Highly stable and luminescent formamidinium-based perovskite nanocrystal probe for temperature and mercury sensors and in vitro imaging in live cells

Abstract

Lead halide perovskite (APbX₃: X = Cl, Br, I) nanocrystals (NCs) have caught massive attention from researchers because of their fascinating photophysical properties, which make them suitable for various optoelectronic, sensing, and bioimaging applications. However, the current issue with methylamine (MA) and Cs-based compounds is that they chemically decompose quickly at elevated temperatures and under intense light. The perovskite phase also degrades rapidly due to the ionic nature and the presence of dynamic organic capping ligands around the NCs. The comparatively better light and thermal stabilities of the formamidinium lead halide (FAPbX₃) materials and the limited reports encouraged us to further explore their inherent properties. Herein, we report a facile synthesis method for Cs-doped FAPbBr₃ NCs by facile ligand-assisted reprecipitation (LARP) synthesis approach. We optimized the Cs-doping ratio in FAPbBr₃ NCs, which revealed the highest luminescence intensity in the green spectral region, with superior stability. To further improve the structural stability, we encapsulated different shelling materials such as polymethylmethacrylate (PMMA), SiO₂, and double-coated SiO₂–PMMA around the NCs. The double-coated NCs displayed superior heat and water stabilities, and they retained their emission intensity over a month while immersed in DI water. The film was demonstrated as a temperature sensor that exhibited good heat sensitivity. Further, we tested these stable NCs as a fluorescent probe to detect highly toxic Hg²⁺-ions inside MDA-MB-231 cells. These results illustrate the feasibility of the NCs for application in cost-effective sensing and bioimaging areas.