Analysis of the NMR Relaxation Enhancement by Core/shell Fe/iron Oxide Nanoparticles

The aim of this work is to study the mechanism of proton relaxation induced by these materials. In this sense, physicochemical and magnetorelaxometry characterization of colloidal suspensions of iron oxide and iron/iron oxide nanoparticles synthesized by laser pyrolysis were carried out and the origin of the contrast improvement was analysed. In the case of the colloidal dispersion formed by ferromagnetic iron core-shell nanoparticles, the longitudinal NMRD profile showed a strong increase of the Rl values at low applied magnetic fields and a strong increase of the transverse relaxation rate measured at high applied magnetic field. This behavior was explained considering the larger magnetic aggregate size and saturation magnetization values measured for this sample, 92 nm and 31 emu/g Fe respectively, with respect to those measured for the colloidal dispersion of iron oxide nanoparticles (61 nm and 23 emu/g Fe).