Electrochemical sensors based on graphene/silver sulfide nanocomposites for the indirect detection of mercury sulfide in the Tibetan medicine "Zuo Tai".

Mercury sulfide (HgS) is one of the primary constituents of the Tibetan medicine "Zuo Tai," and its content directly impacts the drug's efficacy and safety. Therefore, developing rapid, direct, and highly sensitive detection methods is of significant importance. In this study, a novel electrochemical sensor based on graphene/silver sulfide (G/Ag2S) nanocomposites was developed for the rapid detection of HgS in Tibetan medicine "Zuo Tai." The G/Ag2S nanocomposite was prepared using the hydrothermal synthesis method. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) analysis indicated that the G/Ag2S nanocomposite enhanced the electrochemical signal response and improved the electrochemical activity of the glassy carbon electrode (GCE) after modification. Under optimized conditions, linear detection of HgS was achieved using differential pulse voltammetry (DPV). The DPV oxidation peak current decreased with increasing HgS concentration due to its adsorption onto the G/Ag2S-modified electrode, which altered the redox properties. The detection range of this analytical method was 0.1-10 mg/L, with a detection limit of 0.0194 mg/L. Further studies revealed that the modified electrode prepared in this paper exhibited excellent selectivity toward HgS. When detecting the HgS content in the "Zuo Tai" sample, the sensor demonstrated high sensitivity, with an average HgS content of 54.38 % in the sample and a relative standard deviation (RSD) of 1.07 %, consistent with the results reported in the literature. This analytical method provides a rapid and reliable quality control method for traditional medicines containing HgS.