Abstract:

L-Cysteine functionalized nanogold particles were synthesized with hydrogen tetrachloroaurate tetrahydrate and L-cysteine as raw materials. The functionalized nanogold particles were attached to the surface of gold disk electrode and then were covalently coupled with laccase. Electrochemical behavior of this laccasebased electrode in deaerated phosphate buffer solution and its electrocatalytic effect for oxygen reduction were investigated by cyclic voltammetry. Furthermore, the performance of this laccase based cathode as oxygen sensor was evaluated: oxygen detection limit of this sensor and its affinity towards oxygen(characterized with Michaelis-Menten constant KM) were measured with chronoamperometry. The long-term usability, thermal stability of O2 sensor together with the relationship between pH value and catalytic current were also studied. The results indicate that a direct electron transfer between the redox active centre T2 of laccase and the conductive functionalized nanogold particle occurs without any additional electron relay(formal potential of redox peaks:192.5 mV vs AgCl/Ag), and oxygen reduction occurs at a potential similar to that of T3 redox centre in laccase(780 mV vs NHE). The affinity of the laccase based sensor towards O2 was relatively high(KM=216.4 μmol/L) and the detection limit of oxygen was 0.22 μmol/L. Catalytic current for oxygen reduction can still retain approximately 78% of the initial value after storage at 4 ℃ refrigerator for 60 days. However, this laccase based O.2 sensor displayed inferior thermal stability, and its catalytic current corresponding to O2 reduction was strongly influenced by pH value in buffer solution:when pH value of the buffer solution comes close to physiological condition, near all catalytic activity towards O2 was lost.

Key words: laccase, nanogold particle, oxygen sensor, direct electron transfer