New MRI contrast agents based on silicon nanotubes loaded with superparamagnetic iron oxide nanoparticles

This article describes the preparation and fundamental properties of a new possible material as a MRI contrast agent based on the incorporation of preformed iron oxide nanocrystals into hollow silicon nanotubes. Specifically, superparamagnetic iron oxide nanoparticles Fe3O4 of two different average sizes (5 nm and 8 nm) were loaded into silicon nanotubes of two different shell thicknesses (40 nm and 70 nm). To achieve proper aqueous solubility, the nanotubes were functionalized with an outer polyethylene glycol (PEG)-diacid (600) moiety via an aminopropyl linkage. Relaxometry parameters r1 and r2 were measured, with the corresponding r2/r1 ratios in PBS confirming the expected negative contrast agent behaviour for these materials. For a given nanocrystal size, the observed r2 values are found to be inversely proportional to nanotube wall thickness, thereby demonstrating the role of nanostructured silicon template on associated relaxometry properties.