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 T₁ and the T₂ relaxation times of hydrogen protons in aqueous solutions with various concentrations of silicacoated nanoparticles were determined by using a magnetic resonance (MR) scanner. We found that the T₂ relaxivity was much larger than the T₁ relaxivity for the nanoparticle contrast agent, which reflected the fact that the T₂ relaxation was 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.