Understanding Fe3O4 nanorod magnetism for biomedical applications

Abstract

Iron oxide nanoparticles have been extensively studied for a variety of applications; however, to optimize a system for a particular use requires a complete understanding of the underlying physics. Seemingly minor changes to size and shape can significantly affect a system's behaviour. In this work, we show how spherical iron oxide nanoparticles can be used to remove MRSA biofilms, with results that suggest anisotropic nanoparticles could be advantageous.

As a result, we have synthesized magnetite (Fe3O4) nanorods. By using a variety of techniques, such as x-ray diffraction, Mössbauer spectroscopy, XAS/XMDC and magnetometry, we have characterized this system. We observe a modified Verwey transition, where the low temperature monoclinic phase reveals a high degree of strain. By tracking the Fe3O4 nanorods' structure as a function of temperature, a multistep transition is observed with both transition temperatures elevated from the bulk Verwey temperature of ~120 K. This suggests that the Verwey temperature could be controlled by manipulating the intrinsic strain. Of perhaps greater interest for biological applications is the response of the nanoparticles to a magnetic field. Much of the work thus far for applications such as hyperthermia treatments have been focused on nanoparticles with domains that reverse via coherent rotation; however, our Fe3O4 nanorod domains reverse via curling. This effect is observed in the dependence of the intrinsic loss power on applied magnetic field and frequency. The measured heating efficiency of these Fe3O4 nanorods makes them excellent candidates for biomedical applications.