Immobilization, Direct Electrochemistry and Electrocatalysis of Hemoglobin on Peptide-Carbon Nanotube Modified Electrode

The direct electrochemistry of hemoglobin (Hb) immobilized on a glassy carbon electrode (GCE) by mixing with a hybrid dispersion of self-assembling peptide EFK8 and single-walled carbon nanotubes (SWNT) was investigated and shown to have effective properties as a biosensor for hydrogen peroxide (H2O2). Preliminary experiments involving cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) showed that the presence of SWNTs in the modifying peptide layer on GCE significantly enhanced the electrochemical response of the electrode for the ferricyanide/ferrocyanide redox couple. Also, when more layers of the peptide-SWNT dispersion were applied to the surface, the electrochemical response of the GCE was further increased. This behavior was then exploited to fabricate a biosensor for H2O2 by mixing hemoglobin with the hybrid peptide-SWNT dispersion and casting this mixture on a glassy carbon electrode. AFM imaging, CV and EIS analysis revealed successful immobilization of Hb on the electrode and the ability of the electrode to enable direct electron transfer from Hb to the electrode surface. In particular, CVs obtained in 0.1M PBS (pH 7.0) showed that the immobilized Hb retained its bio-catalytic activity for Fe ions, indicating that it had not denatured and the hybrid layer remained biocompatible with Hb. Furthermore, this electrode was found to accurately measure the H2O2 concentration over the range from 20 to 9.6x102 M in 0.1M PBS (pH 7.0) under mediatorless conditions using both CV and amperometry techniques. In this way, the EFK8-SWNT hybrid layer shows promise as a biocompatible layer for simple non-covalent enzyme immobilization and the basis of a mediatorless biosensor.