Magnetic hyperthermia is a promising tool as an adjuvant therapy for multimodal cancer treatment. However, the heating efficiency of magnetic nanoparticles in biological conditions is not yet fully understood, especially regarding their dispersion state. In this work, dynamic light scattering (DLS) and hyperthermia experiments were coupled to highlight the role of the aggregation of iron oxide nanoparticles on their heating properties induced by an alternating magnetic field. Bare, poly(acrylic acid), and poly(acrylic acid-co-maleic acid) coated nanoparticles were studied. More precisely, the interparticular interactions were investigated by varying the ionic strength and the pH. Our results show that the specific loss power (SLP) of nanoparticles in small and loose aggregates is similar to that of well dispersed nanoparticles while the formation of large and dense aggregates observed by DLS can be correlated to a decrease of the SLP of the nanoparticles. However, at intermediate aggregation states, DLS experiments alone do not allow to fully comprehend the heating properties of magnetic nanoparticles. Small angle X-ray scattering experiments (SAXS) were performed to get information about the inner structure of the aggregates: the closer the nanoparticles in the aggregates, the less they heat the surrounding medium. These results shed a new light on the negative influence of the interparticular interactions in aggregates on the particles heating efficiency.

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