A cost-effective disposable graphene-modified electrode decorated with alternating layers of Au NPs for the simultaneous detection of dopamine and uric acid in human urine

A disposable electrode based on a highly sensitive and readily fabricated arrangement of alternating AuNP and graphene layers was introduced for the simultaneous determination of dopamine and uric acid. The process by which the disposable electrodes were fabricated is simple, fast, and accomplished through the direct electrochemical reduction of graphene oxide and Au(III) onto a graphite pencil electrode surface. Extraordinary electrocatalytic activities of the graphene nanocomposite were observed in the presence of dopamine and uric acid. The synthesized graphene oxide was characterized by Raman and FTIR spectroscopy. The surface morphology, elemental, and electrochemical characterization of the bare and modified electrodes were analyzed by field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Good linear sensitivity was obtained over the ranges of 0.1-25 mu M for dopamine and 0.09-25 mu M for uric acid under optimal conditions using square wave voltammetry. Very low limits of detection of 0.024 mu M (dopamine) and 0.029 mu M (uric acid) were attained from the fabricated electrochemical sensors. The dopamine and uric acid peak separation was 151 mV. The graphene nanocomposite on the GPE surface effectively improved the peak separation, electroactive surface area, sensitivity, selectivity, and reproducibility. The fabricated electrode behaved well in the presence of high concentrations of ascorbic acid and in the presence of other potentially interfering compounds. The electrochemical sensors did not undergo surface fouling, particularly in the presence of dopamine, which tends to severely foul surfaces after a single measurement. The cost effectiveness of the sensor, the short fabrication time, and the lack of surface fouling, especially in the presence of dopamine, render these novel electrodes both multi-use and disposable.