Quantification of aggregates of magnetic nanoparticles in different suspension media by magnetorelaxometry

D. Eberbeck¹ - Ch. Bergemann² - F. Wiekhorst¹ - G. Glöckl³

¹ Physikalisch-Technische-Bundesanstalt, Abbestraße 2-12, 10587 Berlin, Germany
² CHEMICELL GmbH, Berlin, Germany
³ Institute of Pharmacy, Ernst-Moritz-Arndt-University, Greifswald, Germanya

Abstract
With highly sensitive magnetorelaxometry measurements we could detect aggregation within suspensions of magnetic nanoparticles (MNP). We developed a momentum superposition model, which allows the description of the relaxation curves by MNP-clusters. Fitting the model to our data yields the mean and the standard deviation of the cluster size distribution as well as the degree of the aggregation. Due to aging phenomena, aggregation occurs predominantly at low MNP-concentrations (c (Fe) ≤ 10⁻⁴ mol/l). As a consequence, the relaxation curves do not scale with the MNP-concentration. The MNP suspended in fetal calf serum (FCS) aggregate in dependence on the MNP-concentration. We relate this to agglutination (cross-linking) among the MNP, presumably caused by positively charged macromolecules. This agglutination takes place in anionic MNP-suspensions but does not occur in MNP suspensions, where the MNP are neutral. Tables 2, Figs 6, Refs 17.