Hydrothermal synthesis of N, P co-doped graphene quantum dots for high-performance Fe3+ detection and bioimaging

Doped carbon-based materials have attracted considerable attentions due to their extraordinary optical, thermal, and electronic properties. Herein, we demonstrate a facile and universal approach, which involves the hydrothermal treatment of citric acid and phosphonitrilic chloride trimer (Cl6N3P3), for the production of nitrogen and phosphorus co-doped graphene quantum dots (N, P-GQDs). The obtained N, P-GQDs with a mean size of about 3.4 nm exhibit bright yellow fluorescence, good-solubility, and attractive optical stability. Although the quantum yield as high as 34.8% has been proved in our synthesized N, P-GQDs, the fluorescence can be also fleetly and selectively quenched by Fe3+ ions. Therefore, high-performance Fe3+ sensors are fabricated with N, P-GQDs, with an ultra-sensitive detection limit of 146 nM. Furthermore, high ionic strength, mild acids, and alkaline are demonstrated to have a small impact on the fluorescence intensity of the N, P-GQDs. Finally, the as-synthesized N, P-GQDs, with bright luminescence and excellent biocompatibility, are applied for bioimaging, e.g., fibroblast cells.