Effect of sampling volume on measurements of size and chemical homogeneity of MRI contrast agent FeraSpin™ R

The use of iron oxide nanoparticles as contrast agents for magnetic resonance imaging (MRI) poses key questions regarding accurate determination of particle size and chemical composition within micro-heterogeneous systems. Here we present the first systematic study on homogeneity for particle size and chemical composition on the nanoparticle-based MRI contrast agent FeraSpin™ R, combining complementary analytical tools across a multidisciplinary consortium, clustered around the EURAMET project MetrINo. Our results indicate that, depending on the target measurand, sizing methods can provide consistent values for the particle colloidal diameter and for the size of the particle core, independently of the effective volume of the sample probed. Conversely, the evaluation of homogeneity for chemical composition depends on the length-scale of the sampling, in agreement with Benedetti-Pichler description of multicomponent systems. This case study highlights the importance of measurement length-scale for comparison and integration of data from complementary analytical methods, opening new avenues for standardization to support regulatory positioning of emerging nanomedicines.