A novel nitrite biosensor was constructed by simultaneous immobilization of hemoglobin (Hb) and a room temperature ionic liquid, octylpyridinium chloride ([OcPy][Cl]), on multi-walled carbon ionic liquid electrode (MWILE). The direct electron transfer of Hb showed a pair of redox peaks with a formal potential of -0.187 V vs. Ag/AgCl in pH 5.0 acetate buffer solution. Nitrite (NO2_) catalysis on the modified electrode was investigated by cyclic voltammetry and amperometry. The biosensor exhibited a wide linear range for NO2_ detection from 0.01 to 15 mM, with a detection limit (3σ) of 1.46 µM. MWILE provided an excellent matrix for protein immobilization and biosensor fabrication which could be used for the determination of NO2_ with a low detection limit, fast response, long linearity, and excellent sensitivity.
