A Smart Self‐Immobilization Magnetic Resonance Contrast Agent for Delayed Tumor Imaging In Vivo

(0.5 T, 21.3 MHz, 32 °C) and effectively "traps" the probe at the tumor site. P-QM-Gd showed rapid tumor uptake and efficient covalent labeling, achieving distinct MR contrast enhancement (> 60%). The imaging window was extended for up to 24 h in subcutaneous HeLa and orthotopic K7M2 tumor models. Notably, delayed MRI with P-QM-Gd enabled precision visualization of ∼1.3 mm orthotopic K7M2 tumors in mice. By overcoming the rapid washout and low sensitivity inherent to traditional small-molecule MRI probes through this enzymatic self-immobilization strategy, P-QM-Gd offers a promising approach for high-sensitivity, high-spatial resolution delayed tumor MRI, making it particularly effective for early-stage lesion detection.