Direct electron-transfer and electrochemical catalysis of hemoglobin immobilized on mesoporous Al2O3

The direct electrochemistry of hemoglobin (Hb) has been achieved by immobilizing Hb on mesoporous Al2O3 (meso-Al2O3) film modified glassy carbon (GC) electrode. Meso-Al2O3 shows significant promotion to the direct electron-transfer of Hb, thus it exhibits a pair of well defined and quasi-reversible peaks with a formal potential of -0.345 V (vs. SCE). The electron-transfer rate constant (k(s)) is estimated to be 3.17 s(-1). The immobilized Hb retains its biological activity well and shows high catalytic activity to the reduction of hydrogen peroxide (H2O2) and nitrite (NO2-). Under the optimized experimental conditions, the catalytic currents are linear to the concentrations of H2O2 and NO2- in the ranges of 0.195-20.5 mu M and 0.2-10 mM, respectively. The corresponding detection limits are 1.95 x 10(-8) M and 3 x 10-(5) M (S/N = 3). The resulting protein electrode has high thermal stability and good reproducibility due to the protection effect of meso-Al2O3. Ultraviolet visible (UV-vis) absorption spectra and reflection-absorption infrared (RAIR) spectra display that Hb keeps almost natural structure in the meso-Al2O3 film. The N-2 adsorption-desorption experiments show that the pore size of meso-Al2O3 is about 14.4 nm, suiting for the encapsulation of Hb (average size: 5.5 nm) well. Therefore, meso-Al2O3 is an alternative matrix for protein immobilization and biosensor preparation. (C) 2007 Elsevier Ltd. All rights reserved.