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

• Direct electrochemistry of GOD has been achieved at graphene-Co3O4 nanoparticles composite modified electrode.
• The GF-Co3O4 nanoparticles composite has been synthesized by hydrothermal method.
• A novel glucose biosensor has been constructed using GOD as a model enzyme.
• The non-enzymatic H2O2 sensor has been developed using GF-Co3O4 composite modified 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/Co3O4-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 (Ks) 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 H2O2 sensor has been further developed using GF/Co3O4-NPs composite modified electrode. The GF/Co3O4-NPs composite electrode shows an excellent electrocatalytic activity towards H2O2 with the response time of <10 s. The H2O2 response at GF/Co3O4-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.