Electrical communication metal electrodes

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... 

The electrochemical insulation of the enzyme-active site by its protein or glycoprotein shell usually precludes the possibility of any direct electron-transfer with bulk electrodes [15]. However, under carefully controlled conditions, some enzymes can exhibit direct, nonmediated electrical communication with electrode supports, and biocatalytic transformations can be driven by these processes [16, 17]. For example, the direct electroreduction of O2 and H2O2 biocatalyzed by laccase [18] and horseradish peroxidase (HRP) [19], respectively, have been demonstrated. This unusually facile electronic contacting is believed to be the consequence of incompletely encapsulated redox centers. When these enzymes are properly orientated at the electrode surface, the electrodeactive site distance is short enough for the electron-transfer to proceed relatively unencumbered. Direct electron communication between enzyme-active sites and electrodes may also be facilitated by the nanoscale morphology of the electrode. The modification of electrodes with metal nanoparticles allows the tailoring of surfaces with features that can penetrate close enough to the enzyme active site to make direct electron-transfer possible [20, 21]. 

Y. Degani and A. Heller, Direct electrical communication between chemically modified enzymes and metal electrodes. I. Electron transfer from glucose oxidase to metal electrodes via electron relays, bound covalently to the enzyme. J. Phys. Chem. 91, 1285-1289 (1987). 

Direct electrical communication between enzyme aetive sites and electrodes may also be facilitated by the nanoscale morphology of the electrode. The modification of electrodes with metal nanoparticles allows the tailoring of surfaees with features that can penetrate close enough to the enzyme aetive site to make non-mediated electron transfer possible. Electrodes modified by unaggregated 12 nm diameter gold nanoparticles have been found to have the eorrect morphology to allow direct electron transfer between the cytochrome c active site and the eleetrode [41]. Elec-... 

Degani, Y., Heller, A., Direct Electrical Communication between Chemically Modified Enzymes and Metal Electrodes. 2. Methods for Bonding Electron-Transfer Relays to Glucose Oxidase and D-Amino-Acid Oxidase , J. Am. Chem. Soc. 110 (1988) 2615-2620. 

This electron transfer was positively affected by the immobilization of glucose oxidase on glassy carbon modified by aminophenyl boronic acid [193] or adsorption on to metalized carbons [194]. Nevertheless, it was possible to achieve good electron transfer only by modification ( functionalization ) of the enzyme with redox compounds (ferrocene derivatives). The direct electrical communication between the modified enzyme and an electrode has been proved by cyclic voltammetry. Thus attention was paid to the construction of various types of modified glucose oxidase electrodes. For instance, Benneto et al. [195] describe an... 

Zinc is also attractive for electrically rechargeable metal/air systems because of its relative stability in alkaline electrolytes and also because it is the most active metal that can be electrodeposited from an aqueous electrolyte. The development of a practical rechargeable zinc/air battery with an extended cycle life would provide a promising high-capacity power source for many portable applications (computers, communications equipment) as well as, in larger sizes, for electric vehicles. Problems of dendrite formation, nonuniform zinc dissolution and deposition, limited solubility of the reaction product, and unsatisfactory air electrode performance have slowed progress toward the development of a commercial rechargeable battery. However, there is a continued search for a practical system because of the potential of the zinc/air battery. 

DIRECT ELECTRICAL COMMUNICATION BETWEEN CHEMICALLY MODIFIED ENZYMES AND METAL ELECTRODES III. ELECTRON-TRANSFER RELAY MODIFIED GLUCOSE OXIDASE AND D-AMINO-ACID OXIDASE... 

Electrical communications between enzymes and metal electrodes is an element in the bridging of electronics and biochemistry and is of specific relevance to the electrochemical assay of biochemicals. In such assays, the enzyme is usually first reduced by the substrate, then is reoxidized either directly at an electrode, or indirectly by oxygen or a diffusing redox mediator - . Electrochemical or chemical assays of the oxygen consumed, or of the hydrogen peroxide or reduced mediator products, serve in... 

Here we discuss chemical modification of redox enzymes. We show that by bonding electron-transfer relays to their protein one can establish direct electrical communication between their redox centers and metal or carbon electrodes. 

Key to electrical communication between glucose oxidase and the electrodes is the spacing, i.e., the density, of relays. The relays must be sufficiently close to both the FAD/FADH2 centers and to the metal electrodes (and possibly also to each other) for the electron transfer to be rapid. The distance-dependence of electron transfer rates in biosystems has been the subject of intensive theoretical and experimental research in recent years . It is now evident that for distances greater than 8 A electron transfer rates (k) within and between molecules, as well as between electrodes and ions or molecules in their proximity, or between the ions themselves, decay exponentially with the distance (d) between the involved centers, i.e., k = In proteins the electron... 

From the results we conclude the following. First, that direct electrical communication can be established between redox enzymes (such as glucose oxidase or D-amino-acid oxidase) and metal electrodes, by chemi-... 

Direct Electrical Communication Between Chemically Modified Enzymes and Metal Electrodes ... 

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