Direct electrochemistry and electrocatalysis of hemoglobin in composite film based on ionic liquid and NiO microspheres with different morphologies

Flowerlike, spherical, and walnutlike NiO microspheres were respectively mixed with ionic liquid (IL) to form three stable composite films, which were used to immobilize hemoglobin (Hb) on carbon paste electrodes. Spectroscopic and electrochemical examinations revealed that the three NiO/IL composites were biocompatible matrix for immobilizing Hb, which showed good stability and bioactivity. However, electrochemical studies demonstrated that flowerlike NiO microspheres were far more effective than the other two in adsorbing Hb and facilitating the electron transfer between Hb and underlying electrode, which resulted from its unique flower architecture and large surface area. With advantages of flowerlike NiO and ionic liquid, a pair of stable and well-defined quasi-reversible redox peaks of Hb were obtained with a formal potential of −0.275 V (vs. Ag/AgCl) in pH 7.0 buffer. Meantime, flowerlike NiO modified electrode showed better electrocatalytic activity toward hydrogen peroxide reduction with a high sensitivity (15.7 μA mM−1), low detection limit (0.68 μM) and small apparent Michaelis–Menten constant KM (0.18 mM). Flowerlike NiO could be a promising matrix for the fabrication of direct electrochemical biosensors in biomedical analysis.