Brightly luminescent (NH₄)_xCs_1-xPbBr₃ quantum dots for in vitro imaging and efficient photothermal ablation therapy

Herein, we report for the first time a facile strategy for the highly efficient (NH₄)_xCs_1-xPbBr₃ quantum dots (QDs). By modulating the amount of ammonium, (NH₄)_xCs_1-xPbBr₃ QDs with different photoluminescence (PL) quantum yields (QY) were synthesized. The results of X-ray diffraction and X-ray photoelectron spectroscopy showed that the crystal structure of (NH₄)_xCs_1-xPbBr₃ was altered by incorporation of NH₄⁺ cations into the CsPbBr₃ lattice. The (NH₄)_xCs_1-xPbBr₃ QDs showed enhanced PL QY, higher photostability, and long-term storage stability compared to CsPbBr₃ QDs. Furthermore, (NH₄)_xCs_1-xPbBr₃ QDs could be conjugated with a photothermal dye (IR780) via a one-pot reaction using poly(styrene-co-maleic anhydride) and IR780-MPTS. To the best of our knowledge, the present work is the first attempt integrating perovskite QDs and phototherapeutic molecules into one system (abbreviated as PQD-IR780), demonstrating good water dispersibility and high photothermal conversion efficiency of 57.85%. In vitro experiments performed to examine subcellular uptake showed high fluorescence brightness was observed in HeLa, B16F1, and HepG2 cancer cells cultured with PQD-IR780. The results indicate that the internalization mechanism for uptaking of PQD-IR780 inside HeLa cells is energy-dependent and caveolin-mediated endocytosis. The in vitro cell viability assays and photothermal therapy revealed that PQD-IR780 showed good biocompatibility and can induce hyperthermia upon laser irradiation.