Tunable High Aspect Ratio Iron Oxide Nanorods for Enhanced Hyperthermia

Abstract

Despite magnetic hyperthermia being considered one of the most promising techniques for cancer treatment, until now spherical magnetite (Fe 3 O 4 ) or maghemite (γ-Fe 2 O 3 ) nanoparticles, which are the most commonly employed and only FDA approved materials, yield the limited heating capacity. Therefore, there is an increasing need for new strategies to improve the heating efficiency or the specific absorption rate (SAR) of these nanosystems. Recently, a large improvement in SAR has been reported for nanocubes of Fe 3 O 4 relative to their spherical counterpart, as a result of their enhanced surface anisotropy and chainlike particle formation. Considering the proven advantages of high aspect ratio onedimensional (1D) Fe 3 O 4 nanostructures over their spherical and cubic counterparts, such as larger surface area, multisegmented capabilities, enhanced blood circulation time, and prolonged retention in tumors, we propose a novel approach that utilizes this 1D nanostructure for enhanced hyperthermia. Here, we demonstrate that the SAR of iron oxide nanostructures can be enhanced and tuned by altering their aspect ratio. Calorimetric and ac magnetometry experiments performed for the first time on highly crystalline Fe 3 O 4 nanorods consistently show large SAR values (862 W/g for an ac field of 800 Oe), which are superior to spherical and cubic nanoparticles of similar volume (∼140 and ∼314 W/g, respectively). Increasing the aspect ratio of the nanorods from 6 to 11 improves the SAR by 1.5 times. The nanorods are rapidly aligned by the applied ac field, which appreciably increases the SAR values. A detailed analysis of the effect of the alignment of the nanorods in agar indicates an appreciable SAR increase up to 30% when the nanorods are parallel to the field. These findings pave a new pathway for the design of novel high-aspect ratio magnetic nanostructures for advanced hyperthermia.

Unlocking the Potential of Magnetotactic Bacteria as Magnetic Hyperthermia Agents

“…Computer simulations carried out by different groups suggest that aligned chain‐like structures of magnetic nanoparticles, exhibiting a well‐defined anisotropy axis, could give rise to AC loops that resemble this optimum shape. This has also been supported by the experimental results obtained in highly anisotropic nanostructures, such as magnetite nanorods . Unfortunately, assembling this kind of chains and preventing them from collapsing is not an easy task, due to, among other factors, the presence of attractive magnetic interactions between chains.…”

“…When the bacteria are randomly oriented the AC loops are tilted and do not saturate, giving rise to lower hysteresis losses. This can be related to the increase of the effective anisotropy field as the bacteria deviate from the parallel orientation …”

Light/magnetic hyperthermia triggered drug released from multi-functional thermo-sensitive magnetoliposomes for precise cancer synergetic theranostics

“…It is applied widely in biomedical fields [25,26]. For instance, MNPs can be used in magnetic targeting, thermal therapy, and magnetic resonance imaging (MRI) [27,28], which allow to monitor the biodistribution in vivo non-invasively.…”

Fabrication of magnetic nanorods and their applications in medicine

“…Many of these features are effective when the nanorods show superparamagnetic behavior in a magnetic field [54]. So, in this situation each sample which has a better surface to volume ratio, nontoxic and biocompatible properties will be more favorable for biological systems [55]. In this section, we illustrate the use of magnetic nanorods in medicine.…”