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

Glucose oxidase (GOx) electrodes were constructed by complexing GOx with the redox osmium macromolecule, [Os(bpy)(2)(PVP)(20)Cl]Cl(abbreviated Os-Polymer). The biosensor produced high catalytic current densities in response to beta-D-glucose in solvent media that were up to 100% in acetonitrile. The sensor, which functions by relaying electrons between GOx flavin adenine dinucleotide redox sites {GOx(FAD/FADH(2))} and the electrode, showed great improvement in its organic-phase responses in the presence of certain amounts of water. Cyclic voltammograms were analyzed for the elucidation of reaction mechanism and determination of the formal electrode potential (E degrees'). The electrode potential E degrees' decreased as water content of the medium increased. Steady-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 charge propagation within the polymer compared to the enzyme kinetics. Maximum steady-state current density j(max) and apparent Michaelis-Menten constant K'(M) were evaluated from electrochemical Eadie-Hofstee plots. Our results show that j(max) reached an optimal value of 282 mu A cm(-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 not bind to, or act as a cosubstrate for, the immobilized GOx. Effect of water on sensor response in the polar organic solvent has been explained on the basis of its role in increasing the flexibility of the immobilized GOx active site environment.