Tailoring the magnetic core of organic-coated iron oxides nanoparticles to influence their contrast efficiency for Magnetic Resonance Imaging

An experimental 1H NMR relaxometry investigation on iron oxide nanoparticles with different magnetic core size and coated with PolyAcrylic Acid (PAA), is presented. A full structural, morphodimensional and magnetic characterization of the nanoparticles has been performed by means of X-ray diffraction, Dynamic Light Scattering, Transmission Electron Microscopy, Atomic Force Microscopy and SQUID DC magnetometry. The application of a heuristic model for the field dependence of the NMR relaxivity curves allowed us to evaluate the distance of minimum approach of the solvent molecules from the magnetic centers, and to conclude that the local correlation times, namely the Neél time τN and the diffusion time τD related to the magnetization reversal and to the diffusion process respectively, depend strongly on the core size. A preliminary evaluation of their r2 efficiency as Magnetic Resonance Imaging (MRI) contrast agents is also performed by means of a universal scaling law model. The results of our experimental investigation should allow to tailor the physical properties of the nanoparticles for obtaining systems with a resultant contrast efficiency optimized for the in-vivo application of MRI at pre-clinical and clinical level.