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Optimal environment for glucose oxidase in perfluorosulfonated ionomer membranes: improvement of first-generation biosensors.

An optimal environment for glucose oxidase (GOx) in Nafion membranes is achieved using an advanced immobilization protocol based on a nonaqueous immobilization route. Exposure of glucose oxidase to water-organic mixtures with a high (85-95%) content of the organic solvent resulted in stabilization of the enzyme by a membrane-forming polyelectrolyte. Such an optimal environment leads to the highest enzyme specific activity in the resulting membrane, as desired for optimal use of the expensive oxidases. Casting solution containing glucose oxidase and Nafion is completely stable over 5 days in a refrigerator, providing almost absolute reproducibility of GOx-Nafion membranes. A glucose biosensor was prepared by casting the GOx-Nafion membranes over Prussian Blue-modified glassy carbon disk electrodes. The biosensor operated in the FIA mode allows the detection of glucose down to the 0.1 microM level, along with high sensitivity (0.05 A M(-1) cm(-2)), which is only 10 times lower than the sensitivity of the hydrogen peroxide transducer used. A comparison with the recently reported enzyme electrodes based on similar H2O2 transducers (transition metal hexacyanoferrates) shows that the proposed approach displays a dramatic (100-fold) improvement in sensitivity of the resulting biosensor. Combined with the attractive performance of a Prussian Blue-based hydrogen peroxide transducer, the proposed immobilization protocol provides a superior performance for first-generation glucose biosensors in term of sensitivity and detection limits.