Concentration Of Magnetic Beads Research Articles

Low LOD and Non-Adsorption Probing of Functionalized Magnetic Beads Using Quartz Crystal Microbalance Under Bimodal Magnetic Field

Low limit of detection (LOD) and highly sensitive probing of functional magnetic nanobead labels is the cornerstone of magnetic label molecular detection technology, which is of great significance in analytical chemistry and biomolecular analysis. Here we present a probing technology based on quartz crystal microbalance (QCM) combines bimodal magnetic fields to accurate and rapid probing of magnetic beads. The proposed technique uses QCM to detect the change of viscosity and density of tested solution under a bimodal magnetic field, thereby enabling the quantification of magnetic bead concentration. The experimental findings demonstrate that the technique can detect magnetic beads accurately and rapidly within 0 ng/mL to 100 μg/mL without anchoring magnetic beads on the QCM. Furthermore, when the particle size of magnetic beads is 1 μm and 0.28 μm, the LOD is reached at 4.62 ng/mL and 2.31 ng/mL, respectively. The versatility of the no-modification probing platform yet the wide detection range and low LOD to various magnetic particles, showcase the potential of the proposed technology to enable swift, repeatable, and dependable assays across a broad range of applications, including but not limited to biomolecule analysis, Molecular genetics, pre-symptomatic diagnosis, and biosafety.

Dynamic Magnetic Excitation Detection Method for Low-Concentration Superparamagnetic Particles via Quartz Crystal Microbalance

Magnetic biomarker detection and monitoring at low concentrations are critical for the early diagnosis of many diseases and for accurately identifying specific biomolecules. Previously reported highly sensitive detection methods rely on magnetic sensors to detect the stray fields of magnetic labels (usually magnetic beads). The random noise generated by the Brownian motion of magnetic beads in solution makes it difficult to reduce further the limit of detection (LOD) of this measurement. Therefore, we propose a low-concentration magnetic beads sensor and a dynamic magnetic excitation detection method. The intensity of magnetization motion under the ac excitation magnetic field detected by the quartz crystal microbalance (QCM) realizes the measurement of the magnetic bead concentration in the solution. The experimental results show that the LOD of the proposed sensor in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.8~\mu \text{m}$ </tex-math></inline-formula> magnetic bead solution is 10 ng/mL and displays an approximate linear detection characteristic in the range of 20–100 ng/mL. The intensity of magnetization detected by QCM has an approximately linear relationship with the magnetic bead concentration. Given the wide application of magnetic-labeled biomolecule detection and its huge application prospects in early disease detection and precision medicine, this method provides an inexpensive, fast, and flexible detection technology for the general labeling analysis of magnetic labels in biomolecule detection.

Continuous separation of magnetic beads using a Y-shaped microfluidic system integrated with hard-magnetic elements

A Y-shaped microfluidic separator with an array of hard-magnetic elements integrated in a non-magnetic substrate is designed to realize continuous separation of magnetic beads under an external bias field. By fixing the magnetization directions of the hard-magnetic elements parallel to the wall of microchannel, the spatial distribution of the magnetic field can be adjusted by the geometrical size of elements, the gap between two neighboring elements, and the direction of the external bias field. In this work, magnetic beads comprising of multiple magnetic/superparamagnetic nanoparticles (10 nm Fe5Si3, Fe3Si or Fe3O4) in polymer matrixes are used. Herein, Kelvin force on the magnetic bead is described by treating each magnetized superparamagnetic nanoparticle as an equivalent magnetic dipole. With the closed-form Kelvin force, a two-way model that takes bead-fluid interaction into account is adopted to investigate the trajectories of magnetic beads in our Y-shaped microfluidic system. Using the two-way model, the influence of the beads’ size, the direction of the external bias field, the magnetic bead concentration and the bead-fluid interaction on the trajectories of magnetic beads is also investigated. 100% collection or separation efficiency can be realized just by adjusting inlet velocities. In addition, it is theoretically demonstrated that two kinds of magnetic beads with small size difference (down to 100 nm) can be successfully separated by using our Y-shaped microfluidic separator.

Manipulation of Magnetic Beads with Thin Film Microelectromagnet Traps.

Integration of point-of-care assays can be facilitated with the use of actuated magnetic beads (MB) to perform testing in less expensive settings to enable the delivery of cost-effective care. In this paper we present six different designs of planar microelectromagnets traps (MEMT) with four external coils in series and one central coil connected for an opposite direction of manipulation of MB in microfluidic flows. The development of a simulation tool facilitated the rapid and efficient optimization of designs by presenting the influence of system variables on real time concentrations of MB. Real time experiments are in good agreement with the simulations and showed that the design enabled synchronous concentration and dispersion of MB on the same MEMT. The yield of local concentration is seen to be highly dependent on coil design. Additional coil turns between the central and external coils (inter-windings) doubled magnetic concentration and repulsion with no significant electrical resistance increase. The assemblage of a copper microchannel closed loop cooling system to the coils successfully eliminated the thermal drift promoted by joule heating generated by applied current.

Effects of diverse materials-based methods on DNA extraction for Clostridium difficle from stool samples

Nosocomial infections, including Clostridium difficile infection (CDI), and their fatality rates have increased in the past few decades. Despite emerging molecular diagnostic technologies with rapid, accurate outcomes, nucleic acid extraction from stool samples remains the first limiting step before downstream applications. Commercial nucleic acid extraction kits greatly decrease labor and time requirements, and also provide nucleic acid preparations with higher quality and purity for enzyme digestion analysis or genotyping. The magnetic bead based technique is a novel method compared with the conventional spin-column method, and currently has widespread use in nucleic acid extraction. We evaluated five DNA extraction kits with magnetic beads using materials with various properties (particle size, concentration of magnetic beads, grinding beads) and reagents (proteinase K, lysozyme, isopropanol, and absolute ethanol) to determine the cost, hands-on time, number of essential operations, and quality and purity of the DNA preparations, compared with those obtained using the QIAamp Fast DNA Stool Mini Kit. The six DNA extraction kits yielded A260/280 ratios ranging from 0.85 to 1.9 (average 1.57), and concentrations from 3.70 to 108.09 ng/μL (average 34.64 ng/μL). All the DNA samples had acceptable downstream application effects, except for those obtained using the TIANGEN Magnetic Soil and Stool DNA Kit. However, gel electrophoresis analysis of the DNA samples resulted in a light strip on the gel, indicating that the proteinaceous contaminant may not have been removed completely. A rapid and accurate molecular diagnostic technique could allow for more suitable treatment and prognosis outcomes for inpatients, depending, in large part, on the quality and purity of DNA preparations, which are frequently neglected. Our study focused on the quality of commercial kits with a primary focus on the treatment of stool samples and molecular diagnostic applications.

Droplet Microfluidics in Thermoplastics: Device Fabrication, Droplet Generation, and Content Manipulation using Integrated Electric and Magnetic Fields.

We have developed droplet microfluidic devices in thermoplastics and demonstrated the integration of key functional components that not only facilitate droplet generation, but also include electric field-assisted reagent injection, droplet splitting, and magnetic field-assisted bead extraction. We manufactured devices in poly(methyl methacrylate) and cyclic olefin polymer using a hot-embossing procedure employing silicon masters fabricated via photolithography and deep reactive ion etching techniques. Device characterization showed robust fabrication with uniform feature transfer and good embossing yield. Channel modification with heptadecafluoro-1,1,2,2-tetrahydrodecyltrichlorosilane increased device hydrophobicity, allowing stable generation of 330-pL aqueous droplets using T-junction configuration. Picoinjector and K-channel motifs were also both successfully integrated into the thermoplastic devices, allowing for robust control over electric field-assisted reagent injection, as well as droplet splitting with the K-channel. A magnetic field was also introduced to the K-channel geometry to allow for selective concentration of magnetic beads while decanting waste volume through droplet splitting. To show the ability to link multiple, modular features in a single thermoplastic device, we integrated droplet generation, reagent injection, and magnetic field-assisted droplet splitting on a single device, realizing a magnetic bead washing scheme to selectively exchange the fluid composition around the magnetic particles, analogous to the washing steps in many common biochemical assays. Finally, integrated devices were used to perform a proof-of-concept in-droplet β-galactosidase enzymatic assay combining enzyme-magnetic bead containing droplet generation, resorufin-β-D-galactopyranoside substrate injection, enzyme-substrate reaction, and enzyme-magnetic bead washing. By integrating multiple droplet operations and actuation forces we have demonstrated the potential of thermoplastic droplet microfluidic devices for complex (bio)chemical analysis, and we envision a path toward mass fabrication of droplet microfluidic devices for a range of (bio)chemical applications.

激光透射法磁珠浓度测量系统

激光透射法磁珠浓度测量系统

Image Processing and Cell Phone Microscopy to Analyze the Immunomagnetic Beads on Micro-Contact Printed Gratings

In this paper we report an ultra-low-cost spherical ball lens based cell phone microscopy and image processing algorithms to analyze the amount of immunomagnetic beads on micro-contact printed gratings. The spherical ball lens provides approximately 100× magnification but the recorded images are not clear and are noisy. By using the image-processing algorithms, the noise can be reduced and the images can be enhanced to quantify the amount of immunomagnetic beads on micro-contact printed lines. This method, which is portable and low-cost, can be an alternative read out mechanism for biosensing applications using immunomagnetic beads on micro-contact printed surface receptors. Further, 0.0335 mg/mL was the lowest magnetic bead concentration that could be detected above the inherent noise level of the spherical ball lens.

Quantification of rolling circle amplified DNA using magnetic nanobeads and a Blu-ray optical pick-up unit.

We present the first implementation of a Blu-ray optical pickup unit (OPU) for the high-performance low-cost readout of a homogeneous assay in a multichamber microfluidic disc with a chamber thickness of 600 μm. The assay relies on optical measurements of the dynamics of magnetic nanobeads in an oscillating magnetic field applied along the light propagation direction. The laser light provided by the OPU is transmitted through the sample chamber and reflected back onto the photo detector array of the OPU via a mirror. Spectra of the 2nd harmonic photo detector signal vs. the frequency of the applied magnetic field show a characteristic peak due to freely rotating magnetic nanobeads. Beads bound to ~1 μm coils of DNA formed off-chip by padlock probe recognition and rolling circle amplification show a different dynamics and the intensity of the characteristic peak decreases. We have determined the optimum magnetic bead concentration to 0.1mg/mL and have measured the response vs. concentration of DNA coils formed from Escherichia Coli. We have found a limit of detection of 10 pM and a dynamic range of about two orders of magnitude, which is comparable to the performance obtained using costly and bulky laboratory equipment. The presented device leverages on the advanced but low-cost technology of Blu-ray OPUs to provide a low-cost and high-performance magnetic bead-based readout of homogeneous bioassays. The device is highly flexible and we have demonstrated its use on microfluidic chambers in a disc with a thickness compatible with current optical media mass-production facilities.

Bead capture increases the sensitivity of sputum microscopy for the diagnosis of tuberculosis in Beijing, China

A review of the scientific literature concluded that indirect smear can improve detection of TB in sputum compared to direct smear. However few laboratories have access to centrifugation in order to perform indirect smear. This study investigated whether an alternative method of magnetic bead concentration could enhance diagnosis of TB in China in laboratories which only perform direct smear microscopy. A total of 129 sputum samples were investigated by direct smear microscopy, microscopy after TB-Bead extraction and by solid and liquid culture. Direct smear had a sensitivity of 40% by Ziehl-Neelsen (ZN) and 45% by auramine compared to combined culture results. After TB-Bead extraction, this increased to 65% for ZN and 70% for auramine. Magnetic bead concentration of mycobacteria from sputum led to a significant improvement (p<0.05) in the sensitivity of microscopy compared with direct smear.

Increased case finding of tuberculosis from sputum and sputum deposits after magnetic bead concentration of mycobacteria

Concentration of mycobacteria from sputum by centrifugation prior to acid-fast microscopy increases case finding compared to direct microscopy of the sputum (direct smear). However, centrifugation has to be performed outside the safety cabinet and many laboratories do not have access to a centrifuge. Magnetic bead extraction of the mycobacteria is an alternative method that can be performed in a cabinet with just a magnet. Magnetic TB-Bead (Microsens Medtech Ltd) extraction of mycobacteria from sputum prior to microscopy was compared to direct smear on 78 sputum samples. Microscopy of the TB-Bead extracts identified all of 26 of the direct smear positive samples either with the same microscopy score or, in 19/27 of samples, with an increased microscopy score which aided microscopy detection. In addition, microscopy of the TB-Bead extracts identified 10 additional positive samples compared to direct smear; which represents a statistically significant increase in case finding of 38% (p=0.002) compared to direct smear. In a separate study, TB-Beads enabled further 4 positive samples to be detected from 30 centrifuged pellets that were originally smear negative; two of these were subsequently found to be positive when the original deposits were reinvestigated by smear microscopy. By concentrating mycobacteria from sputum and sputum deposits, TB-Beads have been demonstrated to increase the number of positive sputum samples which could increase case-finding. The TB-Bead method is simple and rapid and compatible with use within a safety cabinet.

Out of the cleanroom, self-assembled magnetic artificial cilia

Micro-sized hair-like structures, such as cilia, are abundant in nature and have various functionalities. Many efforts have been made to mimic the fluid pumping function of cilia, but most of the fabrication processes for these "artificial cilia" are tedious and expensive, hindering their practical application. In this paper a cost-effective in situ fabrication technique for artificial cilia is demonstrated. The cilia are constructed by self-assembly of micron sized magnetic beads and encapsulated with soft polymer coatings. Actuation of the cilia induces an effective fluid flow, and the cilia lengths and distribution can be adjusted by varying the magnetic bead concentration and fabrication parameters.

Ultrasensitive detection of E. coli O157:H7 with biofunctional magnetic bead concentration via nanoporous membrane based electrochemical immunosensor

In this paper, biofunctional magnetic beads were investigated for bacterial cells concentration in a nanoporous alumina membrane based immunosensor for ultra-sensitive detection of E. coli O157:H7. The specific antibody modified magnetic beads were used for concentration of E coli O157:H7 from samples in a small region to enhance sensitivity. The magnetic bead conjugated E. coli O157:H7 cells were then captured on the nanoporous alumina membrane with immobilized antibody via assembled PEG-silane linker. Scanning electron microscopy and fluorescent microscopy were used to demonstrate the magnetic bead-bacteria cell conjugation and bacteria cells magnetic concentration, respectively. Impedance spectroscopy was used to monitor the pure E coli O157:H7 cells and magnetic bead conjugated E coli O157:H7 cells binding on antibody immobilized nanoporous membrane with or without magnetic field. Compared with direct detection of pure bacteria cells, this method via magnetic bead conjugation and concentration demonstrated the ultrasensitivity of 10CFU/mL for E coli O157:H7 detection.

Concentration of Magnetic Beads Utilizing Light-Induced Electro-Osmosis Flow

Magnetic beads are widely utilized for separating biomolecules, DNA and RNA. Traditionally, bulk magnet is utilized for manipulation these particles but when it comes to microscale bulk magnet is not the efficient method. Here, we utilize an organic photoconductive material, TiOPc, to generate light-induced electro-osmosis flow on chip. The fabrication process is convenient to be handled by the researchers and biologists without cleanroom IC fabrication facility. When specifically designed light pattern is projected onto the TiOPc substrate, the conductivity of the organic material layer within the illuminating region increases and the charges are locally assembled on its surface to form a virtual electrode. With an external ac voltage of 5 Vpp at 10 kHz, numerous magnetic beads are attracted from the nonilluminating region toward the center of light-pattern illuminating region. Driven by the moving light image, the grouped magnetic beads can be manipulated and merged in a desired way or direction. The light manipulation process provides a flexible and convenient approach for in vitro control of magnetic beads. We expect that this light-driven technology would display a multifunctional platform for manipulation of microparticles.

GMI detection of magnetic-particle concentration in continuous flow

We describe a microfluidic device for the determination of the concentration of magnetic beads under continuous flow of the carrier fluid by means of the Giant Magneto-Impedance effect (GMI). The microfluidic chip is composed of a 10μl chamber situated on top of the GMI sensing material, which is inserted in a microstrip transmission line for the impedance measurements. Two different GMI materials have been used for the experiments: an amorphous ribbon and a permalloy based multilayer, sputtered onto the same polymeric material of the microfluidic chamber. Detection tests in continuous flow have been performed using solutions containing two types of beads: one made of ferromagnetic microparticles and the other made of superparamagnetic nanoparticles. A basic calculation of the magnitude of the fringe field created by the beads assures a detectable signal on the sensors, but the experimental difficulties severely condition the measurements. The results show a promising sensitivity for both types of particles but also reveal an important number of detection problems that must be overcame before the prototype become functional.

A planar conducting microstructure to guide and confine magnetic beads to a sensing zone

A novel planar conducting microstructure is proposed to transport and confine magnetic micro/nano beads to a sensing zone. Manipulation and concentration of magnetic beads are achieved by employing square-shaped conducting micro-loops, with a few hundred nano-meters in thickness, arranged in a unique fashion. These microstructures are designed to produce high magnetic field gradients which are directly proportional to the force applied to manipulate the magnetic beads. Furthermore, the size of the microstructures allows greater maneuverability and control of magnetic beads than what could be achieved by permanent magnets. The aim of the microstructures is to guide magnetic beads from a large area and confine them to a smaller area where for example quantification would take place. Experiments were performed with different concentrations of 2μm diameter magnetic beads. Experimental results showed that magnetic beads could be successfully guided and confined to the sensing zone.

Immunomagnetic Separation and Flow Cytometry for Rapid Detection of Escherichia coli O157:H7

A rapid method for detecting Escherichia coli O157:H7 combining immunomagnetic beads (IMB) and flow cytometry was developed. Labeling antigens separated by IMB with fluorescent antibody enabled the detection of <103 CFU bacteria per ml in pure culture. The optimum concentration of magnetic beads for flow cytometry was lower (ca. 105 particles per ml) than that reported for conventional IMB assay (more than 6 × 106 to 8 × 106 particles per ml). Immunomagnetic separation and flow cytometry (IMFC) were evaluated for detecting E. coli O157:H7 in the presence of a competing microorganism and for detecting antibodies in potassium phosphate buffer. The total assay time from separating antigens with IMB to analyzing with flow cytometry was about 1 h. IMFC detected 103 to 104 CFU of E. coli O157:H7 per ml in ground beef enrichment broth and could effectively discriminate between E. coli O157:H7 and competing natural flora. The new assay system provides another approach to separation and detection of low populations of pathogens and shows potential for detecting low concentrations of toxins and other soluble antigens directly from food in a short time.