Microfluidic immunomagnetic cell separation from whole blood

Microfluidic System Consisting of a Magnetic 3D-Printed Microchannel Filter for Isolation and Enrichment of Circulating Tumor Cells Targeted by Anti-HER2/MOF@Ferrite Core-Shell Nanostructures: A Theranostic CTC Dialysis System

Low number of circulating tumor cells (CTCs) in the blood samples and time-consuming properties of the current CTC isolation methods for processing a small volume of blood are the biggest obstacles to CTC usage in practice. Therefore, we aimed to design a CTC dialysis system with the ability to process cancer patients' whole blood within a reasonable time. Two strategies were employed for developing this dialysis setup, including (i) synthesizing novel in situ core-shell Cu ferrites consisting of the Cu-CuFe2O4 core and the MIL-88A shell, which are targeted by the anti-HER2 antibody for the efficient targeting and trapping of CTCs; and (ii) fabricating a microfluidic system containing a three-dimensional (3D)-printed microchannel filter composed of a polycaprolactone/Fe3O4 nanoparticle composite with pore diameter less than 200 μm on which a high-voltage magnetic field is focused to enrich and isolate the magnetic nanoparticle-targeted CTCs from a large volume of blood. The system was assessed in different aspects including capturing the efficacy of the magnetic nanoparticles, CTC enrichment and isolation from large volumes of human blood, side effects on blood cells, and the viability of CTCs after isolation for further analysis. Under the optimized conditions, the CTC dialysis system exhibited more than 80% efficacy in the isolation of CTCs from blood samples. The isolated CTCs were viable and were able to proliferate. Moreover, the CTC dialysis system was safe and did not cause side effects on normal blood cells. Taken together, the designed CTC dialysis system can process a high volume of blood for efficient dual diagnostic and therapeutic purposes.

Fully Integrated Microfluidic Device for Magnetic Bead Manipulation to Assist Rapid Reaction and Cleaning

Methods to manipulate magnetic beads are essential factors to determine the efficiency and dimension of an in vitro diagnostic system. Currently, using movable permanent magnets and planar electromagnets is still the major approach to achieve magnetic bead control, causing significant constraint in the miniaturization of in vitro diagnostic systems. Here, we propose techniques to construct a fully integrated microfluidic device that can conduct automatic magnetic bead manipulation as well as rapid chemical reaction and cleaning in a minimized dimension similar to a USB disk. The device combines the precision control of multiple electromagnetic coils with the compactness of microfluidic channels, leading to one of the smallest automatic magnetic bead manipulation systems that can complete several major magnetic bead-based operation steps such as sample injection, reaction, cleaning, and collection. The influencing factors such as coil driving parameters, surface treatment of the microchannels, and properties of magnetic particles have also been investigated to optimize the device performance. The device can drive mixtures of Fe3O4 microparticles and polymer magnetic beads (PMBs) with a weight ratio of 1:1 at a maximum speed of 0.5 cm·s-1 and reduce the time for DNA binding and dissociation reactions from 20 min to only 48 s. This device has significantly advanced the conventional manipulation methods of magnetic beads and has demonstrated the possibility to construct an automatic and ultraminiaturized in vitro diagnostic system that may facilitate portable or even wearable chemical analysis.

Microfluidic pumps for cell sorting

Microfluidic cell sorting has shown promising advantages over traditional bulky cell sorting equipment and has demonstrated wide-reaching applications in biological research and medical diagnostics. The most important characteristics of a microfluidic cell sorter are its throughput, ease of use, and integration of peripheral equipment onto the chip itself. In this review, we discuss the six most common methods for pumping fluid samples in microfluidic cell sorting devices, present their advantages and drawbacks, and discuss notable examples of their use. Syringe pumps are the most commonly used method for fluid actuation in microfluidic devices because they are easily accessible but they are typically too bulky for portable applications, and they may produce unfavorable flow characteristics. Peristaltic pumps, both on- and off-chip, can produce reversible flow but they suffer from pulsatile flow characteristics, which may not be preferable in many scenarios. Gravity-driven pumping, and similarly hydrostatic pumping, require no energy input but generally produce low throughputs. Centrifugal flow is used to sort cells on the basis of size or density but requires a large external rotor to produce centrifugal force. Electroosmotic pumping is appealing because of its compact size but the high voltages required for fluid flow may be incompatible with live cells. Emerging methods with potential for applications in cell sorting are also discussed. In the future, microfluidic cell sorting methods will trend toward highly integrated systems with high throughputs and low sample volume requirements.

Combination of filtration and immunomagnetic separation based on real-time PCR to detect foodborne pathogens in fresh-cut apple

Rapid detection methods require pre-enrichment culture in order to detect low levels of foodborne pathogens. To rapidly detect foodborne pathogens, enrichment culture processes could be replaced. Filtration and immunomagnetic separation methods have been identified to effectively concentrate and separate target pathogens from foods. In this study, a combination of filtration and immunomagnetic separation (IMS) has enabled the rapid and sensitive detection of foodborne pathogens. The pretreatment method, including separation and concentration procedures, increased sensitivity 10-100-fold. The sensitivity of a combination method using filtration and IMS to detect Escherichia coli O157:H7 and Salmonella enterica subsp. enterica serovar Typhimurium was 10⁰-10¹ CFU/10 mL. In fresh-cut apples, IMS combined with filtration effectively improved the detection limit of real-time PCR to 2.70 × 10¹ CFU/g in E. coli O157:H7 and 1.80 × 10² CFU/g in Salmonella. The filtration simplified processing of large-volumes (250 mL) and effectively concentrated pathogens while decreasing immunomagnetic beads used in IMS. Bacterial concentration by IMS combined with filtration increased sensitivity 10-100-fold compared with control. In addition, the application of IMS effectively removed concentrated residual food material (10-15 mg/mL) after filtration, improving relative sensitivity. In conclusion, this method may detect foodborne pathogen in foods such as fresh-cut fruits in a more rapid and sensitive fashion than traditional culture-based methods.

A pump-free microfluidic device for fast magnetic labeling of ischemic stroke biomarkers

This research proposes a low-cost and simple operation microfluidic chip to enhance the magnetic labeling efficiency of two ischemic stroke biomarkers: cellular fibronectin (c-Fn) and matrix metallopeptidase 9 (MMP9). This fully portable and pump-free microfluidic chip is operated based on capillary attractions without any external power source and battery. It uses an integrated cellulose sponge to absorb the samples. At the same time, a magnetic field is aligned to hold the target labeled by the magnetic nanoparticles (MNPs) in the pre-concentrated chamber. By using this approach, the specific targets are labeled from the beginning of the sampling process without preliminary sample purification. The proposed study enhanced the labeling efficiency from 1 h to 15 min. The dynamic interactions occur in the serpentine channel, while the crescent formation of MNPs in the pre-concentrated chamber, acting as a magnetic filter, improves the biomarker-MNP interaction. The labeling optimization by the proposed device influences the dynamic range by optimizing the MNP ratio to fit the linear range across the clinical cutoff value. The limits of detection (LODs) of 2.8 ng/mL and 54.6 ng/mL of c-Fn measurement were achieved for undiluted and four times dilutions of MNP, respectively. While for MMP9, the LODs were 11.5 ng/mL for undiluted functionalized MNP and 132 ng/mL for four times dilutions of functionalized MNP. The results highlight the potential use of this device for clinical sample preparation and specific magnetic target labeling. When combined with a detection system, it could also be used as an integrated component of a point-of-care platform.

Basic Principles and Recent Advances in Magnetic Cell Separation

Magnetic cell separation has become a key methodology for the isolation of target cell populations from biological suspensions, covering a wide spectrum of applications from diagnosis and therapy in biomedicine to environmental applications or fundamental research in biology. There now exists a great variety of commercially available separation instruments and reagents, which has permitted rapid dissemination of the technology. However, there is still an increasing demand for new tools and protocols which provide improved selectivity, yield and sensitivity of the separation process while reducing cost and providing a faster response. This review aims to introduce basic principles of magnetic cell separation for the neophyte, while giving an overview of recent research in the field, from the development of new cell labeling strategies to the design of integrated microfluidic cell sorters and of point-of-care platforms combining cell selection, capture, and downstream detection. Finally, we focus on clinical, industrial and environmental applications where magnetic cell separation strategies are amongst the most promising techniques to address the challenges of isolating rare cells.

The Origins and the Current Applications of Microfluidics-Based Magnetic Cell Separation Technologies

The magnetic separation of cells based on certain traits has a wide range of applications in microbiology, immunology, oncology, and hematology. Compared to bulk separation, performing magnetophoresis at micro scale presents advantages such as precise control of the environment, larger magnetic gradients in miniaturized dimensions, operational simplicity, system portability, high-throughput analysis, and lower costs. Since the first integration of magnetophoresis and microfluidics, many different approaches have been proposed to magnetically separate cells from suspensions at the micro scale. This review paper aims to provide an overview of the origins of microfluidic devices for magnetic cell separation and the recent technologies and applications grouped by the targeted cell types. For each application, exemplary experimental methods and results are discussed.

The Streaming Potential of Fluid through a Microchannel with Modulated Charged Surfaces

In this paper, the effects of asymmetrically modulated charged surfaces on streaming potential, velocity field and flow rate are investigated under the axial pressure gradient and vertical magnetic field. In a parallel-plate microchannel, modulated charged potentials on the walls are depicted by the cosine function. The flow of incompressible Newtonian fluid is two-dimensional due to the modulated charged surfaces. Considering the Debye-Hückel approximation, the Poisson-Boltzmann (PB) equation and the modified Navier-Stokes (N-S) equation are established. The analytical solutions of the potential and velocities (u and v) are obtained by means of the superposition principle and stream function. The unknown streaming potential is determined by the condition that the net ionic current is zero. Finally, the influences of pertinent dimensionless parameters (modulated potential parameters, Hartmann number and slip length) on the flow field, streaming potential, velocity field and flow rate are discussed graphically. During the flow process and under the impact of the charge-modulated potentials, the velocity profiles present an oscillating characteristic, and vortexes are generated. The results show that the charge-modulated potentials are beneficial for the enhancement of the streaming potential, velocity and flow rate, which also facilitate the mixing of fluids. Meanwhile, the flow rate can be controlled through the use of a low-amplitude magnetic field.

Tunable hydrodynamic focusing with dual-neodymium magnet-based microfluidic separation device

Microfluidic separation technologies are the focus of various biological applications, such as disease diagnostics, single-cell analysis, and therapeutics. Different methods and devices were proposed in the micro-separation field, focusing on minimizing the chemical deformation and physical damage to the particles throughout the separation process; however, it is still a challenge. This paper proposes a hydrodynamic focusing-based microfluidic separation device equipped with a dual-neodymium magnet for positive magnetophoretic microparticles and cell separation. Hydrodynamic focusing is used to help to sort the particles and minimize the damage to the microparticles through the proposed different inlet flow rates between the two focusing channels. The dual magnets help to separate the particles in two stages. The system's novelty is integrating the hydrodynamic focusing with the dual magnetics system, where the hydrodynamic focusing is with variable inlet flow rates. The performance of the proposed microfluidic particle separator is numerically assessed under various operating parameters, including the concentration of the particle in the injected solution and flow rate ratios of high to the low focusing flows on the efficiency of the separation. Following the proposed separation method, it was possible to separate the 16 and 10 [Formula: see text] microparticles with the first-round efficiency of 21% with a quality of 92%, respectively. The developed particle separation system can significantly broaden its applications in a variety of biomedical research studies.

Negative enrichment of circulating tumor cells from unmanipulated whole blood with a 3D printed device

Reliable and routine isolation of circulating tumor cells (CTCs) from peripheral blood would allow effective monitoring of the disease and guide the development of personalized treatments. Negative enrichment of CTCs by depleting normal blood cells ensures against a biased selection of a subpopulation and allows the assay to be applied on different tumor types. Here, we report an additively manufactured microfluidic device that can negatively enrich viable CTCs from clinically-relevant volumes of unmanipulated whole blood samples. Our device depletes nucleated blood cells based on their surface antigens and the smaller anucleated cells based on their size. Enriched CTCs are made available off the device in suspension making our technique compatible with standard immunocytochemical, molecular and functional assays. Our device could achieve a ~ 2.34-log depletion by capturing > 99.5% of white blood cells from 10 mL of whole blood while recovering > 90% of spiked tumor cells. Furthermore, we demonstrated the capability of the device to isolate CTCs from blood samples collected from patients (n = 15) with prostate and pancreatic cancers in a pilot study. A universal CTC assay that can differentiate tumor cells from normal blood cells with the specificity of clinically established membrane antigens yet require no label has the potential to enable routine blood-based tumor biopsies at the point-of-care.

Design and operation of magnetophoretic systems at microscale: Device and particle approaches

Combining both device and particle designs are the essential concepts to be considered in magnetophoretic system development. Researcher efforts are often dedicated to only one of these design aspects and neglecting the interplay between them. Herein, to bring out importance of the idea of integration between device and particle, we reviewed the working principle of magnetophoretic system (includes both device and particle design concepts). Since, the magnetophoretic force is influenced by both field gradient and magnetization volume, hence, accurate prediction of the magnetophoretic force is relying on the availability of information on both parameters. In device design, we focus on the different strategies used to create localized high-field gradient. For particle design, we emphasize on the scaling between hydrodynamic size and magnetization volume. Moreover, we also briefly discussed the importance of magnetoshape anisotropy related to particle design aspect of magnetophoretic systems. Next, we illustrated the need for integration between device and particle design using microscale applications of magnetophoretic systems, include magnetic tweezers and microfluidic systems, as our working example. On the basis of our discussion, we highlighted several promising examples of microscale magnetophoretic systems which greatly utilized the interplay between device and particle design. Further, we concluded the review with several factors that possibly resulted in the lack of research efforts related to device and particle design integration.

A simple magnetic-assisted microfluidic method for rapid detection and phenotypic characterization of ultralow concentrations of bacteria

Isolation and enumeration of bacteria at ultralow concentrations and antibiotic resistance profiling are of great importance for early diagnosis and treatment of bacteremia. In this work, we describe a simple, rapid, and versatile magnetic-assisted microfluidic method for rapid bacterial detection. The developed method enables magnetophoretic loading of bead-captured bacteria into the microfluidic chamber under external static and dynamic magnetic fields in 4 min. A shallow microfluidic chamber design that enables the monolayer orientation and transportation of the beads and a glass substrate with a thickness of 0.17 mm was utilized to allow high-resolution fluorescence imaging for quantitative detection. Escherichia coli (E. coli) with green fluorescent protein (GFP)-expressing gene and streptavidin-modified superparamagnetic microbeads were used as model bacteria and capturing beads, respectively. The specificity of the method was validated using Lactobacillus gasseri as a negative control group. The limit of detection and limit of quantification values were determined as 2 CFU/ml and 10 CFU/ml of E. coli, respectively. The magnetic-assisted microfluidic method is a versatile tool for the detection of ultralow concentrations of viable bacteria with the linear range of 5-5000 CFU/ml E. coli in 1 h, and providing growth curves and phenotypic characterization bead-captured E. coli in the following 5 h of incubation. Our results are promising for future rapid and sensitive antibiotic susceptibility testing of ultralow numbers of viable cells.

Scalable Signature-Based Molecular Diagnostics Through On-chip Biomarker Profiling Coupled with Machine Learning

Molecular diagnostics have traditionally relied on discrete biological substances as diagnostic markers. In recent years however, advances in on-chip biomarker screening technologies and data analytics have enabled signature-based diagnostics. Such diagnostics aim to utilize unique combinations of multiple biomarkers or diagnostic 'fingerprints' rather than discrete analyte measurements. This approach has shown to improve both diagnostic accuracy and diagnostic specificity. In this review, signature-based diagnostics enabled by microfluidic and micro-/nano- technologies will be reviewed with a focus on device design and data analysis pipelines and methodologies. With increasing amounts of data available from microfluidic biomarker screening, isolation, and detection platforms, advanced data handling and analytics approaches can be employed. Thus, current data analysis approaches including machine learning and recent advances with image processing, along with potential future directions will be explored. Lastly, the needs and gaps in current literature will be elucidated to inform future efforts towards development of molecular diagnostics and biomarker screening technologies.

Detection and isolation of free cancer cells from ascites and peritoneal lavages using optically induced electrokinetics (OEK)

Detection of free gastric cancer cells in peritoneal lavages and ascites plays a vital role in gastric cancer. However, due to the low content of cancer cells in patients' peritoneal lavages, traditional detection methods lack sensitivity and cannot satisfy clinical demand. In this study, we used an optically induced electrokinetics (OEK) microfluidic method for label-free separation and characterization of patient gastric cancer cells. This method showed high effectiveness and sensitivity. We successfully separated cancer cells from a simulated peritoneal lavage mixture of gastric cancer cell lines and peritoneal lavage cells in a ratio of 1:1000. We further separated gastric cancer cells from six patients' ascites with purity up to 71%. In addition, we measured the cell membrane capacitances, which may be used as a biomarker for gastric cancer cells. Thus, our method can be used to effectively and rapidly detect peritoneal metastasis and to acquire cellular electrical information.

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.

Magnetic nanoparticles in nanomedicine: a review of recent advances

Nanomaterials, in addition to their small size, possess unique physicochemical properties that differ from bulk materials, making them ideal for a host of novel applications. Magnetic nanoparticles (MNPs) are one important class of nanomaterials that have been widely studied for their potential applications in nanomedicine. Due to the fact that MNPs can be detected and manipulated by remote magnetic fields, it opens a wide opportunity for them to be used in vivo. Nowadays, MNPs have been used for diverse applications including magnetic biosensing (diagnostics), magnetic imaging, magnetic separation, drug and gene delivery, and hyperthermia therapy, etc. Specifically, we reviewed some emerging techniques in magnetic diagnostics such as magnetoresistive (MR) and micro-Hall (μHall) biosensors, as well as the magnetic particle spectroscopy, magnetic relaxation switching and surface enhanced Raman spectroscopy (SERS)-based bioassays. Recent advances in applying MNPs as contrast agents in magnetic resonance imaging and as tracer materials in magnetic particle imaging are reviewed. In addition, the development of high magnetic moment MNPs with proper surface functionalization has progressed exponentially over the past decade. To this end, different MNP synthesis approaches and surface coating strategies are reviewed and the biocompatibility and toxicity of surface functionalized MNP nanocomposites are also discussed. Herein, we are aiming to provide a comprehensive assessment of the state-of-the-art biological and biomedical applications of MNPs. This review is not only to provide in-depth insights into the different synthesis, biofunctionalization, biosensing, imaging, and therapy methods but also to give an overview of limitations and possibilities of each technology.

Continuous-Flow Separation and Efficient Concentration of Foodborne Bacteria from Large Volume Using Nickel Nanowire Bridge in Microfluidic Chip

Separation and concentration of target bacteria has become essential to sensitive and accurate detection of foodborne bacteria to ensure food safety. In this study, we developed a bacterial separation system for continuous-flow separation and efficient concentration of foodborne bacteria from large volume using a nickel nanowire (NiNW) bridge in the microfluidic chip. The synthesized NiNWs were first modified with the antibodies against the target bacteria and injected into the microfluidic channel to form the NiNW bridge in the presence of the external arc magnetic field. Then, the large volume of bacterial sample was continuous-flow injected to the channel, resulting in specific capture of the target bacteria by the antibodies on the NiNW bridge to form the NiNW–bacteria complexes. Finally, these complexes were flushed out of the channel and concentrated in a lower volume of buffer solution, after the magnetic field was removed. This bacterial separation system was able to separate up to 74% of target bacteria from 10 mL of bacterial sample at low concentrations of ≤10² CFU/mL in 3 h, and has the potential to separate other pathogenic bacteria from large volumes of food samples by changing the antibodies.

Recent advances in microfluidic methods in cancer liquid biopsy

Early cancer detection, its monitoring, and therapeutical prediction are highly valuable, though extremely challenging targets in oncology. Significant progress has been made recently, resulting in a group of devices and techniques that are now capable of successfully detecting, interpreting, and monitoring cancer biomarkers in body fluids. Precise information about malignancies can be obtained from liquid biopsies by isolating and analyzing circulating tumor cells (CTCs) or nucleic acids, tumor-derived vesicles or proteins, and metabolites. The current work provides a general overview of the latest on-chip technological developments for cancer liquid biopsy. Current challenges for their translation and their application in various clinical settings are discussed. Microfluidic solutions for each set of biomarkers are compared, and a global overview of the major trends and ongoing research challenges is given. A detailed analysis of the microfluidic isolation of CTCs with recent efforts that aimed at increasing purity and capture efficiency is provided as well. Although CTCs have been the focus of a vast microfluidic research effort as the key element for obtaining relevant information, important clinical insights can also be achieved from alternative biomarkers, such as classical protein biomarkers, exosomes, or circulating-free nucleic acids. Finally, while most work has been devoted to the analysis of blood-based biomarkers, we highlight the less explored potential of urine as an ideal source of molecular cancer biomarkers for point-of-care lab-on-chip devices.

Numerical evaluation and experimental validation of cross-flow microfiltration device design

This research presents a comprehensive analysis of the design and validation of a cross-flow microfiltration device for separation of microspheres based on size. Simulation results showed that pillar size, pillar shape, incorporation of back-flow preventers, and rounding of pillar layouts affected flow patterns in a cross-flow microfiltration device. Simulation results suggest that larger pillar sizes reduce filtration capacity by decreasing the density of microfiltration gaps in the device. Therefore, 10 μm rather than 20 μm diameter pillars were incorporated in the device. Fluid flow was not greatly affected when comparing circular, octagonal, and hexagonal pillars. However, side-channel fluid velocities decreased when using triangular and square pillars. The lengths of back-flow prevention walls were optimized to completely prevent back flow without inhibiting filtration ability. A trade-off was observed in the designs of the pillar layouts; while rounding the pillars layout in the channels bends eliminated stagnation areas, the design also decreased side-channel fluid velocity compared to the right-angle layout. Experimental separation efficiency was tested using polydimethylsiloxane (PDMS) and silicon microfluidic devices with microspheres simulating white and red blood cells. Efficiencies for separation of small microspheres to the side channels ranged from 73 to 75%. The silicon devices retained the large microspheres in the main channel with efficiencies between 95 and 100%, but these efficiencies were lower with PDMS devices and were affected by sphere concentration. Additionally, PDMS devices resulted in greater agglomeration of spheres when compared to silicon devices. PDMS devices, however, were easier and less expensive to fabricate.

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.

Recent advances and current challenges in magnetophoresis based micro magnetofluidics

The combination of magnetism and microscale fluid flow has opened up a new era for handling and manipulation of samples in microfluidics. In particular, magnetophoresis, the migration of particles in a magnetic field, is extremely attractive for microfluidic handling due to its contactless nature, independence of ionic concentration, and lack of induced heating. The present paper focuses on recent advances and current challenges of magnetophoresis and highlights the key parameters affecting the manipulation of particles by magnetophoresis. The magnetic field is discussed according to their relative motion to the sample as stationary and dynamic fields. The migration of particles is categorized as positive and negative magnetophoresis. The applications of magnetophoresis are discussed according to the basic manipulation tasks such as mixing, separation, and trapping of particles or cells. Finally, the paper highlights the limitations of current approaches and provides the future perspective for this research area.

Advances in microfluidic devices made from thermoplastics used in cell biology and analyses

Silicon and glass were the main fabrication materials of microfluidic devices, however, plastics are on the rise in the past few years. Thermoplastic materials have recently been used to fabricate microfluidic platforms to perform experiments on cellular studies or environmental monitoring, with low cost disposable devices. This review describes the present state of the development and applications of microfluidic systems used in cell biology and analyses since the year 2000. Cultivation, separation/isolation, detection and analysis, and reaction studies are extensively discussed, considering only microorganisms (bacteria, yeast, fungi, zebra fish, etc.) and mammalian cell related studies in the microfluidic platforms. The advantages/disadvantages, fabrication methods, dimensions, and the purpose of creating the desired system are explained in detail. An important conclusion of this review is that these microfluidic platforms are still open for research and development, and solutions need to be found for each case separately.

Microfluidic Adaptation of Density-Gradient Centrifugation for Isolation of Particles and Cells

Density-gradient centrifugation is a label-free approach that has been extensively used for cell separations. Though elegant, this process is time-consuming (>30 min), subjects cells to high levels of stress (>350 g) and relies on user skill to enable fractionation of cells that layer as a narrow band between the density-gradient medium and platelet-rich plasma. We hypothesized that microfluidic adaptation of this technique could transform this process into a rapid fractionation approach where samples are separated in a continuous fashion while being exposed to lower levels of stress (<100 g) for shorter durations of time (<3 min). To demonstrate proof-of-concept, we designed a microfluidic density-gradient centrifugation device and constructed a setup to introduce samples and medium like Ficoll in a continuous, pump-less fashion where cells and particles can be exposed to centrifugal force and separated via different outlets. Proof-of-concept studies using binary mixtures of low-density polystyrene beads (1.02 g/cm³) and high-density silicon dioxide beads (2.2 g/cm³) with Ficoll–Paque (1.06 g/cm³) show that separation is indeed feasible with >99% separation efficiency suggesting that this approach can be further adapted for separation of cells.

Advances in rare cell isolation: an optimization and evaluation study

Background

Rare nucleated CD45 negative cells in peripheral blood may be malignant such as circulating tumor cells. Untouched isolation thereof by depletion of normal is favored yet still technological challenging. We optimized and evaluated a novel magnetic bead-based negative selection approach for enhanced enrichment of rare peripheral blood nucleated CD45 negative cells and investigated the problem of rare cell contamination during phlebotomy.

Methods

Firstly, the performance of the magnetic cell separation system was assessed using leukocytes and cultivated fibroblast cells in regard to depletion efficiency and the loss of cells of interest. Secondly, a negative selection assay was optimized for high performance, simplicity and cost efficiency. The negative selection assay consisted of; a RBC lysis step, two depletion cycles comprising direct magnetically labelling of leukocytes using anti-CD45 magnetic beads followed by magnetic capture of leukocytes using a duopole permanent magnet. Thirdly, assay evaluation was aligned to conditions of rare cell frequencies and comprised cell spike recovery, cell viability and proliferation, and CD45 negative cell detection. Additionally, the problem of CD45 negative cell contamination during phlebotomy was investigated.

Results

The depletion factor and recovery of the negative selection assay measured at most 1600-fold and 96%, respectively, leaving at best 1.5 × 10⁴ leukocytes unseparated and took 35 min. The cell viability was negatively affected by chemical RBC lysis. Proliferation of 100 spiked ovarian cancer cells in culture measured 37% against a positive control. Healthy donor testing revealed findings of nucleated CD45 negative cells ranging from 1 to 22 cells /2.5 × 10⁷ leukocytes or 3.5 mL whole blood in 89% (23/26) of the samples.

Conclusion

Our assay facilitates high performance at shortest assay time. The enrichment assay itself causes minor harm to cells and allows proliferation. Our findings suggest that rare cell contamination is unavoidable. An unexpected high variety of CD45 negative cells have been detected. It is hypothesized that a rare cell profile may translate into tumor marker independent screening.