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1 May 2010

Volume 107, Issue 9, Articles (09xxxx)

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back to top Biomagnetism, Biosensing, and Biological Applications

Magnetic nanostructures for the manipulation of individual nanoscale particles in liquid environments (invited)

P. Vavassori, M. Gobbi, M. Donolato, M. Cantoni, R. Bertacco, V. Metlushko, and B. Ilic

J. Appl. Phys. 107, 09B301 (2010); http://dx.doi.org/10.1063/1.3352579 (5 pages) | Cited 4 times

Online Publication Date: 19 April 2010

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The manipulation of geometrically constrained magnetic domain walls (DWs) in nanoscale magnetic strips attracted much interest recently, with proposals for prospective memory and logic devices. Here we demonstrate that the high controllability of the motion of geometrically constrained DWs allows for the manipulation of individual nanoparticles in solution on a chip with the active control of position at the nanometer scale. Our approach exploits the fact that magnetic nanoparticles in suspension can be captured by a DW, whose position can be manipulated with nanometer scale accuracy in specifically designed magnetic nanowire structures. We hereby show that the precise control over DW nucleation, displacement, and annihilation processes in such nanostructures allows for the capture, transport, and release of magnetic nanoparticles. As magnetic nanoparticles with functionalized surfaces are widely used as molecule carriers or labels for single molecule studies, cell manipulation, and biomagnetic sensing, the accurate control over the handling of the single magnetic nanoparticle in suspension is a crucial building block for several applications in biotechnology, nanochemistry, and nanomedicine.
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75.75.Fk Domain structures in nanoparticles
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ch Domain walls and domain structure
75.70.Kw Domain structure (including magnetic bubbles and vortices)

Magnetic link design for a robotic laparoscopic camera

Massimiliano Simi, Gastone Ciuti, Selene Tognarelli, Pietro Valdastri, Arianna Menciassi, and Paolo Dario

J. Appl. Phys. 107, 09B302 (2010); http://dx.doi.org/10.1063/1.3352581 (3 pages) | Cited 1 time

Online Publication Date: 19 April 2010

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The use of magnetic fields to control and steer assistive and operative devices is increasing in minimally invasive surgical applications. The design of the magnetic link between an external permanent magnet, maneuvered by an industrial robot, and a robotic laparoscopic camera was investigated in this paper, with the objective to obtain accurate positioning and steering in visualization.
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87.63.L- Visual imaging

Localized surface plasmon resonance enhanced magneto-optical activity in core-shell Fe–Ag nanoparticles

L. Wang, K. Yang, C. Clavero, A. J. Nelson, K. J. Carroll, E. E. Carpenter, and R. A. Lukaszew

J. Appl. Phys. 107, 09B303 (2010); http://dx.doi.org/10.1063/1.3355905 (3 pages) | Cited 4 times

Online Publication Date: 20 April 2010

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Metallic nanoparticles (NPs) are suitable platforms for miniaturized biosensing based on their optical and magneto-optical properties. It is possible to enhance the sensitivity of specific kinds of NPs by exploiting their optical and magneto-optical properties under suitable external magnetic field modulation. Here, the magneto-optical properties of Fe–Ag core-shell ferromagnet-noble metal NPs have been investigated as a function of the incident light frequency. For Fe–Ag NPs with a concentration ratio around 25:75, an optical absorption band centered at 3 eV due to localized surface plasmon resonance (LSPR) excitation is observed. A strong enhancement of the Faraday rotation is also observed, greatly exceeding the value estimated for pure Fe NPs, also associated with the LSPR excitation. Our findings open up the possibility of highly sensitive miniaturized magneto-optically modulated biosensing.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
75.75.-c Magnetic properties of nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Bb Fe and its alloys
87.85.Rs Nanotechnologies-applications
78.40.Kc Metals, semimetals, and alloys
78.68.+m Optical properties of surfaces

High magnetization aqueous ferrofluid: A simple one-pot synthesis

Kyler J. Carroll, Michael D. Shultz, Panos P. Fatouros, and Everett E. Carpenter

J. Appl. Phys. 107, 09B304 (2010); http://dx.doi.org/10.1063/1.3357342 (3 pages) | Cited 4 times

Online Publication Date: 20 April 2010

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A one-step polyol method was utilized to prepare a stable aqueous iron/iron oxide ferrofluid. The dried powders were characterized by x-ray diffraction, electron microscopy, x-ray absorption spectroscopy, and vibrating sample magnetometry for the determination of phase, morphology, and magnetic properties. To show its potential for imaging applications, the ferrofluid was also investigated as a magnetic resonance imaging contrast agent.
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75.50.Mm Magnetic liquids
78.70.Dm X-ray absorption spectra

Efficiency test of filtering methods for the removal of transcranial magnetic stimulation artifacts on human electroencephalography with artificially transcranial magnetic stimulation-corrupted signals

Nicolas A. Zilber, Yoshinori Katayama, Keiji Iramina, and Wintermantel Erich

J. Appl. Phys. 107, 09B305 (2010); http://dx.doi.org/10.1063/1.3357345 (3 pages)

Online Publication Date: 20 April 2010

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A new approach is proposed to test the efficiency of methods, such as the Kalman filter and the independent component analysis (ICA), when applied to remove the artifacts induced by transcranial magnetic stimulation (TMS) from electroencephalography (EEG). By using EEG recordings corrupted by TMS induction, the shape of the artifacts is approximately described with a model based on an equivalent circuit simulation. These modeled artifacts are subsequently added to other EEG signals—this time not influenced by TMS. The resulting signals prove of interest since we also know their form without the pseudo-TMS artifacts. Therefore, they enable us to use a fit test to compare the signals we obtain after removing the artifacts with the original signals. This efficiency test turned out very useful in comparing the methods between them, as well as in determining the parameters of the filtering that give satisfactory results with the automatic ICA.
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87.19.le EEG and MEG

In vitro stimulation with a strongly pulsed electromagnetic field on rat basophilic leukemia cells

J. W. Choi, S. C. Shin, S. Kim, E. R. Chung, J. H. Bang, G. I. Cho, S. D. Choi, Y. S. Park, T. S. Jang, Y. M. Yoo, S. S. Lee, and D. G. Hwang

J. Appl. Phys. 107, 09B306 (2010); http://dx.doi.org/10.1063/1.3357349 (3 pages)

Online Publication Date: 20 April 2010

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In this study, the effects of pulsed electromagnetic field stimulation with a strong magnetic field on rat basophilic leukemia (RBL-2H3) cells were investigated to confirm the efficacy of the magnetic stimulator for biomedical applications. The maximum intensity of the magnetic field generated from the stimulation coil was 0.203 T, and the transition time was 126 μs. The oscillation time and frequency of the pulsed field were almost 0.1 ms and 8 kHz, respectively. The cell count as well as the mRNA expression and DNA sequence of the cytokine genes, such as the tumor necrosis factor-α (TNF-α) and interleukin-4 (IL-4), of the stimulated RBL-2H3 cells were analyzed with a hemocytometer and via reverse transcriptase polymerase chain reaction to determine the physiological response under a strong pulse field. After 12 h stimulation, cell death was observed at an increasing scale with the increase in the stimulation time. On the other hand, the cells that were stimulated for 10 min almost doubled as the interval time between the stimulations was extended.
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87.50.cf Biophysical mechanisms of interaction
87.17.-d Cell processes

Embedding of magnetic nanoparticles in polycaprolactone nanofiber scaffolds to facilitate bone healing and regeneration

Jacob T. Kannarkat, Jugdersuren Battogtokh, John Philip, Otto C. Wilson, and Patrick M. Mehl

J. Appl. Phys. 107, 09B307 (2010); http://dx.doi.org/10.1063/1.3357340 (3 pages) | Cited 3 times

Online Publication Date: 21 April 2010

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Scaffolds used for tissue engineering are made to mimic natural surroundings of tissues, the extracellular matrix (ECM). The ECM plays a large part in maintaining the structural integrity of the connective tissue. When producing a tissue in the laboratory, structural integrity of the cells is ensured only when a biomimetic ECM is present. Nanofibrous polymer fibers have been chosen for their resemblance to natural fibers of the ECM and their capability to provide the support necessary for cells to grow and differentiate into tissue. Polycaprolactone based nanofibrous scaffolds for tissue engineering have been fabricated through the electrospinning process. Electrospinning is a simple and cost-effective method for producing nanofibers which involves applying a high voltage to a falling polymer solution to form a fluid jet producing nanofibers. Magnetic nanoparticles (MNPs) have been incorporated within the nanofibers by addition of MNPs to the polymer solution to increase the rate of bone cell growth, proliferation, and differentiation. Studies by Nomura and Takano-Yamamoto, [Matrix Biol. 19, 91 (2000) ] demonstrated an increase in the expression levels of multiple genes in bone tissue including growth factors when shear stress was applied at the cellular level. MNPs are around 1–100 nm and exhibit superparamagnetism. These properties of MNPs allow for high noninvasive control over them using an external magnetic field. While under an ac (15 Hz, 1–6 Gauss) or pulsed magnetic fields, MNPs will induce low level mechanical stresses within the scaffold causing shear stresses at the cellular level of the preosteoblast MC3T3-E1 cells to stimulate their growth, proliferation, and differentiation.
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87.85.Lf Tissue engineering
87.85.Rs Nanotechnologies-applications
87.17.Ee Growth and division
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Whole-heart magnetic resonance coronary angiography with multiple breath-holds and automatic breathing-level tracking

Shigehide Kuhara, Ayako Ninomiya, Tomohisa Okada, Shotaro Kanao, Toshikazu Kamae, and Kaori Togashi

J. Appl. Phys. 107, 09B308 (2010); http://dx.doi.org/10.1063/1.3357347 (2 pages) | Cited 1 time

Online Publication Date: 21 April 2010

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Whole-heart (WH) magnetic resonance coronary angiography (MRCA) studies are usually performed during free breathing while monitoring the position of the diaphragm with real-time motion correction. However, this results in a long scan time and the patient’s breathing pattern may change, causing the study to be aborted. Alternatively, WH MRCA can be performed with multiple breath-holds (mBH). However, one problem in the mBH method is that patients cannot hold their breath at the same position every time, leading to image degradation. We have developed a new WH MRCA imaging method that employs both the mBH method and automatic breathing-level tracking to permit automatic tracking of the changes in breathing or breath-hold levels. Evaluation of its effects on WH MRCA image quality showed that this method can provide high-quality images within a shorter scan time. This proposed method is expected to be very useful in clinical WH MRCA studies.
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87.61.Np Flow imaging
87.57.N- Image analysis
87.57.C- Image quality
87.19.uj Peripheral vascular dynamics

Formulation of iron oxides by nanoparticles of poly-lactide- co-D-α-tocopherol-polyethylene glycol 1000 succinate biodegradable polymer for magnetic resonance imaging

Chandrasekharan Prashant, Maity Dipak, Yang Chang-Tong, Chuang Kai-Hsiang, Ding Jun, and Feng Si-Shen

J. Appl. Phys. 107, 09B309 (2010); http://dx.doi.org/10.1063/1.3357341 (3 pages)

Online Publication Date: 22 April 2010

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Iron oxide nanocrystals of superparamagnetic nature provide diverse applications, which are extended for assessing and treating diseases in humans. Such nanocrystals are usually coated with a hydrophilic layer which enhances the property of the particles in vivo. In the current study, we have used a novel amphiphilic copolymer, poly-lactide-co-D-α-tocopherol-polyethylene glycol 1000 succinate to encapsulate Iron oxide nanocrystals to form polymer nanospheres with high encapsulation efficiency; the magnetic study of the nanoparticles showed that the iron oxide nanocrystals retained their magnetic property with a slight loss in the magnetic saturation. The relaxivity study performed using magnetic resonance imaging (MRI) showed that such nanoparticles formulation of iron oxides are useful for T2 weighted imaging, which is thus of great potential for MRI with better imaging effects and less clinical side effects. The particles were tested for the contrast enhancement in an in vivo model.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Bc Nanocrystalline materials

Polyol-based synthesis of hydrophilic magnetite nanoparticles

Dipak Maity, Prashant Chandrasekharan, Feng Si-Shen, Jun-Min Xue, and Jun Ding

J. Appl. Phys. 107, 09B310 (2010); http://dx.doi.org/10.1063/1.3355898 (3 pages) | Cited 5 times

Online Publication Date: 27 April 2010

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In this paper, we report direct synthesis of hydrophilic magnetite (Fe3O4) nanoparticles by thermolysis of iron (III) acetylacetonate in four different liquid polyols, e.g., di(ethylene glycol) (DEG), tri(ethylene glycol) (TEG), tetra(ethylene glycol) (TTEG), and poly(ethylene glycol) (PEG) and characterization of the properties relevant to their surface structure and colloidal stability in an aqueous medium. Fe3O4 nanoparticles prepared in the medium DEG or TEG can be well suspended in aqueous solution, while Fe3O4 nanoparticles prepared in TTEG or PEG agglomerate when these nanoparticles are prepared at their refluxing temperature. However, the aqueous stability of the PEG coated particles prepared at 220 °C are good due to the increase in amount of surface-adsorbed polyol coating (27 wt %) and associated positive charges (+30 mV).
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81.16.Be Chemical synthesis methods
81.07.Bc Nanocrystalline materials
68.35.bt Other materials
82.70.Kj Emulsions and suspensions
82.70.Dd Colloids

Platinum attachments on iron oxide nanoparticle surfaces

Soubantika Palchoudhury, Yaolin Xu, Wei An, C. Heath Turner, and Yuping Bao

J. Appl. Phys. 107, 09B311 (2010); http://dx.doi.org/10.1063/1.3355899 (3 pages) | Cited 4 times

Online Publication Date: 30 April 2010

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Platinum nanoparticles supported on metal oxide surfaces have shown great potential as heterogeneous catalysts to accelerate electrochemical processes, such as the oxygen reduction reaction in fuel cells. Recently, the use of magnetic supports has become a promising research topic for easy separation and recovery of catalysts using magnets, such as Pt nanoparticles supported on iron oxide nanoparticles. The attachment of Pt on iron oxide nanoparticles is limited by the wetting ability of the Pt (metal) on ceramic surfaces. A study of Pt nanoparticle attachment on iron oxide nanoparticle surfaces in an organic solvent is reported, which addresses the factors that promote or inhibit such attachment. It was discovered that the Pt attachment strongly depends on the capping molecules of the iron oxide seeds and the reaction temperature. For example, the attachment of Pt nanoparticles on oleic acid coated iron oxide nanoparticles was very challenging, because of the strong binding between the carboxylic groups and iron oxide surfaces. In contrast, when nanoparticles are coated with oleic acid/tri-n-octylphosphine oxide or oleic acid/oleylamine, a significant increase in Pt attachment was observed. Electronic structure calculations were then applied to estimate the binding energies between the capping molecules and iron ions, and the modeling results strongly support the experimental observations.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.07.Bc Nanocrystalline materials
68.08.Bc Wetting

Optimization of magnetic anisotropy and applied fields for hyperthermia applications

Hweerin Sohn and R. H. Victora

J. Appl. Phys. 107, 09B312 (2010); http://dx.doi.org/10.1063/1.3355903 (3 pages) | Cited 2 times

Online Publication Date: 3 May 2010

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Magnetic anisotropy and applied fields for hyperthermia applications have been optimized for iron cobalt nanocrystalline particles using numerical micromagnetics. The optimized anisotropy energy is 7.6 kBT at 500 KHz and the hysteresis loss at this optimized energy is approximately 120×106 ergs/(s∗g) for a very small oscillating field of magnitude 10 Oe. We have also investigated the effects of varying the applied field and find that the addition of a 20 Oe static field applied perpendicular to the oscillating field approximately doubles the energy loss without subjecting the patient to additional radiation. This is an important benefit for magnetic hyperthermia.
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87.19.Pp Biothermics and thermal processes in biology
75.30.Gw Magnetic anisotropy
75.60.-d Domain effects, magnetization curves, and hysteresis

Compact electromagnetically operated microfluidic system for detection of sub-200-nm magnetic labels for biosensing without external pumps

Y. Morimoto, T. Takamura, and A. Sandhu

J. Appl. Phys. 107, 09B313 (2010); http://dx.doi.org/10.1063/1.3352584 (3 pages) | Cited 1 time

Online Publication Date: 4 May 2010

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The combination of small sample analyte volumes, high sensitivity, ease of use, high speed, and portability is an important factor for the development of protocols for point of care biodiagnosis. Currently, handling small amounts of liquids is achieved using microfluidic systems but it is challenging to satisfy the remaining factors using conventional approaches based on biosensors employing detection of fluorescent labels. Thus to resolve the other requirements, biosensing systems based on the detection of functionalized superparamagnetic beads acting as “magnetic labels” are being studied as an alternative approach. Notably, for greater quantification, there are increasing demands for the use of sub-200-nm magnetic labels, which are comparable in size to actual biomolecules. However, detection of small numbers of sub-200-nm diameter magnetic beads by magnetoresistive device-based platforms is extremely challenging due to the intrinsic noise of the electronic devices. In order to overcome the limitation, we have developed a simple procedure for detecting sub-200-nm diameter magnetic labels for biosensing via magnetically induced self-assembly of superparamagnetic beads. Applying our approach to conventional microfluidic systems satisfies the most of prerequisites; however conventional microfluidic systems attached to the external pumps are yet suitable for point of care biodiagnosis. Here we propose the development of an alternative biosensing system based on our previous work that does not require external pumps to achieve miniaturization.
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87.85.Rs Nanotechnologies-applications
87.85.Ox Biomedical instrumentation and transducers, including micro-electro-mechanical systems (MEMS)
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
75.50.Tt Fine-particle systems; nanocrystalline materials

Effects of static magnetic fields on light scattering in red chromatophore of goldfish scale

M. Iwasaka

J. Appl. Phys. 107, 09B314 (2010); http://dx.doi.org/10.1063/1.3357348 (3 pages) | Cited 2 times

Online Publication Date: 4 May 2010

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Light scattering in a guanine crystal plate of goldfish scales was observed with and without static magnetic field exposure. Under a microscopic image with dark-field-illumination, the structural color of the scale by guanine plates was observed, and isolated chromatophores showed a twinkling which was the intermittent light scattering of the light from the side. The light scattering was quenched by static magnetic fields of more than 0.26 tesla (T). The quenching was reversibly occurred when the applied external magnetic fields were changed between ambient fields and 5 T. The quenched light scattering did not improve when the magnetic field was decreased from 5 to 0.3 T. It recovered to the original twinkling state about one minute after reaching an ambient geomagnetic field level. The mechanism of the quenched light scattering was speculated to be concerned with the possible magnetic orientation of guanine crystal plates, which were sustained by protein fibers in the red chromatophore. The diamagnetic complex of guanine crystal plates and protein fibers are the candidates for the nanosized light scattering controller based on the magnetic orientation mechanism.
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87.50.C- Static and low-frequency electric and magnetic fields effects
87.64.Cc Scattering of visible, uv, and infrared radiation
87.14.E- Proteins
36.20.-r Macromolecules and polymer molecules

Beamformer for simultaneous magnetoencephalography and electroencephalography analysis

Seokha Ko and Sung Chan Jun

J. Appl. Phys. 107, 09B315 (2010); http://dx.doi.org/10.1063/1.3360184 (3 pages) | Cited 1 time

Online Publication Date: 5 May 2010

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We proposed the beamformer for simultaneous magnetoencephalography (MEG)/electroencephalography (EEG) analysis which has the synergy effects such as high spatial resolution, low localization bias and robustness for orientation of brain sources. Through Monte Carlo simulation study, it was found that the localization performance of our proposed beamformer was far superior to those of MEG-only and EEG-only. For the given specific sensor geometry (160 MEG, 50 EEG sensors), we investigated comparative localization performance of our proposed beamformer over various weighting factors of MEG data, while weighting factor of EEG keeps fixed. Furthermore, we demonstrated its capability for simulated two dipole problem and empirical somatosensory median nerve stimulation data.
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87.19.le EEG and MEG
87.85.D- Applied neuroscience
87.19.lt Sensory systems: visual, auditory, tactile, taste, and olfaction

Dosimetry of typical transcranial magnetic stimulation devices

Mai Lu and Shoogo Ueno

J. Appl. Phys. 107, 09B316 (2010); http://dx.doi.org/10.1063/1.3357343 (3 pages) | Cited 1 time

Online Publication Date: 6 May 2010

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The therapeutic staff using transcranial magnetic stimulation (TMS) devices could be exposed to magnetic pulses. In this paper, dependence of induced currents in real human man model on different coil shapes, distance between the coil and man model as well as the rotation of the coil in space have been investigated by employing impedance method. It was found that the figure-of-eight coil has less leakage magnetic field and low current density induced in the body compared with the round coil. The TMS power supply cables play an important role in the induced current density in human body. The induced current density in TMS operator decreased as the coil rotates from parallel position to perpendicular position. Our present study shows that TMS operator should stand at least 110 cm apart from the coil.
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87.50.cm Dosimetry/exposure assessment
87.85.jc Electrical, thermal, and mechanical properties of biological matter

Visualization of the sensitivity of the magnetoencephalographic sensor array based on the three-dimensional modeling of cortical surface and volume conductor

Sunao Iwaki and Kouichi Sutani

J. Appl. Phys. 107, 09B317 (2010); http://dx.doi.org/10.1063/1.3367885 (3 pages)

Online Publication Date: 6 May 2010

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Here, we present a system to visualize (i) the distribution of magnetoencephalographic (MEG) signal strength in the subject-specific measurement settings predicted by a realistic MEG signal generation model (forward model) and previously published results that are typically presented in the standardized brain coordinates, and (ii) the distribution of the sensitivity of arbitrary selected group of MEG sensors on the subject-specific cortical surface. The current results suggest that (a) our methods to predict MEG field distribution from a priori information about the possible “active” cortical regions obtained from standardized functional magnetic resonance imaging results are useful for determining the sensor sets of interest in the MEG studies for a specific subject under specific measurement condition, and that (b) visualization of the sensitivity of sensor groups could provide the approximate distribution of the MEG sources without solving the MEG inverse problem.
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87.85.D- Applied neuroscience
87.85.Ng Biological signal processing
87.19.le EEG and MEG

Multifunctional doxorubicin/superparamagnetic iron oxide-encapsulated Pluronic F127 micelles used for chemotherapy/magnetic resonance imaging

Jian-Ren Lai, Yong-Wei Chang, Hung-Chi Yen, Nai-Yi Yuan, Ming-Yuan Liao, Chia-Yen Hsu, Jai-Lin Tsai, and Ping-Shan Lai

J. Appl. Phys. 107, 09B318 (2010); http://dx.doi.org/10.1063/1.3357344 (3 pages) | Cited 3 times

Online Publication Date: 10 May 2010

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Polymeric micelles are frequently used to transport and deliver drugs throughout the body because they protect against degradation. Research on functional polymeric micelles for biomedical applications has generally shown that micelles have beneficial properties, such as specific functionality, enhanced specific tumor targeting, and stabilized nanostructures. The particular aim of this study was to synthesize and characterize multifunctional polymeric micelles for use in controlled drug delivery systems and biomedical imaging. In this study, a theranostic agent, doxorubicin/superparamagnetic iron oxide (SPIO)-encapsulated Pluronic F127 (F127) micelles, was developed for dual chemotherapy/magnetic resonance imaging (MRI) purposes, and the structure and composition of the micellar SPIO were characterized by transmission electron microscopy and magnetic measurements. Our results revealed that the micellar SPIO with a diameter of around 100 nm led to a significant advantage in terms of T2 relaxation as compared with a commercial SPIO contrast agent (Resovist®) without cell toxicity. After doxorubicin encapsulation, a dose-dependent darkening of MR images was observed and HeLa cells were killed by this theranostic micelle. These findings demonstrate that F127 micelles containing chemotherapeutic agents and SPIO could be used as a multifunctional nanocarrier for cancer treatment and imaging.
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87.85.J- Biomaterials
87.85.Rs Nanotechnologies-applications
87.61.-c Magnetic resonance imaging
82.70.Dd Colloids
75.50.Tt Fine-particle systems; nanocrystalline materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Enabling suspension-based biochemical assays with digital magnetic microtags

T. Mitrelias, J. F. K. Cooper, K. N. Vyas, J. J. Palfreyman, B. Hong, T. J. Hayward, and C. H. W. Barnes

J. Appl. Phys. 107, 09B319 (2010); http://dx.doi.org/10.1063/1.3352580 (3 pages)

Online Publication Date: 11 May 2010

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Microarrays and suspension-based technologies have attracted significant interest over the past decade with applications in medical diagnostics and biochemical multiplexed assays. However, the throughput of microarrays will always be limited by the array density and the slow kinetics, while the suspension (or bead)-based technologies are currently limited by the number of distinct codes the beads can carry. A novel digital magnetic tagging technology based on magnetic tags that can be used as encoded microcarriers for biomolecular probes, is presented here. The highly disruptive platform technology can provide a very large number of unique codes, enabling a high degree of multiplexing. The design principles of a novel magnetic laboratory-on-a-chip device comprising microfluidic channels with embedded magnetic tunneling magnetoresistive sensors are also discussed.
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87.80.Ek Mechanical and micromechanical techniques
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
82.70.Kj Emulsions and suspensions

Effect of the stimulus frequency and pulse number of repetitive transcranial magnetic stimulation on the inter-reversal time of perceptual reversal on the right superior parietal lobule

Kazuhisa Nojima, Sheng Ge, Yoshinori Katayama, Shoogo Ueno, and Keiji Iramina

J. Appl. Phys. 107, 09B320 (2010); http://dx.doi.org/10.1063/1.3357987 (3 pages) | Cited 1 time

Online Publication Date: 11 May 2010

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The aim of this study is to investigate the effect of the stimulus frequency and pulses number of repetitive transcranial magnetic stimulation (rTMS) on the inter-reversal time (IRT) of perceptual reversal on the right superior parietal lobule (SPL). The spinning wheel illusion was used as the ambiguous figures stimulation in this study. To investigate the rTMS effect over the right SPL during perceptual reversal, 0.25 Hz 60 pulse, 1 Hz 60 pulse, 0.5 Hz 120 pulse, 1 Hz 120 pulse, and 1 Hz 240 pulse biphasic rTMS at 90% of resting motor threshold was applied over the right SPL and the right posterior temporal lobe (PTL), respectively. As a control, a no TMS was also conducted. It was found that rTMS on 0.25 Hz 60 pulse and 1 Hz 60 pulse applied over the right SPL caused shorter IRT. In contrast, it was found that rTMS on 1 Hz 240-pulse applied over the right SPL caused longer IRT. On the other hand, there is no significant difference between IRTs when the rTMS on 0.5 Hz 120 pulse and 1 Hz 120 pulse were applied over the right SPL. Therefore, the applying of rTMS over the right SPL suggests that the IRT of perceptual reversal is effected by the rTMS conditions such as the stimulus frequency and the number of pulses.
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87.50.C- Static and low-frequency electric and magnetic fields effects
87.19.lt Sensory systems: visual, auditory, tactile, taste, and olfaction

Heating characteristics of ferromagnetic iron oxide nanoparticles for magnetic hyperthermia

Eiji Kita, Shinji Hashimoto, Takeru Kayano, Makoto Minagawa, Hideto Yanagihara, Mikio Kishimoto, Keiichi Yamada, Tatsuya Oda, Nobuhiro Ohkohchi, Toshiyuki Takagi, Toshiyuki Kanamori, Yoshio Ikehata, and Isamu Nagano

J. Appl. Phys. 107, 09B321 (2010); http://dx.doi.org/10.1063/1.3355917 (3 pages) | Cited 4 times

Online Publication Date: 12 May 2010

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Heating characteristics of Fe oxide nanoparticles designed for hyperthermia were examined. Samples with coercive forces from 50 to 280 Oe(codoped magnetite) were produced with a coprecipitation technique following by hydrothermal reaction. The maximum specific loss powers (SLPs) of 420 W/g was obtained at 117 kHz (640 Oe) for a dispersant sample with coercive force of 280 Oe (ATH9D). SLPs measured on dry powder samples at 17 kHz and measured at 117 kHz on dispersant samples were compared. The measured SLP amplitudes are lower for 17 kHz and higher for 117 kHz than those expected from ferromagnetic dc minor loops. For the 117 kHz case, friction of particles in a carrier fluid (similar mechanism to Brown relaxation in superparamagnetic dispersant samples) is considered to contribute to the heating mechanism.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Vv High coercivity materials
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.-c Magnetic properties of nanostructures
75.50.Dd Nonmetallic ferromagnetic materials
87.85.J- Biomaterials

Self-heating property under ac magnetic field and its evaluation by ac/dc hysteresis loops of NiFe2O4 nanoparticles

H. Kobayashi, A. Hirukawa, A. Tomitaka, T. Yamada, M. Jeun, S. Bae, and Y. Takemura

J. Appl. Phys. 107, 09B322 (2010); http://dx.doi.org/10.1063/1.3355936 (3 pages) | Cited 7 times

Online Publication Date: 12 May 2010

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The temperature rise of NiFe2O4 nanoparticles having diameters of 242 and 7.7 nm was measured. The results of the measurement were analyzed by comparing the areas of the hysteresis loops in order to clarify the mechanism of heat dissipation in the samples. The hysteresis loops were obtained by applying both ac and dc magnetic fields. It was found that the contribution of magnetic relaxation losses to the heat dissipation was negligible in the case of NiFe2O4 nanoparticle of diameter 242 nm. The contribution of the Néel relaxation to the heat dissipation in the case of NiFe2O4 nanoparticle of diameter 7.7 nm was observed as the difference between the areas of ac and dc hysteresis loops. From the dependences of temperature rise and hysteresis loops of the nanoparticles on the intensity and frequency of an applied magnetic field, the relaxation time for NiFe2O4 nanoparticle of diameter 7.7 nm was obtained as approximately 0.5–0.7 μs.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.-s Critical-point effects, specific heats, short-range order
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
75.75.-c Magnetic properties of nanostructures
75.50.Kj Amorphous and quasicrystalline magnetic materials

Reduction of artifact of metallic implant in magnetic resonance imaging by combining paramagnetic and diamagnetic materials

Yanhui Gao, Kazuhiro Muramatsu, Atsumichi Kushibe, Keita Yamazaki, Akihiko Chiba, and Toru Yamamoto

J. Appl. Phys. 107, 09B323 (2010); http://dx.doi.org/10.1063/1.3352582 (3 pages) | Cited 1 time

Online Publication Date: 14 May 2010

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The method of coating the metallic implant made of paramagnetic materials with diamagnetic materials has been proposed to reduce the magnetic disturbance of metallic implants which causes artifact in magnetic resonance imaging. The optimal thicknesses of the diamagnetic coatings have been obtained for a straight cylindrical hip joint and an aneurysm clip by using the magnetic field analysis of the finite element method (FEM). Whereas in the manufacturing, with respect to the mechanical force of the diamagnetic material, etc., the new structure of dual-material model with diamagnetic material inside and paramagnetic material outside is considered better. In this paper, first the effectiveness of the structure of the dual-material model with actual diamagnetic material inside and paramagnetic material outside is investigated by using the FEM. Then optimal thicknesses of paramagnetic coating of two models are obtained. Finally the effectiveness of the dual-material model is verified by the experiment.
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87.85.J- Biomaterials
87.61.-c Magnetic resonance imaging
75.20.Ck Nonmetals
75.20.En Metals and alloys

Exploring magneto-optical properties of biofunctionalized magnetic chains for developing label-free immunoassays

Sang Yoon Park, Pil Joo Ko, Hiroshi Handa, and Adarsh Sandhu

J. Appl. Phys. 107, 09B324 (2010); http://dx.doi.org/10.1063/1.3355896 (3 pages) | Cited 3 times

Online Publication Date: 14 May 2010

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We describe a magneto-optical transmittance read-out method for bioassays utilizing rotating chains in a solution composed of biotinylated superparamagnetic magnetic nanobeads. Highly sensitive and fast optical transmission signals from ultradiluted magnetic fluids containing biomolcules were obtained by rotating the magnetic chains, which acted as microstirring devices. Interaction of biomolecules with functionalized magnetic nanobeads yielded longer chains of self-assembled magnetic nanobeads, resulting in an increase in the optical transmittance compared to magnetic chains formed by only magnetic dipolar interactions without biomolecules in the solution.
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87.80.-y Biophysical techniques (research methods)
42.25.Bs Wave propagation, transmission and absorption
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.70.Sq Magnetooptical devices
75.20.-g Diamagnetism, paramagnetism, and superparamagnetism
87.85.Rs Nanotechnologies-applications
75.30.Cr Saturation moments and magnetic susceptibilities

Silane-based functionalization of synthetic antiferromagnetic nanoparticles for biomedical applications

Mingliang Zhang, Wei Hu, Christopher M. Earhart, Mary Tang, Robert J. Wilson, and Shan X. Wang

J. Appl. Phys. 107, 09B325 (2010); http://dx.doi.org/10.1063/1.3355906 (3 pages)

Online Publication Date: 14 May 2010

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Synthetic antiferromagnetic nanoparticles (SAFNPs) have been successfully coated with two different kinds of silanes, 3-aminopropyltrimethoxysilane and 2-[methoxy(polyethyleneoxy)propyl]trimethoxysilane. The morphology of SAF particles is characterized by scanning electron microscopy and magnetic properties by alternating gradient magnetometry. The attachment of silane molecules is verified by Fourier-transform infrared spectroscopy and colloidal stability is studied using dynamic light scattering. These two silanes change the surface chemical properties of SAFNPs dramatically in different ways, which in turn affects the stability of these particles.
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87.85.J- Biomaterials
77.80.-e Ferroelectricity and antiferroelectricity
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
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