Direct electrochemistry and electrocatalysis of heme proteins immobilised in carbon-coated nickel magnetic nanoparticle–chitosan–dimethylformamide composite films in room-temperature ionic liquids

• The electrochemistry of heme proteins were investigated in nonaqueous conditions.
• The sensors displayed low detection limit and improved sensitivity for H2O2.
• Some electrochemical and kinetic parameters for heme proteins were calculated.
• The biosensors posed good reproducibility and storage stability.

The direct electrochemistry and electrocatalysis of heme proteins entrapped in carbon-coated nickel magnetic nanoparticle–chitosan–dimethylformamide (CNN–CS–DMF) composite films were investigated in the hydrophilic ionic liquid [bmim][BF4]. The surface morphologies of a representative set of films were characterised via scanning electron microscopy. The proteins immobilised in the composite films were shown to retain their native secondary structure using UV–vis spectroscopy. The electrochemical performance of the heme proteins–CNN–CS–DMF films was evaluated via cyclic voltammetry and chronoamperometry. A pair of stable and well-defined redox peaks was observed for the heme protein films at formal potentials of − 0.151 V (HRP), − 0.167 V (Hb), − 0.155 V (Mb) and − 0.193 V (Cyt c) in [bmim][BF4]. Moreover, several electrochemical parameters of the heme proteins were calculated by nonlinear regression analysis of the square-wave voltammetry. The addition of CNN significantly enhanced not only the electron transfer of the heme proteins but also their electrocatalytic activity toward the reduction of H2O2. Low apparent Michaelis–Menten constants were obtained for the heme protein–CNN–CS–DMF films, demonstrating that the biosensors have a high affinity for H2O2. In addition, the resulting electrodes displayed a low detection limit and improved sensitivity for detecting H2O2, which indicates that the biocomposite film can serve as a platform for constructing new non-aqueous biosensors for real detection.