Ultrasensitive detection of mercury(II) in aqueous solutions via the spontaneous precipitation of CsPbBr 3 crystallites.

Mercury(II) is one of the most toxic ions and has the lowest allowed concentration in water. Lowering the detection limits of Hg 2+ based on fluorescence methods is challenging compared to the detection of other heavy metal ions. Co-precipitation of the CsPbBr 3 precursor and mercury ions in aqueous solutions was developed for the ultra-trace level detection of Hg 2+ . It was found that the formed CsPbBr 3 crystals with sizes in the range of nanometers to micrometers exhibited strong fluorescence in the solid state free of water, and the incorporation of Hg 2+ in the crystals would cause fluorescence quenching. Therefore, the decrease in fluorescence intensity could be used to quantitatively detect Hg 2+ . 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 Hg 2+ in the crystals. This evaporation-induced co-precipitation strategy successfully solved the problem of the instability of perovskite materials in water. The concentration of Hg 2+ can be obtained according to the decrease in the fluorescence intensity, which is caused by the replacement of Pb 2+ by Hg 2+ in the crystals during the crystallization process. The CsPbBr 3 crystallites can be used to detect ultra-trace levels of Hg 2+ 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 Hg 2+ in aqueous solutions.