(315a) Development of Chemically Modified Graphene Quantum Dots-Carbon Nanotubes Hybrid Material for the Electrochemical Detection of Dopamine, Uric Acid, and Ascorbic Acid

Dopamine is a crucial catecholamine neurotransmitter that governs vital body functions and serves as a stress biomarker. Abnormality in dopamine levels could reflect cardiotoxicity and neurological disorders. Hence, accurate detection and monitoring of dopamine concentration both in vivo and in vitro is important both academically and clinically. Tremendous efforts have been put into designing different electrode modifiers to enhance sensitivity and selectivity, such as enzymes, antibodies, molecularly imprinted polymers, and colloidal nanoparticles. Among them, carbon nanostructures offer strong potential due to its abundance, biocompatibility, good electrical conductivity and chemical tunability. However, there is a trade-off between electrochemical activity from structural defects and high electrical conductivity from defect-free structures, and it persists to be an issue to be addressed effectively.

In this study, GQDs were synthesized by a top-down method and characterized with AFM, FT-IR, UV-Vis, raman spectroscopy, and fluorometer. The GQDs are then grafted onto acid-treated MWCNT (TDGQD@a-MWCNT) via π-π interactions by ultrasonication and drop-casted onto glassy carbon electrodes to fabricate an electrochemical sensor. Electrochemical (EC) reduction of TDGQD@a-MWCNT was conducted by cyclic voltammetry (CV), and dopamine response was obtained by differential pulse voltammetry (DPV). The dopamine response enhanced by 10-fold, exceeding that of just the a-MWCNT. Electrochemical characterization results attributed the enhanced performance to a lowered charge transfer resistance (R_ct), higher double layer capacitance (C_dl) and electrochemically active surface area (ECSA). Moreover, we showed experimentally that an optimal reduction potential window exists, and the approach works for uric acid and ascorbic acid as well. We hypothesized that while the abundant oxygen-containing functional groups on the GQDs provide adsorption sites for analytes, they also hinder electron transport between the CNT and GQD. The EC reduction step enhances the π-π interaction between the materials, creating an electronic skin on a conductive substrate, which is a potential pathway to facile fabrication of modular sensing units for a sensor array.