Facile synthesis of phosphorus‐nitrogen doped carbon quantum dots from cyanobacteria for bioimaging

Abstract Carbon quantum dots (CQDs) are becoming powerful fluorophore materials in the field of biosensors and bioimaging thanks to their small size, optical properties, biocompatibility, and low toxicity. Heteroatom doping can endow CQDs with new or improved photoluminescent properties. In this paper, the bio‐waste cyanobacteria, H 3 PO 4 and C 2 H 8 N 2 were used as precursors for synthesizing P‐doped, N‐doped and P/N co‐doped CQDs via a simple hydrothermal method. Under the irradiation of ultraviolet light (UV), the optimal emission peaks of undoped CQDs and P‐doped CQDs were located in the blue‐light region, while those of N‐doped CQDs and P/N co‐doped CQDs were located in the green‐light region. Compared with the undoped, N‐doped and P‐doped CQDs, the P/N co‐doped CQDs had higher quantum yield (QY) and more favourable photoluminescent (PL) properties. The as‐prepared P/N co‐doped CQDs were highly fluorescent and exhibited excitation wavelength‐dependent fluorescence; its maximum emission wavelength was at 501 nm under the excitation of 420 nm. Furthermore, the percentage of survival cells kept at 90.4% when the P/N co‐doped CQDs concentration was up to 200 μg/mL by MTS assay. Such P/N co‐doped CQDs were then used as an effective fluorescent probe for cell imaging due to their high QY, good water dispersibility, strong fluorescence properties, fine biocompatibility, and low cytotoxicity.