Electrocatalytic reduction of dioxygen by redox mediator and laccase immobilized in silicate thin film

Laccase from Cerrena unicolor was immobilized in thin hydrophilic silicate gel obtained from tetramethoxysilane deposited on gold electrode. Its catalytic activity towards oxygen reduction was studied by cyclic voltammetry and chronocoulometry. Immobilized laccase was found to be active only in the presence of dissolved ABTS as mediator. Catalytic reaction starts immediately after immersion of the electrode into oxygen saturated mediator solution. However, the time when laccase maximum performance is achieved depends on pH. Immobilized laccase exhibits maximum activity in pH range 4.2–5.2 at temperatures ranging form 40 to 50 °C. Activation energy of dioxygen reduction by laccase with ABTS as mediator equals 52.5 kJ mol−1, typical for laccase enzymatic reaction. Rate of electrocatalytic reaction is slow, however turnover number is high, reaching 1400 s−1, indicating that active form of the enzyme participates in enzymatic reaction. The behavior of laccase immobilized in silicate film is similar to that of native enzyme, indicating that silicate matrix does not affect its biological and physicochemical properties.