Stable black phosphorus/Bi₂O₃ heterostructures for synergistic cancer radiotherapy

X-ray induced photodynamic therapy (X-ray-PDT) is a promising approach for synergistic cancer radiotherapy and development of suitable radiosensitizers is highly desired. In this paper, we propose black phosphorus/Bi₂O₃ (BP/Bi₂O₃) heterostructures as efficient and biocompatible radiosensitizers for synergistic cancer radiotherapy. The heterostructures are synthesized by growth of ultrasmall Bi₂O₃ nanoparticles onto BP nanosheets. The Bi₂O₃ decoration inhibits the rapid degradation of BP nanosheets by occupation of the defect sites, and the synergistic effects of BP and Bi₂O₃ enable ¹O₂ overproduction under X-ray irradiation. This X-ray-PDT effect of the BP/Bi₂O₃ nanosheets enhances the radiotherapy activity towards cancer cells by inducing cell apoptosis and cycle arrest. In vivo treatment of melanoma conducted on a clinical radiotherapeutic instrument demonstrates that the BP/Bi₂O₃ sensitized radiotherapy inhibits tumor growth efficiently. Furthermore, the BP/Bi₂O₃ nanosheets composed of biological friendly P, O, and Bi elements shows good biocompatibility in vitro and in vivo. This radiosensitizer thus has immense clinical potential for cancer therapy, and our findings reveal a general strategy to fabricate stable BP-based heterostructures for different applications.