Direct electrochemistry of redox proteins and enzymes promoted by carbon nanotubes

Abstract: The redox protein and enzyme, such as hemoglobin (Hb), horseradish peroxidase (HRP) and glucose oxidase (GOx), was immobilized on the surface of the carbon nanotube modified glassy carbon (CNT/GC) electrode, respectively. The cyclic voltammetric results indicated that the redox protein and enzyme underwent effective and stable direct electron transfer reaction with a pair of nearly symmetrical redox peaks. The formal redox potential, E0’, was almost independent on the scan rates, the average value of E0 ’ for Hb, HRP and GOx was –0.343 ± 0.001, –0.319 ± 0.002 and –0.456 ± 0.0008 V (vs. SCE，pH 6.9), respectively. The dependence of E0 ’ on the pH solution indicated that the direct electron transfer of Hb and HRP was a one-electron-transfer reaction process coupled with one-proton-transfer, while the GOx was a two-electron-transfer coupled with two-proton-transfer. The apparent heterogeneous electron transfer rate constant (ks) was 1.25 ± 0.25, 2.07 ± 0.69 and 1.74 ± 0.42 s-1 for Hb, HRP and GOx, respectively. The method presented here can be easily extended to immobilize other redox enzymes or proteins and obtain their direct electrochemistry