Effects of inter- and intra-aggregate magnetic dipolar interactions on the magnetic heating efficiency of iron oxide nanoparticles

TLDR

Iron oxide nanoparticles are increasingly used in biomedical sensing, trapping, therapy, and diagnostics, and their magnetic properties—affected by aggregation state and concentration—require a better understanding of dipolar interactions to ensure reliable hyperthermia responses in biological matrices. The study evaluates how inter‑ and intra‑aggregate magnetic dipolar interactions influence heat dissipation power and AC hysteresis loops as nanoparticle concentration and aggregate size increase. The authors varied nanoparticle concentration and hydrodynamic aggregate size to measure heat dissipation power and AC hysteresis loops, thereby assessing dipolar interaction effects. Inter‑aggregate interactions magnetize the particles while intra‑aggregate interactions demagnetize them, leading to heat dissipation power that strongly reflects these opposing effects, and the intra‑aggregate behavior was successfully reproduced by numerical simulations.

Abstract

Iron oxide nanoparticles have found an increasing number of biomedical applications as sensing or trapping platforms and therapeutic and/or diagnostic agents. Most of these applications are based on their magnetic properties, which may vary depending on the nanoparticle aggregation state and/or concentration. In this work, we assess the effect of the inter- and intra-aggregate magnetic dipolar interactions on the heat dissipation power and AC hysteresis loops upon increasing the nanoparticle concentration and the hydrodynamic aggregate size. We observe different effects produced by inter- (long distance) and intra-aggregate (short distance) interactions, resulting in magnetizing and demagnetizing effects, respectively. Consequently, the heat dissipation power under alternating magnetic fields strongly reflects such different interacting phenomena. The intra-aggregate interaction results were successfully modeled by numerical simulations. A better understanding of magnetic dipolar interactions is mandatory for achieving a reliable magnetic hyperthermia response when nanoparticles are located into biological matrices.