A simple and accurate method for quantification of magnetosomes in magnetotactic bacteria by common spectrophotometer

A simple apparatus for measuring the magnetism of magnetotactic bacteria was developed with a common laboratory spectrophotometer, which was based on measuring the change in light scattering resulting from cell alignment in a magnetic field. A multiple coils were built around the cuvette holder of the spectrophotometer to compensate geomagnetic field and to generate two mutually perpendicular magnetic fields. In addition, we defined a novel magnetism parameter, R(mag), by modifying the definition of C(mag) to a normalized parameter with the culture absorbance obtained without application of magnetic field. The number of magnetosomes in each cell was determined by transmission electron microscopy to assess the relationship between the two magnetism parameters and the distribution of magnetosomes in the cells. We found that both R(mag) and C(mag) were linearly correlated rather with the percentage of magnetosome-containing bacteria than with the average magnetosome numbers, and R(mag) exhibited a better linearity than C(mag) with respect to the percentage of magnetosome-containing bacteria.     

Magnetophoresis and magnetic susceptibility of HeLa tumor cells

A method for measuring the magnetic susceptibility of separate cells has been theoretically developed and implemented in experiments. It is based on fitting the videocomputer and predicted data for the integral motion curve of cells that settle in a fluid along a thin ferromagnetic bar by the action of a uniform magnetic field. The magnetic susceptibility of HeLa tumor cells and culture medium 199 has been measured.     

An integrated microfluidic platform for magnetic microbeads separation and confinement

An innovative microfluidic platform for magnetic beads manipulation is introduced, consisting of novel microfabricated 3D magnetic devices positioned in a microfluidic chamber. Each magnetic device comprises of an embedded actuation micro-coil in various design versions, a ferromagnetic pillar, a magnetic backside plate and a sensing micro-coil. The various designs of the micro-coils enable efficient magnetic beads trapping and concentration in different patterns. The finite element analysis (FEA) results show a significant increase of the developed force on suspended magnetic beads when the magnetic pillar and backside plate were integrated into the device structure. These simulation results were confirmed experimentally by measuring the magnetic beads trapping ratios for the different designs and structures of the devices under continuous flow conditions. The trapping ratios and profiles were studied using beads counting, measuring the change of inductance with the sensing micro-coil and by image processing. The devices have efficiently demonstrated a controlled and localized magnetic beads trapping and concentration at small spatial locations for the first time. The new results shown in this study demonstrate the feasibility of efficiently using these original devices as key elements in complex bio-analysis systems.     

Feasibility of using a magnetic tracking device for measuring carpal kinematics

While several different methods have been used to measure carpal kinematics, biplanar radiography is generally considered to be the most accurate and popular one. However, biplanar radiography is tedious and so only pseudo-dynamic kinematics can be measured. Recently, magnetic tracking system has been developed for the measurement of joint kinematics which is versatile and easy to use and so the possibility of measuring motions dynamically. In this study, the capability of a magnetic tracking device to accurately measure carpal kinematics was investigated by comparing it with biplanar radiography. The kinematics of the third metacarpal, scaphoid, and lunate in five fresh cadaveric specimens were measured using both methods as the wrists were placed in eight positions. The finite screw rotation of each bone with respect to the distal radius during selecting the seven wrist motions was calculated for both measuring techniques and compared. In general, the kinematics for all three bones measured by using either magnetic tracking device or biplanar radiography was identical and showed no statistical difference. The averaged differences ranged from 0.0 to 2.0°. These differences were due to the potential effect of the weight of the sensors and the interference of the attaching rod to the surrounding tissue. It is concluded that the application of the magnetic tracking device to carpal kinematics is warranted, if proper technical procedures as suggested are followed.     

Adsorption of bovin serum albumin (BSA) onto the magnetic chitosan nanoparticles prepared by a microemulsion system

The adsorption characteristics of BSA onto the magnetic chitosan nanoparticles have been investigated in this paper. The magnetic chitosan nanoparticles were prepared by adding the basic precipitant of NaOH solution into a W/O microemulsion system. The morphology of magnetic chitosan nanoparticles was observed by transmission electron microscope (TEM). It was found that the diameter of magnetic chitosan nanoparticles was from 10nm to 20 nm, and the nanoparticles suspending in the aqueous solution could easily aggregate by a magnet, which suggested that the nanoparticles had good magnetic characteristics. The BSA adsorption experiment indicated that when pH of BSA solution was equal to 4, the maximum adsorption loading reached 110 mg/g. Through measuring the zeta potential of BSA solution and the magnetic nanoparticles, it was found that under this situation the surface of BSA took the negative charge, but the magnetic nanoparticles took the positive charge. Due to the small diameter, the adsorption equilibrium of BSA onto the nanoparticles reached very quickly within 10 min. The adsorption equilibrium of BSA onto the magnetic chitosan nanoparticles fitted well with the Freundlich model. The experimental results showed that the magnetic chitosan nanoparticles have potential to be used for the quick pretreatment in the protein analysis process.     

Magnetophoresis and the magnetic susceptibility of HeLa tumor cells

A method for measuring the magnetic susceptibility of a single cell is developed and theoretically justified. The method is based on use of a computer-aided video recording of the integral curve of magnetophoretic motion of a cell settling in liquid medium near a thin vertical magnetic rod under the influence of a uniform magnetic field. The magnetic susceptibility of HeLa tumor cells and nutrient medium 199 is measured.     

Behavior of supercoiled DNA.

We study DNA supercoiling in a quantitative fashion by micromanipulating single linear DNA molecules with a magnetic field gradient. By anchoring one end of the DNA to multiple sites on a magnetic bead and the other end to multiple sites on a glass surface, we were able to exert torsional control on the DNA. A rotating magnetic field was used to induce rotation of the magnetic bead, and reversibly over- and underwind the molecule. The magnetic field was also used to increase or decrease the stretching force exerted by the magnetic bead on the DNA. The molecule's degree of supercoiling could therefore be quantitatively controlled and monitored, and tethered-particle motion analysis allowed us to measure the stretching force acting on the DNA. Experimental results indicate that this is a very powerful technique for measuring forces at the picoscale. We studied the effect of stretching forces ranging from 0.01 pN to 100 pN on supercoiled DNA (-0.1 < sigma < 0.2) in a variety of ionic conditions. Other effects, such as stretching-relaxing hysteresis and the braiding of two DNA molecules, are discussed.     

Use of NMR for measurement of total body water and estimation of body fat

A nuclear magnetic resonance (NMR) method is described for quantitatively measuring total body water (TBW) and for estimating the fat content of baboons. The hydrogen associated with water was measured as the amplitude of the free-induction decay voltage following a series of 90 degree radio frequency pulses at the Lamour frequency for hydrogen with a pulse length of 14 microseconds and a peak measuring time of 50 microseconds. TBW was calculated by multiplying the peak amplitude (volts) by the experimentally determined constant for a water standard (g water/V). This NMR method yielded TBW contents similar to those obtained in the same baboons by direct gravimetric procedures. In contrast, the widely used 3H2O-dilution method usually and variably overestimated body water. By providing an accurate measure of body water, this NMR procedure provides a rapid, noninvasive, reasonably accurate way of estimating body fat content.     

Single, brief exposure to a 50 Hz magnetic field does not affect the performance of an object recognition task in adult mice

A number of studies have shown that power frequency magnetic fields may affect spatial memory functions in rodents. An experiment was performed using a spontaneous object recognition task to investigate if nonspatial working memory was similarly affected. Memory changes in adult, male C57BL/6J mice were assessed by measuring the relative time within which the animals explored familiar or novel stimulus objects. Between initial testing and retesting, the animals were exposed for 45 min to a 50 Hz magnetic field at either 7.5 microT, 75 microT or 0.75 mT. Other animals were sham-exposed with ambient fields of less than 50 nT. No significant field-dependent effects on the performance of the task were observed at any flux density (for all measures, P > 0.05). These data provide no evidence to suggest that nonspatial working memory was affected in mice by acute exposure to an intense 50 Hz magnetic field.     

A simple and accurate method for quantification of magnetosomes in magnetotactic bacteria by common spectrophotometer

A simple apparatus for measuring the magnetism of magnetotactic bacteria was developed with a common laboratory spectrophotometer, which was based on measuring the change in light scattering resulting from cell alignment in a magnetic field. A multiple coils were built around the cuvette holder of the spectrophotometer to compensate geomagnetic field and to generate two mutually perpendicular magnetic fields. In addition, we defined a novel magnetism parameter, R_mag, by modifying the definition of C_mag to a normalized parameter with the culture absorbance obtained without application of magnetic field. The number of magnetosomes in each cell was determined by transmission electron microscopy to assess the relationship between the two magnetism parameters and the distribution of magnetosomes in the cells. We found that both R_mag and C_mag were linearly correlated rather with the percentage of magnetosome-containing bacteria than with the average magnetosome numbers, and R_mag exhibited a better linearity than C_mag with respect to the percentage of magnetosome-containing bacteria.     

Advances in magnetic resonance imaging of lung physiology.

This review presents an overview of some recent magnetic resonance imaging (MRI) techniques for measuring aspects of local physiology in the lung. MRI is noninvasive, relatively high resolution, and does not expose subjects to ionizing radiation. Conventional MRI of the lung suffers from low signal intensity caused by the low proton density and the large degree of microscopic field inhomogeneity that degrades the magnetic resonance signal and interferes with image acquisition. However, in recent years, there have been rapid advances in both hardware and software design, allowing these difficulties to be minimized. This review focuses on some newer techniques that measure regional perfusion, ventilation, gas diffusion, ventilation-to-perfusion ratio, partial pressure of oxygen, and lung water. These techniques include contrast-enhanced and arterial spin-labeling techniques for measuring perfusion, hyperpolarized gas techniques for measuring regional ventilation, and apparent diffusion coefficient and multiecho and gradient echo techniques for measuring proton density and lung water. Some of the major advantages and disadvantages of each technique are discussed. In addition, some of the physiological issues associated with making measurements are discussed, along with strategies for understanding large and complex data sets.     

The Effect of Pulsed Magnetic Field on the Molecular Uptake and Medium Conductivity of Leukemia Cell

The cell membrane acts as a barrier that hinders free entrance of most hydrophilic molecules into the cell. Owing to the numerous applications, the introduction of non-permeate molecules into biologic cells has drawn considerable attention in the past years. The aim of our study was to investigate the effect of time-varying magnetic field on transmembrane molecular transport by measuring bleomycin cytotoxicity and conductivity modifying in K562 cells. The cells were exposed to magnetic pulses of 2.2 T strength peak and about 250-μs duration via Magstim stimulator and double 70-mm coil. Three different frequencies of 0.25, 1, and 10 Hz pulses for 56,112, and 28 numbers of pulses, respectively, were applied (nine experimental groups) and uptake and conductivity was measured in each group. Our results show that time-varying magnetic field increase transmembrane molecular transport and media conductivity; this enhancement is greater for 28 pulses with 1 Hz frequency. The observed uptake enhancement due to magnetic exposure is considerable.     

Cell tracking velocimetry as a tool for defining saturation binding of magnetically conjugated antibodies.

BACKGROUND: Continuous flow immunomagnetic separation is an attractive alternative to current batch mode immunomagnetic separation methods because it is capable of high sorting speeds at mild cell conditions, and grants the operator better control of separation process. The control of the separation is dependent on knowledge of the amount of magnetic label attached to the cell (magnetic labeling intensity), however. Determination of the magnetic labeling is accomplished by measuring cell magnetophoretic mobility using a newly developed technique of Cell Tracking Velocimetry (CTV). METHODS: Flow cytometry was used to define the antibody binding characteristics of a fluorescently tagged primary antibody. Subsequently, CTV was used to measure antibody-binding characteristics of a magnetically tagged secondary antibody. RESULTS: The results of this study show that CTV is capable of providing valuable information concerning the cell labeling by magnetically tagged antibodies. It was demonstrated that the magnetically conjugated antibody binding curve exhibits the same exponential increase to saturation characteristics as that seen with the fluorescently tagged antibody. Further, it was shown that the intensity of the secondary magnetic labeling is directly proportional to the intensity of the primary fluorescent label. CONCLUSIONS: CTV is an accurate tool for evaluation of magnetically conjugated antibodies. The ability to determine the intensity of magnetic labeling is necessary for the development of continuous flow immunomagnetic separations based on cell magnetophoresis.     

Magnetic characterization of Daphnia resting eggs

This study characterized the magnetic materials found within Daphnia resting eggs by measuring static magnetization with a superconducting quantum interference device (SQUID) magnetometer, after forming two types of conditions, each of which consists of zero-field cooling (ZFC) and field cooling (FC). Magnetic ions, such as Fe(3+), contained in Daphnia resting eggs existed as (1) paramagnetic and superparamagnetic particles, demonstrated by a magnetization and temperature dependence of the magnetic moments under an applied magnetic field after ZFC and FC, and (2) ferromagnetic particles with definite magnetic moments, the content of which was estimated to be very low, demonstrated by the Moskowitz test. Conventionally, biomagnets have been directly detected by transmission electron microscopes (TEM). As demonstrated in this study, it is possible to nondestructively detect small biomagnets by magnetization measurement, especially after two types of ZFC and FC. This nondestructive method can be applied in detecting biomagnets in complex biological organisms.     

Calcium binding to metallochromic dyes and calmodulin in the presence of combined, AC-DC magnetic fields.

The possibility that weak, ac and dc magnetic fields in combination may affect binding equilibria of calcium-ions (Ca2+) was investigated with two metallochromic dyes as calcium-binding molecules: murexide and arsenazo III. Calcium-dye equilibria were followed by measuring solution absorbances with a fiber-optic spectrophotometer. A Ca(2+)-arsenazo solution was also used indirectly to monitor the binding of Ca2+ to calmodulin. Parallel, ac and dc magnetic fields were applied to each preparation. The ac magnetic field was held constant during each of a series of experiments at a frequency in the range between 50 and 120 Hz (sine wave) or at 50 pps (square wave) and at an rms flux density in the range between 65 and 156 microT. The dc magnetic field was then varied from 0 to 299 microT at 1.3 microT increments. The magnetic fields did not measurably affect equilibria in the binding of metallochromic dyes or calmodulin to Ca2+.     

Determination of the plasma velocity in an imploding wire array from magnetic field measurements by a gradient probe

A method for measuring the gradient of the magnetic field in the plasma of an imploding wire array is described. Results from measurements of the magnitude and gradient of the magnetic field in a tungsten wire array on the Angara-5-1 facility at currents of ∼3 MA are presented. A novel method for calculating the velocity of the current-carrying plasma in the framework of MHD equations from data on the magnitude and gradient of the magnetic field at a certain point inside the array is proposed. It is demonstrated that a gradient magnetic probe can be used to investigate the plasma current sheath in plasma focus facilities.     

Simulation of the propagation effects in the HF-EPR spectra of non-diluted magnetic materials

The high field EPR spectra of non-diluted magnetic material are affected by propagation effects when the wavelength of the exciting radiation is of the same order of magnitude of the optical path within the sample. Beyond the optical path, the shape of the spectra is determined by the dielectric constant and by the magnetization of the material and through these quantities it depends on the temperature. A detailed knowledge of the physical properties of the material is therefore mandatory for a complete study of the phenomenon. In order to demonstrate the propagation effect, the 285 GHz EPR spectra of tetramethyl-ammonium manganese chloride (TMMC) were recorded as a function of temperature and a simulation of the spectra was performed on the basis of a simplified model of the propagation of far infrared radiation around the resonance field. The universality of the effect was illustrated by measuring other magnetic materials such as ferrite.     

Measuring single cardiac myocyte contractile force via moving a magnetic bead

One of the biggest problems of heart failure is the heart's inability to effectively pump blood to meet the body's demands, which may be caused by disease-induced alterations in contraction properties (such as contractile force and Young's modulus). Thus, it is very important to measure contractile properties at single cardiac myocyte level that can lay the foundation for quantitatively understanding the mechanism of heart failure and understanding molecular alterations in diseased heart cells. In this article, we report a novel single cardiac myocyte contractile force measurement technique based on moving a magnetic bead. The measuring system is mainly composed of 1), a high-power inverted microscope with video output and edge detection; and 2), a moving magnetic bead based magnetic force loading module. The main measurement procedures are as follows: 1), record maximal displacement of single cardiac myocyte during contraction; 2), attach a magnetic bead on one end of the myocyte that will move with myocyte during the contraction; 3), repeat step 1 and record contraction processes under different magnitudes of magnetic force loading by adjusting the magnetic field applied on the magnetic bead; and 4), derive the myocyte contractile force base on the maximal displacement of cell contraction and magnetic loading force. The major advantages of this unique approach are: 1), measuring the force without direct connections to the cell specimen (i.e., "remote sensing", a noninvasive/minimally invasive approach); 2), high sensitivity and large dynamic range (force measurement range: from pico Newton to micro Newton); 3), a convenient and cost-effective approach; and 4), more importantly, it can be used to study the contractile properties of heart cells under different levels of external loading forces by adjusting the magnitude of applied magnetic field, which is very important for studying disease induced alterations in contraction properties. Experimental results demonstrated the feasibility of proposed approach.     

A method for quick measurement of protein binding to unilamellar vesicles.

A general method for measuring interaction of liposome-protein (or potentially small molecules) was developed. This method utilizes biotinylated liposomes to incubate with interactants. Streptavidin-coated paramagnetic resins were then added and the liposomes (along with bound materials) can be quickly separated under a magnetic field or by low speed centrifugation. Subsequently, concentration of unbound materials (in the supernatants) can be directly determined. The described method is particularly useful for proteins or compounds that are not very soluble under certain assay conditions.     

MagSNiPer: a new single nucleotide polymorphism typing method based on single base extension, magnetic separation, and chemiluminescence

We have developed a new method for typing single nucleotide polymorphisms (SNPs), MagSNiPer, based on single base extension, magnetic separation, and chemiluminescence. Single base nucleotide extension reaction is performed with a biotinylated primer whose 3' terminus is contiguous to the SNP site with a tag-labeled ddNTP. Then the primers are captured by magnetic-coated beads with streptavidin, and unincorporated labeled ddNTP is removed by magnetic separation. The magnetic beads are incubated with anti-tag antibody conjugated with alkaline phosphatase. After the removal of excess conjugates by magnetic separation, SNP typing is performed by measuring chemiluminescence. The incorporation of labeled ddNTP is monitored by chemiluminescence induced by alkaline phosphatase. MagSNiPer is a simple and robust SNP typing method with a wide dynamic range and high sensitivity. Using MagSNiPer, we could perform SNP typing with as little as 10(-17) mol of template DNA.