Photoacoustic Imaging-Guided Synergistic Photothermal/Radiotherapy Using Plasmonic Bi/Bi₂O_3−x Nanoparticles

The integration of photothermal agents and radiosensitizers has been widely implemented in synergistic antitumor treatment because it maintains the advantages of the single model; however, they result in unsatisfactory treatment effects due to their multi-component, unstable, and non-degradable nature. Herein, plasmonic Bi/Bi₂O_3−x is synthesized by in situ fabrication of Bi₂O_3−x on elemental Bi through a facile hydrothermal method. After encapsulation with DSPE-PEG2000-folate, the Bi/Bi₂O_3−x nanoparticles (NPs) effectively accumulate in tumor sites to serve as a multifunctional therapeutic agent that can damage tumor sections by absorbing near-infrared light and X-rays. As demonstrated in penetration depth experiments, the NPs exhibit excellent photoacoustic imaging capabilities for deep tissues. Both blood biochemistry tests and histological assays demonstrate the biosafety of Bi/Bi₂O_3−x NPs in vivo due to their acceptable toxicity and biological clearance properties. Consequently, the prepared NPs are a desirable candidate for effective second near-infrared photothermal/radiotherapy.