Chemical Sensors and Biosensors: Fundamentals and Applications Book

Preface xix

Acknowledgements xxi

List of Symbols xxiii

List of Acronyms xxxi

1 What are Chemical Sensors? 1

1.1 Chemical Sensors: Definition and Components 1

1.2 Recognition Methods 2

1.2.1 General Aspects 2

1.2.2 Ion Recognition 3

1.2.3 Recognition by Affinity Interactions 3

1.2.4 Recognition by Nucleic Acids 3

1.2.5 Recognition by Enzymes 4

1.2.6 Recognition by Cells and Tissues of Biological Origin 4

1.2.7 Gas and Vapor Sorption 4

1.3 Transduction Methods 4

1.3.1 General Aspects 4

1.3.2 Thermometric Transduction 5

1.3.3 Transduction Based on Mechanical Effects 5

1.3.4 Resistive and Capacitive Transduction 5

1.3.5 Electrochemical Transduction 5

1.3.6 Optical Transduction 6

1.4 Sensor Configuration and Fabrication 6

1.5 Sensor Calibration 7

1.6 Sensor Figures of Merit 8

1.6.1 Reliability of the Measurement 9

1.6.2 Selectivity and Specificity 10

1.6.3 Detection and Quantification Capabilities 10

1.6.4 Response Time 11

1.7 Sensor Arrays 11

1.7.1 Quantitative Analysis by Cross-Sensitive Sensor Arrays 11

1.7.2 Qualitative Analysis by Cross-Sensitive Sensor Arrays 12

1.7.3 Artificial Neural Network Applications in the Artificial Nose/Tongue 13

1.7.4 Outlook 14

1.8 Sensors in Flow Analysis Systems 14

1.9 Applications of Chemical Sensors 14

1.9.1 Environmental Applications of Chemical Sensors 15

1.9.2 Healthcare Applications of Chemical Sensors 15

1.9.3 Application of Chemical Sensors in the Food Industry, Agriculture and Biotechnology 16

1.9.4 Chemical Sensors in Defense Applications 16

1.10 Literature on Chemical Sensors and Biosensors 17

1.11 Organization of the Text 17

References 19

2 Protein Structure and Properties 21

2.1 Amino Acids 21

2.2 Chemical Structure of Proteins 21

2.3 Conformation of Protein Macromolecules 22

2.4 Noncovalent Chemical Bonds in Protein Molecules 24

2.5 Recognition Processes Involving Proteins 25

2.6 Outlook 26

References 27

3 Enzymes and Enzymatic Sensors 28

3.1 General 28

3.2 Enzyme Nomenclature and Classification 28

3.3 Enzyme Components and Cofactors 30

3.4 Some Enzymes with Relevance to Biosensors 32

3.4.1 Oxidases 32

3.4.2 Dehydrogenases 33

3.4.3 Hydrolases 34

3.4.4 Lyases 35

3.4.5 Outlook 35

3.5 Transduction Methods in Enzymatic Biosensors 36

3.5.1 Transduction Methods 36

3.5.2 Multienzyme Sensors 37

3.6 Kinetics of Enzyme Reactions 38

3.6.1 The Michaelis–Menten Mechanism 38

3.6.2 Other Mechanisms 40

3.6.3 Expressing the Enzyme Activity 41

3.6.4 pH Effect on Enzyme Reactions 42

3.6.5 Temperature Effect on Enzyme Reactions 43

3.6.6 Outlook 43

3.7 Enzyme Inhibition 44

3.7.1 Reversible Inhibition 44

3.7.2 Irreversible Inhibition 46

3.7.3 Enzymatic Sensors for Inhibitors: Design and Operation 46

3.7.4 Applications of Enzyme-Inhibition Sensors 47

3.8 Concluding Remarks 48

References 49

4 Mathematical Modeling of Enzymatic Sensors 50

4.1 Introduction 50

4.2 The Enzymatic Sensor Under External Diffusion Conditions 50

4.2.1 The Physical Model 50

4.2.2 The Mathematical Model 51

4.2.3 The Zero-Order Kinetics Case 52

4.2.4 The First-Order Kinetics Case 52

4.2.5 The Dynamic Range and the Limit of Detection Under External Diffusion Conditions 54

4.3 The Enzymatic Sensor Under Internal Diffusion Control 55

4.3.1 The Steady-State Response 55

4.3.2 The Transient Regime and the Response Time Under Internal Diffusion Conditions 58

4.4 The General Case 60

4.4.1 The Model 60

4.4.2 Effect of the Biot Number 61

4.4.3 Effect of Partition Constants and Diffusion Coefficients 63

4.4.4 Experimental Tests for the Kinetic Regime of an Enzymatic Sensor 63

4.5 Outlook 64

References 64

5 Materials and Methods in Chemical-Sensor Manufacturing 66

5.1 Introduction 66

5.2 Noncovalent Immobilization at Solid Surfaces 66

5.3 Covalent Conjugation 67

5.3.1 Zero-Length Crosslinkers 68

5.3.2 Bifunctional Crosslinkers 69

5.3.3 Immobilization by Protein Crosslinking 69

5.4 Supports and Support Modification 70

5.4.1 General Aspects 70

5.4.2 Natural Polymers 71

5.4.3 Synthetic Polymers 72

5.4.4 Coupling to Active Polymers 72

5.4.5 Coupling to Inactive Polymers 72

5.4.6 Inorganic Supports 73

5.4.7 Carbon Material Supports 74

5.4.8 Metal Supports 75

5.4.9 Semiconductor Supports 76

5.5 Affinity Reactions 77

5.6 Thin Molecular Layers 78

5.6.1 Self-Assembly of Amphiphilic Compounds 78

5.6.2 Bilayer Lipid Membranes 79

5.6.3 Alternate Layer-by-Layer Assembly 80

5.7 Sol-Gel Chemistry Methods 81

5.8 Hydrogels 83

5.8.1 Physically Crosslinked Hydrogels 84

5.8.2 Chemically Crosslinked Hydrogels 84

5.8.3 Redox Hydrogels 84

5.8.4 Responsive Hydrogels 84

5.9 Conducting Polymers 86

5.10 Encapsulation 88

5.11 Entrapment in Mesoporous Materials 89

5.12 Polymer Membranes 90

5.12.1 Deposition of Polymers onto Solid Surfaces 90

5.12.2 Perm-Selective Membranes 91

5.13 Microfabrication Methods in Chemical-Sensor Technology 92

5.13.1 Spot Arraying 92

5.13.2 Thick-Film Technology 92

5.13.3 Thin-Film Techniques 94

5.13.4 Soft Lithography 95

5.13.5 Microcontact Printing of Biocompounds 95

5.14 Concluding Remarks 97

References 97

6 Affinity-Based Recognition 101

6.1 General Principles 101

6.2 Immunosensors 101

6.2.1 Antibodies: Structure and Function 101

6.2.2 Antibody–Antigen Affinity and Avidity 103

6.2.3 Analytical Applications 103

6.2.4 Label-Free Transduction Methods in Immunosensors 104

6.2.5 Label-Based Transduction Methods in Immunosensors 104

6.2.6 Enzyme Labels in Immunoassay 105

6.3 Immobilization Methods in Immunosensors 106

6.4 Immunoassay Formats 106

6.5 Protein and Peptide Microarrays 109

6.6 Biological Receptors 110

6.7 Artificial Receptors 111

6.7.1 Cyclodextrins and Host–Guest Chemistry 111

6.7.2 Calixarenes 113

6.7.3 Molecularly Imprinted Polymers (MIPs) 113

6.8 Outlook 115

References 115

7 Nucleic Acids in Chemical Sensors 118

7.1 Nucleic Acid Structure and Properties 118

7.2 Nucleic Acid Analogs 121

7.3 Nucleic Acids as Receptors in Recognition Processes 122

7.3.1 Hybridization: Polynucleotide Recognition 122

7.3.2 Recognition of Non-Nucleotide Compounds 123

7.3.3 Recognition by Aptamers 124

7.4 Immobilization of Nucleic Acids 126

7.4.1 Adsorption 126

7.4.2 Immobilization by Self-Assembly 127

7.4.3 Immobilization by Polymerization 127

7.4.4 Covalent Immobilization on Functionalized Surfaces 128

7.4.5 Coupling by Affinity Reactions 128

7.4.6 Polynucleotides–Nanoparticles Hybrids 129

7.5 Transduction Methods in Nucleic Acids Sensors 129

7.5.1 Label-Free Transduction Methods 129

7.5.2 Label-Based Transduction 129

7.5.3 DNA Amplification 130

7.6 DNA Microarrays 131

7.7 Outlook 132

References 133

8 Nanomaterial Applications in Chemical Sensors 135

8.1 Generals 135

8.2 Metallic Nanomaterials 136

8.2.1 Synthesis of Metal Nanoparticles 136

8.2.2 Functionalization of Gold Nanoparticles 137

8.2.3 Applications of Metal Nanoparticles in Chemical Sensors 138

8.3 Carbon Nanomaterials 138

8.3.1 Structure of CNTs 139

8.3.2 Synthesis of CNTs 140

8.3.3 Chemical Reactivity and Functionalization 140

8.3.4 CNTApplications in Chemical Sensors 142

8.3.5 Carbon Nanofibers (CNFs) 142

8.4 Polymer and Inorganic Nanofibers 144

8.5 Magnetic Micro- and Nanoparticles 145

8.5.1 Magnetism and Magnetic Materials 145

8.5.2 Magnetic Nanoparticles 146

8.5.3 Magnetic Biosensors and Biochips 146

8.5.4 Magnetic Nanoparticles as Auxiliary Components in Biosensors 148

8.5.5 Outlook 148

8.6 Semiconductor Nanomaterials 149

8.6.1 Synthesis and Functionalization of Quantum Dots 149

8.6.2 Applications of Quantum Dots 151

8.7 Silica Nanoparticles 151

8.7.1 Synthesis, Properties, and Applications 151

8.8 Dendrimers 152

8.8.1 Properties and Applications 152

8.9 Summary 153

References 153

9 Thermochemical Sensors 157

9.1 Temperature Transducers 157

9.1.1 Resistive Temperature Transducers 157

9.1.2 Thermopiles 157

9.2 Enzymatic Thermal Sensors 158

9.2.1 Principles of Thermal Transduction in Enzymatic Sensors 158

9.2.2 Thermistor-Based Enzymatic Sensors 159

9.2.3 Thermopile-Based Enzymatic Sensors 160

9.2.4 Multienzyme Thermal Sensors 160

9.2.5 Outlook 161

9.3 Thermocatalytic Sensors for Combustible Gases 162

9.3.1 Structure and Functioning Principles 162

References 163

10 Potentiometric Sensors 165

10.1 Introduction 165

10.2 The Galvanic Cell at Equilibrium 165

10.2.1 Thermodynamics of Electrolyte Solutions 166

10.2.2 Thermodynamics of the Galvanic Cell 167

x Contents

10.3 Ion Distribution at the Interface of Two Electrolyte Solutions 170

10.3.1 Charge Distribution at the Junction of Two Electrolyte Solutions.

The Diffusion Potential 170

10.3.2 Ion Distribution at an Aqueous/Semipermeable Membrane Interface 172

10.4 Potentiometric Ion Sensors – General 173

10.4.1 Sensor Configuration and the Response Function 173

10.4.2 Selectivity of Potentiometric Ion Sensors 175

10.4.3 The Response Range of Potentiometric Ion Sensors 177

10.4.4 Interferences by Chemical Reactions Occurring in the Sample 177

10.4.5 The Response Time of Potentiometric Ion Sensors 177

10.4.6 Outlook 178

10.5 Sparingly Soluble Solid Salts as Membrane Materials 178

10.5.1 Membrane Composition 178

10.5.2 Response Function and Selectivity 179

10.6 Glass Membrane Ion Sensors 181

10.6.1 Membrane Structure and Properties 181

10.6.2 Response Function and Selectivity 182

10.6.3 Chalcogenide Glass Membranes 183

10.7 Ion Sensors Based on Molecular Receptors. General Aspects 184

10.8 Liquid Ion Exchangers as Ion Receptors 185

10.8.1 Ion Recognition by Liquid Ion Exchangers 185

10.8.2 Charged Receptor Membranes 185

10.8.3 Response Function and Selectivity 186

10.8.4 Outlook 187

10.9 Neutral Ion Receptors (Ionophores) 187

10.9.1 General Principles 187

10.9.2 Chemistry of Ion Recognition by Neutral Receptors 188

10.9.3 Effect of Bonding Multiplicity, Steric, and Conformational Factors 189

10.9.4 Neutral Receptor Ion-Selective Membranes: Composition, Selectivity and

Response Function 190

10.9.5 Neutral Noncyclic Ion Receptors 192

10.9.6 Macrocyclic Cation Receptors 193

10.9.7 Macrocyclic Anion Receptors 194

10.9.8 Neutral Receptors for Organic Ions 194

10.9.9 Porphyrins and Phthalocyanines as Anion Receptors 195

10.9.10 Outlook 196

10.10 Molecularly Imprinted Polymers as Ion-Sensing Materials 197

10.11 Conducting Polymers as Ion-Sensing Materials 198

10.12 Solid Contact Potentiometric Ion Sensors 198

10.13 Miniaturization of Potentiometric Ion Sensors 199

10.14 Analysis with Potentiometric Ion Sensors 200

10.15 Recent Advances in Potentiometric Ion Sensors 201

10.16 Potentiometric Gas Sensors 203

10.17 Solid Electrolyte Potentiometric Gas Sensors 204

10.17.1 General Principles 204

10.17.2 Solid Electrolyte Potentiometric Oxygen Sensors 205

10.17.3 Applications of Potentiometric Oxygen Sensors 206

10.17.4 Types of Solid Electrolyte Potentiometric Gas Sensors 207

10.17.5 Mixed Potential Potentiometric Gas Sensors 208

10.17.6 Outlook 209

10.18 Potentiometric Biocatalytic Sensors 210

10.19 Potentiometric Affinity Sensors 211

10.20 Summary 212

References 213

11 Chemical Sensors Based on Semiconductor Electronic Devices 217

11.1 Electronic Semiconductor Devices 217

11.1.1 Semiconductor Materials 217

11.1.2 Band Theory of Semiconductors 218

11.1.3 Metal-Insulator-Semiconductor (MIS) Capacitors 219

11.1.4 Metal-Insulator-Semiconductor Field Effect Transistors (MISFETs) 221

11.1.5 Outlook 224

11.2 FED Ion Sensors and Their Applications 224

11.2.1 Electrolyte-Insulator-Semiconductor (EIS) Devices 224

11.2.2 FEDpH Sensors 226

11.2.3 pH ISFET-Based Gas Probes 228

11.2.4 Membrane-Covered ISFETs 229

11.2.5 Light-Addressable Potentiometric Sensors (LAPS) 230

11.2.6 Reference Electrodes for ISFET Sensors 231

11.2.7 Enzymatic FET Sensors (EnFETs) 232

11.2.8 Outlook 232

11.3 FED Gas Sensors 234

11.3.1 FED Hydrogen Sensors 234

11.3.2 Metal Gate FED Sensors for Other Gases 235

11.3.3 Organic Semiconductors as Gas-Sensing Materials 236

11.3.4 Organic Semiconductors FED Gas Sensors 237

11.3.5 Response Mechanism of FED Gas Sensors 238

11.3.6 Outlook 240

11.4 Schottky-Diode-Based Gas Sensors 240

11.5 Carbon-Nanotube-Based Field-Effect Transistors 242

11.6 Concluding Remarks 243

References 244

12 Resistive Gas Sensors (Chemiresistors) 246

12.1 Semiconductor Metal Oxide Gas Sensors 246

12.1.1 Introduction 246

12.1.2 Gas-Response Mechanism 246

12.1.3 Response to Humidity 247

12.1.4 Sensor Configuration 248

12.1.5 Synthesis and Deposition of Metal Oxides 249

12.1.6 Fabrication of Metal-Oxide Chemiresistors 249

12.1.7 Selectivity and Sensitivity 250

12.1.8 Outlook 251

12.2 Organic-Material-Based Chemiresistors 252

12.3 Nanomaterial Applications in Resistive Gas Sensors 253

12.4 Resistive Gas Sensor Arrays 254

12.5 Summary 255

References 256

13 Dynamic Electrochemistry Transduction Methods 258

13.1 Introduction 258

13.2 Electrochemical Cells in Amperometric Analysis 258

13.3 The Electrolytic Current and its Analytical Significance 260

13.3.1 Current–Concentration Relationships 260

13.3.2 The Current–Potential Curve: Selecting the Working Potential 262

13.3.3 Irreversible Electrochemical Reactions 264

13.3.4 Sign Convention 265

13.3.5 Geometry of the Diffusion Process 265

13.3.6 Outlook 265

13.4 Membrane-Covered Electrodes 266

13.5 Non-Faradaic Processes 267

13.5.1 Origin of Non-Faradaic Currents 267

13.5.2 The Electrical Double Layer at the Electrode/Solution Interface 268

13.5.3 The Charging Current 269

13.5.4 Applications of Capacitance Measurement in Chemical Sensors 270

13.6 Kinetics of Electrochemical Reactions 270

13.6.1 The Reaction Rate of an Electrochemical Reaction 270

13.6.2 Current–Potential Relationships 272

13.6.3 Mass-Transfer Effect on the Kinetics of Electrochemical Reactions 273

13.6.4 Equilibrium Conditions 274

13.6.5 The Electrochemical Reaction in the Absence of Mass-Transfer Restrictions 275

13.6.6 Polarizable and Nonpolarizable Electrodes 276

13.7 Achieving Steady-State Conditions in Electrochemical Measurements 277

13.7.1 Outlook 278

13.8 Electrochemical Methods 280

13.8.1 Steady-State Method 280

13.8.2 Constant-Potential Chronoamperometry 280

13.8.3 Polarography 281

13.8.4 Linear-Scan Voltammetry(LSV) and Cyclic Voltammetry (CV) 282

13.8.5 Pulse Voltammetry 285

13.8.6 Square-Wave Voltammetry (SWV) 286

13.8.7 Alternating-Current Voltammetry 287

13.8.8 Chronopotentiometric Methods 288

13.8.9 Electrochemistry at Ultramicroelectrodes 289

13.8.10 Current Amplification by Reactant Recycling 291

13.8.11 Scanning Electrochemical Microscopy 292

13.8.12 Outlook 293

13.9 Electrode Materials 294

13.9.1 Carbon Electrodes 295

13.9.2 Noble-Metal Electrodes 296

13.9.3 Metal-Oxide Films 297

13.9.4 Electrode Fabrication 297

13.9.5 Carbon Nanomaterial Applications in Electrochemistry 298

13.9.6 Outlook 298

13.10 Catalysis in Electrochemical Reactions 299

13.10.1 Homogeneous Redox Catalysis 299

13.10.2 Homogeneous Mediation in Electrochemical Enzymatic Reactions 300

13.10.3 Catalysis by Immobilized Enzymes 301

13.10.4 Heterogeneous Redox Catalysis 302

13.10.5 Surface Activation of Electrochemical Reactions 304

13.10.6 Outlook 304

13.11 Amperometric Gas Sensors 306

13.11.1 The Clark Oxygen Sensor 306

13.11.2 Nitric Oxide Sensors 307

13.11.3 Other Types of Amperometric Gas Sensors 308

13.11.4 Galvanic Cell-Type Gas Sensors 309

13.11.5 Solid Electrolyte Amperometric Gas Sensors 309

References 310

14 Amperometric Enzyme Sensors 314

14.1 First-Generation Amperometric Enzyme Sensors 314

14.2 Second-Generation Amperometric Enzyme Sensors 316

14.2.1 Principles 316

14.2.2 Inorganic Mediators 317

14.2.3 Organic Mediators 317

14.2.4 Ferrocene Derivatives as Mediators 319

14.2.5 Electron-Transfer Mediation by Redox Polymers 320

14.2.6 Sensing by Organized Molecular Multilayer Structures 321

14.3 The Mediator as Analyte 322

14.4 Conducting Polymers in Amperometric Enzyme Sensors 323

14.5 Direct Electron Transfer: 3rd-Generation Amperometric Enzyme Sensors 324

14.5.1 Conducting Organic Salt Electrodes 324

14.5.2 Direct Electron Transfer with FAD-Heme Enzymes 325

14.5.3 Achieving Direct Electron Transfer by Means of Nanomaterials 326

14.6 NAD/NADH+ as Mediator in Biosensors 327

14.7 Summary 328

References 328

15 Mathematical Modeling of Mediated Amperometric Enzyme Sensors 332

15.1 External Diffusion Conditions 332

15.1.1 Model Formulation 332

15.1.2 Sensor Response: Limiting Cases 334

15.1.3 The Dynamic Range and the Limit of Detection 336

15.1.4 Other Theoretical Models 338

15.1.5 Outlook 338

15.2 Internal Diffusion Conditions 339

15.2.1 Model Formulation 339

15.2.2 Dimensionless Parameters and Variables 340

15.2.3 Limiting Conditions 342

15.2.4 Solving the Differential Equations. The Case Diagram 343

15.2.5 Kinetic Currents 343

15.2.6 Diffusion Currents 343

15.2.7 Outlook 345

References 345

16 Electrochemical Affinity and Nucleic Acid Sensors 347

16.1 Amperometric Affinity Sensors 347

16.1.1 Redox Labels in Amperometric Immunosensors 347

16.1.2 Enzyme-Linked Amperometric Immunosensors 347

16.1.3 Separationless Amperometric Immunosensors 349

16.1.4 Nanomaterials Applications in Amperometric Immunosensors 350

16.1.5 Imprinted Polymers in Amperometric Affinity Sensors 351

16.1.6 Outlook 353

16.2 Electrochemical Nucleic Acid-Based Sensors 354

16.2.1 Electrochemical Reactions of Nucleobases 354

16.2.2 Amperometric Nucleic Acid Sensors Based on Self-Indicating Hybridization 355

16.2.3 Intercalating Redox Indicators 357

16.2.4 Covalently Bound Redox Indicators in Sandwich Assays 357

16.2.5 Covalently Bound Redox Indicators in Spatially Resolved Transduction 359

16.2.6 Enzyme Labels in Amperometric Nucleic Acid Sensors 359

16.2.7 Electrochemical DNA Arrays 361

16.2.8 Nucleic Acids as Recognition Materials for Non-Nucleotide Compounds 361

16.2.9 Aptamer Amperometric Sensors 361

16.2.10 Outlook 363

References 364

17 Electrical-Impedance-Based Sensors 367

17.1 Electrical Impedance: Terms and Definitions 367

17.2 Electrochemical Impedance Spectrometry 369

17.2.1 Basic Concepts and Definitions 369

17.2.2 Non-Faradaic Processes 370

17.2.3 Faradaic Processes 372

17.2.4 Probing the Electrode Surface by Electrochemical Impedance Spectrometry 373

17.3 Electrochemical Impedance Affinity Sensors 375

17.3.1 Electrochemical Impedance Transduction in Affinity Sensors 375

17.3.2 Configuration of Impedimetric Biosensors 376

17.3.3 Capacitive Biosensors 377

17.3.4 Signal Amplification 379

17.3.5 Synthetic Receptor-Based Impedimetric Sensors 379

17.3.6 Applications of Impedimetric Affinity Sensors 380

17.4 Biocatalytic Impedimetric Sensors 381

17.5 Outlook 382

17.6 Nucleic Acid Impedimetric Sensors 383

17.6.1 Non-Faradaic Impedimetric DNA Sensors 383

17.6.2 Faradaic Impedimetric DNA Sensors 384

17.6.3 Impedimetric Aptasensors 385

17.7 Conductometric Sensors 386

17.7.1 Conductivity of Electrolyte Solutions 386

17.7.2 Conductance Measurement 388

17.7.3 Conductometric Transducers 389

17.7.4 Conductometric Enzymatic Sensors 389

17.7.5 Conductometric Transduction by Chemoresistive Materials 391

17.7.6 Ion-Channel-Based Conductometric Sensors 394

17.7.7 Outlook 394

17.8 Impedimetric Sensors for Gases and Vapors 395

17.8.1 Humidity: Terms and Definitions 395

17.8.2 Resistive Humidity Sensors 396

17.8.3 Capacitive Humidity Sensors 397

17.8.4 Capacitive Gas Sensors 399

17.8.5 Integrated Impedimetric Gas Sensors and Sensor Arrays 399

17.8.6 Outlook 400

References 400

18 Optical Sensors – Fundamentals 404

18.1 Electromagnetic Radiation 404

18.2 Optical Waveguides in Chemical Sensors 405

18.2.1 Optical Fibers: Structure and Light Propagation 406

18.2.2 Passive Fiber Optic Sensor Platforms 407

18.2.3 Active Fiber Optic Sensor Platforms 407

18.2.4 Planar Waveguides 408

18.2.5 Capillary Waveguides 409

18.2.6 Outlook 409

18.3 Spectrochemical Transduction Methods 409

18.3.1 Light Absorption 409

18.3.2 Diffuse Reflectance Spectrometry 410

18.3.3 Luminescence 411

18.3.4 Fluorescence Spectrometry 412

18.3.5 Steady-State Fluorescence Measurements 413

18.3.6 Time-Resolved Fluorimetry 414

18.3.7 Fluorescence Quenching 416

18.3.8 Resonance Energy Transfer 417

18.3.9 Chemiluminescence and Bioluminescence 417

18.3.10 Electrochemically Generated Chemiluminescence 418

18.3.11 Raman Spectrometry 419

18.3.12 Outlook 420

18.4 Transduction Schemes in Spectrochemical Sensors 421

18.4.1 Direct Transduction 421

18.4.2 Indirect (Competitive-Binding) Transduction 423

18.4.3 Outlook 424

18.5 Fiber Optic Sensor Arrays 424

18.6 Label-Free Transduction in Optical Sensors 425

18.6.1 Surface Plasmons Resonance Spectrometry 425

18.6.2 Interferometric Transduction 426

18.6.3 The Resonant Mirror 428

18.6.4 Resonant Waveguide Grating 429

18.6.5 Outlook 429

18.7 Transduction by Photonic Devices 430

18.7.1 Optical Microresonators 430

18.7.2 Photonic Crystals 431

18.7.3 Outlook 433

References 433

19 Optical Sensors – Applications 435

19.1 Optical Sensors Based on Acid–Base Indicators 435

19.1.1 Optical pH Sensors 435

19.1.2 Optical Sensors for Acidic and Basic Gases 437

19.2 Optical Ion Sensors 438

19.2.1 Direct Optical Ion Sensors 438

19.2.2 Indirect Optical Ion Sensors 439

19.3 Optical Oxygen Sensors 440

19.4 Enzymatic Optical Sensors 442

19.4.1 Principles and Design 442

19.4.2 Optical Monitoring of Reactants or Products 442

19.4.3 Coenzyme-Based Optical Transduction 443

19.4.4 Outlook 443

19.5 Optical Affinity Sensors 444

19.5.1 Optical Immunosensors 444

19.5.2 Optical Sensors Based on Biological Receptors 445

19.5.3 Outlook 446

19.6 Optical DNA Sensors and Arrays 447

19.6.1 Fluorescence Transduction in Nucleic Acid Sensors 447

19.6.2 Fiber Optic Nucleic Acid Sensors 448

19.6.3 Fiber Optic Nucleic Acid Arrays 450

19.6.4 Optical DNA Microarrays 451

19.6.5 Outlook 451

References 452

20 Nanomaterial Applications in Optical Transduction 454

20.1 Semiconductor Nanocrystals (Quantum Dots) 454

20.1.1 Quantum Dots: Structure and Properties 454

20.1.2 Applications of Quantum Dots in Chemical Sensing 456

20.1.3 Outlook 461

20.2 Carbon Nanotubes as Optical Labels 462

20.2.1 Light Absorption and Emission by CNTs 462

20.2.2 Raman Scattering by CNTs 464

20.2.3 CNT Optical Sensors and Arrays 464

20.2.4 Outlook 466

20.3 Metal Nanoparticle in Optical Sensing 466

20.3.1 Optical Properties of Metal Nanoparticles 466

20.3.2 Optical Detection Based on Metal Nanoparticles 467

20.3.3 Metal Nanoparticles in Optical Sensing 468

20.4 Porous Silicon 470

20.5 Luminescent Lanthanide Compound Nanomaterials 471

20.6 Summary 471

References 471

21 Acoustic-Wave Sensors 473

21.1 The Piezoelectric Effect 473

21.2 The Thickness–Shear Mode Piezoelectric Resonator 474

21.2.1 The Quartz Crystal Microbalance 474

21.2.2 The Unperturbed Resonator 476

21.2.3 QCM Loading by a Rigid Overlayer. The Sauerbrey

Equation 477

21.2.4 The QCM in Contact with Liquids 478

21.2.5 The QCM in Contact with a newtonian Liquid 479

21.2.6 The QCM in Contact with a Viscoelastic Fluid 480

21.2.7 Modeling the Loaded TSM Resonator 480

21.2.8 The Quartz Crystal Microbalance with Dissipation

Monitoring (QCM-D) 485

21.2.9 Operation of QCM Sensors 486

21.2.10 Calibration of the QCM 487

21.2.11 Outlook 488

21.3 QCM Gas and Vapor Sensors 489

21.4 QCM Affinity Sensors 489

21.4.1 QCM Immunosensor 490

21.4.2 Amplification in QCM Immunosensors 491

21.4.3 Determination of Small Molecules Using Natural Receptors 492

21.4.4 QCM Sensors Based on Molecularly Imprinted Polymers 492

21.4.5 QCM Sensors Based on Small Synthetic Receptors 494

21.4.6 Outlook 494

21.5 QCM Nucleic Acid Sensors 495

21.5.1 Hybridization Sensors 495

21.5.2 Piezoelectric Aptasensors 496

21.5.3 Outlook 497

21.6 Surface-Launched Acoustic-Wave Sensors 497

21.6.1 Principles 497

21.6.2 The Surface Acoustic Wave 498

21.6.3 Plate-Mode SLAW Devices 498

21.6.4 SLAW Gas and Vapor Sensors 499

21.6.5 Liquid-Phase SLAW Sensing 501

21.6.6 Outlook 502

21.7 Summary 503

References 504

22 Microcantilever Sensors 507

22.1 Principles of Microcantilever Transduction 507

22.1.1 The Microcantilever 507

22.1.2 Static Deformation Transduction 508

22.1.3 Resonance-Mode Transduction 509

22.2 Measurement of Cantilever Deflection 510

22.2.1 Optical Measurement of