Bead Populations Research Articles

Efficient discovery of antibody binding pairs using a photobleaching strategy for bead encoding.

Dye-encoded bead-based assays are widely used for diagnostics. Multiple bead populations are required for multiplexing and can be produced using different dye colors, labeling levels, or combinations of dye ratios. Ready-to-use multiplex bead populations restrict users to specific targets, are costly, or require specialized instrumentation. In-house methods produce few bead plexes or require many fine-tuning steps. To expand bead encoding strategies, we present a simple, safe, and cost-effective bench-top system for generating bead populations using photobleaching. By photobleaching commercially available dye-encoded magnetic beads for different durations, we produce three times as many differentiable bead populations on flow cytometry from a single dye color. Our photobleaching system uses a high-power LED module connected to a light concentrator and a heat sink. The beads are photobleached in solution homogeneously by constant mixing. We demonstrate this photobleaching method can be utilized for cross-testing antibodies, which is the first step in developing immunoassays. The assay uses multiple photobleached encoded beads conjugated with capture antibodies to test many binding pairs simultaneously. To further expand the number of antibodies that can be tested at once, several antibodies were conjugated to the same bead, forming a pooled assay. Our assay predicts the performance of antibody pairs used in ultrasensitive Simoa assays, narrowing the number of cross-tested pairs that need to be tested by at least two-thirds and, therefore, providing a rapid alternative for an initial antibody pair screening. The photobleaching system can be utilized for other applications, such as multiplexing, and for photobleaching other particles in solution.

SeParate: multiway fluorescence-activated droplet sorting based on integration of serial and parallel triaging concepts.

Fluorescence-activated droplet sorting (FADS) has emerged as a versatile high-throughput sorting tool that is, unlike most fluorescence-activated cell sorting (FACS) platforms, capable of sorting droplet-compartmentalized cells, cell secretions, entire enzymatic reactions and more. Recently, multiplex FADS platforms have been developed for the sorting of multi-fluorophore populations towards different outlets in addition to the standard, more commonly used, 2-way FADS platform. These multiplex FADS platforms consist of either multiple 2-way junctions one after the other (i.e. serial sorters) or of one junction sorting droplets in more than 2 outlets (i.e. parallel sorters). In this work, we present SeParate, a novel platform based on integrating s̲e̲rial and p̲a̲r̲allel sorting principles for accura̲t̲e̲ multiplex droplet sorting that is able to mitigate limitations of current multiplex sorters. We show the SeParate platform and its capability in highly accurate 4-way sorting of a multi-fluorophore population into four subpopulations with the potential to expand to more. More specifically, the SeParate platform was thoroughly validated using mixed populations of fluorescent beads and picoinjected droplets, yielding sorting accuracies up to 100% and 99.9%, respectively. Finally, transfected HEK-293T cells were sorted employing two different optical setups, resulting in an accuracy up to 99.5%. SeParate's high accuracy for a diverse set of samples, including highly variable biological specimens, together with its scalability beyond the demonstrated 4-way sorting, warrants a broad applicability for multi-fluorophore studies in life sciences, environmental sciences and others.

A universal model for the permeability of sintered materials

Sintered materials are used as permeable filters and flow controllers, for which a validated and general model of porosity and permeability is required. Here, we prepare samples built from mono- and polydisperse glass bead populations sintered for known times at high temperature, and then measure the sample porosity and permeability. We supplement our new dataset with published permeability data for sintered systems including high-temperature in situ determinations of permeability during sintering. We test a range of mathematical models for the change in permeability with porosity as sintering progresses from a value for the initial granular particle packing geometry, down to the percolation threshold at low porosity. We find good agreement between our datasets and a preferred theoretical approach – a percolation theory model – with no explicit requirement for empirical adjustment. However, we propose semi-empirical steps that generalize this theory to a universal description across all porosities. Finally, we quantify the inertial component of fluid transport at high flow rates through these materials. Our model framework is made available via a user-friendly downloadable spreadsheet which takes particle size distribution as an input and provides permeability as an output.

A Modified Method for the Quantification of Immune Checkpoint Ligands on Exosomes from Human Serum using Flow Cytometry.

Objectives: Exosomes are the smallest of the extracellular vesicles and can contain a variety of different cargos, including nucleic acids, lipids, and proteins. Ultracentrifugation followed by electron microscopy has historically been used for the isolation and visualization of exosomes; Western blot and ELISA have also been used, but these techniques are only semiquantitative and are unable to distinguish different exosome markers in the same sample. To resolve some of these issues, we propose a modification of a bead-based flow cytometry method. Methods: Peripheral blood serum was mixed with a commercial exosome separation reagent and incubated for 30 min at 4°, centrifuged, exosome pellet was isolated and resuspended in PBS. Exosomes were then added to magnetic beads, incubated 18 h, then incubated with exosome-specific antibodies for 1 h. The resulting bead:exosome complexes were centrifuged and then washed, then washed again using a magnetic separator, resuspended in PBS, and analyzed via flow cytometry. Results: Using commercial magnetic beads bound with anti-CD63, our protocol modifies starting conditions, washing steps, and magnetic separation and uses the FSC and SSC determination of the flow cytometer to result in increased yield and identification of the exosome populations of interest. Our modified protocol increased the yield of specific populations approximately 10-fold. Conclusion: The new protocol was used to identify exosomes positive for 2 immune checkpoint ligands in serum-derived exosomes from cervical cancer patients. We suspect that this protocol can also be used for the identification of other exosome proteins since we also quantified the exosome membrane-enriched tetraspanins CD9 and CD81. Identification of proteins rarely expressed in exosomes is complicated in this technique as serum is an inherently dirty source of exosomes, and great care must be taken in the washing and gating of the exosome:bead populations.

Effect of Polymer Concentrations on Pores Mechanism in Electrospun Fibre

Advanced material science has resulted in materials with atomic-scale dimensions whose tremendous application includes filtration, drug delivery, membrane, sensor, and encapsulation. Nanoporous fibre has been formed using temperature-induced phase separation (TIPS) and vapour-induced phase separation (VIPS) mechanism, but polymer concentration has been underestimated in the electrospinning parameter. This work aims at showcasing the effect of electrospinning parameters including polymer concentration and resultant phases on pore formation on fibre. Pore formation in electrospun fibre was carried out by electrospinning expanded polystyrene (EPS). The surface morphology of the resulting nanoporous fibre was characterized with Scanning Electron Microscope (SEM) while the pore distribution was analyzed with a BET (Brunauer, Emmet, Teller) micromeritics analyzer. From the result, an increased concentration of polymer from 10 % decreased bead population to zero, meanwhile, bombardment with high electrostatic power resulted in beaded fibres at 10% and 15% w/v. Further increase in EPS concentration resulted in beadless fibres and electrospun 20% EPS fibre at 8.5 kV resulted in porous fibre with meso, micro and macropores. At 11.5 kV, pore dimension in fibre reduced with predominant pore width less than 100 nm. An increased voltage to 13.5 kV resulted in morphologies showing brittled fibre probably due to excess pores formed. Conclusively, polymer concentration moderates variables interaction that resulted in phase separation which controls fibre orientation. Therefore, pore formation does not solely depend on TIPS, VIPS, and breath figures but also polymer concentration.

Sources of Variability in the Response of Labeled Microspheres and B Cells during the Analysis by a Flow Cytometer.

A stochastic model of the flow cytometer measurement process was developed to assess the nature of the observed coefficient of variation (CV%) of the mean fluorescence intensity (MFI) from a population of labeled microspheres (beads). Several sources of variability were considered: the total number of labels on a bead, the path through the laser beam, the optical absorption cross-section, the quantum yield, the numerical aperture of the collection optics, and the photoelectron conversion efficiency of the photomultiplier (PMT) cathode. The variation in the number of labels on a bead had the largest effect on the CV% of the MFI of the bead population. The variation in the path of the bead through the laser beam was minimized using flat-top lasers. The variability in the average optical properties of the labels was of minor importance for beads with sufficiently large number of labels. The application of the bead results to the measured CV% of labeled B cells indicated that the measured CV% was a reliable measure of the variability of antibodies bound per cell. With some modifications, the model can be extended to multicolor flow cytometers and to the study of CV% from cells with low fluorescence signal.

Mechanical Compaction of Crustal Analogs Made of Sintered Glass Beads: The Influence of Porosity and Grain Size

AbstractThe fundamentals of our understanding of the mechanical compaction of porous rocks stem from experimental studies. Yet, many of these studies use natural materials for which microstructural parameters are intrinsically coupled, hampering the diagnosis of relationships between microstructure and bulk sample behavior. To probe the influence of porosity and grain size on the mechanical compaction of granular rocks, we performed experiments on synthetic samples prepared by sintering monodisperse populations of glass beads, which allowed us to independently control porosity and grain diameter. We conducted hydrostatic and triaxial compression tests on synthetic samples with grain diameters and porosities in the ranges 0.2–1.15 mm and 0.18–0.38 mm, respectively. During hydrostatic compaction, sample porosity decreased suddenly and substantially at the onset of inelastic compaction due to contemporaneous and extensive grain crushing, a consequence of the monodisperse grain size. During triaxial tests at high confining pressure, our synthetic samples failed by shear‐enhanced compaction and showed evidence for the development of compaction bands. Critical stresses at the onset of inelastic compaction map out linear‐shaped yield caps for the porosity‐grain diameter combinations for which the critical stress for inelastic hydrostatic compaction is known. Our yield caps reinforce the first‐order importance of porosity on the compactive yield strength and show, all else being equal, that grain size also exerts a first‐order control and should therefore be routinely measured. Our study further reveals the suitability of sintered glass beads as analogs for crustal rocks, which facilitate the study of the deconvolved influence of microstructural parameters on their mechanical behavior.

Extracellular Vesicles Surface Protein Profile as Biomarkers to Characterize Allograft Rejection in Heart Transplanted Patients

Purpose Circulating extracellular vesicles (EVs) are raising considerable interest as a non-invasive diagnostic tool.We aimed to investigate differences in plasma-derived EV surface protein profiles as a biomarker to be used in combination with endomyocardial biopsies (EMBs) for the diagnosis of allograft rejection. Methods Plasma was collected from 90 patients (53 training cohort, 37 validation cohort) before EMB. EV concentration was assessed by nanoparticle tracking analysis. EV surface antigens were measured using a multiplex flow cytometry assay composed of 37 fluorescently labeled capture bead populations coated with specific antibodies directed against respective EV surface epitopes. According to differential EV-markers expression two diagnostic model were built and validated through supervised learning algorithms (linear discriminant analysis-LDA- and random forest model- RF) Results The concentration of EVs was significantly increased and their diameter decreased in patients undergoing rejection as compared with negative ones. The trend was highly significant for both antibody-mediated rejection and acute cellular rejection (p Conclusion Circulating EVs are highly promising as a new tool to characterize cardiac allograft rejection and to be complementary to EMB monitoring

Morphological Manipulation of DNA Gel Microbeads with Biomolecular Stimuli.

Hydrogels are essential in many fields ranging from tissue engineering and drug delivery to food sciences or cosmetics. Hydrogels that respond to specific biomolecular stimuli such as DNA, mRNA, miRNA and small molecules are highly desirable from the perspective of medical applications, however interfacing classical hydrogels with nucleic acids is still challenging. Here were demonstrate the generation of microbeads of DNA hydrogels with droplet microfluidic, and their morphological actuation with DNA strands. Using strand displacement and the specificity of DNA base pairing, we selectively dissolved gel beads, and reversibly changed their size on-the-fly with controlled swelling and shrinking. Lastly, we performed a complex computing primitive—A Winner-Takes-All competition between two populations of gel beads. Overall, these results show that strand responsive DNA gels have tantalizing potentials to enhance and expand traditional hydrogels, in particular for applications in sequencing and drug delivery.

Quantification of Light Scattering Detection Efficiency and Background in Flow Cytometry.

Knowledge of the sensitivity of a flow cytometer is essential for data interpretation and comparison. However, light scatter sensitivity currently cannot be quantified due to a lack of a standardized unit. Analogous to the QB approach for fluorescence, we show that it is possible to derive the detection efficiency Q and background B for light scatter detectors, using the scattering cross section (σs) in nm2 as a standardized unit. Side scatter of a mixture of polystyrene beads with known diameter and refractive index was measured at different illumination powers on a customized BD FACSCanto. Poisson statistics was used to derive the number of statistical photoelectrons from the measured coefficient of variation of the bead populations. The resulting light scatter sensitivity was expressed as Q in photoelectrons/nm2, B in nm2, and a resolution limit (R) in nm2. As expected, Q scales linearly with the illumination power (R2 = 0.999), and B is constant over the illumination power (difference < 15%). The resulting R decreased from 1.75·105 nm2 at 20 mW, to 4.03·104 nm2 at 200 mW, which resembles the light scattering of a 450 nm and a 314 nm polystyrene bead, respectively. Comparison of R with the side scatter histograms confirmed that R describes the lower limit at which light scatter signals can be fully discriminated from the background noise. In conclusion, as a proof of principle, we derived Q, B, and R for a scatter detector of a flow cytometer where photon noise associated with the light scattering signal originating from the particle is the dominant source of the measured variation. To quantify the sensitivity of scatter detectors with nanoparticle (<100 nm) sensitivity, our approach requires monodisperse (variation coefficient < 2%) nanoparticles that scatter light isotropically. © 2020 The Authors. Cytometry Part A published by Wiley Periodicals LLC on behalf of International Society for Advancement of Cytometry.

Interpreting holographic molecular binding assays with effective medium theory.

Holographic molecular binding assays use holographic video microscopy to directly detect molecules binding to the surfaces of micrometer-scale colloidal beads by monitoring associated changes in the beads' light-scattering properties. Holograms of individual spheres are analyzed by fitting to a generative model based on the Lorenz-Mie theory of light scattering. Each fit yields an estimate of a probe bead's diameter and refractive index with sufficient precision to watch a population of beads grow as molecules bind. Rather than modeling the molecular-scale coating, however, these fits use effective medium theory, treating the coated sphere as if it were homogeneous. This effective-sphere analysis is rapid and numerically robust and so is useful for practical implementations of label-free immunoassays. Here, we assess how measured effective-sphere properties reflect the actual properties of molecular-scale coatings by modeling coated spheres with the discrete-dipole approximation and analyzing their holograms with the effective-sphere model.

Circulating extracellular vesicles as non-invasive biomarker of rejection in heart transplant

Circulating extracellular vesicles (EVs) are raising considerable interest as a non-invasive diagnostic tool, as they are easily detectable in biologic fluids and contain a specific set of nucleic acids, proteins, and lipids reflecting pathophysiologic conditions. We aimed to investigate differences in plasma-derived EV surface protein profiles as a biomarker to be used in combination with endomyocardial biopsies (EMBs) for the diagnosis of allograft rejection. Plasma was collected from 90 patients (53 training cohort, 37 validation cohort) before EMB. EV concentration was assessed by nanoparticle tracking analysis. EV surface antigens were measured using a multiplex flow cytometry assay composed of 37 fluorescently labeled capture bead populations coated with specific antibodies directed against respective EV surface epitopes. The concentration of EVs was significantly increased and their diameter decreased in patients undergoing rejection as compared with negative ones. The trend was highly significant for both antibody-mediated rejection and acute cellular rejection (p < 0.001). Among EV surface markers, CD3, CD2, ROR1, SSEA-4, human leukocyte antigen (HLA)-I, and CD41b were identified as discriminants between controls and acute cellular rejection, whereas HLA-II, CD326, CD19, CD25, CD20, ROR1, SSEA-4, HLA-I, and CD41b discriminated controls from patients with antibody-mediated rejection. Receiver operating characteristics curves confirmed a reliable diagnostic performance for each single marker (area under the curve range, 0.727-0.939). According to differential EV-marker expression, a diagnostic model was built and validated in an external cohort of patients. Our model was able to distinguish patients undergoing rejection from those without rejection. The accuracy at validation in an independent external cohort reached 86.5%. Its application for patient management has the potential to reduce the number of EMBs. Further studies in a higher number of patients are required to validate this approach for clinical purposes. Circulating EVs are highly promising as a new tool to characterize cardiac allograft rejection and to be complementary to EMB monitoring.

P1604SIGNIFICANT DETECTION OF UNEXPLAINED HLA ANTIBODIES WITH SINGLE-ANTIGEN BEADS IN PATIENTS ON THE WAITING-LIST WITHOUT PREVIOUS SENSITIZING EVENTS

Abstract Background and Aims The introduction of more sensitive and specific tools as solid phase immunoasssays has improved the ability to detect HLA antibodies. The techniques based on solid phase immunoassays in Luminex system can be performed either as screening assays (with pooled antigen panels that use bead populations coated in affinity-purified class I or class II HLA molecules) or to assess the specificity with single-antigen bead (SAB) assays (single cloned allelic HLA antigen).The sensitivity of each assay Is different, and their results may be discordant. Our objective was to evaluate the potential discrepancies between tests in a cohort of patients on our waiting list with no previous sensitizing events, for their potential influence in the access to transplantation. Method Observational study of 184 patients included in the kidney-transplant waiting list on March 31st, 2019. All possible sensitizing events (pregnancy, transfusion and previous transplants) were registered. HLA antibodies where analyzed both by screening and SAB tests. Results We limited the observations to males (64.7% of the cohort), as most women (95.4%) had a known sensitizing event, not being possible to discard possible pregnancies in the remaining. Of men, 46.2% had a sensitizing event and 63.8% did not. All 63 unsensitized patients showed a negative screening test, and 49 (77,78%) had at least one SAB done being positive in 73.4% (36/49). The positive SAB yielded a cPRA &amp;gt;10% in 30 cases (between 21-85%), mostly (27/30) due to HLA class II antibodies (88.8% with at least one DQ antibody) with a median MFI of 1571 (range:752-17650). A thorough review of specificities showed that 81% DQB1* and 89.6% DQA1* antibodies did not show consistency in all beads included for the same allele. Conclusion Screening and SAB assays show a significant discordancy in unsensitized men included in the waiting list for kidney transplantation. Automated detection of antibodies by SAB without a proper specialized interpretation may wrongly limit access to transplantation.

Rapid, multiplexed detection of biomolecules using electrically distinct hydrogel beads.

Rapid, low-cost, and multiplexed biomolecule detection is an important goal in the development of effective molecular diagnostics. Our recent work has demonstrated a microfluidic biochip device that can electrically quantitate a protein target with high sensitivity. This platform detects and quantifies a target analyte by counting and capturing micron-sized beads in response to an immunoassay on the bead surface. Existing microparticles limit the technique to the detection of a single protein target and lack the magnetic properties required for separation of the microparticles for direct measurements from whole blood. Here, we report new precisely engineered microparticles that achieve electrical multiplexing and adapt this platform for low-cost and label-free multiplexed electrical detection of biomolecules. Droplet microfluidic synthesis yielded highly-monodisperse populations of magnetic hydrogel beads (MHBs) with the necessary properties for multiplexing the electrical Coulter counting on chip. Each bead population was designed to contain a different amount of the hydrogel material, resulting in a unique electrical impedance signature during Coulter counting, thereby enabling unique identification of each bead. These monodisperse bead populations span a narrow range of sizes ensuring that all can be captured sensitively and selectively under simultaneously flow. Incorporating these newly synthesized beads, we demonstrate versatile and multiplexed biomolecule detection of proteins or DNA targets. This development of multiplexed beads for the electrical detection of biomolecules, provides a critical advancement towards multiplexing the Coulter counting approach and the development of a low cost point-of-care diagnostic sensor.

Rapid, High-Resolution Magnetic Microscopy of Single Magnetic Microbeads.

Magnetic microparticles or "beads" are used in a variety of research applications from cell sorting through to optical force traction microscopy. The magnetic properties of such particles can be tailored for specific applications with the uniformity of individual beads critical to their function. However, the majority of magnetic characterization techniques quantify the magnetic properties from large bead ensembles. Developing new magnetic imaging techniques to evaluate and visualize the magnetic fields from single beads will allow detailed insight into the magnetic uniformity, anisotropy, and alignment of magnetic domains. Here, diamond-based magnetic microscopy is applied to image and characterize individual magnetic beads with varying magnetic and structural properties: ferromagnetic and superparamagnetic/paramagnetic, shell (coated with magnetic material), and solid (magnetic material dispersed in matrix). The single-bead magnetic images identify irregularities in the magnetic profiles from individual bead populations. Magnetic simulations account for the varying magnetic profiles and allow to infer the magnetization of individual beads. Additionally, this work shows that the imaging technique can be adapted to achieve illumination-free tracking of magnetic beads, opening the possibility of tracking cell movements and mechanics in photosensitive contexts.

Magnetic Separation: A Trisymmetric Magnetic Microchip Surface for Free and Two‐Way Directional Movement of Magnetic Microbeads (Adv. Mater. Interfaces 22/2018)

The guidance of labelled microcarriers in microfluidic environments is vital for lab-on-chip technology. In article number 1801201, Umer Sajjad, Enno Lage and Jeffrey McCord realize the independent positioning and sorting of mixed populations of superparamagnetic beads across magnetic patterns for biodiagnostic applications. Using hexagonally arranged ferromagnetic elements, a flexible two-way separational motion of beads along spatial microcorridors is achieved.

Critical Evaluation of Microfluidic Resistive Pulse Sensing for Quantification and Sizing of Nanometer- and Micrometer-Sized Particles in Biopharmaceutical Products

The objective was to evaluate performance, strengths, and limitations of the microfluidic resistive pulse sensing (MRPS) technique for the characterization of particles in the size range from about 50 to 2000 nm. MRPS, resonant mass measurement (RMM), nanoparticle tracking analysis (NTA) and dynamic light scattering were compared for the analysis of nanometer-sized polystyrene (PS) beads, liposomes, bacteria, and protein aggregates. An electrical conductivity of at least 3 mS/cm (equivalent to 25 mM NaCl) was determined as a key requirement for reliable analysis with MRPS. Particle size distributions of PS beads determined by MRPS, NTA, and RMM correlated well. However, counting precision varied significantly among the techniques and was best for RMM followed by MRPS and NTA. As determined by measuring single and mixed PS bead populations, MRPS showed the highest peak resolution for sizing. RMM and MRPS were superior over dynamic light scattering and NTA for the characterization of stressed protein samples. Finally, MRPS proved to be the only analytical technique able to characterize both bacteria and liposomes. In conclusion, MRPS is an orthogonal technique alongside other established techniques for a comprehensive analysis of a samples particle size distribution and particle concentration.

Trapping, separating, and palpating microbead clusters in droplets and flows using capacitive micromachined ultrasonic transducers (CMUTs)

Bead-based assays are incredibly popular in clinical and pharmacological settings for detecting single or multiple analytes. Separating and trapping beads are often integral steps, especially when such assays are conducted in microfluidic environments. Here, we report a first instance of the use of a capacitive micromachined ultrasonic transducer (CMUT) microarray for acoustically trapping silica beads within droplets into discrete, well-formed, circular clusters. We then demonstrate that the expansion and contraction of these clusters may be regulated via adjustments to the CMUT driving frequency. To our knowledge, this palpating action of aggregates has not been reported in other non-contact techniques. Bead manipulations are also replicated in a microchannel against flows with fluid velocities of 1.9 ± 0.2 mm s−1. The laminar flow conditions are exploited to sequentially trap bead clusters or separate large populations of beads into discrete streams by operating the CMUT microarray at threshold voltages. Unlike piezoelectric materials, CMUTs offer superior miniaturization through well established microfabrication techniques, better acoustic matching to fluids, and lower risk of sample heating. Thus, we believe this work illustrates the versatility of CMUT microarrays for use in future bead-based assays in lab-on-a-chip (LOC) platforms.

The strengths and limitations of effective centroid force models explored by studying isotopic effects in liquid water.

The development of effective centroid potentials (ECPs) is explored with both the constrained-centroid and quasi-adiabatic force matching using liquid water as a test system. A trajectory integrated with the ECP is free of statistical noises that would be introduced when the centroid potential is approximated on the fly with a finite number of beads. With the reduced cost of ECP, challenging experimental properties can be studied in the spirit of centroid molecular dynamics. The experimental number density of H2O is 0.38% higher than that of D2O. With the ECP, the H2O number density is predicted to be 0.42% higher, when the dispersion term is not refit. After correction of finite size effects, the diffusion constant of H2O is found to be 21% higher than that of D2O, which is in good agreement with the 29.9% higher diffusivity for H2O observed experimentally. Although the ECP is also able to capture the redshifts of both the OH and OD stretching modes in liquid water, there are a number of properties that a classical simulation with the ECP will not be able to recover. For example, the heat capacities of H2O and D2O are predicted to be almost identical and higher than the experimental values. Such a failure is simply a result of not properly treating quantized vibrational energy levels when the trajectory is propagated with classical mechanics. Several limitations of the ECP based approach without bead population reconstruction are discussed.

Architecture for Directed Transport of Superparamagnetic Microbeads in a Magnetic Domain Wall Routing Network

Directed transport of biological species across the surface of a substrate is essential for realizing lab-on-chip technologies. Approaches that utilize localized magnetic fields to manipulate magnetic particles carrying biological entities are attractive owing to their sensitivity, selectivity, and minimally disruptive impact on biomaterials. Magnetic domain walls in magnetic tracks produce strong localized fields and can be used to capture, transport, and detect individual superparamagnetic microbeads. The dynamics of magnetic microbead transport by domain walls has been well studied. However, demonstration of more complex functions such as selective motion and sorting using continuously driven domain walls in contiguous magnetic tracks is lacking. Here, a junction architecture is introduced that allows for branching networks in which superparamagnetic microbeads can be routed along dynamically-selected paths by a combination of rotating in-plane field for translation, and a pulsed out-of-plane field for path selection. Moreover, experiments and modeling show that the select-field amplitude is bead-size dependent, which allows for digital sorting of multiple bead populations using automated field sequences. This work provides a simple means to implement complex routing networks and selective transport functionalities in chip-based devices using magnetic domain wall conduits.