Preparation for Highly Sensitive MRI Contrast Agents Using Core/Shell Type Nanoparticles Consisting of Multiple SPIO Cores with Thin Silica Coating

We describe here the facile and robust preparation methods for the multiple-SPIO-containing silica-coated core/shell type nanoparticles which can serve as a highly sensitive MRI contrast agent. The imidazolium-tethered core/shell type particles were synthesized, and the centrifugal selection for the multiple-SPIO-containing particles and the etching process to fabricate thin silica layers were carried out to improve the proton relaxivity of water tissue. We found that the synthetic particles can provide ∼7-fold clearer contrasts than that of the particles before treatments. In addition, the particles can show good dispersibility at least for 1 week in aqueous media.