Aggregation effects on the magnetic properties of iron oxide colloids

Magnetic nanoparticles (MNPs), and in particular iron oxide nanoparticles (mainly magnetite and maghemite), are being widely used in the form of aqueous colloids for biomedical applications. In such colloids, nanoparticles tend to form assemblies, either aggregates, if the union is permanent, or agglomerates, if it is reversible. These clustering processes have a strong impact on the MNPs' properties that are often not well understood. In this review, the causes and consequences of MNPs aggregation/agglomeration are reviewed and discussed. Special attention has been paid to the impact of the MNPs aggregation/agglomeration on their magnetic properties and heating properties, when exposed to an alternating magnetic field in the frame of magnetic hyperthermia. In addition, a model system with MNPs of two different sizes coated with three different molecules oleic acid, meso-2, 3-dimercaptosuccinic acid and poly(maleic anhydride-alt-1-octadecene) has been characterized and the results used to support the ideas reviewed.This work was supported by Fondo Social de la DGA (grupos DGA, BIONANOSURF), Ministerio de la Economía y Competitividad del Gobierno de España for the public funding of Proyectos I+D+I—Programa Estatal de Investigación, Desarrollo e Innovación Orientada a los Retos de la Sociedad (projects MAT2017-88148-R, MAT2015-71806-R and SAF2014-54763-C2-2-R), Comunidad de Madrid (Project NANOFRONTMAG-CM, S2013/MIT-2850), and ERCStarting Grant 239931-NANOPUZZLE. IMDEA Nanociencia acknowledges support from the ‘Severo Ochoa’ Programme for Centres of Excellence in R&D (MINECO, Grant SEV-2016-0686). LG acknowledges financial support from the Ramón y Cajal subprogram (RYC-2014-15512).Peer reviewe