Enhancing the Magnetic Heating Capacity of Iron Oxide Nanoparticles through Their Postproduction Incorporation into Iron Oxide–Gold Nanocomposites

Abstract

Small variations in the synthesis conditions of iron oxide–gold nanocomposites, made in an aqueous medium by a coprecipitation reaction, have a significant effect on the magnetic‐heating properties of the iron oxide nanoparticles. Citric acid coated magnetite/maghemite (Fe3O4/γ‐Fe2O3) nanoparticles were used as a Turkevich‐style reducing agent and added to varying concentrations of HAuCl4 to form iron oxide–gold nanoparticle composites with Fe/Au molar ratios ranging from ca. 5:1 to ca. 300:1. The magnetic‐heating capacities of the products were measured in a high‐frequency alternating field (peak amplitude 6.6 kA/m, frequency 967 kHz), to determine both the specific absorption rates (SARs) and the intrinsic loss powers (ILPs) of the products. The iron oxide (FeOx) precursor presented a moderately high SAR of 33.9 W/gFeOx and an ILP of 0.8 nH m2/kgFeOx, but the iron oxide–gold nanocomposite formed with 0.75 mm HAuCl4 had an almost threefold‐enhanced heating capacity with a SAR of 88.3 W/gFeOx and an ILP of 2.1 nH m2/kgFeOx. This corresponds to an ILP of 3.0 nH m2/kgFe, which is as high as that of any commercially available material to date. This result has implications for the possible postproduction enhancement of the magnetic‐heating capacities of similar iron oxide systems as well as increasing the theranostic potential of such materials through the incorporation of Au nanoparticles, which may act as integrated binding sites for drugs or other beneficial biomolecules.