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

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^2 + . The detection mechanism is driven by a specific anion-exchange reaction between Hg²⁺ 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 Pb²⁺, Sn²⁺, K⁺, Zn²⁺, Cd²⁺, Mn²⁺, Fe³⁺, Ni²⁺, Co²⁺, Mg²⁺, and Cu²⁺, making it suitable for use in complex environmental matrices. Practical utility was validated through successful detection of Hg²⁺ 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.