Methylammonium Tin Tribromide Quantum Dots for Heavy Metal Ion Detection and Cellular Imaging

Development of luminescent and nontoxic Pb-free perovskite quantum dots (PQDs) for quantification of toxic/nontoxic heavy metal ions has attracted much attention recently. In this paper, blue emissive Pb-free bare and poly(ethylenimine), oleic acid stabilized methylammonium tin tribromide quantum dots (MASnBr3QDs and PEI-OA-MASnBr3QDs) are developed via modified synthetic routes with fluorescent quantum yields of (Φf) of 8.7 and 14.6%, respectively. The particle size, structures, diffraction patterns, and surface potential of PQDs are investigated using a high-resolution transmission electron microscope (HR-TEM), powder X-ray diffraction (PXRD), dynamic light scattering (DLS), and zeta potential techniques. Photoluminescence (PL) investigations demonstrate agglomeration-mediated energy transfer at various precursor concentrations and water sensitivity of PQDs. At 20 μL precursor concentration in DMSO, both QDs exhibit diverse fluorescent quenching to Fe3+ and Cr6+ with linear regression between 1–500 μM and nanomolar detection limits (LODs). Estimated Stern–Volmer quenching constant values are on the order of 103–104 M–1 higher than those of other ions. PL and time-resolved PL studies confirm involvement of dynamic and static quenching in quantification of Fe3+/Cr6+ for MASnBr3QDs and PEI-OA-MASnBr3QDs, respectively. Agglomeration of PQDs, Sn2+/MA+ cationic displacement by Fe3+/Cr6+, and the existence of metal-oxide/hydroxide layer above the surface of QDs are confirmed by HR-TEM, DLS, zeta potential, X-ray photoelectron spectroscopy, and energy-dispersive spectroscopy investigations and supported by the density functional theory optimization. Biocompatibility of PQDs is authenticated by the methyl thiazolyl tetrazolium assay and IC50 interrogations with supporting results from time-dependent cellular imaging of Fe3+ and Cr6+ ions. Individual titrations of PQDs with Fe3+ and Cr6+ in tap, lake, and seawater samples display linear behavior with micro/nanomolar LODs. Fe3+ and Cr6+ in spiked real water sample experiments show exceptional PL recoveries (>100%), which agree with the inductively coupled plasma-mass analysis.