Abstract: Poly benzimidazole and laccase were co-deposited on the surface of glassy carbon electrode by cyclic voltammetry method. Apparent catalytic reduction current was observed when the as-prepared laccase based electrode was immersed in oxygen-saturated phosphate buffer solution, indicating the viability of direct electron transfer between electrode and immobilized enzyme without external mediator existence. The result showed the onset potential of oxygen reduction reaction(ORR) was 645 mV, in the vicinity of the formal potential corresponding to T1 copper site in laccase(580 mV), while the limited diffusion catalytic current density could be up to 318.5×10-6 A/cm2. The slow diffusion in the dense-packed conductive polymer thin film layer on the surface of electrode (the diffusion coefficient is only 1.25％ of measured value in solution) resulted in a slight enhancement in limited diffusion catalytic current density:～1×10-3 A/cm2 at the relatively high rotating speed. The average turn-over frequency of catalytic oxygen reduction induced by entrapped laccase was evaluated to be 21.7/s according to the stationary limit catalytic current density. This laccase based electrode displayed favorable reproducibility and long-term usability (catalytic activity could retain ca. 80％ of its initial value after a storage for 10 days). This biocathode had superior activity at physiological temperature of human being and under weak acidic conditions, and demonstrated excellent sensor function for oxygen molecules: low detection limit(0.5 μmol/L), high sensitivity(71.1 μA·L/mmol) and favorable affinity(KM=8.9 μmol/L).

Key words: laccase, benzimidazole, conductive polymer, oxygen reduction reaction