Engineered plasmonic copper (II) sulfide-wrapped polystyrene nanoparticles for spectroscopic detection of mercury ions.

We report a novel and highly effective UV-Vis sensing platform based on plasmonic copper (II) sulfide-capsulated polystyrene nanoparticles (PS@CuS NPs) for the rapid, ultrasensitive, and selective detection of Hg . The detection mechanism is driven by a specific anion-exchange reaction between Hg and CuS, resulting in the in-situ transformation of plasmonic CuS into non-plasmonic HgS, which induces a distinct and quantifiable shift in UV-Vis absorption. This structural and optical evolution enables the platform to achieve an exceptionally low detection limit of 20 pM within just 5 min, far below most regulatory thresholds, and a wide linear detection range from 20 pM to 30 nM. Importantly, the engineered PS@CuS NPs exhibit remarkable selectivity, maintaining consistent performance in the presence of common coexisting metal ions such as Pb, Sn, K, Zn, Cd, Mn, Fe, Ni, Co, Mg, and Cu, making it suitable for use in complex environmental matrices. Practical utility was validated through successful detection of Hg in real water samples, including tap and river water, with high recovery rates ranging from 94 % to 105 %. Compared to conventional detection methods, this platform offers a compelling combination of speed, sensitivity, selectivity, and simplicity. Overall, this work represents a significant advancement in UV-Vis-based heavy metal sensing and provides a promising tool for real-time, on-site environmental monitoring of toxic mercury ions.