X‐Ray Activatable Au/Ag Nanorods for Tumor Radioimmunotherapy Sensitization and Monitoring of the Therapeutic Response Using NIR‐II Photoacoustic Imaging

Radioimmunotherapy (RIT) is an advanced physical therapy used to kill primary cancer cells and inhibit the growth of distant metastatic cancer cells. However, challenges remain because RIT generally has low efficacy and serious side effects, and its effects are difficult to monitor in vivo. This work reports that Au/Ag nanorods (NRs) enhance the effectiveness of RIT against cancer while allowing the therapeutic response to be monitored using activatable photoacoustic (PA) imaging in the second near‐infrared region (NIR‐II, 1000–1700 nm). The Au/Ag NRs can be etched using high‐energy X‐ray to release silver ions (Ag(+)), which promotes dendritic cell (DC) maturation, enhances T‐cell activation and infiltration, and effectively inhibits primary and distant metastatic tumor growth. The survival time of metastatic tumor‐bearing mice treated with Au/Ag NR‐enhanced RIT is 39 days compared with 23 days in the PBS control group. Furthermore, the surface plasmon absorption intensity at 1040 nm increases fourfold after Ag(+) are released from the Au/Ag NRs, allowing X‐ray activatable NIR‐II PA imaging to monitor the RIT response with a high signal‐to‐background ratio of 24.4. Au/Ag NR‐based RIT has minimal side effects and shows great promise for precise cancer RIT.