Immobilization of Glucose Dehydrogenase on Epoxy Group-Modified MgO-Templated Porous Carbon Electrode for Improvement of Biofuel Cell Stability

Abstract

Enzymatic glucose/O2 biofuel cells (BFCs) are energy conversion systems in which enzymes oxidize glucose at a bioanode and reduce oxygen at a biocathode. These enzymes are highly safe toward humans, and highly selective for substrates, without leaving toxic residues at room temperature and neutral pH conditions. There are many recent studies on self-powered biosensing systems based on BFCs. We have reported that the output power is dramatically improved by using MgO-templated porous carbon (MgOC) for electrodes of biofuel cells [1-2]. MgOC has suitable mesopores for entrapping an enzyme whose redox center can approach the carbon surface with high probability. In addition, the long-term stability may be improved because the ellusion of the enzyme was suppressed by entrapping the enzyme in the mesopore. In this study, we newly performed chemical immobilization of glucose dehydrogenase (GDH) on the MgOC surface to improve the long-term stability further. A MgOC poweder having an average pore diameter of 100 nm was purchased from by Toyo Carbon Co. Ltd. The epoxy group-modified MgOC was synthesized by graft polymerization technique. The epoxy group-modified MgOC was coated on a glassy carbon electrode, and then 1,2-naphthoquinone(1,2-NQ) was modified as a mediator and glucose dehydrogenase (FAD-GDH) was modified as an enzyme to be prepared an enzyme electrode. Cyclic voltammetry and chronoamperometry of the enzyme electrode were measured in a 3-electrode system in 1.0 M phosphate buffer solution (PBS) containing 100 mM glucose. Stability of the enzyme electrode was evaluated by performing cyclic voltammetry in multiple cycle measurement. Figure 1 shows the cyclic voltammogram of enzyme electrode. Catalytic oxidation current was observed at a nobler potential than -0.1 V. Also, the maximum current value in the 1st cycle was 11.2 mA cm-2. The peak current value of the present enzyme electrode was almost the same compared with that of an enzyme electrode in which epoxy group-unmodified MgOC was used as the electrode material. The results indicated that the enzymatic activity of FAD-GDH was not changed by the chemical immobilization. Figure 2 shows the relation between the number of cycles and normalized current density at 0.3 V. When the MgOC was modified by epoxy group, the current value of 90% was retained after 25 cycles, whereas it was 52% in the case of unmodified MgOC. From the above results, Elution of FAD-GDH could be suppressed by using epoxy group-modified MgOC because the amino group of the enzyme shell and the epoxy group on the carbon surface are bonded successfully.