Sulfur quantum dots as effective fluorescent nanoprobes for detecting Co2+ in Salviae miltiorrhizae Radix et Rhizoma

Excessive residues of Co2+ in Chinese herbal medicines (CHMs) have attracted much attention because of their potential health hazards. This research synthesized sulfur quantum dots (SQDs) with excellent stability and water solubility via a facile one-pot route. During the illumination with ultraviolet light (λmax = 320 nm), the as-prepared SQDs emitted bright blue fluorescence at 431 nm. Meanwhile, the prepared SQDs could be used as fluorescent nanoprobes for detecting Co2+, showing an excellent linear relationship (R2 = 0.998) when the Co2+ concentrations were 5–50 μM, and the determination of the limit of detection (LOD) yielded a value of 4.51 μM. The introduction of Co2+ resulted in the efficient quenching of SQD luminescence, attributable to the inner filter effect (IFE) that occurs between SQDs and Co2+. Finally, the feasibility of the proposed methodology was demonstrated by achieving a recovery rate of 98%–106% and a relative standard deviation (RSD) of 0.75%–3.51% during the detection of Co2+ in Salviae miltiorrhizae Radix et Rhizoma. The results demonstrated that the fluorescent nanoprobes had broad application prospects in analyzing and detecting heavy metal ions in CHMs.