Direct Electrochemistry of Hemoglobin on Graphene Nanosheet-based Modified Electrode and Its Electrocatalysis to Nitrite

A novel amperometric nitrite (NO2 − ) sensor was developed based on immobilization of hemoglobin (Hb) on a graphene nanosheet modified electrode by chitosan-N, N-Dimethylformamide (CS-DMF) hydrogel. The surface morphologies of the modified electrode were characterized by SEM, and direct electrochemistry of Hb on the graphene nanosheet-based electrode were investigated by cyclic voltammetry. The results indicated that Hb immobilized on the surface of the graphene modified electrode could keep its bioactivity, exhibited a surface-controlled electrochemical process and had a fast heterogeneous electron transfer rate with the rate constant (ks) of 58.77 s −1 . Moreover, the resulting biosensor showed excellent electrocatalytic activities toward nitrite reduction with a low detection limit of 1.8×10 −7 M and a small apparent Michaelis-Menten constant (km) up to 12 μM. The good performance of the proposed sensor is attributed to excellent conductivity and electron mobility of graphene, and good biocompatibility of chitosan, which enhances the Hb content and promotes direct electron transfer between redox Hb and the surface of