Hemoglobin immobilized on whisker-like carbon composites and its direct electrochemistry

We developed a novel mesoporous carbon/whisker-like carbon (MCWC) composite which can promote the direct electron transfer of hemoglobin (Hb) immobilized on its surface. The cyclic voltammetric results showed that Hb immobilized on the surface of the MCWC composite could undergo a direct quasi-reversible electrochemical reaction. Its formal redox potential, E^0' is -0.313 V in the phosphate buffer solution (pH 6.9) at a scan rate of 200 mV/s and is almost independent of the scan rate in the range of 100-600 mV/s. The dependence of E^0' on the pH of phosphate buffer solution indicated that the redox reaction of Hb includes a one-electron-transfer reaction process coupled with one-proton-transfer. The experiment obtained larger value of electron transfer rate constant, k_s, than that of Hb immobilized on other carriers reported previously due to its special structure of loosely packed nanometer-scale carbon whiskers and thus formed 'V-type' nano-pores. Furthermore, Hb immobilized on the surface of the MCWC composite can retain the stable bioelectrocatalytic activity for the reduction of H₂O₂