Responsive Theranostic Nanoprobe for Ratiometric Photoacoustic Monitoring of Hypochlorous Acid‐Mediated Inflammation in Cancer Photothermal Therapy

Abstract Cancer detection and inflammation monitoring during photothermal therapy (PTT) enable timely cancer intervention and precise inflammation control, advancing to address inflammation‐related tumor recurrence and metastasis associated with PTT. This can be achieved through real‐time monitoring biomarker for cancer and inflammation, like hypochlorous acid (HOCl), a highly reactive oxygen species (hROS) in body with elevated levels in inflammation. Here, a HOCl‐responsive theranostic nanoprobe is introduced, AuNRs@SiO 2 ‐CAA for ratiometric photoacoustic (PA) cancer detection and inflammation monitoring during PTT. AuNRs@SiO 2 ‐CAA emits PA signals at 680 and 820 nm, with only PA680 undergoing changes in the presence of HOCl, enabling precise HOCl imaging via recording changes of ratiometric PA signals (PA680/PA820). AuNRs@SiO 2 ‐CAA exhibits high selectivity and sensitivity, with a detection limit of 0.34 µM for ratiometric PA imaging of HOCl. In vivo, it effectively detects tumor, drives PTT, and monitors inflammation during PTT by sensing HOCl. The successful development of AuNRs@SiO 2 ‐CAA offers a novel theranostic nanoprobe system for cancer diagnosis, poised to enhance PTT through precise inflammation control.