Facile Light-Driven Synthesis of Highly Luminous Sulfur Quantum Dots for Fluorescence Sensing and Cell Imaging

Sulfur quantum dots (SQDs) are emerging fluorescent nanomaterials, whereas most of the methods for synthesizing SQDs are limited to thermal synthesis. In this study, we report the first case of a light-driven strategy for facile synthesis of SQDs and further applied the SQDs for fluorescence cell imaging. The light-driven synthesis strategy only utilized Na₂S as the sulfur source and nano-TiO₂ as the photosensitizer. Under ultraviolet illumination, the nano-TiO₂ photosensitizer generated a large number of ^•O^2- and ^•OH to oxidize S^2- to S^2- and further to elemental sulfur, which could be obtained as monodispersed SQDs after etching by H₂O₂. The prepared SQDs exhibit excellent tunable photoluminescence properties, superior stability, and a uniform small size, with particle diameters in the range of 0.5-4 nm, and the fluorescence absolute quantum yield is as high as 27.8%. Meanwhile, the prepared SQDs also exhibited extreme biocompatibility and stability, and we further applied it for intracellular imaging and Hg²⁺ sensing with satisfactory results. In comparison to the widely reported thermal synthesis, the light-driven synthesis method is greener and simpler, opening a new way for the preparation of biocompatible SQDs.