Chemical Sensors An Introduction for Scientists and Engineers Peter Gründler Chemical Sensors An Introduction for Scientists and Engineers With 179 Figures and 25 Tables 123 Peter Gründler Hallwachsstraße 5 D-01069 Dresden Germany e-mail: [email protected] Library of Congress Control Number: 2006933730 ISBN 978-3-540-45742-8 Springer Berlin Heidelberg New York DOI 10.1007/978-3-540-45743-5 This work is subject to copyright. All rights reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilm or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer. Violations are liable for prosecution under the German Copyright Law. Springer is a part of Springer Science+Business Media springer.com © Springer-Verlag Berlin Heidelberg 2007 The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Product liability: The publishers cannot guarantee the accuracy of any information about dosage and application contained in this book. In every individual case the user must check such information by consulting the relevant literature. Cover design: KünkelLopka GmbH, Heidelberg Typesetting and production: LE-TEX Jelonek, Schmidt & Vöckler GbR, Leipzig, Germany Printed on acid-free paper 52/3100/YL - 5 4 3 2 1 0 Preface When this book appeared in German, its main task was to bridge the gap between the traditional ways of thinking of scientists and engineers. The dif- ferences in how scientists and engineers think stem from the fact that chemical sensors may be interpreted, on the one hand, as a kind of artificial sense or- gan developed by engineers to equip automatic machines. On the other hand, chemical sensors are not unlike the other myriad small analytical instruments common in analytical chemistry. The book was written with the aim of providing students of technical dis- ciplines with a basic understanding of certain aspects of chemical science as well as providing students of chemistry with a basic knowledge of electronics and other technical aspects of their discipline. Whenthebookfirstappeared,theauthorwasunawareofasinglepublication that he could recommend to his students without reservations. It seems that this situation has not changed markedly in the time since then. Thus, the author feels encouraged in presenting this English version of his textbook, which is more or less a translation of the German edition. November 2006 Peter Grundler¨ Contents 1 Introduction ........................... 1 1.1 SensorsandSensorScience................... 1 1.1.1 Sensors–EyesandEarsofMachines.............. 1 1.1.2 TheTerm‘Sensor’........................ 3 1.2 ChemicalSensors........................ 3 1.2.1 Characteristics of a Chemical Sensor . ............. 3 1.2.2 ElementsofChemicalSensors................. 7 1.2.3 Characterisation of Chemical Sensors ............. 11 1.3 References............................ 13 2 Fundamentals ........................... 15 2.1 SensorPhysics.......................... 15 2.1.1 Solids............................... 15 2.1.2 OpticalPhenomenaandSpectroscopy............. 25 2.1.3 PiezoelectricityandPyroelectricity.............. 37 2.2 SensorChemistry........................ 38 2.2.1 ChemicalEquilibrium...................... 38 2.2.2 KineticsandCatalysis...................... 41 2.2.3 ElectrolyticSolutions...................... 42 2.2.4 Acids and Bases, Deposition Processes andComplexCompounds................... 43 2.2.5 RedoxEquilibria......................... 48 2.2.6 Electrochemistry........................ 51 2.2.7 Ion Exchange, Solvent Extraction and Adsorption Equilibria . 72 2.2.8 SpecialFeaturesofBiochemicalReactions........... 78 2.3 SensorTechnology........................ 82 2.3.1 Thick-FilmTechnology..................... 83 2.3.2 Thin-FilmTechnologyandPatterningProcedures...... 85 2.3.3 SurfaceModificationandOrderedMonolayers........ 87 2.3.4 MicrosystemsTechnology.................... 96 2.4 MeasurementwithSensors................... 99 2.4.1 PrimaryElectronicsforSensors................ 99 2.4.2 InstrumentsforElectricMeasurements............ 103 2.4.3 OpticalInstruments....................... 104 2.5 References............................ 112 VIII Contents 3 Semiconductor Structures as Chemical Sensors .......... 115 3.1 References............................ 117 4 Mass-Sensitive Sensors ...................... 119 4.1 BAWSensors........................... 120 4.2 SAWSensors........................... 121 5 Conductivity Sensors and Capacitive Sensors ........... 123 5.1 ConductometricSensors.................... 124 5.2 ResistiveandCapacitiveGasSensors.............. 126 5.2.1 GasSensorsBasedonPolycrystallineSemiconductors.... 126 5.2.2 GasSensorsMadeofPolymersandGels............ 129 5.3 ResistiveandCapacitiveSensorsforLiquids.......... 130 5.4 References............................ 132 6 Thermometric and Calorimetric Sensors .............. 133 6.1 SensorswithThermistorsandPellistors............ 133 6.2 PyroelectricSensors....................... 135 6.3 SensorsBasedonOtherThermalEffects............ 136 6.4 References............................ 136 7 Electrochemical Sensors ...................... 137 7.1 PotentiometricSensors..................... 138 7.1.1 SelectivityofPotentiometricSensors.............. 141 7.1.2 Ion-SelectiveElectrodes..................... 142 7.1.3 TheIon-SelectiveFieldEffectTransistor(ISFET)....... 159 7.1.4 MeasurementwithPotentiometricSensors.......... 162 7.2 AmperometricSensors..................... 166 7.2.1 SelectivityofAmperometricSensors.............. 167 7.2.2 ElectrodeDesignandExamples................ 169 7.2.3 MeasurementwithAmperometricSensors........... 173 7.3 SensorsBasedonOtherElectrochemicalMethods...... 175 7.4 ElectrochemicalBiosensors................... 175 7.4.1 Fundamentals.......................... 175 7.4.2 ClassesofElectrochemicalBiosensors............. 179 7.5 References............................ 196 8 Optical Sensors .......................... 199 8.1 OpticalFibresasaBasisforOpticalSensors.......... 199 8.2 Fibre Sensors Without Chemical Receptors (Mediators) . 202 8.3 Optodes:FibreSensorswithaChemicalReceptor....... 205 8.3.1 Overview............................. 205 8.3.2 OptodeswithSimpleReceptorLayers............. 208 8.3.3 OptodeswithComplexReceptorLayers............ 211 Contents IX 8.4 SensorswithPlanarOpticalTransducers............ 211 8.4.1 PlanarWaveguides....................... 211 8.4.2 Surface Plasmon Resonance andResonant-MirrorPrismCouplers............. 213 8.5 OpticalBiosensors........................ 215 8.5.1 Fundamentals.......................... 215 8.5.2 OpticalEnzymeSensors..................... 215 8.5.3 OpticalBioaffinitySensors................... 218 8.5.4 OpticalDNASensors...................... 221 8.6 SensorSystemswithIntegratedOptics............. 223 8.7 References............................ 225 9 Chemical Sensors as Detectors and Indicators ........... 227 9.1 IndicatorsforTitrationProcesses................ 227 9.2 Flow-Through Detectors for Continuous Analysers andforSeparationTechniques................. 229 9.2.1 ContinuousAnalysers...................... 230 9.2.2 SeparationMethods....................... 234 9.3 References............................ 239 10 Sensor Arrays and Micro Total Analysis Systems .......... 241 10.1 TwoTrendsandTheirCauses.................. 241 10.2 SmartSensorsandSensorArrays............... 242 10.2.1 IntelligenceinSensors...................... 242 10.2.2 SensorArrays.......................... 245 10.3 Micro Total Chemical Analysis Systems (µ-TASs)....... 253 10.3.1 History.............................. 253 10.3.2 TechnologicalAspects...................... 258 10.3.3 Characteristic Operations and Processes inMicroTotalAnalysers.................... 259 10.3.4 Examples of µ-TAS....................... 262 10.4 References............................ 265 Subject Index ................................ 267 1 Introduction 1.1 Sensors and Sensor Science Sensors belong to the modern world like the mobile phone, the compact disc or the personal computer. The term ‘sensor’ is easily understood. People may imagine a sensor similar to a sensing organ or a tentacle of an ant. Chemical sensors, as a special variety of sensors, can be found, for example, in a cold storage place in the form of a freshness sensor which detects spoiled food. A generation ago, the word sensor was not widely used. Today, however, sensors are becoming ubiquitous in our daily lives. Our world is changing rapidly, and sensors play an important role in this process. Chemical sensors analyse our environment, i.e. they detect which substances are present and in what quantity. Generally, this is the task of analytical chem- istry, which aims to solve such problems by means of precise instruments in well-equipped laboratories. For a long time there was a trend towards increased centralization of analytical laboratories, but in certain respects we now see a re- versal of this tendency away from instrumental gigantism. Such a tendency to buildsmallerdevicesinsteadofeverbiggeronesoccurredmanyyearsagowhen