Magnetic properties of novel superparamagnetic MRI contrast agents based on colloidal nanocrystals

Novel systems based on colloidal magnetic nanocrystals (NCs), potentially useful as superparamagnetic (SP) contrast agents for
magnetic resonance imaging (MRI) have been investigated. The NCs we have studied comprise organic-capped single-crystalline
maghemite (g-Fe2O3) cores possessing controlled sizes and shapes. We have comparatively examined spherical and tetrapod-like NCs,
the latter being branched particles possessing four arms which depart out at tetrahedral angles from a central point. The NCs have been made soluble in aqueous solution by applying a procedure based on the surface intercalation and coating with an amphiphilic polymer shell.
NMR relaxivities R1 and R2 were compared with ENDOREMs, one of the standard commercial SP-MRI contrast agent. We found that
the spherical NCs exhibit R1 and R2 relaxivities slightly lower than those of ENDOREMs, over the whole frequency range; on the
contrary, tetrapods show relaxivities about one order of magnitude lower.