Highly stable multi-encapsulated red-emitting cesium lead halide nanocrystals for efficient copper ion detection and imaging in live cells

Abstract

Recently, cesium lead halide (CsPbX3: X = Cl, Br, I) perovskite nanocrystals (NCs) have shown potentiality in the detection of different heavy metal ions and bioimaging applications for their smaller particle size, tunable emission spectra, high luminescent intensity, narrow emission spectra, multiphoton absorption property, etc. CsPbBr3 NCs are explored extensively in bioimaging applications for their comparatively higher stability in water. A longer wavelength excitation light source is recommended due to less scattering of light results in deeper penetration in living cells. However, imaging in live cells with red-emitting perovskite NCs is not suitable because of their poor structural stability, low emission intensity, and complex synthesis process. To tackle these issues, we introduce a specific halide exchange to the NCs and then multi-encapsulation shelling techniques that eventually improve the structural and environmental stability of the red-emitting NCs. Here, we synthesized Zn-doped CsPbBr3 NCs via the ligand-assisted reprecipitation (LARP) synthesis method in an open atmosphere. Then the highly luminescent red emitting CsPbBrxI3−x NCs with Zn doping were grown via the exchange of halide ions from pre-synthesized Zn-doped CsPbBr3 NCs to maintain the stable perovskite crystal structure in the nanoscale regime. Such NCs were further encapsulated with different shelling materials and then compared their photophysical properties. Among them, n-isopropyl acrylamide passivated Zn-doped CsPbBrxI3−x/SiO2/polyvinylpyrrolidone core/shell/shell NCs showed the highest stability against water and UV-irradiation. These NCs efficiently detect Cu2+-ions in water and achieved a detection limit of around 9.68 µM. The NCs were also tested for their compatibility as a fluorescent probe for live cell imaging using mammalian Chinese Hamster Ovary cells. As a proof-of-principle, we demonstrate both the efficient uptake and biocompatibility of the perovskite NCs. This work provides insight for expanding research activities on red-emitting perovskite NCs by developing a new strategy to improve the stability of the NCs, which is beneficial for both cost-effective bioimaging applications and heavy metal ion detection in water.