Ultrasmall Fe3O4@Au Composite Nanoparticles with Different Sizes of Fe3O4 for Magnetic Hyperthermia

We reported the synthesis and characterization of ultrasmall iron oxide/gold composite nanoparticles (Fe3O4@Au NPs) with different sizes of Fe3O4, and the evaluation of their heating efficiency for potential use in magnetic hyperthermia application. The Fe3O4 NPs were synthesized using the thermal decomposition method with three types of sizes of ~5 nm, ~10 nm, and ~13 nm. Gold was then deposited onto the surface of Fe3O4 NPs by reducing gold acetate at 190°C. The synthesized Fe3O4 and their Fe3O4@Au NPs were characterized using TEM, EDX, XRD, and VSM analyses. The magnetization of Fe3O4 NPs increased with increasing their size with 74.7 emu/g for ~13 nm. The mass percentage of Au in Fe3O4@Au NPs estimated from the magnetization values were 94.3, 96.3, 77.0wt% for Fe3O4 ~5 nm@Au, Fe3O4 ~10 nm@Au, Fe3O4 ~13 nm@Au, respectively. The specific absorption rate (SAR) increased with increasing size of Fe3O4 with the maximum values of 136.7 and 23,4 W/g under an applied magnetic field of 25.7 kA/m and 267 kHz for Fe3O4 ~13 nm, Fe3O4 ~13 nm@Au NPs, respectively, exhibiting high heating efficient capabilities and indicating potential use for magnetic hyperthermia.

I. Introduction

Theranostic agents and their applications using Fe₃O₄@Au composite magnetic nanoparticles (Fe₃O₄@Au NPs) are of great interest in cancer therapy owing to their potential for targeted delivery, multimodal imaging diagnosis, and therapeutics [1]. To the best of our knowledge, there is little or no information on the synthesis and characterization of ultrasmall Fe₃O₄@Au NPs especially core/shell nanostructure with different core sizes for magnetic hyperthermia. We previously developed ultrasmall core/shell Fe₃O₄@Au NPs (core ~5.2 nm, shell thickness ~0.5 nm) as theranostic agents toward combining our magnetic hyperthermia system [2] and computed tomography (CT) imaging [3]. Although there is no significant difference in CT contrast generation with different sizes of Au NPs [4], the heating efficiency of Fe₃O₄ NPs is strongly dependent on their size [5]. For this reason, in the current study to further improve their heating efficiency, we developed Fe₃O₄@Au NPs with various types of Fe₃O₄ sizes and evaluate them for magnetic hyperthermia application.