Highly stable aqueous phase black phosphorus quantum dots with enhanced fluorescence property

Black phosphorus quantum dots (BPQDs) are a kind of outstanding optical material due to the tunable band structure. However, their fluorescence property and stability are obviously weakened in the aqueous phase, which extremely restricts the development of BPQDs. Here, we propose a new method to prepare stable BPQDs in an aqueous solution directly with high absolute fluorescence quantum yield. Aqueous phase BPQDs are synthesized by liquid exfoliation and hydrothermal with NH2-polyethylene glycol (PEG)-NH2 as the modification agent to protect the BPQDs, which have high stability more than six months. In addition, NH2-PEG-NH2 is also a surface passivation agent to enhance the emission of BPQDs by forming P–N bonds, which is confirmed by an absolute fluorescent quantum yield of 11.5%. Moreover, BPQDs show excellent resistance to a strong acid environment and high ionic strengths except for Fe3+. Therefore, the BPQDs are a kind of highly selective and linear response fluorescence probe for Fe3+. Considering the good biocompatibility of BPQDs, they are employed as cell fluorescent label probes and show excellent fluorescence imaging contrast. Based on the unique structural stability and fluorescence performance in the aqueous phase, BPQDs are potential candidates for Fe3+ detection and optical bio-imaging.