Preparation and cell imaging of robustly stable fluorescent carbon dots through nitrogen and phosphorus co-doping

Robustly stable fluorescent carbon dots (N/P-CDs) were designed through co-doping strong electron-withdrawing nitrogen and phosphorus heteroatoms and synthesized via a solvothermal method. N/P-CDs demonstrated fluorescence emission at 461 nm under excitation at their optimal wavelengths of 370 nm and 380 nm, achieving a notable fluorescence quantum yield of 48.2%. Nitrogen and phosphorus co-doping allowed the emission of the intrinsic state from carbon core to dominate the fluorescence emission behavior and ensured fluorescence stability. The N/P-CDs’ fluorescence intensity in solution showed no significant change and remained stable after being stored at room temperature for 7 days. The N/P-CDs’ fluorescence intensity remained largely unchanged under varying conditions, including a pH range of 1 to 12, temperatures between 20 and 60 °C, and continuous xenon light exposure for 3600 s. Moreover, MCF-7 and EC cells’ viability incubated with N/P-CDs for 24 h exceeded 90%, confirming their high biocompatibility and lower toxicity. Cell imaging studies demonstrated N/P-CDs emitted stable and strong fluorescence which predominantly localized in the cell membrane. The incorporation of nitrogen and phosphorus heteroatoms into carbon dots can enhance carbon dots’ stability and endows carbon dots with significant potential for use in cell imaging applications.