We synthesized iron oxide (Fe3O4) nanoparticles by the reverse micelle method, and coated them with biocompatible silica. The coated nanoparticles were found to be spherical in TEM images, and showed a uniform size distribution with an average diameter of 10nm. The T1 and T2 relaxation times of hydrogen protons in the aqueous solution of various concentrations of silica-coated nanoparticles were determined by a magnetic resonance (MR) scanner. We found that the T2 relaxivity is much larger than the T1 relaxivity for the nanoparticle contrast agent, which reflects the fact that the T2 relaxation is mainly influenced by outer sphere processes. The T2 relaxivity was found to be 15 times larger than that for the commercial Gd-DTPA-BMA contrast agent. This result demonstrates that silica-coated iron oxide nanoparticles are applicable as a T2 agent in magnetic resonance imaging.
Keywords: Iron oxide nanoparticle, silica coating, relaxivity, contrast agent