Reactivities of organic phase biosensors. 2. The amperometric behaviour of horseradish peroxidase immobilised on a platinum electrode modified with an electrosynthetic polyaniline film

An amperometric peroxide biosensor was prepared by electrochemical deposition of horseradish peroxidase (HRP) on a Pt disc electrode modified with polyaniline (PANI) film doped with polyvinyl sulphonate (PVS). Electrochemical characterisation of the PANI-PVS film (without HRP) indicates a conducting electroactive polymer that exhibits fast reversible electrochemistry in 1M HCl. The HRP-based sensor was stable and gave rise to reproducible steady state responses for up to two weeks, when operated as both organic phase and aqueous phase H(2)O(2) biosensors at -100 mV/Ag-AgCl and 25 degrees C. The aqueous phase for the H(2)O(2) assay was 0.05 M phosphate buffer, pH 6.88, while acetone, acetonitrile, propan-2-ol and tetrahydrofuran (THF) organic phases were used. The analyses 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 Michaelis Menten constant), k(cat)' (apparent biosensor turnover rate constant), and k(cat)'/K(m)' biosensing efficiency parameter) were evaluated from the steady-state amperometric data obtained in the five solvent media. The values of the biosensor efficiency factor, k(cat)'/K(m)', show that the sensor exhibits greater efficiency for analyte detection when operated in organic-phase mode in acetonitrile medium than in aqueous buffer. (C) 1997 Elsevier Science Limited.