A novel enzymatic glucose biosensor and sensitive non-enzymatic hydrogen peroxide sensor based on graphene and cobalt oxide nanoparticles composite modified glassy carbon electrode

In the present study, we have demonstrated the fabrication of novel enzymatic glucose biosensor using glucose oxidase (GOD) as a model enzyme which has been immobilized onto the graphene (GF) and cobalt oxide nanoparticles (Co₃O₄-NPs) composite modified electrode. The GF/Co ₃O₄-NPs composite was prepared by hydrothermal method and characterized by using scanning electron microscopy, X-ray diffraction and elemental analysis. The GOD immobilized GF/Co₃O₄-NPs modified electrode shows a well defined redox behaviour indicating the reversible proton and electron transfer reaction of GOD. A heterogeneous electron transfer rate constant (K_s) of immobilized GOD has been calculated to be 3.52 s^-1 which is much higher than that of GOD immobilized GF supports. The fast electron transfer of GOD is attributed to the excellent biocompatibility of Co₃O₄-NPs and high conductivity of the GF. The fabricated glucose biosensor exhibits a wider linear response for glucose from 0.5 mM to 16.5 mM with the sensitivity of 13.52 μA mM^-1 cm^-2. In addition, a non-enzymatic H ₂O₂ sensor has been further developed using GF/Co ₃O₄-NPs composite modified electrode. The GF/Co ₃O₄-NPs composite electrode shows an excellent electrocatalytic activity towards H₂O₂ with the response time of <10 s. The H₂O₂ response at GF/Co ₃O₄-NPs composite modified electrode displays a linear response ranging from 0.2 to 211.5 μM with a limit of detection of 0.06 μM.