Direct Electrochemistry and Electrocatalysis of the Hemoglobin Immobilized on Diazonium-Functionalized Aligned Carbon Nanotubes Electrode

A simple and efficient electrochemical method is utilized to functionalize aligned carbon nanotubes (ACNTs) by the electrochemical reduction of 4-carboxyphenyl diazonium salt. Thus hemoglobin (Hb) molecules were covalently immobilized on the diazonium-ACNTs surface via carbodiimide chemistry. Direct electrochemistry and bio-electrocatalytic activity of the immobilized Hb were then investigated by cyclic voltammetry (CV) and amperometry techniques. It is showed that the Hb film on the diazonium-ACNTs electrode had well-defined redox peaks with a formal potential (E degrees) at - 312 mV (vs. Ag/AgCl), and the Hb-ACNTs electrode displayed good electrocatalytic activity to H2O2 reduction. Owing to the high Hb covering on the ACNTs surface (Gamma* = 2.7 x 10(-9) mol cm(-2)), the catalytic current were significantly improved when compared to the current measured at an Hb-tangled carbon nanotubes electrode. The Hb-ACNTs electrode exhibited high sensitivity, long-term stability and wide concentration range from 40 mu M to 3 mM for the amperometric detection of H2O2. The heterogeneous reaction rate constant (k(s)) was 0.95 +/- 0.05 s(-1) and the apparent Michaelis-Menten constant (K-m(app)) was 0.15 mM.