K. Simeonidis

Arrangement at the nanoscale: Effect on magnetic particle hyperthermia

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.

A versatile large-scale and green process for synthesizing magnetic nanoparticles with tunable magnetic hyperthermia features

This work proposes a large-scale synthesis methodology for engineered and functional magnetic nanoparticles (i.e. ferrites, sulfides) designed towards the principles of green and sustainable production combined with biomedical applicability. The experimental setup consists of a two-stage continuous-flow reactor in which single-crystalline nanoparticles are formed by the coprecipitation of metal salts in an aqueous environment. A series of optimized iron-based nanocrystals (Fe3O4, Fe3S4, CoFe2O4 and MnFe2O4) with diameters between 18 and 38 nm has been obtained. The samples were validated as potential magnetic hyperthermia agents by their heating efficiency as determined by specific loss power (SLP) in calorimetric experiments. In an effort to enhance colloidal stability and surface functionality, nanoparticles were coated by typical molecules of biomedical interest in a single step process. Finally, two-phase particle systems have been produced by a two-stage procedure to enhance the heating rate by the effective combination of different magnetic features. Results indicate relatively high SLP values for uncoated nanoparticles (420 W g−1 for Fe3O4) and a reduction of 20–60% in the heat dissipation rate upon covering by functional groups. Eventually, such effect was more than counterbalanced by the magnetic coupling of different phases in binary systems, since SLP was multiplied up to ∼1700 W g−1 for MnFe2O4/Fe3O4 suggesting a novel route to tune the efficiency of magnetic hyperthermia agents.

OXIDATION PROCESS OF Fe NANOPARTICLES

The natural oxidation process is studied in the case of 15 nm iron nanoparticles produced by the thermal decomposition of Fe(CO)5. X-ray diffraction spectra of the nanoparticles at different timescales after exposure to air revealed the instant oxidation of iron and the formation of wustite and magnetite. Wustite mainly occupies the interior of nanoparticles, as evidenced by microscopy, but is slowly transformed to a spinel structure. The shape, the dispersion and the role of surfactant were investigated by conventional microscopy and Fourier Transformed-Infrared (FT-IR) spectroscopy. Magnetic hysteresis loops confirmed the expected variation of magnetic properties till the steady state.

Optimum nanoscale design in ferrite based nanoparticles for magnetic particle hyperthermia

The study demonstrates the multiplex enhancement of the magnetic hyperthermia response in ferrites by nanoscale design and tuning without sparing the biocompatibility of iron-oxide. We propose core/shell nanoparticles with a 7–9 nm ferrite core, either magnetically soft MnFe2O4 or hard CoFe2O4, encapsulated by a 2–3 nm Fe3O4 shell providing a core/shell interface. In this case, the exchange interaction between core and shell dramatically affects the macroscopic magnetic behavior and, at the same time, a biocompatible shell prevents interactions of the toxic cores with their environment. The tunable, yet superior, magnetic hyperthermia response is proven by an increase of the specific loss power by a factor of 24 for CoFe2O4–Fe3O4 core/shell particles. This gain is directly connected with the magnetic coupling strength at the core/shell interface and opens the possibility of further optimization.