Mobility measurements of immunomagnetically labeled cells allow quantitation of secondary antibody binding amplification

Simultaneous and Multimodal Antigen-Binding Profiling and Isolation of Rare Cells via Quantitative Ferrohydrodynamic Cell Separation

Simultaneous cell profiling and isolation based on cellular antigen-binding capacity plays an important role in understanding and treating diseases. However, fluorescence-activated cell sorting (FACS) and magnetic-activated cell sorting (MACS) are not able to meet this need, due to their requirement for a large quantity of target cells and the limitation stemming from bimodal separation. Here we report a microfluidic method, termed quantitative ferrohydrodynamic cell separation (qFCS), that achieved multimodal rare cell sorting and simultaneous antigen profiling at a ∼30,000 cell min^-1 throughput with a 96.49% recovery rate and a 98.72% purity of recovered cells. qFCS profiles and sorts cells via cellular magnetic content of the magnetically labeled cells, which correlates to cellular antigen-binding capacity. By integrating cellular magnetophoresis and diamagnetophoresis in biocompatible ferrofluids, we demonstrate that the resulting qFCS device can accurately profile and isolate rare cells even when present at ∼1:50,000 target to background cells frequency. We show that the qFCS device could accurately profile and isolate T lymphocytes based on a low-expression CD154 antigen and allow on-device analysis of cells after processing. This method could address the need for simultaneous and multimodal rare cell isolation and profiling in disease diagnostics, prognostics, and treatment.

Isolation Methods for Human CD34 Subsets Using Fluorescent and Magnetic Activated Cell Sorting: an In Vivo Comparative Study

INTRODUCTION

Acute myocardial infarction (AMI) and resulting cardiac damage and heart failure are leading causes of morbidity and mortality worldwide. Multiple studies have examined the utility of CD34⁺ cells for the treatment of acute and ischemic heart disease. However, the optimal strategy to enrich CD34 cells from clinical sources is not known. We examined the efficacy of fluorescence activated cell sorting (FACS) and magnetic beads cell sorting (MACS) methods for CD34 cell isolation from mobilized human mononuclear peripheral blood cells (mhPBMNCs).

METHODS

mhPBCs were processed following acquisition using FACS or MACS according to clinically established protocols. Cell viability, CD34 cell purity and characterization of surface marker expression were assessed using a flow cytometer. For in vivo characterization of cardiac repair, we conducted LAD ligation surgery on 8-10 weeks female NOD/SCID mice followed by intramyocardial transplantation of unselected mhPBMNCs, FACS or MACS enriched CD34⁺ cells.

RESULTS

Both MACS and FACS isolation methods achieved high purity rates, viability, and enrichment of CD34⁺ cells. In vivo studies following myocardial infarction demonstrated retention of CD34⁺ in the peri-infarct region for up to 30 days after transplantation. Retained CD34⁺ cells were associated with enhanced angiogenesis and reduced inflammation compared to unselected mhPBMNCs or PBS treatment arms. Cardiac scar and fibrosis as assessed by immunohistochemistry were reduced in FACS and MACS CD34⁺ treatment groups. Finally, reduced scar and augmented angiogenesis resulted in improved cardiac functional recovery, both on the global and regional function and remodeling assessments by echocardiography.

CONCLUSION

Cell based therapy using enriched CD34⁺ cells sorted by FACS or MACS result in better cardiac recovery after ischemic injury compared to unselected mhPBMNCs. Both enrichment techniques offer excellent recovery and purity and can be equally used for clinical applications.

Magnetic characterization of paramagnetic reagents by particle tracking velocimetry

Magnetic particle characterization determines the quality of magnetic particles and is of great importance in particle technology, drug delivery, cell separation, in vivo diagnostics, and other biomedical applications. The quality of the sample depends on the particle size, intrinsic magnetic properties of the particles, and the uniformity of these properties. A commercial particle tracking velocimeter was used to record and capture dark field images of particle trajectories in an applied isodynamic magnetic field. The calibrated particle size, magnetophoretic mobility, and additional image data were collected for each magnetic bead imaged. Using twenty-one different de-identified calibration beads and transmission electron microscopy to validate the vendor-reported particle size enabled the estimation of intrinsic magnetic properties, namely, apparent magnetic susceptibility and saturation magnetization, of individual paramagnetic particles. The distributions of volume magnetic susceptibility based on the magnetophoretic mobility and size of the particle for different magnetic beads were determined and displayed as two-parameter distributions. The measured apparent susceptibility and saturation magnetization were found to be directly proportional to the percentage of iron oxide in the reagent particles.

Ultrasmall, Bright, and Photostable Fluorescent Core-Shell Aluminosilicate Nanoparticles for Live-Cell Optical Super-Resolution Microscopy

Stochastic optical reconstruction microscopy (STORM) is an optical super-resolution microscopy (SRM) technique that traditionally requires toxic and non-physiological imaging buffers and setups that are not conducive to live-cell studies. It is observed that ultrasmall (<10 nm) fluorescent core-shell aluminosilicate nanoparticles (aC' dots) covalently encapsulating organic fluorophores enable STORM with a single excitation source and in a regular (non-toxic) imaging buffer. It is shown that fourfold coordinated aluminum is responsible for dye blinking, likely via photoinduced redox processes. It is demonstrated that this phenomenon is observed across different dye families leading to probes brighter and more photostable than the parent free dyes. Functionalization of aC' dots with antibodies allows targeted fixed cell STORM imaging. Finally, aC' dots enable live-cell STORM imaging providing quantitative measures of the size of intracellular vesicles and the number of particles per vesicle. The results suggest the emergence of a powerful ultrasmall, bright, and photostable optical SRM particle platform with characteristics relevant to clinical translation for the quantitative assessment of cellular structures and processes from live-cell imaging.

The Fabrication and Application Mechanism of Microfluidic Systems for High Throughput Biomedical Screening: A Review

Microfluidic systems have been widely explored based on microfluidic technology, and it has been widely used for biomedical screening. The key parts are the fabrication of the base scaffold, the construction of the matrix environment in the 3D system, and the application mechanism. In recent years, a variety of new materials have emerged, meanwhile, some new technologies have been developed. In this review, we highlight the properties of high throughput and the biomedical application of the microfluidic chip and focus on the recent progress of the fabrication and application mechanism. The emergence of various biocompatible materials has provided more available raw materials for microfluidic chips. The material is not confined to polydimethylsiloxane (PDMS) and the extracellular microenvironment is not limited by a natural matrix. The mechanism is also developed in diverse ways, including its special physical structure and external field effects, such as dielectrophoresis, magnetophoresis, and acoustophoresis. Furthermore, the cell/organ-based microfluidic system provides a new platform for drug screening due to imitating the anatomic and physiologic properties in vivo. Although microfluidic technology is currently mostly in the laboratory stage, it has great potential for commercial applications in the future.

A guide to integrating immunohistochemistry and chemical imaging

A ‘how-to’ guide for designing chemical imaging experiments using antibodies and immunohistochemistry.

Magnetically-responsive, multifunctional drug delivery nanoparticles for elastic matrix regenerative repair

Arresting or regressing growth of abdominal aortic aneurysms (AAAs), localized expansions of the abdominal aorta are contingent on inhibiting chronically overexpressed matrix metalloproteases (MMPs)-2 and -9 that disrupt elastic matrix within the aortic wall, concurrent with providing a stimulus to augmenting inherently poor auto-regeneration of these matrix structures. In a recent study we demonstrated that localized, controlled and sustained delivery of doxycycline (DOX; a tetracycline-based antibiotic) from poly(lactic-co-glycolic acid) nanoparticles (PLGA NPs), enhances elastic matrix deposition and MMP-inhibition at a fraction of the therapeutically effective oral dose. The surface functionalization of these NPs with cationic amphiphiles, which enhances their arterial uptake, was also shown to have pro-matrix regenerative and anti-MMP effects independent of the DOX. Based on the hypothesis that the incorporation of superparamagnetic iron oxide NPs (SPIONs) within these PLGA NPs would enhance their targetability to the AAA site under an applied external magnetic field, we sought to evaluate the functional effects of NPs co-encapsulating DOX and SPIONs (DOX-SPION NPs) on elastic matrix regeneration and MMP synthesis/activity in vitro within aneurysmal smooth muscle cell (EaRASMC) cultures. The DOX-SPION NPs were mobile under an applied external magnetic field, while enhancing elastic matrix deposition 1.5-2-fold and significantly inhibiting MMP-2 synthesis and MMP-2 and -9 activities, compared to NP-untreated control cultures. These results illustrate that the multifunctional benefits of NPs are maintained following SPION co-incorporation. Additionally, preliminary studies carried out demonstrated enhanced targetability of SPION-loaded NPs within proteolytically-disrupted porcine carotid arteries ex vivo, under the influence of an applied external magnetic field. Thus, this dual-agent loaded NP system proffers a potential non-surgical option for treating small growing AAAs, via controlled and sustained drug release from multifunctional, targetable nanocarriers.

STATEMENT OF SIGNIFICANCE

Proactive screening of high risk elderly patients now enables early detection of abdominal aortic aneurysms (AAAs). There are no established drug-based therapeutic alternatives to surgery for AAAs, which is unsuitable for many elderly patients, and none which can achieve restore disrupted and lost elastic matrix in the AAA wall, which is essential to achieve growth arrest or regression. We have developed a first generation design of polymer nanoparticles (NPs) for AAA tissue localized delivery of doxycycline, a modified tetracycline drug at low micromolar doses at which it provides both pro-elastogenic and anti-proteolytic benefits that can augment elastic matrix regenerative repair. The nanocarriers themselves are also uniquely chemically functionalized on their surface to also provide them pro-elastin-regenerative & anti-matrix degradative properties. To provide an active driving force for efficient uptake of intra-lumenally infused NPs to the AAA wall, in this work, we have rendered our polymer NPs mobile in an applied magnetic field via co-incorporation of super-paramagnetic iron oxide NPs. We demonstrate that such modifications significantly improve wall uptake of the NPs with no significant changes to their physical properties and regenerative benefits. Such NPs can potentially stimulate structural repair in the AAA wall following one time infusion to delay or prevent AAA growth to rupture. The therapy can provide a non-surgical treatment option for high risk AAA patients.

Magnetic fingerprints of rolling cells for quantitative flow cytometry in whole blood

Over the past 50 years, flow cytometry has had a profound impact on preclinical and clinical applications requiring single cell function information for counting, sub-typing and quantification of epitope expression. At the same time, the workflow complexity and high costs of such optical systems still limit flow cytometry applications to specialized laboratories. Here, we present a quantitative magnetic flow cytometer that incorporates in situ magnetophoretic cell focusing for highly accurate and reproducible rolling of the cellular targets over giant magnetoresistance sensing elements. Time-of-flight analysis is used to unveil quantitative single cell information contained in its magnetic fingerprint. Furthermore, we used erythrocytes as a biological model to validate our methodology with respect to precise analysis of the hydrodynamic cell diameter, quantification of binding capacity of immunomagnetic labels, and discrimination of cell morphology. The extracted time-of-flight information should enable point-of-care quantitative flow cytometry in whole blood for clinical applications, such as immunology and primary hemostasis.

Magnetically Responsive Bone Marrow Mesenchymal Stem Cell-Derived Smooth Muscle Cells Maintain Their Benefits to Augmenting Elastic Matrix Neoassembly

Abdominal aortic aneurysms (AAA) represent abnormal aortal expansions that result from chronic proteolytic breakdown of elastin and collagen fibers by matrix metalloproteases. Poor elastogenesis by adult vascular smooth muscle cells (SMCs) limits regenerative repair of elastic fibers, critical for AAA growth arrest. Toward overcoming these limitations, we recently demonstrated significant elastogenesis by bone marrow mesenchymal stem cell-derived SMCs (BM-SMCs) and their proelastogenesis and antiproteolytic effects on rat aneurysmal SMCs (EaRASMCs). We currently investigate the effects of super paramagnetic iron oxide nanoparticle (SPION) labeling of BM-SMCs, necessary to magnetically guide them to the AAA wall, on their functional benefits. Our results indicate that SPION-labeling is noncytotoxic and does not adversely impact the phenotype and elastogenesis by BM-SMCs. In addition, SPION-BM-SMCs showed no changes in the ability of the BM-SMCs to stimulate elastin regeneration and attenuate proteolytic activity by EaRASMCs. Together, our results are promising toward the utility of SPIONs for magnetic targeting of BM-SMCs for in situ AAA regenerative repair.

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.

Application of magnetic particle tracking velocimetry to quadrupole magnetic sorting of porcine pancreatic islets

Magnetic isolation is a promising method for separating and concentrating pancreatic islets of Langerhans for transplantation in Type 1 diabetes patients. We are developing a continuous magnetic islet sorter to overcome the restrictions of current purification methods that result in limited yield and viability. In Quadrupole Magnetic Sorting (QMS) islets are magnetized by infusing superparamagnetic microbeads into islets' vasculature via arteries that serve the pancreas. The performance of the islet sorter depends on the resulting speed of the islets in an applied magnetic field, a property known as magnetophoretic mobility. Essential to the design and successful operation of the QMS is a method to measure the magnetophoretic mobilities of magnetically infused islets. We have adapted a Magnetic Particle Tracking Velocimeter (MPTV) to measure the magnetophoretic mobility of particles up to 1,000 µm in diameter. Velocity measurements are performed in a well-characterized uniform magnetic energy gradient using video imaging followed by analysis of the video images with a computer algorithm that produces a histogram of absolute mobilities. MPTV was validated using magnetic agarose beads serving as islet surrogates and subjecting them to QMS. Mobility distributions of labeled porcine islets indicated that magnetized islets have sufficient mobility to be captured by the proposed sorting method, with this result confirmed in test isolations of magnetized islets.

Quantification of non-specific binding of magnetic micro- and nanoparticles using cell tracking velocimetry: Implication for magnetic cell separation and detection

The maturation of magnetic cell separation technology places increasing demands on magnetic cell separation performance. While a number of factors can cause sub-optimal performance, one of the major challenges can be non-specific binding of magnetic nano- or microparticles to non-targeted cells. Depending on the type of separation, this non-specific binding can have a negative effect on the final purity, the recovery of the targeted cells, or both. In this work, we quantitatively demonstrate that non-specific binding of magnetic nanoparticles can impart a magnetization to cells such that these cells can be retained in a separation column and thus negatively impact the purity of the final product and the recovery of the desired cells. Through experimental data and theoretical arguments, we demonstrate that the number of MACS magnetic particles needed to impart a magnetization that is sufficient to cause non-targeted cells to be retained in the column to be on the order of 500-1,000 nanoparticles. This number of non-specifically bound particles was demonstrated experimentally with an instrument, cell tracking velocimeter, CTV, and it is demonstrated that the sensitivity of the CTV instrument for Fe atoms contained in magnetic nanoparticles on the order of 1 x 10(-15) g/mL of Fe.

Development of multistage magnetic deposition microscopy

Magnetic deposition microscropy (MDM) combines magnetic deposition and optical analysis of magnetically tagged cells into a single platform. Our multistage MDM uses enclosed microfabricated channels and a magnet assembly comprising four zones in series. The enclosed channels alleviate the problem plaguing previous versions of MDM: scouring of the cell deposition layer by the air-liquid interface as the channel is drained. The four-zone magnet assembly was designed to maximize capture efficiency, and experiments yielded total capture efficiencies of >99% of fluorescent- and magnetically-labeled Jurkat cells at reasonable throughputs (10(3) cells/min). A digital image processing protocol was developed to measure the average pixel intensities of the deposited cells in different zones, indicative of the marker expression. Preliminary findings indicate that the multistage MDM may be suitable for depositing cells and particles in successive zones according to their magnetic properties (e.g., magnetic susceptibilities or magnetophoretic mobilities). The overall goal is to allow the screening of multiple disease conditions in a single platform.

An optimized immunomagnetic bead-based negative selection protocol for CD4 T-cell isolation from mouse lymph nodes and spleen

This study describes an immunomagnetic bead-based methodology for optimal purification of mouse CD4+ T cells. It reproducibly yields highly pure CD4+ T cells from mouse lymph nodes (95-99%) and spleen (93-96%) with no residual antigen-presenting cell (APC) function in the purified population. The recovery of the starting CD4+ T-cell population is consistently high ( > 70%) and many samples can be simultaneously processed in a short period of time. The key factors responsible for improved purity are combinations of monoclonal antibodies that were found, through trial and error, to yield T cells of maximal purity achievable by non-flow sort-based negative selection. These cocktails efficiently target unwanted cell subsets with antibodies against multiple surface markers expressed by non-CD4+ T cells. Because immunomagnetic bead-based protocols do not require the expensive and cumbersome processes required by flow sort-based purification, the methodology described here should find widespread use.

Analysis of ryanodine receptor clusters in rat and human cardiac myocytes

Single rat ventricular myocytes and human ventricle tissue sections were labeled with antibodies against the ryanodine receptor (RyR) and alpha-actinin to examine the 3D distribution of RyRs with confocal microscopy. Image contrast was maximized by refractive index matching and deconvolution. The RyR label formed discrete puncta representing clusters of RyRs or "couplons" around the edges of the myofilaments with a nearest-neighbor spacing of 0.66 +/- 0.06 microm in rat and 0.78 +/- 0.07 microm in human. Each bundle of myofibrils was served by approximately six couplons, which supplied a cross-sectional area of approximately 0.6 microm(2) in rat and approximately 0.8 microm(2) in human. Although the couplons were in reasonable registration with z-lines, there were discontinuities in the longitudinal position of sarcomeres so that dislocations in the order of RyR clusters occurred. There was approximately 53% longitudinal registration of RyR clusters, suggesting a nonrandom placement of couplons around the sarcomere. These data can explain the spherical propagation of Ca(2+) waves and provide quantitative 3D data sets needed for accurate modeling of cardiac Ca(2+)-induced Ca(2+) release. By quantifying labeling intensity in rat ventricular myocytes, a lower limit of 78 RyRs per cluster (on average) was obtained. By modeling the couplon as a disk wrapping around a t-tubule and fitting cluster images, 95% of couplons contained between 120 and 260 RyRs (assuming that RyRs are tight packed with a spacing of 29 nm). Assuming similar labeling efficiency in human, from the fluorescence intensity alone we estimate that human ventricular myocytes contain approximately 30% fewer RyRs per couplon than rat.

Blood progenitor cell separation from clinical leukapheresis product by magnetic nanoparticle binding and magnetophoresis

Positive selection of CD34+ blood progenitor cells from circulation has been reported to improve patient recovery in applications of autologous transplantation. Current magnetic separation methods rely on cell capture and release on solid supports rather than sorting from flowing suspensions, which limits the range of therapeutic applications and the process scale up. We tested CD34+ cell immunomagnetic labeling and isolation from fresh leukocyte fraction of peripheral blood (leukapheresis) using the continuous quadrupole magnetic flow sorter (QMS), consisting of a flow channel (SHOT, Greenville, IN) and a quadrupole magnet with a maximum field intensity (B(o)) of 1.42 T and a mean force field strength (S(m)) of 1.45 x 10(8) TA/m(2). Both the sample magnetophoretic mobility (m) and the inlet and outlet flow patterns highly affect the QMS performance. Seven commercial progenitor cell labeling reagent combinations were quantitatively evaluated by measuring magnetophoretic mobility of a high CD34 expression cell line, KG-1a, using the cell tracking velocimeter (CTV). The CD34 Progenitor Cell Isolation Kit (Miltenyi Biotec, Bergisch Gladbach, Germany) showed the strongest labeling of KG-1a cells and was selected for progenitor cell enrichment from 11 fresh and 11 cryopreserved clinical leukapheresis samples derived from different donors. The CD34+ cells were isolated with a purity of 60-96%, a recovery of 18-60%, an enrichment rate of 12-169, and a throughput of (1.7-9.3) x 10(4) cells/s. The results also showed a highly regular dependence of the QMS performance on the flow conditions that agreed with the theoretical predictions based on the CD34+ cell magnetophoretic mobility.

Droplet-based magnetically activated cell separation

In this study, we developed a method that target cells in suspension can be separated by combining magnetic force and gravitation force. Since the newly developed method involves a separating process of a droplet containing nontarget cells in suspension by applying magnetic force to separate target cells, we called it droplet-based magnetic activated cell sorting (dMACS). To demonstrate the efficiency of the dMACS system, Ter119 (+) cells from mouse bone marrow cells were separated by both conventional MACS and our dMACS systems. Effects of three parameters on separation efficiency were examined in the dMACS system. As a result, both volume of droplet of cell suspension, and magnetic force did not affect the efficiency of cell separation markedly. However, the time for cell settlement in the droplet showed a critical role in the efficiency of cell separation according to increasing time. Therefore, we tried to verify that the saturation time affected increase of its efficiency and that flow rate injected to get rid of the negative cell resulted in the decrease of its efficiency. Using this dMACS system, we were able to pinpoint that the flow rate of cell suspension injected into a magnetic platform results in disturbance in the droplet, leading to turbulence in the cell suspension.

Comparison of two immunomagnetic separation technologies to deplete T cells from human blood samples

The objective of this study was to compare the performance of two immunomagnetic separation technologies to deplete T cells from buffy coats of human blood. Specifically, two versions of the commercial MACS(R) Technology: MiniMACS and SuperMACS, and a prototype, flow-through system, the QMS, were evaluated. Peripheral blood mononuclear leukocytes (PBL) were isolated from buffy coats and an immunomagnetic separation of CD3(+) cells was conducted using company and optimized labeling protocols. To mimic peripheral blood containing bone marrow purged hematopoietic stem cells, HSC, CD34 expressing-cells (KG1a) were spiked into PBL prior to T-cell depletion once optimized depletion conditions were determined. Once the labeling protocol was optimized, the MiniMACS system performed well by producing a highly enriched CD3(+) fraction, and a respectable level of depletion of T cells and recovery of KG1a cells in the depleted fraction; an average log(10) depletion of T cells of 2.88 +/- 0.17 and an average recovery of the KG1a cells of 60.8 +/- 5.94% (n = 14). The performance of the SuperMACS system was very similar with an average log(10) depletion of T cells of 2.89 +/- 0.22 and an average recovery of KG1a of 63.1 +/- 8.55% (n = 10). In contrast, the QMS system produced an average log(10) depletion of T cells of 3.98 +/- 0.33 (n = 16) with a corresponding average recovery of 57.9 +/- 16.6% of the spiked CD34+ cells. The aforementioned QMS performance values were obtained using sorting speeds ranging from 2.5 x 10(4) to 1.7 x 10(5) cells per second. It is suggested that the lack of a 100% recovery of the unlabeled KG1a cells is the result of a previously reported "drafting" phenomena which pulls unlabeled cells in the direction of the magnetically labeled cells thereby resulting in loss of the unlabeled cells.

Establishment and implications of a characterization method for magnetic nanoparticle using cell tracking velocimetry and magnetic susceptibility modified solutions

Magnetic micro and nanoparticles conjugated to affinity labels have become a significant, commercial reagent. It has been demonstrated that the performance of cell separation systems using magnetic labels is a function of the magnitude of the magnetic force that can be generated through labeling. This magnetic force is proportional to the number of magnetic particles bound to the cell, the magnetic energy gradient, and the particle-field interaction parameter. This particle-field interaction parameter, which is the product of the relative volumetric, magnetic susceptibility and the volume of the micro or nanoparticle, is a fundamental parameter which can be used to characterize the magnetic particles. An experimental technique is presented which measures the volumetric magnetic susceptibility of particles through the use of susceptibility modified solutions and an experimental instrument, Cell Tracking Velocimetry, CTV. Experimental studies were conducted on polystyrene microspheres alone and those bound to four different magnetic nanoparticles. The experimentally determined values of the magnetic susceptibility of the polystyrene microspheres are consistent with values found from literature. Consequently, magnetic susceptibility measurements of these polystyrene microspheres bound with the magnetic nanoparticles combined with particle size measurements using commercial dynamic light scattering instrument allowed estimates of the particle-field interaction parameter to be made for four commercial, magnetic nanoparticles. The value found for MACS beads is close to what is reported from an independent study. The values for MACS beads and Imag beads are found to agree with what is observed from experiments. Finally, an experimental demonstration of the impact that differences in this field interaction parameter has on the labeling of human lymphocytes is presented.

Migration Analysis of Micro-Particles in Liquids Using Microscopically Designed External Fields

The recent development of new migration methods of micro-particles in liquids using various external fields is reviewed. The combination of a laser scattering force and a photothermal effect produced photothermal-conversion laser-photophoresis. A dielectric field generated in a planer or a capillary quadrupole electrode realized dielectrophoresis. Using a micrometer-scaled magnetic field gradient, the "Magnetophoretic velocimetry" of micro-particles was invented. Furthermore, the Lorentz force generated by combining an electric field and a magnetic field was utilized for electromagnetophoresis. These new methods were overlooked and the advantages in analytical use were discussed.

Magnetic Cell Separation: Characterization of Magnetophoretic Mobility

Magnetic cell separation has become a popular technique to enrich or deplete cells of interest from a heterogeneous cell population. One important aspect of magnetic cell separation is the degree to which a cell binds paramagnetic material. It is this paramagnetic material that imparts a positive magnetophoretic mobility to the target cell, thus allowing effective cell separation. A mathematical relationship has been developed to correlate magnetic labeling to the magnetophoretic mobility of an immunomagnetically labeled cell. Four parameters have been identified that significantly affect magnetophoretic mobility of an immunomagnetically labeled cell: the antibody binding capacity (ABC) of a cell population, the secondary antibody amplification (psi), the particle-magnetic field interaction parameter (DeltachiV(m)), and the cell diameter (D(c)). The ranges of these parameters are calculated and presented along with how the parameters affect the minimum and maximum range of magnetophoretic mobility. A detailed understanding of these parameters allows predictions of cellular magnetophoretic mobilities and provides control of cell mobility through selection of antibodies and magnetic particle conjugates.

Characterization of antibody binding to three cancer-related antigens using flow cytometry and cell tracking velocimetry

Proper antibody labeling is a fundamental step in the positive selection/isolation of rare cancer cells using immunomagnetic cell separation technology. Using either a two-step or single-step labeling protocol, we examined a combination of six different antibodies specific for three different antigens (epithelial specific antigen, epithelial membrane antigen, and HER-2/Neu) on two different breast cancer cell lines (HCC1954 and MCF-7). When a two-step labeling protocol was used (i.e., anti-surface marker-fluoroscein-isothiocyanate [FITC] [primary Ab], anti-FITC magnetic colloid [secondary Ab]) saturation of the primary antibody was determined using fluorescence intensity measurements from flow cytometry (FCM). The saturation of the secondary antibody (or saturation of a single-step labeling) was determined using magnetophoretic mobility measurements from cell tracking velocimetry (CTV). When the maximum magnetophoretic mobility was the primary objective, our results demonstrate that the quantities necessary for antibody saturation with respect to fluorescence intensity were generally higher than those recommended by the manufacturer. The results demonstrate that magnetophoretic mobility varies depending on the types of cell lines, primary antibodies, and concentration of secondary magnetic colloid-conjugated antibody. It is concluded that saturation studies are a vital preparatory step in any separation method involving antibody labeling, especially those that require the specificity of rare cell detection.