External Magnetic Field Gradient Research Articles

Combining positive and negative magnetophoreses to separate particles of different magnetic properties

A new separation method that combines both positive and negative magnetophoreses based on ferrofluids is used to separate mixtures of particles with different magnetic properties. Ferrofluids are stable magnetic nanoparticles suspensions. Under external magnetic field gradients, particles with a larger magnetization within the ferrofluids are attracted to a magnet while the ones with a smaller magnetization are pushed away from it. Based on this principle, we report the design, modeling, fabrication, and characterization of the separation device and use it to separate magnetic and non-magnetic particles, as well as particles with different magnetizations. This scheme is simple, cost-effective, and label-free compared to other existing techniques.

Synthetic spin-orbit interactions and magnetic fields in ring-cavity QED

The interactions between light and matter are strongly enhanced when atoms are placed in high-finesse quantum cavities, offering tantalizing opportunities for generating exotic new quantum phases. In this work we show that both spin-orbit interactions and strong synthetic magnetic fields result when a neutral atom is confined within a ring cavity, whenever the internal atomic states are coupled to two off-resonant counter-propagating modes. We diagonalize the resulting cavity polariton Hamiltonian and find characteristic spin-orbit dispersion relations for a wide range of parameters. An adjustable uniform gauge potential is also generated, which can be converted into a synthetic magnetic field for neutral atoms by applying an external magnetic field gradient. Very large synthetic magnetic fields are possible as the strength is proportional to the (average) number of photons in each of the cavity modes. The results suggest that strong-coupling cavity quantum electrodynamics can be a useful environment for the formation of topological states in atomic systems.

Facile synthesis of monodispersed silica-coated magnetic nanoparticles

Silica-coated magnetic nanoparticles (MNPs) have great potential for use in field of biotechnology owing to their unique properties, which can be manipulated by an external magnetic field gradient. Herein, we describe a method for facile synthesis of monodispersed silica-coated MNPs (MNP@SiO2 NPs). Commercially available oleate-MNPs were successfully converted to polyvinylpyrrolidone-MNPs (PVP-MNPs), and then coated with silica by the modified Stöber method. More than 95% of MNPs were individually coated with a silica shell; non-magnetic core silica nanoparticles (NPs) were not detected. Notably, the MNP@SiO2 NPs are highly monodispersed in size (size distribution<2.5%) and synthesis at the scale of grams was easily obtained by a simple scale up process. Moreover, aggregation was not detected upon storage of over three months.

Hydrothermal synthesis of magnetic carbon microspheres for effective adsorption of Cd(II) in water

BACKGROUND Heavy metals present a great challenge due to pollution of the water environment. Conventional adsorption materials may be problematic for sustainable applications due to energy-intensive processing, low adsorption capacity and difficult liquid/solid separation. To address this issue, this study investigated monosaccharide biomass (i.e. glucose) as starting material for hydrothermal synthesis of carbon microspheres (CMS), followed by immobilization of magnetic iron oxide nanoparticles by a chemical co-precipitation method. RESULTS The results demonstrated that the hydrothermal method could yield high-quality homogeneous carbon microspheres (0.2−0.6 µm in diameter) with abundant oxygen-containing functional groups. The alkali treatment and chemical co-precipitation process produced magnetic Fe3O4 nanoparticles (10–20 nm) uniformly dispersed on the CMS surface. The MCMS exhibited effective adsorption of Cd(II) ions in water, which was consistent with quasi-second-order kinetics and Langmuir isotherms. On reaching adsorption equilibrium, the MCMS could be separated from the liquid phase instantly and completely in the presence of an applied external magnetic field gradient. CONCLUSION The MCMS synthesized by a hydrothermal and co-precipitation method show great promise as a new sustainable carbon-based adsorbent for potential application in the elimination of heavy metals from water and wastewater. © 2013 Society of Chemical Industry

Precise Control of the Drug Kinetics by Non-Invasive Magnetic Drug Delivery System

To solve the problems of side effects and medicinal lowering, studies on the magnetic drug delivery system (MDDS) have been applied. MDDS is a technique to accumulate drugs by using magnetic force as the physical driving force. It is necessary to apply a strong external magnetic field and high magnetic gradient to accumulate the ferromagnetic drugs to a deep diseased part noninvasively. However, by applying a static magnetic field from one direction, the drug accumulates only at the body surface near the magnet. In this study, we proposed a new method of MDDS in which a high-temperature superconducting (HTS) bulk magnet rotates around a target part. First, the particle trajectory simulation was conducted to examine the drug kinetics in a capillary blood vessel under the condition of rotating a magnet. Based on the results, the accumulation experiments of ferromagnetic particles with model blood vessels were conducted. As a result, the accumulation possibility of the ferromagnetic particles in the deep targeted part of the body was confirmed.

Reusable superparamagnetic nanocomposite particles for magnetic separation of iron hydroxide precipitates to remove and recover heavy metal ions from aqueous solutions

Superparamagnetic nanocomposite microparticles act as seeds for iron hydroxide precipitates. Flocculation of iron hydroxide is applied to adsorb and entrap heavy metal ions dissolved in water. The flocculation product gets deposited on the surface of the nanocomposite microparticles. Due to the nano-property superparamagnetism the particles are switchable magnets and can be separated together with their load from water by an external magnetic field gradient. In an acidic solution, particles are cleaned by dissolution of the iron hydroxide precipitate. A silica surface protects the superparamagnetic microparticles from dissolution rendering their reuse as seeds and magnetic carriers possible. Repetition of the separation and recovery process leads to a significant increase of concentration of heavy metals in the acid cleaning solution, which paves the way for further recycling procedures of these elements.

Dynamic scaling in magnetophoretic separation

Using numerical solutions of the Langevin equations, to simulate a magnetic separation of colloidal suspensions under an external magnetic-field gradient, we show the existence of a regime of dynamic scaling. We find that the separation time depends strongly on the size (or length) of aggregates taking place in the separation process. In the irreversible aggregation regime, we show that linear chains of particles steadily grow and their average size, S, increases with time as a power low. The chain-size (s) distribution-function (cs) approaches (for long times) the following scaling form cs(t)∝s−2f(s/S). The exponent, z, of the mean chain size S(t)∝tz is compatible with Smoluchowski's coagulation equation, with a homogeneous kernel, even if the separation is a process with particle migration. We also show that the regime corresponding to the dynamic scaling is limited in time due to the separation. Furthermore, we find a characteristic time, which we identify as a similarity variable, and we relate it to the separation time.

Magnetic bead nanoactuator

This paper presents the development of nanoactuators of free-standing Ti beam cantilevers with integrated superparamagnetic (SPM) beads at their front end that allow a controlled deflection by an external magnetic field gradient. A process flow is investigated based on three-step electron-beam lithography, reactive ion etching and the deposition of functionalized magnetic beads. While the thickness of the beams is 50nm, the lateral dimensions are designed to be 400nm, in order to carry beads of 360nm size. Magnetization measurements confirm the superparamagnetic behaviour of the beads having a saturation magnetization of 63kA/m. The position accuracy of multi-step electron beam lithography is about 10nm, allowing an exact deposition of functionalized beads.

A utilization of internal/external quasi-static magnetic field gradients: transport phenomenon and magnetic resonance imaging of solid polymers

Two topics concerning the utilization of internal and external magnetic field gradients are discussed. The first topic concerns the transport of conformons in the quasi-ordered phase of a regioregular, π-conjugated polymer, poly(4-methylthiazole-2,5-diyl), using a combination of longitudinal and transverse relaxation dispersion measurements. The effects of conformon diffusion on the relaxation exponent were successfully estimated via a numerical approach that used the Fourier spectrum solution of the one-dimensional Bloch-Torrey equation. The second topic demonstrates a low-cost magnetic resonance imaging method using a magnetic field gradient from a neodymium ferromagnet. Spin echo experiments are shown for three-layered thin films of PDMS/PTFE/PDMS under a large magnetic field.

Magnetically Vectored Platforms for The Targeted Delivery of Therapeutics to Tumors: History and Current Status

Superparamagnetic iron oxide nanoparticles (SPIONs) are being developed as vehicles for the selective targeting of therapeutics and bioactive compounds. Presented herein is a brief review of the history of approaches to magnetic-based drug delivery platforms, leading to current concepts of magnetically vectored therapeutics via functionalized SPION-prodrugs. With this background, recent experimental results are discussed that demonstrate the use of shaped external magnetic field gradients, generated by designed configurations of permanent magnets, to drive the concentration/accumulation of modified SPION-prodrug constructs at a tumor site, followed by tumor extravasation and activation of the prodrug within the tumor microenvironment. In order to successfully translate this approach to clinical application, one of the key requirements is the ability to magnetically drive ('vector') the SPION to human-scale tumor settings. In this review, various configurations of permanent magnets are described and models are presented that demonstrate that magnetic field gradients can potentially be focused and extended to lengths of several inches in vivo. This modification thereby increases the range of the delivery platform, and offers the potential for the treatment of visceral as well as superficial tumors and for translation from preclinical animal tumor models to clinical settings. The methodology of magnetically vectored prodrug therapeutics, as a means for selective localized targeting of tumor tissue, and minimizing harm to normal tissue, has the additional advantage of raising the therapeutic index compared with that of free drugs, thus, offering great potential as a cancer treatment modality.

TEMPERATURE DEPENDENCE OF SPIN CURRENTS CARRIED BY JORDAN–WIGNER FERMIONS AND MAGNONS IN INSULATORS

The temperature dependence of spin currents in insulators at the finite temperature near zero Kelvin is theoretically studied. The spin currents are carried by Jordan–Wigner fermions and magnons in one- and three-dimensional insulators. These spin currents are generated by the external magnetic field gradient along the quantization axis and also by the two-particle interaction gradient. In one-dimensional insulators, quantum fluctuations are strong and the spin current carried by Jordan–Wigner fermions shows the stronger dependence on temperatures than the one by magnons.

Magnetic field anisotropy based MR tractography

Non-invasive measurements of structural orientation provide unique information regarding the connectivity and functionality of fiber materials. In the present study, we use a capillary model to demonstrate that the direction of fiber structure can be obtained from susceptibility-induced magnetic field anisotropy. The interference pattern between internal and external magnetic field gradients carries the signature of the underlying anisotropic structure and can be measured by MRI-based water diffusion measurements. Through both numerical simulation and experiments, we found that this technique can determine the capillary orientation within 3°. Therefore, susceptibility-induced magnetic field anisotropy may be useful for an alternative tractography method when diffusion anisotropy is small at higher magnetic field strength without the need to rotate the subject inside the scanner.

Simultaneous gravity and gradient measurements from a recoil-compensated absolute gravimeter

This paper discusses simultaneous gravity and vertical gravity gradient measurements obtained with a newly designed recoil-compensated dropping chamber adapted to an FG5 absolute gravimeter. The new dropping chamber incorporates counterweights to compensate recoil effects. It has the same physical length as the standard FG5 dropping chamber but the free-fall distance was increased from 20 cm to 25 cm. The new drive train pulls on the centre of the system to reduce unwanted horizontal velocity and rotation of the free-falling test mass. The test-mass material was chosen to reduce possible magnetic eddy-current damping caused by external magnetic field gradients. External lead masses were used to change the gravity and vertical gravity gradient. The measurements agree well with the theoretical gravity field changes derived from the position of the external weights. The experiment clearly demonstrates the efficacy of using an absolute gravity meter to measure both the gravity and the gravity gradient signals caused by variations in the external gravity field. This technique shows promise for passive gravity-monitoring applications.

Theranostics With Multifunctional Magnetic Gold Nanoshells

to investigate the multifunctional imaging and therapeutic capabilities of core-shell nanoparticles composed of a superparamagnetic iron oxide (SPIO) core and a gold shell (SPIO@AuNS). the magnetic/optical properties of SPIO@AuNS were examined both in an agar gel phantom and in vivo by evaluating contrast-enhanced magnetic resonance imaging (MRI) and by measuring near-infrared (NIR) light-induced temperature changes mediated by SPIO@AuNS. In addition, the biodistribution and pharmacokinetics of In-labeled SPIO@AuNS after intravenous injection in mice bearing A431 tumors were evaluated in the presence and absence of an external magnet. : In agar phantoms containing SPIO@AuNS, a significant contrast enhancement in T2-weighted MRI was observed and a linear increase in temperature was observed with increasing concentration and laser output power when irradiated with NIR light centered at an 808 nm. In vivo, T2*-MRI delineated SPIO@AuNS and magnetic resonance temperature imaging of the same tumors revealed significant temperature elevations when intratumorally injected with SPIO@AuNS (1 × 10 particles/mouse) and irradiated with NIR light (65.70°C ± 0.69°C vs. 44.23°C ± 0.24°C for saline + laser). Biodistribution studies in mice intravenously injected with In-labeled-SPIO@AuNS(1 × 10 particles/mouse) had an approximately 2-fold increase in SPIO@AuNS delivered into tumors in the presence of an external magnet compared with tumors without the magnet. owing to its ability to mediate efficient photothermal ablation of cancer cells under MRI guidance, as well as the ability to be directed to solid tumors with an external magnetic field gradient, multifunctional SPIO@AuNS is a promising theranostic nanoplatform.

Magnetically Driven Single DNA Nanomotor

Magnetically driven DNA nanomotors: one end of a set of DNA hairpins is immobilized on a glass surface and the other is conjugated to magnetic particles. The DNA hairpin molecules are opened by an external magnetic field gradient, and subsequently closed through DNA hybridization after the removal of the magnetic field. The separation of the ends of the DNA hairpin during opening is interpreted as the power stroke of the nanomotor and the hybridization of the hairpin as the recovery stroke.

Development of magnetic nanoactuator systems

This paper presents the development of mechanically active arrays, which consist of free-standing Ti beam cantilevers with an integrated NiFe cube with critical dimensions of 100nm allowing for control by an external magnetic field gradient. A process flow is investigated based on two-step electron-beam lithography and reactive ion etching combined with magnetron sputtering of the functional magnetic nanostructures. A sacrificial layer technology is developed for dry etching of Ti anisotropically and Si isotropically at the same time. The saturation magnetization of the deposited NiFe is 0.78T giving rise of magneto-static forces in order of pN. AFM and MFM measurements confirm the size and position of the magnetic cubes.

Controlling friction using magnetic nanofluids

We study the thin-film rheological performance of superparamagnetic nanofluids in full film hydrodynamic regime under the presence of external magnetic field gradients. Ferrohydrodynamic Reynolds equation is numerically solved and compared to results obtained from tribo-rheological experiments in model face seals. A theoretical and experimental friction master curve is proposed that satisfactorily captures the lubrication behavior including hydrodynamics and magnetostatics in the problem without any fitting parameter.

Detection of Magnetic Particles in Live DBA/2J Mouse Eyes Using Magnetomotive Optical Coherence Tomography

To demonstrate in vivo molecular imaging of the eye using spectral-domain magnetomotive optical coherence tomography (MMOCT). A custom-built, high-speed, and high-resolution MMOCT was developed for imaging magnetic particle-coupled molecules in living mouse eyes by applying an external dynamic magnetic field gradient during optical coherence tomography (OCT) scanning. The magnetomotive signals were tested in vitro by scanning magnetic beads embedded within an agarose gel (1.5%) and in vivo in the anterior segment of a mouse eye. Cross-sectional OCT images of the gel and the anterior segment of the eye were acquired by regular OCT structural scanning. Magnetomotive optical coherence tomography signals were successfully captured in the agarose gel with embedded magnetic beads. The signals were captured in the anterior segment of the mouse eyes after injecting the beads. The signal was overlaid successfully onto the structural OCT image. We demonstrated the ability to detect particles injected into the anterior chamber of the mouse eye using MMOCT. This suggests that MMOCT is effective for future live detection of molecular (protein) targets in various ocular diseases in mouse models.

SU‐GG‐J‐117: Nanoparticle Assembled Capsules for Target Drug Delivery, Controllled Release and Hyperthermia

Purpose: To develop a combined targeted, drug release and hyperthermia delivery system for simultaneous multimodality therapy with radiation therapy. Method and Materials: The system is based on nanoparticle‐assembled capsules (NACs) where a polymer, multivalent ion, and a nanoparticle are the only constituents required for self‐assembly formation. Poly(allylamine hydrochloride), disodium phosphate, and citrate bound magnetite nanoparticles were used to create the exterior NAC nanoshell, which encapsulates doxorubicin in the microcapsule core. An alternating magnetic field (AMF) of 20 A/m at 267 kHz was used to release the doxorubicin and heat the NAC solution. Three different nanoparticle sizes were used for these studies; 10, 30, and 50 nm to study heating rates and release profiles. Results: Magnetic nanoparticle NACs, with doxorubicin cores, were created with dimensions of ∼ 1 m capsule diameter and a ∼ 200 nm shell thickness. Heating rates of the NAC‐solution as a function of particle size were measured. Doxorubicin release profiles were measured as a function of time, nanoparticle size, and concentration. Heating rates were substantially larger for the 50 nm nanoparticles than the 10 nm particles, where temperatures in excess of 90° C over 15 minutes were measured as compared to 70° for the smaller particles. Release rate measurements show that rate is proportional to particle size. Radiation in excess of 100 Gy delivered to the NACs showed no behavioral or morphology change. Conclusion: We developed a magnetic, nanoparticle‐assembled capsule, which is a multifunctional device that can be used simultaneously for both controlled drug release and hyperthermia. The system is controlled externally through magnetic heat loss processes. These devices have many advantages; their surface can be functionalized for molecular targeting in conjunction with external magnetic field gradients and these capsules can easily be scaled up for pharmaceutical production.

Functional magnetic nanoshells integrated nanosensor for trace analysis of environmental uranium contamination

Transuranic radionuclides such as uranium tend to be a pervasive environmental contaminant. It is absorbed through the intestine or a lung, deposited in the tissues, predominantly kidney and bone, and is carcinogenic. A novel nanosensor system has been developed for voltammetric tracing of environmental uranium contamination. The sensor consists of an organophosphorous ligand, ( t-butylphenyl)- N, N-di-(isobutyl) carbamoylmethylphosphineoxide (CMPO) functionalized superparamagnetic core–shell magnetic nanoparticles and magnet based electrodes. It exploits the natural affinity of uranium for phosphate molecules to fabricate a highly specific and reproducible sensor. The small dimension along with a dramatically increased contact surface has lead to a faster response and higher sensitivity. The system uses an external magnetic field gradient for preconcentration and removal of the analyte from the surrounding aqueous media. The redox properties of the analyte are exploited for enumeration of variables by electrochemical techniques such as square wave voltammetry. The detection limit of the system is observed to be in parts-per-billion (ppb) of the uranyl concentration.