A novel platform of hemoglobin on core–shell structurally Fe3O4@Au nanoparticles and its direct electrochemistry

A novel platform, which hemoglobin (Hb) was immobilized on core–shell structurally Fe3O4/Au nanoparticles (simplified as Fe3O4@Au NPs) modified glassy carbon electrode (GCE), has been developed for fabricating the third biosensors. Fe3O4@Au NPs, characterized using transmission electron microscope (TEM), scanning electron microscope (SEM) and energy dispersive spectra (EDS), were coated onto GCE mediated by chitosan so as to provide larger surface area for anchoring Hb. The thermodynamics, dynamics and catalysis properties of Hb immobilized on Fe3O4@Au NPs were discussed by UV–visible spectrum (UV–vis), electrochemical impedance spectroscopy (EIS), electrochemical quartz crystal microbalance technique (EQCM) and cyclic voltammetry (CV). The electrochemical parameters of Hb on Fe3O4@Au NPs modified GCE were further carefully calculated with the results of the effective working area as 3.61 cm2, the surface coverage concentration (Γ) as 1.07 × 10−12 mol cm−2, the electron-transfer rate constant (Ks) as 1.03 s−1, the number of electron transferred (n) as 1.20 and the standard entropy of the immobilized Hb (ΔS0′) as calculated to be −104.1 J mol−1 K−1. The electrocatalytic behaviors of the immobilized Hb on Fe3O4@Au NPs were applied for the determination of hydrogen peroxide (H2O2), oxygen (O2) and trichloroacetic acid (TCA). The possible functions of Fe3O4 core and Au shell as a novel platform for achieving Hb direct electrochemistry were discussed, respectively.

Research highlights
► In recent years, immobilization of biomolecule onto nanomaterials, which could be utilized in the investigation of biomolecule reactions and the preparations of the biosensors, has attracted much research attention. A novel platform, which hemoglobin (Hb) was immobilized on core–shell structurally Fe3O4/Au nanoparticles (simplified as Fe3O4@Au NPs) modified glassy carbon electrode (GCE), has been developed for fabricating the third biosensors in this paper.
► Magnetic NPs stand out because of their added properties. However, naked Fe3O4 NPs are very sensitive to oxidation because of their high chemical reactivity and being prone to aggregate. Those defects limit their further applications. We presented a simple approach to synthesize Au modified Fe3O4 NPs with core–shell structure, which was characterized by transmission electron microscopy, scanning electron microscope, energy dispersive spectra and UV–vis spectroscopy.
► The thermodynamics, dynamics and catalysis properties of Hb immobilized on Fe3O4@Au NPs were discussed by UV–visible spectrum, electrochemical impedance spectroscopy, electrochemical quartz crystal microbalance technique and cyclic voltammetry. The electrocatalytic behaviors of the immobilized Hb on Fe3O4@Au NPs were applied for the determination of hydrogen peroxide, oxygen and trichloroacetic acid. The possible functions of Fe3O4 core and Au shell as a novel platform for achieving Hb direct electrochemistry were also discussed, respectively.