Influence of morphology and surface exchange reaction on magnetic properties of monodisperse magnetite nanoparticles

Monodisperse magnetite nanoparticles (Fe3O4 NPs) were synthesized by thermal decomposition of Fe(oleate)3 in 1-octadecene containing oleic acid. Two kinds of oleic acid capped Fe3O4 nanoparticles (Fe3O4@OA) with different shape but similar size were obtained, quasi-cubical and spherical respectively. Ligand exchange reaction with 2,3-dimercaptosuccinic acid (DMSA) was performed to transfer Fe3O4 NPs from organic phase to aqueous phase. TEM, DLS and EDS were used to characterize and evaluate these samples. TEM showed that ligand exchange reaction made the nanoparticles shape changed, especially the quasi-cubical ones. With EDS analysis, effects of surface exchange on Fe3O4@DMSA NPs were further studied. Magnetic properties, including saturation magnetization (Ms), relaxivity (r2) of Fe3O4 NPs as MRI contrast agent and specific absorption rate (SAR) in alternating magnetic field, were investigated with respect to Fe3O4 nanoparticle morphology and surface exchange time. Results showed that nanoparticles of quasi-cubical shape, obtained using shorter surface exchange time, had stronger saturation magnetization which accordingly resulted in better MRI contrast and heat conversion efficiency under magnetic induction.