Direct electrochemistry of hemoglobin and glucose oxidase in electrodeposited sol-gel silica thin films on glassy carbon

This work points out that electrogeneration of silica gel (SG) films on glassy carbon electrodes (GCEs) can be applied to immobilize biomolecules - hemoglobin (Hb) or glucose oxidase (GOD) or both of them in mixture - without preventing their activity. These proteins were physically entrapped in the sol-gel material in the course of the electro-assisted deposition process applied to form the thin films onto the electrode surface. SG films were prepared from a precursor solution by applying a suitable cathodic potential likely to induce a local pH increase at the electrode/solution interface, accelerating thereby polycondensation of the silica precursors with concomitant film formation. Successful immobilization of proteins was checked by various physico-chemical techniques. Both Hb and GOD were found to undergo direct electron transfer, as demonstrated by cyclic voltammetry. GCE-SG-Hb gave rise to well-defined peaks at potentials E-c = -0.29 V and E-a = -0. 17 V in acetate buffer, corresponding to the Fe-III/Fe-II redox system of heme group of the protein, while GCE-SG-GOD was characterized by the typical signals of FAD group at E-c = -0.41 V and E-a = -0.33 V in phosphate buffer. These two redox processes were also evidenced on a single voltammogram when both Hb and GOD were present together in the same SG film. Hb entrapped in the silica thin film displayed an electrocatalytic behavior towards O-2 and H2O2 in solution, respectively in the mM and mu M concentration ranges. Immobilized GOD kept its biocatalytic properties towards glucose. Combined use of these two proteins in mixture has proven to be promising for detection of glucose in solution via the electrochemical monitoring of oxygen consumption (decrease of the oxygen electrocatalytic signal). (c) 2007 Elsevier B.V. All rights reserved.