Nitrogen-Doping Enhanced Fluorescent Carbon Dots: Green Synthesis and Their Applications for Bioimaging and Label-Free Detection of Au3+ Ions

Fluorescent carbon dots (CDs) hold great promise for a myriad applications due to their fascinating attributes. However, the development of CDs with high fluorescence quantum yield (QY) and unique surface property is still in its infancy. Herein, we report a simple and green strategy to produce water-soluble nitrogen-doped CDs (N-CDs) via the one-pot hydrothermal carbonization of the mixture of natural peach gum polysaccharide (PGP) and ethylenediamine. The resulting N-CDs exhibit a remarkably enhanced QY (28.46%) as compared with that of undoped CDs (5.31%). In addition, the N-CDs show stable fluorescence against ionic strength variation and pH change. Preliminary biological studies reveal that N-CDs possess low cytotoxicity and high fluorescent contrast in cells. Moreover, we present here for the first time that the obtained N-CDs can exhibit a fast and highly sensitive and selective fluorescence quenching effect toward Au3+ ions. The detection limit can reach 6.4 X 10(-8) M, which compares favorably to other reported fluorescent probes. We have also demonstrated that the N-CDs can be employed to sense Au3+ ions in real river water. Considering the easy synthetic process and excellent performance of the N-CDs, this investigation opens up new opportunities for preparing high-quality fluorescent CDs to meet the requirement of many applications.