A fluorescence probe of sulfur quantum dots for sensitive detection of copper ions in Paris polyphylla var. yunnanensis

A novel turn-off fluorescent probe of SQDs based on inner filter effect was developed and used as an alternative analytical method for the detection of Cu 2+ residues among Chinese medicinal materials. • Sulfur quantum dots (SQDs) was prepared by “assemble-fission” approach. • The synthesized SQDs has high dispersibility and stability. • The as-obtained SQDs demonstrated high selectivity compared with other probes. • SQDs acted as a sensor for assaying of Cu 2+ in Paris polyphylla var. yunnanensis . The excessive residue of copper ion (Cu 2+ ) has an important impact on the quality of traditional Chinese medicine (TCM). In this work, a sulfur quantum dots (SQDs) fluorescent probe was developed for rapid and sensitive detection of Cu 2+ in Paris polyphylla. Smith var. yunnanensis (Franch.) Hand. -Mazz. ( P. polyphylla var. yunnanensis ). SQDs were synthesized by the “assemble-fission” method. The synthesized SQDs were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM), and their fluorescence properties were studied. The prepared SQDs have advantages of ultra-small size, good optical properties and excellent stability. The addition of Cu 2+ could effectively quench the fluorescence of SQDs due to the inner filter effect (IFE) between Cu 2+ and SQDs. The detection linear range of this method was 20–200 μM. The limit of detection (LOD) was 6.78 μM. It has high selectivity in the simultaneous presence of other ions, and the possible fluorescence quenching mechanism was discussed in detail. Finally, the prepared SQDs were applied to the detection of actual samples of P. polyphylla var. yunnanensis with satisfactory results, which confirmed the great potential of SQDs in the actual measurement of Cu 2+ in TCM.