Direct Electrochemistry and Electrocatalysis of Hemoglobin Immobilized on the Functionalized Graphene-Carbon Nanotube Composite Film

The direct electrochemistry of hemoglobin (Hb) immobilized on the designed carboxyl functionalized polystyrene/graphene-carbon nanotube-Nafion modified indium tin oxide (PS/GE-CNT-Nafion/ITO) electrode and its electrocatalysis for hydrogen peroxide (H2O2) were investigated. UV-visible and Fourier-transform infrared spectra of the resulting Hb-PS/GE-CNT-Nafion composite film suggested that the immobilized Hb retained its original structure. The direct electron transfer behaviors of Hb at the Hb-PS/GE-CNT-Nafion/ITO electrode were investigated by cyclic voltammetry in which a pair of well-defined, quasi-reversible redox peaks with the formal potential (E0') of -0.249 V (vs. SCE) in phosphate buffer solution (0.05 M, pH 7.0) was obtained. The proposed ITO modified electrode exhibited an excellent electrocatalytic activity to the reduction of H2O2, and the peak currents were linearly related to H2O2 concentration in a wider linearity range from 5.0 x 10(-7) to 1.4 x 10(-3) M with a correlation coefficient of 0.9983 and a detection limit of 2.0 x 10(-7) M (S/N = 3). The sensitivity and the apparent Michaelis-Menten constant (K-M(app)) were determined to be 59.1 mu A center dot mM(-1) and 8.3 x 10(-5) M, respectively. It is expected that the synergetic effects of GE-CNT hybrid materials and functionalized PS provide a general platform for studying of the electron transfer of redox proteins and the design of novel biosensors. (C) 2012 The Electrochemical Society. [DOI:10.1149/2.070206jes] All rights reserved.