GRAPHITE-POLY(TETRAFLUOROETHYLENE) COMPOSITE ENZYME ELECTRODES AS SUITABLE BIOSENSORS IN PREDOMINANTLY NONAQUEOUS MEDIA

The performance of a graphite-poly(tetrafluoroethylene) Tenon composit e amperometric ferrocyanide-mediated peroxidase electrode in a predomi nantly nonaqueous medium such as reversed micelles is discussed and co mpared with the behavior in a medium formed by acetonitrile/water, The composite electrode was constructed by purely physical entrapment of both the enzyme and the mediator into the bulk of the graphite-Tenon m atrix with no need of covalent attachments. This biosensor responded r apidly to the changes in the concentration of both hydrogen peroxide a nd 2-butanone peroxide in reversed micelles formed with ethyl acetate, 0.1 mol L-1 dioctyl sulfosuccinate as the surfactant, and a 4% phosph ate buffer (pH 7.4) as the dispersed phase. The electrode showed a lon g-term operation due to the renew-ability of its surface, Moreover, re producible responses were obtained with different electrodes fabricate d from different composite matrixes. No significant loss of the enzyme activity was observed after four months of dry storage at 4 degrees C of the composite electrode, Limits of detection of 2.1 x 10(-7) and 3 .5 x 10(-7) mol L-1 were obtained for H2O2 and 2-butanone peroxide, re spectively. The possibility of using this biocomposite electrode in fl owing systems, using the reversed micelles as the carrier, has been de monstrated. The kinetic of the enzymatic reaction was faster in a 90:1 0 acetonitrile/phosphate buffer medium than in reversed micelles, whic h can be attributed to the higher water content present in the former medium. A similar stability of the biosensor and a slightly better sen sitivity for peroxides was observed in the acetonitrile/water mixture when compared with reversed micelles, Finally, the electrode also perf ormed well in the now injection mode.