IMPROVED MODEL OF A POLYPYRROLE GLUCOSE-OXIDASE MODIFIED ELECTRODE

The behaviour of an electrode modified by entrapment of glucose oxidase in an insulating polypyrrole film is examined using both an experimental study and a theoretical model. Although adsorption of glucose oxidase at the electrode surface and at the polymer\solution interface was shown experimentally, more than 90% of the amperometric response due to the glucose oxidation was generated by the enzyme confined inside the polymeric matrix. The maximum amperometric response was obtained with a polypyrrole film of thickness 250 nm; the global process rate was governed by the kinetics of the catalysed reaction for thin films and by the mass transport of the species in the polymer for thicker films. All the experimental results were fitted correctly by a complete model using the same values of the physicochemical parameters in all cases. In particular, the theoretical results agreed well with the enzyme location determined experimentally; furthermore, they permitted the prediction that the amperometric response decreased when solution stirring increased. The simulation of the theoretical concentration profiles confirmed that the external mass transport of all species in the solution had to be taken into account and showed that the enzymatic reaction occurred preferentially near the polymer\solution interface. This last result suggested some improvements in the design of the electrode.