Halide salt-tuning at interface: Highly water-stable and anion-exchange-active CsPbX3@SiO2 Trimurti nanoparticles for multicolor metabolite assay

High water stability and fast anion exchange (FAE) activity are indispensable requirements of CsPbX3 (X = Cl, Br, I) nanoparticles (NPs) for achieving multicolor fluorescence sensing in aqueous samples. In this study, we prove that the crystal phase transition rate from Cs4PbX6 to CsPbX3 can be finely tuned by halide salt, thereby facilitating the exposure of in-situ SiO2 nucleation sites to CsPbX3. Through the sol–gel method triggered by KX-containing water, monodisperse CsPbX3@SiO2 Trimurti nanoparticles (TNPs), i.e., double-side SiO2-coated CsPbX3 NPs, are successfully synthesized for the first time. As an example, the CsPbBr3@SiO2 TNPs exhibit significantly enhanced photoluminescence quantum yield (80%), fluorescence lifetime (22.09 ns) and water stability (only 11.4% drop in FL intensity after 60 min reaction with water), meanwhile maintain consistent high FAE activity, compared to bare CsPbBr3 NPs (57%, 6.56 ns, 97.9% drop) and single-side SiO2-coated NPs (69%, 9.76 ns, 39.1% drop). Furthermore, we propose an H2O2 recognition strategy at the organic/aqueous phase interface based on the FAE effect between oleylammonium iodide (OLAI) and CsPbX3@SiO2 TNPs. Thus, the TNPs-based multicolor sensing platform for small molecule metabolites is constructed and utilized for uric acid detection in serum, which obtains consistent results with the commercial method (relative error ≤ 5.67%). This work not only provides a guidance for the tunable surface modification of high-performance CsPbX3 NPs, but also designs a universal strategy for selectively detecting small molecule metabolites in biological fluids based on the intrinsic FAE effect.