Magnetic Field Manipulation Research Articles

An Optical Sensing Strategy Leading to In Situ Monitoring of the Degradation of Mesoporous Magnetic Supraparticles in Cells

Mesoporous magnetic supraparticles (meso-MSPs) as multifunctional targeted drug carriers have attracted much attention, because of their easy magnetic-field manipulation and in situ sensing functionality. In this paper, a Fe(3+)-selective chemodosimeter fluorescent probe (FP-1) was synthesized and loaded inside of the meso-MSPs (meso-MSPs/probe); the meso-MSPs/probe nanocomposites were then used to monitor the degradation of meso-MSPs in cells. In our experiments, strong fluorescence intensity was observed in HeLa cells, because of their acidic intracellular environment, which can quickly degrade the meso-MSPs and then release Fe(3+) ions in cells that, in turn, activate the fluorescence of FP-1. Meanwhile, a very weak fluorescence signal was detected in HEK 293T cells due to the relative neutral intracellular environment of HEK 293T cells, which prevented the Fe(3+) ion from leaching out of meso-MSPs. Moreover, this degradation-luminescence relationship of the meso-MSPs/probe nanocomposites not only assisted us to understand the degradation status of meso-MSPs in cells, but also allowed us to recognize the peculiarity of different cells with various intracellular environments.

Obtaining of new magnetic nanocomposites based on modified polysaccharide

The study presents the preparation of some composite materials with magnetic properties by two different encapsulation methods of magnetite (Fe3O4) in a polymer matrix based on carboxymethyl starch-g-polylactic acid (CMS-g-PLA). The copolymer matrix used to obtain the magnetic nanocomposites was synthesized by grafting reaction of carboxymethyl starch (CMS) with d,l-lactic acid (DLLA), in the presence of Sn octanoate [Sn(Oct)2] as catalyst. Magnetite was obtained by co-precipitation from aqueous salt solutions FeCl2/FeCl3 (molar ratio 1/2). The magnetic composites were prepared by precipitation method in acetone (non-solvent) of the DMSO solutions of magnetite and copolymer, and synthesis in situ of the nanocomposites. In the first case, the particle size measured by DLS-technique was 168nm, and the magnetization was 46.82emu/g, while after in situ synthesis, the composite materials showed smaller size (141nm), but the magnetization was reduced (3.04emu/g). The higher magnetization in the first case is due to the great degree of encapsulation of the magnetite, which was about 43.4wt.%, compared to 4.37wt.% for the in situ synthesis (determined by thermogravimetry). The CMS-g-PLA copolymer, magnetite, and the nanocomposites were characterized by infrared spectroscopy (FTIR), near infrared chemical imagistic (NIR-CI), dynamic light scattering (DLS) technique, X-ray diffraction (WAXD), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM) and thermal analyses. Since the polymer matrix and magnetite are biodegradable and biocompatible, the magnetic nanocomposites can be used for conjugation of some drugs. The polymer matrix CMS-g-PLA acts as a shell, and vehicle for the active component, whereas magnetite is the component which makes targeting possible by external magnetic field manipulation.

Magneto‐Controllable Capture and Release of Cancer Cells by Using a Micropillar Device Decorated with Graphite Oxide‐Coated Magnetic Nanoparticles

Aiming to highly efficient capture and analysis of circulating tumor cells, a micropillar device decorated with graphite oxide-coated magnetic nanoparticles is developed for magneto-controllable capture and release of cancer cells. Graphite oxide-coated, Fe3 O4 magnetic nanoparticles (MNPs) are synthesized by solution mixing and functionalized with a specific antibody, following by the immobilization of such modified MNPs on our designed micropillar device. For the proof-of-concept study, a HCT116 colorectal cancer cell line is employed to exam the capture efficiency. Under magnetic field manipulation, the high density packing of antibody-modified MNPs on the micropillars increases the local concentration of antibody, as well as the topographic interactions between cancer cells and micropillar surfaces. The flow rate and the micropillar geometry are optimized by studying their effects on capture efficiency. Then, a different number of HCT116 cells spiked in two kinds of cell suspension are investigated, yielding capture efficiency >70% in culture medium and >40% in blood sample, respectively. Moreover, the captured HCT116 cells are able to be released from the micropillars with a saturated efficiency of 92.9% upon the removal of applied magnetic field and it is found that 78% of the released cancer cells are viable, making them suitable for subsequent biological analysis.

Aging and neuroplasticity

Neuroplasticity can be defined as a final common pathway of neurobiological processes, including structural, functional or molecular mechanisms, that result in stability or compensation for age- or disease-related changes. The papers in this issue address the aging process, as well as depression, dementia, and stroke and a range of interventions, including manipulations in behavior (physical and cognitive activity/exercise), physiological factors (caloric restriction, cholesterol), pharmacologic treatments (AMPA receptors) and manipulation of brain magnetic fields and electrical activity (transcranial magnetic stimulation, magnetic seizure therapy, and deep brain stimulation).This editorial will address different facets of neuroplasticity, the need for translational research to interpret neuroimaging data thought to reflect neuroplasticity in the human brain, and the next steps for testing interventions in aging and in disease.

Integrated three-dimensional system-on-chip for direct quantitative detection of mitochondrial DNA mutation in affected cells

We report a microfluidic system for automatic mitochondrial mutation diagnostics from sample purification to quantitative analysis. The system achieved direct DNA (mtDNA) mutation quantification in affected cells using a new 3D-microfluidic system, which integrated a mtDNA extraction module and a mutation detection module. Effective direct mtDNA extraction from the cells was realized using magnetic field manipulation. The obtained mtDNAs were subject to a fully automatic processing for quantitative mutation detection using integrated micropumps, micromixer and microtemperature control modules capable of mutation sensing by restriction enzyme digestion and real-time on-chip micro-PCR. Compared with traditional methods, this microfluidic system demonstrates the advantages of faster detection, requirement of fewer amount of specimens and reagents, much compact design and lower cost as well as lower risks for human errors. Thus, such system-on-chip would encourage the future translational development of rapid pathogenic mtDNA defects detection to provide more efficient clinical diagnosis and disease management strategies.

Homogeneous Bioassays Based on the Manipulation of Magnetic Nanoparticles by Rotating and Alternating Magnetic Fields—A Comparison

The rotating magnetic field as a source of magnetic nanoparticle manipulation for the use in homogenous bioassays is presented and compared with the frequently used alternating magnetic field technique. For the investigation of the impact of the rotating and alternating field mode on the biomolecule detection, a fluxgate based measurement system has been used. This system detects the MNPs magnetization stray field and calculates the phase lag between the aligning field and the MNPs magnetization. By analyzing the phase lag, the analysis is not altered by changes in MNP concentration. The measured phase lag spectra show a significant difference between both magnetic field modes and agree well with simulations based on the Fokker-Planck equation. A modeling of binding experiments based on these simulations predicts a higher sensitivity for the rotating magnetic field manipulation.

Magnetic force enhancement in a linear actuator by air-gap magnetic field distribution optimization and design

The focus of this paper is to show that the magnetic force generated by a linear actuator may be enhanced through the optimization and design of the devices air-gap magnetic field distribution. Specifically, the use of a periodic ladder structure is proposed for magnetic field manipulation, and a simplified finite element analysis is adopted in lieu of a higher cost computational model. The optimal magnetic field distribution that maximizes the actuator force is then found via structural topology optimization. This force enhancement is explained using a Maxwell stress tensor analysis and validated through experimental studies. Finally, a periodic-ladder structure is designed for an equivalent optimal magnetic field distribution, and the linear actuator force enhancement is confirmed.

Kilohertz magnetic field focusing in a pair of metallic periodic-ladder structures

Here, we show, analytically and numerically, that in a pair of metallic periodic-ladder structures placed with a central gap, the normally incident magnetic field is focused on a spot of 3 mm (0.6 × 10−5 free space wavelength) full width at half maximum at a 1 mm distance away at 600 kHz. The ladder structures are designed by exploiting the curl of the induced current at each unit cell in the periodic structure. This investigation paves the way for kilohertz magnetic field manipulations.

Quantitative detection of E. coli O157:H7 eaeA gene using quantum dots and magnetic particles

A quantitative gene detection technique targeting the pathogenic E. coli O157:H7 eaeA gene was developed using magnetic bead (MB)-quantum dots (QDs) nanoparticle complexes. MBs allowed for the separation of DNA-conjugated QD nanoparticles via magnetic field manipulation. QDs provided internal fluorescence calibration to account for the intrinsically different numbers of nanoparticles interrogated in each assay. Based on the measurement of normalized fluorescence (Cy3/QD655), the linear quantification ranges of ssDNA and dsDNA targets were determined to be 10 through 103 fM (R2 = 0.992) and 2 × 102 through 6 × 107 gene copies (R2 = 0.972), with detection limits of 9.72 fM and 104 gene copies, respectively. The kinetic results indicate that adjustment of hybridization temperature in accordance to the amount of target DNA was required to maximize the efficiency of DNA hybridization. We were able to discriminate perfectly matched target DNA, 1-, 2-, and 41-base pair mismatched target DNAs in our approach and therefore demonstrated excellent selectivity. Our technique was also used on pure bacterial culture to showcase its ability to analyze environmental samples.

Quantitative gene monitoring of microbial tetracycline resistance using magnetic luminescent nanoparticles

A magnetic/luminescent nanoparticles (MLNPs) based DNA hybridization method was developed for quantitative monitoring of antibiotic resistance genes and gene-expression in environmental samples. Manipulation of magnetic field enabled the separation of the MLNPs-DNA hybrids from the solution and the fluorescence of MLNPs normalized the quantity of target DNA. In our newly developed MLNPs-DNA assay, linear standard curves (R(2) = 0.99) of target gene was determined with the detection limit of 620 gene copies. The potential risk of increased bacterial antibiotic resistance was assessed by quantitative monitoring of tetracycline resistance (i.e., tetQ gene) in wastewater microcosms. The gene abundance and its expression showed a significant increase of tetQ gene copies with the addition of tetracycline, triclosan (TCS), or triclocarban (TCC). A real-time PCR assay was employed to verify the quantification capability of the MLNPs-DNA assay and accordingly both assays have shown strong correlation (R(2) = 0.93). This non-PCR based MLNPs-DNA assay has demonstrated its potential for gene quantification via a rapid, simple, and high throughput platform and its novel use of internal calibration standards.

Gold Nanotubes Synthesized via Magnetic Alignment of Cobalt Nanoparticles as Templates

We report an aqueous solution-phase synthesis of continuous gold nanotubes with controllable shape, size, and length, tens of nm in diameter, a few nm in wall thickness, and up to 5 μm in length. Alignment is induced by magnetic field manipulation and synthetic parameters using cobalt nanoparticles as sacrificial templates. Because of the ease with which magnetic fields may be manipulated, precise placement should be not only possible, but also relatively simple as compared to other methods. This approach represents an important alternative for producing one-dimensional metal nanotube structures.

Computed tomography and magnetic resonance imaging: past, present and future

The aims of this paper are to summarize the current recommendations for the use of computed tomography (CT) and magnetic resonance imaging (MRI) in the chest and to suggest some possible future developments. The main developments of CT in the chest have been the introduction of high-resolution CT (HRCT), spiral CT and, more recently, multidetector spiral CT. HRCT is defined as thin-section CT (1- to 2-mm collimation scans), optimized by using a high-spatial resolution (edge-enhancing) algorithm. Several studies have shown that HRCT closely reflects macroscopic (gross) pathological findings. HRCT currently has the best sensitivity and specificity of any imaging method used for the assessment of focal and diffuse lung diseases. The advent of spiral CT and, more recently, multidetector CT scanners, has allowed for major improvements in the imaging of airways, pulmonary and systemic vessels, and lung nodules. Spiral CT facilitates multiplanar and three-dimensional display of structures and visualization of pulmonary and systemic vessels, with a level of detail that is comparable to that of conventional angiography. With the use of graphics-based software programs, spiral CT enables depiction of the luminal surface of the airways with images that resemble those of bronchoscopy (virtual bronchoscopy) or bronchography (virtual bronchography). Several studies have shown a high sensitivity and specificity for spiral CT in the diagnosis of acute pulmonary embolism. Therefore, spiral CT is rapidly becoming the imaging modality of choice in the diagnosis of pulmonary embolism. Like the radiograph, signal intensity on computed tomography is mainly due to a single parameter: electron density. The signal intensity of the magnetic resonance image depends on four parameters: nuclear density, two relaxation times called T1 and T2, and motion of the nuclei within the imaged lung volume. Abnormal soft tissue can be identified more easily through measurement of these four parameters than through use of computed tomography. Furthermore, because the spatial orientation of the image is determined by manipulation of magnetic fields, scans can be performed in any plane. The main indications for magnetic resonance in the chest have been in the evaluation of the heart, major vessels, mediastinum, and hilar structures because of the natural contrast provided by flowing blood. Of particular interest for the respirologist has been the recent development of magnetic resonance angiography. This technique consists of three-dimensional single breath-hold images obtained using gadolinium-based contrast agents. This is a promising technique for the diagnosis of acute and chronic pulmonary embolism.

Comparative orientation experiments with different species of passerine long-distance migrants: effect of magnetic field manipulation

Abstract. The orientation of four species of passerine long-distance migrants was studied in spring and autumn by orientation cage experiments during the twilight period after sunset in Sweden. Two groups of migrants from the Palaearctic-African migration system were used: migrants wintering mainly north of the magnetic equator in west Africa (pied flycatcher, Ficedula hypoleuca, and redstart, Phoenicurus phoenicurus) and migrants wintering south of the magnetic equator in southeast Africa (thrush nightingale, Luscinia luscinia, and marsh warbler, Acrocephalus palustris). Orientation experiments were conducted in three magnetic conditions, in the local geomagnetic field and in a deflected and in a vertical magnetic field, under clear and simulated total overcast conditions, respectively. The results did not provide any convincing indications about differences in the orientation system between the two groups of migrants. The responses of all species seemed to be affected in a similarly complex way by celestial as well as magnetic cues, involving conflicting elements of a possible attraction towards the brightest part of the twilight sky as well as orientation in the migratory direction. Shifting the horizontal component of the magnetic field neither shifted nor disrupted orientation. Abolishing the horizontal component of the magnetic field increased the orientational scatter in three species in spring and one in autumn. Simulated total overcast largely abolished orientation, except in two species (in the local geomagnetic field only) that do not migrate across the geomagnetic equator.

Overview of MR imaging modalities.

Practical approaches to optimization of the use of gadolinium in MR imaging comprise a range of advances in data-acquisition techniques and pulse sequences that augment tissue contrast and reduce scanning times, increasing throughput and patient comfort. In addition to the effects of magnetic field strengths and manipulation of contrast doses for routine spin-echo (SE) imaging, several approaches are reviewed. These include: fat suppression, which helps to resolve enhancing lesions from tissues with inherently high signal on post-gadolinium T1-weighted imaging; gradient-echo (GRE) and partial radio-frequency (RF) echoplanar techniques, which tend to reduce data acquisition times; MR angiography, which enables elucidation of slow-flow vessels and mass-vessel relationships; and three-dimensional GRE scan displays, which relate lesion location to regional and surface anatomy.