AMPEROMETRIC GLUCOSE SENSOR CONTAINING NONDIFFUSIONAL OSMIUM REDOX CENTERS - ANALYSIS OF ORGANIC-PHASE RESPONSES

Glucose oxidase (GOx) electrodes were constructed by complexing GOx wi th the redox osmium macromolecule, [Os(bpy)(2)(PVP)(20)Cl]Cl(abbreviat ed Os-Polymer). The biosensor produced high catalytic current densitie s in response to beta-D-glucose in solvent media that were up to 100% in acetonitrile. The sensor, which functions by relaying electrons bet ween GOx flavin adenine dinucleotide redox sites {GOx(FAD/FADH(2))} an d the electrode, showed great improvement in its organic-phase respons es in the presence of certain amounts of water. Cyclic voltammograms w ere analyzed for the elucidation of reaction mechanism and determinati on of the formal electrode potential (E degrees'). The electrode poten tial E degrees' decreased as water content of the medium increased. St eady-state responses of the sensor in CH3CN/H2O mixtures, 1 to 35% v/v in H2O, were observed at 450 mV. The kinetic analysis of the stead)I- state amperometric response of the biosensor was based on a rapid char ge propagation within the polymer compared to the enzyme kinetics. Max imum steady-state current density j(max) and apparent Michaelis-Menten constant K'(M) were evaluated from electrochemical Eadie-Hofstee plot s. Our results show that j(max) reached an optimal value of 282 mu A c m(-2) in CH3CN/H2O (80 + 20% v/v). There was no drastic change in K'(M ) for the different CH3CN/H2O media. This indicates that. CH3CN does n ot bind to, or act as a cosubstrate for, the immobilized GOx. Effect o f water on sensor response in the polar organic solvent has been expla ined on the basis of its role in increasing the flexibility of the imm obilized GOx active site environment.