Magnetic Cell Separation: Characterization of Magnetophoretic Mobility

Surface Reaction of Electroosmotic Flow-Driven Free Antigens With Immobilized Magnetic-Microbeads-Tagged-Antibodies in Microchannels

Immunoassays based on reactions between target pathogen (antigen; Ag) and antibody (Ab) are frequently used for Ag detection. An external magnetic field was used to immobilize magnetic microbeads-tagged-antibodies (mMB-Ab) on the surface of a microchannel in the capture zone. The mMB-Ab was subsequently used for Ag detection. The objective of this numerical study, with experimental validation, is to assess the surface reaction between mMB-Ab and Ag in the presence of electro-osmotic flow (EOF). First, immobilization of mMB-Ab complex in the wall of the capture zone was achieved. Subsequently, the Ag was transported by EOF toward the capture zone to bind with the immobilized mMB-Ab. Lastly, mMB-Ab:Ag complex was formed and immobilized in the capture zone. A finite volume solver was used to implement the above steps. The surface reaction between the mMB-Ab and Ag was investigated in the presence of electric fields (E): 150 V/cm-450 V/cm and Ag concentrations: 0.001 M-1000 M. The depletion of mMB-Ab increases with time as the E decreases. Furthermore, as the concentration of Ag decreases, the depletion of mMB-Ab increases with time. These results quantify the detection of Ag using the EOF device; thus, signifying its potential for rapid throughput screening of Ag. This platform technology can lead to the development of portable devices for the detection of target cells, pathogens, and biomolecules for testing water systems, biological fluids, and biochemicals.

Development of MWCNT/Magnetite Flexible Triboelectric Sensors by Magnetic Patterning

The fabrication of low-electrical-percolation-threshold polymer composites aims to reduce the weight fraction of the conductive nanomaterial necessary to achieve a given level of electrical resistivity of the composite. The present work aimed at preparing composites based on multiwalled carbon nanotubes (MWCNTs) and magnetite particles in a polyurethane (PU) matrix to study the effect on the electrical resistance of electrodes produced under magnetic fields. Composites with 1 wt.% of MWCNT, 1 wt.% of magnetite and combinations of both were prepared and analysed. The hybrid composites combined MWCNTs and magnetite at the weight ratios of 1:1; 1:1/6; 1:1/12; and 1:1/24. The results showed that MWCNTs were responsible for the electrical conductivity of the composites since the composites with 1 wt.% magnetite were non-conductive. Combining magnetite particles with MWCNTs reduces the electrical resistance of the composite. SQUID analysis showed that MWCNTs simultaneously exhibit ferromagnetism and diamagnetism, ferromagnetism being dominant at lower magnetic fields and diamagnetism being dominant at higher fields. Conversely, magnetite particles present a ferromagnetic response much stronger than MWCNTs. Finally, optical microscopy (OM) and X-ray micro computed tomography (micro CT) identified the interaction between particles and their location inside the composite. In conclusion, the combination of magnetite and MWCNTs in a polymer composite allows for the control of the location of these particles using an external magnetic field, decreasing the electrical resistance of the electrodes produced. By adding 1 wt.% of magnetite to 1 wt.% of MWCNT (1:1), the electric resistance of the composites decreased from 9 × 10⁴ to 5 × 10³ Ω. This approach significantly improved the reproducibility of the electrode's fabrication process, enabling the development of a triboelectric sensor using a polyurethane (PU) composite and silicone rubber (SR). Finally, the method's bearing was demonstrated by developing an automated robotic soft grip with tendon-driven actuation controlled by the triboelectric sensor. The results indicate that magnetic patterning is a versatile and low-cost approach to manufacturing sensors for soft robotics.

Semi-circle magnetophoretic separation under rotated magnetic field for colorimetric biosensing of Salmonella

Magnetic separation was often applied to isolate and concentrate foodborne bacteria using immunomagnetic nanobeads before downstream bacterial detection. However, nanobead-bacteria conjugates (magnetic bacteria) were coexisting with excessive unbound nanobeads, limiting these nanobeads on magnetic bacteria to further act as signal probes for bacterial detection. Here, a new microfluidic magnetophoretic biosensor was elaboratively developed using a rotated high gradient magnetic field and platinum modified immunomagnetic nanobeads for continuous-flow isolation of magnetic bacteria from free nanobeads, and combined with nanozyme signal amplification for colorimetric biosensing of Salmonella. First, the platinum modified immunomagnetic nanobeads were mixed with the bacterial sample to form the magnetic bacteria, and magnetically separated to eliminate non-magnetic background. Then, the mixture of free immunomagnetic nanobeads and magnetic bacteria was injected with sheath flow (PBS) at higher flowrate into the semi-circle magnetophoretic separation channel under rotated magnetic field, which was generated by two repulsive cylindric magnets and their in-between ring iron gear, leading to continuous-flow isolation of magnetic bacteria from free immunomagnetic nanobeads because they suffered from different magnetic forces and thus had different deviating positions at the outlet. Finally, the separated magnetic bacteria and unbound magnetic nanobeads were respectively collected and used to catalyze coreless substrate into blue product, which was further analyzed using the microplate reader to obtain bacterial amount. This biosensor could determinate Salmonella as low as 41 CFU/mL in 40 min.

Magnetic nanofluids (Ferrofluids): Recent advances, applications, challenges, and future directions

Impelled by the need to find solutions to new challenges of modern technologies new materials with unique properties are being explored. Among various new materials that emerged over the decades, magnetic fluids exhibiting interesting physiochemical properties (optical, thermal, magnetic, rheological, apparent density, etc.) under a magnetic stimulus have been at the forefront of research. In the initial phase, there has been a fervent scientific curiosity to understand the field-induced intriguing properties of such fluids but later a plethora of technological applications emerged. Magnetic nanofluid, popularly known as ferrofluid, is a colloidal suspension of fine magnetic nanoparticles, has been at the forefront of research because of its magnetically tunable physicochemical properties and applications. Due to their stimuli-responsive behaviour, they have been finding more applications in biology and other engineering disciplines in recent years. Therefore, a critical review of this topic highlighting the necessary background, the potential of this material for emerging technologies, and the latest developments is warranted. This review also provides a summary of various applications, along with the key challenges and future research directions. The first part of the review addresses the different types of magnetic fluids, the genesis of magnetic fluids, their synthesis methodologies, properties, and stabilization techniques are discussed in detail. The second part of the review highlights the applications of magnetic nanofluids and nanoemulsions (as model systems) in probing order-disorder transitions, scattering, diffraction, magnetically reconfigurable internal structures, molecular interaction, and weak forces between colloidal particles, conformational changes of macromolecules at interfaces and polymer-surfactant complexation at the oil-water interface. The last part of the review summarizes the interesting applications of magnetic fluids such as heat transfer, sensors (temperature, pH, urea detection, cations, defect detection sensors), tunable optical filters, removal of dyes, dynamic seals, magnetic hyperthermia-based cancer therapy and other biomedical applications. The applications of magnetic nanofluids in diverse disciplines are growing day by day, yet there are challenges in their practical adaptation as field-worthy or packaged products. This review provides a pedagogical description of magnetic fluids, with the necessary background, key concepts, physics, experimental protocols, design of experiments, challenges and future directions.

Assessing the Challenges of Nanotechnology-Driven Targeted Therapies: Development of Magnetically Directed Vectors for Targeted Cancer Therapies and Beyond

Targeted delivery, in which therapeutic agents are preferentially concentrated at the diseased site, has the potential to improve therapeutic outcomes by minimizing off-target interactions in healthy tissue. Both passive and active methods of targeting delivery have been proposed, often with particular emphasis on cancer treatment. Passive methods rely on the overexpression of a biomarker in diseased tissue that can then be used to target the therapy. Active techniques involve physically guiding therapeutic agents toward the target region. Since the motion of magnetic particles can be remotely controlled by external magnetic fields, magnetic technologies have the potential to drive and hold drugs or other cargo at the required therapeutic site, increasing the localized dose while minimizing overall exposure. Directed motion may be generated either by simple magnetic attraction or by causing the particles to perform swimming strokes to produce propulsion. This chapter will compare the different strategies using magnetic nanotechnology to produce directed motion compatible with that required for targeted cargo delivery and magnetically assisted therapies and assess their potential to meet the challenges of operating within the human body.

Advances in magnetic nanoparticles for the separation of foodborne pathogens: Recognition, separation strategy, and application

Foodborne pathogens contamination is one of the main sources of food safety problems. Although the existing detection methods have been developed for a long time, the complexity of food samples is still the main factor affecting the detection time and sensitivity, and the rapid separation and enrichment of pathogens is still an objective to be studied. Magnetic separation strategy based on magnetic nanoparticles (MNPs) is considered to be an effective tool for rapid separation and enrichment of foodborne pathogens in food. Therefore, this study comprehensively reviews the development of MNPs in the separation of foodborne pathogens over the past decade. First, various biorecognition reagents for identification of foodborne pathogens and their modifications on the surface of MNPs are introduced. Then, the factors affecting the separation of foodborne pathogens, including the size of MNPs, modification methods, separation strategies and separation forms are discussed. Finally, the application of MNPs in integrated detection methods is reviewed. Moreover, current challenges and prospects of MNPs for the analysis of foodborne pathogens are discussed. Further research should focus on the design of multifunctional MNPs, the processing of large-scale samples, the simultaneous analysis of multiple targets, and the development of all-in-one small analytical device with separation and detection.

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.

Columnar dipolar clusters defying gravity

A striking and highly versatile feature of magnetic (nano)particles is their ability to be manipulated at will at a distance by external fields. In this paper, the influence of gravity on the self-assembly of dipolar particles near a surface in the presence of a strong vertical magnetic field is investigated theoretically. A rich ground-state phase diagram stems from the effects of the number of particles N and gravity. Two distinct regimes are discovered for the gravity-mediated breakup of a standing chain. When N is small, there is a chain fragmentation (with two widely separated repulsive chain fragments) above a critical value for the gravity, whereas for higher chains, ribbonization (with two cohesive chain fragments) sets in. In both scenarios, simple algebraic decays for the transition gravity as a function of N are analytically predicted and accurately corroborate the exact numerical results. Further intricate chain fragmentations and internal ribbon transformations operate upon further increasing the gravity until all N constitutive particles lie on the surface. Our findings shed additional light on various recent experiments and computer simulations on magnetic colloids and granular media.

Origin of Magnetization in Silica-coated Fe3O4 Nanoparticles Revealed by Soft X-ray Magnetic Circular Dichroism

Abstract

Magnetite (Fe₃O₄) nanoparticles (NPs) and SiO₂-coated Fe₃O₄ nanoparticles have successfully been synthesized using co-precipitation and modified Stöber methods, respectively. The samples were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, high-resolution transmission electron microscopy (HRTEM), vibrating sample magnetometer (VSM) techniques, X-ray absorption spectroscopy (XAS), and X-ray magnetic circular dichroism (XMCD). XRD and FTIR data confirmed the structural configuration of a single-phase Fe₃O₄ and the successful formation of SiO₂-coated Fe₃O₄ NPs. XRD also confirmed that we have succeeded to synthesize nano-meter size of Fe₃O₄ NPs. HRTEM images showed the increasing thickness of SiO₂-coated Fe₃O₄ with the addition of the Tetraethyl Orthosilicate (TEOS). Room temperature VSM analysis showed the magnetic behaviour of Fe₃O₄ and its variations that occurred after SiO₂ coating. The magnetic behaviour is further authenticated by XAS spectra analysis which cleared about the existence of SiO₂ shells that have transformed the crystal as well as the local structures of the magnetite NPs. We have performed XMCD measurements, which is a powerful element-specific technique to find out the origin of magnetization in SiO₂-coated Fe₃O₄ NPs, that verified a decrease in magnetization with increasing thickness of the SiO₂ coating.

Graphical Abstract

Magnetite (Fe₃O₄) nanoparticles (NPs) and SiO₂-coated Fe₃O₄ nanoparticles have successfully been synthesized using co-precipitation and modified Stöber methods, respectively. The samples were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, high-resolution transmission electron microscopy (HRTEM), vibrating sample magnetometer (VSM) techniques, X-ray absorption spectroscopy (XAS), and X-ray magnetic circular dichroism (XMCD). XRD and FTIR data confirmed the structural configuration of a single-phase Fe₃O₄ and the successful formation of SiO₂-coated Fe₃O₄ NPs. XRD also confirmed that we have succeeded to synthesize nano-meter size of Fe₃O₄ NPs. HRTEM images showed the increasing thickness of SiO₂-coated Fe₃O₄ with the addition of the Tetraethyl Orthosilicate (TEOS). Room temperature VSM analysis showed the magnetic behaviour of Fe₃O₄ and its variations that occurred after SiO₂ coating. The magnetic behaviour is further authenticated by XAS spectra analysis which cleared about the existence of SiO₂ shells that have transformed the crystal as well as the local structures of the magnetite NPs. We have performed XMCD measurements, which is a powerful element-specific technique to find out the origin of magnetization in SiO₂-coated Fe₃O₄ NPs, that verified a decrease in magnetization with increasing thickness of the SiO₂ coating.

Magnetic Polymers for Magnetophoretic Separation in Microfluidic Devices

Magnetophoresis offers many advantages for manipulating magnetic targets in microsystems. The integration of micro-flux concentrators and micro-magnets allows achieving large field gradients and therefore large reachable magnetic forces. However, the associated fabrication techniques are often complex and costly, and besides, they put specific constraints on the geometries. Magnetic composite polymers provide a promising alternative in terms of simplicity and fabrication costs, and they open new perspectives for the microstructuring, design, and integration of magnetic functions. In this review, we propose a state of the art of research works implementing magnetic polymers to trap or sort magnetic micro-beads or magnetically labeled cells in microfluidic devices.

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.

Microfluidic Devices for Magnetic Separation of Biological Particles: A Review

Separation of microparticles and cells serves a critical step in many applications such as in biological analyses, food production, chemical processing, and medical diagnostics. Sorting on the microscale exhibits certain advantages in comparison with that on the macroscale as it requires minuscule sample or reagents volume and thus reduced analysis cycle time, smaller size of devices, and lower fabrication costs. Progresses have been made over time to improve the efficiency of these microscale particle manipulation techniques. Many different techniques have been used to attain accurate particle sorting and separation in a continuous manner on the microscale level, which can be categorized as either passive or active methods. Passive techniques achieve accurate manipulation of particles through their interaction with surrounding flow by carefully designed channel structures, without using external fields. As an alternative, active techniques utilize external fields (e.g., acoustic, electronic, optical, and magnetic field, etc.) to realize desired pattern of motion for particles with specific properties. Among numerous active methods for microfluidic particle sorting, the magnetic field has been widely used in biomedical and chemical applications to achieve mixing, focusing, and separating of reagents and bioparticles. This paper aims to provide a thorough review on the classic and most up-to-date magnetic sorting and separation techniques to manipulate microparticles including the discussions on the basic concept, working principle, experimental details, and device performance.

Magnetic Particles for CTC Enrichment

Simple Summary

For the enrichment of very rare cells, such as Circulating Tumor Cells (CTCs), immunomagnetic enrichment is frequently used. For this purpose, magnetic nanoparticles (MNPs) coated with specific antibodies directed against cancer cells are used. In this review, we look at the properties such a particle needs to have in order to be used successfully, and describe the different methods used in the production of such a particle as well as the methods for their separation. Additionally, an overview is given of the antibodies that could potentially be used for this purpose.

Abstract

Here, we review the characteristics and synthesis of magnetic nanoparticles (MNPs) and place these in the context of their usage in the immunomagnetic enrichment of Circulating Tumor Cells (CTCs). The importance of the different characteristics is explained, the need for a very specific enrichment is emphasized and different (commercial) magnetic separation techniques are shown. As the specificity of an MNP is in a large part dependent on the antibody coated onto the particle, different strategies in the coupling of specific antibodies as well as an overview of the available antibodies is given.

Intrinsically Magnetic Cells: A Review on Their Natural Occurrence and Synthetic Generation

The magnetization of non-magnetic cells has great potential to aid various processes in medicine, but also in bioprocess engineering. Current approaches to magnetize cells with magnetic nanoparticles (MNPs) require cellular uptake or adsorption through in vitro manipulation of cells. A relatively new field of research is "magnetogenetics" which focuses on in vivo production and accumulation of magnetic material. Natural intrinsically magnetic cells (IMCs) produce intracellular, MNPs, and are called magnetotactic bacteria (MTB). In recent years, researchers have unraveled function and structure of numerous proteins from MTB. Furthermore, protein engineering studies on such MTB proteins and other potentially magnetic proteins, like ferritins, highlight that in vivo magnetization of non-magnetic hosts is a thriving field of research. This review summarizes current knowledge on recombinant IMC generation and highlights future steps that can be taken to succeed in transforming non-magnetic cells to IMCs.

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.

Evaluating and forecasting movement patterns of magnetically driven microbeads in complex geometries

The manipulation of superparamagnetic microbeads for lab-on-a-chip applications relies on the steering of microbeads across an altering stray field landscape on top of soft magnetic parent structures. Using ab initio principles, we show three-dimensional simulations forecasting the controlled movement of microbeads. Simulated aspects of microbead behaviour include the looping and lifting of microbeads around a magnetic circular structure, the flexible bead movement along symmetrically distributed triangular structures, and the dragging of magnetic beads across an array of exchange biased magnetic microstripes. The unidirectional motion of microbeads across a string of oval elements is predicted by simulations and validated experimentally. Each of the simulations matches the experimental results, proving the robustness and accuracy of the applied numerical method. The computer experiments provide details on the particle motion not accessible by experiments. The simulation capabilities prove to be an essential part for the estimation of future lab-on-chip designs.

Mathematical modeling and computational analysis of centrifugal microfluidic platforms: a review

Centrifugal microfluidic platforms or lab-on-discs (LODs) have evolved into a popular technology for automating chemical and biological assays. LODs today enable scientists to implement and integrate different operational units, including fluid mixing, droplet generation, cell-sorting, gene amplification, analyte detection, and so forth. For an efficient design and cost-effective implementation of any microfluidic device, including LODs, theoretical analysis and considerations should play a more important role than they currently do. The theoretical analysis we will show is especially essential to the investigation of detailed phenomena at the small length scales and high-speed typical for LODs where a wide range of forces may be involved. Previous LOD review papers presented mostly experimental results with theory as an afterthought. Hence, a review paper focused on the theoretical aspects, and associated computational studies of LOD devices is an urgent need. In the present review paper, all previous computational studies on LOD devices are categorized as single-phase flows, two-phase flows, network simulation, and solids. For each of these categories, the governing equations and important formulas are presented and explained. Moreover, a handy scaling analysis is introduced to aid scientists when comparing different competing forces in LOD devices. We hope that by surveying and contrasting various theoretical LOD studies, we shed some light on existing controversies and reveal where additional theoretical work is needed.

Electroosmotic flow driven microfluidic device for bacteria isolation using magnetic microbeads

The presence of bacterial pathogens in water can lead to severe complications such as infection and food poisoning. This research proposes a point-of-care electroosmotic flow driven microfluidic device for rapid isolation and detection of E. coli in buffered solution (phosphate buffered saline solution). Fluorescent E. coli bound to magnetic microbeads were driven through the microfluidic device using both constant forward flow and periodic flow switching at concentrations ranging from 2 × 105 to 4 × 107 bacteria/mL. A calibration curve of fluorescent intensity as a function of bacteria concentration was created using both constant and switching flow, showing an increase in captured fluorescent pixel count as concentration increases. In addition, the use of the flow switching resulted in a significant increase in the capture efficiency of E. coli, with capture efficiencies up to 83% ± 8% as compared to the constant flow capture efficiencies (up to 39% ± 11%), with a sample size of 3 µL. These results demonstrate the improved performance associated with the use of the electroosmotic flow switching system in a point-of-care bacterial detection assay.

Guidelines for the use of flow cytometry and cell sorting in immunological studies (second edition)

These guidelines are a consensus work of a considerable number of members of the immunology and flow cytometry community. They provide the theory and key practical aspects of flow cytometry enabling immunologists to avoid the common errors that often undermine immunological data. Notably, there are comprehensive sections of all major immune cell types with helpful Tables detailing phenotypes in murine and human cells. The latest flow cytometry techniques and applications are also described, featuring examples of the data that can be generated and, importantly, how the data can be analysed. Furthermore, there are sections detailing tips, tricks and pitfalls to avoid, all written and peer-reviewed by leading experts in the field, making this an essential research companion.

Raman spectroscopy to unravel the magnetic properties of iron oxide nanocrystals for bio-related applications

Iron oxide nanocrystals have become a versatile tool in biomedicine because of their low cytotoxicity while offering a wide range of tuneable magnetic properties that may be implemented in magnetic separation, drug and heat delivery and bioimaging. These capabilities rely on the unique magnetic features obtained when combining different iron oxide phases, so that an important portfolio of magnetic properties can be attained by the rational design of multicomponent nanocrystals. In this context, Raman spectroscopy is an invaluable and fast-performance tool to gain insight into the different phases forming part of the nanocrystals to be used, allowing correlation of the magnetic properties with the envisaged bio-related applications.

Biochemical functionality of magnetic particles as nanosensors: how far away are we to implement them into clinical practice?

Magnetic nanosensors have become attractive instruments for the diagnosis and treatment of different diseases. They represent an efficient carrier system in drug delivery or in transporting contrast agents. For such purposes, magnetic nanosensors are used in vivo (intracorporeal application). To remove specific compounds from blood, magnetic nanosensors act as elimination system, which represents an extracorporeal approach. This review discusses principles, advantages and risks on recent advances in the field of magnetic nanosensors. First, synthesis methods for magnetic nanosensors and possibilities for enhancement of biocompatibility with different coating materials are addressed. Then, attention is devoted to clinical applications, in which nanosensors are or may be used as carrier- and elimination systems in the near future. Finally, risk considerations and possible effects of nanomaterials are discussed when working towards clinical applications with magnetic nanosensors.

Remote Control in Formation of 3D Multicellular Assemblies Using Magnetic Forces

Cell constructs have been utilized as building blocks in tissue engineering to closely mimic the natural tissue and also overcome some of the limitations caused by two-dimensional cultures or using scaffolds. External forces can be used to enhance the cells' adhesion and interaction and thus provide better control over production of these structures compared to methods like cell seeding and migration. In this paper, we demonstrate an efficient method to generate uniform, three-dimensional cell constructs using magnetic forces. This method produced spheroids with higher densities and more symmetrical structures than the commonly used centrifugation method for production of cell spheroids. It was also shown that shape of the cell constructs could be changed readily by using different patterns of magnetic field. The application of magnetic fields to impart forces on the cells enhanced the fusion of these spheroids, which could be used to produce larger and more complicated structures for future tissue engineering applications.

Quantitative characterization of the regulation of iron metabolism in glioblastoma stem-like cells using magnetophoresis

This study focuses on different iron regulation mechanisms of glioblastoma (GBM) cancer stem-like cells (CSCs) and non-stem tumor cells (NSTCs) using multiple approaches: cell viability, density, and magnetophoresis. GBM CSCs and NSTCs were exposed to elevated iron concentration, and their magnetic susceptibility was measured using single cell magnetophoresis (SCM), which tracks the magnetic and settling velocities of thousands of individual cells passing through the magnetic field with a constant energy gradient. Our results consistently demonstrate that GBM NSTCs have higher magnetic susceptibility distribution at increased iron concentration compared with CSCs, and we speculate that it is because CSCs have the ability to store a high amount of iron in ferritin, whereas the free iron ions inside the NSTCs lead to higher magnetic susceptibility and reduced cell viability and growth. Further, their difference in magnetic susceptibility has led us to pursue a separate experiment using a quadrupole magnetic separator (QMS), a novel microfluidic device that uses a concentric channel and permanent magnets in a special configuration to separate samples based on their magnetic susceptibilities. GBM CSCs and NSTCs were exposed to elevated iron concentration, stained with two different trackers, mixed and introduced into QMS; subsequently, the separated fractions were analyzed by fluorescent microscopy. The separation results portray a successful label-less magnetic separation of the two populations.

Deciphering magnetic hyperthermia properties of compositionally and morphologically modulated FeNi nanoparticles using first-order reversal curve analysis

Magnetic hyperthermia based on nanoparticles (NPs) is considered a significant approach in cancer therapy. However, less attention has been paid to the correlation between hyperthermia properties and detailed magnetic characteristics. Herein, the hyperthermia capability of Fe_xNi_100-x (8 ≤ × ≤ 40) NPs synthesized using a polyol method was studied by investigating the temperature rise and specific loss power (SLP) of their ferrofluid (FF) solutions while also performing first-order reversal curve (FORC) analysis. The colloidal stability of magnetic NPs in the FFs was enhanced by coating their surface with polyethylene glycol, and the hyperthermia experiments were carried out in ethylene glycol and DI water (DIW) dispersion media using different concentrations (1.25, 2.5 and 5 mg ml^-1). A field-emission scanning electron microscope was employed to characterize the morphology of the FeNi NPs, evidencing mean diameters ranging between 64-112 nm. Hysteresis loop measurements showed a decreasing trend of average coercive field from 94 to 52 Oe when decreasing the diameter, coinciding with a 13% increase in the reversible fraction of single-domain and superparamagnetic (SP) NPs, according to FORC results. In this way, the corresponding SLP value increased from 55 to 264 W g^-1 for FFs in 1.25 mg ml^-1 concentrated DIW medium with an SP fraction of 40%.

Shaping iron oxide nanocrystals for magnetic separation applications

Iron oxide nanostructures are attractive for a variety of bio-related applications given their wide range of magnetic properties. Here, we report on the study of the magnetophoretic mobility of octapod-shaped nanocrystals, which we relate to stoichiometry, quality and elongation in the 111 direction of these cubic structures. This special morphology combines magnetocrystalline anisotropies, increases shape anisotropy and hinders the formation of an epitaxial wüstite-magnetite interface. As a result, one obtains nanocrystals with large magnetic susceptibility and small coercivity, that is, with optimum characteristics for magnetic guidance, separation, and drug delivery, due to the increased magnetophoretic mobility displayed.

Efficient magnetic enrichment of antigen-specific T cells by engineering particle properties

Magnetic particles can enrich desired cell populations to aid in understanding cell-type functions and mechanisms, diagnosis, and therapy. As cells are heterogeneous in ligand type, location, expression, and density, careful consideration of magnetic particle design for positive isolation is necessary. Antigen-specific immune cells have low frequencies, which has made studying, identifying, and utilizing these cells for therapy a challenge. Here we demonstrate the importance of magnetic particle design based on the biology of T cells. We create magnetic particles which recognize rare antigen-specific T cells and quantitatively investigate important particle properties including size, concentration, ligand density, and ligand choice in enriching these rare cells. We observe competing optima among particle parameters, with 300 nm particles functionalized with a high density of antigen-specific ligand achieving the highest enrichment and recovery of target cells. In enriching and then activating an endogenous response, 300 nm aAPCs generate nearly 65% antigen-specific T cells with at least 450-fold expansion from endogenous precursors and a 5-fold increase in numbers of antigen-specific cells after only seven days. This systematic study of particle properties in magnetic enrichment provides a case study for the engineering design principles of particles for the isolation of rare cells through biological ligands.

Analysis of Magnetic Microbead Capture With and Without Bacteria in a Microfluidic Device Under Different Flow Scenarios

Efficient detection of pathogens is essential for the development of a reliable point-of-care diagnostic device. Magnetophoretic separation, a technique used in microfluidic platforms, utilizes magnetic microbeads (mMBs) coated with specific antigens to bind and remove targeted biomolecules using an external magnetic field. In order to assure reliability and accuracy in the device, the efficient capture of these mMBs is extremely important. The aim of this study was to analyze the effect of an electroosmotic flow (EOF) switching device on the capture efficiency (CE) of mMBs in a microfluidic device and demonstrate viability of bacteria capture. This analysis was performed at microbead concentrations of 2 × 106 beads/mL and 4 × 106 beads/mL, EOF voltages of 650 V and 750 V, and under constant flow and switching flow protocols. Images were taken using an inverted fluorescent microscope and the pixel count was analyzed to determine to fluorescent intensity. A capture zone was used to distinguish which beads were captured versus uncaptured. Under the steady-state flow protocol, CE was determined to range from 31% to 42%, while the switching flow protocol exhibited a CE of 71–85%. The relative percentage increase due to the utilization of the switching protocol was determined to be around two times the CE, with p < 0.05 for all cases. Initial testing using bacteria-bead complexes was also performed in which these complexes were captured under the constant flow protocol to create a calibration curve based on fluorescent pixel count. The calibration curve was linear on a log-log plot, with R2-value of 0.96. The significant increase in CE highlights the effectiveness of flow switching for magnetophoretic separation in microfluidic devices and prove its viability in bacterial analysis.

A simplified sheathless cell separation approach using combined gravitational-sedimentation-based prefocusing and dielectrophoretic separation

Prefocusing of the cell mixture is necessary for achieving a high-efficiency and continuous dielectrophoretic (DEP) cell separation. However, prefocusing through sheath flow requires a complex and tedious peripheral system for multi-channel fluid control, hindering the integration of DEP separation systems with other microfluidic functionalities for comprehensive clinical and biological tasks. This paper presented a simplified sheathless cell separation approach that combines gravitational-sedimentation-based sheathless prefocusing and DEP separation methods. Through gravitational sedimentation in a tubing, which was inserted into the inlet of a microfluidic chip with an adjustable steering angle, the cells were focused into a stream at the upstream region of a microchannel prior to separation. Then, a DEP force was applied at the downstream region of the microchannel for the active separation of the cells. Through this combined strategy, the peripheral system for the sheath flow was no longer required, and thus the integration of cell separation system with additional microfluidic functionalities was facilitated. The proposed sheathless scheme focused the mixture of cells with different sizes and dielectric properties into a stream in a wide range of flow rates without changing the design of the microfluidic chip. The DEP method is a label-free approach that can continuously separate cells on the basis of the sizes or dielectric properties of the cells and thus capable of greatly flexible cell separation. The efficiency of the proposed approach was experimentally assessed according to its performance in the separation of human acute monocytic leukemia THP-1 cells from yeast cells with respect to different sizes and THP-1 cells from human acute myelomonocytic leukemia OCI-AML3 cells with respect to different dielectric properties. The experimental results revealed that the separation efficiency of the method can surpass 90% and thus effective in separating cells on the basis of either size or dielectric property.

Correlation of simulation/finite element analysis to the separation of intrinsically magnetic spores and red blood cells using a microfluidic magnetic deposition system

Magnetic separation of cells has been, and continues to be, widely used in a variety of applications, ranging from healthcare diagnostics to detection of food contamination. Typically, these technologies require cells labeled with antibody magnetic particle conjugate and a high magnetic energy gradient created in the flow containing the labeled cells (i.e., a column packed with magnetically inducible material), or dense packing of magnetic particles next to the flow cell. Such designs, while creating high magnetic energy gradients, are not amenable to easy, highly detailed, mathematic characterization. Our laboratories have been characterizing and developing analysis and separation technology that can be used on intrinsically magnetic cells or spores which are typically orders of magnitude weaker than typically immunomagnetically labeled cells. One such separation system is magnetic deposition microscopy (MDM) which not only separates cells, but deposits them in specific locations on slides for further microscopic analysis. In this study, the MDM system has been further characterized, using finite element and computational fluid mechanics software, and separation performance predicted, using a model which combines: 1) the distribution of the intrinsic magnetophoretic mobility of the cells (spores); 2) the fluid flow within the separation device; and 3) accurate maps of the values of the magnetic field (max 2.27 T), and magnetic energy gradient (max of 4.41 T2 /mm) within the system. Guided by this model, experimental studies indicated that greater than 95% of the intrinsically magnetic Bacillus spores can be separated with the MDM system. Further, this model allows analysis of cell trajectories which can assist in the design of higher throughput systems.

A low voltage nanopipette dielectrophoretic device for rapid entrapment of nanoparticles and exosomes extracted from plasma of healthy donors

An insulator-based dielectrophoresis (iDEP) is a label-free method that has been extensively utilized for manipulation of nanoparticles, cells, and biomolecules. Here, we present a new iDEP approach that can rapidly trap nanoparticles at the close proximity of a glass nanopipette’s tip by applying 10 V/cm direct current (DC) across the pipette’s length. The trapping mechanism was systemically studied using both numerical modeling and experimental observations. The results showed that the particle trapping was determined to be controlled by three dominant electrokinetic forces including dielectrophoretic, electrophoretic and electroosmotic force. Furthermore, the effect of the ionic strength, the pipette’s geometry, and the applied electric field on the entrapment efficiency was investigated. To show the application of our device in biomedical sciences, we demonstrated the successful entrapment of fluorescently tagged liposomes and unlabeled plasma-driven exosomes from the PBS solution. Also, to illustrate the selective entrapment capability of our device, 100 nm liposomes were extracted from the PBS solution containing 500 nm polystyrene particles at the tip of the pipette as the voltage polarity was reversed.

Folic Acid Targeting for Efficient Isolation and Detection of Ovarian Cancer CTCs from Human Whole Blood Based on Two-Step Binding Strategy

Studies regarding circulating tumor cells (CTCs) have great significance for cancer prognosis, treatment monitoring, and metastasis diagnosis. However, due to their extremely low concentration in peripheral blood, isolation and enrichment of CTCs are the key steps for early detection. To this end, targeting the folic acid receptors (FRs) on the CTC surface for capture with folic acid (FA) using bovine serum albumin (BSA)-tether for multibiotin enhancement in combination with streptavidin-coated magnetic nanoparticles (MNPs-SA) was developed for ovarian cancer CTC isolation. The streptavidin-biotin-system-mediated two-step binding strategy was shown to capture CTCs from whole blood efficiently without the need for a pretreatment process. The optimized parameters for this system exhibited an average capture efficiency of 80%, which was 25% higher than that of FA-decorated magnetic nanoparticles based on the one-step CTC separation method. Moreover, the isolated cells remained highly viable and were cultured directly without detachment from the MNPs-SA-biotin-CTC complex. Furthermore, when the system was applied for the isolation and detection of CTCs in ovarian cancer patients' peripheral blood samples, it exhibited an 80% correlation with clinical diagnostic criteria. The results indicated that FA targeting, in combination with BSA-based multibiotin enhancement magnetic nanoparticle separation, is a promising tool for CTC enrichment and detection of early-stage ovarian cancer.

Safe core-satellite magneto-plasmonic nanostructures for efficient targeting and photothermal treatment of tumor cells

Magneto-plasmonic nanostructures functionalized with cell targeting units are of great interest for nanobiotechnology applications. Photothermal treatment of cells targeted with antibody functionalized nanostructures and followed by magnetic isolation, allows killing selected cells and hence is one of the applications of great interest. The magneto-plasmonic nanostructures reported herein were synthesized using naked gold and magnetite nanoparticles obtained through a green approach based on laser ablation of bulk materials in water. These particles do not need purifications steps for biocompatibility and are functionalized with a SERRS (surface enhanced resonance Raman scattering) active molecule for detection and with an antibody for targeting prostate tumor cells. Quantitative results for the cell targeting and selection efficiency show an overall accuracy of 94% at picomolar concentrations. The photothermal treatment efficiently kills targeted and magneto-selected cells producing a viability below 5% after 3 min of irradiation, compared with almost 100% viability of incubated and irradiated, but non targeted cells.

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.

Development of anti-CD47 single-chain variable fragment targeted magnetic nanoparticles for treatment of human bladder cancer

Aim: To develop a novel anti-CD47 single-chain variable fragment (scFv) functionalized magnetic nanoparticles (MNPs) for targeting bladder cell lines and its applicability in thermotherapy. Material & methods: An immunized murine antibody phage display library was constructed and screened to isolate anti-CD47 binders. A scFv was selected and conjugated to MNPs which was then utilized to discriminate CD47+ bladder cells along with assessing its efficacy in thermotherapy. Results: An scFv with high affinity to bladder cells was efficiently conjugated to MNPs. Following a hyperthermia treatment, the function of scFv–MNP conjugates led to a considerable reduction in cell viability. Conclusion: The anti-CD47 scFv–MNP conjugate was an effective cancer cell thermotherapy tool that might pave the way for development of bionano-based targeting techniques in both early detection and treatment of cancer.

In situ single cell detection via microfluidic magnetic bead assay

We present a single cell detection device based on magnetic bead assay and micro Coulter counters. This device consists of two successive micro Coulter counters, coupled with a high gradient magnetic field generated by an external magnet. The device can identify single cells in terms of the transit time difference of the cell through the two micro Coulter counters. Target cells are conjugated with magnetic beads via specific antibody and antigen binding. A target cell traveling through the two Coulter counters interacts with the magnetic field, and have a longer transit time at the 1st counter than that at the 2nd counter. In comparison, a non-target cell has no interaction with the magnetic field, and hence has nearly the same transit times through the two counters. Each cell passing through the two counters generates two consecutive voltage pulses one after the other; the pulse widths and magnitudes indicating the cell’s transit times through the counters and the cell’s size respectively. Thus, by measuring the pulse widths (transit times) of each cell through the two counters, each single target cell can be differentiated from non-target cells even if they have similar sizes. We experimentally proved that the target human umbilical vein endothelial cells (HUVECs) and non-target rat adipose-derived stem cells (rASCs) have significant different transit time distribution, from which we can determine the recognition regions for both cell groups quantitatively. We further demonstrated that within a mixed cell population of rASCs and HUVECs, HUVECs can be detected in situ and the measured HUVECs ratios agree well with the pre-set ratios. With the simple device structure and easy sample preparation, this method is expected to enable single cell detection in a continuous flow and can be applied to facilitate general cell detection applications such as stem cell identification and enumeration.

Inertial microfluidics combined with selective cell lysis for high throughput separation of nucleated cells from whole blood

The ability to rapidly analyze blood cells provides a wealth of information about our health. Here, we report on an automated, high-throughput, method that completely removes red blood cells and sort cells into subpopulation for downstream analysis.