Two samples were used in this study. One was a commercial magnetite-based starch-coated nanoparticle suspension (BNF-starch S31009, micromod Partikeltechnologie, GmbH, Rostock, Germany) synthesized by high-pressure homogenization according to the core-shell method35 . The other colloid was synthesized by the co-precipitation procedure previously described and consisted of manganese ferrite-based (MNF-citrate) nanoparticles surface-coated with citrate54 . Both colloids are dispersed in water at physiological conditions.