Direct electrochemistry and electrocatalysis of hemoglobin immobilized on carbon paste electrode by silica sol-gel film.

Direct electrochemical and electrocatalytic behaviors of hemoglobin (Hb) immobilized on carbon paste electrode (CPE) by a silica sol-gel film derived from tetraethylorthosilicate (TEOS) were investigated for the first time. Hb/sol-gel film modified electrodes showed a pair of well-defined and nearly reversible cyclic voltammetric peaks for Hb Fe(III)/Fe(II) redox couple at about -0.312 V (versus Ag/AgCl) in a pH 7.0 phosphate buffer. The formal potential of Hb heme Fe(III)/Fe(II) couple varied linearly with the increase of pH in the range of 5.0-10.0 with a slope of 49.44 mV pH(-1), which suggests that a proton transfer is accompanied with each electron transfer (ET) in the electrochemical reaction. The immobilized Hb displayed the features of peroxidase and gave excellent electrocatalytic performance to the reduction of O2, NO2(-) and H2O2. The calculated apparent Michaelis-Menten constant was 8.98 x 10(-4)M, which indicated that there was a large catalytic activity of Hb immobilized on CPE by sol-gel film toward H2O2. In comparison with other electrodes, the chemically modified electrodes, used in this direct electrochemical study of Hb, are easy to be fabricated and rather inexpensive. Consequently, the Hb/sol-gel film modified electrode provides a convenient approach to perform electrochemical research on this kind of proteins. It also has potential use in the fabrication of the third generation biosensors and bioreactors.