Silica-coated Iron-oxide Nanoparticles Synthesized as a T2 Contrast Agent for Magnetic Resonance Imaging by Using the Reverse Micelle Method

We synthesized iron-oxide (Fe3O4) nanoparticles by using the reverse micelle method and coated them with biocompatible silica. The coated nanoparticles were found to be spherical in the TEM images and showed a uniform size distribution with an average diameter of 10 nm. The T-1 and the T-2 relaxation times of hydrogen protons in aqueous solutions with various concentrations of silica-coated nanoparticles were determined by using a magnetic resonance (MR) scanner. We found that the T-2 relaxivity was much larger than the T-1 relaxivity for the nanoparticle contrast agent, which reflected the fact that the T-2 relaxation was mainly influenced by outer sphere processes. The T-2 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 T-2 agent in magnetic resonance imaging.