Biosensors, amperometric configurations

The amperometric biosensor based on carbon paste electrode ensures proximity at the molecular level between the catalytic and electrochemical sites because the carbon electrode is both the biocatalytic phase and the electrode sensor (Table 17.2). The tissue containing carbon paste can be incorporated in various electrode configurations and these have very rapid response times, extended lifetimes, high rigidity, mechanical stability and very low cost. 

Amperometric sensors monitor current flow, at a selected, fixed potential, between the working electrode and the reference electrode. In amperometric biosensors, the two-electrode configuration is often employed. However, when operating in media of poor conductivity (hydroalcoholic solutions, organic solvents), a three-electrode system is best (29). The amperometric sensor exhibits a linear response versus the concentration of the substrate. In these enzyme electrodes, either the reactant or the product of the enzymatic reaction must be electroactive (oxidizable or reducible) at the electrode surface. Optimization of amperometric sensors, with regard to stability, low background currents, and fast electron-transfer kinetics, constitutes a complete task. 

This study describes initial electrochemical experiments, aimed at the development of an amperometric glucose biosensor using ferrocene as the electron mediator, incorporated into an oriented polypyrrole LB film. A variety of monolayer samples were prepared for cyclic voltammetry (CV) studies to determine if the ferrocene was detectable electrochemically in such a configuration. This was an important criterion,as... 

One investigative study that has raised considerable queries is the report of direct electrical communication between the active site of the enzyme and the conducting polymer when the enzyme is immobilized in polypyrrole microtubules. These microtubules were produced by electropolymerization of the pyrrole monomer inside the pores of a microporous filtration membrane. This configuration is reported to favor direct electron transfer across the polymer structure as well as direct reoxidation of the enzyme at lower potentials than typically used, hence promoting increased selectivity of the resulting amperometric biosensor [178]. Another report investigating the same system claims that it is the underlying platinum metal rather than polypyrrole tubules that is responsible for the observed direct enzyme reoxidation [179]. 

Shin, M.-C., H.C. Yoon, and H.-S. Kim. 1996. In situ biochemical reduction of interference in an amperometric biosensor with a novel heterobilayer configuration of polypyrrol glucose oxidase/horseradish peroxidase. Anal Chim Acta 329 (3) 223. 

Enzymatic Electrochemical Biosensors, Fig. 6 (top) Scheme of configuration and FESEM image of cholesterol ester with Pt decorated graphene nanosheet (bottom) amperometric response of free cholesterol (a) and... 

Mathematical modeling of biosensors has been successfully used to investigate the kinetic peculiarities of the biosensor action. The numerical simulation became a powerful framework for numerical investigation of the impact of model parameters on the biosensor action and to optimize the biosensor configuration [7]. Recently, the computational modeling of the laccase-based biosensor qualitatively explained and confirmed the experimentally observed synergistic effect of the mediator on the biosensor response [21]. The numerical simulation of an amperometric biosensor based on an enzyme-loaded carbon nanotube (CNT) layer deposited on a perforated membrane highlighted the dependence of the steady-state biosensor current on the anisotropic properties of CNT. It was also shown that the sensitivity of the biosensors... 

Electrochemical biosensors operate by measuring a signal such as current, power, or open circuit voltage which change in proportion to the amount of target analyte present. These devices can be constructed in several configurations. The simplest is an amperometric biosensor, where a three-electrode set-up is used. The working electrode is where the... 

It is beyond the scope of this chapter to attempt to describe the myriad combinations of biological and sensor elements possible, so only improvements in the design of amperometric biosensors, commonly referred to as enzyme-modified electrodes, wiU be discussed. The favored configuration for biosensors utilizes amperometry (measurement of electric current) for transduction of the chenfical signal into an electroinc signal [3]. Electrochemical instrumentation is simple and... 

In the simplest format, amperometric biosensors are constructed in such a way that in the absence of other electroactive sample components, the faradaic current produced at the electrode surface is produced solely due to presence of the product of an enzyme-catalyzed reaction as illustrated in Figure 1. Three possible configurations available for an amperometric biosensing electrode system [4] are illustrated in Figure 2 ... 

Figure 2 Amperometric biosensor configurations. Detailed descriptions are in the text. (A) Addition of substrate to a solution containing enzyme and cofactor. (B) Immobilized enzyme upstream from sensing electrode. (C) Enzyme immobilized directly on detecting surface.

Amperometry is probably one of the most common electroanalytical techniques used in food analysis and there are numerous examples in the literature. Among others, it is worth mentioning analysis of cholesterol [72], vitamins [73, 74], carbohydrates [75, 76], antioxidants [4, 77-79], pesticides [80, 81], and toxins [82]. It is also important to point out that, although not discussed in this chapter, the same instrumental configuration used in amperometry can be used for the development of amperometric biosensors [83-86], electrochemical ELISA assays [87-89], and electrochemical tongues [90,91]. 

A choline amperometric biosensor based on screen-printed configuration, immobilized by adsorption from aqueous solution on the surface of ruthenium-activated carbon electrodes, was assembled and used to assess the inhibitory effect of organophosphoms and carbamic pesticides on acetylcholinesterase activity both... 

Dithiocarbamate fungicides inhibit aldehyde dehydrogenase. In order to produce an amperometric biosensor with this enzyme also a bi-enzymatic system was designed with the enzyme diaphorase. Reaction of propiraialdehyde and NAD" in the presence of ADH produced NADH which could be detected via its reaction with hexacyanoferrate(in) by diaphorase. The changes of hexacyanoferrate (11) concentrations were monitored amperometrically with a Pt electrode or bi-amperometrically with two platinum electrodes. A bi-amperometric biosensor was also developed in screen-printed configuration with Pt-sputtered carbon paste In aU these biosensors both enzymes were immobilized in a poly(vinyl alcohol)-styrylpyridinium (PVA-SbQ) layer. 

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