Enzyme biosensors catalytic elements

The most often used recognition elements for the construction of biosensors are enzymes. Their catalytic activity usually derives from prosthetic groups (nonproteins such as heme, FAD, or pyridox-alphosphate) or metal ions. The prosthetic groups are usually covalently bound to the enzyme, while coenzymes or cosubstrates are only associated with it, binding in close proximity to the substrate binding site during the catalytic action. For their application in biosensors, enzymes have to be isolated from the biological... 

Enzymes (and all biological elements, such as tissues, cells, microorganisms, which contain enzymes) represent the class of what are called catalytic elements. Enzyme biosensors have several advantages. These include the catalytic amplification of the biosensor response by modulation of the enzyme activity with respect to the target analyte a stable source of... 

XOD is one of the most complex flavoproteins and is composed of two identical and catalytically independent subunits each subunit contains one molybdenium center, two iron sulfur centers, and flavine adenine dinucleotide. The enzyme activity is due to a complicated interaction of FAD, molybdenium, iron, and labile sulfur moieties at or near the active site [260], It can be used to detect xanthine and hypoxanthine by immobilizing xanthine oxidase on a glassy carbon paste electrode [261], The elements are based on the chronoamperometric monitoring of the current that occurs due to the oxidation of the hydrogen peroxide which liberates during the enzymatic reaction. The biosensor showed linear dependence in the concentration range between 5.0 X 10 7 and 4.0 X 10-5M for xanthine and 2.0 X 10 5 and 8.0 X 10 5M for hypoxanthine, respectively. The detection limit values were estimated as 1.0 X 10 7 M for xanthine and 5.3 X 10-6M for hypoxanthine, respectively. Li used DNA to embed xanthine oxidase and obtained the electrochemical response of FAD and molybdenum center of xanthine oxidase [262], Moreover, the enzyme keeps its native catalytic activity to hypoxanthine in the DNA film. So the biosensor for hypoxanthine can be based on... 

It is possible to attach photochromic molecules onto naturally occurring receptors and enzymes and by so doing be able to photoregulate their binding and catalytic activities. These materials have the potential to be used as chemotherapeutic agents and biosensors, and as bioelectronic materials. In most of this work to date spiropyrans have been used as the photochromic element in the system. 

Among the biological recognition elements enzymes are by far the most important. The reason for this lies in the fact that these molecules provide not only the recognition of analyte-substrate, but also have the catalytic function important for the amplification of the signal. Enzymes are quite flexible molecules and have various complex conformations with sometimes different catalytic activity. The biorecognition molecules can be integrated in biosensors with a variety of electrochemical transducers (Table 1). 

The catalytic hydrolysis of each molecule of these compounds releases two protons, the measurement and correlation of which to the OP concentration forms the basis of a potentiometric enzyme electrode. The basic element of this very simple enzyme potentiometric electrode is a pH electrode modified with an immobilized purified organophosphorus hydrolase (OPH) layer formed by cross-linking OPH with bovine serum albumin and glutaraldehyde. Thus, potentiometric OP biosensors were prepared by coupling OPH and a glass pH electrode. The sensors were constructed by immobilizing OPH on the surface of a pH-sensitive... 

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