One-step synthesis of N-doped carbon dots, and their applications in curcumin sensing, fluorescent inks, and super-resolution nanoscopy.

Nitrogen-doped carbon dots (N-CDs) with fluorescence excitation/emission maxima at 365/450 nm were prepared by a one-step hydrothermal approach. The dots possess remarkable photostability, fluorescence blinking and good biocompatibility, and this favors utilization in stochastic optical reconstruction microscopy (STORM). A spatial resolution down to ~60 nm was achieved when imaging HeLa cells using 647-nm laser excitation. This opens new possibilities for various super-resolution techniques based on stochastic optical switching. The remarkable optical properties of the N-CDs also enable them to be applied as invisible security ink for use in patterning, information storage and anti-counterfeiting. Further, it is found that the fluorescence of the N-CDs can be quenched by curcumin with high efficiency due to a combination of inner filter effect and static quenching. Based on this, a fluorometric assay with a detection limit of 21 ng mL was developed for the determination of curcumin. Graphical abstract Schematic representation of the applications of N-doped carbon dots (N-CDs). Curcumin quenches the fluorescence of N-CDs with high efficiency. The remarkable optical properties of the N-CDs enable them to be applied in fluorescent ink, cell imaging and stochastic optical reconstruction microscopy (STORM).