H2O/air plasma-functionalized carbon nanotubes decorated with MnO2 for glucose sensing

Abstract

Multi-walled carbon nanotubes (MWCNTs) were functionalized using dielectric barrier discharge plasma in water vapor-saturated air at 70 °C. MnO₂ was deposited on the MWCNTs by chronoamperometry, followed by glucose oxidase (GOx) immobilization, and the resulting GOx/MnO₂/MWCNTs electrode was used for electrochemical detection of glucose. Structural, morphological, and elemental microanalysis was performed. Plasma-induced oxygen-based functional groups were confirmed on the MWCNT surfaces and improved their dispersion in aqueous solutions. The maximum amount of these groups was created at the optimum exposure time of 4 min. The GOx immobilized on the MnO₂/MWCNTs hybrid showed a well-defined, reversible and surface-controlled redox wave around −0.45 V and a peak to peak separation of 0.04 V. The coefficient and rate constant for electron transfer of GOx were calculated as 0.41 and 1.08 s⁻¹, respectively. The GOx/MnO₂/MWCNT-modified electrode exhibited a linear behavior in the range of 0.1–3.2 mM glucose concentration with the competitive detection limit of 3.0 μM and a sensitivity of 24.2 μA mM⁻¹ cm⁻². This highly-stable glucose sensing electrode retained more than 76% of its initial faradic current value after 71 days. These results are relevant to the development of next-generation glucose sensors for diverse health- and food-related applications.