Colloidal stability of ultrasmall superparamagnetic iron oxide (USPIO) particles with different coatings.

Ultrasmall superparamagnetic iron oxide (USPIO) particles are efficient contrast agents used in vivo to enhance relaxation differences between healthy and pathological tissues. Detailed understanding of their physicochemical properties in suspension is necessary to guarantee the quality and safety of biological USPIO particles application. The ferrofluids stability against aggregation and gravitational settling affects their biodistribution and consequently the resulting contrast. In this study, the stability of iron oxide particles was investigated by dynamic light scattering (DLS) at different NaCl concentrations in order to monitor the evolution of the hydrodynamic radius of the particles with time. The results were interpreted using the classical DLVO theory of colloidal stability. The electrophoretic mobility and the models generally used to convert it to zeta potential were discussed and related to the stability results.