Conducting polymer sensors

Chemical sensors for gas molecules may, in principle, monitor physisorp-tion, chemisorption, surface defects, grain boundaries or bulk defect reactions [40]. Several chemical sensors are available mass-sensitive sensors, conducting polymers and semiconductors. Mass-sensitive sensors include quartz resonators, piezoelectric sensors or surface acoustic wave sensors [41-43]. The basis is a quartz resonator coated with a sensing membrane which works as a chemical sensor. 

Biosensors based on nanomaterials exploit many new signal transduction technologies in their manufacture [345], In molecular electronics and sensors, conducting polymers represent innovative systems for the immobilization of enzymes [346, 347], The entrapment of enzymes in polymeric films provides a controlled method to fasten biologically active molecules in a defined area on the electrodes. These examples show that conducting polymers in the area of bioanalytical sciences are of great interest since their biocompatibility opens up the possibility of using them as in vivo biosensors. 

Biosensors for e-tongue are systems with a biochemical transducer, an enzyme, and solid electrode in intimate proximity. Enzymes are oxidases that consume oxygen and produce hydrogen peroxide or the reduced form of -nicotinamide adenine dinucleotide (phosphate) NAD(P)H as a dehydrogenase. Improvement in the performance of metal sensors, conductive polymers or biosensors is linked to scaling down of size to nanodimensions which increases the surface-to-volume ratio of the sensors, lowering detection limits. 

Functionalized conducting monomers can be deposited on electrode surfaces aiming for covalent attachment or entrapment of sensor components. Electrically conductive polymers (qv), eg, polypyrrole, polyaniline [25233-30-17, and polythiophene/23 2JJ-J4-j5y, can be formed at the anode by electrochemical polymerization. For integration of bioselective compounds or redox polymers into conductive polymers, functionalization of conductive polymer films, whether before or after polymerization, is essential. In Figure 7, a schematic representation of an amperomethc biosensor where the enzyme is covalendy bound to a functionalized conductive polymer, eg, P-amino (polypyrrole) or poly[A/-(4-aminophenyl)-2,2 -dithienyl]pyrrole, is shown. Entrapment of ferrocene-modified GOD within polypyrrole is shown in Figure 7. 

Chemical and Biochemical Sensors. The sensitivity of the electrical properties of conductive polymers to chemical stimuli suggests they may prove useful in a number of sensing applications. 

Entrapment of biochemically reactive molecules into conductive polymer substrates is being used to develop electrochemical biosensors (212). This has proven especially useful for the incorporation of enzymes that retain their specific chemical reactivity. Electropolymerization of pyrrole in an aqueous solution containing glucose oxidase (GO) leads to a polypyrrole in which the GO enzyme is co-deposited with the polymer. These polymer-entrapped GO electrodes have been used as glucose sensors. A direct relationship is seen between the electrode response and the glucose concentration in the solution which was analyzed with a typical measurement taking between 20 to 40 s. 

J. Janata and M. Josowicz, Nature Materials, 2 (1), (2003) 19-24, Conducting polymers in electronic chemical sensors ... 

The development of highly selective chemical sensors for complex matrixes of medical, environmental, and industrial interest has been the object of greate research efforts in the last years. Recently, the use of artificial materials - molecularly imprinted polymers (MIPs) - with high recognition properties has been proposed for designing biomimetic sensors, but only a few sensor applications of MIPs based on electrosynythesized conductive polymers (MIEPs) have been reported [1-3]. 

One of the major potential applications of conducting polymers is as mediators or catalysts for electrochemical sensors and electrosynthesis. 

J.K. Park, P.H. Tran, J.K.T. Chao, R. Ghodadra, R. Rangarajan, and N.V. Thakor, In vivo nitric oxide sensor using non-conducting polymer-modified carbon fiber. Biosens. Bioelectron. 13, 1187—1195 (1998). 

J. Bobacka, J., A. Ivaska, and A. Lewenstam, Potentiometric ion sensors based on conducting polymers. 

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