(494d) Development of Chemically Modified Graphene Quantum Dots-Carbon Nanotubes Hybrid for Simultaneous Electrochemical Detection of Dopamine, Uric Acid, and Ascorbic Acid

An electrochemical sensor capable of simultaneous detection of dopamine, uric acid, and ascorbic acid is developed using functionalized graphene quantum dots (GQDs) grafted onto multi-walled carbon nanotubes (MWCNT). Dopamine, a biochemical belonging to the catecholamine family, acts as both hormone and neurotransmitter in our bodies. Abnormality in dopamine levels could indicate diseases such as Parkinson’s disease, schizophrenia, etc. Hence, it is crucial to accurately monitor dopamine concentration both in vivo and in vitro. Tremendous efforts have been put into designing different electrochemically active materials to achieve optimal selectivity since the electrochemical detection of dopamine is sometimes obscured by the presence of ascorbic acid and uric acid due to their similar chemical structures, resulting in overlapping oxidation potential. Nevertheless, how these three biochemicals react with the electrode’s active sites is seldom discussed in detail.

In this study, GQDs with different chemical modifications and heteroatom doping are synthesized and characterized with AFM, SEM, FT-IR, UV-Vis and Fluorometer. The GQDs are then grafted onto MWCNT via π-π interactions by ultrasonication and drop-casted onto glassy carbon electrodes to fabricate the electrochemical sensor. The effects of functional groups and heteroatom doping on overpotential and sensor sensitivity are systematically investigated using voltametric techniques such as cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Results showed that the abundant oxygen-containing functional groups on the GQDs would decrease sensor performance and can be restored through in situ electrochemical reduction. Additionally, GQDs prepared with carbon black and glucose also showed distinct overpotentials for ascorbic acid, while maintaining dopamine and uric acid overpotential. Combined with FT-IR results, it can be inferred that the carboxylic groups play an important role in ascorbic acid oxidation, possibly due to a local pH effect. This material system not only offers great sensitivity and selectivity, but also provides deeper mechanistic insights for the simultaneous detection of dopamine, ascorbic acid, and uric acid.