Manipulation Of Beads Research Articles

Multiplexed single-molecule measurements with magnetic tweezers

We present a method for performing multiple single-molecule manipulation experiments in parallel with magnetic tweezers. We use a microscope with a low magnification, and thus a wide field of view, to visualize multiple DNA-tethered paramagnetic beads and apply an optimized image analysis routine to track the three-dimensional position of each bead simultaneously in real time. Force is applied to each bead using an externally applied magnetic field. Since variations in the field parameters are negligible across the field of view, nearly identical manipulation of all visible beads is possible. However, we find that the error in the position measurement is inversely proportional to the microscope's magnification. To mitigate the increased error caused by demagnification, we have developed a strategy based on tracking multiple fixed beads. Our system is capable of simultaneously manipulating and tracking up to 34 DNA-tethered beads at 60 Hz with approximately 1.5 nm resolution and with approximately 10% variation in applied force.

Heterogeneous immunoassays using magnetic beads on a digital microfluidic platform

A digital microfluidic platform for performing heterogeneous sandwich immunoassays based on efficient handling of magnetic beads is presented in this paper. This approach is based on manipulation of discrete droplets of samples and reagents using electrowetting without the need for channels where the droplets are free to move laterally. Droplet-based manipulation of magnetic beads therefore does not suffer from clogging of channels. Immunoassays on a digital microfluidic platform require the following basic operations: bead attraction, bead washing, bead retention, and bead resuspension. Several parameters such as magnetic field strength, pull force, position, and buffer composition were studied for effective bead operations. Dilution-based washing of magnetic beads was demonstrated by immobilizing the magnetic beads using a permanent magnet and splitting the excess supernatant using electrowetting. Almost 100% bead retention was achieved after 7776-fold dilution-based washing of the supernatant. Efficient resuspension of magnetic beads was achieved by transporting a droplet with magnetic beads across five electrodes on the platform and exploiting the flow patterns within the droplet to resuspend the beads. All the magnetic-bead droplet operations were integrated together to generate standard curves for sandwich heterogeneous immunoassays on human insulin and interleukin-6 (IL-6) with a total time to result of 7 min for each assay.

Magnetic Bead Sensing Platform for the Detection of Proteins

Over the past 5 years, the on-chip detection and manipulation of magnetic beads via magnetoelectronics has emerged as a promising new biosensor platform. Magnetic bead sensing (MBS) provides a highly sensitive and specific technique, enabling these sensors to meet the diagnostic needs that are currently not met by existing technologies. Although many studies have proven the high physical sensitivity of magnetic sensors, the establishment of dose-response curves using MBS is unexplored and their capability to sensitively detect low concentrations of target molecules for diagnostic applications has remained unproven. In this study, we have exploited an alternative MBS concept based on the repositioning of the magnetic beads toward the most sensitive location on the spin valve sensors to allow for highly sensitive immunosensing over a wide range of target concentrations. Furthermore, we present the optimization of the magnetoimmuno assay, i.e., the surface chemistry, the blocking procedure, and the type of magnetic particle, for the highly sensitive and specific detection of S100betabeta, a diagnostic marker for stroke and minor head injury. Finally, a dose-response curve was established that illustrates that our MBS platform can specifically detect S100betabeta down to 27 pg/mL, while maintaining a broad dynamic detection range of approximately 2 decades.

CXCR5 may be involved in the attraction of human metastatic neuroblastoma cells to the bone marrow.

Up-regulation of some chemokine receptors on tumor cells is associated with increased metastatic potential. In this respect, limited information is available on chemokine receptor in human neuroblastoma (NB). Purpose of the study was to identify chemokines/chemokine receptors involved in bone marrow (BM) localization of metastatic NB cells in view of the development of targeted therapeutic strategies. CD45- metastatic NB cells were isolated from the BM of six patients by immunomagnetic bead manipulation. Some experiments were carried out using a panel of human neuroblastoma cell lines (GI-ME-N, GI-LI-N, LAN-5, HTLA-230, SH-SY-5Y and IMR-32). Immunophenotypic analyses were performed by flow cytometry. Cell migration assays were carried out using transwell systems. Calcium ion mobilization, chemokine receptor internalization and cell proliferation were investigated by flow cytometry. In all BM samples, CXCR5 was expressed by the majority of primary neuroblasts and mediated their chemotaxis in response to CXCL13. Primary metastatic NB cells from all BM samples expressed CXCR6, but were not attracted by soluble CXCL16. Studies performed with two CXCR6+ NB cell lines showed that the mechanism whereby neuroblasts did not migrate to CXCL16 was likely related to defective calcium ion mobilization. CXCR5 is the first chemokine receptor so far identified able to attract in vitro primary metastatic NB cells. CXCR6 may be involved in retention of metastatic neuroblasts in the BM through interaction with CXCL16 expressing stromal cells in the absence of signal transduction.

Digital microfluidic design and optimization of classic and new fluidic functions for lab on a chip systems

This paper deals with microfluidic studies for lab-on-a-chip development. The first goal was to develop microsystems immediately usable by biologists for complex protocol integrations. All fluid operations are performed on nano-liter droplet independently handled solely by electrowetting on dielectric (EWOD) actuation. A bottom-up architecture was used for chip design due to the development and validation of elementary fluidic designs, which are then assembled. This approach speeds up development and industrialization while minimizing the effort in designing and simplifying chip-fluidic programming. Dispensing reproducibility for 64 nl droplets obtained a CV below 3% and mixing time was only a few seconds. Ease of the integration was demonstrated by performing on chip serial dilutions of 2.8-folds, four times. The second part of this paper concerns the development of new innovative fluidic functions in order to extend EWOD-actuated digital fluidics’ capabilities. Experiments of particle dispensing by EWOD droplet handling are reported. Finally, work is shown concerning the coupling of EWOD actuation and magnetic fields for magnetic bead manipulation.

Optically Controlled Cell Discrimination and Trapping Using Optoelectronic Tweezers

Optoelectronic tweezers (OET) provide a powerful tool for the manipulation of micro- and nanoparticles. The OET device produces an optically controlled dielectrophoretic force, allowing complex dynamic manipulation patterns using light intensities up to 100 000 times lower than that of optical tweezers. Using OET, we demonstrate the separation of live and dead human B cells, and the separation of HeLa and Jurkat cells. We also present, for the first time, a modified single-sided OET device that promises to facilitate the integration of OET and microfluidics. Unlike standard OET, this single-sided OET device produces electric fields that are oriented parallel to the plane of the device. We demonstrate the manipulation of polystyrene beads using this new single-sided OET device, and discuss its capabilities

Optical 3D Manipulation and Observation in Real-Time

Three-dimensional light structures can be created by modulating the spatial phase and polarization properties of the laser light. A particularly promising technique is the Generalized Phase Contrast (GPC) method invented and patented at Risø National Laboratory. Based on the combination of programmable spatial light modulator devices and an advanced graphical user-interface the GPC method enables real-time, interactive and arbitrary control over the dynamics and geometry of synthesized light patterns. Recent experiments have shown that GPC-driven micro-manipulation provides a unique technology platform for fully user-guided assembly of a plurality of particles in a plane, control of particle stacking along the beam axis, manipulation of multiple hollow beads, and the organization of living cells into three-dimensional colloidal structures. These demonstrations illustrate that GPC-driven micro-manipulation can be utilized not only for the improved synthesis of functional microstructures but also for non-contact and parallel actuation crucial for sophisticated opto- and micro-fluidic based lab-on-a-chip systems.

A micromagnetic actuator for biomolecule manipulation

An efficient and low cost way to attract and mix magnetic beads is reported, in which microserpentines wires shape were used in combination with a permanent magnet to polarize and magnetically saturate beads. The research included the design, modelling and an empirical evaluation of a novel device for manipulation of paramagnetic beads. The results reported indicate that the performance of this device agrees with expectations from the modelling, and suggests that the device has significant potential for applications requiring manipulation of biomolecules within BioMEMS, such isolation and purification of nucleic acids and proteins.

Prospective demonstration of brain plasticity after intensive abacus-based mental calculation training: An fMRI study

Abacus-based mental calculation is a unique Chinese culture. The abacus experts can perform complex computations mentally with exceptionally fast speed and high accuracy. However, the neural bases of computation processing are not yet clearly known. This study used a BOLD contrast 3T fMRI system to explore the brain activation differences between abacus experts and non-expert subjects. All the acquired data were analyzed using SPM99 software. From the results, different ways of performing calculations between the two groups were seen. The experts tended to adopt efficient visuospatial/visuomotor strategy (bilateral parietal/frontal network) to process and retrieve all the intermediate and final results on the virtual abacus during calculation. By contrast, coordination of several networks (verbal, visuospatial processing and executive function) was required in the normal group to carry out arithmetic operations. Furthermore, more involvement of the visuomotor imagery processing (right dorsal premotor area) for imagining bead manipulation and low level use of the executive function (frontal-subcortical area) for launching the relatively time-consuming sequentially organized process was noted in the abacus expert group than in the non-expert group. We suggest that these findings may explain why abacus experts can reveal the exceptional computational skills compared to non-experts after intensive training.

Magnetic bead manipulation in a sub-microliter fluid volume applicable for biosensing

Magnetic actuation principles using superparamagnetic beads suspended in a fluid are studied in this paper. An experimental setup containing a sub-microliter fluid volume surrounded by four miniaturized electromagnets was designed and fabricated. On the basis of optical velocity measurements, the induced behavior of single beads and ordered chains was analyzed and compared to a theoretical model. This research can be used to develop new techniques for accelerated transportation in lab-on-a-chip bio-assays.

Manipulation of superparamagnetic beads using on-chip current lines placed on a ferrite magnet

Manipulation of superparamagnetic beads in a static solution is demonstrated using on-chip current striplines placed on a ferrite magnet. The ferrite magnet fits the requirement to enhance the bead’s magnetic moment while still keeping beads randomly dispersed in the liquid, so allowing easy and selective manipulation of single beads. By applying currents up to hundreds of milliampere, the tapered stripline first attracts the beads to its edge, then the magnetic force along the edge drives the trapped beads moving continuously towards the chip center. On arriving into the chip central area (a square zone which acts as a site to collect the arriving beads), fine manipulation of selected single beads is further performed by switching on/off and/or tuning the current passing through the nearby quadruple striplines. We suggest that the present system may provide a simple but effective platform for handling magnetic tags for biological and biomedical applications.

An integrated microfluidic cell for detection, manipulation, and sorting of single micron-sized magnetic beads

A lab-on-a-chip integrated microfluidic cell has been developed for magnetic biosensing, which is comprised of anisotropic magnetoresistance (AMR) sensors optimized for the detection of single magnetic beads and electrodes to manipulate and sort the beads, integrated into a microfluidic channel. The device is designed to read out the real-time signal from 9μm diameter magnetic beads moving over AMR sensors patterned into 18×4.5μm rectangles and 10μm diameter rings and arranged in Wheatstone bridges. The beads are moved over the sensors along a 75×75μm wide channel patterned in SU8. Beads of different magnetic moments can be sorted through a magnetostatic sorting gate into different branches of the microfluidic channel using a magnetic field gradient applied by lithographically defined 120nm thick Cu striplines carrying 0.2A current.

Response of super-paramagnetic beads in microfluidic devices with integrated magnetic micro-columns

Ferromagnetic micro-columns (FMCs) have been fabricated on glass substrates using standard photolithography and electroplating and then integrated in micro-fluidic channels in order to study the response of super-paramagnetic beads suspended in an aqueous solution. We observed that under low external magnetic fields, the integrated micro-columns could generate sufficiently strong magnetic field gradients to trap super-paramagnetic beads in a flowing stream of water. The trapping behavior of the integrated FMCs was studied by considering different micro-patterns and different magnetic field intensities. In addition, the formation of magnetic micro-beads chains has been observed due to the magnetic dipole interactions. We believe that the integration of ferromagnetic micro-columns in micro-fluidic channels can have a variety of advanced applications, considering different possibilities of surface functionalization and manipulation of super-paramagnetic beads in an aqueous solution.

Evaluation of trapping efficiency of optical tweezers by dielectrophoresis

A relatively new method for measuring optically induced forces on microparticles and cells, different from the conventional Brownian motion and viscous drag force calibration methods widely used, is introduced. It makes use of the phenomenon of dielectrophoresis for the calibration of optical tweezers through the dielectrophoretic force calculations. A pair of microelectrodes is fabricated by photolithography on a microscope slide and it is connected to a high-frequency generator. The calibration of the optical tweezers setup is performed by the manipulation of polystyrene beads and yeast cells. Calibration diagrams of the transverse forces versus power are deduced for different cell radii and numerical apertures of the objective lenses. The optical system and the related technique provide a fast and easy method for optical tweezers calibration.

CXCL12 Does Not Attract CXCR4+ Human Metastatic Neuroblastoma Cells: Clinical Implications

The role of CXCR4 in bone marrow localization of neuroblastoma cells has been recently proposed. The aim of this study was to investigate the expression and chemotactic functionality of CXCR4 in human metastatic neuroblastoma cells isolated from the bone marrow and, for comparison, in a panel of neuroblastoma cell lines. CXCR4 expression and chemotactic functionality were investigated in metastatic neuroblastoma cells isolated from patient bone marrow and in neuroblastoma cell lines. The former cells were isolated as CD45- or GD2+ cells by immunomagnetic bead manipulation. Chemotactic assays were done in a transwell system. Regulator of G protein signaling expression was investigated by reverse transcription-PCR. Metastatic neuroblastoma cells consistently expressed CXCR4, which was also detected in 5 of 10 neuroblastoma cell lines. CXCL12 did not stimulate the chemotaxis of primary tumor cells or cell lines in either normoxia or hypoxia, irrespective of CXCR4 up-regulation detected under the latter condition. Accordingly, neuroblastoma cells failed to modulate filamentous actin and to activate mitogen-activated protein kinase upon treatment with CXCL12. RGS16 mRNA was consistently expressed in primary tumor cells and cell lines, but its down-regulation by RNA interference did not restore CXCR4 chemotactic functionality. These results show unambiguously that CXCR4 expressed in human metastatic neuroblastoma cells is not functional and do not support the clinical use of CXCR4 antagonists to prevent neuroblastoma metastasis.

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.

Versatile force–feedback manipulator for nanotechnology applications

A nanoscale manipulation system has been designed and built through the integration of a force–feedback haptic device and a commercial atomic force microscope. The force–feedback interaction provides a very intuitive, efficient and reliable way for quick manipulation of nanoscale objects. Unlike other nanomanipulators, ours allows the user to feel the actual tip–sample interaction during the manipulation process. Various modes of manipulation have been implemented and evaluated. As a proof of concept, we show a contact-mode nanomanipulation of a carbon nanotube and a noncontact manipulation of silicon beads. In addition to nanomanipulation itself, all relevant signals can be recorded during the manipulation process which allows quantitative interpretation of nanomechanics experiments.

Magnetic biosensors for genetic screening of cystic fibrosis

The paper reports on the development of a magnetic biosensing platform for genetic analysis. The sensing technique is based on the on-chip manipulation of magnetically labelled biomolecules by the magnetic field gradient force created by current-carrying conductors; on biomolecular reactions such as the binding of complementary DNA material; and on the detection of the fringe field of the magnetic label by a magnetoresistive spin valve sensor. Different experiments will demonstrate the advantages, difficulties, prospects and potential of the combination of magnetic bead manipulation and detection on a single microchip. Early detection of DNA coding for the cystic fibrosis (CF) gene is used as a model system for proof-of-concept of the magnetic DNA biosensor platform.

Electrochemical Polishing Technique Yields Apparatus for Manipulation of Microto Nanometer-Sized Magnetic Beads

Electrochemical Polishing Technique Yields Apparatus for Manipulation of Microto Nanometer-Sized Magnetic Beads

The fabrication of high sensitive spin-valve sensor for magnetic bead detection

Manipulation and detection of magnetic beads on a chip open up new perspectives for analysis of magnetically labeled specimens in biological and medical applications. This work has studied to achieve the high sensitive spin-valve (SV) sensor detecting the stray field from a spherical-shaped superparamagnetic bead magnetized by external field. First of all, SV structures of Ta(50)/NiFe(45)/CoFe(15)/Cu(26)/ CoFe(40)/IrMn(150)/Ta(50) [unit of ( ) is A] with 8 - 9% magnetoresistive ratio (MR) were deposited on substrate Si/SiO 2 (1500) by UHV magnetron sputter system. SV sensor was fabricated through photolithographic techniques and ion milling processes. The working of sensor was confirmed by obtaining the output signal as a function of sense current under the external field parallel to magnetization direction of pinned layer. The sensitivity of the fabricated SV sensor was about 0.3%/Oe (sense current 10 mA). Sensor signal (AV) output of 2 mV was obtained for 2.8 μm magnetic beads positioned over the SV sensor using an external in-plane field and 10 mA sense current.