Effect of silica shell thickness of Fe3O4–SiOx core–shell nanostructures on MRI contrast
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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 r 2 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 r 2 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, r 2 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 (Δω) of water molecules. These results provide a rational basis for optimization of SiOx-coated MNS for biomedical applications.
KeywordsMagnetic nanoparticles T2 contrast agents Core–shell nanostructures Relaxivity MRI
This research is supported by the Center for Cancer Nanotechnology Excellence (CCNE) initiative of the National Institutes of Health’s National Cancer Institute under Award U54CA119341 at Northwestern University. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect those of the National Institutes of Health. Part of this work was performed in the EPIC/NIFTI facility of the NUANCE centre (supported by NSF-NSEC, NSFMRSEC, Keck Foundation, the State of Illinois, and Northwestern University) at Northwestern University. MRI measurements were performed at NorthShore University HealthSystem with the kind support of Center for Advanced Imaging. We would like to acknowledge paper by Blasiak et al. (2011) on similar research topic, which was published at nearly the same time when this contribution was under reviewing process.
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