Nitrogen-doped carbon dots with heterogeneous multi-layered structures

Photoluminescent carbon dots (CDs) with graphite-like phase structure have been widely reported. Herein, we first report nitrogen-doped carbon dots (NCDs) with heterogeneous multi-layered structures by bottom-up hydrothermal carbonization process. The formation and surface passivation of NCDs was accomplished simultaneously. The as-prepared NCDs possess stable photoluminescence, solubility in water and various functional groups on their surface. XRD results clearly showed that there were two kinds of interlayer lattice spaces in the phase structure of prepared NCDs, which corresponded to the {002} plane of graphite and the {001} plane of graphite oxide. We further demonstrated that NCDs with good biocompatibility were easily and quickly internalized by cancer cells and are particularly suitable for multicolour real-time cellular imaging.