Catalytic amperometric biosensors

In AChE-based biosensors acetylthiocholine is commonly used as a substrate. The thiocholine produced during the catalytic reaction can be monitored using spectromet-ric, amperometric [44] (Fig. 2.2) or potentiometric methods. The enzyme activity is indirectly proportional to the pesticide concentration. La Rosa et al. [45] used 4-ami-nophenyl acetate as the enzyme substrate for a cholinesterase sensor for pesticide determination. This system allowed the determination of esterase activities via oxidation of the enzymatic product 4-aminophenol rather than the typical thiocholine. Sulfonylureas are reversible inhibitors of acetolactate synthase (ALS). By taking advantage of this inhibition mechanism ALS has been entrapped in photo cured polymer of polyvinyl alcohol bearing styrylpyridinium groups (PVA-SbQ) to prepare an amperometric biosensor for... 

J. Newman, S. White, I. Tothill, and A.P. Turner, Catalytic materials, membranes, and fabrication technologies suitable for the construction of amperometric biosensors. Anal. Chem. 67, 4594-4599 (1995). 

Fortier [6] found that AQ polymer from Eastman was not deleterious for the activity of a variety of enzymes such as L-amino acid oxidase, choline oxidase, galactose oxidase, and GOD. Following mixing of the enzyme with the AQ polymer, the mixture was cast and dried onto the surface of a platinum electrode. The film was then coated with a thin layer of Nafion to avoid dissolution of the AQ polymer film in the aqueous solution when the electrode was used as a biosensor. These easy-to-make amperometric biosensors, which were based on the amperometric detection of H202, showed high catalytic activity. 

A quantitative model for the electrocatalyitic response of enzymatic amperometric biosensors requires consideration of the diffusion of all the involved species and the kinetics of the redox-enzyme catalytic cyde, as is depicted in Figure 2.27. 

Catalytic Oxidation of NAD(P)H A Continuously Improved Selection of Suitable ROMs This research is triggered hy at least two reasons (1) the importance of NAD(P)H/NAD(P)- - redox couples in biological systems is known, as is known the dependence of oxidation mechanisms on the oxidants [14, 82, 172-174] (2) the possibility of developing amperometric biosensors for NAD(P)+-dependent dehydrogenases. As a consequence, much attention is devoted to the regeneration of these coenzymes in their reduced or oxidized forms for their application in biosensors or in enzymatic synthesis [180]. Here, we are concerned with electrochemical regeneration [181]. 

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. 

I Katakis, E Dominguez. Catalytic electrooxidation of NADH for dehydrogenase amperometric biosensors. Mikrochim Acta 126 11—32, 1997. 

The application of direct electrochemistry of small redox proteins is not restricted to cytochrome c. For example, the hydroxylation of aromatic compounds was possible by promoted electron transfer from p-cresol methylhydroxylase (a monooxygenase from Pseudomonas putida) to a modified gold electrode [87] via the blue copper protein azurin. All these results prove that well-oriented non-covalent binding of redox proteins on appropriate electrode surfaces increases the probability of fast electron transfer, a prerequisite for unmediated biosensors. Although direct electron-transfer reactions based on small redox proteins and modified electrode surfaces are not extensively used in amperometric biosensors, the understanding of possible electron-transfer mechanisms is important for systems with proteins bearing catalytic activity. 

Composite based electrodes have shown improved selectivity by inhibiting the interference reaction at the electrode. The large surface area, electrochemical properties, catalytic abilities and inherent biocompatibility make composites suitable for use in amperometric biosensors. Composites of gold nanopaiticles carbon based materials, Prussian blue nanopaiticles have been utilized for the fabrication of electrochemical... 

An amperometric biosensor for trans-resveratrol determination in aqueous solutions by means of carbon paste electrodes modified with peroxidase basic isoenzymes (PBIs) from Brassica napus was developed [182]. Catalytic properties of PBIs from Brassica napus toward trows-resveratrol oxidation were demonstrated by conventional UV-vis spectroscopic measurements. The enzymatic reaction rate was studied and kinetics parameters were detected. An amperometric biosensor based on Brassica... 

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