Direct electrochemistry of myoglobin based on ionic liquid–clay composite films

The direct electron transfer of myoglobin (Mb) was realized by immobilizing Mb onto ionic liquid (1-butyl-3-methyl imidazolium tetrafluoraborate, [bmim][BF4])–clay composite film modified glassy carbon electrode. A pair of well-defined redox peaks of Mb with a formal potential (Eo′) of −0.297 V (vs. Ag/AgCl) was observed in 0.1 M phosphate buffer solution (pH 6.0). The ionic liquid–clay composite film showed good biocompatibility and an obvious promotion capability for the direct electron transfer between Mb and electrode. The electron transfer rate constant (ks) of Mb was calculated to be (3.58 ± 0.12) s−1. UV–vis spectrum suggested that Mb retained its native conformation in the ionic liquid–clay system. Basal plane spacing of clay obtained by X-ray diffraction (XRD) indicated that there was an intercalation–exfoliation–restacking process, in ionic liquid and clay during the drying process of the modification, and the ionic liquid played the key role for promotion of the direct electron transfer between Mb and the ionic liquid–clay composite film modified electrode. The biocatalytic activity of Mb in the composite film was exemplified by the reduction of hydrogen peroxide. Under the optimal conditions, the reduction peak currents of Mb increased linearly with the concentration of H2O2 in the range of 3.90 × 10−6 to 2.59 × 10−4 M, with a detection limit of 7.33 × 10−7 M. The kinetic parameter Imax and the apparent Michaelis constant (Km) for the electrocatalytic reactions were 3.87 × 10−8 A and 17.6 μM, respectively. The proposed method would be valuable for the construction of a new third-generation H2O2 sensor.