Enzyme electrodes protein

The high specificity required for the analysis of physiological fluids often necessitates the incorporation of permselective membranes between the sample and the sensor. A typical configuration is presented in Fig. 7, where the membrane system comprises three distinct layers. The outer membrane. A, which encounters the sample solution is indicated by the dashed lines. It most commonly serves to eliminate high molecular weight interferences, such as other enzymes and proteins. The substrate, S, and other small molecules are allowed to enter the enzyme layer, B, which typically consist of a gelatinous material or a porous solid support. The immobilized enzyme catalyzes the conversion of substrate, S, to product, P. The substrate, product or a cofactor may be the species detected electrochemically. In many cases the electrochemical sensor may be prone to interferences and a permselective membrane, C, is required. The response time and sensitivity of the enzyme electrode will depend on the rate of permeation through layers A, B and C the kinetics of enzymatic conversion as well as the charac-... 

More recently, nanotechnology has faciUtated progress in miniaturizing redox enzyme electrodes and extending their application. In order to achieve contact between the active site of the redox enzyme where electron transfer takes place, usually buried within the protein structure, and the electrode electrical contact, cofactor-functionaUzed nanomaterials have been developed [75]. Diffusible cofactors such as FAD can be used as the relay system for carrying electrons to electrical... 

Willner and coworkers have extended this approach to electron relay systems where core-based materials facilitate the electron transfer from redox enzymes in the bulk solution to the electrode.56 Enzymes usually lack direct electrical communication with electrodes due to the fact that the active centers of enzymes are surrounded by a thick insulating protein shell that blocks electron transfer. Metallic NPs act as electron mediators or wires that enhance electrical communication between enzyme and electrode due to their inherent conductive properties.47 Bridging redox enzymes with electrodes by electron relay systems provides enzyme electrode hybrid systems that have bioelectronic applications, such as biosensors and biofuel cell elements.57... 

Table 2 summarizes different possible applications of photoswitchable biomaterials, while detailing the nature of the biomaterial, the area of application, and, when possible, specific examples. Reversible light-induced activation and deactivation of redox proteins (enzymes) corresponds to write - read - erase functions. The photonic activation of the biomaterial corresponds to the write function, whereas the amperometric transduction of the recorded optical information represents the read function of the systems. Switching off of the redox functions of the proteins erases the stored photonic information and regenerates the photosensory biomaterial. These integrated, photoswitchable redox enzyme electrode assemblies mimic logic functions of computers, and may be considered as first step into the era of biocomputers. 

This problem lies at the heart of all enzyme electrode manufacture. Proteins are biological molecules, and there is an apocryphal tale concerning Bragg when he was head of the Cavendish Laboratory, and Frances Crick told him he was going to study DNA crystal structure. Bragg s reply was gruff, and as it turned out quite apt, thats no... 

Nevertheless, the possibility of demonstrating the very remarkable specificity of the catalytic power of proteins immobilized on electrodes—to collect or supply electrons from the encounter of enzyme electrodes with entities in solution—looks so attractive that it has spurred investigators (e.g., Bowden, 1993) to efforts that have proved rewarding. The most important advance was made by replacing a bare metal or metal oxide surface with monolayers of organics of a particular type (Fig 14.37) (Eddowes and Hill, 1979). 

In electrochemistry, the term bioelectrochemistry is generally used to indicate electrochemistry of or in biological systems [ii]. Examples are -> enzyme electrodes, - biofuel cells, -> biosensors, -> immunoassays, electrochemical -> protein electrochemistry. 

Redox mediators have been introduced into enzyme electrodes to circumvent the problems associated with the sluggish redox behavior of protein structures at the electrode surface. Indeed, mainy enzymes involved in the oxidation and reduction reactions contain electroactive centers (hemin, flavin) surrounded by a protein matrix, preventing efficient electron transfer to electrodes. 

Enzyme electrodes containing cross-linked cofactors, polypeptides or protein affinity complexes... 

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