A novel glucose biosensor has been prepared by deposition of a mixture containing glucose oxidase dissolved in water and Nafion dissolved in methanol at the surface of a platinum disk electrode. Glucuse concentration is evaluated by measuring the amperometric current corresponding to hydrogen peroxide electrooxidation at 0.7 iJ vs. SCE. The addition of glucose oxidase to Nafion resulted in a Nafion-glucose oxidase film that was more permeable to anionic species than Nafion alone. The calibration curve for glucose is linear from 5 p M u p to about 10 mM. Tn oxygen-saturated solution, the linear range extended to 15 mM. The optimum pH for the assay was found to be 5.5. The enzyme is not stabilized against temperature deactivation when it is immobilized in Nafion. The Pt/Nafion-glucose oxidase electrodes showed good stability when stored dry at room temperature with 80% of the initial response retained after 250 days.

Na®on-glucose oxidase-ferrocene electrodes have been used to study the electron transfer between an electrode and the active site of the enzyme. These electrodes were prepared by casting a mixture of Na®on and glucose oxidase, GOx, (both dissolved in methanol) at the surface of a platinum disk electrode. The ferrocene mediators were incorporated by either soaking PtyNa®on and PtyNa®on-GOx electrodes in an aqueous solutions of N,N H -dimethylaminomethylferrocene, DMAFc, or by depositing an aliquot of a ferrocene solution at the surface of the enzyme ®lm electrode. The Na®on-GOx electrodes are characterized by a slower incorporation rate of the ferrocene than the plain Na®on electrode indicating that the af®nity of Na®on for the ferrocene derivative is increased by the addition of the enzyme. Accordingly, the ion-exchange distribution coef®cient is larger for plain Na®on (3.2610 3 ) than for Na®on-GOx (7.2610 2 ). The cyclic voltammetry of the PtyNa®on-GOx electrode in the presence of glucose and in deaerated solution show a well developed catalytic wave indicating that the ferrocene acts as a mediator for the electron transfer between the enzyme and the platinum electrode. For a high glucose concentration (75 mM), the amperometric response of these electrodes increased and the apparent diffusion coef®cient DMAFc decreased with an increase of DMAFc concentration in the enzymatic layer. These observations suggest that the glucose response is limited by the probability of an encounter between the reduced enzyme and the oxidized ferrocene rather than by the charge transfer between the reduced ferrocene and the electrode. The effective Michaelis constant, K m , for glucose and DMAFc were evaluated and values of 25 mM and 4 nmolycm 2 were obtained, respectively.