ZnO nanoparticle and multiwalled carbon nanotubes for glucose oxidase direct electron transfer and electrocatalytic activity investigation

A new amperometric enzyme biosensor for the determination of glucose has been constructed. Firstly, multiwalled carbon nanotubes (MWCNTs) were modified on the surface of a glassy carbon electrode (GCE). Then, the first layer of glucose oxidase (GOx) was assembled onto it. Subsequently, ZnO nanoparticles (nano-ZnO) were electrodeposited onto the electrode to immobilize the second layer of GOx. The assembly processes were characterized with cyclic voltammetry (CV), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The direct electron transfer (DET) of immobilized GOx displays a pair of well defined and nearly reversible redox peaks with a formal potential (E0′) of −0.434 V in pH 7.0 phosphate buffer solution. The electrochemical parameters including apparent heterogeneous electron transfer rate constant (ks), charge transfer coefficient (α) and surface coverage (Γ) were estimated. The proposed enzyme biosensor showed a rapid and highly sensitive amperometric response to glucose in the range of 6.67 μM to 1.29 mM with a detection limit of 2.22 μM (S/N = 3). The apparent Michaelis–Menten constant ( K M app ) was calculated to be 2.48 mM. Furthermore, the biosensor showed an acceptable stability and reproducibility.