One-Step Hydrothermal Synthesis of Nitrogen-Doped Conjugated Carbonized Polymer Dots with 31% Efficient Red Emission for In Vivo Imaging

Carbon dots with long-wavelength emissions, high quantum yield (QY) and good biocompatibility are highly desirable for biomedical applications. Herein, a green, facile hydrothermal synthesis of highly efficient red emissive nitrogen-doped carbonized polymer dots (CPDs) with optimal emission at around 630 nm are reported. The red emissive CPDs possess a variety of superior properties including excellent water dispersibility, good biocompatibility, narrow bandwidth emission, an excitation-independent emission, and high QY (10.83% (in water) and 31.54% (in ethanol)). Further studies prove that such strong red fluorescence is ascribed to the efficient conjugated aromatic systems and hydrogen bonds of CPDs. And the fluorescence properties of CPDs can be regulated by adjusting the dosage of HNO3 before the reaction. Additionally, the as-prepared CPDs are successfully used as a fluorescent probe for bioimaging, both in vitro and in vivo. More importantly, biodistribution results demonstrate that most CPDs and their metabolites are not only excreted in urine but also excreted by hepatobiliary system in a rapid manner. Besides, the CPDs could easily cross the blood brain barrier, which may provide a valuable strategy for the theranostics of some brain diseases through real-time tracking.