N-Doped Reduced Graphene Oxide/Gold Nanoparticles Composite as an Improved Sensing Platform for Simultaneous Detection of Dopamine, Ascorbic Acid, and Uric Acid

Gold nanoparticles (AuNPs) were homogeneously electrodeposited on nitrogen-doped reduced graphene oxide (N-rGO) to modify a glassy carbon electrode (GCE/N-rGO-Au) in order to improve the simultaneous detection of dopamine (DA), ascorbic acid (AA), and uric acid (UA). N-rGO was prepared by the hydrothermal treatment of graphene oxide (GO) and urea at 180 °C for 12 h. AuNPs were subsequently electrodeposited onto the surface of GCE/N-rGO using 1 mM HAuCl(4) solution. The morphology and chemical composition of the synthesized materials were characterized by field-emission scanning electron microscopy and X-ray photoelectron spectroscopy. The electrochemical performance of the modified electrodes was investigated through cyclic voltammetry and differential pulse voltammetry measurements. Compared to GCE/rGO-Au, GCE/N-rGO-Au exhibited better electrochemical performance towards the simultaneous detection of the three analytes due to the more homogeneous distribution of the metallic nanoparticles as a result of more efficient anchoring on the N-doped areas of the graphene structure. The GCE/N-rGO-Au-based sensor operated in a wide linear range of DA (3–100 µM), AA (550–1500 µM), and UA (20–1000 µM) concentrations with a detection limit of 2.4, 58, and 8.7 µM, respectively, and exhibited satisfactory peak potential separation values of 0.34 V (AA-DA), 0.20 V, (DA-UA) and 0.54 V (AA-UA). Remarkably, GCE/N-rGO-Au showed a very low detection limit of 385 nM towards DA, not being susceptible to interference, and maintained 90% of its initial electrochemical signal after one month, indicating an excellent long-term stability.