Biosensor bioaffinity

Biosensors may be classified into two categories biocatalytic biosensors and bioaffinity biosensors. Biocatalytic sensors contain a biocatalyst such as an enzyme to recognize the analytic selectively. Bioaflinity biosensors, on the other hand, may involve antibody, binding protein or receptor protein, which form stable complexes with the corresponding ligand. An immunosensor in which antibody is used as the receptor may represent a bioaflinity biosensor. 

Aizawa presented an overview on the principles and applications of the electrochemical and optical biosensors [61]. The current development in the biocatalytic and bioaffinity bensensor and the applications of these sensors were given. The optical enzyme sensor for acetylcholine was based on use of an optical pH fiber with thin polyaniline film. 

Wittmann C. and Schmid R. D., Bioaffinity sensors for enviroiunental monitoring, in Handbook of Biosensors and Electronic Noses—Medicine, Food, and the Environment, ed. E. Kress-Rogers, pp. 333-349. (Boca Raton, FL CRC Press, 1997). 

DNA-based biosensors possess specificity of response, which is typical for biosensors taking advantage of the bioaffinity properties of DNA. Compared with enzyme sensors and immunosensors, DNA biosensors are mostly used for the investigation of DNA interactions rather than for conventional determination of the concentration of an anal3 e. They exhibit typical biosensor selec-tivity/specificity to the anal3d e (e.g., nucleotide bases sequence. 

Keywords-. Conducting polymers, nanocomposites, biosensors, immunosen-sors, bioaffinity sensors, DNA biosensors, cholesterol biosensors, glucose biosensors, electrochemical biosensor, sensitivity, response time, recovery time selectivity, reversibility, polyanihne, polypyrrole, graphene, carbon nanotubes, nanoparticles... 

The development of conducting polymer (CP) nanocomposites has opened up novel fundamental and applied frontiers. The present chapter overviews recent works dealing with synthesis, characterization of CP nanocomposites, and then-applications related to biosensors. Various synthesis strategies, mechanism, and process parameters along with their characterization techniques are discussed. Some potential areas for biosensor-related applications of CP nanocomposites are highhghted, including catalytic biosensors and bioaffinity biosensors. 

B. Bioaffinity biosensors These are devices in which receptor molecules bind analyte molecules irreversibly, causing a physicochemical change that is detected by a transducer. Receptor molecules ... 

Electrochemical Biosensors Based on Nanomaterials 321 11.3.2 Nanomaterial-based Bioaffinity Sensors... 

FIGURE 16 Schematic principles of bioaffinity fiber-optic biosensors. (a) Detection of intrinsically fluorescent molecule using immobilized antibody, (b) Competition assay using a fluorescent-labeled antigen, (c) Sandwich immunoassay using an immobilized antibody and a fluorescent-labeled antibody. 

Biosensors either work as biocatalytic or as bioaffinity sensors. In biocat-alytic sensors, mostly enzymes are immobihzed at an electrode surface to act as selective catalysts. Enzymes catalyse slow reactions. The reaction rate, under appropriate conditions, is a quantitative measure for the substrate concentration. If the sample is one of the reactants, i.e. if the sample itself is the substrate, then chemical sensors can be created on this basis. The reaction rate can be measured in terms of an electrolysis current if amperometric biosensors are appHed. An alternative approach is to indicate the reaction product of the catalysed reaction selectively, as is done with potentiometric biosensors, hi bioaffinity sensors, as the second group, commonly very stable complexes with sample molecules are formed and bound strongly to the sensor surface. The extent of this complex formation is a quantitative measure of the sample concentration. It can be measured indirectly, since many properties of the electrode are changed by complex formation. In bioaffinity sensors, mostly the antibody-antigen reaction is utilized. 

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