Fluoride doped γ-Fe2O3 nanoparticles with increased MRI relaxivity

Iron oxide nanoparticles (IONs) are being actively researched and experimented with as contrast agents for Magnetic Resonance Imaging (MRI), as well as image-directed delivery of therapeutics. The efficiency of an MRI contrast agent can be described by its longitudinal and transverse relaxivities, r(1) and r(2). gamma-Fe2O3 nanoparticles -doped with fluoride in a controlled manner and functionalised with citric acid showed a 3-fold increase in r(1) and a 17-fold increase in r(2) in a magnetic field of 3 T and almost 6-fold increase in r(1) and a 14-fold increase in r(2) at 11 T. Following fluorination, PXRD shows that the crystal structure of g-Fe2O3 is maintained, Mossbauer spectroscopy shows that the oxidation state of the Fe cation is unchanged and HREM shows that the particle size does not vary. However, magnetisation curves show a large increase in the coercive field, pointing towards a large increase in the magnetic anisotropy for the fluorinated nanoparticles compared to the un-doped g-Fe2O3 nanoparticles. Therefore, a chemically induced increase in magnetic anisotropy appears to be the most relevant parameter responsible for the large increase in relaxivity for gamma-Fe2O3 nanoparticles.