A novel sulfur quantum dot for the detection of cobalt ions and norfloxacin as a fluorescent “switch”

Sulfur nanomaterials exceed carbon nanomaterials in terms of the antimicrobial or antifungal properties. To date, there have been no reports on sulfur dots being used as fluorescence sensors. Herein, we report a simple assay based on aggregation-caused quenching (ACQ) of sulfur quantum dots (SQDs) to detect cobalt ions (Co²⁺). The S QDs allows the detection of Co²⁺ ions in the range of 0-9 × 10^-5 mol L^-1. This reliable, rapid, sensitive, and selective S QD probe has been utilized for the determination of the concentrations of Co²⁺ ions in water samples (I = 61.89C + 1.72, R² = 0.9485). After adding norfloxacin, the fluorescence intensity recovered. There were good linear correlations between the concentrations of norfloxacin and the fluorescence-recovered intensities. A new determination strategy of norfloxacin was built using the S QDs as a "switch". The recovered photoluminescence intensity of S QDs-Co²⁺ was proportional to the concentration of norfloxacin in the range of 0-2 × 10^-4 mol L^-1 (I = -44.18C + 138.45, R² = 0.9943). Co²⁺ coordinated with the carbonyl oxygen and the hydroxyl oxygen on the side chain of the norfloxacin molecule. This is the first time S QDs were used as a sensing platform.