NODESINNDIANAZ115From gadolinium (III) to iron (III): coordination polymers for T1-MRI and photothermal therapy

Coordination polymer-based systems, particularly those incorporating Fe(III), are gaining attention for biomedical imaging due to their tunable morphology, biocompatibility, and potential for surface functionalization1. Thanks to its five unpaired electrons, Fe(III) represents a safer and valuable alternative to Gd(III) for MRI, especially for T₁-weighted imaging. While low molecular weight Fe(III) chelates have been explored, the development of Fe(III)-based nanostructures as efficient T₁ MRI contrast agents remains less investigated. In this study, we report the synthesis and characterization of Fe(III)/gallic acid coordination nanoparticles coated with low molecular weight polyethylene glycol (PEG), designed to enhance second-sphere water interactions with Fe(III) ions exposed on the nanoparticle surface and increase longitudinal relaxivity at clinical magnetic fields (1.5 – 3.0 T)2. This strategy proved to be effective, as PEG/Fe(III)-GA nanoparticles exhibited relaxivity values per Fe(III) ion exceeding those of the PVP-coated analogues by more than 150% at 3 T and 298 K. Moreover, these nanoparticles demonstrated excellent performance in photothermal therapy (PTT), highlighting their potential for cancer theranostics. Furthermore, their aqueous suspensions showed prolonged colloidal stability, high biocompatibility, and satisfactory in vivo MRI contrast, even at low administered doses.