Tuning Tumor Targeting and Ratiometric Photoacoustic Imaging by Fine‐Tuning Torsion Angle for Colorectal Liver Metastasis Diagnosis

Abstract Photoacoustic (PA) tomography is an emerging biomedical imaging technology for precision cancer medicine. Conventional small‐molecule PA probes usually exhibit a single PA signal and poor tumor targeting that lack the imaging reliability. Here, we introduce a series of cyanine/hemicyanine interconversion dyes (denoted Cy‐HCy) for PA/fluorescent dual‐mode probe development that features optimized ratiometric PA imaging and tunable tumor‐targeting ability for precise diagnosis and resection of colorectal cancer (CRC). Importantly, Cy‐HCy can be presented in cyanine (inherent tumor targeting and long NIR PA wavelength) and hemicyanine (poor tumor targeting and short NIR PA wavelength) by fine‐tuning torsion angle and the ingenious transformation between cyanine and hemicyanine through regulation optically tunable group endows the NIR ratiometric PA and tunable tumor‐targeting properties. To demonstrate the applicability of Cy‐HCy dyes, we designed the first small‐molecule tumor‐targeting and NIR ratiometric PA probe Cy‐HCy‐H 2 S for precise CRC liver metastasis diagnosis, activated by H 2 S (a CRC biomarker). Using this probe, we not only visualized the subcutaneous tumor and liver metastatic cancers in CRC mouse models but also realized PA and fluorescence image‐guided tumor excision. We expect that Cy‐HCy will be generalized for creating a wide variety of inherently tumor‐targeting NIR ratiometric PA probes in oncological research and practice.