Optical biosensors offer huge variations based on the constructiontypes, of which (i) SPR biosensors including localized SPR and (ii) evanescentwave fluorescence biosensors are of particular interest and require furtherdiscussion.

1.5.2.1 Surface Plasmon ResonanceSurface plasmon resonance biosensors that could detect biomolecular inter-actions came into existence after 80 years of discovery of SPR phenomenon(first observed in 1902) [54]. The basic physics involved in the fabrication ofSPR biosensors is the generation of surface plasmons after illuminating metallicsurfaces (or similar conducting materials separated at the interface by a glass ora liquid) by a polarized light directed at a specific angle [57]. The subsequentgeneration of surface plasmons and reflected light of reduced intensity at aspecific angle (known as resonance angle) therefore provides information aboutthe proportionate mass attached to the surface of the transducer. Unlike con-ventional techniques, SPR is widely acknowledged as a primary tool to providedirect information on biomolecular interaction without the use of any labelingstrategies. However, limitations resulting from nonspecific binding, limitedmass transfer, and avidity can often complicate SPR analysis. Despite this, SPRhas received a profound application in drug development, clinical diagnosis,food industry, biological sciences, and many more [58–60]. An advanced versionincorporating the sensitivity of SPR and imaging technique to yield spatiallyresolved images of biointeractions has opened a new avenue in medicine,especially for the screening or identification of biomarkers and therapeutictargets [61]. On the other hand, localized surface plasmon resonance (LSPR) is astrikingly similar technique to SPR but of higher importance for nanostructures,mainly metallic nanoparticles such as Au and Ag exhibiting unique opticalproperties that are normally absent in larger metallic structures [62]. Themajor difference between these two techniques is the oscillation of plasmons,which is confined locally on the nanostructured surface rather than along themetal/dielectric interface as in SPR. Biosensors based on LSPR technology aremainly popular because of the ease of miniaturization resulting in increasedthroughput and lower operational costs. Moreover, LSPR biosensors known asthe state-of-the-art analytical devices have demonstrated excellent performancecompared to the SPR systems even at significantly lower surface densities ofinteracting molecules [63]. However, fabrication strategies may require addi-tional care to control factors such as shape, material types, dimension, and alsothe interparticle distance that may otherwise compromise sensitivity of LSPRsensors.

1.5.2.2 Evanescent Wave Fluorescence BiosensorsBiosensors constructed on the basis of evanescent wave principle have becomeparticularly useful in the development of immunosensors (different from the


enzymatic biosensors) [64]. So far, total internal reflection fluorescence (TIRF) isoften applied to evanescent wave spectroscopy (EWS). Guided light in an opticalwaveguide or fibers surrounded by a low refractive index medium is totallyinternally reflected after striking the interface. This results in the generationof a wave that normally extends out from the interface into the lower indexmedium called as an evanescent wave. Such evanescent waves have a very shortlifespan and are subjected to decay exponentially over a distance of 100 nm to anapproximate wavelength. The important attraction for the use of such techniquelies in the minimization of background signals to a large extent because thedetection limit of the excited fluorophore by irradiating light is very narrowand is largely captured only at the surface excluding unwanted backgroundsignals from the bulk. The construction of devices based on EWS geometryoffers a wide range of applications from clinical diagnostics to the food safetyand biodefense [56]. The very near future may experience a larger numberof ESW biosensors in health care areas. Such biosensors, while minimizingthe background interference, would also offer advantages such as specificityattributed only to the labeled species or performance improvement besides theuse of turbid or absorbing media similar to the biological solutions.

Based on the transduction mechanism, optical biosensors can be furtherclassified into several types such as absorption, fluorescence, or luminescencethat have received immense market priorities. All these three methods repre-sent a unique property of detecting the output light intensity in reference tothe incoming light beam, also called self-referenced (exception may includefluorescence measurement at a single wavelength). Design of these biosensorsalso follows a similar strategy comprising a biomolecule-immobilized sur-face/transducer for receiving and processing information based on the opticalproperties such as absorption, emission, reflectance, or change in an interfer-ometric pattern. The only difference in the construction of such biosensorsis the use of photodetectors that can transform incoming light into electricalsignal. Absorption, fluorescence-based biosensors are a common example in thefamily of spectroscopy and are extremely convenient to use compared to otherimportant types of spectroscopic techniques such as optical waveguide lightmode spectroscopy, reflectometric interference spectroscopy, light scattering,or supercritical angle fluorescence [51]. Altogether, the advantage of the opticalbiosensor is the flexibility to combine with (micro)fluidic devices regardless ofthe applied voltages up to several kilovolts. This is a major limitation for most ofthe ECB, which makes electrochemical detection difficult.

1.5.3 Piezoelectric Biosensors

Piezoelectric biosensors are basically composed of a mechanical component ora piezoelectric material that can transform the mass or thickness of an analyteinto an electrical signal [65, 66]. This is mainly possible because of the use ofnoncentric piezoelectric materials that can resonate at a natural resonance fre-quency under the application of an external alternating electrical field. In mostof the cases, quartz crystals can serve this purpose and are used most widely.Typically, construction of these sensors is relatively easy and integrates the use


of a biosensing material coated with the piezoelectric material and an externalelectronic device that produces an electric signal that resonates at the naturalfrequency of quartz crystal. However, during the time of detection, when thebiosensing component encounters the target analyte, there is a shift in frequency,resulting in the changes of output current with respect to the mass of the targetanalyte. In general, piezoelectric biosensors can be classified as two main types:(i) bulk wave (BW) and (ii) surface acoustic wave (SAW). BWs are studied mostwidely and are represented by various names such as quartz crystal microbal-ance (QCM) or thickness shear mode (TSM) referred to the mass sensitivity andmotion of crystal vibration, respectively [67]. In a particular example of QCM,the antigen–antibody interaction occurring at the surface of the crystal leads tothe changes in the loading of mass resulting in the corresponding decrease in theresonant frequency. Such changes can be measured down to the nanogram (ng)level depending on the sensitivity of the QCM. In contrast, SAW devices are adifferent class of biosensors in which the physical deformation of the wave islimited only to the crystal surface. Although SAW biosensors are known to besensitive than piezoelectric quartz crystal (PQC), attenuation of acoustic wavesin a biological environment might be problematic and requires more attention.

1.5.4 Electronic Biosensors: Based on Field-Effect Transistor

Electronic biosensors have gained immense popularity in the detection of biolog-ical and chemical compounds. The rapid development of electronic devices hashelped to widen its application from electronic paper, low-cost photovoltaics,and organic light-emitting diodes (OLEDs) to the design of the state-of-the-artbiosensors [68]. The recent trend in the fabrication of these biosensors typicallyfocuses on minimization of cost, size, and higher throughput. This is possiblebecause of the improvised synthetic methodology in the field of organic elec-tronics by virtue of which has led to the yield of novel materials and abridgedthe knowledge gap in semiconductor–analyte interactions. Other advantagessuch as the elimination of bulky components used in the construction of opticalor electrochemical biosensors such as photodetectors and excitation sourcesby the use of simple electrical sensing unit have revitalized its success. Atpresent, electronic biosensors are mainly constructed by the use of FETs andrequire further explanation. FETs are commonly used semiconductor devicescomprising three major components, the source (s), the drain (D), and thegate (G), which therefore functions as an on/off switch based on the appliedelectrical field [69]. Unlike most of the conventional biosensors, FET-basedbiosensors follow a different construction mechanism. In brief, the source andthe drain terminals of semiconductor consist of nanowire channels to establish aconnection; however, during construction of biosensors, these nanowire surfacescan be further modified by a biorecognition element. This can eventually leadto the generation of an electric field after binding with target analytes, similar tothe control electric field applied to a conventional FET. An electronic circuitryconnected to the FET sensor helps to monitor the specific conductance of thesurface based on the type of interaction mechanism. In a particular example ofa traditional metal oxide semiconductor field-effect transistor (MOSFET)-based

1.6 On the Basis of the Use of Biorecognition Elements: Catalytic Versus Affinity Biosensors 13

biosensors, the gate is biologically modified by an enzyme, receptor, antibody,DNA, or other similar recognition units that can capture the target analyte. Uponinteraction with the target analyte, there is an accumulation of carriers, which isanalogous to applying a voltage to a gate. Therefore, FET whose conductance iscontrolled by the gate voltage can be used to fabricate a similar type of electricalbiosensors [68]. In brief, electronic biosensors are the most widely exploredbiosensors; however, the future realization should concentrate on the fabricationstrategy, choice of electrodes, device stability, reproducibility, and sensitivity.

1.6 On the Basis of the Use of Biorecognition Elements:Catalytic Versus Affinity Biosensors

Catalytic biosensors mainly resemble the use of (bio)chemical species to obtain aproduct mainly via a chemical reaction. A most common example of this categoryis an enzymatic biosensor that is fabricated by using either specific or a combina-tion of enzymes. In a stark contrast, affinity biosensors are specific in nature andconfer binding of an analyte to a specific biorecognition element [70]. Examplesof such biosensors mainly include immunosensors that facilitate binding of spe-cific antibody–antigen or nucleic acid-based biosensors that assist binding ofcomplementary oligonucleotide sequences or ligand–receptor interaction-basedbiosensors [71].

1.6.1 Enzymatic Biosensors

Enzymatic biosensors received profound interest after Leland C. Clark, Jr. firstinvented the oxygen electrode that was later used for the fabrication of glucosebiosensors [72]. The general overview of enzymatic biosensors mainly consti-tutes of an enzyme as the essential components that determine the specificitywhen used as an electrochemical detection tool. The time lapse of an enzymaticbiosensor mainly spotlights on three major types: oxygen-based (first genera-tion), mediator-based (second generation), and direct electrochemistry-based(third generation) electrodes. Enzymes that are commonly used in the construc-tion of biosensors include globular proteins, nucleases (both RNase and DNase),and nucleic acid molecules such as ribozymes/DNAzymes. In the history ofbiosensors, enzyme-based detection methodology is the most commonly usedas a biorecognition element [4]. Nevertheless, enzyme-based biosensors are stillsusceptible to several limitations owing to the poor stability, stringent opera-tional requirements, and variations in pH/temperature that limits the detectionability of the enzymatic biosensors. Recent progress to overcome existingchallenges has been mostly addressed by the use of recombinant enzymes in theaid of genetic engineering that can help to modify the catalytic enzymatic sitesof the target enzyme [73].

1.6.2 Immunosensors

Biosensors that consider the use of antibody or antibody fragment as abiorecognition element is basically referred as immunosensors. Normally,


immunosensors are considered as a highly specific sensor type because therecognition process involved at the interface takes account of an antigen–antibody interaction [74]. Immunosensors have experienced a remarkablepopularity in a very short span of time. This is mainly because of the ability ofimmunosensors to detect analytes at a lowest possible concentration with highspecificity and selectivity. Moreover, rapid technological advancement in thefield of biology and electronics observed by the miniaturization of the transducerand purity of antibodies has helped to foster the application and performanceof immunosensors remarkably. However, there is still room for improvements inthe design of such biosensors. The few limitations may include poor solubility,aggregation induced by changes in temperature, retention of binding affinities ata higher temperature, and limited thermal stability. Recent development in theisolation of recombinant antibody fragments using phage display libraries havegreatly improved the performance of immunosensors.

1.6.3 DNA Aptamer Biosensors

Aptamer-based biorecognition technique is also highly specific because it usescomplementary DNA strands or oligonucleotides as a recognition element [5,75]. Moreover, in comparison to antibodies as a recognition unit, aptamers arerelatively convenient to use because of easy fabrication technique (using selectiveevolution of ligands by exponential enrichment [SELEX]) and no need to dependon cells or animals. The affinity of aptamers to the target has a dissociation con-stant almost close to the nano–picomolar range and can be used for detectionof a wide range of target analytes [76]. The application of aptamer-based biosen-sors may include the detection of mycotoxins, cyanotoxins, and bacterial toxins.Recent progress in the field of aptasensors includes detection of multiple toxinssimultaneously.

1.6.4 Peptide-Based Biosensors

Peptides have gained immense popularity because of its inherent natureto self-assemble in 1D, 2D, and 3D structures via noncovalent interactions(H-bonding, electrostatic, aromatic, π-stacking, hydrophobic, and Van derWaals) [77]. Such unique properties have helped to fabricate various flexible andsupramolecular frameworks for a variety of applications including the biosensor.Other advantages might also include their ability to transfer electrons and con-ductive nature for electrical applications (helical conformation), easy synthesisof peptides sequences, excellent biocompatibility, and so on. The application ofpeptide-based biosensors includes detection of several analytes such as proteins,cells, small molecules, and ions [78]. The general immobilization techniquessuch as adsorption, covalent attachment, or self-assembled monolayers allowpreparing the biorecognition unit of biosensors.

1.6.5 Whole-Cell Biosensors

In recent years, enzyme-based biosensors are gradually being replaced by the useof whole cell as a biorecognition element in a biosensor. The relatively low-cost

nanobiosensors - download.e-bookshelf.de€¦ · vi contents 1.8 conclusion 17 acknowledgment 17...

Documents