Biorecognition elements enzymes

L-lactate-cytochrome c-oxidoreductase (flavocytochrome was isolated for the first time from the thermo-tolerant yeast H. polymorpha. The mentioned above enzyme preparations were used for construction of the biorecognition elements of electrochemical sensors. 

The main advantages of immobilizing whole cells over the isolated enzymes are (i) cells are more resistant to changes in pH or temperature and (ii) a single cell can contain all the enzymes and cofactors needed for bioconversion of the analyte [82], Most of the whole cell-based optical biosensors used in toxicity or bioremediation studies [83,84] employ microorganisms [85— 87], animal [88], plant tissues [89,90] or cell receptors [91] as biorecognition elements. 

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). 

Molecular recognition is central to biosensor technology. Receptors, enzymes, antibodies, aptamers, molecular beacons, and nucleic acids are mainly used as molecular recognition elements in biosensor development (Chambers etal., 2008). Since 1990, nucleic acids, especially deoxyribonucleic acid (DNA) have been used as biorecognition elements in biosensor technology. These biosensors are named as DNA-based biosensors. 

The selectivity of biosensors mainly derives from the role the biorecognition elements play in nature. Enzymes not only often exhibit a selectivity for the binding of a single substrate (or sometimes a class of compounds) but they additionally exclusively catalyze a single type of reaction, sometimes with high stereoselectivity. However, in addition to the selectivity... 

The range of biosensors for the analysis of vitamins that use enzymes as the biorecognition elements is rather restricted. However, affinity biosensors have opened a new horizon in the field of vitamin analysis with surface plasmon resonance (SPR) biosensors at the forefront. Commercialization of optical SPR... 

Enzymes have been widely used as biorecognition elements in biosensors as they are able to catalyze reactions that produce electrochemical, optical, and thermal sig-nals." " Most popularly, glucose oxidase is widely used in electrochemical glucose biosensors that have found wide usage in clinical and medical settings. Enzymes offer ease of immobilization on transducers by physical adsorption, covalent linkage, and... 

A FI calorimetric biosensor was developed for the determination of dichlorvos (Zheng et al., 2006). The enzyme chicken liver esterase was used as the biorecognition element and acetyl-l-naphthol as the substrate. This enzyme was immobilized on an ion exchange resin, which was then packed in the enzyme reaction cell. The reference cell was filled with the same batch of the resin, but with a completely inactivated enzyme. As a result, the enzymatic reaction occurred in the enzyme reaction cell, but not in the reference cell and there was a temperature difference at the outlets of the two cells. The detection was based on the inhibition of the enzyme by the analyte, measuring the difference of the signal obtained with and without inhibition. 

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