A Hypoxia‐Responsive Near‐Infrared Phosphorescence Nanoprobe for High‐Sensitive Detection of Tumor Cells and Imaging of Colorectal Cancer In Situ

ABSTRACT Colorectal cancer (CRC) is the third most commonly diagnosed cancer in the world, exhibiting persistently high mortality rates due to delayed diagnosis and imprecise lesion localization. Leveraging the prevalent hypoxic microenvironment characteristic of CRC lesions, this study innovatively developed a PEGylated iridium‐based near‐infrared (NIR) hypoxia nanoprobe, Ir‐PEG. This nanoprobe can be activated in situ under hypoxic conditions, providing high‐contrast imaging of colonic lesions, even though the intestine is inherently a low oxygen environment. In vitro evaluation demonstrated that Ir‐PEG had excellent oxygen sensitivity, water solubility, and deep tissue penetration capability. These properties enabled Ir‐PEG to achieve precise imaging of CRC in the native colonic microenvironment. Remarkably, in both in vitro and in vivo models, Ir‐PEG achieved highly sensitive detection of cancer cell populations, and could detect as few as 10 4 CT26 cells in vivo. In addition, the nanoprobe could successfully identify different tumor types based on differential oxygen consumption rates across various cancer cells, suggesting its potential to identify intratumoral heterogeneity. As a molecular imaging tool, Ir‐PEG enabled early non‐invasive detection of CRC with high sensitivity and specificity, and holding significant promise for clinical translation.