Enzyme electrodes wired

Acetylcholineesterase and choline oxidase Coated wire enzyme electrode was prepared by coating a Ag wire with a homogenized solution of CH2C12 containing 0.28 gm of polyvinyl bytyral, 0.15 gm of di-n-amylphthalate, 10 mg of tridodecy-lamine and 2 mg of sodium tetraphenylborate. Three different methods for immobilizing the enzyme on the coated electrode are described with use of AChE. The model electrode was used to determine ACh from 0.1 to 10 mM. Response time was 3-6 min. [94]... 

T. Huang, M. E. Garceau, and P. Gao, Liquid chromatographic determination of residual hydrogen peroxide in pharmaceutical excipients using platinum and wired enzyme electrodes, J. Pharm. Biomed. Anal. 31 (2003), 1203-1210. 

Binyamin, Chen and Heller reported that wired enzyme electrodes constituted of glassy carbon electrodes coated with poly(4-vinylpyridine) complexed with [Os(bpy)2Cl] and quarternized with 2-bromoethylamine or poly[(iV-vinylimidazole) complexed with [Os(4,4 -dimethyl-2,2 -bypyridine)2Cl] or poly(vinylpyridine) complexed with [Os(4,4 -dimethoxy-2,2 -bypyridine)2Cl] quaternized with methyl groups lost their electrocatalytic activity more rapidly in serum or saline phosphate buffer (pH 7.2) in the presence of urate and transitional metal ions such as Zn and Fe " " than in plain saline phosphate buffer (pH 7.2). It was reported that as much as two-thirds of the current is lost in 2 h in some anodes. However, when a composite membrane of cellulose acetate, Nafion, and the polyaziridine-cross-linked co-polymer of poly(4-vinyl pyridine) quaternized with bromoacetic acid was applied, the glucose sensor stability in serum was improved and maintained for at least 3 days [27,50]. 

Ohara TJ, Rajagopalan R, Heller A. Wired enzyme electrodes for amperometric determination of glucose or lactate in the presence of interfering substances. Anal Chem 1994 66 2451-7. 

The enzyme is attached to the sensing electrode itself. Solution flow is shown in Figure 2C only to suggest a method of analyte introduction to the biosensor. This system does not require flow past the enzyme and detector but instead relies on diffusion of substrate to the enzyme, and diffusion of the enzymatically generated reduced cofactor fi om the inunobilized enzyme to the working electrode. As will be shown, inuno-biUzation of enzymes on the electrode surface often reduces the detector efficiency because both enzyme conversion efficiency and diffusion of analytes can limit the time response of such a system. This type of system is amenable to the immobilization of the cofactor as well (e.g., wired enzyme electrodes [5-7], which use intrinsic FAD/FADHj as cofactors). 

Conducting polymer-based immobilization or wired enzymes is a global enzyme immobilization method that differs in many respects from those just described. In one example, a redox polymer is formed on the surface by the oxidation of pyrrole molecules to pyrrole radical cations, which then polymerize on the surface to form conductive polypyrrole [60,68]. Other conducting polymers include polyvinylpyridine, polythiophene, polyaniline, and polyindole. If enzymes are present in the solution as polymerization takes place, they are entrapped within the polymer. When these polymers are cross-linked with redox mediators such as [Os(bpy)2Cl]+ 2 the resulting amperometric (or potentiomet-ric) biosensors are referred to as wired enzyme electrodes [5-7]. The distance between the redox centers of the polymer and the FADH2 centers of the reduced enzyme is reduced sufficiently for electrons to be transferred and, therefore, for the mediated electro-oxidation of glucose on conventional electrodes. These electrodes do not require diffusing redox mediators or membranes to contain the enzyme and the redox polymer. 

With the exception of wired enzyme electrodes discussed above, the enzymatically produced cofactor needs an available electron transfer site for the electrochemical reaction to take place to be monitored. As has been discussed, the procedures used for the derivatization of the electrode surface can reduce the rate of electron transfer for the redox mediator (NADH) [8,15], decreasing the sensitivity of the measurement dramatically. Thus, at least two principal factors influence the response of an enzyme-modified electrode the amount of enzyme present near the electrode surface and the availability of electron transfer sites. Therefore, to get a more general protocol for the immobilization of any enzyme to an electrode surface, it would be advantageous to covalently modify only specific parts of the microelectrode surface, leaving other (directly adjacent) regions available for facile electron transfer. 

Biosensors Based on Electrically Wired Enzyme Electrodes... 

Mano N, Fernandez JL, Kim Y, Shin W, Bard AJ, Heller A. Oxygen is electroreduced to water on a wired enzyme electrode at a lesser overpotential than on platinum. J Am Chem Soc 2003 125 15290-15291. 

FIGURE 6-8 Composition of an electron-relaying redox polymer used for wiring enzymes to electrode transducer. (Reproduced with permission from reference 14.)... 

Electroosmotic flow, 195 End column detection, 89 Energy barrier, 16 Enzyme electrodes, 172, 174 Enzyme immunoassays, 185 Enzyme inhibition, 181 Enzyme reconstitution, 178 Enzyme wiring, 178 Equilibrium potential, 15 Ethanol electrodes, 87, 178 Exchange current, 14... 

Structurally well-defined enzyme electrodes wired by redox polymers have been constructed using different interactions, such as antigen-antibody [173-175] or avidin-biotin [176-181]. Hodak et al. described for the first time the layer-by-layer... 

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... 

Besides the broad applications of electrically contacted enzyme electrodes as amperometric biosensors, substantial recent research efforts are directed to the integration of these functional electrodes as biofuel cell devices. The biofuel cell consists of an electrically contacted enzyme electrode acting as anode, where the oxidation of the fuel occurs, and an electrically wired cathode, where the biocatalyzed reduction of the oxidizer proceeds (Fig. 12.4a). The biocatalytic transformations occurring at the anode and the cathode lead to the oxidation of the fuel substrate and the reduction of the oxidizer, with the concomitant generation of a current through the external circuit. Such biofuel cells can, in principle, transform chemical energy stored in biomass into electrical energy. Also, the use... 

A flow injection system combined with an enzyme electrode was used to detect and quantify a variety of pesticides [41]. Photocrosslinkable polyfyinyl alcohol) was used to immobilise AChE onto platinum wire working electrodes. These were then placed inside a flow injection cell and the electrochemical response to injections of thiocholine measured. A series of measurements were made before and following the injection... 

Yang L, Janie E, Huang T, Gitzen J, Kissinger PT, Vreeke M, Heller A. Applications of wired peroxidase electrodes for peroxide determination in liquid chromatography coupled to oxidase immobilized enzyme reactors. Analytical Chemistry 1995, 34, 1326-1331. 

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