Highly stable fluorescent CsPbBr3 perovskite nanocrystals with reduced in-vitro toxicity for bioimaging and mercury ion detection in cells

Heavy metal ions are seriously responsible for contaminating aquatic systems and damaging biological systems. Recently, fluorescent CsPbX3 (X = Cl, Br, I) perovskite nanocrystals (NCs) have been explored for the qualitative and quantitative measurements of heavy metal ions. The excellent multi-photon absorption property of the perovskite NCs also allows the integration of infrared light for fluorescent bioimaging applications. However, the poor structural stability of the perovskite materials against water, intense UV-irradiation, and leaching of Pb-ions into the environment remain great challenges for practical applications. Encapsulating different stable shelling materials grown around the NCs significantly enhances the stability and luminescent properties. In view of this, we encapsulated the CsPbBr3 NCs with different capping agents, such as silica and polyvinylpyrrolidone (PVP), to improve NCs' stability while maintaining superior emission properties. Among them, tetraethylorthosilicate (TEOS) mediated silica-coated NCs exhibited the highest emission intensity in the green spectral region with a maximum photoluminescence quantum yield (PLQY) of up to 85 %. The silica shell also improved the stability of the NCs and remained stable for several days while dispersed in water. The NCs also exhibited better stability under UV irradiation and wider pH regions. These NCs were executed as a fluorescent probe for detecting Hg2+-ions in water, resulting in one of the most effective detections of Hg2+-ions with a low detection limit of ∼57 nM. In addition to this, the cells' viability and morphology almost remained unaffected even after prolonged incubation times (up to 72 h) using Methyl thiazolyl tetrazolium (MTT) assay in the presence of the silica-coated CsPbBr3 NCs. Finally, these NCs were tested for sensing Hg2+-ions inside the mammalian 3T3L-1 cells, demonstrating superior sensitivity for Hg2+-ion detection. This work provides insight for expanding the research field related to the sensing of metal ions in different biological systems.