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 magnetic resonance imaging contrast agent based on the incorporation of preformed iron oxide (Fe(3)O(4)) nanocrystals into hollow silicon nanotubes (Si NTs). Specifically, superparamagnetic Fe(3)O(4) nanoparticles of two different average sizes (5 nm and 8 nm) were loaded into Si NTs of two different shell thicknesses (40 nm and 70 nm). To achieve proper aqueous solubility, the NTs were functionalized with an outer polyethylene glycol-diacid (600) moiety via an aminopropyl linkage. Relaxometry parameters r(1) and r(2) were measured, with the corresponding r(2)/r(1) ratios in phosphate buffered saline confirming the expected negative contrast agent behaviour for these materials. For a given nanocrystal size, the observed r(2) values are found to be inversely proportional to NT wall thickness, thereby demonstrating the role of nanostructured silicon template on associated relaxometry properties.