Breaking the Gadolinium Mold: A Metal–Organic Framework Contrast Agent for Magnetic Resonance Imaging

The formulation of magnetic resonance imaging (MRI) contrast agents (CAs) that are both biologically safe and effective continues to be a significant focus and a challenge in biomedical research. This study aims to address the limitations inherent in commercially available MRI CAs by introducing a bimetallic (Gd)-Fe-metal-organic framework prepared through a streamlined, one-step solvothermal approach, thereby eliminating the need for complex postsynthetic modifications. Through the meticulous optimization of parameters, exceptionally high crystallinity was achieved in a bimetallic MOF, ensuring structural stability and enhanced performance. Notably, the integration of gadolinium (Gd) into a monometallic Fe-MOF induced a magnetic transition, shifting from ferromagnetism to paramagnetism, which unlocks inherent dual T₁-T₂ contrast properties without requiring external magnetic nanomaterials. This intrinsic dual relaxivity provides a self-sustained MRI signal, distinguishing it from conventional CAs. The material exhibits impressive relaxivity values: its r₁ was found to be 6.03 mM^-1 s^-1 in agar media and 3.85 mM^-1 s^-1 in water media; the corresponding r₂ values were 53.65 mM^-1 s^-1 in agar media and 26.72 mM^-1 s^-1 in water media. Moreover, (Gd)-Fe-MOF exhibits superior biocompatibility, with an 88.3% cell viability in MTT assays conducted on the Y79 cell line, significantly outperforming the clinically used Gd-DTPA. This work focuses on the development of an improved MRI CA that offers enhanced safety, optimized crystalline structure, and intrinsic multimodal imaging capabilities, making a significant advancement in MRI diagnostics.