New type of biosensor based on magnetic nanoparticle detection

A new type of biosensor has been developed based on detection of nanosized superparamagnetic particles that serve as labels in bioreactions. The method is based on non-linear magnetic material detection by a magnetic field having components at two frequencies f₁ and f₂. The response is measured at the combinatorial frequencies f_i=mf₁+nf₂, where m and n are integers, e.g., f_i=f₁±2f₂. Several highly sensitive readers of superparamagnetic particles have been designed and used for development of various formats of immunoassays, including those compatible with immunoconcentration and magnetic enrichment of antigens.     

Towards a programmable magnetic bead microarray in a microfluidic channel

A new hybrid magnetic bead separator that combines an external magnetic field with 175 μm thick current lines buried in the back side of a silicon wafer is presented. A microfluidic channel was etched into the front side of the wafer. The large cross-section of the current lines makes it possible to use larger currents and obtain forces of longer range than from thin current lines at a given power limit. Guiding of magnetic beads in the hybrid magnetic separator and the construction of a programmable microarray of magnetic beads in the microfluidic channel by hydrodynamic focusing is presented.     

Theoretical analysis of a simple yet efficient portable magnetic separator design for separation of magnetic nano/micro-carriers from human blood flow

A technology that could physically remove substances from the blood such as biological, chemical, or radiological toxins could dramatically improve treatment of disease. One method in development proposes to use magnetic-polymer spheres to selectively bind toxins and remove them by magnetic filtration. Although magnetic filtration is a developed technology, the clinical boundary conditions described here require a new filter design. We investigated the removal of toxin-bound magnetic carriers from the blood stream using 2-D FEMLAB simulations. The magnetic separator consisted of a permanent magnet with parallel ferromagnetic prisms on the faces and in contact with a straight tube carrying the magnetic-polymer spheres in suspension. We varied the following parameters: blood flow velocity, the size, and number of ferromagnetic prisms, and the ferromagnetic material in both prisms and magnets. The capture efficiency reached maximum values when the depth of the prisms equaled the diameter of the tubing and the saturation magnetization of the prism material equaled twice that of the magnet. With this design a piece of 2 mm (diameter) tube carrying the fluid resulted in 95% capture of 2.0 μm magnetic-polymer spheres at 10 cm/s flow velocity.     

Combinatorial synthesis and characterization of a ternary epitaxial film of Co and Mn doped Ge (0 0 1)

We report combinatorial molecular beam epitaxy synthesis and properties of a ternary epitaxial film of Co and Mn co-doped Ge grown on Ge (0 0 1) substrate. Structural effects were examined in situ by reflection high-energy electron diffraction and ex situ by microbeam X-ray diffraction techniques, and magnetic properties were probed by using magnetooptic Kerr effect. Ternary epitaxial phase diagrams have been studied for total doping concentrations up to 30 at.%, where regions of coherent epitaxy and rough disordered growth and those of near room temperature ferromagnetic ordering have been identified.     

MCeO3：Eu^3＋（M=Sr，Ba）的合成及发光性质研究

利用高温固相反应法合成了Eu^3＋掺杂的MCeO3（M=Sr，Ba）发光粉末样品，采用X射线衍射技术和荧光光谱等测试手段分别对其物相组成和发光性质进行了研究。X射线衍射结果显示，Eu^3＋离子容易替代MCeO3晶格中M^2＋离子的位置。荧光光谱测试结果表明，Eu^3＋掺杂的SrCeO3和BaCeO3样品在紫外波段存在着非常宽的吸收带，峰值分别位于311和320nm左右，它们属于Ce^4＋-O^2-的电荷迁移带，SrCeO3和BaCeO3基质与Eu^3＋离子之间存在着能量转移。在MCeO3：Eu^3＋样品中，Eu^3＋的发射主要来自于^5D0激发态能级，其中以磁偶极跃迁^5D0-^7F1发射强度为最大；此外样品中还存在着较高的^5D1激发态能级的辐射跃迁。SrCe03：EU^3＋样品的发射强度远大于BaCeO3：EU^3＋样品。     

Surface antiferromagnetic domain structures of NiO (0 0 1) studied using UV photoemission electron microscope

Direct observation of the antiferro (AF) magnetic domain structures of a NiO (0 0 1) surface is found to be possible using a spectroscopy photoelectron low-energy electron microscope (SPELEEM) and a commercial UV Hg excitation light source without using any polarizers. The principle is based on the magnetic linear dichroism (MLD) effect, where different domain contrasts are produced according to the relative angle between the antiferromagnetic axis and the linearly polarized light. The observed AF magnetic domain structures are strongly affected by both bulk AF magnetic domain structures and the stresses induced during the sample cleaving process. Moreover, the AF magnetic domain structures are found to be irreversible when the sample is heated to over its Néel temperature and then cooled. The possibility of imaging AF magnetic domain structures without using synchrotron radiation or a polarizer is attractive.     

Study of molecular surface coating on the stability of maghemite nanoparticles

In this study γ-Fe₂O₃ nanoparticle, surface-coated with increasing amount of oleic acid, have been prepared while the stability against particle degradation under laser excitation intensity was investigated. Maghemite nanoparticle was obtained via oxidation of magnetite nanoparticle, the latter synthesized by co-precipitation of Fe (II) and Fe (III) ions in alkaline medium. By varying the experimental conditions of surface-coating maghemite nanoparticles with oleic acid, samples with different grafting coefficient were obtained and investigated using X-ray diffraction and different spectroscopic techniques, namely Raman, Mössbauer, and infrared. The amount of oleic acid adsorbed on the maghemite surface was estimated via the carbon content obtained from elemental analysis.     

Magnetoelectric characterization of xNi0.75Co0.25Fe2O4-(1−x)BiFeO3 nanocomposites

Magnetoelectric (ME) nanocomposites containing Ni_0.75Co_0.25Fe₂O₄-BiFeO₃ phases were prepared by citrate sol-gel process. X-ray diffraction (XRD) analysis showed phase formation of xNi_0.75Co_0.25Fe₂O₄-(1−x)BiFeO₃ (x=0.1, 0.2, 0.3 and 0.4) composites on heating at 700 °C. Transmission electron microscopy revealed the formation of powders of nano order size and the crystal size was found to vary from 30 to 85 nm. Dispersion in dielectric constant (ε) and dielectric loss (tan δ) in the low-frequency range have been observed. It is seen that nanocomposites exhibit strong magnetic properties and a large ME effect. On increasing Ni_0.75Co_0.25Fe₂O₄ contents in the nanocomposites, the saturation magnetization (M_S) and coercivity (H_C) increased after annealing at 700 °C. The large ME output in the nanocomposites exhibits strong dependence on magnetic bias and magnetic field frequency. The large value of ME output can be attributed to small grain size of ferrite phase of nanocomposite being prepared by citrate precursor process.     

Crystal and magnetic structures of Y2CrS4

Chromium(II) sulfide, Y₂CrS₄, prepared by a solid-state reaction of Y₂S₃ and CrS, showed an antiferromagnetic transition at 65 K. The neutron diffraction patterns at 10 and 90 K were both well refined with the space group Pca2₁. At 90 K, cell parameters were a=12.5518(13) Å, b=7.5245(8) Å, and c=12.4918(13) Å. At 10 K, magnetic peaks were observed, which could be indexed on the same unit cell. Magnetic moments of chromium ions were parallel to the b-axis and antiferromagnetically ordered in each set of the 4a sites.     

Deposition of SiOx barrier films by O2/TMDSO RF-PECVD

This paper reports that the SiOx barrier films are deposited on polyethylene terephthalate substrate by plasmaenhanced chemical vapour deposition （PECVD） for the application of transparent barrier packaging. The variations of 02/Tetramethyldisiloxane （TMDSO） ratio and input power in radio frequency （RF） plasma are carried out to optimize barrier properties of the SiOx coated film. The properties of the coatings are characterized by Fourier transform infrared, water vapour transmission rate （WVTR）, oxygen transmission rate （OTR）, and atomic force microscopy analysers. It is found that the 02/TMDSO ratio exceeding 2：1 and the input power over 200 W yield SiOx films with low carbon contents which can be good to the barrier （WVTR and OTR） properties of the SiOx coatings. Also, the film properties not only depend on oxygen concentration of the inlet gas mixtures and input power, but also relate to the surface morphology of the coating.