Facile non-hydrothermal synthesis of oligosaccharide coated sub-5 nm magnetic iron oxide nanoparticles with dual MRI contrast enhancement effects

Abstract

Ultrafine sub-5 nm magnetic iron oxide nanoparticles coated with oligosaccharides (SIO) with dual T₁-T₂ weighted contrast enhancing effect and fast clearance has been developed as magnetic resonance imaging (MRI) contrast agent. Excellent water solubility, biocompatibility and high stability of such sub-5 nm SIO nanoparticles were achieved by using the "<i>in-situ</i> polymerization" coating method, which enables glucose forming oligosaccharides directly on the surface of hydrophobic iron oxide nanocrystals. Reported ultrafine SIO nanoparticles exhibit a longitudinal relaxivity (r₁) of 4.1 mM^-1s^-1 and a r₁/r₂ ratio of 0.25 at 3 T (clinical field strength), rendering improved T₁ or "brighter" contrast enhancement in T₁-weighted MRI in addition to typical T₂ or "darkening" contrast of conventional iron oxide nanoparticles. Such dual contrast effect can be demonstrated in liver imaging with T₂ "darkening" contrast in the liver parenchyma but T₁ "bright" contrast in the hepatic vasculature. More importantly, this new class of ultrafine sub-5 nm iron oxide nanoparticles showed much faster body clearance than those with larger sizes, promising better safety for clinical applications.