Engineering Shape Anisotropy of Fe₃O₄-γ-Fe₂O₃ Hollow Nanoparticles for Magnetic Hyperthermia

Abstract

The use of microwave-assisted synthesis (in water) of α-Fe 2 O 3 nanomaterials followed by their transformation onto iron oxide Fe 3 O 4 -γ-Fe 2 O 3 hollow nanoparticles encoding well-defined sizes and shapes [nanorings (NRs) and nanotubes (NTs)] is henceforth described. The impact of experimental variables such as concentration of reactants, volume of solvent employed, and reaction times/temperatures during the shape-controlled synthesis revealed that the key factor that gated generation of morphologically diverse nanoparticles was associated to the initial concentration of phosphate anions employed in the reactant mixture. All the nanomaterials presented were fully characterized by powder X-ray diffraction, field emission scanning electron microscopy, Fourier transform infrared, Mossbauer spectroscopy, and superconducting quantum interference device (SQUID). The hollow nanoparticles that expressed the most promising magnetic responses, NTs and NRs, were further tested in terms of efficiencies in controlling the magnetic hyperthermia, in view of their possible use for biomedical applications, supported by their excellent viability as screened by in vitro cytotoxicity tests. These systems NTs and NRs expressed very good magneto-hyperthermia properties, results that were further validated by micromagnetic simulations. The observed specific absorption rate (SAR) and intrinsic loss power of the NRs and NTs peaked the values of 340 W/g and 2.45 nH m 2 kg −1 (NRs) and 465 W/g and 3.3 nH m 2 kg −1 (NTs), respectively, at the maximum clinical field 450 Oe and under a frequency of 107 kHz and are the highest values among those reported so far in the hollow iron-oxide family. The higher SAR in NTs accounts the importance of magnetic shape anisotropy, which is well-predicted by the modified dynamic hysteresis (β-MDH) theoretical model.

Using small-angle scattering to guide functional magnetic nanoparticle design

“…392,393 This concept can be easily transferred to other scattering techniques such as SANS to classify the most appropriate model. 394 Regarding future experiments, we think that combining small-angle scattering experiments with micromagnetic simulations could be particularly useful to investigate exotic nanoparticles such as hollow particles 42 including nanorings, 43 nanotubes, 44 and other shape-anisotropic hollow particles, 45 or nanodots 46 and nano-octopods. 47 Recently, it was shown that the coercivity of MNPs is enhanced by the exchange coupling at the interface of ferrimagnetic and antiferromagnetic selfassembled monolayers.…”

“…41 More exotic magnetization states can be found, e.g. in hollow particles, 42 nanorings, 43 nanotubes, 44 and other shape-anisotropic hollow particles, 45 or nanodots 46 and nano-octopods. 47 In many cases, the MNPs consist of the typical 3d ferromagnetic elements Fe, Co, Ni, alloys (FePt, FePd) or their oxides, with iron oxides being the most prominent example.…”

Magnetic Nanomaterials for Arterial Embolization and Hyperthermia of Parenchymal Organs Tumors: A Review

“…The magnetization reversal mechanism in nanosized magnetic materials differs from that for MD ferromagnets. In SD particles smaller than 100 nm, magnetization occurs only by coherent rotation of all atomic magnetic moments within the sample against an energy barrier (∆E) given mainly by the shape and the crystalline anisotropy fields [85][86][87][88][89][90]:…”

“…A dominant effect of the size and shape anisotropy on H C and M S and the heating efficiency has been observed in anisotropic magnetite NPs, such as wire, ring, rod, cube, octahedron, etc. (Figure 6) [87][88][89][90].…”

“…A dominant effect of the size and shape anisotropy on HC and MS and the heating efficiency has been observed in anisotropic magnetite NPs, such as wire, ring, rod, cube, octahedron, etc. (Figure 6) [87][88][89][90]. It is known that MNPs with particle sizes larger than 20 nm are in a stable-domain state with ferromagnetic-like behavior when the magnetic moment is pinned along the magnetic anisotropy axis as a result of effective magnetic anisotropy.…”