Luminescent carbon dots (CDs) have become attractive materials because of their superior photophysical properties and various potential applications. However, most of the formerly developed CDs only have strong blue emission, which limits their further applications, particularly in bioimaging. Herein luminescent CDs have been successfully synthesized via a one-pot solvothermal process using 4-bromoaniline and ethylenediamine as starting materials. The luminescent CDs emit strong green fluorescence with high quantum yield as well as excellent biocompatibility and biolabeling potentials. At first, the luminescent CDs exhibited high selectivity for phosgene with a turn-off fluorescence detection. The limit of detection was 81 nM, which is sensitive for the determination of phosgene over other competing toxic pollutants. In addition, the luminescent CDs have shown a three-state "on-off-on" emission with the stepwise addition of Ag+ and cysteine (Cys). Luminescent CDs show fluorescence quenching by Ag+ and fluorescence regaining with further addition of Cys, with lower detection limits of 3.9 μM (Ag+) and 3.4 μM (Cys), respectively. The luminescent CDs were utilized to obtain a clear fingerprint. During the drying process, the coffee ring effect and electrostatic interaction between the positive surface charge of amine-functionalized CDs and negatively charged fingerprint residues facilitate the formation of clear fingerprints on different platforms.
Keywords: cell imaging; cysteine; fingerprint; fluorescent ink; luminescent carbon dots; phosgene; silver ions; toxic gas-detection.