Electrochemical immobilisation of enzymes on conducting organic salt electrodes: characterisation of an oxygen independent and interference-free glucose biosensor

A glucose biosensor, based on the electrochemical immobilisation of glucose oxidase (GOD) in a poly(o-phenylendiamine) (PPD) film synthesised onto a NMP TCNQ conducting organic salt (COS) electrode, is described and its performances are evaluated. The electrochemical cycling of the bare conducting organic salt electrode, in a phosphate buffer (pH 7) supporting electrolyte, accumulated a surface layer of TCNQ(0), which was supposed to be the active mediator for the heterogeneous reoxidation 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 biosensor. Moreover, when the electrolysis is fast, such a model was demonstrated 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 indicated:hat substrate diffusion through the membrane and unsaturated enzyme kinetics were the rate-limiting processes. COS/PPD/GOD electrode respond 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 investigated. The sensor response, tested in a day to-day experiment, remained quite 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 Science S.A.