Red-Emissive Carbon Dots for “Switch-On” Dual Function Sensing Platform Rapid Detection of Ferric Ions and l-Cysteine in Living Cells

[Image: see text] Ferric ions (Fe(3+) ions) and l-cysteine (( l-Cys) in the human body have always played an irreplaceable role in biological processes, and overload or deficiency of Fe(3+) ions and l-Cys in the biological system leads to various diseases. In this work, N,S-co-doped red-emitting carbon dots (R-CDs) were synthesized by a facile hydrothermal method. Because the doping of N and S gives a unique functional group distribution on the surface of R-CDs, it can be complexed with Fe(3+) ions to construct an energy transfer quenching system. However, the presence of l-Cys competitively binds to Fe(3+) ions, thus resulting in the photoluminescence recovery of R-CDs. Therefore, a “switch-on” dual function sensing platform has successfully been developed based on R-CDs for rapid identification and quantification of Fe(3+) ions and l-Cys. The linear detection range of Fe(3+) ions is 0–30 μM (limit of detection (LOD): 0.27 μM) and that of l-Cys is 0–24 μM (LOD: 0.14 μM). The sensor platform was used to detect Fe(3+) ions and l-Cys in human serum samples with satisfactory results. Compared with traditional detection methods, this method is more time-saving and efficient and can be completed in 3 min. It is worth mentioning that the R-CDs not only has high optical stability but also has negligible cytotoxicity and has been successfully applied to in vitro/vivo imaging, indicating that R-CDs have excellent tissue penetration and biomarker potential. More interestingly, the switch-on fluorescence behavior for stepwise detection of Fe(3+) ions and l-Cys can also be observed in cell imaging, which provides the possibility of visual detection of the probe to be applied in vivo.