Improving heating performance in Iron-based nanoparticles by tuning saturation magnetization

Abstract

Nanoparticles (NPs) with higher magnetization compared to the conventionally used iron oxides have potential in magnetic fluid hyperthermia [1] and possibly beyond. In this study, the saturation magnetization was tuned by changing the ratio of surfactant ligands during the thermal decomposition process of Iron pentacarbonyl Fe(CO)₅. Firstly, only one type of surfactant ligand has been added separately to prepare Iron-NPs @oleic acid and Iron-NPs @ oleylamine. Additionally, a third nanosystem has been prepared by a mixture of ratios between oleic acid/oleylamine (1/1)  (Iron-NPs @oleic acid/oleylamine). Monodispersed core-shell nanoparticles with narrow size distribution were obtained after carefully controlled synthesis. The presence of a core-shell structure has been confirmed by high-resolution transmission electron microscopy (HRTEM). The mean size of the nanoparticles is 13.45nm, 14.55nm, and 15.75nm for  Iron-NPs @oleic acid, Iron-NPs @ oleylamine, and Iron-NPs @oleic acid/oleylamine, respectively. The shape was mainly spherical for nanoparticles synthesized with oleic acid. However, the shape is changed after adding the oleylamine.  The interaction between both surfactants has contributed to an increase in the saturation magnetization M_sat at room temperature from 80 Am²/kg for Iron-NPs @oleic acid to 140 Am²/kg under an applied magnetic field ?₀H=2T for Iron-NPs@oleic acid/oleylamine. Furthermore, to test these nanoparticles for magnetic hyperthermia application, their magnetic heating properties have been measured with an AC magnetic field applicator under an AC magnetic field 30mT, with different frequencies (98 kHz, 200 kHz, and 400 kHz). The intrinsic loss power (ILP)  values are determined as a normalization of specific absorption rate (SAR) values measured at different magnetic field amplitudes/frequencies [2]. The ILP values are 2,  0.48, and  1.14 nH.m²/kg for Iron-NPs @oleic acid/oleylamine, Iron-NPs @oleic acid, and Iron-NPs @ oleylamine, respectively. In conclusion, the surface modification of the core-shell nanoparticles using a mixture of surfactants has significantly improved the magnetic fluid hyperthermia heating rate..