Direct electrochemistry and enhanced electrocatalytic activity of hemoglobin entrapped in graphene and ZnO nanosphere composite film

A biocomposite film for sensing hydrogen peroxide (HP) is described that is based on nanospheres made from hemoglobin (Hb), graphene, and zinc oxide. The composition, morphology and size of the film were studied by transmission electron microscopy. UV-vis spectroscopy revealed that the Hb entrapped in the graphene and ZnO nanosphere retains its native structure. A pair of stable and well-defined quasi-reversible redox peaks of Hb was obtained, with a formal potential of -30 mV at pH 6.5. Hb exhibits excellent long-term bioelectrocatalytic activity towards HP. The apparent heterogeneous electron transfer rate constant is 1.0 s(-1), indicating that the presence of graphene in the composite film facilitates the electron transfer between matrix and the electroactive center of Hb. The sensor responds linearly to HP in the range from 1.8 mu M to 2.3 mM, with a detection limit of 0.6 mu M (at S/N=3). The apparent Michaelis-Menten constant is 1.46 mM. The biosensor displays high sensitivity, good reproducibility, and long-term stability.