Electrochemistry and biosensing activity of cytochrome c immobilized in macroporous materials

An amperometric biosensor for hydrogen peroxide (H₂O₂) has been constructed by immobilizing cytochrome c on an indium/tin oxide (ITO) electrode modified with a macroporous material. Cyclic voltammetry showed that the direct and quasi-reversible electron transfer of cytochrome c proceeds without the need for an electron mediator. A surface-controlled electron transfer process can be observed with an apparent heterogeneous electron-transfer rate constant (k_s) of 29.2 s^-1. The biosensor displays excellent electrocatalytic responses to the reduction of H₂O₂ to give amperometric responses that increase steadily with the concentration of H₂O₂ in the range from 5 μM to 2 mM. The detection limit is 0.61 μM at pH 7.4. The apparent Michaelis-Menten constant (K_m) of the biosensor is 1.06 mM. This investigation not only provided a method for the direct electron transfer of cytochrome c on macroporous materials, but also established a feasible approach for durable and reliable detection of H₂O₂.