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

TLDR

Ultrasmall superparamagnetic iron oxide particles are used as MRI contrast agents, and their coatings, size, surface charge, and coating density critically influence in vitro stability, in vivo fate, pharmacokinetics, and safety, yet no precise structure–activity relationship has been established. The review aims to evaluate classical and recent techniques for probing the magnetic core and surface of USPIOs to improve understanding of their properties. The authors analyze these techniques to provide insight into the core structure and surface characteristics of USPIOs. The review demonstrates that USPIOs’ small size limits analytical resolution, making comprehensive physicochemical characterization challenging.

Abstract

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 inorganic core play a major role in both the in vitro stability and, over all, USPIO's in vivo fate. Different physicochemical properties such as final size, surface charge and coating density 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 organic surface of these particles. Concurrently, this work clearly shows the difficulty to obtain a complete physicochemical characterization of USPIOs particles owing to their small dimensions, reaching the analytical resolution limits of many commercial instruments. An extended characterization is therefore necessary to improve the understanding of the properties of USPIOs when dispersed in an aqueous environment and to set the specifications and limits for their conception.