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1.  Characterization of Non-Specific Crossover in SPLITT Fractionation 
Analytical chemistry  2008;80(18):7105-7115.
Split-flow thin channel (SPLITT) fractionation is a technique for continuous separation of particles or macromolecules in a fluid stream into fractions according to the lateral migration induced by application of a field perpendicular to the direction of flow. Typical applications have involved isolation of different fractions from a polydisperse sample. Some specialized applications involve the separation of the fraction influenced by the transverse field from the fraction that is not. For example, immuno-magnetically labeled biological cells may be separated from non-labeled cells with the application of a transverse magnetic field gradient. In such cases, it may be critically important to minimize contamination of the labeled cells with non-labeled cells while at the same time maximizing the throughput. Such contamination is known as non-specific crossover (NSC) and refers to the real or apparent migration of non-mobile particles or cells across streamlines with the mobile material. The possible mechanisms for NSC are discussed, and experimental results interpreted in terms of shear-induced diffusion (SID) caused by viscous interactions between particles in a sheared flow. It is concluded that SID may contribute to NSC, but that further experiments and mathematical modeling are necessary to more fully explore the phenomenon.
PMCID: PMC2805962  PMID: 18698797
2.  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.
PMCID: PMC3389787  PMID: 22773885
magnetic relaxometry; SQUID; atomic magnetometer; magnetic nanoparticle; cancer
3.  Induction of Biogenic Magnetization and Redox Control by a Component of the Target of Rapamycin Complex 1 Signaling Pathway 
PLoS Biology  2012;10(2):e1001269.
Most organisms are simply diamagnetic, while magnetotactic bacteria and migratory animals are among organisms that exploit magnetism. Biogenic magnetization not only is of fundamental interest, but also has industrial potential. However, the key factor(s) that enable biogenic magnetization in coordination with other cellular functions and metabolism remain unknown. To address the requirements for induction and the application of synthetic bio-magnetism, we explored the creation of magnetism in a simple model organism. Cell magnetization was first observed by attraction towards a magnet when normally diamagnetic yeast Saccharomyces cerevisiae were grown with ferric citrate. The magnetization was further enhanced by genetic modification of iron homeostasis and introduction of ferritin. The acquired magnetizable properties enabled the cells to be attracted to a magnet, and be trapped by a magnetic column. Superconducting quantum interference device (SQUID) magnetometry confirmed and quantitatively characterized the acquired paramagnetism. Electron microscopy and energy-dispersive X-ray spectroscopy showed electron-dense iron-containing aggregates within the magnetized cells. Magnetization-based screening of gene knockouts identified Tco89p, a component of TORC1 (Target of rapamycin complex 1), as important for magnetization; loss of TCO89 and treatment with rapamycin reduced magnetization in a TCO89-dependent manner. The TCO89 expression level positively correlated with magnetization, enabling inducible magnetization. Several carbon metabolism genes were also shown to affect magnetization. Redox mediators indicated that TCO89 alters the intracellular redox to an oxidized state in a dose-dependent manner. Taken together, we demonstrated that synthetic induction of magnetization is possible and that the key factors are local redox control through carbon metabolism and iron supply.
Author Summary
Most organisms do not respond to magnetic fields. However, “magnetotactic” bacteria and migratory animals can sense geomagnetic fields and alter their behavior accordingly. These organisms often contain small magnetic particles that may be responsible for sensing magnetic fields. In magnetotactic bacteria, specific genes are crucial for the formation of these magnetic particles, but no such genes have yet been characterized in migratory animals. In humans, formation of magnetic particles can be observed in the neuronal tissue in neurodegenerative diseases. One explanation for the appearance of these magnetic particles is that they are the result of alterations in metabolism, which occur in neurodegenerative diseases. Here, we explore this hypothesis by inducing magnetism in yeast cells, which are not naturally magnetic and examine how changes in metabolism contribute to particle formation and magnetism. We find that yeast cells expressing a set of human proteins that sequester iron contain iron particles and become attracted by a magnet when grown with ferric citrate. Through physiological and genetic studies we show that target of rapamycin complex 1 (TORC1) signaling, which responds to nutritional signals, is important for the magnetization of these cells by altering the intracellular oxidation (or redox) state. We also show that genes involved in carbon metabolism affect magnetization. We propose that local redox control mediated by carbon metabolism and iron homeostasis, processes that exist in normal unmagnetized cells, are key for iron particle formation and magnetization. We conclude that magnetization of normal cells will be possible with these existing gene sets.
PMCID: PMC3289596  PMID: 22389629
4.  The use of a linear Halbach array combined with a step-SPLITT channel for continuous sorting of magnetic species 
The Quadrupole Magnetic Sorter (QMS), employing an annular flow channel concentric with the aperture of a quadrupole magnet, is well established for cell and particle separations. Here we propose a magnetic particle separator comprising a linear array of cylindrical magnets, analogous to the array proposed by Klaus Halbach, mated to a substantially improved form of parallel-plate SPLITT channel, known as the step-SPLITT channel. While the magnetic force and throughput are generally lower than for the QMS, the new separator has advantages in ease of fabrication and the ability to vary the magnetic force to suit the separands. Preliminary experiments yield results consistent with prediction and show promise regarding future separations of cells of biomedical interest.
PMCID: PMC3050493  PMID: 21399709
Magnetic separation; Particle fractionation; SPLITT; step-SPLITT
5.  Simulating Magnetic Nanoparticle Behavior in Low-field MRI under Transverse Rotating Fields and Imposed Fluid Flow 
In the presence of alternating-sinusoidal or rotating magnetic fields, magnetic nanoparticles will act to realign their magnetic moment with the applied magnetic field. The realignment is characterized by the nanoparticle’s time constant, τ. As the magnetic field frequency is increased, the nanoparticle’s magnetic moment lags the applied magnetic field at a constant angle for a given frequency, Ω, in rad/s. Associated with this misalignment is a power dissipation that increases the bulk magnetic fluid’s temperature which has been utilized as a method of magnetic nanoparticle hyperthermia, particularly suited for cancer in low-perfusion tissue (e.g., breast) where temperature increases of between 4°C and 7°C above the ambient in vivo temperature cause tumor hyperthermia. This work examines the rise in the magnetic fluid’s temperature in the MRI environment which is characterized by a large DC field, B0. Theoretical analysis and simulation is used to predict the effect of both alternating-sinusoidal and rotating magnetic fields transverse to B0. Results are presented for the expected temperature increase in small tumors (~1 cm radius) over an appropriate range of magnetic fluid concentrations (0.002 to 0.01 solid volume fraction) and nanoparticle radii (1 to 10 nm). The results indicate that significant heating can take place, even in low-field MRI systems where magnetic fluid saturation is not significant, with careful The goal of this work is to examine, by means of analysis and simulation, the concept of interactive fluid magnetization using the dynamic behavior of superparamagnetic iron oxide nanoparticle suspensions in the MRI environment. In addition to the usual magnetic fields associated with MRI, a rotating magnetic field is applied transverse to the main B0 field of the MRI. Additional or modified magnetic fields have been previously proposed for hyperthermia and targeted drug delivery within MRI. Analytical predictions and numerical simulations of the transverse rotating magnetic field in the presence of B0 are investigated to demonstrate the effect of Ω, the rotating field frequency, and the magnetic field amplitude on the fluid suspension magnetization. The transverse magnetization due to the rotating transverse field shows strong dependence on the characteristic time constant of the fluid suspension, τ. The analysis shows that as the rotating field frequency increases so that Ωτ approaches unity, the transverse fluid magnetization vector is significantly non-aligned with the applied rotating field and the magnetization’s magnitude is a strong function of the field frequency. In this frequency range, the fluid’s transverse magnetization is controlled by the applied field which is determined by the operator. The phenomenon, which is due to the physical rotation of the magnetic nanoparticles in the suspension, is demonstrated analytically when the nanoparticles are present in high concentrations (1 to 3% solid volume fractions) more typical of hyperthermia rather than in clinical imaging applications, and in low MRI field strengths (such as open MRI systems), where the magnetic nanoparticles are not magnetically saturated. The effect of imposed Poiseuille flow in a planar channel geometry and changing nanoparticle concentration is examined. The work represents the first known attempt to analyze the dynamic behavior of magnetic nanoparticles in the MRI environment including the effects of the magnetic nanoparticle spin-velocity. It is shown that the magnitude of the transverse magnetization is a strong function of the rotating transverse field frequency. Interactive fluid magnetization effects are predicted due to non-uniform fluid magnetization in planar Poiseuille flow with high nanoparticle concentrations.
PMCID: PMC2901184  PMID: 20625540
Magnetic nanoparticles; MRI; rotating magnetic field; interactive magnetization; magnetic particle imaging
6.  Comparison of a triaxial fluxgate magnetometer and Toftness sensometer for body surface EMF measurement 
The use of magnetic fields to treat disease has intrigued mankind since the time of the ancient Greeks. More recently it has been shown that electromagnetic field (EMF) treatment aids bone healing, and repetitive transcranial magnetic stimulation (rTMS) appears to be beneficial in treating schizophrenia and depression. Since external EMFs influence internal body processes, we hypothesized that measurement of body surface EMFs might be used to detect disease states and direct the course of subsequent therapy. However, measurement of minute body surface EMFs requires use of a sensitive and well documented magnetometer. In this study we evaluated the sensitivity and frequency response of a fluxgate magnetometer with a triaxial probe for use in detecting body surface EMF and we compared the magnetometer readings with a signal from a Toftness Sensometer, operated by an experienced clinician, in the laboratory and in a clinical setting.
A Peavy Audio Amplifier and variable power output Telulex signal generator were used to develop 50 μT EMFs in a three coil Merritt coil system. A calibrated magnetometer was used to set a 60 Hz 50 μT field in the coil and an ammeter was used to measure the current required to develop the 50 μT field. At frequencies other than 60 Hz, the field strength was maintained at 50 μT by adjusting the Telulex signal output to keep the current constant. The field generated was monitored using a 10 turn coil connected to an oscilloscope. The oscilloscope reading indicated that the field strength was the same at all frequencies tested. To determine if there was a correspondence between the signals detected by a fluxgate magnetometer (FGM1) and the Toftness Sensometer both devices were placed in the Merritt coil and readings were recorded from the FGM1 and compared with the ability of a highly experienced Toftness operator to detect the 50 μT field. Subsequently, in a clinical setting, FGM1 readings made by an FGM1 technician and Sensometer readings were made by 4 Toftness Sensometer operators, having various degrees of experience with this device. Each examiner obtained instrument readings from 5 different volunteers in separate chiropractic adjusting rooms. Additionally, one of the Toftness Sensometers was equipped with an integrated fluxgate magnetometer (FGM2) and this magnetometer was used to obtain a second set of EMF readings in the clinical setting.
The triaxial fluxgate magnetometer was determined to be moderately responsive to changes in magnetic field frequency below 10 Hz. At frequencies above 10 Hz the readings corresponded to that of the ambient static geofield. The practitioner operating the Toftness Sensometer was unable to detect magnetic fields at high frequencies (above 10 Hz) even at very high EMFs. The fluxgate magnetometer was shown to be essentially a DC/static magnetic field detector and like all such devices it has a limited frequency range with some low level of sensitivity at very low field frequencies. The interexaminer reliability of four Toftness practitioners using the Sensometer on 5 patients showed low to moderate correlation.
The fluxgate magnetometer although highly sensitive to static (DC) EMFs has only limited sensitivity to EMFs in the range of 1 to 10 Hz and is very insensitive to frequencies above 10 Hz. In laboratory comparisons of the Sensometer and the fluxgate magnetometer there was an occasional correspondence between the two instruments in detecting magnetic fields within the Merritt coil but these occasions were not reproducible. In the clinical studies there was low to moderate agreement between the clinicians using the Sensometer to diagnosing spinal conditions and there was little if any agreement between the Sensometer and the fluxgate magnetometer in detecting EMFs emanating from the volunteers body surface.
PMCID: PMC1769295  PMID: 17549105
Toftness; Magnetometer; EMF; Chiropractic
7.  Characterization of magnetic nanoparticles using programmed quadrupole magnetic field-flow fractionation 
Quadrupole magnetic field-flow fractionation is a relatively new technique for the separation and characterization of magnetic nanoparticles. Magnetic nanoparticles are often of composite nature having a magnetic component, which may be a very finely divided material, and a polymeric or other material coating that incorporates this magnetic material and stabilizes the particles in suspension. There may be other components such as antibodies on the surface for specific binding to biological cells, or chemotherapeutic drugs for magnetic drug delivery. Magnetic field-flow fractionation (MgFFF) has the potential for determining the distribution of the magnetic material among the particles in a given sample. MgFFF differs from most other forms of field-flow fractionation in that the magnetic field that brings about particle separation induces magnetic dipole moments in the nanoparticles, and these potentially can interact with one another and perturb the separation. This aspect is examined in the present work. Samples of magnetic nanoparticles were analysed under different experimental conditions to determine the sensitivity of the method to variation of conditions. The results are shown to be consistent and insensitive to conditions, although magnetite content appeared to be somewhat higher than expected.
PMCID: PMC2981903  PMID: 20732895
magnetic nanoparticles; field-flow fractionation; characterization; quadrupole magnet; magnetic field-flow fractionation; magnetic dipole interaction
8.  Poly-l-lysine-coated magnetic nanoparticles as intracellular actuators for neural guidance 
It has been proposed in the literature that Fe3O4 magnetic nanoparticles (MNPs) could be exploited to enhance or accelerate nerve regeneration and to provide guidance for regenerating axons. MNPs could create mechanical tension that stimulates the growth and elongation of axons. Particles suitable for this purpose should possess (1) high saturation magnetization, (2) a negligible cytotoxic profile, and (3) a high capacity to magnetize mammalian cells. Unfortunately, the materials currently available on the market do not satisfy these criteria; therefore, this work attempts to overcome these deficiencies.
Magnetite particles were synthesized by an oxidative hydrolysis method and characterized based on their external morphology and size distribution (high-resolution transmission electron microscopy [HR-TEM]) as well as their colloidal (Z potential) and magnetic properties (Superconducting QUantum Interference Devices [SQUID]). Cell viability was assessed via Trypan blue dye exclusion assay, cell doubling time, and MTT cell proliferation assay and reactive oxygen species production. Particle uptake was monitored via Prussian blue staining, intracellular iron content quantification via a ferrozine-based assay, and direct visualization by dual-beam (focused ion beam/scanning electron microscopy [FIB/SEM]) analysis. Experiments were performed on human neuroblastoma SH-SY5Y cell line and primary Schwann cell cultures of the peripheral nervous system.
This paper reports on the synthesis and characterization of polymer-coated magnetic Fe3O4 nanoparticles with an average diameter of 73 ± 6 nm that are designed as magnetic actuators for neural guidance. The cells were able to incorporate quantities of iron up to 2 pg/cell. The intracellular distribution of MNPs obtained by optical and electronic microscopy showed large structures of MNPs crossing the cell membrane into the cytoplasm, thus rendering them suitable for magnetic manipulation by external magnetic fields. Specifically, migration experiments under external magnetic fields confirmed that these MNPs can effectively actuate the cells, thus inducing measurable migration towards predefined directions more effectively than commercial nanoparticles (fluidMAG-ARA supplied by Chemicell). There were no observable toxic effects from MNPs on cell viability for working concentrations of 10 μg/mL (EC25 of 20.8 μg/mL, compared to 12 μg/mL in fluidMAG-ARA). Cell proliferation assays performed with primary cell cultures of the peripheral nervous system confirmed moderate cytotoxicity (EC25 of 10.35 μg/mL).
These results indicate that loading neural cells with the proposed MNPs is likely to be an effective strategy for promoting non-invasive neural regeneration through cell magnetic actuation.
PMCID: PMC3394465  PMID: 22811603
magnetic nanoparticle; actuator; migration; neural regeneration
9.  Motion and twisting of magnetic particles ingested by alveolar macrophages in the human lung: effect of smoking and disease 
Magnetic microparticles being ingested by alveolar macrophages can be used as a monitor for intracellular phagosome motions and cytoskeletal mechanical properties. These studies can be performed in the human lung after voluntary inhalation. The influence of cigarette smoking and lung diseases on cytoskeleton dependent functions was studied.
Spherical 1.3 μm diameter ferrimagnetic iron oxide particles were inhaled by 17 healthy volunteers (40 – 65 years), 15 patients with sarcoidosis (SAR), 12 patients with idiopathic pulmonary fibrosis (IPF), and 18 patients with chronic obstructive bronchitis (COB). The retained particles were magnetized and aligned in an external 100 mT magnetic field. All magnetized particles induce a weak magnetic field of the lung, which was detected by a sensitive SQUID (superconducting quantum interference device) sensor. Cytoskeletal reorganizations within macrophages and intracellular transport cause stochastic magnetic dipole rotations, which are reflected in a decay of the magnetic lung field, called relaxation. Directed phagosome motion was induced in a weak magnetic twisting field. The resistance of the cytoplasm to particle twisting was characterized by the viscosity and the stiffness (ratio between stress to strain) of the cytoskeleton.
One week after particle inhalation and later macrophage motility (relaxation) and cytoskeletal stiffness was not influenced by cigarette smoking, neither in healthy subjects, nor in the patients. Patients with IPF showed in tendency a faster relaxation (p = 0.06). Particle twisting revealed a non-Newtonian viscosity with a pure viscous and a viscoelastic compartment. The viscous shear was dominant, and only 27% of the shear recoiled and reflected viscoelastic properties. In patients with IPF, the stiffness was reduced by 60% (p < 0.02). An analysis of the shear rate and stress dependence of particle twisting allows correlating the rheological compartments to cytoskeletal subunits, in which microtubules mediate the pure viscous (non-recoverable) shear and microfilaments mediate the viscoelastic (recoverable) behavior. The missing correlation between relaxation and particle twisting shows that both stochastic and directed phagosome motion reflect different cytoskeletal mechanisms.
Faster relaxation and a soft cytoskeleton in patients with IPF indicate alterations in cytoskeleton dependent functions of alveolar macrophages, which may cause dysfunction's in the alveolar defense, like a slower migration, a retarded phagocytosis, a disturbed phagosome lysosome fusion and an impaired clearance.
PMCID: PMC1524958  PMID: 16700919
10.  Simultaneous suppression of disturbing fields and localization of magnetic markers by means of multipole expansion 
Magnetically marked capsules serve for the analysis of peristalsis and throughput times within the intestinal tract. Moreover, they can be used for the targeted disposal of drugs. The capsules get localized in time by field measurements with a superconducting quantum interference device (SQUID) magnetometer array. Here it is important to ensure an online localization with high speed and high suppression of disturbing fields. In this article we use multipole expansions for the simultaneous localization and suppression of disturbing fields.
We expand the measurement data in terms of inner and outer multipoles. Thereby we obtain directly a separation of marker field and outer disturbing fields. From the inner dipoles and quadrupoles we compute the magnetization and position of the capsule. The outer multipoles get eliminated.
The localization goodness has been analyzed depending on the order of the multipoles used and depending on the systems noise level. We found upper limits of the noise level for the usage of certain multipole moments. Given a signal to noise ratio of 40 and utilizing inner dipoles and quadrupoles and outer dipoles, the method enables an accuracy of 5 mm with a speed of 10 localizations per second.
The multipole localization is an effective method and is capable of online-tracking magnetic markers.
PMCID: PMC519033  PMID: 15341659
11.  Development of oxaliplatin encapsulated in magnetic nanocarriers of pectin as a potential targeted drug delivery for cancer therapy 
Superparamagnetic iron oxide nanoparticles (SPIONs) and oxaliplatin (OHP) were in-situ encapsulated in pectin cross-linked with Ca2+ forming 100–200 nm sized magnetically functionalized pectin nanocarriers, referred here as MP-OHP nanocarriers. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies revealed formation of spherical nanostructures. The magnetic measurements by vibration sample magnetometer (VSM) revealed high saturation magnetization (Ms=45.65 emu/g). The superparamagnetic property of MP-OHP was confirmed from the blocking temperature (TB) determined from field cooled and zero field cooled magnetization, measured by superconducting quantum unit interference device (SQUID) magnetometry. The stability of the aqueous dispersion of MP-OHP nanocarriers was confirmed from its high zeta potential (−30.5 mV). The drug encapsulation efficiency (55.2±4.8% w/w) and the drug loading content (0.10±0.04 wt%) in MP-OHP nanocarriers were determined from corresponding platinum contents in OHP and MP-OHP batches measured by inductively coupled plasma mass spectrometry (ICPMS). These nanocarriers exhibited a sustained release of OHP in phosphate buffer solution maintained at pH 5.5 and 7.4, where the drug release profile satisfied a combination of diffusion and swelling controlled mechanism. The cytotoxicity effect of MP-OHP nanocarriers was studied on MIA-PaCa-2 (pancreas) cancer cell line, where the GI50 values were more than 5 mg/mL and it exhibited 10 folds higher cytoxicity than the equivalent concentration of free drug.
Graphical abstract
Development of novel MP-OHP nanocarriers showing cytotoxicity effect in pancreas cancer cell.
► Development of novel oxaliplatin and SPIONs encapsulated in pectin nanocarrier (MP-OHP). ► The sizes of nanocarriers are100–200 nm, stable in aqueous medium with zeta potential of −30.5 mV. ► The MP-OHP nanocarriers are superparamagnetic with high saturation magnetization (45.65 emu/g). ► The MP-OHP nanocarriers exhibited higher in vitro cytotoxicity effect on pancreas cancer cells than free drug.
PMCID: PMC4210274  PMID: 25755993
Pectin; SPIONs; Polymer nanocarrier; Oxaliplatin; Controlled release; Targeted drug delivery
12.  Characteristics of magnetic labeling on liver tumors with anti-alpha-fetoprotein-mediated Fe3O4 magnetic nanoparticles 
For preoperative and intraoperative detection of tumor distribution, numerous multimodal contrast agents, such as magnetic nanoparticles (MNPs) with several examination indicators, are currently in development. However, complex materials, configuration, and cost are required for multimodal contrast agents, accompanied by a high possibility of toxicity and low popularity in clinics. Nevertheless, the magnetic labeling of MNPs using bioprobes should be feasible not only in preoperative magnetic resonance imaging (MRI), but also in intraoperative examination based on other magnetic properties. In this study, anti-alpha-fetoprotein (AFP)-mediated Fe3O4 MNPs, injected into mice with liver tumors, were used to examine the characteristics of magnetic labeling. Using MRI and scanning superconducting-quantum-interference-device biosusceptometry (SSB), based on alternating current (AC) susceptibility, the magnetic labeling occurred significantly on the first day post-injection of anti-AFP magnetic fluid (MF), and then decreased over time. However, for both MF without antibodies and an anti-carcinoembryonic antigen MF, no magnetic labeling occured on the first day of their respective post-injection. The favorable agreement indicates that magnetic labeling possesses two magnetic characteristics: distortion of the imaging field and AC susceptibility. In addition, the results of the biopsy tests, anti-AFP staining, and Prussian blue staining show the same dynamics as those of magnetic methodologies and prove that bound MNPs on tumor tissue are rotatable by an AC magnetic field to express AC susceptibility. Therefore, with the simple configuration of antibody-mediated MNPs, magnetic labeling is also feasible for intraoperative examinations using SSB with high mobility and sensitivity.
PMCID: PMC3392145  PMID: 22787394
alpha-fetoprotein; magnetic resonance imaging; scanning SQUID biosusceptometry
13.  Theoretical and Computational Multiple Regression Study of Gastric Electrical Activity Using Dipole Tracing from Magnetic Field Measurements 
Journal of Biological Physics  2004;30(3):239-259.
The biomagnetic inverse problem has captured the interest of both mathematicians and physicists due to its important applications in the medical field. As a result of our experience in analyzing the electrical activity of the gastric smooth muscle, we present here a theoretical model of the magnetic field in the stomach and a computational implementation whereby we demonstrate its realism and usefulness. The computational algorithm developed for this purpose consists of dividing the magnetic field signal input surface into centroid-based grids that allow recursive least-squares approximations to be applied, followed by comparison tests in which the locations of the best-fitting current dipoles are determined. In the second part of the article, we develop a multiple-regression analysis of experimental gastric magnetic data collected using Superconducting QUantum Interference Device (SQUID) magnetometers and successfully processed using our algorithm. As a result of our analysis, we conclude on statistical grounds that it is sufficient to model the electrical activity of the GI tract using only two electric current dipoles in order to account for the magnetic data recorded non-invasively with SQUID magnetometers above the human abdomen.
PMCID: PMC3456086  PMID: 23345871
gastrointestinal electrical activity; biomagnetic inverse problem; current dipole
14.  Synthesis of Amine-stabilized Aqueous Colloidal Iron Oxide Nanoparticles 
Crystal growth & design  2007;7(3):471-475.
We demonstrate a simple one-step process for the synthesis of iron oxide nanoparticle aqueous colloids using the multifunctional molecule, dodecylamine (DDA), that electrostatically complexes with aqueous iron ions (one precursor Fe2+ from FeCl2), reduces them, and subsequently caps the nanoparticles. The iron oxide particles thus synthesized are of the face-centered cubic (FCC) phase with high degree of monodispersity with appropriate concentration of amine capping molecular layer. The aqueous magnetic nanocrystalline colloids were characterized by TEM, XRD, XPS, TGA/DTA and FTIR spectroscopy techniques. The relaxivity, stability, and hydrodynamic size of the nanoparticles were investigated for potential application in magnetic resonance imaging (MRI). The magnetic properties were also studied by using a superconducting quantum interference device (SQUID) magnetometer at room temperature. We believe that such simple one-step synthesis of biocompatible aqueous nanomagnetic colloids will have viable applications in biomedical imaging, diagnostics and therapeutics.
PMCID: PMC2659353  PMID: 19305647
15.  Development of a compact superconducting rotating-gantry for heavy-ion therapy 
Journal of Radiation Research  2014;55(Suppl 1):i24-i25.
An isocentric superconducting rotating-gantry for heavy-ion therapy is being developed [ 1]. This rotating gantry can transport heavy ions having 430 MeV/u to an isocenter with irradiation angles of over ±180°, and is further capable of performing fast raster-scanning irradiation [ 2]. A layout of the beam-transport line for the compact rotating-gantry is presented in Fig. 1. The rotating gantry has 10 superconducting magnets (BM01-10), a pair of the scanning magnets (SCM-X and SCM-Y) and two pairs of beam profile- monitor and steering magnets (ST01-02 and PRN01-02). For BM01-BM06 and BM09-BM10, the combined-function superconducting magnets are employed. Further, these superconducting magnets are designed for fast slewing of the magnetic field to follow the multiple flattop operation of the synchrotron [ 3]. The use of the combined-function superconducting magnets with optimized beam optics allows a compact gantry design with a large scan size at the isocenter; the length and the radius of the gantry will be to be ∼13 and 5.5 m, respectively, which are comparable to those for the existing proton gantries. Furthermore, the maximum scan size at the isocenter is calculated to be as large as ∼200 mm square for heavy-ion beams at the maximum energy of 430 MeV/u.
All of the superconducting magnets were designed, and their magnetic fields were calculated using the Opera-3d code [ 4]. With the calculated magnetic fields, beam-tracking simulations were made. The simulation results agreed well with those of the linear beam-optics calculation, proving validity of the final design for the superconducting magnets. The five out of 10 superconducting magnets, as well as the model magnet were currently manufactured. With these magnets, rotation tests, magnetic field measurements and fast slewing tests were conducted. However, we did not observe any significant temperature increase, which may cause a quench problem. Further, results of the magnetic field measurements roughly agreed with those calculated by the Opera-3d code.
The design study as well as major tests of the superconducting magnets was completed, and the construction of the superconducting rotating-gantry is in progress. The construction of the superconducting rotating-gantry will be completed at the end of FY2014, and be commissioned within FY2015. Fig. 1.Layout of the superconducting rotating-gantry. The gantry consists of 10 superconducting magnets (BM01–BM10), a pair of the scanning magnets (SCM-X and SCMY), and two pairs of beam profile-monitor and steering magnets (STR01–STR02 and PRN01–PRN02).
PMCID: PMC3941506
heavy-ion therapy; rotating gantry; superconducting magnet; scanning irradiation
16.  Detection of breast cancer cells using targeted magnetic nanoparticles and ultra-sensitive magnetic field sensors 
Breast Cancer Research : BCR  2011;13(5):R108.
Breast cancer detection using mammography has improved clinical outcomes for many women, because mammography can detect very small (5 mm) tumors early in the course of the disease. However, mammography fails to detect 10 - 25% of tumors, and the results do not distinguish benign and malignant tumors. Reducing the false positive rate, even by a modest 10%, while improving the sensitivity, will lead to improved screening, and is a desirable and attainable goal. The emerging application of magnetic relaxometry, in particular using superconducting quantum interference device (SQUID) sensors, is fast and potentially more specific than mammography because it is designed to detect tumor-targeted iron oxide magnetic nanoparticles. Furthermore, magnetic relaxometry is theoretically more specific than MRI detection, because only target-bound nanoparticles are detected. Our group is developing antibody-conjugated magnetic nanoparticles targeted to breast cancer cells that can be detected using magnetic relaxometry.
To accomplish this, we identified a series of breast cancer cell lines expressing varying levels of the plasma membrane-expressed human epidermal growth factor-like receptor 2 (Her2) by flow cytometry. Anti-Her2 antibody was then conjugated to superparamagnetic iron oxide nanoparticles using the carbodiimide method. Labeled nanoparticles were incubated with breast cancer cell lines and visualized by confocal microscopy, Prussian blue histochemistry, and magnetic relaxometry.
We demonstrated a time- and antigen concentration-dependent increase in the number of antibody-conjugated nanoparticles bound to cells. Next, anti Her2-conjugated nanoparticles injected into highly Her2-expressing tumor xenograft explants yielded a significantly higher SQUID relaxometry signal relative to unconjugated nanoparticles. Finally, labeled cells introduced into breast phantoms were measured by magnetic relaxometry, and as few as 1 million labeled cells were detected at a distance of 4.5 cm using our early prototype system.
These results suggest that the antibody-conjugated magnetic nanoparticles are promising reagents to apply to in vivo breast tumor cell detection, and that SQUID-detected magnetic relaxometry is a viable, rapid, and highly sensitive method for in vitro nanoparticle development and eventual in vivo tumor detection.
PMCID: PMC3262221  PMID: 22035507
17.  Noise amplification in parallel whole-head ultra-low-field magnetic resonance imaging using 306 detectors 
In ultra-low-field (ULF) magnetic resonance imaging (MRI), arrays of up to hundreds of highly sensitive superconducting quantum interference devices (SQUIDs) can be used to detect the weak magnetic fields emitted by the precessing magnetization. Here we investigate the noise amplification in sensitivity encoded (SENSE) ULF MRI at various acceleration rates using a SQUID array consisting of 102 magnetometers, 102 gradiometers, or 306 magnetometers and gradiometers, to cover the whole head. Our results suggest that SQUID arrays consisting of 102 magnetometers and 102 gradiometers are similar in g-factor distribution. A SQUID array of 306 sensors (102 magnetometers and 204 gradiometers) only marginally improves the g-factor. Corroborating with previous studies, the g-factor in 2D SENSE ULF MRI with 9 to 16-fold 2D accelerations using the SQUID array studied here may be acceptable.
PMCID: PMC3706472  PMID: 23023497
SENSE; g-factor; ULF MRI; MEG; MEG-MRI; conjugated gradient; parallel MRI
18.  Activation of Schwann cells in vitro by magnetic nanocomposites via applied magnetic field 
Schwann cells (SCs) are attractive seed cells in neural tissue engineering, but their application is limited by attenuated biological activities and impaired functions with aging. Therefore, it is important to explore an approach to enhance the viability and biological properties of SCs. In the present study, a magnetic composite made of magnetically responsive magnetic nanoparticles (MNPs) and a biodegradable chitosan–glycerophosphate polymer were prepared and characterized. It was further explored whether such magnetic nanocomposites via applied magnetic fields would regulate SC biological activities. The magnetization of the magnetic nanocomposite was measured by a vibrating sample magnetometer. The compositional characterization of the magnetic nanocomposite was examined by Fourier-transform infrared and X-ray diffraction. The tolerance of SCs to the magnetic fields was tested by flow-cytometry assay. The proliferation of cells was examined by a 5-ethynyl-2-deoxyuridine-labeling assay, a PrestoBlue assay, and a Live/Dead assay. Messenger ribonucleic acid of BDNF, GDNF, NT-3, and VEGF in SCs was assayed by quantitative real-time polymerase chain reaction. The amount of BDNF, GDNF, NT-3, and VEGF secreted from SCs was determined by enzyme-linked immunosorbent assay. It was found that magnetic nanocomposites containing 10% MNPs showed a cross-section diameter of 32.33±1.81 µm, porosity of 80.41%±0.72%, and magnetization of 5.691 emu/g at 8 kOe. The 10% MNP magnetic nanocomposites were able to support cell adhesion and spreading and further promote proliferation of SCs under magnetic field exposure. Interestingly, a magnetic field applied through the 10% MNP magnetic scaffold significantly increased the gene expression and protein secretion of BDNF, GDNF, NT-3, and VEGF. This work is the first stage in our understanding of how to precisely regulate the viability and biological properties of SCs in tissue-engineering grafts, which combined with additional molecular factors may lead to the development of new nerve grafts.
PMCID: PMC4275057  PMID: 25565803
Schwann cell; magnetic field; nanocomposite; cell proliferation
19.  Microchip-based Immunomagnetic Detection of Circulating Tumor Cell 
Lab on a Chip  2011;11(20):3449-3457.
Screening for circulating tumor cells (CTCs) in blood has been an object of interest for evidence of progressive disease, status of disease activity, recognition of clonal evolution of molecular changes and for possible early diagnosis of cancer. We describe a new method of microchip-based immunomagnetic CTC detection, in which the benefits of both immunomagnetic assay and the microfluidic device are combined. As the blood sample flows through the microchannel closely above arrayed magnets, cancer cells labeled with magnetic nanoparticles are separated from blood flow and deposited at the bottom wall of the glass coverslip, which allows direct observation of captured cells with a fluorescence microscope. A polydimethylsiloxane (PDMS)-based microchannel fixed on a glass coverslip was used to screen blood samples. The thin, flat dimensions of the microchannel, combined with the sharp magnetic field gradient in the vicinity of arrayed magnets with alternate polarities, lead to an effective capture of labeled cells. Comparing to the commercially available CellSearch™ system, less (25%) magnetic particles are required to achieve a comparable capture rate, while the screening speed (at optimal blood flow rate of 10 mL/hour) is more than five times faster than those reported previously with a microchannel-based assay. For the screening experiment, blood drawn from healthy subjects into CellSave™ tubes was spiked with cultured cancer cell lines of COLO205 and SKBR3. The blood was then kept at room temperature for 48 hours before the screening, emulating the actual clinical cases of blood screening. Customized Fe3O4 magnetic nanoparticles (Veridex Ferrofluid™) conjugated to anti-Epithelial cell adhesion molecule (EpCAM) antibodies were introduced into the blood samples to label cancer cells, and the blood was then run through the microchip device to capture the labelled cells. After capture, the cells were stained with fluorescently labelled anti-cytokeratin, DAPI and anti-CD45. Subsequent immunofluorescence images were taken for the captured cells, followed by comprehensive computer aided analysis based on fluorescence intensities and cell morphology. Rare cancer cells (from ~1000 cells down to ~5 cells per mL) with very low tumor cell to blood cell ratios (about 1: 107~109, including red blood cells) were successfully detected. Cancer cell capture rates of 90% and 86% were demonstrated for COLO205 and SKBR3cells, respectively.
PMCID: PMC3379551  PMID: 21863182
20.  When Pigs Fly: Immunomagnetic separation facilitates rapid determination of Pig-a mutant frequency by flow cytometric analysis 
Mutation research  2011;721(2):163-170.
In vivo mutation assays based on the Pig-a null phenotype, that is, the absence of cell surface glycosylphosphatidylinositol (GPI) anchored proteins such as CD59, have been described. This work has been accomplished with hematopoietic cells, most often rat peripheral blood erythrocytes (RBCs) and reticulocytes (RETs). The current report describes new sample processing procedures that dramatically increase the rate at which cells can be evaluated for GPI anchor deficiency. This new method was applied to blood specimens from vehicle, 1,3-propane sultone, melphalan, and N-ethyl-N-nitrosourea treated Sprague Dawley rats. Leukocyte- and platelet- depleted blood samples were incubated with anti-CD59-phycoerythrin (PE) and anti-CD61-PE, and then mixed with anti-PE paramagnetic particles and Counting Beads (i.e., fluorescent microspheres). An aliquot of each specimen was stained with SYTO 13 and flow cytometric analysis was performed to determine RET percentage, RET:Counting Bead ratio, and RBC:Counting Bead ratio. The major portion of these specimens were passed through ferromagnetic columns that were suspended in a magnetic field, thereby depleting each specimen of wild-type RBCs (and platelets) based on their association with anti-PE paramagnetic particles. The eluates were concentrated via centrifugation and the resulting suspensions were stained with SYTO 13 and analyzed on the flow cytometer to determine mutant phenotype RET:Counting Bead and mutant phenotype RBC:Counting Bead ratios. The ratios obtained from pre- and post-column analyses were used to derive mutant phenotype RET and mutant phenotype RBC frequencies. Results from vehicle control and genotoxicant-treated rats are presented that indicate the scoring system is capable of returning reliable mutant phenotype cell frequencies. Using this wild-type cell depletion strategy, it was possible to interrogate ≥ 3 million RETs and ≥ 100 million RBCs per rat in approximately 7 minutes. Beyond considerably enhancing the throughput capacity of the analytical platform, these blood-processing procedures were also shown to enhance the precision of the measurements.
PMCID: PMC3064711  PMID: 21277384
Pig-a gene; mutation; erythrocytes; GPI anchor; flow cytometry; CD59
21.  Characterization of Single-core Magnetite Nanoparticles for Magnetic Imaging by SQUID-relaxometry 
Physics in medicine and biology  2010;55(19):10.1088/0031-9155/55/19/023.
Optimizing the sensitivity of SQUID (superconducting quantum interference device)-relaxometry for detecting cell-targeted magnetic nanoparticles for in vivo diagnostics requires nanoparticles with a narrow particle size distribution to ensure that the Néel relaxation times fall within the measurement timescale (50 ms - 2 s, in this work). To determine the optimum particle size, single-core magnetite nanoparticles (with nominal average diameters 20, 25, 30, and 35 nm) were characterized by SQUID-relaxometry, transmission electron microscopy (TEM), SQUID-susceptometry, dynamic light scattering, and zeta potential analysis. The SQUID-relaxometry signal (detected magnetic moment/kg) from both the 25 nm and 30 nm particles was an improvement over previously-studied multi-core particles. However, the detected moments were an order of magnitude lower than predicted based on a simple model that takes into account the measured size distributions (but neglects dipolar interactions and polydispersity of the anisotropy energy density), indicating that improved control of several different nanoparticle properties (size, shape, coating thickness) will be required to achieve the highest detection sensitivity. Antibody conjugation and cell incubation experiments show that single-core particles enable a higher detected moment per cell, but also demonstrate the need for improved surface treatments to mitigate aggregation and improve specificity.
PMCID: PMC3883308  PMID: 20858918
22.  A Novel High Throughput Immunomagnetic Cell Sorting System for Potential Clinical Scale Depletion of T Cells for Allogeneic Stem Cell Transplantation 
Experimental hematology  2007;35(10):1613-1622.
To develop an immunomagnetic cell separation system for Allogeneic hematopoietic stem cell (HSC) transplantations which can achieve a high level of T-cell depletion (at least 4.0 log10), high level of recovery of hematopoietic stem cells (> 90%), with a high throughput (> 106 cells/s).
Peripheral blood leukocytes (PBLs) from buffy coats were spiked with CD34 expressing cells (KG1a) to mimic a leukaphoresis product containing stimulated HSCs. T-cells were labeled with anti-CD3+ Dynabeads and separated in a Quadrupole Magnetic Cell Sorter, QMS. The performance of the system with respect to T-cell depletion and recovery of non T-cells and spiked KG1a was determined using four-color, flow cytometry analysis, with the aid of Trucount® cell concentration calibration beads. Limiting dilution assays were also performed to quantify the log10 depletion of clonable T cells.
While the general performance of the QMS system is governed by proven theoretical principles, significant system variability exist, not all of which can be explained by our current understanding. Consequently, a factorial design was employed guided by JMP software to optimize the labeling conditions and operation of the QMS focused on maximizing the depletion of T cell, and recovery of unlabeled cells including KG1a cells. From these studies, an optimized, no wash, immunomagnetic labeling protocol and optimized QMS operating conditions were developed. For an average initial cell concentration of 1.7 × 108 total cells, an average 3.96 ± 0.33 log10 depletion (range of 3.53 to 4.34) of CD3+CD45+ cells with a mean 99.43 ± 4.23% recovery of CD34+CD45+ cells (range of 94.38% to 104.90%) was achieved at a sorting speed of 106 cells/s (n=6). Limiting dilution assays (LDA) on the T-cell depleted fractions, which gave a log10 depletion of 3.51 for the clonable T cells.
We suggest that this system will provide superior performance with respect to T-cell depletion and CD34+ recovery for clinical allogeneic bone marrow transplants. Ongoing studies, on a clinical scale are being conducted to demonstrate this claim.
PMCID: PMC2094009  PMID: 17697744
23.  Dual-imaging model of SQUID biosusceptometry for locating tumors targeted using magnetic nanoparticles 
For intraoperative imaging in operating theaters or preoperative imaging in clinics, compact and economic integration rather than large and expensive equipment is required to coregister structural and functional imaging. However, current technologies, such as those integrating optical and gamma cameras or infrared and fluorescence imaging, involve certain drawbacks, including the radioactive biorisks of nuclear medicine indicators and the inconvenience of conducting measurements in dark environments.
To specifically and magnetically label liver tumors, an anti-alpha-fetoprotein (AFP) reagent was synthesized from biosafe iron oxide magnetic nanoparticles (MNPs) coated with anti-AFP antibody and solved in a phosphate buffered saline solution. In addition, a novel dual-imaging model system integrating an optical camera and magnetic scanning superconducting-quantum-interference device (SQUID) biosusceptometry (SSB) was proposed. The simultaneous coregistration of low-field magnetic images of MNP distributions and optical images of anatomical regions enabled the tumor distribution to be determined easily and in real time. To simulate targeted MNPs within animals, fewer reagents than the injected dose were contained in a microtube as a sample for the phantom test. The phantom test was conducted to examine the system characteristics and the analysis method of dual images. Furthermore, the animal tests were classified into two types, with liver tumors implanted either on the backs or livers of rats. The tumors on the backs were to visually confirm the imaging results of the phantom test, and the tumors on the livers were to simulate real cases in hepatocellular carcinoma people.
A phantom test was conducted using the proposed analysis method; favorable contour agreement was shown between the MNP distribution in optical and magnetic images. Consequently, the positioning and discrimination of liver tumors implanted on the backs and livers of rats were verified by conducting in vivo and ex vivo tests. The results of tissue staining verified the feasibility of using this method to determine the distribution of liver tumors.
The results of this study indicate the clinical potential of using anti-AFP-mediated MNPs and the dual-imaging model SSB for discriminating and locating tumors.
PMCID: PMC4329206  PMID: 25889863
Magnetic nanoparticle; Tumor; Dual imaging; Scanning superconducting-quantum-interference device
24.  Preparation and Cytotoxic Evaluation of Magnetite (Fe3O4) Nanoparticles on Breast Cancer Cells and its Combinatory Effects with Doxorubicin used in Hyperthermia 
Magnetic nanoparticles in a variable magnetic field are able to produce heat. This heat (42-45°C) has more selective effect on fast dividing cancer cells than normal tissues.
In this work magnetite nanoparticles have been prepared via co-precipitation and phase identification was performed by powder x-ray diffraction (XRD). Magnetic parameters of the prepared nanoparticles were measured by a Vibrating Sample Magnetometer (VSM). A sensitive thermometer has been used to measure the increase of temperature in the presence of an alternating magnetic field. To evaluate the cytotoxicity of nanoparticles, the suspended magnetite nanoparticles in liquid paraffin, doxorubicin and a mixture of both were added to the MDA-MB-468 cells in separate 15 ml tubes and left either in the RT or in the magnetic field for 30 min. Cell survival was measured by trypan blue exclusion assay and flow cytometer. Particle size distribution of the nanoparticles was homogeneous with a mean particles size of 10 nm. A 15°C temperature increase was achieved in presence of an AC magnetic field after 15 min irradiation.
Biological results showed that magnetite nanoparticles alone were not cytotoxic at RT, while in the alternative magnetic filed more than 50% of cells were dead. Doxorubicin alone was not cytotoxic during 30 min, but in combination with magnetite more than 80% of the cells were killed.
It could be concluded that doxorubicin and magnetite nanoparticles in an AC magnetic field had combinatory effects against cells.
PMCID: PMC3689562  PMID: 23799178
Doxorubicin; Flow cytometry; Hyperthermia; Magnetite nanoparticles
25.  A biomagnetic system for in vivo cancer imaging 
Physics in medicine and biology  2005;50(6):1273-1293.
An array of highly sensitive biomagnetic sensors of the superconducting quantum interference detector (SQUID) type can identify disease in vivo by detecting and imaging microscopic amounts of nanoparticles. We describe in detail procedures and parameters necessary for implementation of in vivo detection through the use of antibody-labelled magnetic nanoparticles as well as methods of determining magnetic nanoparticle properties. We discuss the weak field magnetic sensor SQUID system, the method of generating the magnetic polarization pulse to align the magnetic moments of the nanoparticles, and the measurement techniques to measure their magnetic remanence fields following this pulsed field. We compare these results to theoretical calculations and predict optimal properties of nanoparticles for in vivo detection.
PMCID: PMC2041897  PMID: 15798322

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