Biosensors bioaffinity sensors

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. 

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). 

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... 

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

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. 

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. 

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. 

Potentiometric biosensors based in both ISE and ISFET for water analysis have been widely developed in the last few years, with recent research leading to nanomaterial-based devices. New nanoparticle (NP)-based signal amplification and coding strategies for bioaffinity assays are in use, along with molecular carbon-nanotube (CNT) wires for achieving efficient electrical communication with redox-enzyme and nanowire-based label-free DNA sensors. ... 

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