Ultrasensitive detection of mercury(ii) in aqueous solutions via the spontaneous precipitation of CsPbBr3 crystallites

Abstract

Mercury(II) is one of the most toxic ions and has the lowest allowed concentration in water. Lowering the detection limits of Hg²⁺ based on fluorescence methods is challenging compared to the detection of other heavy metal ions. Co-precipitation of the CsPbBr₃ precursor and mercury ions in aqueous solutions was developed for the ultra-trace level detection of Hg²⁺. It was found that the formed CsPbBr₃ crystals with sizes in the range of nanometers to micrometers exhibited strong fluorescence in the solid state free of water, and the incorporation of Hg²⁺ in the crystals would cause fluorescence quenching. Therefore, the decrease in fluorescence intensity could be used to quantitatively detect Hg²⁺. A microwell array was designed by dispersing the sample solution with the perovskite probe and evaporating water for 3 min to form solid fluorescent crystals, leading to the incorporation of Hg²⁺ in the crystals. This evaporation-induced co-precipitation strategy successfully solved the problem of the instability of perovskite materials in water. The concentration of Hg²⁺ can be obtained according to the decrease in the fluorescence intensity, which is caused by the replacement of Pb²⁺ by Hg²⁺ in the crystals during the crystallization process. The CsPbBr₃ crystallites can be used to detect ultra-trace levels of Hg²⁺ simply and quickly, with a linear range of 5–100 nM and limit of detection (LOD) as low as 0.1 nM. More importantly, no organic molecules are required to prepare crystals since the micron-sized crystals have obvious fluorescence. This method demonstrates great promise in detecting low concentrations of Hg²⁺ in aqueous solutions.