Gold Electrode Modified with an Alloy of Silver Nanoparticles and Cysteine-Coated Carbon Quantum Dots for the Electrochemical Detection of Melamine

This study focuses on the development of a chemical electrode sensor for detecting melamine in powdered milk. The work in this study first involved fabricating the electrochemical sensor by modifying a gold electrode with an alloy of silver nanoparticles and carbon quantum dots functionalized with L-cysteine. This new electrode was then tested using cyclic voltammetry and subsequently pulsed differential voltammetry for melamine detection. This study is part of a doctoral thesis conducted at the Doctoral School of Science, Technology and Sustainable Agriculture at Félix Houphouët-Boigny University in Abidjan, Ivory Coast. To achieve our objectives, firstly, L-cysteine ​​functionalized carbon quantum was synthesized hydrothermally from calcined lemon peel mixed with L-cysteine ​​(cCDs). Once obtained, silver nanoparticles were synthesized in the presence of cCDs (cCDs/AgNPs), and this nanomaterial alloy was then used to modify a gold electrode to obtain our working electrode: cCDs/AgNPs/Au. Secondly, the newly fabricated electrode was applied for the electrochemical detection of melamine, both in isolation and in samples of locally consumed powdered milk. This electrochemical activity between the new electrode and melamine is only possible in sodium sulfate solution and is optimized at a concentration of 0.1 M at pH 7.5, with a scan rate of 50 mV/s during the voltammetric cycles. Furthermore, the pulsed differential voltammetry study, conducted under optimal cyclic voltammetry conditions, demonstrated the linearity of melamine detection by this new electrode. This study, carried out on a range of melamine concentrations from 5 ng/mL to 50 ng/mL, established a limit of detection of 3.488 µg/L and a limit of quantification of 11.627 µg/L. Performance analysis revealed a recovery rate between 98% and 100% in the absence of interfering substances, and between 90% and 98% in a food matrix such as powdered milk with a soluble solids (RSD) content of less than 8%. The cCDs/AgNPs/Au working electrode showed strong sensitivity with melamine dissolved in the different samples tested; however, further studies could help improve the selectivity of the new electrode with certain mineral salts used to enrich powdered milks.