Filter Capacity Predictions for the Capture of Magnetic Microparticles by High-Gradient Magnetic Separation

We present experimental and theoretical methods to predict maximum and working filter capacities for the capture of superparamagnetic microparticles through high-gradient magnetic separation (HGMS). For this, we employed various combinations of nine different HGMS filter matrices and two types of superparamagnetic microparticles. By calculating the separated particle mass per filter mesh area, we clearly demonstrated the influences of wire diameter and wire mesh spacing on the particle build-up density. Here, we introduce a simple experimental method for estimating average build-up densities in HGMS. Together with known physical parameters of the filter matrix and the background field, such average build-up densities allow good predictions of the operational working filter capacities.      

Quantitative Magnetic Separation of Particles and Cells Using Gradient Magnetic Ratcheting

Extraction of rare target cells from biosamples is enabling for life science research. Traditional rare cell separation techniques, such as magnetic activated cell sorting, are robust but perform coarse, qualitative separations based on surface antigen expression. A quantitative magnetic separation technology is reported using high‐force magnetic ratcheting over arrays of magnetically soft micropillars with gradient spacing, and the system is used to separate and concentrate magnetic beads based on iron oxide content (IOC) and cells based on surface expression. The system consists of a microchip of permalloy micropillar arrays with increasing lateral pitch and a mechatronic device to generate a cycling magnetic field. Particles with higher IOC separate and equilibrate along the miropillar array at larger pitches. A semi‐analytical model is developed that predicts behavior for particles and cells. Using the system, LNCaP cells are separated based on the bound quantity of 1 μm anti‐epithelial cell adhesion molecule (EpCAM) particles as a metric for expression. The ratcheting cytometry system is able to resolve a ±13 bound particle differential, successfully distinguishing LNCaP from PC3 populations based on EpCAM expression, correlating with flow cytometry analysis. As a proof‐of‐concept, EpCAM‐labeled cells from patient blood are isolated with 74% purity, demonstrating potential toward a quantitative magnetic separation instrument.     

Magnetic Interaction Force and a Couple on a Superconducting Sphere in an Arbitrary Dipole Field

The calculation of the magnetostatic potential and levitation force due to a point magnetic dipole placed in front of a superconducting sphere in the Meissner state is readdressed. Closed-form analytical expression for the scalar potential function that yields the image system for an arbitrarily oriented magnetic dipole located in the vicinity of a superconducting sphere is given. Analytic expression for the lifting or levitation force acting on the sphere is extracted from the solution for a general dipole. A special case of our expression where the initial magnetic dipole makes an angle with the z-axis is derived. Our expression for the force in this particular case shows that a recently obtained result (J. Supercond. Nov. Magn. 21:93–96, 2008) for an arbitrary dipole is incorrect. A brief discussion of another erroneous result (J. Supercond. Nov. Magn. 15:257–262, 2002) for a transverse/tangential dipole–sphere configuration, corrected elsewhere recently, is reproduced. Correct expressions for the interaction energy with some limiting cases are also provided. The result derived here demonstrates that the value of the levitation force for a dipole that makes an angle with z-axis lies between the values for a radial dipole–sphere and transverse dipole–sphere configurations providing upper and lower bounds. It is found that for a magnetic dipole making an angle with z-axis, there exits a second force component along the negative y-direction, which influences a couple acting on the superconducting sphere. It is also shown that the couple is proportional to the second force component and that both the couple and second force components vanish for a radial dipole–sphere and transverse dipole–sphere configurations, respectively. These results appear to be new and have not had received due attention in the context of superconductivity.     

Setting up High Gradient Magnetic Separation for combating eutrophication of inland waters

To find new approaches to devise technologies for handling with eutrophication of inland waters is a global challenge. Separation of the P from water under conditions of continuous flow is proposed as an alternative and effective method. This work is based on using highly magnetic particles as the seeding adsorbent material and their later removal from solution by High Gradient Magnetic Separation (HGMS). Contrast to other methods based on batch conditions, large volumes of water can be easily handled by HGMS because of decreasing retention times. This study identifies the best working conditions for removing P from solution by investigating the effects of a set of four different experimental variables: sonication time, flow rate (as it determines the retention time of particles in the magnetic field), magnetic field strength and the iron (Fe) particles/P concentration ratio. Additionally, the change of P removal efficiency with time (build up effect) and the possibility of reusing magnetic particles were also studied. Our results evidenced that while flow rate does not significantly affect P removal efficiency in the range 0.08-0.36 mL s(-1), sonication time, magnetic field strength and the Fe particles/P concentration ratio are the main factors controlling magnetic separation process.     

The Vortex-Magnetic Dipole Interaction in the London Approximation

The interaction between a vortex in a superconducting film and a magnetic dipole with in- or out-of-plane magnetization is studied within the London approximation. We investigate the magnetic pinning properties of such magnetic dipoles. The dependence of the interaction energy on the parameters of the system is investigated and analytical results are obtained in limiting cases.     

富铁相形态对电磁净化效率的影响

研究了Al-2％Fe初生富铁相形貌的改变对电磁分离效率的影响。以Mn作为变质剂来改变富铁相形态，当摩尔比Mn／Fe=1．3～1．5时，富铁相由针状转变为规则的块状或球状。分别在变质前后进行电磁分离试验，并且分析了试样不同部位的微观组织，试验表明：变质后，富铁相的形貌有利于在熔体中迁移，并且电磁净化的效率比变质前提高了20％，可达到90％以上。     

富铁相形态对电磁净化效率的影响

研究了Al-2?初生富铁相形貌的改变对电磁分离效率的影响.以Mn作为变质剂来改变富铁相形态,当摩尔比Mn/Fe=1.3～1.5时,富铁相由针状转变为规则的块状或球状.分别在变质前后进行电磁分离试验,并且分析了试样不同部位的微观组织,试验表明:变质后,富铁相的形貌有利于在熔体中迁移,并且电磁净化的效率比变质前提高了20%,可达到90%以上.     

Self-Assembly of Magnetic Nanochains in an Intrinsic Magnetic Dipole Force-Dominated Regime

Magnetic nanoparticle chains offer the anisotropic magnetic properties that are often desirable for micro- and nanoscale systems; however, to date, large-scale fabrication of these nanochains is limited by the need for an external magnetic field during the synthesis. In this work, the unique self-assembly of nanoparticles into chains as a result of their intrinsic dipolar interactions only is examined. In particular, it is shown that in a high concentration reaction regime, the dipole–dipole coupling between two neighboring magnetic iron cobalt (FeCo) nanocubes, was significantly strengthened due to small separation between particles and their high magnetic moments. This dipole–dipole interaction enables the independent alignment and synthesis of magnetic FeCo nanochains without the assistance of any templates, surfactants, or even external magnetic field. Furthermore, the precursor concentration ([M] = 0.016, 0.021, 0.032, 0.048, 0.064, and 0.096 m ) that dictates the degree of dipole interaction is examined—a property dependent on particle size and inter-particle distance. By varying the spinner speed, it is demonstrated that the balance between magnetic dipole coupling and fluid dynamics can be used to understand the self-assembly process and control the final structural topology from that of dimers to linear chains (with aspect ratio >10:1) and even to branched networks. Simulations unveil the magnetic and fluid force landscapes that determine the individual nanoparticle interactions and provide a general insight into predicting the resulting nanochain morphology. This work uncovers the enormous potential of an intrinsic magnetic dipole-induced assembly, which is expected to open new doors for efficient fabrication of 1D magnetic materials, and the potential for more complex assemblies with further studies.     

Effects of Dipole Interaction on the Collapse-revival Phenomenon of Rabi Oscillations

Abstract

The sensitivity of the collapse-revival phenomenon of Rabi oscillations of two identical atoms to dipole-dipole interaction is brought out by deriving the analytical expression of the excitation probability of two interacting atoms in a coherent field. We study this effect in a two-photon model in which the time evolution is exactly periodic.     

Continuous Flow Low Gradient Magnetophoresis of Magnetic Nanoparticles: Separation Kinetic Modelling and Simulation

Journal of Superconductivity and Novel Magnetism - In recent years, magnetophoresis of magnetic nanoparticles (MNPs) has been emerged as one of the most appealing separation technologies in water...     

Bead Capture on Magnetic Sensors in a Microfluidic System

The accumulation of magnetic beads by gravitational sedimentation and magnetic capture on a planar Hall-effect sensor integrated in a microfluidic channel is studied systematically as a function of the bead concentration, the fluid flow rate, and the sensor bias current. It is demonstrated that the sedimentation flux is proportional to the bead concentration and has a power law relation to the fluid flow rate. The mechanisms for the bead accumulation are investigated and it is found that gravitational sedimentation dominates the bead accumulation, whereas the stability of the sedimented beads against the fluid flow is defined by the localized magnetic fields from the sensor.      

等离子喷涂沉积率对梯度涂层结合强度影响研究

研究了等离子喷涂粉末沉积率对功能梯度涂层的结合强度影响,结果表明,在设计比例下,由于ZrO2的沉积率低,使涂层表面纯陶瓷层与次表层的成分梯度增大,应力梯度增加,导致界面结合变弱,涂层结合强度降低,通过增加次表层ZrO2含量,可较大幅度增加涂层的结合强度。     

Nanotentacle‐Structured Magnetic Particles for Efficient Capture of Circulating Tumor Cells

Circulating tumor cells (CTCs) have attracted considerable attention as promising markers for diagnosing and monitoring the cancer status. Despite many technological advances in isolating CTCs, the capture efficiency and purity still remain challenges that limit clinical practice. Here, the construction of “nanotentacle”‐structured magnetic particles using M13‐bacteriophage and their application for the efficient capturing of CTCs is demonstrated. The M13‐bacteriophage to magnetic particles followed by modification with PEG is conjugated, and further tethered monoclonal antibodies against the epidermal receptor 2 (HER2). The use of nanotentacle‐structured magnetic particles results in a high capture purity (>45%) and efficiency (>90%), even for a smaller number of cancer cells (≈25 cells) in whole blood. Furthermore, the cancer cells captured are shown to maintain a viability of greater than 84%. The approach can be effectively used for capturing CTCs with high efficiency and purity for the diagnosis and monitoring of cancer status.     

磁性流体在均匀梯度磁场中的摩擦学性能测试研究

基于均匀梯度磁场能较准确反映出磁场影响磁性流体摩擦性能的认识,制造了一对产生均匀梯度磁场的线圈安置于改造后的UMT3摩擦试验机中。选用聚α-烯烃合成油基磁性流体为润滑油,测试不同均匀梯度磁场大小、不同载荷和不同往复频率下的磁性流体摩擦学性能。结果显示：载荷、往复运动频率一定时,磁性流体的摩擦系数随均匀梯度磁场的增大而减小;载荷、均匀梯度磁场一定时,磁性流体的摩擦系数随随往复运动频率的增大而减小;磁性流体在均匀梯度磁场中比无磁场中具有更高的承载能力和更长的耐磨寿命。     

Structure–Relaxivity Relationships of Magnetic Nanoparticles for Magnetic Resonance Imaging

Magnetic nanoparticles (MNPs) have been extensively explored as magnetic resonance imaging (MRI) contrast agents. With the increasing complexity in the structure of modern MNPs, the classical Solomon–Bloembergen–Morgan and the outer‐sphere quantum mechanical theories established on simplistic models have encountered limitations for defining the emergent phenomena of relaxation enhancement in MRI. Recent progress in probing MRI relaxivity of MNPs based on structural features at the molecular and atomic scales is reviewed, namely, the structure–relaxivity relationships, including size, shape, crystal structure, surface modification, and assembled structure. A special emphasis is placed on bridging the gaps between classical simplistic models and modern MNPs with elegant structural complexity. In the pursuit of novel MRI contrast agents, it is hoped that this review will spur the critical thinking for design and engineering of novel MNPs for MRI applications across a broad spectrum of research fields.