CHAPTER 11. CHEMICAL SENSORS AND BIOSENSORS

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I. Sensors

(A) Definitions1. Transducer: A device that converts an observed change (physical or chemical) into a

measurable signal (usually an electronic signal).2. Physical sensor: A device which measures physical quantities such as length, weight,

temperature, pressure, and electricity.3. Chemical sensor• A device which responds to a particular analyte in a selective way through a chemical

reaction and can be used for the qualitative or quantitative determination of the analyte. (R. W. Catterall, Chemical Sensors, Oxford University Press, Oxford, UK, 1997.)

• Classification of sensors:(a) Single use sensors(b) Intermittent use sensors(c) Continuous use sesnors

4. Biosensor• A device incorporating a biological sensing element connected to a transducer. (B. R.

Eggins, Chemical Sensors and Biosensors, Wiley, New York, USA, 2002.)• A device where a biological recognition element is built in (physically attached or

confined) and is the primary selective element. (Peter T. Kissinger, Biosens. Bioelectron. 2005, 20, 2512.)

• Classes of biosensors:(a) Catalytic biosensors(b) Affinity biosensors

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(B) Historical Development• 1962, Clark and Lyons - first mentioned the possibility of using enzyme-containing

membranes to transform urea or glucose into a product that was detectable with a pH or oxygen electrode.

• 1967, Updike and Hicks – prepared an enzyme electrode by polymerizing a gel containing glucose oxidase onto an oxygen electrode.

• 1973-75, Yellow Springs Instrument Company – first glucose biosensor based on amperometric detection of hydrogen peroxide.FIGURE 11-1. Figures 2&3, Biosens. Bioelectron. 2005, 20, 2512.

• 1984, Anthony P. F. Turner – first mediated amperometric glucose biosensor.FIGURE 11-2. Figures 4&6, Biosens. Bioelectron. 2005, 20, 2512.

• Summary of events in the history of commercial biosensor development.TABLE 11-3. Table 2, Biosens. Bioelectron. 2005, 20, 2512. Implantable glucose sensor ? Minimally invasive systems ? non-invasive systems ?

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(C) Principles of BiosensorsFIGURE 11-4. “Cahn” Figures 2.1 (p. 18).

Classification:FIGURE 11-5. “Mohanty” Figure 1, IEEE Potentials 2006.

1. Recognition elements• Key component of any sensor device• e.g., enzymes, antibodies, nucleic acids, receptors, etc.

FIGURE 11-6. “Mohanty” Figure 2, IEEE Potentials 2006.

2. Transducers• Electrochemical transducers – potentiometric, voltammetric, conductometric, FET-

based sensors.• Optical transducers – fiber optics allow greater flexibility and miniaturization,

techniques include absorption spectroscopy, fluorescence spectroscopy, chemiluminescence spectroscopy, internal reflection spectroscopy, light scattering, surface plasmon spectroscopy, etc.

• Piezoelectric devices – measures the mass of a sample deposited on the surface of a piezoelectric crystal (e.g., -quartz) by detecting the variation in its characteristic frequency. Surface acoustic wave devices are a related system.

• Thermal sensors – all biochemical processes involve production or absorption of heat, which can be measured by sensitive thermisters.FIGURE 11-6. “Mohanty” Figure 2, IEEE Potentials 2006.

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3. Methods of Immobilization• Adsorption on to a surface• Microencapsulation – trapping between membranes• Entrapment – trapped in a matrix of a gel, paste, or polymer.• Covalent attachment – covalent bonds are formed between the selective component

and the transducer.• Cross-linking – a bifunctional agent is used to bond the transducer to the selective

component.

4. Performance Factors• Selectivity• Sensitivity range• Accuracy – needs to be better than 5%• Precision• Nature of solution• Response time• Recovery time• Working lifetime• Shelf life

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5. Areas of Application• Health care

TABLE 11-7. “Eggins” Table 1.1 (p. 8).A potential “dream application” is to have an implanted sensor for continuous monitoring of a metabolite, and might be linked to a controlled drug-delivery system through the skin.

• Control of industrial processes(i) Off-line in a laboratory, (ii) Off-line, but close to the operation site, (iii) On-line in real-time.

• Environmental monitoringAreas include pollution applications, farming, gardening, veterinary science, mining, etc.Potential analytes in air, water, soils, and other environmental situations.Continuous real-time monitoring is required for some substances while occasionalrandom monitoring for others.

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(D) Emerging Catalytic Electrochemical Sensors1. Third generation glucose biosensorFIGURE 11-8. Willner et al., Science 2003, 299, 1877.

2. Nanoelectrode EnsemblesFIGURE 11-9. Lin et al., Nano Lett. 2004, 4, 191

(E) Affinity Biosensors1. Antibody-Based Systemse.g., ELISA FIGURE 11-10.e.g., Lateral flow strip FIGURE 11-11. 化學, 2003, 61, 161.Immunosensor formats: FIGURE 11-12. Rogers, Mol. Biotechnol. 2000, 14, 109.

2. Receptor-Based SystemsReceptor affinity proteins which are noncatalytic and of nonimmunue origin are typically classified as membrane bound ion channels or part of secondary messenger systems.

3. Nucleic Acid-Based Systems

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II. Chemically Modified Electrodes

Modified electrodes can be prepared in several different ways, including irreversible adsorption, covalent attachment of a monolayer, and coating the electrode with films of polymers or other materials.

Analytical Applications:1. Increase hydrogen overpotential.2. Enhance electron-transfer rate.3. Electrocatalysis, i.e., decrease the redox potential of an analyte to a potential near the

thermodynamic one.e.g., biological redox systems.

4. Preconcentration of an analyte.5. Provides an opportunity to study the basis of electrochemical reactions.

e.g., characterization of electron- and mass transfer processes in polymers and other materials.e.g., gaining insight into how surface structures can be designed to carry out specified reactions or processes.

9FIGURE 11-1. Biosens. Bioelectron. 2005, 20, 2512.

10FIGURE 11-2. Biosens. Bioelectron. 2005, 20, 2512.

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TABLE 11-3. Biosens. Bioelectron. 2005, 20, 2512.

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甚麼是甚麼是生物生物感測器感測器??

Figure 11-4. T.M. Cahn, Biosensors, Chapman & Hall, 1993.

樣本

生物受器 換能器 訊號

生物感測器

13Figure 11-5. Mohanty et al., IEEE Potentials 2006, March/April, 35.

14Figure 11-6. Mohanty et al., IEEE Potentials 2006, March/April, 35.

15TABLE 11-7. B.R. Eggins, Chemical Sensors and Biosensors, Wiley, 2002.

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Electron transfer turner rate = ~5000/s vs. ~700/s with oxygen as cosubstrate.

FIGURE11-8.Willner et al.,Science 2003, 299, 1877.

GOx = glucose oxidaseFAD = flavin adenine dinucleotide

Third generation glucose biosensor

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Nanoelectrode Ensembles

Carbon nanotube (CNT) has a strong catalytic effect on reduction of hydrogen peroxide and, hence, eliminates the need for permselectivemembrane barriers or artificial electron mediators.

FIGURE 11-9.Lin et al., NanoLett. 2004, 4, 191.

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酵素免疫分析法酵素免疫分析法 (ELISA)(ELISA)

FIGURE 11-10.

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Au nanoparticle

hCG

anti-hCG

anti-globulin

hCG = human chorionic gonadotropin

FIGURE 11-11. 化學, 2003, 61, 161.

Lateral Flow Strip

20FIGURE 11-12. Rogers, Mol. Biotechnol. 2000, 14, 109.