Myoglobin within graphene oxide sheets and Nafion composite films as highly sensitive biosensor

A highly sensitive biosensor was fabricated by incorporating myoglobin (Mb) within graphene oxide (GO) sheets and Nafion composite films. The stable composite Mb–GO–Nafion films were characterized by electrochemistry, scanning electron microscopy, Fourier transform infrared spectroscopy and UV–vis spectroscopy. It was found that Mb in Mb–GO–Nafion films retained its secondary structure similar to its native states. Cyclic voltammetry of Mb–GO–Nafion films showed a pair of well defined, quasi-reversible peaks at about −0.312 V vs saturated calomel electrode (SCE) at pH 5.5, corresponding to direct electron transfer (DET) between Mb and the glassy carbon electrode. Electrochemical parameter of Mb in Mb–GO–Nafion film such as apparent heterogeneous electron transfer rate constant (ks) and formal potential (Eo′) were obtained. The dependence of Eo′ on solution pH indicated that the DET reaction of Mb was coupled with proton transfer. Mb in the films displayed good electrocatalytic activities towards various substrates such as hydrogen peroxide, nitrite and oxygen, indicating that the composite films have potential applications in fabricating novel biosensors without using mediators.