Enzyme-based biosensor

Biosensors may provide the basis for in-field analyses and real-time process analysis. However, biosensors are generally limited to the determination of a limited range of analytes in defined matrices. Enzyme-based biosensors, principally acetylcholinesterase (AChE) inhibition, have been successfully used in environmental analysis for residues of dichlorvos and paraoxon, " carbaryl " and carbofuran. " Immunochemically based biosensors may be the basis for the determination of pesticide residues in liquid samples, principally water and environmental samples, but also fruit juices. The sensors can be linked to transducers, for example based on a piezo-... 

Table 3. Early optical enzyme-based biosensors, and respective transducers (work published until 1992). Data on work by Schaffar Wolfbeis from ref. 130. For a recent review see ref. (131).

More than 90% of commercially available enzyme-based biosensors and analytical kits contain oxidases as terminal enzymes responsible for generation of analytical signal. These enzymes catalyze oxidation of specific analyte with molecular oxygen producing hydrogen peroxide according to the reaction ... 

Electrochemical biosensors are analytical devices in which an electrochemical device serves as a transduction element. They are of particular interest because of practical advantages, such as operation simplicity, low expense of fabrication, and suitability for real-time detection. Since the first proposal of the concept of an enzyme-based biosensor by Clark, Jr [1], significant progress in this field has been achieved with the inherited sensitivity and selectivity of enzymes for analytical purposes. 

The enzyme-based biosensor has come through three steps (1) with oxygen for the media (2) with artificial intermediate for media and (3) without media and based for the direct electron transfer of redox proteins. The following is an example ... 

It has been said above that cyt c was one of the most important and extensively studied electron-transfer proteins with active heme centers. Thus, cyt c was widely used in enzyme-based biosensors and to study the mechanism of the catalytic process between redox enzyme and substrate. 

The determination of H202 is very important in many different fields, such as in clinical, food, pharmaceutical, and environmental analyses [202], Many techniques such as spectrophotometry, chemiluminesence, fluorimetry, acoustic emission, and electrochemistry methods have been employed to determine H202. Electrochemical methods are often used because of their advantages. Among these electrochemical methods, the construction of the mediator-free enzyme-based biosensors based on the direct electrochemistry of redox proteins has been reported over the past decade [203— 204], The enzyme-based biosensors, which use cyt c as biocatalyzer to catalyze H202, were widely studied. 

Numerous enzyme-based biosensors have been described. Wang and Arnold reported the use of a dual-enzyme approach to induce spectral changes in NAD+ in... 

S. Jawaheer, S.F. White, S.D.D.V. Rughooputh and D.C. Cullen, Development of a common biosensor format for an enzyme based biosensor array to monitor fruit quality, Biosens. Bioelectron., 18(12) (2003) 1429-1437. 

Wilson GS, Hu Y. Enzyme-based biosensors for in vivo measurements. Chemical Reviews 2000, 100, 2693-2704. 

At the present time, qualitative and quantitative determination of lower aliphatic alcohols, e.g. a mixture of methanol with ethanol, is being performed with the use of enzymatic and enzyme-based biosensor methods [9,10]. 

In recent years the electrochemistry of the enzyme membrane has been a subject of great interest due to its significance in both theories and practical applications to biosensors (i-5). Since the enzyme electrode was first proposed and prepared by Clark et al. (6) and Updike et al. (7), enzyme-based biosensors have become a widely interested research field. Research efforts have been directed toward improved designs of the electrode and the necessary membrane materials required for the proper operation of sensors. Different methods have been developed for immobilizing the enzyme on the electrode surface, such as covalent and adsorptive couplings (8-12) of the enzymes to the electrode surface, entrapment of the enzymes in the carbon paste mixture (13 etc. The entrapment of the enzyme into a conducting polymer has become an attractive method (14-22) because of the conducting nature of the polymer matrix and of the easy preparation procedure of the enzyme electrode. The entrapment of enzymes in the polypyrrole film provides a simple way of enzyme immobilization for the construction of a biosensor. It is known that the PPy-... 

Enzyme-based biosensors continue to play important roles in this area because of the wide range of enzymes available and the selective responses that can... 

Enzyme-based biosensors are very suitable for the antioxidant status evaluation, since they show excellent selectivity for biological substances and can directly determine and/or monitor antioxidant compounds in a complex media such as biological or vegetable samples without needing a prior separation step. During the course of the catalytic reaction on the electroactive substrates, the current produced at an applied potential is related to the concentration of a specific biomarker, for which the biosensor is selective. HRP-based biosensors for antioxidant status evaluation have been applied in the detection of superoxide radical [119], nitric oxide [120], glutathione [119, 121], uric acid [122, 123], and phenolic compounds [124—126],... 

In common with enzyme based biosensors (equations (7.3) and (7.4)) the reduced mediator can be re-oxidized when it diffuses to an electrode poised at a suitably oxidising potential, e.g.,... 

Despite their potential importance, there are few analytical models of whole cell biosensing devices—particularly when compared to the plethora of models describing enzyme based biosensors [62]. Although aspects of cellular biochemistry are similar to those of isolated enzymes [63], problems arise in modelling the physicochemistry of whole cells due to their complex nature they are large (typically 0.2-10 jxm) they may contain a variety of biological structures (membranes, organelles, etc.) they incorporate a diversity of biochemical pathways and they may contain many types of active site. 

Table 11.19 Liquid Membrane Electrodes (LME), Gas-Sensing Electrodes (GSME), and Enzyme-Based Biosensors (EBB) [56]...

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