Role of 2-mercaptoethanol in direct electron transfer-type bioelectrocatalysis of fructose dehydrogenase at Au electrodes

•The state of FDH on the Au electrode is voltammetrically monitored with DET catalytic current, O2 reduction current, and [Fe(CN)6]3−/4− redox signal.•FDH shows the highest activity at around the pzc of Au electrode.•The DET activity of FDH decreases with time at positive electrode potentials due to the strong positive electric field.•Mercaptoethanol-Au binding located in the gap of the adsorbed FDH plays a significant role in the stability of the adsorbed FDH on the Au electrode.

Effects of the electrode potential on a direct electron transfer (DET)-type bioelectrocatalysis of fructose dehydrogenase (FDH) at Au electrodes were investigated. Adsorbed FDH showed the highest DET activity at an adsorption potential (Ead) around the point of zero charge (Epzc). Since FDH stock solution contains 2-mercaptoethanol (ME) for stabilization, ME is partially bound to the Au electrode. However, the DET activity drastically decreased at Ead >> Epzc. Au oxide layer is formed at the positive potentials to hinder the interfacial electron transfer. In contrast, only slight decrease in the DET activity was observed at sufficiently negative Ead (<