Reversible metal–organic polymer template for enhanced platinum nanoparticle self-assemblies and accelerated POD-like catalysis for the rapid and ultrasensitive detection of multiple forms of mercury

Abstract

Monitoring the distribution characteristics of the various forms of mercury is crucial for understanding its biogeochemical cycling and assessing its health risks. The accurate detection of inorganic and organic mercury still relies on techniques requiring large instruments such as CVAAS, ICP-MS, and LC-ICP-MS. Although these traditional methods can accurately analyze and differentiate the different forms of mercury, their complexity, high cost, and inability to facilitate immediate on-site analysis at environmental sample locations represent significant limitations. Therefore, based on a reversible metal–organic polymer template for platinum nanoenzymes, we developed a colorimetric detection method that does not require sample pretreatment to rapidly and sensitively detect mercury in multiple forms. This method detected Hg²⁺ within a range of 0.001–5000 nM in 3 min, with a detection limit of 0.0006 nM (equivalent to 0.12 ng L⁻¹). Additionally, the total mercury content in samples could be quantified by this colorimetric method, enabling the precise analysis of organic mercury with an accuracy on par with traditional ICP-MS. Notable enhancements in sensitivity and analysis speed were demonstrated, which could be attributed to the distinct molecular structure of the PNAs(HCl). Studies on the reaction mechanisms revealed that the dense assembly of platinum nanoparticles within PNAs(HCl) and their porous external structure not only effectively protect the catalytic active sites and offer ample reaction space, thereby efficiently mimicking the POD-like enzymatic activity, but also facilitate effective and specific binding to Hg²⁺. To further affirm the reliability and practicality of this analysis method, a variety of real environmental water samples were evaluated, including from rivers, lakes, polluted waters, and garden soil extracts. The analytical data were consistent with those obtained from traditional ICP-MS analysis. Our results demonstrated that the PNAs(HCl)-based colorimetric method offers a rapid and precise technique for the analysis of Hg²⁺ and organic mercury, making it ideally suited for immediate on-site analysis following environmental sample collection.