Stable nitrogen and sulfur co-doped carbon dots for selective folate sensing, in vivo imaging and drug delivery

Here, innovative nitrogen and sulfur co-doped bright orange fluorescent carbon dots (CDs) are easily obtained using methyl-beta-cyclodextrin (Me-beta-CD) and methylene blue as original materials via the hydrothermal method. The as-prepared CDs showed excellent fluorescence stability in the wide pH range and external anions and cations, while its fluorescence can be quenched by folate (FA), indicating its sensitivity to FA with a detection limit as low as 0.85 nM. The commendable biocompatibility and superior photobleaching resistance of CDs make it superior to applications in living cell imaging and drug tracking, respectively. Bioimaging of CDs in zebrafish larvae manifests that it is easily circulated to other tissues due to the small size. Moreover, the positively charged CDs exhibits drug loading capabilities of the antitumor drug mitoxantrone (MTO) to achieve a fluorescent nanomedicine system (CDs-MTO) combining tracking and therapy. It was found that the cells exposed to the CDs-MTO showed a significant reduction in numbers by both MTT assay and detection of cell morphology, indicating CDs-MTO has a good ability to inhibit cell growth. The results demonstrate that the CDs can be sensitive to FA and served as a good platform for drug delivery and imaging.