Ultrasound-Assisted Hydrothermal Synthesis of Highly Fluorescent Sulfur Quantum Dots for Fe Ion and Ascorbic Acid Detection in Real Samples.

In this work, the ultrasound-assisted hydrothermal synthesis method offers a facile method to synthesize highly efficient photoluminescence sulfur quantum dots (SQDs). Impressively, a switchable fluorescent "on-off-on" sensor was developed using the acquired SQDs, which are capable of sequentially detecting iron ions (Fe) and ascorbic acid (AA) with exceptional sensitivity and selectivity. Meanwhile, SQDs and Fe formed complexes through coordination, causing the fluorescence quenching of SQDs because of the static quenching effect. Upon the addition of AA into the SQDs/Fe system, a redox-reaction-mediated mechanism leads to the recovery of fluorescence. The fluorescence intensity of SQDs exhibits a linear relationship with the concentrations of Fe and AA in the ranges 5-30 and 20-100 μM, respectively. Notably, the detection limits achieved are 14.31 nM for Fe and 0.64 μM for AA. Moreover, the chemosensor was successfully employed for monitoring Fe in real water samples and AA in fruits. These results demonstrate the excellent analysis and detection capabilities of SQDs in the complex environment.