Physical immobilization of laccase on an electrode by means of poly(ethyleneimine) microcapsules

Microcapsules of poly(ethyleneimine) were used to immobilize laccase on the surface of an electrode and its mediated electron transfer was studied with the redox mediator p-phenylenediamine (PPD). The microcapsules consisted of a cross-linked PEI wall generated from an emulsion of an aqueous phase containing the enzyme. The reaction of encapsulated laccase with PPD was studied by spectrophotometry and oxygen consumption. We found that the encapsulation resulted in a small shift for the optimum pH and a lower K_m value when compared to free laccase. These differences are attributed to the charged micro-environment offered by the microcapsules. The microcapsules were then deposited on a glassy carbon electrode and chronoamperometry was used to evaluate the mediated electron transfer between the enzyme and the electrode. No significant differences in term of optimum pH and K_m occurred upon capsules deposition on the electrode. The response time of the electrode for PPD oxidation was higher than those found in the literature, which suggests that the PEI capsule wall offers some resistance to mediator permeation, an hypothesis that was verified by RDE measurements. The charged nature of the PEI membrane appeared to affect several parameters of the laccase-mediator reaction and the effect of pH and mediator charge on this reaction are reported. The immobilization platform under study can be applied to different enzyme-mediator systems than the laccase-PPD used here and is relevant to the development of bioelectrocatalytic systems.