Graphite-teflon-peroxidase composite electrodes. Application to the direct determination of glucose in musts and wines

The performance of graphite-70% Teflon-peroxidase-ferrocene composite electrodes, fabricated by simple physical inclusion of the enzyme and the mediator into the bulk of a graphite-Teflon matrix, by using both batch and flow-injection modes, is reported. The electrode responds very rapidly to changes in H2O2 concentration due to the absence of a membrane barrier on the electrode surface and of a covalent attachment of the enzyme to graphite. The composite enzyme electrode showed a long-term operation due to the renewability of its surface by polishing. Reproducible amperometric responses were achieved with different electrodes fabricated from different composite matrices, and no significant loss of the enzyme activity was observed after seven months of dry-storage at 4 degrees C. A bienzymatic graphite-70% Teflon-peroxidase-glucose oxidase-ferrocene electrode has been developed, too, showing a rapid response to the changes in the glucose concentration. The stability of the bienzymatic composite electrode was similar to that of the peroxidase biosensor. This biosensor was applied to the determination of glucose in must and wine samples by batch amperometry and dow injection with amperometric detection modes.