FAP-targeting peptide-directed nanoprobes enable tumor microenvironment-activatable MR/NIRF imaging of breast cancer primary tumor and lung metastases

-weighted MR contrast enhancement; Cy7 fluorescence increase achieving tumor-to-background ratio in NIRF imaging. In orthotopic and metastatic breast cancer models, the nanoprobes enabled high-resolution visualization of primary tumors and lung metastases as small as a diameter of 0.3 mm. In addition, the novel molecular imaging probe demonstrated favorable biosafety and efficient renal clearance, supporting the potential for clinical translation. This work establishes a tumor stroma-targeted activatable platform advancing metastasis-sensitive diagnosis and providing a blueprint for microenvironment-responsive theranostics.