Graphite-poly(tetrafluoroethylene) composite enzyme electrodes as suitable biosensors in predominantly nonaqueous media

The performance of a graphite-poly(tetrafluoroethylene) Tenon composite amperometric ferrocyanide-mediated peroxidase electrode in a predominantly nonaqueous medium such as reversed micelles is discussed and compared 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 matrix with no need of covalent attachments. This biosensor responded rapidly to the changes in the concentration of both hydrogen peroxide and 2-butanone peroxide in reversed micelles formed with ethyl acetate, 0.1 mol L-1 dioctyl sulfosuccinate as the surfactant, and a 4% phosphate buffer (pH 7.4) as the dispersed phase. The electrode showed a long-term operation due to the renew-ability of its surface, Moreover, reproducible responses were obtained with different electrodes fabricated 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, respectively. The possibility of using this biocomposite electrode in flowing systems, using the reversed micelles as the carrier, has been demonstrated. The kinetic of the enzymatic reaction was faster in a 90:10 acetonitrile/phosphate buffer medium than in reversed micelles, which can be attributed to the higher water content present in the former medium. A similar stability of the biosensor and a slightly better sensitivity for peroxides was observed in the acetonitrile/water mixture when compared with reversed micelles, Finally, the electrode also performed well in the now injection mode.