Uniform mesoporous silica coated iron oxide nanoparticles as a highly efficient, nontoxic MRI T(2) contrast agent with tunable proton relaxivities.

Monodisperse mesoporous silica (mSiO(2) ) coated superparamagnetic iron oxide (Fe(3) O(4) @mSiO(2) ) nanoparticles (NPs) have been developed as a potential magnetic resonance imaging (MRI) T(2) contrast agent. To evaluate the effect of surface coating on MRI contrast efficiency, we examined the proton relaxivities of Fe(3) O(4) @mSiO(2) NPs with different coating thicknesses. It was found that the mSiO(2) coating has a significant impact on the efficiency of Fe(3) O(4) NPs for MRI contrast enhancement. The efficiency increases with the thickness of mSiO(2) coating and is much higher than that of the commercial contrast agents. Nuclear magnetic resonance (NMR) relaxometry of Fe(3) O(4) @mSiO(2) further revealed that mSiO(2) coating is partially permeable to water molecules and therefore induces the decrease of longitudinal relaxivity, r(1) . Biocompatibility evaluation of various sized (ca. 35-95 nm) Fe(3) O(4) @mSiO(2) 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 Fe(3) O(4) @mSiO(2) highlights these core-shell particles as highly efficient T(2) contrast agents with high biocompatibility.