ELECTROCHEMICAL IMMOBILIZATION OF ENZYMES ON CONDUCTING ORGANIC SALT ELECTRODES - CHARACTERIZATION OF AN OXYGEN INDEPENDENT AND INTERFERENCE-FREE GLUCOSE BIOSENSOR

A glucose biosensor, based on the electrochemical immobilisation of gl ucose oxidase (GOD) in a poly(o-phenylendiamine) (PPD) film synthesise d onto a NMP TCNQ conducting organic salt (COS) electrode, is describe d and its performances are evaluated. The electrochemical cycling of t he bare conducting organic salt electrode, in a phosphate buffer (pH 7 ) supporting electrolyte, accumulated a surface layer of TCNQ(0), whic h was supposed to be the active mediator for the heterogeneous reoxida tion of GOD. Under certain boundary conditions, Chen et al.'s model [C .J. Chen, C.C. Liu, R. Savinell, J. Electroanal. Chem., 248 (1993) 317 ] has been applied to describe the catalysis occurring at our biosenso r. Moreover, when the electrolysis is fast, such a model was demonstra ted to be equivalent to Albery et al.'s mathematics [W.J. Albery, P.N. Bartlett, D.H. Craston. J. Electroanal Chem., 194 (1985) 223], which allows the estimation of the kinetic constants. Such parameters indica ted:hat substrate diffusion through the membrane and unsaturated enzym e kinetics were the rate-limiting processes. COS/PPD/GOD electrode res pond rapidly to glucose, the steady-state current being reached in 10- 16 s. Biosensor responses under different operating conditions such as applied potential, presence of oxygen or interferents were investigat ed. The sensor response, tested in a day to-day experiment, remained q uite stable for 4 days, then decreased to 60% of the initial value on day 5. The shelf lifetime was at least 1 month. (C) 1997 Elsevier Scie nce S.A.