The direct electron transfer of glucose oxidase (GOx) immobilized onto the surface of the carbon nanotube (CNT)-modified glassy carbon (CNT/GC) electrode is reported. The di-rect electron transfer rate of GOx is greatly enhanced when it was immobilized onto the surface of CNT/GC electrode. Cyclic voltammetric results show a pair of well-defined and nearly sym-metric redox peaks, which corresponds to the direct electron transfer of GOx, with the formal potential 0()E, which is almost independent on the scan rates, of about 0.456 V (vs. SCE) in the phosphate buffer solution (pH 6.9). The apparent heterogeneous electron transfer rate con-stant (ks) of GOx at the CNT/GC electrode surface is estimated to be (1.74 ?0.42) s-1, which is much higher than that reported previously. The dependence of 0E on solution pH indicates that the direct electron transfer of GOx is a two-electron-transfer coupled with two-proton-transfer reaction process. The experimental results also demonstrate that the immobilized GOx retains its bioelectrocatalytic activity toward the oxidation of glucose. The method presented here can be easily extended to obtain the direct electrochemistry of other enzymes or proteins.
