Preparation of blue sulfur quantum dots in ammonia for the detection of Rutin and cell imaging

Sulfur quantum dots (SQDs) have garnered increasing attention for their versatile applications in bioimaging, LEDs, and fluorescence sensing. As a new type of heavy-metal-free fluorescent nanomaterial, developing high quantum yield SQDs using small molecules as capping agents poses a significant challenge. Here, we present a novel synthesis approach of SQDs using (NH₄)₂S_x and sulfur powder as sulfur sources, and the small molecule N-acetyl-L-cysteine (NAC) as a stabilizer in a weak alkaline system. The synthesized blue SQDs (B-SQDs) were extensively characterized using various techniques. B-SQDs exhibited a fluorescence quantum yield of 15.55 % and particle sizes ranging from 2.7 nm to 6.2 nm, showcasing exceptional optical stability, dispersibility, low cytotoxicity, and efficient cell uptake. The as-acquired B-SQDs were explored for potential applications in sensing and cell bioimaging. The findings revealed that B-SQDs exhibited high sensitivity and selectivity towards the drug molecule Rutin. The detection limit was calculated as 50 nM. This methodology was effectively employed for Rutin determination in actual urine samples, yielding satisfactory recovery rates ranging from 95.68 % to 103.93 % with a relative standard deviation below 4.28 %. The fluorescence quenching of B-SQDs by Rutin is influenced by the concentration levels of Rutin. At high Rutin concentrations, fluorescence quenching mechanisms include dynamic quenching and static quenching. Conversely, at low Rutin concentrations, it mainly involves a dynamic quenching mechanism and the IFE process. Moreover, B-SQDs could also accurately identify intracellular Rutin. This research offers a robust approach for Rutin detection in biological samples with implications for disease diagnosis and pharmacology.