Magnetic and structural properties of iron phosphate-phenolic soft magnetic composites

This work focuses on the effect of phosphate modification on the magnetic and surface properties of iron-phenolic soft magnetic composite materials. Fourier transform infrared (FTIR) spectra, EDX analysis, distribution maps, X-ray diffraction pattern and density measurements show that the particles surface layer contains a thin layer of nanocrystalline/amorphous phosphate with high coverage of powders surface. Magnetic measurements show that phosphating treatment decreases the loss factor, imaginary part of permeability, increases the electrical resistivity and operating frequencies by decreasing the effective particle size. The operating frequency increases from 200 kHz for uncoated-powders samples to 1 MHz for phosphated-powders samples at optimum concentration. Phosphated iron powders that are covered by 0.7 wt% of phenolic resin exhibits lower magnetic loss and higher frequency stability. The minimum loss factor and maximum permeability at each frequency can be obtained for 0.01 g/ml orthophosphoric acid concentration in comparison with other concentrations including 0.005 and 0.04 g/ml.     

Magnetic model for a horse-spleen ferritin with a three-phase core structure

The increasing interests in magnetic nanoparticles has prompted research on ferritin, which is naturally a well-defined iron-storage protein in most living organisms. However, the exact magnetic behavior of ferritin is not well understood, because the crystal structures of ferritin and ferrihydrite, its major component, are not fully understood. Briefly, we discuss the previous magnetization models of ferritin and ferrihydrite and we present a new model (Σ3L) of the initial magnetization of ferritin, considering its different phases. The new model includes three Langevin-function terms, which represent three different magnetic moments provided by the likely hydroxide and oxide mineral phases in ferritin. Compared to previous models, our simple model fits the experimental data 12 times better in terms of the sum of least squares. The magnetic independence of each component supports the multi-phase compositional model of the mineral core of horse-spleen ferritin. This Σ3L model gives a quantization of the amounts of the different phases within horse-spleen ferritins that matches other published experimental data: 60-80% ferrihydrite, 15-25% maghemite/magnetite, and 1-10% hematite.     

Magnetic Relaxometry with an Atomic Magnetometer and SQUID Sensors on Targeted Cancer Cells

Magnetic relaxometry methods have been shown to be very sensitive in detecting cancer cells and other targeted diseases. Superconducting Quantum Interference Device (SQUID) sensors are one of the primary sensor systems used in this methodology because of their high sensitivity with demonstrated capabilities of detecting fewer than 100,000 magnetically-labeled cancer cells. The emerging technology of atomic magnetometers (AM) represents a new detection method for magnetic relaxometry with high sensitivity and without the requirement for cryogens. We report here on a study of magnetic relaxometry using both AM and SQUID sensors to detect cancer cells that are coated with superparamagnetic nanoparticles through antibody targeting. The AM studies conform closely to SQUID sensor results in the measurement of the magnetic decay characteristics following a magnetization pulse. The AM and SQUID sensor data are well described theoretically for superparamagnetic particles bound to cells and the results can be used to determine the number of cells in a cell culture or tumor. The observed fields and magnetic moments of cancer cells are linear with the number of cells over a very large range. The AM sensor demonstrates very high sensitivity for detecting magnetically labeled cells does not require cryogenic cooling and is relatively inexpensive.     

Magnetic characterization of surface-coated magnetic nanoparticles for biomedical application

The influence of the oleic acid surface coating on Fe₃O₄ and NiFe₂O₄ nanoparticles on their magnetic and calorimetric characterization was investigated. Fe₃O₄ nanoparticles (particle sizes of 15-20 and 20-30 nm) and NiFe₂O₄ nanoparticles (particle sizes of 20-30 nm) were dispersed in oleic acid. The surface coating resulted in a decrease in the dipole-dipole interaction between the particles, which in turn affected the coercivity and heat dissipation of the nanoparticles. The coercivity of the oleic-acid-coated nanoparticles was found to be lower than that of the uncoated nanoparticles. The temperature rise in the oleic-acid-coated nanoparticles was greater than that of the uncoated nanoparticles; this temperature rise was associated with the relaxation losses. The viscosity dependence on the self-heating temperature of Fe₃O₄ nanoparticles (15-20 and 20-30 nm) under an ac magnetic field was measured. The temperature rise for both the Fe₃O₄ nanoparticles (15-20 and 20-30 nm) exhibited a strong dependence on viscosity at each magnetic field frequency, and the contribution of Brownian relaxation loss to the temperature rise was revealed. Moreover, an in vitro cytotoxicity test of Fe₃O₄ and NiFe₂O₄ was performed using human cervical carcinoma cells (HeLa), and the cytotoxicity of NiFe₂O₄ nanoparticles was compared to that of Fe₃O₄ nanoparticles.     

Fabrication of water-soluble magnetic nanoparticles by ligand-exchange with thermo-responsive polymers

We report the use of thermo-responsive polymers in the synthesis of Co and γ-Fe₂O₃ nanoparticles using a two-step method involving thermal decomposition of the organometallic complexes in the presence of oleic acid and then followed by ligand-exchange process with thermo-responsive polymer. Among different thermo-responsive polymers investigated, it was found that the polymer based on poly(N-isopropylacrylamide) with a co-monomer component of acrylic acid and acrylamide can be used in the ligand-exchange to coat Co and γ-Fe₂O₃ nanoparticles, respectively. The nanoparticles are found to be water-soluble at temperatures below coil-to-globule phase transition of the coating polymer.     

Functionalization of magnetic gold/iron-oxide composite nanoparticles with oligonucleotides and magnetic separation of specific target

Magnetic composite nanoparticles of gold and iron-oxide synthesized with gamma-rays or ultrasonics were functionalized with thiol-modified oligonucleotides. The amount of oligonucleotides bound to the functionalized nanoparticle probes via hybridization was quantified with fluorescently-labeled target oligonucleotides. Our composite nanoparticles magnetically separated the specific target oligonucleotides without the non-specific adsorption.     

Magnetic nanoparticles coated with carboxymethylated polysaccharide shells—Interaction with human cells

The interaction of magnetic core shell nanoparticles with living cells depends on the structure of the shell. In this paper we demonstrate a strong difference in the cell-nanoparticle interaction depending on the backbone of carboxymethylated polysaccharides used as shell material. Carboxymethyl cellulose with its β-1→4 linked structure and the carboxymethylated pullulan [α-1→6 linked maltotriose with α-1→4 linkages] show a constant interaction rate with both, tumor cells and leukocytes. In contrast, carboxymethyl dextran with a α-1→6 linked backbone exhibits a rapid interaction kinetic with tumor cells that is reduced with leukocytes as target.     

Magnetic hyperthermia with biphasic gel of La1−xSrxMnO3 and maghemite

Magnetic hyperthermia experiments were carried out using a biphasic gel of La_1−xSr_xMnO₃(LSMO) and γ-Al_0.07 Fe_1.93O₃ with an AC magnetic field of amplitude 88 mT and a frequency of 108 kHz. Specific absorption rate (SAR) increases with the increased ratio of Al-substituted maghemite. The T_max value for the gels prepared by the mixture of LSMO and Al-substituted maghemite can be adjusted to suit therapeutic temperature. The time required to reach optimum temperature decreased with the increased ratio of later. Such biphasic gel could be very useful for magnetic hyperthermia with in vivo control of temperature.     

A novel approach to preparing magnetic protein microspheres with core-shell structure

Magnetic protein microspheres with core-shell structure were prepared through a novel approach based on the sonochemical method and the emulsion solvent evaporation method. The microspheres are composed of the oleic acid and undecylenic acid modified Fe₃O₄ cores and coated with globular bovine serum albumin (BSA). Under an optimized condition, up to 57.8 wt% of approximately 10 nm superparamagnetic Fe₃O₄ nanoparticles could be uniformly encapsulated into the BSA microspheres with the diameter of approximately 160 nm and the high saturation magnetization of 38.5 emu/g, besides of the abundant functional groups. The possible formation mechanism of magnetic microspheres was discussed in detail.     

Semiconductor Research Needs in the Nanoscale Physical Sciences: A Semiconductor Research Corporation Working Paper

The purpose of this paper is to identify areas in the basic physical sciences where additional research is needed to sustain the extraordinary progress in electronics that has now extended for several decades. Also, it is argued that basic research will provide the foundation for the discovery of new generations of nanoelectronic devices that will continue the experimental rate of reduction in cost per function. Some of the fundamental areas requiring further research are the chemistry and physics of material interfaces, conductivity at small dimensions, deterministic doping effects, and nanomagnetics. Discovery research also is needed in the functional synergy of nanoelectronic materials and non-traditional fabrication methods.     

Overcoming the Inhibition Effects of Citrate: Precipitation of Ferromagnetic Magnetite Nanoparticles with Tunable Morphology,Magnetic Properties,and Surface Charge via Ferrous Citrate Oxidation

This study demonstrates how the method of thermally assisted oxidative precipitation in water can be opened for—the so far neglected—metal organic iron(II) complexes (herein: citrate) in order to obtain, in one step, ferromagnetic magnetite nanoparticles, possessing essential ligand properties. Based on a dedicated analysis of the specific precursor in combination with the consideration of known properties of the ligand, it is possible to identify existing inhibition-attributes of the iron organyl such that these can be overcome. Moreover, they can be exploited in a targeted manner; thus, simply by changing concentrations, a variety of magnetite nanoparticle morphologies with distinct properties can be obtained. In the case of the herein investigated ferrous citrate, three major inhibition effects are identified. While two of them efficiently prevent the formation of magnetite and need to be addressed to be overcome, the third can be exploited to selectively synthesize, for example, relatively stable carboxyl group-bearing nuclei clusters, exhibiting the properties of magnetically responsive photonic crystals, or relatively large mesocrystals, whose intraparticular magnetic interactions are apparently disturbed.     

Magnetic properties of xNi0.53Cu0.12Zn0.35Fe1.88O4+(1−x)BaTiO3 nanocomposites

The nanocrystalline Ni_0.53Cu_0.12Zn_0.35Fe_1.88O₄ and BaTiO₃ powders were prepared using Microwave-Hydrothermal (M-H) method at 160 °C/45 min. The as synthesized powders were characterized using the X-ray diffraction (XRD) and Transmission Electron Microscope (TEM). The size of the powders that were synthesized using M-H system was found to be ∼30 and ∼50 nm for ferrite phase and ferroelectric phases, respectively. The powders were densified using microwave sintering method at 900 °C/30 min. The ferrite and ferroelectric phases were observed from XRD and morphology of the composites was observed with the Scanning Electron Microscope (SEM).The magnetic hysteresis loops were recorded using the Vibrating Sample Magnetometer (VSM).The frequency dependence of real (μ′) and imaginary (μ″) parts of permeability was measured in the range of 1 MHz-1.8 GHz. The permeability decreases with an increase of BaTiO₃ content at 1 MHz. The transition temperature (T_C) of ferrite was found to be 245 °C. The T_C of composite materials decreases with an increase in BaTiO₃ content.     

铜配合物的光物理与电致发光性能

以中心原子为铜的磷光材料Cu4(C≡Cph)4L2[L=1，8-bis(diphenylphosphino)-3，6-dioxaoctane](简称Cu4)作为掺杂材料，选用空穴传输材料聚乙烯基咔唑(PVK)为母体材料，制作结构为ITO／Cu4PVK／TAZ／Mg：Ag／Ag的双层器件。其发光颜色随掺杂的变化而改变，在较高掺杂浓度的条件下，可观察到单纯Cu4的发光，即实现了单重态到三重态的能量转移。着重讨论了主客体材料间的能量转移过程，并研究了影响器件效率的外界因素如氧气的猝灭对Cu4发光强度的影响。     

A facile method to synthesize magnetic polymer nanospheres with multifunctional groups

Magnetic poly(styrene methyl methacrylate)/Fe₃O₄ nanospheres with ester groups were prepared by a modified one-step mini-emulsion polymerization in the presence of Fe₃O₄ ferrofluids. The effects of monomer dose, surfactant content, ferrofluid concentration and initiator content on the particle characteristics such as the size, morphology and magnetic properties were investigated by Fourier-transform infrared spectroscopy, transmission electron microscopy, thermogravimetric analysis and vibrating sample magnetometer. The results indicated that magnetic nanospheres were superparamagnetic with high saturation magnetization of 51.0 emu/g and corresponding magnetite content of 61.5 wt%. Subsequently, magnetic nanospheres with carboxyl and amino groups were also obtained by hydrolysis and ammonolysis reaction. These magnetic nanospheres with multifunctional groups have biomedical applications.     

Dual‐Polymer‐Functionalized Nanoscale Graphene Oxide as a Highly Effective Gene Transfection Agent for Insect Cells with Cell‐Type‐Dependent Cellular Uptake Mechanisms

Efficient and safe gene transfection carriers, especially for hard‐to‐transfect cells, are urgently demanded in basic biological research and gene therapy applications. Many insect cell lines widely used in molecular cell biology exhibit relatively low transfection efficiencies when treated by conventional non‐viral agents. Herein, we develop a novel gene delivery vector by coating graphene oxide (GO) with both polyethylene glycol (PEG) and polyethylenimine (PEI), obtaining a dual‐polymer‐functionalized nanoscale GO (nGO‐PEG‐PEI) to transfect insect cells. While exhibiting remarkably reduced cytotoxicity compared with PEI, nGO‐PEG‐PEI, when used as the plasmid DNA transfection agent to treat Drosophila S2 cells, offers ≈7‐fold and ≈2.5‐fold higher efficiency compared with those achieved by using bare PEI and Lipofectamine 2000, a widely used commercial transfection agent, respectively. Interestingly, the advantages of nGO‐PEG‐PEI are even more dramatic when transfecting cells with lower‐quality linearized DNA. It is revealed that nGO‐PEG‐PEI/pDNA complexes enter insect cells via a unique pathway working even at a low temperature, rather different from their entry into mammalian adherent cells. Our results encourage the development of nano‐GO‐based gene carriers to treat special types of hard‐to‐transfect cells (e.g., insect cells), and indicate that nanomaterials would enter cells by cell‐type‐dependent mechanisms, which merit significantly more future attentions.     

带铁磁屏蔽的高场磁体系统磁场计算与优化设计

In this paper, an optimization design method for high field superconducting magnet with ferromagnetic shield is discussed. Firstly, the analytical formula for calculating the magnetic field at any space point is derived based on the equivalent magnetic charge model. Then the validity and accuracy of the formula are discussed by comparing the results with that of the finite element method (FEM)for the same model. Finally, a joint optimization of MRI magnet system with ferromagnetic shielding is carried out in order to improve the homogeneity of magnetic field in the DSV(diameter of spherical volume)region and enhance the field intensity in the center.     

Magnetic and electronic properties of zigzag BN nanoribbons with nonmetallic atom terminations: A first-principles study

The boron nitride (BN) nanosheet is an isostructural analog of graphene and can be viewed as the structure that C atoms in graphene are replaced with alternating B and N. The easily modulated band-gap of BN nanosheet by simply passivating its edge(s) makes it is promising for many potential applications in nanodevices and nanoelectronics. We further systematically theoretically study the magnetic and electronic properties of passivated-ZBNNR by nonmetallic atom(s), here. According to our calculations, all considered structures show magnetic feature, and the ZBNNRs can be metal or half-metal or semiconductor depending on the termination details. The great application-potential of the passivated-ZBNNRs is further confirmed based on our results.     

Magnetic resonance imaging of the chest: A diagnostic comparison with computed tomography and hilar tomography

Computed tomography (with and without contrast enhancement) provides excellent diagnostic accuracy for the evaluation of the chest. Oblique (55°) and anteroposterior hilar tomography is accurate for the evaluation of hilar nodes and masses. Magnetic resonance techniques provide excellent differentiation of vascular and nonvascular structures and therefore should be useful in the hilum and mediastinum. Magnetic resonance imaging was used in 55 patients with known pathologic conditions in the mediastinum, hilum, and lungs to determine the accuracy and efficacy of this technique compared with computed and hilar tomography. The pathologic conditions included primary and metastatic neoplasms, benign masses, vascular abnormalities, and pulmonary nodules and infiltrates. Spatial resolution with magnetic resonance imaging is less than with computed tomography with our instrument (0.15 T resistive magnet). However, in the hilum and mediastinum, magnetic resonance imaging provided diagnostic information equal to that of computed tomography with contrast in 90% of patients. Vascular and nonvascular structures were more easily differentiated than with hilar tomography. Computed tomography was far superior in the evaluation of multiple pulmonary nodules. Lesions of the chest wall were better seen with magnetic resonance imaging because of the improved soft tissue contrast.