Self‐Limiting Growth Nanoscale Coordination Polymers for Fluorescence and Magnetic Resonance Dual‐Modality Imaging

The size and shape of coordination polymers (CPs) are often tuned by external factors including reaction temperature, reaction time, precursor ratio, auxiliary ligand, and surfactant. Here, a self‐limiting growth of uniform nanoscale CPs (NCPs) spheres with Gd³⁺ and Ru[4,4′‐(COOH)₂ bipyridyl(bpy)]₃²⁺ (L_Ru) as precursors is reported. Sexadentate L_Ru and nine‐coordinating Gd³⁺ play key roles in the formation of the NCPs via a simple and robust self‐limiting procedure. Therefore, the formation of NCP spheres is almost unaffected in the reaction temperature of 100–160 °C for 1–6 h. Moreover, no auxiliary ligand or surfactant is required, whereas high yield and simple procedure are obtained. The red fluorescence of L_Ru and high longitudinal relaxivity of Gd³⁺ remain in the NCPs, which are therefore examined as fluorescence‐magnetic resonance (MR) dual‐modality imaging probes. The structural merits of the NCPs enable high MR contrast efficiency. Red emission avoids the auto‐fluorescence and light scattering from tissues and realizes low‐background imaging. The low toxicity and background, and high imaging efficiency of the NCPs are confirmed using HepG2 cells, zebrafish, and tumor‐bearing mice as models.