Earth-friendly metal ion sensing via carbon dot fluorescence spectrometry

The outstanding optical properties, biocompatibility, and ease of surface functionalization of carbon dots (CDs) have made them a promising luminous nanomaterial for metal ion sensing. The concentration-dependent multicolor photoluminescence that CDs can exhibit is a key advantage for ppm-level metal ion monitoring. CDs are excellent fluorimetric detectors because of their surface oxygen moieties, which enable them to couple with metal ions. Adjusting the fluorescence characteristics of CDs following the particle size, initial precursors, and surface physicochemical characteristics might further improve their activity in metal detection. This chapter overviews the latest developments in eco-friendly CDs, comprising their fluorescence characteristics, quenching and fluorescence mechanisms, and sensing applications for heavy metal ion (HMI) detection. Most sensor system studies only show sensitivity and selectivity to a single cation. In addition, the chapter covers the use of a hybrid CD system with a ratiometric fluorescence assay to find the ratio of the fluorescence intensity at two different wavelengths. The hybrids can detect environmental toxins with precision and selectivity because of their dual emission peaks, which provide inherent self-calibration. Finally, issues and possible solutions to thwart CDs’ future trajectory in this sensing field are examined.