A gold electrode modified with hemoglobin and the chitosan@Fe3O4 nanocomposite particles for direct electrochemistry of hydrogen peroxide

We report on a novel electrochemical biosensor that was fabricated by immobilizing hemoglobin (Hb) onto the surface of a gold electrode modified with a chitosan@Fe3O4 nano-composite. The Fe3O4 nanoparticles were prepared by co-precipitation and have an average size of 25 nm. They were dispersed in chitosan solution to obtain the chitosan@Fe3O4 nano-composite particles with an average diameter of 35 nm as verified by transmission electron microscopy. X-ray diffraction patterns and Fourier transform IR spectroscopy confirmed that the crystallite structure of the Fe3O4 particles in the nano-composite has remained unchanged. At pH 7.0, Hb gives a pair of redox peaks with a potential of about -0.21 V and -0.36 V. The Hb on the film maintained its biological activity and displays good electrocatalytic reduction activity towards hydrogen peroxide. The linear range for the determination of H2O2 is from 2.3 mu M to 9.6 mM, with a detection limit at 1.1 mu M concentration (at S/N = 3). The apparent Michaelis-Menten constant is 3.7 mM and indicates the high affinity of Hb for H2O2. This biosensor also exhibits good reproducibility and long-term stability. Thus, it is expected to possess potential applications in the development of the third-generation electrochemical biosensors.