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

Abstract

Core–shell magnetic nanostructures (MNS) such as Fe3O4–SiOx, are being explored for their potential applications in biomedicine, such as a T2 (dark) contrast enhancement agent in magnetic resonance imaging (MRI). Herein, we present the effect of silica shell thickness on its r2 relaxivity in MRI as it relates to other physical parameters. In this effort initially, monodispersed Fe3O4 MNS (nominally 9 nm size) were synthesized in organic phase via a simple chemical decomposition method. To study effect of shell thickness of silica of Fe3O4–SiOx core shell on r2 relaxivity, the reverse micro-emulsion process was used to form silica coating of 5, 10 and 13 nm of silica shell around the MNS, while polyhedral oligomeric silsesquioxane was used to form very thin layer on the surface of MNS; synthesized nanostructures were characterized by transmission electron microscopy (TEM) and high resolution TEM (HRTEM), superconducting quantum interference device magnetometry and MRI. Our observation suggests that, with increase in thickness of silica shell in Fe3O4–SiOx core–shell nanostructure, r2 relaxivity decreases. The decrease in relaxivity could be attributed to increased distance between water molecules and magnetic core followed by change in the difference in Larmor frequencies (Dx) of water molecules. These results provide a rational basis for optimization of SiOx-coated MNS for biomedical applications.

Core–shell superparamagnetic nanoparticles with interesting properties as contrast agents for MRI

“…This result makes their use as negative CA for MRI promising. The same negligible effect T 1 although in a smaller scale was reported for a silica coated SPIONs [14].…”

“…It is a fact that several SPIONs present higher r 2 values [14] but the NPs here studied have outstanding ratios r 2 /r 1 . Since all the synthesized NPs have the same superparamagnetic core, the observed differences in the ratio r 2 /r 1 mus be assigned to the coating.…”

“…It is reported [49,14] that the hydrophilicity of the SPIONs coating affect the obtained relaxivities. The different organic groups bonded to the siloxane skeleton provides different hydrophilicity to the obtained coreeshell NPs and this reflects in the observed relaxivities.…”

“…As for the SPIONs application here presented, the use as CA for MRI, it is known that the coating it-self is important on the enhancement of image contrast [14], this aspect will be explored in this work.…”

Magnetic hydroxyapatite: a promising multifunctional platform for nanomedicine application

“…Metal oxides such as TiO 2 and SiO 2 including calcium phosphate coating over nanoparticles are well studied by several researchers. [47][48][49] Yang et al synthesized mesoporous and nonmesoporous silica-coated iron oxide nanoparticles for luminescent and drug delivery applications. 47 Ye et al reported the synthesis of mesoporous silica-coated iron oxide nanoparticles for use as nontoxic MRI contrast agent.…”