REACTIVITIES OF ORGANIC-PHASE BIOSENSORS - 2 - THE AMPEROMETRIC BEHAVIOR OF HORSERADISH-PEROXIDASE IMMOBILIZED ON A PLATINUM-ELECTRODE MODIFIED WITH AN ELECTROSYNTHETIC POLYANILINE FILM

An amperometric peroxide biosensor was prepared by electrochemical dep osition of horseradish peroxidase (HRP) on a Pt disc electrode modifie d with polyaniline (PANI) film doped with polyvinyl sulphonate (PVS). Electrochemical characterisation of the PANI-PVS film (without HRP) in dicates a conducting electroactive polymer that exhibits fast reversib le electrochemistry in 1M HCl. The HRP-based sensor was stable and gav e rise to reproducible steady state responses for up to two weeks, whe n operated as both organic phase and aqueous phase H2O2 biosensors at -100 mV/Ag-AgCl and 25 degrees C. The aqueous phase for the H2O2 assay was 0.05 M phosphate buffer, pH 6.88, while acetone, acetonitrile, pr opan-2-ol and tetrahydrofuran (THF) organic phases were used. The anal yses of the calibration curves of the biosensor showed that the system followed a Michaelis-Menten kinetics when operated either as organic- or aqueous-phase biosensors. The kinetic parameters K-m' (apparent Mi chaelis Menten constant), k(cat)' (apparent biosensor turnover rate co nstant), and k(cat)'/K-m' biosensing efficiency parameter) were evalua ted from the steady-state amperometric data obtained in the five solve nt media. The values of the biosensor efficiency factor, k(cat)'/K-m', show that the sensor exhibits greater efficiency for analyte detectio n when operated in organic-phase mode in acetonitrile medium than in a queous buffer. (C) 1997 Elsevier Science Limited.