N and S doped carbon dots as novel probes with fluorescence enhancement for fast and sensitive detection of Cr(VI)

Cr(VI) is a toxic heavy metal, which is not readily decomposed and ingested by bacteria. Therefore, there is an urgent need for a sensing method with high selectivity and high sensitivity to detect Cr(VI) in other widely distributed metal ions. Here, a fluorescent probe based on carbon dots (CDs) was developed, with the characteristics of low cost, low environmental impact, high stability, and good water solubility. Although many sensors have been reported for the detection of Cr(VI), most of them are based on the quenching fluorescence method, whereas the one reported here is based on fluorescence enhancement, for which o-phenylenediamine and dl-Thioctic acid were used as raw materials. The transmission electron microscopy, Fourier infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and ultraviolet-visible spectroscopy measurements showed that Cr(VI) can significantly enhance the fluorescence of the probe compared to previous sensors, as the obtained CDs have excellent fluorescence properties (quantum yield up to 21.82%) and high light stability. The detection limit of the probe for Cr(VI) is as low as 0.64 μM, indicating that the developed probe can detect Cr(VI) quickly, sensitively, and selectively, and has broad application prospects in environmental analysis applications. To facilitate rapid detection of Cr(VI), the CDs were also incorporated into a fluorescent composite film suitable for visual inspection.