Fabrication of CuO-CG nanocomposites modified electrode and its application in sunset yellow detection

Abstract: Sunset yellow is a common synthetic colorant in food processing, in order to maintain the orange color of foods. However, excessive consumption of sunset yellow can be harmful to human health, and even cause some symptoms, such as allergies, asthma, diarrhea, and cancer, due to the azo group and benzene ring. It is necessary to establish a fast, sensitive, and accurate analysis for the kind of colorant, in order to prevent and avoid the risks to food safety from the abuse of sunset yellow. In this study, a novel electrochemical sensor was developed to detect sunset yellow using copper oxide-carboxylated graphene (CuO-CG) nanocomposites modified glassy carbon electrode. Electrochemical deposition of CG and Cu was also performed on the surface of a bare glassy carbon electrode in sequence, followed by in situ oxidization of the Cu film to form the CuO layer. Cyclic voltammetry and chronoamperometry were selected to determine the electrochemical oxidation behaviors of sunset yellow on the surface. An outstanding peak was observed at 0.52 V during sunset yellow oxidation. The peak current value was 74.6-fold higher than that of the bare glassy carbon electrode, indicating the better performance of the electrochemical sensor. The experimental conditions were also optimized to obtain a sensitive response using chronoamperometry. Some parameters were utilized to verify the electrochemical detection of sunset yellow, including the deposition order of the electrode materials of CuO and CG, the deposition time and deposition voltage of CG and Cu, the concentration of sodium hydroxide, and the applied voltage for the detection. An optimal combination of experimental conditions was obtained to investigate the analytical performances of the electrochemical sensor, such as response time, linear range, detection limit, reproducibility, stability, selectivity, and accuracy. The results showed as follows. (1) The optimal deposition order was the CG followed by the CuO. The optimal deposition time and deposition voltage of CG and Cu were 900 s and -1.4 V, and 120 s and -1.1 V, respectively. The optimal concentration of sodium hydroxide was 0.10 mol/L, and the optimal applied voltage was 0.55 V to detect the sunset yellow using chronoamperometry. (2) The response time was within 5 s for the developed electrochemical sensor towards sunset yellow detection, indicating a faster response than before. The oxidation current of sunset yellow increased linearly with the increase of the concentration in the range of 0.20 μg/mL- 4.07 mg/mL. The detection limit was 79.36 ng/mL for the electrochemical sensor on sunset yellow. (3) This electrochemical sensor was further used to detect the concentration of sunset yellow in drink samples. There were no complicated sample processing steps during detection. The obtained recoveries using the standard addition method were in the range of 99.35%-105.88%, indicating successful trace detection of sunset yellow in real samples. The developed CuO-CG nanocomposites modified electrode-based electrochemical sensor presented a short response time, wide linear range, low detection limit, as well as high reproducibility, stability, selectivity, and accuracy.