Abstract:

Chitosan-g-N-carboxymethyl-bi(2-benzoimidazole)-1,2-ethandiol(CTS-g-N-CBBIE) was synthesized through grafting on the side chain of chitosan with 2-bromoacetic acid, chitosan, bi(2-benzoimidazole)-1,2-ethandiol, chloroauric acid and sodium citrate as raw materials. Compsosite of CTS-g-N-CBBIE-NGS was obtained by means of intermixing purified nanogold sol(NGS) and CTS-g-N-CBBIE. The composite was adopted to act as the carrier of immobilized laccase from Trametes versicolor mainly by means of physical entrapment. The laccase-entrapped CTS-g-N-CBBIE-NGS composite with superiority of high laccase-loading(31.10 mg/g) and specific activity of immobilized enzyme(1.43 U/mg) was used to modify the glassy carbon electrode(GCE). Results from experiments conducted on this laccase modified glassy carbon electrode showed mediatorless direct electron transfer occurred between active site of laccase and laccase modified electrode in deaerated phosphate-citrate buffer solution(pH=5.0)(formal potential of quasi-reversible redox peaks corresponding to the T1 site copper ion in the laccase:576 mV(vs.AgCl/Ag)). Rate constant of electron transfer:228.3 s-1 was derived from relationship of separation of redox peaks and logarithm of scan rates. Laccase-entrapped matrix modified GCE also displayed bioelectrocatalytic effect on oxygen reduction reaction to some extent under low oxygen concentration(peak potential of laccase modified GCE for oxygen reduction reaction in air-saturated buffer solution at ca. 320 mV(vs.AgCl/Ag)). Oxygen reduction reaction was depressed when oxygen concentration increased. This laccase modified electrode was sensitive to variation of pH and its inferiority originated from undesirable usability and long-term stability. It is essential for higher bioelectrocatalytic function on oxygen reduction reaction of laccse modified electrode that constituent of composite to immobilize enzyme which was used to modify electrode must be optimized.

Key words: Chitosan-g-N-carboxymethyl-bi(benzoimidazole)-ethandiol, direct electron transfer (DET), nanogold sol(NGS), Laccase, Bioelectrocatalysis