Uniform mesoporous silica coated iron oxide nanoparticles as a highly efficient, nontoxic MRI T2 contrast agent with tunable proton relaxivities

Abstract

Monodisperse mesoporous silica (mSiO₂) coated superparamagnetic iron oxide (Fe₃O₄@mSiO₂) nanoparticles (NPs) have been developed as a potential magnetic resonance imaging (MRI) T₂ contrast agent. To evaluate the effect of surface coating on MRI contrast efficiency, we examined the proton relaxivities of Fe₃O₄@mSiO₂ NPs with different coating thicknesses. It was found that the mSiO₂ coating has a significant impact on the efficiency of Fe₃O₄ NPs for MRI contrast enhancement. The efficiency increases with the thickness of mSiO₂ coating and is much higher than that of the commercial contrast agents. Nuclear magnetic resonance (NMR) relaxometry of Fe₃O₄@mSiO₂ further revealed that mSiO₂ coating is partially permeable to water molecules and therefore induces the decrease of longitudinal relaxivity, r₁. Biocompatibility evaluation of various sized (ca. 35–95 nm) Fe₃O₄@mSiO₂ NPs was tested on OC‐k3 cells and the result showed that these particles have no negative impact on cell viability. The enhanced MRI efficiency of Fe₃O₄@mSiO₂ highlights these core–shell particles as highly efficient T₂ contrast agents with high biocompatibility. Copyright © 2012 John Wiley & Sons, Ltd.