Direct electron transfer and enzymatic activity of hemoglobin in a hexagonal mesoporous silica matrix

The direct electrochemistry of hemoglobin (Hb) immobilized on a hexagonal mesoporous silica (HMS)-modified glassy carbon electrode was described. The interaction between Hb and the HMS was investigated using UV-Vis spectroscopy, FT-IR, and electrochemical methods. The direct electron transfer of the immobilized Hb exhibited two couples of redox peaks with the formal potentials of -0.037 and -0.232V in 0.1M (pH 7.0) PBS, respectively, which corresponded to its two immobilized states. The electrode reactions showed a surface-controlled process with a single proton transfer at the scan rate range from 20 to 200mV/s. The immobilized Hb retained its biological activity well and displayed an excellent response to the reduction of both hydrogen peroxide (H ₂O₂) and nitrate (NO₂^-). Its apparent Michaelis-Menten constants for H₂O₂ and NO ₂^- were 12.3 and 49.3μM, respectively, showing a good affinity. Based on the immobilization of Hb on the HMS and its direct electrochemistry, two novel biosensors for H₂O₂ and NO₂^- were presented. Under optimal conditions, the sensors could be used for the determination of H₂O₂ ranging from 0.4 to 6.0μM and NO₂^- ranging from 0.2 to 3.8μM. The detection limits were 1.86×10^-9M and 6.11×10^-7M at 3σ, respectively. HMS provided a good matrix for protein immobilization and biosensor preparation.