Direct electrochemistry and electrocatalysis of myoglobin immobilized on a hexagonal mesoporous silica matrix

The direct electrochemistry of myoglobin (Mb) immobilized on a hexagonal mesoporous silica (HMS)-modified glassy carbon electrode was described. The interaction between Mb and HMS was investigated by using Fourier transfer infrared spectroscopy, nitrogen adsorption isotherm, and cyclic voltammetry. Two couples of redox peaks corresponding to Fe(III) to Fe(II) conversion of the Mb intercalated in the mesopores and adsorbed on the surface of the HMS were observed with the formal potentials of -0.167 and -0.029V in 0.1M, pH 7.0, phosphate buffer solution, respectively. The electrode reaction showed a surface-controlled process with one proton transfer. The immobilized Mb displayed good electrocatalytic responses to the reduction of both hydrogen peroxide (H₂O₂) and nitrite (NO₂^-), which were used to develop novel sensors for H₂O₂ and NO₂^-. The apparent Michaelis-Menten constants of the immobilized Mb for H₂O₂ and NO₂^- were 0.065 and 0.72mM, respectively, showing good affinity. Under optimal conditions, the sensors could be used for the determinations of H ₂O₂ ranging from 4.0 to 124μM and NO₂ ^- ranging from 8.0 to 216μM. The detection limits were 6.2×10^-8 and 8.0×10^-7M at 3 σ, respectively. The HMS provided a novel matrix for protein immobilization and the construction of biosensors via the direct electron transfer of immobilized protein.