Size-Dependent\nHeating of Magnetic Iron Oxide Nanoparticles

Abstract

The ability to generate\nheat under an alternating magnetic field\n(AMF) makes magnetic iron oxide nanoparticles (MIONs) an ideal heat\nsource for biomedical applications including cancer thermoablative\ntherapy, tissue preservation, and remote control of cell function.\nHowever, there is a lack of quantitative understanding of the mechanisms\ngoverning heat generation of MIONs, and the optimal nanoparticle size\nfor magnetic fluid heating (MFH) applications. Here, we show that\nMIONs with large sizes (>20 nm) have a specific absorption rate\n(SAR)\nsignificantly higher than that predicted by the widely used linear\ntheory of MFH. The heating efficiency of MIONs in both the superparamagnetic\nand ferromagnetic regimes increased with size, which can be accurately\ncharacterized with a modified dynamic hysteresis model. In particular,\nthe 40 nm ferromagnetic nanoparticles have an SAR value approaching\nthe theoretical limit under a clinically relevant AMF. An <i>in vivo</i> study further demonstrated that the 40 nm MIONs\ncould effectively heat tumor tissues at a minimal dose. Our experimental\nresults and theoretical analysis on nanoparticle heating offer important\ninsight into the rationale design of MION-based MFH for therapeutic\napplications.