Magnetic and relaxometric properties of polyethylenimine-coated superparamagnetic MRI contrast agents

Novel systems to be employed as superparamagnetic contrast agents (CA) for magnetic resonance imaging (MRI) have been synthesized. These compounds are composed of an iron oxide magnetic core coated by polyethylenimine (PEI) or carboxylated polyethylenimine (PEI-COOH). The aim of the present work was to prepare and study new nanostructured systems (with better or at least comparable relaxivities, R1 and R2, with respect to the commercial ones) with controlled, almost monodisperse average dimensions and shape, as candidates for molecular targeting. By means of atomic force microscopy (AFM) measurements we determined the average diameter, of the order of 200 nm, and the shape of the particles. The superparamagnetic behavior was assessed by SQUID measurements. By NMR-dispersion (NMRD), we found that PEI-COOH60 presents R1 and R2 relaxivities slightly lower than Endorems. The experimental results suggest that these novel compounds can be used as MRI CA.