Luminescent Sulfur Quantum Dots for Colorimetric Discrimination of Multiple Metal Ions

The classical chemistry of sodium thiosulfate was applied to synthesize luminescent Sdots where elemental sulfur produced in situ was etched with NaOH. This method notably reduces the synthesis time of Sdots in comparison to the previously reported etching technique of bulk sulfur. The as-synthesized Sdots exhibited excitation dependent photoluminescence with a QY of 2.5%, photostabality under UV light irradiation, excellent dispersibility in aqueous medium, and also the stability even after several weeks. Notably, no emission was observed due to the oxidation of PEG-400 during the course of reaction. The Sdots was then employed as a dual function probe for the sensing of metal ions. Using fluorimetric method, Sdots showed preferential selectivity toward the Co2+ metal ions. However, a single probe Sdots can colorimetrically distinguish multiple metal ions such as Co2+, Cr6+, and Pb2+ by displaying color change on the immediate addition of analytes. Furthermore, the color change of Sdots is demonstrated with the help of hue images and hue spectra (or histogram) that will help in the development of Sdots based portable device. The present study contributes to the further advancement of this emerging field as a promising single-element nanomaterial an alternative to luminescent metallic nanomaterials.