Dissolved Enzymes Activated by Diffusional Mediators

Ferrocene derivatives, organic dyes, fer-ricyanide, Ru-complexes, and other elec-trochemically active substrates have been employed for diffusional MET and the electrical activation of soluble redox enzymes 

Comparison of the electron-transfer efficiency provided by different mediators in the presence of the same redox enzyme allows the definition of the important parameters of MET. The reaction of glucose oxidase (GOx) has been extensively studied with a number of artificial electron acceptors including organic dyes such as phenazine methosul-fate, 2,6-dichlorophenolindophenol, and N, N, N, A -tetramethyl-4-phenylenedia-mine [26]. However, these mediators have a number of limitations such as poor stability and the pH dependence of their redox potentials. Simple inorganic redox species such as hexacyanofer-rate [27], hexacyanoruthenate, and pen-taamine pyridine ruthenium [28] do not suffer from these problems. These 

The majority of these problems have been overcome by the use of ferrocene derivatives as electron acceptors for soluble oxidases (e.g. GOx). Ferrocene derivatives of varying charge and solubility, with redox potentials (E ) between -1-0.1 V and -1-0.4 V, have been shown to accept electrons from GOx [30]. The published values [22] for the second-order rate constant ( em) for the reaction of the reduced active center of GOx (FADH2) and an oxidized ferrocene derivative range from 0.26 x 10 to 5.25 X 10 There is no simple 

Monolayer- or Multilayer-enzyme Electrodes Activated by DifTusional Mediators 

The organization of ordered enzyme multilayer arrays opens the possibility of assembling multilayers of two or more different enzymes [46], one of which is a redox enzyme electrically contacted via dif-fusional MET. The other enzyme(s) may turn the analyte substrate into a product that is the substrate for the redox enzyme. The resulting transduced current is therefore proportional to the concentration 

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