Gold/cobalt ferrite nanocomposite as a potential agent for photothermal therapy.

The study encompasses an investigation of optical, photothermal and biocompatibility properties of a composite consisting of golden cores surrounded by superparamagnetic CoFe2O4 nanoparticles. Accompanied with the experiment, the computational modeling reveals that each adjusted magnetic nanoparticle redshifts the plasmon resonance frequency in gold and nonlinearly increases the extinction cross-section at ~800 nm. The concentration dependent photothermal study demonstrates a temperature increase of 8.2 K and the photothermal conversion efficiency of 51% for the 100 µg/mL aqueous solution of the composite nanoparticles, when subjected to a laser power of 0.5 W at 815 nm. During an in vitro photothermal therapy, a portion of the composite nanoparticles, initially seeded at this concentration, remained associated with the cells after washing. These retained nanoparticles effectively heated the cell culture medium, resulting in a 22% reduction in cell viability after 15 min of the treatment. The composite features a potential in multimodal magneto-plasmonic therapies.

Modelling the effect of particle arrangement on the magnetoelectric response of a polymer multiferroic film.

In this work the behavior of a three-component composite multiferroic (MF)-an electrically neutral polymer matrix filled with a mixture of piezoelectric and ferromagnetic micrometer-size particles-is investigated in the framework of a simple mesoscopic model. The main issue of interest is the electric polarization generated in a thin film of such an MF in response to a quasistatic magnetic field. The driving mechanism of the effect is rotation of magnetically hard particles inside the matrix which, in turn, transfers the arisen mechanical stresses to the piezoelectric grains. The model MF film is constructed as a periodic set of 2D cells each of which contains one piezoelectric and two ferromagnetic particles. The numerical simulations are performed by means of finite element method on a single cell which, however, is incorporated in an infinite film by means of periodic boundary conditions. The problem of how the spatial arrangement of the particles and the orientation of the anisotropy axis of the piezoelectric one affect the magnetoelectric response is discussed.

Iron Oxide Nanoparticle-Assisted Delamination of Ti3C2Tx MXenes: A New Approach to Produce Magnetic MXene-Based Composites.

Ti3C2Tx MXene is one of the most comprehensively studied 2D materials in terms of its adsorptive, transport, and catalytic properties, cytotoxic performance, etc. Still, conventional MXene synthesis approaches provide low single-flake MXene yield and frequently uncontrollable properties, demanding further post-processing. The MXene family also lacks magnetism, which is helpful for producing effective nanoadsorbents as their magnetic decantation is the cheapest and most convenient way to remove the spent adsorbent from water. Composite materials consisting of magnetic nanoparticles grown on top of MXene flakes are commonly used to provide magnetic properties to the resulting nanocomposite. In this paper, we study the possibility to delaminate multilayer Ti3C2Tx MXene sheets directly by growing iron oxide magnetic nanoparticles inside their interlayer spacing. We find out that, with a mass fraction of particles comparable or exceeding that of MXenes, their growth is accompanied by an effective enhancement of single-layer MXene yield and suitable magnetic properties of the resulting composite. The developed approach can be further used for simplifying synthesis protocols to obtain magnetic MXene-based nanoadsorbents with tunable properties.

Effect of Piezoelectric BaTiO3 Filler on Mechanical and Magnetoelectric Properties of Zn0.25Co0.75Fe2O4/PVDF-TrFE Composites.

Polymer-based multiferroics, combining magnetic and piezoelectric properties, are studied experimentally-from synthesis to multi-parameter characterization-in view of their prospects for fabricating biocompatible scaffolds. The main advantage of these systems is facile generation of mechanical deformations and electric signals in response to external magnetic fields. Herein, we address the composites based on PVDF-TrFE polymer matrices filled with a combination of piezoelectric (BaTiO3, BTO) and/or ferrimagnetic (Zn0.25Co0.75Fe2O4, ZCFO) particles. It is shown that the presence of BTO micron-size particles favors stripe-type structuring of the ZCFO filler and enhances the magnetoelectric response of the sample up to 18.6 mV/(cm∙Oe). Besides that, the admixing of BTO particles is crucial because the mechanical properties of the composite filled with only ZCFO is much less efficient in transforming magnetic excitations into the mechanical and electric responses. Attention is focused on the local surfacial mechanical properties since those, to a great extent, determine the fate of stem cells cultivated on these surfaces. The nano-indentation tests are accomplished with the aid of scanning probe microscopy technique. With their proven suitable mechanical properties, a high level of magnetoelectric conversion and also biocompatibility, the composites of the considered type are enticing as the materials for multiferroic-based polymer scaffolds.

Star-Shaped Magnetic-Plasmonic Au@Fe3O4 Nano-Heterostructures for Photothermal Therapy.

Here, we synthesize a Au@Fe3O4 core@shell system with a highly uniform unprecedented star-like shell morphology with combined plasmonic and magnetic properties. An advanced electron microscopy characterization allows assessing the multifaceted nature of the Au core and its role in the growth of the peculiar epitaxial star-like shell with excellent crystallinity and homogeneity. Magnetometry and magneto-optical spectroscopy revealed a pure magnetite shell, with a superior saturation magnetization compared to similar Au@Fe3O4 heterostructures reported in the literature, which is ascribed to the star-like morphology, as well as to the large thickness of the shell. Of note, Au@Fe3O4 nanostar-loaded cancer cells displayed magneto-mechanical stress under a low frequency external alternating magnetic field (few tens of Hz). On the other hand, such a uniform, homogeneous, and thick magnetite shell enables the shift of the plasmonic resonance of the Au core to 640 nm, which is the largest red shift achievable in Au@Fe3O4 homogeneous core@shell systems, prompting application in photothermal therapy and optical imaging in the first biologically transparent window. Preliminary experiments performing irradiation of a stable water suspension of the nanostar and Au@Fe3O4-loaded cancer cell culture suspension at 658 nm confirmed their optical response and their suitability for photothermal therapy. The outstanding features of the prepared system can be thus potentially exploited as a multifunctional platform for magnetic-plasmonic applications.

Complex Study of Magnetization Reversal Mechanisms of FeNi/FeMn Bilayers Depending on Growth Conditions.

Magnetization reversal processes in the NiFe/FeMn exchange biased structures with various antiferromagnetic layer thicknesses (0-50 nm) and glass substrate temperatures (17-600 °C) during deposition were investigated in detail. Magnetic measurements were performed in the temperature range from 80 K up to 300 K. Hysteresis loop asymmetry was found at temperatures lower than 150 K for the samples with an antiferromagnetic layer thickness of more than 10 nm. The average grain size of FeMn was found to increase with the AFM layer increase, and to decrease with the substrate temperature increase. Hysteresis loop asymmetry was explained in terms of the exchange spring model in the antiferromagnetic layer.

Spatial Manipulation of Particles and Cells at Micro- and Nanoscale via Magnetic Forces.

The importance of magnetic micro- and nanoparticles for applications in biomedical technology is widely recognised. Many of these applications, including tissue engineering, cell sorting, biosensors, drug delivery, and lab-on-chip devices, require remote manipulation of magnetic objects. High-gradient magnetic fields generated by micromagnets in the range of 103-105 T/m are sufficient for magnetic forces to overcome other forces caused by viscosity, gravity, and thermal fluctuations. In this paper, various magnetic systems capable of generating magnetic fields with required spatial gradients are analysed. Starting from simple systems of individual magnets and methods of field computation, more advanced magnetic microarrays obtained by lithography patterning of permanent magnets are introduced. More flexible field configurations can be formed with the use of soft magnetic materials magnetised by an external field, which allows control over both temporal and spatial field distributions. As an example, soft magnetic microwires are considered. A very attractive method of field generation is utilising tuneable domain configurations. In this review, we discuss the force requirements and constraints for different areas of application, emphasising the current challenges and how to overcome them.

FORC-Diagram Analysis for a Step-like Magnetization Reversal in Nanopatterned Stripe Array.

The fabrication approach of a magnonic crystal with a step-like hysteresis behavior based on a uniform non-monotonous iron layer made by shadow deposition on a preconfigured substrate is reported. The origin of the step-like hysteresis loop behavior is studied with local and integral magnetometry methods, including First-Order Reversal Curves (FORC) diagram analysis, accompanied with magnetic microstructure dynamics measurements. The results are validated with macroscopic magnetic properties and micromagnetic simulations using the intrinsic switching field distribution model. The proposed fabrication method can be used to produce magnonic structures with the controllable hysteresis plateau region's field position and width that can be used to control the magnonic crystal's band structure by changing of an external magnetic field.

Boosting Magnetoelectric Effect in Polymer-Based Nanocomposites.

Polymer-based magnetoelectric composite materials have attracted a lot of attention due to their high potential in various types of applications as magnetic field sensors, energy harvesting, and biomedical devices. Current researches are focused on the increase in the efficiency of magnetoelectric transformation. In this work, a new strategy of arrangement of clusters of magnetic nanoparticles by an external magnetic field in PVDF and PFVD-TrFE matrixes is proposed to increase the voltage coefficient (αME) of the magnetoelectric effect. Another strategy is the use of 3-component composites through the inclusion of piezoelectric BaTiO3 particles. Developed strategies allow us to increase the αME value from ~5 mV/cm·Oe for the composite of randomly distributed CoFe2O4 nanoparticles in PVDF matrix to ~18.5 mV/cm·Oe for a composite of magnetic particles in PVDF-TrFE matrix with 5%wt of piezoelectric particles. The applicability of such materials as bioactive surface is demonstrated on neural crest stem cell cultures.

An Indirect Method of Micromagnetic Structure Estimation in Microwires.

The tunable magnetic properties of amorphous ferromagnetic glass-coated microwires make them suitable for a wide range of applications. Accurate knowledge of the micromagnetic structure is highly desirable since it affects almost all magnetic properties. To select an appropriate wire-sample for a specific application, a deeper understanding of the magnetization reversal process is required, because it determines the measurable response (such as induced voltage waveform and its spectrum). However, the experimental observation of micromagnetic structure of micro-scale amorphous objects has strict size limitations. In this work we proposed a novel experimental technique for evaluating the microstructural characteristics of glass-coated microwires. The cross-sectional permeability distribution in the sample was obtained from impedance measurements at different frequencies. This distribution enables estimation of the prevailing anisotropy in the local region of the wire cross-section. The results obtained were compared with the findings of magnetostatic measurements and remanent state analysis. The advantages and limitations of the methods were discussed.

Multiferroic Coupling of Ferromagnetic and Ferroelectric Particles through Elastic Polymers.

Multiferroics are materials that electrically polarize when subjected to a magnetic field and magnetize under the action of an electric field. In composites, the multiferroic effect is achieved by mixing of ferromagnetic (FM) and ferroelectric (FE) particles. The FM particles are prone to magnetostriction (field-induced deformation), whereas the FE particles display piezoelectricity (electrically polarize under mechanical stress). In solid composites, where the FM and FE grains are in tight contact, the combination of these effects directly leads to multiferroic behavior. In the present work, we considered the FM/FE composites with soft polymer bases, where the particles of alternative kinds are remote from one another. In these systems, the multiferroic coupling is different and more complicated in comparison with the solid ones as it is essentially mediated by an electromagnetically neutral matrix. When either of the fields, magnetic or electric, acts on the 'akin' particles (FM or FE) it causes their displacement and by that perturbs the particle elastic environments. The induced mechanical stresses spread over the matrix and inevitably affect the particles of an alternative kind. Therefore, magnetization causes an electric response (due to the piezoeffect in FE) whereas electric polarization might entail a magnetic response (due to the magnetostriction effect in FM). A numerical model accounting for the multiferroic behavior of a polymer composite of the above-described type is proposed and confirmed experimentally on a polymer-based dispersion of iron and lead zirconate micron-size particles.

Green Synthesis of Co-Zn Spinel Ferrite Nanoparticles: Magnetic and Intrinsic Antimicrobial Properties.

Spinel ferrite magnetic nanoparticles have attracted considerable attention because of their high and flexible magnetic properties and biocompatibility. In this work, a set of magnetic nanoparticles of cobalt ferrite doped with zinc was synthesized via the eco-friendly sol-gel auto-combustion method. Obtained particles displayed a room-temperature ferromagnetic behavior with tuned by chemical composition values of saturation magnetization and coercivity. The maximal values of saturation magnetization ~74 Am2/kg were found in cobalt ferrite nanoparticles with a 15-35% molar fraction of cobalt replaced by zinc ions. At the same time, the coercivity exhibited a gradually diminishing trend from ~140 to ~5 mT whereas the concentration of zinc was increased from 0 to 100%. Consequently, nanoparticles produced by the proposed method possess highly adjustable magnetic properties to satisfy the requirement of a wide range of possible applications. Further prepared nanoparticles were tested with bacterial culture to display the influence of chemical composition and magnetic structure on nanoparticles-bacterial cell interaction.

Multifunctional Fe3O4-Au Nanoparticles for the MRI Diagnosis and Potential Treatment of Liver Cancer.

Heterodimeric nanoparticles comprising materials with different functionalities are of great interest for fundamental research and biomedical/industrial applications. In this work, Fe3O4-Au nano-heterostructures were synthesized by a one-step thermal decomposition method. The hybrid nanoparticles comprise a highly crystalline 12 nm magnetite octahedron decorated with a single noble metal sphere of 6 nm diameter. Detailed analysis of the nanoparticles was performed by UV-visible spectroscopy, magnetometry, calorimetry and relaxometry studies. The cytotoxic effect of the nanoparticles in the human hepatic cell line Huh7 and PLC/PRF/5-Alexander was also assessed. These Fe3O4-Au bifunctional nanoparticles showed no significant cytotoxicity in these two cell lines. The nanoparticles showed a good theranostic potential for liver cancer treatment, since the r2 relaxivity (166.5 mM-1·s-1 and 99.5 mM-1·s-1 in water and HepG2 cells, respectively) is higher than the corresponding values for commercial T2 contrast agents and the Specific Absorption Rate (SAR) value obtained (227 W/gFe) is enough to make them suitable as heat mediators for Magnetic Fluid Hyperthermia. The gold counterpart can further allow the conjugation with different biomolecules and the optical sensing.

Magnetocrystalline and Surface Anisotropy in CoFe2O4 Nanoparticles.

The effect of the annealing temperature Tann on the magnetic properties of cobalt ferrite nanoparticles embedded in an amorphous silica matrix (CoFe2O4/SiO2), synthesized by a sol-gel auto-combustion method, was investigated by magnetization and AC susceptibility measurements. For samples with 15% w/w nanoparticle concentration, the particle size increases from ~2.5 to ~7 nm, increasing Tann from 700 to 900 °C. The effective magnetic anisotropy constant (Keff) increases with decreasing Tann, due to the increase in the surface contribution. For a 5% w/w sample annealed at 900 °C, Keff is much larger (1.7 × 106 J/m3) than that of the 15% w/w sample (7.5 ×105 J/m3) annealed at 700 °C and showing comparable particle size. This indicates that the effect of the annealing temperature on the anisotropy is not only the control of the particle size but also on the core structure (i.e., cation distribution between the two spinel sublattices and degree of spin canting), strongly affecting the magnetocrystalline anisotropy. The results provide evidence that the magnetic anisotropy comes from a complex balance between core and surface contributions that can be controlled by thermal treatments.

Progressive lysosomal membrane permeabilization induced by iron oxide nanoparticles drives hepatic cell autophagy and apoptosis.

Iron oxide nanoparticles (IONs) are frequently used in various biomedical applications, in particular as magnetic resonance imaging contrast agents in liver imaging. Indeed, number of IONs have been withdrawn due to their poor clinical performance. Yet comprehensive understanding of their interactions with hepatocytes remains relatively limited. Here we investigated how iron oxide nanocubes (IO-cubes) and clusters of nanocubes (IO-clusters) affect distinct human hepatic cell lines. The viability of HepG2, Huh7 and Alexander cells was concentration-dependently decreased after exposure to either IO-cubes or IO-clusters. We found similar cytotoxicity levels in three cell lines triggered by both nanoparticle formulations. Our data indicate that different expression levels of Bcl-2 predispose cell death signaling mediated by nanoparticles. Both nanoparticles induced rather apoptosis than autophagy in HepG2. Contrary, IO-cubes and IO-clusters trigger distinct cell death signaling events in Alexander and Huh7 cells. Our data clarifies the mechanism by which cubic nanoparticles induce autophagic flux and the mechanism of subsequent toxicity. These findings imply that the cytotoxicity of ION-based contrast agents should be carefully considered, particularly in patients with liver diseases.

Magnetic field sensor based on magnetoplasmonic crystal.

Here we report on designing a magnetic field sensor based on magnetoplasmonic crystal made of noble and ferromagnetic metals deposited on one-dimensional subwavelength grating. The experimental data demonstrate resonant transverse magneto-optical Kerr effect (TMOKE) at a narrow spectral region of 50 nm corresponding to the surface plasmon-polaritons excitation and maximum modulation of the reflected light intensity of 4.5% in a modulating magnetic field with the magnitude of 16 Oe. Dependences of TMOKE on external alternating current (AC) and direct current (DC) magnetic field demonstrate that it is a possibility to use the magnetoplasmonic crystal as a high-sensitive sensing probe. The achieved sensitivity to DC magnetic field is up to 10-6 Oe at local area of 1 mm2.

Ultrasensitive Magnetic Field Sensors for Biomedical Applications.

The development of magnetic field sensors for biomedical applications primarily focuses on equivalent magnetic noise reduction or overall design improvement in order to make them smaller and cheaper while keeping the required values of a limit of detection. One of the cutting-edge topics today is the use of magnetic field sensors for applications such as magnetocardiography, magnetotomography, magnetomyography, magnetoneurography, or their application in point-of-care devices. This introductory review focuses on modern magnetic field sensors suitable for biomedicine applications from a physical point of view and provides an overview of recent studies in this field. Types of magnetic field sensors include direct current superconducting quantum interference devices, search coil, fluxgate, magnetoelectric, giant magneto-impedance, anisotropic/giant/tunneling magnetoresistance, optically pumped, cavity optomechanical, Hall effect, magnetoelastic, spin wave interferometry, and those based on the behavior of nitrogen-vacancy centers in the atomic lattice of diamond.

Direct Magnetoelectric Effect in a Sandwich Structure of PZT and Magnetostrictive Amorphous Microwires.

The magnetoelectric (ME) response in a trilayer structure consisting of magnetostrictive Fe77.5B15Si17.5 amorphous microwires between two piezoelectric PZT (PbZr0.53Ti0.47O3) layers was investigated. Soft magnetic properties of wires make it possible to operate under weak bias magnetic fields below 400 A/m. Enhanced ME voltage coefficients were found when the microwires were excited by ac magnetic field of a frequency of 50-60 kHz, which corresponded to the frequency of electromechanical resonance. The as-prepared microwires were in a glass coat creating a large thermoelastic stress and forming a uniaxial magnetic anisotropy. The effect of glass-coat removal and wire annealing on ME coupling was investigated. The glass coat not only affects the wire magnetic structure but also prevents the interfacial bonding between the electric and magnetic subsystems. However, after its removal, the ME coefficient increased slightly less than 10%. Refining the micromagnetic structure and increasing the magnetostriction by stress release during wire annealing (before or after glass removal) strongly increases the ME response up to 100 mV/(cm×Oe) and reduces the characteristic DC magnetic field down to 240 A/m. Although the achieved ME coefficient is smaller than reported values for multilayered films with layers of PZT and soft magnetic alloys as Metglass, the proposed system is promising considering a small volume proportion of microwires.

Soft Magnetic Amorphous Microwires for Stress and Temperature Sensory Applications.

Amorphous ferromagnetic materials in the form of microwires are of interest for the development of various sensors. This paper analyzes and argues for the use of microwires of two basic compositions of Co71Fe5B11Si10Cr3 and Fe3.9(4.9)Co64.82B10.2Si12Cr9(8)Mo0.08 as stress/strain and temperature sensors, respectively. The following properties make them suitable for innovative applications: miniature dimensions, small coercivity, low anisotropy and magnetostriction, tunable magnetic structure, magnetic anisotropy, and Curie temperature by annealing. For example, these sensors can be used for testing the internal stress/strain condition of polymer composite materials and controlling the temperature of hypothermia treatments. The sensing operation is based on the two fundamental effects: the generation of higher frequency harmonics of the voltage pulse induced during remagnetization in wires demonstrating magnetic bistability, and magnetoimpedance.

Magnetic-Assisted Treatment of Liver Fibrosis.

Chronic liver injury can be induced by viruses, toxins, cellular activation, and metabolic dysregulation and can lead to liver fibrosis. Hepatic fibrosis still remains a major burden on the global health systems. Nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) are considered the main cause of liver fibrosis. Hepatic stellate cells are key targets in antifibrotic treatment, but selective engagement of these cells is an unresolved issue. Current strategies for antifibrotic drugs, which are at the critical stage 3 clinical trials, target metabolic regulation, immune cell activation, and cell death. Here, we report on the critical factors for liver fibrosis, and on prospective novel drugs, which might soon enter the market. Apart from the current clinical trials, novel perspectives for anti-fibrotic treatment may arise from magnetic particles and controlled magnetic forces in various different fields. Magnetic-assisted techniques can, for instance, enable cell engineering and cell therapy to fight cancer, might enable to control the shape or orientation of single cells or tissues mechanically. Furthermore, magnetic forces may improve localized drug delivery mediated by magnetism-induced conformational changes, and they may also enhance non-invasive imaging applications.