Rapid and clean amine functionalization of carbon nanotubes in a dielectric barrier discharge reactor for biosensor development

Multiwalled carbon nanotubes (MWCNTs) were amine-functionalized using the process of dielectric barrier discharge (DBD) plasma treatment. The scanning electron microscope micrographs and Fourier transform infra-red spectroscopy clearly demonstrated that the carbon skeleton structure of the plasma-treated MWCNTs was preserved and amine groups were coupled to MWCNTs during this process. The amine-functionalized MWCNTs were then fixed on glassy carbon (GC) electrode and glucose oxidase (GOX) as a model enzyme was immobilized on the modified GC electrode. Direct electron transfer between the redox active center of the immobilized GOX and the plasma-treated MWCNTs was investigated through cyclic voltammetry. The well-defined, quasi-reversible redox peaks of the immobilized GOX revealed that GOX retained its activity such that it could specifically catalyze the oxidation of glucose with great efficiency. The obtained enzyme electrode was used for glucose biosensing with the linear range from 17 to 646 μM and sensitivity of 12.3 μA/mM cm2. Based on the signal to noise ratio of 3, the detection limit was estimated to be 9 μM. The Michaelis-Menten constant for immobilized GOX was as low as 480 μM.