Immunomagnetic cell sorting--pushing the limits

Dielectrophoretic characterization of peroxidized retinal pigment epithelial cells as a model of age-related macular degeneration

BACKGROUND

Age-related macular degeneration (AMD) is a prevalent ocular pathology affecting mostly the elderly population. AMD is characterized by a progressive retinal pigment epithelial (RPE) cell degeneration, mainly caused by an impaired antioxidative defense. One of the AMD therapeutic procedures involves injecting healthy RPE cells into the subretinal space, necessitating pure, healthy RPE cell suspensions. This study aims to electrically characterize RPE cells to demonstrate a possibility using simulations to separate healthy RPE cells from a mixture of healthy/oxidized cells by dielectrophoresis.

METHODS

BPEI-1 rat RPE cells were exposed to hydrogen peroxide to create an in-vitro AMD cellular model. Cell viability was evaluated using various methods, including microscopic imaging, impedance-based real-time cell analysis, and the MTS assay. Healthy and oxidized cells were characterized by recording their dielectrophoretic spectra, and electric cell parameters (crossover frequency, membrane conductivity and permittivity, and cytoplasm conductivity) were computed. A COMSOL simulation was performed on a theoretical microfluidic-based dielectrophoretic separation chip using these parameters.

RESULTS

Increasing the hydrogen peroxide concentration shifted the first crossover frequency toward lower values, and the cell membrane permittivity progressively increased. These changes were attributed to progressive membrane peroxidation, as they were diminished when measured on cells treated with the antioxidant N-acetylcysteine. The changes in the crossover frequency were sufficient for the efficient separation of healthy cells, as demonstrated by simulations.

CONCLUSIONS

The study demonstrates that dielectrophoresis can be used to separate healthy RPE cells from oxidized ones based on their electrical properties. This method could be a viable approach for obtaining pure, healthy RPE cell suspensions for AMD therapeutic procedures.

Surface Modification of Polystyrene with Boronic Acid for Immunoaffinity-Based Cell Enrichment

Obtaining an enriched and phenotypically pure cell population from heterogeneous cell mixtures is important for diagnostics and biosensing. Existing techniques such as fluorescent-activated cell sorting (FACS) and magnetic-activated cell sorting (MACS) require preincubation with antibodies (Ab) and specialized equipment. Cell immunopanning removes the need for preincubation and can be done with no specialized equipment. The majority of the available antibody-mediated analyte capture techniques require a modification to the Abs for binding. In this work, no antibody modification is used because we take advantage of the carbohydrate chain in the Fc region of Ab. We use boronic acid as a cross-linker to bind the Ab to a modified surface. The process allows for functional orientation and cleavable binding of the Ab. In this study, we created an immunoaffinity matrix on polystyrene (PS), an inexpensive and ubiquitous plastic. We observed a 37% increase in Ab binding compared with that of a passive adsorption approach. The method also displayed a more consistent antibody binding with 17 times less variation in Ab loading among replicates than did the passive adsorption approach. Surface topography analysis revealed that a dextran coating reduced nonspecific antibody binding. Elemental analysis (XPS) was used to characterize the surface at different stages and showed that APBA molecules can bind upside-down on the surface. While upside-down antibodies likely remain functional, their elution behavior might differ from those bound in the desired way. Cell capture experiments show that the new surface has 43% better selectivity and 2.4-fold higher capture efficiency compared to a control surface of passively adsorbed Abs. This specific surface chemistry modification will allow the targeted capture of cells or analytes with the option of chemical detachment for further research and characterization.

Magnetic force-based cell manipulation for in vitro tissue engineering

Cell manipulation techniques such as those based on three-dimensional (3D) bioprinting and microfluidic systems have recently been developed to reconstruct complex 3D tissue structures in vitro. Compared to these technologies, magnetic force-based cell manipulation is a simpler, scaffold- and label-free method that minimally affects cell viability and can rapidly manipulate cells into 3D tissue constructs. As such, there is increasing interest in leveraging this technology for cell assembly in tissue engineering. Cell manipulation using magnetic forces primarily involves two key approaches. The first method, positive magnetophoresis, uses magnetic nanoparticles (MNPs) which are either attached to the cell surface or integrated within the cell. These MNPs enable the deliberate positioning of cells into designated configurations when an external magnetic field is applied. The second method, known as negative magnetophoresis, manipulates diamagnetic entities, such as cells, in a paramagnetic environment using an external magnetic field. Unlike the first method, this technique does not require the use of MNPs for cell manipulation. Instead, it leverages the magnetic field and the motion of paramagnetic agents like paramagnetic salts (Gadobutrol, MnCl2, etc.) to propel cells toward the field minimum, resulting in the assembly of cells into the desired geometrical arrangement. In this Review, we will first describe the major approaches used to assemble cells in vitro-3D bioprinting and microfluidics-based platforms-and then discuss the use of magnetic forces for cell manipulation. Finally, we will highlight recent research in which these magnetic force-based approaches have been applied and outline challenges to mature this technology for in vitro tissue engineering.

Aptamer-Based Traceless Multiplexed Cell Isolation Systems

In both biomedical research and clinical cell therapy manufacturing, there is a need for cell isolation systems that recover purified cells in the absence of any selection agent. Reported traceless cell isolation methods using engineered antigen-binding fragments or aptamers have been limited to processing a single cell type at a time. There remains an unmet need for cell isolation processes that rapidly sort multiple target cell types. Here, we utilized two aptamers along with their designated complementary strands (reversal agents) to tracelessly isolate two cell types from a mixed cell population with one aptamer-labeling step and two sequential cell elution steps with reversal agents. We engineered a CD71-binding aptamer (rvCD71apt) and a reversal agent pair to be used simultaneously with our previously reported traceless purification approach using the CD8 aptamer (rvCD8apt) and its reversal agent. We verified the compatibility of the two aptamer displacement mechanisms by flow cytometry and the feasibility of incorporating rvCD71apt with a magnetic solid state. We then combined rvCD71apt with rvCD8apt to isolate activated CD4⁺ T cells and resting CD8⁺ cells by eluting these target cells into separate fractions with orthogonal strand displacements. This is the first demonstration of isolating different cell types using two aptamers and reversal agents at the same time. Potentially, different or more aptamers can be included in this traceless multiplexed isolation system for diverse applications with a shortened operation time and a lower production cost.

Immunomagnetic microfluidic integrated system for potency-based multiple separation of heterogeneous stem cells with high throughput capabilities

Multipotent adult stem cells (MASCs) derived from Pluripotent stem cells (PSCs) have found widespread use in various applications, including regenerative therapy and drug screening. For these applications, highly pluripotent PSCs need to be selectively separated from those that show low pluripotency for reusage of PSCs, and MASCs need to be collected for further application. Herein, we developed immunomagnetic microfluidic integrated system (IM-MIS) for separation of stem cells depending on potency level. In this system, each stem cell was multiple-separated in microfluidics chip by magnetophoretic mobility of magnetic-activated cells based on the combination of two sizes of magnetic nanoparticles and two different antibodies. Magnetic particles had a difference in the degree of magnetization, and antibodies recognized potency-related surface markers. IM-MIS showed superior cell separation performance than FACS with high throughput (49.5%) in a short time (<15 min) isolate 1 × 10⁷ cells, and higher purity (92.1%) than MACS. IM-MIS had a cell viability of 89.1%, suggesting that IM-MIS had no effect on cell viability during isolation. Furthermore, IM-MIS did not affect the key characteristics of stem cells including its differentiation potency, phenotype, genotype, and karyotype. IM-MIS may offer a new platform for the development of multi-separation systems for diverse stem cell applications.

Immunomagnetic separation is a suitable method for electrophysiology and ion channel pharmacology studies on T cells

Ion channels play pivotal role in the physiological and pathological function of immune cells. As immune cells represent a functionally diverse population, subtype-specific functional studies, such as single-cell electrophysiology require proper subset identification and separation. Magnetic-activated cell sorting (MACS) techniques provide an alternative to fluorescence-activated cell sorting (FACS), however, the potential impact of MACS-related beads on the biophysical and pharmacological properties of the ion channels were not studied yet. We studied the aforementioned properties of the voltage-gated Kv1.3 K+ channel in activated CD4+ T-cells as well as the membrane capacitance using whole-cell patch-clamp following immunomagnetic positive separation, using the REAlease® kit. This kit allows three experimental configurations: bead-bound configuration, bead-free configuration following the removal of magnetic beads, and the label-free configuration following removal of CD4 recognizing antibody fragments. As controls, we used FACS separation as well as immunomagnetic negative selection. The membrane capacitance and of the biophysical parameters of Kv1.3 gating, voltage-dependence of steady-state activation and inactivation kinetics of the current were not affected by the presence of MACS-related compounds on the cell surface. We found subtle differences in the activation kinetics of the Kv1.3 current that could not be explained by the presence of MACS-related compounds. Neither the equilibrium block of Kv1.3 by TEA+ or charybdotoxin (ChTx) nor the kinetics of ChTx block are affected by the presence of the magnetics beads on the cell surface. Based on our results MACS is a suitable method to separate cells for studying ion channels in non-excitable cells, such as T-lymphocytes.

Microfluidics as efficient technology for the isolation and characterization of stem cells

The recent years have been passed with significant progressions in the utilization of microfluidic technologies for cellular investigations. The aim of microfluidics is to mimic small-scale body environment with features like optical transparency. Microfluidics can screen and monitor different cell types during culture and study cell function in response to stimuli in a fully controlled environment. No matter how the microfluidic environment is similar to in vivo environment, it is not possible to fully investigate stem cells behavior in response to stimuli during cell proliferation and differentiation. Researchers have used stem cells in different fields from fundamental researches to clinical applications. Many cells in the body possess particular functions, but stem cells do not have a specific task and can turn into almost any type of cells. Stem cells are undifferentiated cells with the ability of changing into specific cells that can be essential for the body. Researchers and physicians are interested in stem cells to use them in testing the function of the body's systems and solving their complications. This review discusses the recent advances in utilizing microfluidic techniques for the analysis of stem cells, and mentions the advantages and disadvantages of using microfluidic technology for stem cell research.

Interphase fluorescence in situ hybridization analysis of CD19-selected cells: Utility in detecting disease in post-therapy samples of B-cell neoplasms

Context

The detection of low‐level persistent or relapsed B‐cell neoplasms, particularly post‐therapy, can be challenging, often requiring multiple testing modalities.

Objective

Here we investigate the utility of CD19‐based selection of neoplastic B‐cells (CD19S) as an enrichment strategy to improve the detection rate of cytogenetic abnormalities in post‐therapy samples of B‐cell neoplasms, especially those with low‐level disease.

Design

In a cohort largely comprised of post‐therapy B‐ALL and CLL samples, we performed fluorescence in situ hybridization (FISH) analysis on CD19‐selected cells (CD19S FISH) in 128 specimens from 88 patients, and on non‐selected cells (NS FISH) in a subset of cases. The FISH findings were compared with the concurrent flow cytometry (FC) results in all samples and molecular analysis in a subset.

Results

CD19S FISH was able to detect cytogenetic aberrations in 86.0% of post‐therapy samples with evidence of disease as determined by routine or MRD FC, compared to 59.1% of samples by NS FISH. CD19S FISH detected significantly higher percentages of positive cells compared to NS FISH (p < 0.001). Importantly, CD19S FISH enabled the detection of emergent subclones (clonal evolution) associated with poor prognosis.

Conclusions

CD19S FISH can be useful in daily diagnostic practice. Compared to NS FISH, CD19S FISH is quantitatively and qualitatively superior for the detection of cytogenetic aberrations in B‐cell neoplasms, which are important for risk stratification and optimal management of patients with B‐cell neoplasms, especially in the relapsed setting. Although CD19S FISH has a diagnostic sensitivity inferior to that of MRD FC, the sensitivity of this modality is comparable to routine FC for the evaluation of low‐level disease in the post‐therapy setting. Moreover, CD19S samples are invaluable for additional molecular and genetic analyses.

Dielectrophoresis as a tool for electrophysiological characterization of stem cells

Dielectrophoresis (DEP), a nonlinear electrokinetic technique caused by Maxwell-Wagner interfacial polarization of neutral particles in an electrolyte solution, is a powerful cell manipulation method used widely for various applications such as enrichment, trapping, and sorting of heterogeneous cell populations. While conventional cell characterization and sorting methods require tagging or labeling of cells, DEP has the potential to manipulate cells in a label-free way. Due to its unique ability to characterize and sort cells without the need of labeling, there is renewed interest in using DEP for stem cell research and regenerative medicine. Stem cells have the potential to differentiate into various lineages, but achieving homogeneous cell phenotypes from an initially heterogeneous cell population is a challenge. Using DEP to efficiently and affordably identify, sort, and enrich either undifferentiated or differentiated stem cell populations in a label-free way would advance their potential uses for applications in tissue engineering and regenerative medicine. This review summarizes recent, significant research findings regarding the electrophysiological characterization of stem cells, with a focus on cellular dielectric properties, i.e., permittivity and conductivity, and on studies that have obtained these measurements using techniques that preserve cell viability, such as crossover frequency. Potential applications for DEP in regenerative medicine are also discussed. Overall, DEP is a promising technique and, when used to characterize, sort, and enrich stem cells, will advance stem cell-based regenerative therapies.

Past, Present, and Future of Affinity-based Cell Separation Technologies

Progress in cell purification technology is critical to increase the availability of viable cells for therapeutic, diagnostic, and research applications. A variety of techniques are now available for cell separation, ranging from non-affinity methods such as density gradient centrifugation, dielectrophoresis, and filtration, to affinity methods such as chromatography, two-phase partitioning, and magnetic-/fluorescence-assisted cell sorting. For clinical and analytical procedures that require highly purified cells, the choice of cell purification method is crucial, since every method offers a different balance between yield, purity, and bioactivity of the cell product. For most applications, the requisite purity is only achievable through affinity methods, owing to the high target specificity that they grant. In this review, we discuss past and current methods for developing cell-targeting affinity ligands and their application in cell purification, along with the benefits and challenges associated with different purification formats. We further present new technologies, like stimuli-responsive ligands and parallelized microfluidic devices, towards improving the viability and throughput of cell products for tissue engineering and regenerative medicine. Our comparative analysis provides guidance in the multifarious landscape of cell separation techniques and highlights new technologies that are poised to play a key role in the future of cell purification in clinical settings and the biotech industry. STATEMENT OF SIGNIFICANCE: Technologies for cell purification have served science, medicine, and industrial biotechnology and biomanufacturing for decades. This review presents a comprehensive survey of this field by highlighting the scope and relevance of all known methods for cell isolation, old and new alike. The first section covers the main classes of target cells and compares traditional non-affinity and affinity-based purification techniques, focusing on established ligands and chromatographic formats. The second section presents an excursus of affinity-based pseudo-chromatographic and non-chromatographic technologies, especially focusing on magnetic-activated cell sorting (MACS) and fluorescence-activated cell sorting (FACS). Finally, the third section presents an overview of new technologies and emerging trends, highlighting how the progress in chemical, material, and microfluidic sciences has opened new exciting avenues towards high-throughput and high-purity cell isolation processes. This review is designed to guide scientists and engineers in their choice of suitable cell purification techniques for research or bioprocessing needs.

Magnetic Force-Based Microfluidic Techniques for Cellular and Tissue Bioengineering

Live cell manipulation is an important biotechnological tool for cellular and tissue level bioengineering applications due to its capacity for guiding cells for separation, isolation, concentration, and patterning. Magnetic force-based cell manipulation methods offer several advantages, such as low adverse effects on cell viability and low interference with the cellular environment. Furthermore, magnetic-based operations can be readily combined with microfluidic principles by precisely allowing control over the spatiotemporal distribution of physical and chemical factors for cell manipulation. In this review, we present recent applications of magnetic force-based cell manipulation in cellular and tissue bioengineering with an emphasis on applications with microfluidic components. Following an introduction of the theoretical background of magnetic manipulation, components of magnetic force-based cell manipulation systems are described. Thereafter, different applications, including separation of certain cell fractions, enrichment of rare cells, and guidance of cells into specific macro- or micro-arrangements to mimic natural cell organization and function, are explained. Finally, we discuss the current challenges and limitations of magnetic cell manipulation technologies in microfluidic devices with an outlook on future developments in the field.

Serially Ordered Magnetization of Nanoclusters via Control of Various Transition Metal Dopants for the Multifractionation of Cells in Microfluidic Magnetophoresis Devices

A novel method (i.e., continuous magnetic cell separation in a microfluidic channel) is demonstrated to be capable of inducing multifractionation of mixed cell suspensions into multiple outlet fractions. Here, multicomponent cell separation is performed with three different distinguishable magnetic nanoclusters (MnFe2O4, Fe3O4, and CoFe2O4), which are tagged on A431 cells. Because of their mass magnetizations, which can be ideally altered by doping with magnetic atom compositions (Mn, Fe, and Co), the trajectories of cells with each magnetic nanocluster in a flow are shown to be distinct when dragged under the same external magnetic field; the rest of the magnetic characteristics of the nanoclusters are identically fixed. This proof of concept study, which utilizes the magnetization-controlled nanoclusters (NCs), suggests that precise and effective multifractionation is achievable with high-throughput and systematic accuracy for dynamic cell separation.

A Quantitative Perspective on Surface Marker Selection for the Isolation of Functional Tumor Cells

Much effort has gone into developing fluid biopsies of patient peripheral blood for the monitoring of metastatic cancers. One common approach is to isolate and analyze tumor cells in the peripheral blood. Widespread clinical implementation of this approach has been hindered by the current choice of targeting epithelial markers known to be highly variable in primary tumor sites. Here, we review current antigen-based tumor cell isolation strategies and offer biological context for commonly studied cancer surface markers. Expression levels of the most common markers are quantitated for three breast cancer and two non-small cell lung cancer (NSCLC) lineage models. These levels are contrasted with that present on healthy peripheral blood mononuclear cells (PBMC) for comparison to expected background levels in a fluid biopsy setting. A key feature of this work is establishing a metric of markers per square micrometer. This describes an average marker density on the cell membrane surface, which is a critical metric for emerging isolation strategies. These results serve to extend expression of key tumor markers in a sensitive and dynamic manner beyond traditional positive/negative immunohistochemical staining to guide future fluid biopsy targeting strategies.

Synthesis of multifunctional nanocomposites and their application in imaging and targeting tumor cells in vitro

The labeling of cells with nanomaterials for tumor detection is a very important part of various biomedical applications. In this study, multilayer nanocomposites were synthesized to achieve the multiple functions of fluorescence, magnetism, and bioaffinity. Firstly, superparamagnetic Fe3O4 nanoparticles were prepared as a magnetic core. Then, fluorescein isothiocyanate (FITC) was covalently linked to the surface of the silica-coated Fe3O4 core (designated FMNPs). Finally, bovine serum albumin (BSA) was conjugated onto the FMNPs (designated FMNPs-BSA). We also evaluated the feasibility and efficiency of labeling the human liver cancer cell line SMMC-7721 (SMMC-7721) with nanocomposites. SEM, hysteresis loop, EDS, FTIR, fluorescence spectra, and fluorescence microscopy were used to determine the physicochemical properties of nanocomposites. Fluorescence microscopy, SEM-EDS, and TEM were used to determine fluorescence labeling, absorption, and uptake respectively. The results showed that the nanocomposites obtained exhibited fine superparamagnetism, strong fluorescence, and good biological affinity. We succeeded in using the new multilayer nanocomposites to label cells, which had properties of magnetic targeting and fluorescent tracing.

Enriched Intestinal Stem Cell Seeding Improves the Architecture of Tissue-Engineered Intestine

OBJECTIVE

To develop a methodology to separate intestinal stem cell (ISC)-enriched crypts from differentiated epithelial cell (DEC)-containing villi to improve the morphology of tissue-engineered intestine (TEI).

METHODS

Small intestinal tissues from 5- to 7-day-old transgenic Lgr5-EGFP mice (with fluorescently labeled ISCs) were used to measure the height of villi and the depth of crypts. Based on the significant size difference between crypts and villi, a novel cell filtration system was developed. Filtration of mixed organoid units from full-thickness intestine of transgenic Lgr5-EGFP mice allowed determination of the percentage of ISCs in the different size-based filtration fractions obtained. In vivo, 5-7-day-old Lewis rat pups were used as cell donors to obtain purified crypts and villi, and the dams of the pups served as recipients. Flat and tubular polyglycolic acid (PGA) scaffolds were seeded with either ISC-enriched crypts or DEC-containing villi and implanted intra-abdominally on the anterior abdominal wall. After 1, 3, 7, 14, 21, and 28 days of in vivo incubation, explants were processed for histologic evaluation.

RESULTS

Small intestine from transgenic Lgr5-EGFP mice contained villi with an average height of 134.89±41.91 μm and crypts with an average depth of 49.59±8.95 μm. After filtration, we found that the 100-200 μm fractions contained relatively pure villi in which DECs were located, whereas the 25-70 μm range fractions contained concentrated crypts in which ISCs were located. In vivo, flat PGA scaffolds implanted with purified crypts formed well-developed mucosa by day 14 postimplantation, whereas flat scaffolds seeded with villi were replaced with fibrous tissue. Tubular scaffolds seeded with the crypt fraction developed a well-formed mucosal layer on the interior surface, with 80.9% circumferential mucosal engraftment and an average villous height of 478±65 μm, which was very close to native intestine (512±98 μm), whereas tubular scaffolds seeded with the villous fraction only had 21.7% circumferential mucosal engraftment and an average villous height of 243±78 μm.

CONCLUSION

The novel filtration system described can effectively and efficiently isolate ISC-containing crypts. TEI produced from ISC-containing crypts has an improved morphology that is similar to native intestine.

Fundamentals and application of magnetic particles in cell isolation and enrichment: a review

Magnetic sorting using magnetic beads has become a routine methodology for the separation of key cell populations from biological suspensions. Due to the inherent ability of magnets to provide forces at a distance, magnetic cell manipulation is now a standardized process step in numerous processes in tissue engineering, medicine, and in fundamental biological research. Herein we review the current status of magnetic particles to enable isolation and separation of cells, with a strong focus on the fundamental governing physical phenomena, properties and syntheses of magnetic particles and on current applications of magnet-based cell separation in laboratory and clinical settings. We highlight the contribution of cell separation to biomedical research and medicine and detail modern cell-separation methods (both magnetic and non-magnetic). In addition to a review of the current state-of-the-art in magnet-based cell sorting, we discuss current challenges and available opportunities for further research, development and commercialization of magnetic particle-based cell-separation systems.

Multi-shell structured fluorescent-magnetic nanoprobe for target cell imaging and on-chip sorting

In this paper, we have developed a core-triple-shell structured multi-functional nanoprobe Fe3O4/SiO2/CdSeTe@ZnS-SiO2/polydopamine with strong fluorescence and a fast magnetic response for specifically recognizing, fluorescently labeling, and magnetically sorting target tumor cells on a microfluidic chip. The outer polydopamine layer not only effectively alleviated the quenching effect of the interlayer quantum dots but also provided a convenient and versatile functional interface to readily conjugate with the recognizing model molecules of aptamer KH1C12 with amine, thiol, or carboxyl groups. Moreover, the polydopamine isolation and PEG decoration equipped the as-fabricated nanoprobes with little cytotoxicity and nonspecific affinity, leading to the effective and specific profiling of the protein epitopes expressed on the target tumor cells. Taking advantage of the magnetic property and specific recognition, the modified nanoprobe was utilized to label and isolate HL-60 cells from a homogeneous cell mixture of HL-60 and K562 cells on a microfluidic chip. Combining with the high throughput of the microfluidic chip, 1.0 × 10(4) HL-60 cells were readily separated from 2.0 × 10(4) cells in only 10 min with 98% separation efficiency, markedly improved in comparison with conventional strategies. This study presents an innovative strategy for developing highly integrated nanoprobes of strong fluorescence and magnetic controllability, opening up a promising probe-based avenue for biological imaging and separation.

Flow-cytometric analysis of rare antigen-specific T cells

The cytometric enumeration and characterization of antigen-specific lymphocytes, as introduced about 15 years ago, has contributed significantly to our understanding of adaptive immune responses in health and disease. Despite the development of several technologies, allowing to directly or indirectly analyze many aspects of lymphocyte specificity and function, several unresolved issues remain, due to the low frequency of certain antigen-specific lymphocyte subsets and the complexity of T cell antigen recognition. This is especially true for CD4(+) conventional as well as regulatory T cells, which bring major contributions to immune protection and pathology. Here we review the current technologies for the analysis of antigen specific T cells within the physiologic T cell repertoire and with a special focus on recent technologies addressing the analysis of rare antigen-specific T cell populations including naive and regulatory T cells.

Cholesterol loading and ultrastable protein interactions determine the level of tumor marker required for optimal isolation of cancer cells

Cell isolation via antibody-targeted magnetic beads is a powerful tool for research and clinical applications, most recently for isolating circulating tumor cells (CTC). Nonetheless fundamental features of the cell-bead interface are still unknown. Here we apply a clinically relevant antibody against the cancer target HER2 (ErbB2) for magnetic cell isolation. We investigate how many target proteins per cell are sufficient for a cell to be isolated. To understand the importance of primary antibody affinity, we compared a series of point mutants with known affinities and show that even starting with subnanomolar affinity, improving antibody affinity improved cell isolation. To test the importance of the connection between the primary antibody and the magnetic bead, we compared bridging the antibody to the beads with Protein L, secondary antibody, or streptavidin: the high-stability streptavidin-biotin linkage improved sensitivity by an order of magnitude. Cytoskeletal polymerization did not have a major effect on cell isolation, but isolation was inhibited by cholesterol depletion and enhanced by cholesterol loading of cells. Analyzing a panel of human cancer cell lines spanning a wide range of expression showed that the standard approach could only isolate the highest expressing cells. However, our optimization of cholesterol level, primary antibody affinity, and antibody-bead linkage allowed efficient and specific isolation of cells expressing low levels of HER2 or epithelial cell adhesion molecule. These insights should guide future approaches to cell isolation, either magnetically or using other means, and extend the range of cellular antigens and biomarkers that can be targeted for CTC isolation in cancer research and diagnosis.

Stem Cell Separation Technologies

Stem cell therapy and translational stem cell research require large-scale supply of stem cells at high purity and viability, thus leading to the development of stem cell separation technologies. This review covers key technologies being applied to stem cell separation, and also highlights exciting new approaches in this field. First, we will cover conventional separation methods that are commercially available and have been widely adapted. These methods include Fluorescence-activated cell sorting (FACS), Magnet-activated cell sorting (MACS), pre-plating, conditioned expansion media, density gradient centrifugation, field flow fractionation (FFF), and dielectrophoresis (DEP). Next, we will introduce emerging novel methods that are currently under development. These methods include improved aqueous two-phase system, systematic evolution of ligands by exponential enrichment (SELEX), and various types of microfluidic platforms. Finally, we will discuss the challenges and directions towards future breakthroughs for stem cell isolation. Advancing stem cell separation techniques will be essential for clinical and research applications of stem cells.

Cell separation by countercurrent centrifugal elutriation: recent developments

Countercurrent centrifugal elutriation (CCE) is a cell separation technique that separates particles predominantly according to their size, and to some degree according to their specific density, without a need for antibodies or ligands tagging cell surfaces. The principles of this technique have been known for half a century. Still, numerous recent publications confirmed that CCE is a valuable supplement to current cell separation technology. It is mainly applied when homogeneous populations of cells, which mirror an in vivo situation, are required for answering scientific questions or for clinical transplantation, while antibodies or ligands suitable for cell isolation are not available. Currently, new technical developments are expanding its application toward fractionation of healthy and malignant tissue cells and the preparation of dendritic cells for immunotherapy.

Clinically relevant microfluidic magnetophoretic isolation of rare-cell populations for diagnostic and therapeutic monitoring applications

Cells of biomedical interest are, despite their functional significance, often present in very small numbers. Therefore the analysis and isolation of previously inaccessible rare cells, such as peripheral hematopoietic stem cells, endothelial progenitor cells, or circulating tumor cells, require efficient, sensitive, and specific procedures that do not compromise the viability of the cells. The current study builds on previous work on a rationally designed microfluidic magnetophoretic cell separation platform capable of throughputs of 240 μL min(-1). Proof-of-concept was first conducted using MCF-7 (1-1000 total cells) as the target rare cell spiked into high concentrations of Raji B-lymphocyte nontarget cells (~10(6) total cells). These experiments lead to the establishment of a magnet-based separation for the isolation of 50 MCF-7 cells directly from whole blood. Results show an efficiency of collection greater than 85%, with a purity of over 90%. Next, resident endothelial progenitor cells and hematopoietic stem cells are directly isolated from whole human blood in a rapid and efficient fashion (>96%). Both cell populations could be simultaneously isolated and, via immunofluorescent staining, individually identified and enumerated. Overall, the presented device illustrates a viable separation platform for high purity, efficient, and rapid collection of rare cell populations directly from whole blood samples.

Individual organelle pH determinations of magnetically enriched endocytic organelles via laser-induced fluorescence detection

The analysis of biotransformations that occur in lysosomes and other endocytic organelles is critical to studies on intracellular degradation, nutrient recycling, and lysosomal storage disorders. Such analyses require bioactive organelle preparations that are devoid of other contaminating organelles. Commonly used differential centrifugation techniques produce impure fractions and may not be compatible with microscale separation platforms. Density gradient centrifugation procedures reduce the level of impurities but may compromise bioactivity. Here we report on simple magnetic setup and a procedure that produce highly enriched bioactive organelles based on their magnetic capture as they traveled through open tubes. Following capture, in-line laser-induced fluorecence detection (LIF) determined for the first time the pH of each magnetically retained individual endocytic organelle. Unlike bulk measurements, this method was suitable to describe the distributions of pH values in endocytic organelles from L6 rat myoblasts treated with dextran-coated iron oxide nanoparticles (for magnetic retention) and fluorescein/TMRM-conjugated dextran (for pH measurements by LIF). Their individual pH values ranged from 4 to 6, which is typical of bioactive endocytic organelles. These analytical procedures are of high relevance to evaluate lysosomal-related degradation pathways in aging, storage disorders, and drug development.

Target-specific capture enhances sensitivity of electrochemical detection of bacterial pathogens

We report the concentration and purification of bacterial 16S rRNA by the use of a biotinylated DNA target-specific capture (TSC) probe. For both cultivated bacterial and urine specimens from urinary tract infection patients, TSC resulted in a 5- to 8-fold improvement in the sensitivity of bacterial detection in a 16S rRNA electrochemical sensor assay.

Microfluidic technologies for synthetic biology

Microfluidic technologies have shown powerful abilities for reducing cost, time, and labor, and at the same time, for increasing accuracy, throughput, and performance in the analysis of biological and biochemical samples compared with the conventional, macroscale instruments. Synthetic biology is an emerging field of biology and has drawn much attraction due to its potential to create novel, functional biological parts and systems for special purposes. Since it is believed that the development of synthetic biology can be accelerated through the use of microfluidic technology, in this review work we focus our discussion on the latest microfluidic technologies that can provide unprecedented means in synthetic biology for dynamic profiling of gene expression/regulation with high resolution, highly sensitive on-chip and off-chip detection of metabolites, and whole-cell analysis.

Computational design optimization for microfluidic magnetophoresis

Current macro- and microfluidic approaches for the isolation of mammalian cells are limited in both efficiency and purity. In order to design a robust platform for the enumeration of a target cell population, high collection efficiencies are required. Additionally, the ability to isolate pure populations with minimal biological perturbation and efficient off-chip recovery will enable subcellular analyses of these cells for applications in personalized medicine. Here, a rational design approach for a simple and efficient device that isolates target cell populations via magnetic tagging is presented. In this work, two magnetophoretic microfluidic device designs are described, with optimized dimensions and operating conditions determined from a force balance equation that considers two dominant and opposing driving forces exerted on a magnetic-particle-tagged cell, namely, magnetic and viscous drag. Quantitative design criteria for an electromagnetic field displacement-based approach are presented, wherein target cells labeled with commercial magnetic microparticles flowing in a central sample stream are shifted laterally into a collection stream. Furthermore, the final device design is constrained to fit on standard rectangular glass coverslip (60 (L)×24 (W)×0.15 (H) mm(3)) to accommodate small sample volume and point-of-care design considerations. The anticipated performance of the device is examined via a parametric analysis of several key variables within the model. It is observed that minimal currents (<500 mA) are required to generate magnetic fields sufficient to separate cells from the sample streams flowing at rate as high as 7 ml∕h, comparable to the performance of current state-of-the-art magnet-activated cell sorting systems currently used in clinical settings. Experimental validation of the presented model illustrates that a device designed according to the derived rational optimization can effectively isolate (∼100%) a magnetic-particle-tagged cell population from a homogeneous suspension even in a low abundance. Overall, this design analysis provides a rational basis to select the operating conditions, including chamber and wire geometry, flow rates, and applied currents, for a magnetic-microfluidic cell separation device.

Preparation of anti-CD4 monoclonal antibody-conjugated magnetic poly(glycidyl methacrylate) particles and their application on CD4+ lymphocyte separation

Novel immunomagnetic particles have been prepared for separation of CD4(+) lymphocytes. The magnetic nanoparticles with a diameter of approximately 5-6 nm were first synthesized by co-precipitation from ferrous and ferric iron solutions and subsequently encapsulated with poly(glycidyl methacrylate) (PGMA) by precipitation polymerization. Monoclonal antibody specific to CD4 molecules expressed on CD4(+) lymphocytes was conjugated to the surface of magnetic PGMA particles through covalent bonding between epoxide functional groups on the particle surface and primary amine groups of the antibodies. The generated immunomagnetic particles have successfully separated CD4(+) lymphocytes from whole blood with over 95% purity. The results indicated that these particles can be employed for cell separation and provide a strong potential to be applied in various biomedical applications including diagnosis, and monitoring of human diseases.

Aptamer-based microfluidic device for enrichment, sorting, and detection of multiple cancer cells

The ability to diagnose cancer based on the detection of rare cancer cells in blood or other bodily fluids is a significant challenge. To address this challenge, we have developed a microfluidic device that can simultaneously sort, enrich, and then detect multiple types of cancer cells from a complex sample. The device, which is made from poly(dimethylsiloxane) (PDMS), implements cell-affinity chromatography based on the selective cell-capture of immobilized DNA-aptamers and yields a 135-fold enrichment of rare cells in a single run. This enrichment is achieved because the height of the channel is on the order of a cell diameter. The sorted cells grow at the comparable rate as cultured cells and are 96% pure based on flow cytometry determination. Thus, by using our aptamer based device, cell capture is achieved simply and inexpensively, with no sample pretreatment before cell analysis. Enrichment and detection of multiple rare cancer cells can be used to detect cancers at the early stages, diagnose metastatic relapse, stratify patients for therapeutic purposes, monitor response to drugs and therapies, track tumor progression, and gain a deeper understanding of the biology of circulating tumor cells (CTCs).

Shine a light: imaging the immune system

Intra vital microscopy and whole-body imaging promise to revolutionize how we study the immune system. They compel by the intrinsic beauty of the images obtained and the undeniable direct biological relevance of the observations. However, it is important to remember that in many cases, fundamental insights into the underlying biological processes have already been obtained using ex vivo reductionist approaches. Indeed, it is likely that with the advent of microfluidics, new and exciting avenues will open up for ex vivo experimentation. Here, we give a brief but comprehensive overview of the various imaging techniques available, their relative strengths and shortcomings and how these tools have been used to get us to where we are today. The challenge for the future will be to apply the most suitable technology and to integrate the findings across various imaging disciplines to build a unified, comprehensive "big picture" of the immune system.

Micropatterning of poly(dimethylsiloxane) using a photoresist lift-off technique for selective electrical insulation of microelectrode arrays

A poly(dimethylsiloxane) (PDMS) patterning method based on a photoresist lift-off technique to make an electrical insulation layer with selective openings is presented. The method enables creating PDMS patterns with small features and various thicknesses without any limitation in the designs and without the need for complicated processes or expensive equipments. Patterned PDMS layers were created by spin-coating liquid phase PDMS on top of a substrate having sacrificial photoresist patterns, followed by a photoresist lift-off process. The thickness of the patterned PDMS layers could be accurately controlled (6.5-24 µm) by adjusting processing parameters such as PDMS spin-coating speeds, PDMS dilution ratios, and sacrificial photoresist thicknesses. PDMS features as small as 15 µm were successfully patterned and the effects of each processing parameter on the final patterns were investigated. Electrical resistance tests between adjacent electrodes with and without the insulation layer showed that the patterned PDMS layer functions properly as an electrical insulation layer. Biocompatibility of the patterned PDMS layer was confirmed by culturing primary neuron cells on top of the layer for up to two weeks. An extensive neuronal network was successfully formed, showing that this PDMS patterning method can be applied to various biosensing microdevices. The utility of this fabrication method was further demonstrated by successfully creating a patterned electrical insulation layer on flexible substrates containing multi-electrode arrays.

Design, fabrication and demonstration of a magnetophoresis chamber with 25 output fractions

Our goal is to develop an instrument for parallel and multiplexed bioassay using magnetic labels. Toward this end we are developing a multi-outlet magnetophoresis instrument incorporating a fluidic flow chamber placed inside a magnetic field gradient. Magnetic microparticles are sorted by their magnetic moment for eventual use as biological labels based on magnetic signature.In this paper we concentrate on developments in our flow chamber fabrication methods that have allowed us to scale the number of sorting channels from 8 to 25. We present data for instrument performance and reproducibility of sorting.

Simulating the Embolization of Blood Vessels Using Magnetic Microparticles and Acupuncture Needle in a Magnetic Field

Computer models were developed to simulate the capture and subsequent deposition of magnetic microparticles (MMPs) in a blood vessel adjacent to a ferromagnetic wire (e.g., acupuncture needle) magnetized by a uniform external magnetic field. Process parameter conditions were obtained to enable optimal capture of MMPs into the deposit. It was found that the maximum capture distance of the MMPs was within 0.5-2.0 mm when the particles were superparamagnetic and had large size (>1.0 microm) and relative large flow rates (2.5-5.0 cm/s) as in a healthy artery. It was also found that the deposits were asymmetrical and that their size was between 1.0 and 2.0 mm. For the case of lower flow rates as can be found in a tumor (<1.0 mm/s) and using small magnetite particles (0.25-2.0 microm) the maximum capture distance was larger, ranging between approximately 0.5 and 6.4 mm, depending on the blood flow rate, the radius of wire, and particle clustering. The range of embolization (deposition) in this later case was between 0.5 and 5.9 mm. The potential of this technique to generate MMPs deposits to embolize blood vessels inhibiting the blood supply and thus facilitating necrosis of tumors located deep within the patient (3-7 cm) is discussed.

Universal cell labelling with anionic magnetic nanoparticles

Magnetic labelling of living cells creates opportunities for numerous biomedical applications, from individual cell manipulation to MRI tracking. Here we describe a non-specific labelling method based on anionic magnetic nanoparticles (AMNPs). These particles first adsorb electrostatically to the outer membrane before being internalized within endosomes. We compared the labelling mechanism, uptake efficiency and biocompatibility with 14 different cell types, including adult cells, progenitor cells, immune cells and tumour cells. A single model was found to describe cell/nanoparticle interactions and to predict uptake efficiency by all the cell types. The potential impact of the AMNP label on cell functions, in vitro and in vivo, is discussed according to cellular specificities. We also show that the same label provides sufficient magnetization for MRI detection and distal manipulation.

Microfluidic depletion of endothelial cells, smooth muscle cells, and fibroblasts from heterogeneous suspensions

Interactions between ligands and cell surface receptors can be exploited to design adhesion-based microfluidic cell separation systems. When ligands are immobilized on the microfluidic channel surfaces, the resulting cell capture devices offer the typical advantages of small sample volumes and low cost associated with microfluidic systems, with the added benefit of not requiring complex fabrication schemes or extensive operational infrastructure. Cell-ligand interactions can range from highly specific to highly non-specific. This paper describes the design of an adhesion-based microfluidic separation system that takes advantage of both types of interactions. A 3-stage system of microfluidic devices coated with the tetrapeptides arg-glu-asp-val (REDV), val-ala-pro-gly (VAPG), and arg-gly-asp-ser (RGDS) is utilized to deplete a heterogeneous suspension containing endothelial cells, smooth muscle cells, and fibroblasts. The ligand-coated channels together with a large surface area allow effective depletion of all three cell types in a stagewise manner.

Micro- and nanotechnology in cell separation

This review describes recent work in cell separation using micro- and nanoscale technologies. These devices offer several advantages over conventional, macroscale separation systems in terms of sample volumes, low cost, portability, and potential for integration with other analytical techniques. More importantly, and in the context of modern medicine, these technologies provide tools for point-of-care diagnostics, drug discovery, and chemical or biological agent detection. This review describes work in five broad categories of cell separation based on (1) size, (2) magnetic attraction, (3) fluorescence, (4) adhesion to surfaces, and (5) new emerging technologies. The examples in each category were selected to illustrate separation principles and technical solutions as well as challenges facing this rapidly emerging field.

Specific magnetic bead based capture of genomic DNA from clinical samples: application to the detection of group B streptococci in vaginal/anal swabs

BACKGROUND

Group B streptococci (GBS) are a leading cause of sepsis and meningitis in newborns. We previously developed a rapid diagnostic system for GBS detection from vaginal/anal samples obtained from pregnant women during delivery. To facilitate the adaptation of this method for point-of-care testing, we have developed a specific and efficient GBS DNA capture method that is compatible with both PCR and nonamplification detection technologies.

METHODS

Superparamagnetic beads were functionalized with oligonucleotide capture probes of different lengths and used to capture GBS genomic DNA (gDNA). A rapid extraction procedure was used to provide DNA from GBS cultures or vaginal/anal samples with added GBS. Hybridization reactions consisting of functionalized beads and target DNA in 30 muL of hybridization buffer were performed for 1 h at room temperature, followed by washing and resuspension in water. Captured DNA was then detected using quantitative PCR.

RESULTS

A 25-mer capture probe allowed detection of 1000 genome copies of purified GBS DNA. The ability to detect GBS was improved by use of a 50-mer (100 copies) and a 70-mer capture probe (10 copies). Detection of approximately 1250 CFU/mL was achieved for diluted GBS broth culture and for vaginal/anal swab samples with added GBS.

CONCLUSION

Oligonucleotide-functionalized superparamagnetic microbeads efficiently capture GBS gDNA from both bacterial cultures and vaginal/anal samples with added GBS. Efficiency of gDNA capture increases with oligonucleotide length. This technology could be combined with sample preparation and detection technologies in a microfluidic system to allow point-of-care testing for GBS.

Intracellular heating of living cells through Néel relaxation of magnetic nanoparticles

Maghemite and cobalt ferrite anionic magnetic nanoparticles enter tumor cells and can be used as heat sources when exposed to a high-frequency magnetic field. Comparative studies of the two particles enable to unravel the magnetic heating mechanisms (Néel relaxation vs. Brown relaxation) responsible for the cellular temperature rise, and also to establish a simple model, adjusted to the experimental results, allowing to predict the intracellular heating efficiency of iron oxide nanoparticles. Hence, we are able to derive the best nanoparticle design for a given material with a view to intracellular hyperthermia-based applications.

Peptide-mediated selective adhesion of smooth muscle and endothelial cells in microfluidic shear flow

Microfluidic devices have recently emerged as effective tools for cell separation compared to traditional techniques. These devices offer the advantages of small sample volumes, low cost, and high purity. Adhesion-based separation of cells from heterogeneous suspensions can be achieved by taking advantage of specific ligand-receptor interactions. The peptide sequences Arg-Glu-Asp-Val (REDV) and Val-Ala-Pro-Gly (VAPG) are known to bind preferentially to endothelial cells (ECs) and smooth muscle cells (SMCs), respectively. This article examines the roles of REDV and VAPG and fluid shear stress in achieving selective capture of ECs and SMCs in microfluidic devices. The adhesion of ECs in REDV-coated devices and SMCs in VAPG-coated devices increases significantly compared to that of the nontargeted cells with decreasing shear stress. Furthermore, the adhesion of these cells is shown to be independent of whether these cells flow through the devices as suspensions of only one cell type or as a heterogeneous suspension containing ECs, SMCs, and fibroblasts. Whereas the overall adhesion of cells in the devices is determined mainly by shear stress, the selectivity of adhesion depends on the type of peptide and on the device surface as well as on the shear stress.

Binding affinities/avidities of antibody-antigen interactions: quantification and scale-up implications

Bioaffinity interactions have been, and continue to be, successfully adapted from nature for use in separation and detection applications. It has been previously reported that the magnetophoretic mobility of labeled cells show a saturation type phenomenon as a function of the concentration of the free antibody-magnetic nanoparticle conjugate which is consistent with other reports of antibody-fluorophore binding. Starting with the standard antibody-antigen relationship, a model was developed which takes into consideration multi-valence interactions, and various attributes of flow cytometry (FCM) and cell tracking velocimetry (CTV) measurements to determine both the apparent dissociation constant and the antibody-binding capacity (ABC) of a cell. This model was then evaluated on peripheral blood lymphocytes (PBLs) labeled with anti CD3 antibodies conjugated to FITC, PE, or DM (magnetic nanoparticles). Reasonable agreements between the model and the experiments were obtained. In addition, estimates of the limitation of the number of magnetic nanoparticles that can bind to a cell as a result of steric hinderance was consistent with measured values of magnetophoretic mobility. Finally, a scale-up model was proposed and tested which predicts the amount of antibody conjugates needed to achieve a given level of saturation as the total number of cells reaches 10(10), the number of cells needed for certain clinical applications, such as T-cell depletions for mismatched bone marrow transplants.

An instrument for sorting of magnetic microparticles in a magnetic field gradient

BACKGROUND

The goal of our bioassay technique is to demonstrate high throughput, highly parallel, and high sensitivity quantitative molecular analysis that will expand current biomedical research capabilities. To this end, we have built and characterized a magnetophoresis instrument using a flow chamber in a magnetic field gradient to sort magnetic microparticles by their magnetic moment for eventual use as biological labels.

METHODS

The flow chamber consists of a sample inlet, differential sheath streams, and eight outlets for collecting the microparticles after they have traversed the chamber. Magnetic microparticles are injected into the flow chamber that is positioned in a linear magnetic field gradient. The trajectory for each microparticle is determined by its total magnetic moment and size. The resulting populations of monodispersed magnetic microparticles in the different outlet bins are sorted by their magnetic moment; with the highest magnetic moments being deflected the furthest.

RESULTS

We have characterized the system for sorting both superparamagnetic and ferromagnetic microparticles with approximate diameters of 8 microm and 4.0-4.9 microm, respectively. To characterize the instrument, we used microparticles with a known size distribution and varied the transit time through the chamber. This is equivalent to varying the magnetic moment, while allowing us to hold the particle properties constant from run-to-run. We demonstrated the ability to reproducibly change the distribution of the particles in the collection bins by varying transit time in good agreement with theory. We identified hydrodynamic instabilities responsible for causing dispersion in the flow. Improvements to the flow chamber hydrodynamics such as reducing the aspect ratio between the sample inlet and the chamber depth and stabilizing the sheath flow resulted in narrow sorting distributions. We measured a sorting reproducibility (percentage of particles returning to their original bin upon resorting individual populations) of 84-89%.

CONCLUSIONS

We have developed a simple magnetophoresis system for reproducibly sorting magnetic microparticles. This technique will permit the use of microparticles with a wide range of magnetic moments to create a wide range of magnetic labels. Careful consideration of system design and operational parameters enables reliable and reproducible sorting of microparticles with varying size and magnetic content.

Continuous sorting of magnetic cells via on-chip free-flow magnetophoresis

The ability to separate living cells is an essential aspect of cell research. Magnetic cell separation methods are among some of the most efficient methods for bulk cell separation. With the development of microfluidic platforms within the biotechnology sector, the design of miniaturised magnetic cell sorters is desirable. Here, we report the continuous sorting of cells loaded with magnetic nanoparticles in a microfluidic magnetic separation device. Cells were passed through a microfluidic chamber and were deflected from the direction of flow by means of a magnetic field. Two types of cells were studied, mouse macrophages and human ovarian cancer cells (HeLa cells). The deflection was dependent on the magnetic moment and size of the cells as well as on the applied flow rate. The experimentally observed deflection matched well with calculations. Furthermore, the separation of magnetic and non-magnetic cells was demonstrated using the same microfluidic device.

Magnetically and biologically active bead-patterned hydrogels

We present a new approach to the direct patterning of biologically and magnetically active microbeads in nonbiofouling polymer scaffolds for use in microfluidic devices. Briefly, the process involves treatment of a glass substrate, conformal contact bonding of a PDMS microchannel on the substrate, filling of the channel with beads and prepolymer solution, and UV-initiated photopolymerization of a mask-defined pattern using a standard inverted microscope. This versatile and simple method allows for the rapid fabrication of dispersed or packed bead patterns in poly(ethylene glycol) (PEG) hydrogels that are covalently linked to glass surfaces. By exploiting the relative opacity of the microbeads used, we are able to create both partially exposed and fully encapsulated bead patterns. To demonstrate the utility of this new technology, we separated magnetic bead-bound B lymphocytes from T lymphocytes on a PEG-encapsulated magnetic filtration platform and also captured B cells directly on patterned, protein-decorated beads in a flow-through microfluidic device. Beyond cell sorting, the accurate patterning of industrially standardized, chemically diverse microbeads may have significant implications for microchip-based analyte detection.

Enrichment using antibody-coated microfluidic chambers in shear flow: model mixtures of human lymphocytes

Isolation of phenotypically-pure cell subpopulations from heterogeneous cell mixtures such as blood is a difficult yet fundamentally important task. Current techniques such as fluorescent activated cell sorting (FACS) and magnetic-activated cell sorting (MACS) require pre-incubation with antibodies which lead to processing times of at least 15-60 min. In this study, we explored the use of antibody-coated microfluidic chambers to negative deplete undesired cell types, thus obtaining an enriched cell subpopulation at the outlet. We used human lymphocyte cell lines, MOLT-3 and Raji, as a model system to examine the dynamic cell binding behavior on antibody coated surfaces under shear flow. Shear stress ranging between 0.75 and 1.0 dyn/cm2 was found to provide most efficient separation. Cell adhesion was shown to follow pseudo-first order kinetics, and an anti-CD19 coated (Raji-depletion) device with approximately 2.6 min residence time was demonstrated to produce 100% pure MOLT-3 cells from 50-50 MOLT-3/Raji mixture. We have developed a mathematical model of the separation device based on the experimentally determined kinetic parameters that can be extended to design future separation modules for other cell mixtures. We conclude that we can design microfluidic devices that exploits the kinetics of dynamic cell adhesion to antibody coated surfaces to provide enriched cell subpopulations within minutes of total processing time.