In this work, we present the arrangement of Fe3O4 magnetic nanoparticles into 3D linear chains and its effect on magnetic particle hyperthermia efficiency. The alignment has been performed under a 40 mT magnetic field in an agarose gel matrix. Two different sizes of magnetite nanoparticles, 10 and 40 nm, have been examined, exhibiting room temperature superparamagnetic and ferromagnetic behavior, in terms of DC magnetic field, respectively. The chain formation is experimentally visualized by scanning electron microscopy images. A molecular Dynamics anisotropic diffusion model that outlines the role of intrinsic particle properties and inter-particle distances on dipolar interactions has been used to simulate the chain formation process. The anisotropic character of the aligned samples is also reflected to ferromagnetic resonance and static magnetometry measurements. Compared to the non-aligned samples, magnetically aligned ones present enhanced heating efficiency increasing specific loss power value by a factor of two. Dipolar interactions are responsible for the chain formation of controllable density and thickness inducing shape anisotropy, which in turn enhances magnetic particle hyperthermia efficiency.
The use of magnetic nanoparticles (MNPs) to locally increase the temperature at the nanoscale under the remote application of alternating magnetic fields (magnetic particle hyperthermia, MHT) has become an important...
Magnetic particle hyperthermia is a promising cancer therapy, but a typical constraint of its applicability is localizing heat solely to malignant regions sparing healthy surrounding tissues.
The challenge for synthesizing magnetic
nanoparticle chains may
be achieved under the application of fixation fields, which are the
externally applied fields, enhancing collective magnetic features
due to adequate control of dipolar interactions among magnetic nanoparticles.
However, relatively little attention has been devoted to how size,
concentration of magnetic nanoparticles, and intensity of an external
magnetic field affect the evolution of chain structures and collective
magnetic features. Here, iron oxide nanoparticles are developed by
the coprecipitation method at diameters below (10 and 20 nm) and above
(50 and 80 nm) their superparamagnetic limit (at about 25 nm) and
then are subjected to a tunable fixation field (40–400 mT).
Eventually, the fixation field dictates smaller particles to form
chain structures in two steps, first forming clusters and then guiding
chain formation via “cluster–cluster” interactions,
whereas larger particles readily form chains via “particle–particle”
interactions. In both cases, dipolar interactions between the neighboring
nanoparticles augment, leading to a substantial increase in their
collective magnetic features which in turn results in magnetic particle
hyperthermia efficiency enhancement of up to one order of magnitude.
This study provides new perspectives for magnetic nanoparticles by
arranging them in chain formulations as enhanced performance magnetic
actors in magnetically driven magnetic applications.
Size-selected Fe3O4–Au hybrid nanoparticles with diameters of 6–44 nm (Fe3O4) and 3–11 nm (Au) were prepared by high temperature, wet chemical synthesis. High-quality Fe3O4 nanocrystals with bulk-like magnetic behavior were obtained as confirmed by the presence of the Verwey transition. The 25 nm diameter Fe3O4–Au hybrid nanomaterial sample (in aqueous and agarose phantom systems) showed the best characteristics for application as contrast agents in magnetic resonance imaging and for local heating using magnetic particle hyperthermia. Due to the octahedral shape and the large saturation magnetization of the magnetite particles, we obtained an extraordinarily high r
2-relaxivity of 495 mM−1·s−1 along with a specific loss power of 617 W·gFe
−1 and 327 W·gFe
−1 for hyperthermia in aqueous and agarose systems, respectively. The functional in vitro hyperthermia test for the 4T1 mouse breast cancer cell line demonstrated 80% and 100% cell death for immediate exposure and after precultivation of the cells for 6 h with 25 nm Fe3O4–Au hybrid nanomaterials, respectively. This confirms that the improved magnetic properties of the bifunctional particles present a next step in magnetic-particle-based theranostics.
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