Small Magnetic Beads Research Articles

Radiopaque Foreign Bodies Swallowed by the Children during the COVID-19 Period Compared with the Pre-Pandemic Period

Context: The COVID-19 pandemic restricted people to their homes or limited places and boosted online learning and homeschooling for the kids. Metallic foreign body ingestion by children was seen to have increased during this period. Aim: The aim of this study was to highlight types and outcomes of ingested metallic foreign bodies in children during the COVID-19 pandemic period. Methods: We retrospectively reviewed medical records, abdominal radiographs, and computed tomography of children under 14 years during the 2-year pandemic period (from December 2019 to December 2021) with histories or clinical suspicions of ingested metallic foreign bodies. Age, gender, number (single or multiple), and morphology (size and shape) characteristics (magnetic or nonmagnetic) of ingested foreign bodies were recorded. The number of such cases during the COVID-19 pandemic period was compared with the rate of ingestion in 3 years before the COVID-19 period (from January 2017 to December 2019). Outcomes in terms of spontaneous expulsion (through the usual alimentary tract from the anus without the need for intervention) and intervention (endoscopic or surgical removal) were recorded. The Chi-square test was used to measure association. Results: Out of 161 patients (86 in COVID period, and 75 in pre-COVID period), majority were males (n = 98, 61%) and under 5 years (n = 87, 54%). Most of the foreign bodies were single (n = 146, 90%), <2 cm in sizes (n = 93, 58%), regular in shapes (n = 128, 79.5%), and were spontaneously expelled (n = 134, 83%) during 48–72 h of ingestion. Mostly irregular-shaped, larger-sized, and small magnetic beads required either endoscopic removal (n = 23) or surgery (n = 4). Conclusion: A higher rate of ingested foreign bodies by the children is noted during the COVID-19 pandemic period, with irregular shaped and magnetic bead foreign bodies requiring interventions.

Proximity RNA-seq: A Sequencing Method to Identify Co-localization of RNA.

RNA localization is an important regulatory layer of gene expression and cell functioning. The protocol guides through the Proximity RNA-seq method, in which RNA molecules are sequenced in their spatial, cellular context to derive RNA co-localization and transcriptome organization. Transcripts in individual subcellular particles from chemically crosslinked cells are tagged with the same, unique DNA barcode in water-in-oil emulsion droplets. First, single DNA barcodes are PCR amplified and immobilized on single, small magnetic beads in droplets. Subsequently, 3' ends of bead-bound barcode copies are tailed with random pentadecamers. Then beads are encapsulated again into droplets together with crosslinked subcellular particles containing RNA. Reverse transcription using random pentadecamers as primers is performed in droplets, which optimally contain one bead and one particle, in order to tag RNAs co-localized to the same particle. Sequencing such cDNA molecules identifies the RNA molecule and the barcode. Subsequent analysis of transcripts that share the same barcode, i.e., co-barcoding, reveals RNA co-localization and interactions. The technique is not restricted to pairs of RNAs but can as well detect groups of transcripts and estimates local RNA density or connectivity for individual transcripts. We provide here a detailed protocol to perform and analyze Proximity RNA-seq on cell nuclei to study spatial, nuclear RNA organization.

Magnetophoretic Conductors and Diodes in a 3D Magnetic Field.

We demonstrate magnetophoretic conductor tracks that can transport single magnetized beads and magnetically labeled single cells in a 3-dimensional time-varying magnetic field. The vertical field bias, in addition to the in-plane rotating field, has the advantage of reducing the attraction between particles, which inhibits the formation of particle clusters. However, the inclusion of a vertical field requires the re-design of magnetic track geometries which can transport magnetized objects across the substrate. Following insights from magnetic bubble technology, we found that successful magnetic conductor geometries defined in soft magnetic materials must be composed of alternating sections of positive and negative curvature. In addition to the previously studied magnetic tracks taken from the magnetic bubble literature, a drop-shape pattern was found to be even more adept at transporting small magnetic beads and single cells. Symmetric patterns are shown to achieve bi-directional conduction, whereas asymmetric patterns achieve unidirectional conduction. These designs represent the electrical circuit corollaries of the conductor and diode, respectively. Finally, we demonstrate biological applications in transporting single cells and in the size based separation of magnetic particles.

High-efficiency magnetophoretic separation based on synergy of magnetic force field and flow field in microchannels

Magnetophoresis is one of the most important separation methods in biological and chemical engineering. In this paper, a novel impact parameter on separation efficiency, i.e., the angle between the vectors of magnetic force and fluid velocity, was derived from the basic equation describing the motion of magnetic beads in microchannels. It is proposed that one of the most important approaches for separation efficiency enhancement is to improve the coordination of magnetic force field and fluid flow field. A T-shaped microchannel magnetophoretic separator was designed based on the angle. And then a two-dimensional dynamic model of magnetic beads moving in microchannels was established to study the separation efficiency of T-shaped microseparator by combined use of finite element method and Runge-Kutta method. The results show that the capture efficiency of T-shaped microseparator is much higher than that of the straight microseparator at the same conditions. For small magnetic beads at high fluid velocities, the designed T-shaped microseparator could still keep high separation efficiency whereas the conventional straight microseparator fails to separate the magnetic beads. Further analysis shows that the mechanism of separation efficiency enhancement lies in the synergy of magnetic force field and flow field, which directly leads to large deflected velocity of the magnetic beads from the main stream, and thus increasing the separation efficiency. It is anticipated that the results in this paper are theoretically helpful for the optimum design of highly efficient magnetophoretic separators.

Real‐time PCR to study the sequence specific magnetic purification of DNA

The performance of various molecular techniques using complex biological samples greatly depends on the efficient separation and purification of DNA targets. In recent years, magnetic separation technology making use of small magnetic beads, has gained immense popularity. Most of these methods rely on the non-specific adsorption of DNA/RNA. However, as presented here, when functionalizing the beads with complementary DNA probes, the target of interest can selectively be isolated. Such sequence specific purification was evaluated for short DNA targets by means of simple fluorescent measurements, resulting in purification efficiencies around 80%. Besides standard fluorescent techniques, a real-time PCR (qPCR) method was applied for monitoring the purification of longer DNA targets. This qPCR method was specifically optimized for directly quantifying the purification efficiency of low concentrated DNA targets bound to magnetic beads. Additionally, parameters possibly affecting the magnetic isolation, including the length of the used capture probe or the hybridization location, were investigated. Using optimized conditions in combination with qPCR, purification efficiencies between 60% and 80% were observed and this over a large concentration window. These data also show the power of a direct qPCR approach to monitor the magnetic isolation of DNA at very low concentrations.

Manipulation of Magnetic Beads by Magnetic Fields of Narrow Metallic Wires for Use in Biosensors

In this paper, we investigated a means to manipulate small magnetic beads using the magnetic fields of current-carrying wires. Narrow metallic wires were fabricated with optical lithography and vacuum deposition methods. As we applied 20-40 mA of current, the magnetic beads could be collected on the wire. Depending on the magnitude of the currents, the velocity of the beads was 2-20 mum/s. In addition to the motion of the beads by the interaction with the fields, we also observed drift of the beads caused by the local heating of the wire and the resulting temperature gradient. We also demonstrated transfer of beads between wires by switching the current between the wires. We consider that this simple device can be used to transfer the beads to the locations of the sensors and that it can increase the reaction probability between beads and magnetic sensors.

Intracellular manipulation of chromatin using magnetic nanoparticles

Magnetic tweezers are widely used for manipulating small magnetic beads inside the cell cytoplasm in order to gain insight into the structural and mechanical properties of the cytoskeleton. Here we discuss the use of magnetic tweezers for the study of nuclear architecture and the mechanical properties of chromatin in living cells. A custom-built, dedicated micro magnetic tweezer set-up is described. We review progress that has been made in applying this technology for the study of chromatin structure and discuss its prospects for the in situ analysis of nuclear architecture and chromatin function.

Phage display combinatorial libraries of short peptides: ligand selection for protein purification

A library of heptapeptides displayed on the surface of filamentous phage M13 was evaluated as a potential source of affinity ligands for the purification of Rhizomucor miehei lipase. Two independent selection (biopanning) protocols were employed: the enzyme was either physically adsorbed on polystyrene or chemically immobilized on small magnetic beads. From screening with the polystyrene-adsorbed lipase it was found that there was a rapid enrichment of the library with “doublet” clones i.e. the phage species which carried two consecutive sequences of heptapeptides, whilst no such clones were observed from the screening using lipase attached to magnetic beads. The binding of the best clones to the enzyme was unambiguously confirmed by ELISA. However the synthetic heptapeptide of identical sequence to the best “monomeric” clone did not act as a satisfactory affinity ligand after immobilization on Sepharose. This indicated that the interaction with lipase was due to both the heptapeptide and the presence of a part of the phage coat protein. This conclusion was further verified by immobilizing the whole phage on the surface of magnetic beads and using the resulting conjugate as an affinity adsorbent. The scope of application of this methodology and the possibility of preparing phage-based affinity materials are briefly discussed.

Magnetic activated cell sorting (MACS) — a new immunomagnetic method for megakaryocytic cell isolation: Comparison of different separation techniques

Megakaryocytes are difficult to isolate because of their fragility, their tendency to aggregate, and their varying sizes. For purification of cells at different stages of maturation and of different sizes (ploidy classes) we developed an immunomagnetic cell sorting method (MACS) to enrich the whole spectrum of the megakaryocytic cell lineage. The use of small magnetic beads coupled to various antibodies and labelling with fluorescent antibodies allowed direct analysis of enrichment and evaluation of the isolated fraction without further staining or detachment procedures. CD 61 (Y2/51), a monoclonal antibody directed against platelet glycoprotein IIIa, was employed to perform the separation procedure. An enrichment up to 47% of CD 61-positive cells with an average of 37% and a recovery rate of 37% was obtained by using the MACS technique. Pre-enrichment by Percoll density centrifugation, followed by MACS separation, resulted in an enrichment of 65% and a recovery rate of 67%. The relative amount of small megakaryocytic cells in only MACS-enriched cell populations, however, was higher than in Percoll/MACS fractions. As a parameter of vitality we tested cytokine secretion of the enriched megakaryocytes in reverse haemolytic plaque assays. Secretion of IL-1, IL-6, GM-CSF, and PDGF with and without stimulation by phorbol myristate acetate was demonstrable at the single cell level.

An enzyme electrode based on electromagnetic entrapment of the biocatalyst bound to magnetic beads

A new type of biosensor is described. It is based on the use of a Clark-type oxygen electrode placed in an electromagnetic field. The biomolecules used in this sensor are immobilized on small magnetic beads which are added to the system when needed and removed as required. By varying the strength of the magnetic field, a homogeneous distribution of particles at the electrode tip is achieved. The electrode is used for the determination of glucose with immobilized glucose oxidase as well as cells of Saccharomyces cerevisiae.

Control of drug release from polymer matrices impregnated with magnetic beads —a proposed mechanism and model for enhanced release

The need to regulate drug release rates in applications such as suppression of diabetic symptoms and birth control has previously led to the development of delivery systems containing small magnetic beads uniformly imbedded within drug-laden polymer matrices. An oscillating magnetic field imposed on such systems triggers a significant increase in release rate. A mechanism for enhanced release is proposed here, which draws upon the similarity between the observed increase in mass transfer by pulsation, e.g., promotion of axial diffusion in a cylinder with pulsed (but zero net) flow and enhanced drug release by the oscillating field. A mathematical model is derived based on this analogy. Its predictions are consistent with general observations and provide correlations of release rates with the frequency and amplitude of the oscillating magnetic field and the intrinsic drug diffusivity.

REMOVAL OF NEUROBLASTOMA CELLS FROM BONE MARROW WITH MONOCLONAL ANTIBODIES CONJUGATED TO MAGNETIC MICROSPHERES

Monoclonal anibodies bound to polystyrene microspheres containing magnetite have been used to remove tumour cells from bone marrow destined for autologous transplantation. The small magnetic beads can be targeted to the surface of tumour cells to render these magnetic. A flow system using permanent samarium cobalt magnets effects the rapid and efficient removal of "magnetic" tumour cells from bone marrow. The system is designed to be used with any type of tumour cell, so that by changing panels of monoclonal antibody it can be used for "cleaning" the bone marrow in many different malignancies.