The MnxFe3-xO4 MNPs were prepared in organic solvents where they remained stabilized by an OA coating, so a subsequent transfer to aqueous phase is required for biomedical applications. To do that, we employed a well-established polymer coating methodology, using an amphiphilic polymer, poly(maleic anhydride-alt-1-octadecene) (PMAO) that intercalates with the OA chains . All MNPs series were transferred to water using the same protocol, rendering MNPs stable in aqueous media for long periods of time. Table summarizes the characterization of these MNPs coated with PMAO (Mnx@PMAO) in water. As expected, the transference into water did not affect the shape and core size of the final MNPs as can be seen by TEM (Figure ), and the hydrodynamic diameter measured by DLS was similar for all MNP series (Table ). This indicates a similar transfer to water for all the MNPs regardless of the composition, allowing further comparison between the systems. The successful coating of the MNPs was additionally confirmed by thermogravimetric analysis (TGA) (Table ), as an increase of the organic content between 10 to 24 % when compared with samples only coated with OA is in agreement with other reported PMAO-coated MNPs . Surface modification can play a major role in the redistribution of cations, ultimately modifying the final composition of the spinel structure and its functionality . To study the influence of PMAO coating on the composition and, thus, the structural and magnetic properties, the samples were characterized after coating by ICP-OES, FT-IR and XRD. From the ICP-OES results, we confirmed that Mn 2+ ions leached out from the MNPs after PMAO coating (Table ), as previously reported after DMSA or dopamine coating . Mn 2+ losses ranged from 13.0 to 21.4 % of the initially incorporated amount, except for the sample with the lowest content of Mn 2+ , which lost nearly 50 % of its Mn 2+ ions. This is in agreement with the XPS data where for samples with lower Mn incorporation, the heterogeneity of the enriched Mn surface compared with the core is higher than in samples with a high amount of Mn incorporation.