Electrochemistry and electrocatalytic properties of hemoglobin in layer-by-layer films of SiO2 with vapor-surface sol-gel deposition

In this paper, layer-by-layer {Hb/SiO2}(n) films assembled by alternate adsorption of positively charged hemoglobin (Hb) and vapor-surface sol-gel deposition of silica at 50 degrees C onto a glassy carbon electrode were reported. The result films were characterized with cyclic voltametery, electrochemical impedance spectroscopy, UV-vis spectroscopy, and SEM, and the direct electrochemical and electrocatalytic properties of Hb in these layer-by-layer films were investigated. A pair of well-defined quasi-reversible cyclic voltammetric peaks were observed, and the formal potential of the heme Fe-III/Fe-II redox couple was found to be -0.330 V(vs SCE). The electron-transfer behavior of Hb in {Hb/SiO2}(n) films was dependent on the vapor temperature, the number of layers, and the pH of the Hb solution, based on which a set of optimized conditions for film fabrication was inferred. The hemoglobin in{Hb/SiO2}(n) films displayed good electrocatalytic activity to the reduction of hydrogen peroxide, and H2O2 had linear current response from 1.0 x 10(-6) to 2.0 x 10(-4) M with a detection limit of 5.0 x 10(-7) M (S/N = 3). The apparent heterogeneous electron-transfer rate constant (k(s)) was 1.02 +/- 0.03 s(-1), and the apparent Michaeli-Menten constant (K-m(app)) was 0.155 mM, indicating a potential application in the third-generation biosensor.