Physicochemical characterization of ultrasmall superparamagnetic iron oxide particles (USPIO) for biomedical application as MRI contrast agents

A review. Ultrasmall superparamagnetic iron oxide (USPIO) particles are maghemite or magnetite nanoparticles currently used as contrast agent in magnetic resonance imaging. The coatings surrounding the USPIO inorg. core play a major role in both the in vitro stability and, over all, USPIO's in vivo fate. Different physicochem. properties such as final size, surface charge and coating d. are key factors in this respect. Up to now no precise structure - activity relationship has been described to predict entirely the USPIOs stability, as well as their pharmacokinetics and their safety. This review is focused on both the classical and the latest available techniques allowing a better insight in the magnetic core structure and the org. surface of these particles. Concurrently, this work clearly shows the difficulty to obtain a complete physicochem. characterization of USPIOs particles owing to their small dimensions, reaching the anal. resoln. limits of many com. instruments. An extended characterization is therefore necessary to improve the understanding of the properties of USPIOs when dispersed in an aq. environment and to set the specifications and limits for their conception.