Direct electrochemistry of hemoglobin immobilized on the water-soluble phosphonate functionalized multi-walled carbon nanotubes and its application to nitric oxide biosensing

The direct electron transfer and electrocatalysis of hemoglobin (Hb) immobilized on the phosphonate functionalized multi-walled carbon nanotubes (MWCNTs) are investigated. Fourier transform infrared (FT-IR) spectra, UV–vis spectra and cyclic voltammetry (CV) analyses reveal that the phosphonate functionalized MWCNTs have good biocompatibility for Hb immobilization, and promote the electron communication between Hb and electrode. The immobilized Hb shows a pair of redox peak with a formal potential of −406±10 mV (vs. SCE) and the electrochemical behavior of Hb was a surface-controlled process in a pH 7.0 phosphate buffer solution. And the immobilized Hb can act in an electrocatalytic manner in the electrochemical reduction of nitric oxide (NO). Accordingly, an unmediated NO electrochemical biosensor is constructed. Under optimized experimental conditions, the NO electrochemical biosensor shows the fast response (less than 3 s), the wide linear range (1.5×10−7 to 2.7×10−4 M) and the low detection limit (1.5×10−8 M), which is attributed to the good mass transport, the large Hb loading per unit area and the fast electron transfer rate of Hb.