Electrochemical behaviour of monolayer quinoprotein adsorbed on the electrode surface

Direct electron transfer between a monolayer of quinoprotein oxidoreductase, fructose dehydrogenase (FDH) and various electrodes such as Pt, Au and GC was investigated. To achieve direct and reversible electron transfer, monolayer FDH was prepared on these electrodes by a voltage-assisted adsorption method. The monolayer preparation depended on the applied potential, the adsorption time, the pH of the incubation medium and the protein concentration. The electron transfer between adsorbed FDH and the electrode proceeded directly and reversibly at all the electrodes. The redox potentials of FDH at pH 4.5 were 80, 80 and 40 mV (vs. Ag/AgCl) for the Pt, Au and GC electrodes, respectively. This electrochemical property depended on the electrode material, i.e. one electrode retained the enzyme with more enzyme activity than did the others, while another retained the enzyme with more electrochemical activity than the others. This suggests that partial orientation is possible by a particular electrode material. The mode of orientation on each metallic surface was different from that on the carbon electrode: the former provided more rapid electron transfer with lower enzyme activity, whereas the latter produced slower electron transfer with higher dehydrogenase activity. In addition, an attempt was made to determine fructose with a FDH-adsorbed electrode by detecting the direct electron transfer from the enzyme to the electrode.