Synthesis of red/black phosphorus-based composite nanosheets with a Z-scheme heterostructure for high-performance cancer phototherapy

Two dimensional black phosphorus nanosheets (BP NSs) have attracted plenty of attention in the research field of cancer photonic therapy. However, the poor stability and relatively low efficiency of reactive oxygen species (ROS) generation of BP NSs limit their practical application. To address these drawbacks, herein we report a red/black phosphorus (RP/BP) composite nanosheet, M-RP/BP@ZnFe₂O₄, which was synthesized by (1) partially converting red phosphorus (RP) to black phosphorus (BP) followed by liquid-phase ultrasonic exfoliation to form RP/BP NSs, (2) in situ synthesis of ZnFe₂O₄ nanoparticles on the surface of RP/BP NSs, (3) and wrapping with the MCF-7 cell membrane. Due to the presence of RP, BP, ZnFe₂O₄ and the cell membrane, the M-RP/BP@ZnFe₂O₄ NSs exhibited high performance in cancer phototherapy with the following features: (i) a Z-scheme heterojunction structure was formed between RP/BP NSs thus enabling high separation efficiency of the photogenerated electrons and holes; (ii) the photoexcitation holes in the valence band of RP can break the tumor microenvironment by oxidizing glutathione; (iii) the NSs could decompose water to produce H₂O₂ and O₂, which can be further converted to toxic ˙OH through the ZnFe₂O₄ catalyzed Fenton reaction and ¹O₂ through energy transfer, respectively; and (iv) the cell membrane wrapping improved the targeting of the composite NSs at the tumor site and photonic therapy can be finally triggered by a 660 nm laser to convert O₂ to ˙O₂^- and ¹O₂. The in vitro cytotoxicity experiments showed that more than 90% cells were killed after photodynamic therapy (PDT) at 0.3 mg mL^-1 M-RP/BP@ZnFe₂O₄ NSs, and the animal experiments with xenograft tumor model mice indicated that tumor growth was completely inhibited and the highest survival rate of 83.3% at 60 days post PDT was obtained.