Magnetism and microfluidics

Nano Meets Micro-Translational Nanotechnology in Medicine: Nano-Based Applications for Early Tumor Detection and Therapy

Nanomaterials have great potential for the prevention and treatment of cancer. Circulating tumor cells (CTCs) are cancer cells of solid tumor origin entering the peripheral blood after detachment from a primary tumor. The occurrence and circulation of CTCs are accepted as a prerequisite for the formation of metastases, which is the major cause of cancer-associated deaths. Due to their clinical significance CTCs are intensively discussed to be used as liquid biopsy for early diagnosis and prognosis of cancer. However, there are substantial challenges for the clinical use of CTCs based on their extreme rarity and heterogeneous biology. Therefore, methods for effective isolation and detection of CTCs are urgently needed. With the rapid development of nanotechnology and its wide applications in the biomedical field, researchers have designed various nano-sized systems with the capability of CTCs detection, isolation, and CTCs-targeted cancer therapy. In the present review, we summarize the underlying mechanisms of CTC-associated tumor metastasis, and give detailed information about the unique properties of CTCs that can be harnessed for their effective analytical detection and enrichment. Furthermore, we want to give an overview of representative nano-systems for CTC isolation, and highlight recent achievements in microfluidics and lab-on-a-chip technologies. We also emphasize the recent advances in nano-based CTCs-targeted cancer therapy. We conclude by critically discussing recent CTC-based nano-systems with high therapeutic and diagnostic potential as well as their biocompatibility as a practical example of applied nanotechnology.

Stability criterion for the magnetic separation of rare-earth ions

The stability criterion for the magnetic separation of rare-earth ions is studied, taking dysprosium Dy(iii) ions as an example. Emphasis is placed on quantifying the factors that limit the desired high enrichment. During magnetic separation, a layer enriched in Dy(iii) ions is generated via the surface evaporation of an aqueous solution which is levitated by the Kelvin force. Later, mass transport triggers instability in the enriched layer. The onset time and position of the instability is studied using an interferometer. The onset time signals that an advective process which significantly accelerates the stratification of enrichment is taking place, although the initial phase is quasi-diffusion-like. The onset position of the flow agrees well with that predicted with a generalized Rayleigh number (Ra^{*}=0) criterion which includes the Kelvin force term acting antiparallel to gravity. Further three-dimensional analysis of the potential energy, combining magnetic and gravitational terms, shows an energy barrier that has to be overcome to initiate instability. The position of the energy barrier coincides well with the onset position of the instability.

Calculation of Diamagnetic Susceptibility Tensors of Organic Crystals: From Coronene to Pharmaceutical Polymorphs

Understanding why crystallization in strong magnetic fields can lead to new polymorphs requires methods to calculate the diamagnetic response of organic molecular crystals. We develop the calculation of the macroscopic diamagnetic susceptibility tensor, χ^cryst, for organic molecular crystals using periodic density functional methods. The crystal magnetic susceptibility tensor, χ^cryst, for all experimentally known polymorphs, and its molecular counterpart, χ^mol, are calculated for flexible pharmaceuticals such as carbamazepine, flufenamic acid, and chalcones, and rigid molecules, such as benzene, pyridine, acridine, anthracene, and coronene, whose molecular magnetic properties have been traditionally studied. A tensor addition method is developed to approximate the crystal diamagnetic susceptibility tensor, χ^cryst, from the molecular one, χ^mol, giving good agreement with those calculated directly using the more costly periodic density functional method for χ^cryst. The response of pharmaceutical molecules and crystals to magnetic fields, as embodied by χ^cryst, is largely determined by the packing in the crystal, as well as the molecular conformation. The anisotropy of χ^cryst can vary considerably between polymorphs though the isotropic terms are fairly constant. The implications for developing a computational method for predicting whether crystallization in a magnetic field could produce a novel or different polymorph are discussed.

Integrated Microfluidic Preconcentration and Nucleic Amplification System for Detection of Influenza A Virus H1N1 in Saliva

Influenza A viruses are often present in environmental and clinical samples at concentrations below the limit of detection (LOD) of molecular diagnostics. Here we report an integrated microfluidic preconcentration and nucleic amplification system (μFPNAS) which enables both preconcentration of influenza A virus H1N1 (H1N1) and amplification of its viral RNA, thereby lowering LOD for H1N1. H1N1 virus particles were first magnetically preconcentrated using magnetic nanoparticles conjugated with an antibody specific for the virus. Their isolated RNA was amplified to cDNA through thermocycling in a trapezoidal chamber of the μFPNAS. A detection limit as low as 100 TCID50 (50% tissue culture infective dose) in saliva can be obtained within 2 hours. These results suggest that the LOD of molecular diagnostics for virus can be lowered by systematically combining immunomagnetic separation and reverse transcriptase-polymerase chain reaction (RT-PCR) in one microfluidic device.

Direct identification of the herpes simplex virus UL27 gene through single particle manipulation and optical detection using a micromagnetic array

Magnetophoretic lab on a chip technologies are rapidly evolving into integrated systems for the identification of biomarkers and cells with ultra-high sensitivity. We demonstrate the highly efficient detection of the Human herpes simplex virus type 1 (HSV) UL27 gene through the programmed assembly of superparamagnetic (SPM) nanoparticles based on oligonucleotide hybridization. The state of assembly of the SPM nanoparticles was determined by optical signature of the synchronized motion on the beads on a micromagnetic array (MMA). This technique has been used to identify <200 copies of the HSV UL27 gene without amplification in less than 20 minutes. The MAA can also be used to separate gene-SPM bead aggregates from millions of unreacted SPM beads based on nonlinear magnetophoresis (NLM). The MMA-optical detection system promises to enable highly sensitive, nucleic acid analysis to be performed without amplification and with the consumption of minimal amounts of reagent.

Micro-nanoparticles magnetic trap: Toward high sensitivity and rapid microfluidic continuous flow enzyme immunoassay

In this work, we developed a microfluidic system for immunoassays where we combined the use of magnetic nanoparticles as immunosupport, a microfluidic magnetic trap, and a fluorogenic substrate in continuous flow for detection which, together with the optimization of the functionalization of surfaces to minimize nonspecific interactions, resulted in a detection limit in the order of femtomolar and a total assay time of 40 min for antibiotin antibody detection. A magnetic trap made of carbonyl-iron microparticles packaged inside a 200  μ m square microchannel was used to immobilize and concentrate nanoparticles. We functionalized the surface of the iron microparticles with a silica-polyethylene glycol (PEG) shell to avoid corrosion and unspecific protein binding. A new one-step method was developed to coat acrylic microchannels with an organofunctional silane functionalized with PEG to minimize unspecific binding. A model immunoassay was performed using nanoparticles decorated with biotin to capture antibiotin rabbit Immunoglobulin G (IgG) as target primary antibody. The detection was made using antirabbit IgG labeled with the enzyme alkaline phosphatase as a secondary antibody, and we measured fluorescence with a fluorescence microscope. All steps of the immunoassay were performed inside the chip. A calibration curve was obtained in which a detection limit of 8 pg/ml of antibiotin antibody was quantified. The simplicity of the device and the fact that it is made of acrylic, which is compatible with mass production, make it ideal for Point-Of-Care applications.

Numerical Study of Paramagnetic Elliptical Microparticles in Curved Channels and Uniform Magnetic Fields

We numerically investigated the dynamics of a paramagnetic elliptical particle immersed in a low Reynolds number Poiseuille flow in a curved channel and under a uniform magnetic field by direct numerical simulation. A finite element method, based on an arbitrary Lagrangian-Eulerian approach, analyzed how the channel geometry, the strength and direction of the magnetic field, and the particle shape affected the rotation and radial migration of the particle. The net radial migration of the particle was analyzed after executing a π rotation and at the exit of the curved channel with and without a magnetic field. In the absence of a magnetic field, the rotation is symmetric, but the particle-wall distance remains the same. When a magnetic field is applied, the rotation of symmetry is broken, and the particle-wall distance increases as the magnetic field strength increases. The causation of the radial migration is due to the magnetic angular velocity caused by the magnetic torque that constantly changes directions during particle transportation. This research provides a method of magnetically manipulating non-spherical particles on lab-on-a-chip devices for industrial and biological applications.

Microelectrofluidic probe for sequential cell separation and patterning

Cell separation and patterning are of interest to several biological and medical applications including rare cell isolation and co-culture models. Numerous microfluidic devices have been used for cell separation and patterning, however, the typical closed channel configuration comes with challenges and limitations. Here, we report a dielectrophoresis (DEP) enabled microelectrofluidic probe (MeFP) for sequentially separating and patterning of mammalian cells in an open microfluidic system. The MeFP is a microfluidic probe with injection and aspiration apertures, integrated with an array of micro-hump electrodes on its tip. Aligning the MeFP parallel, and in close proximity, to a conductive substrate forms a vertical pin-plate electrode configuration that allows for an integration of DEP forces within the hydrodynamic flow confinement. Upon confining a heterogeneous cell suspension in the gap between the MeFP and the substrate, target cells are selectively captured on the micro-hump electrodes using positive DEP forces, and then deposited on the substrate in defined patterns. Characterization of the MeFP showed an increase in cell-capture efficiency when the MeFP is of a higher microfluidic multipole configuration. Separation of cancer cells from T lymphocytes was demonstrated with capture purity as high as 89.6%. Deposited patterns of isolated cells match the numerically calculated particle trajectories of the evaluated microfluidic multipoles configurations. By adjusting the flow configuration of the MeFP, we show that the patterned co-culture of two different cell types can be dynamically controlled for homotypic and heterotypic cell interaction studies. This work presents a multifunctional microfluidic tool that bio-fabricates selective multicellular patterns directly on an open substrate without the need for confined conduits.

Magnetically Actuated Tunable Soft Electronics

Variable electronics are vital in tunable filters, transmitters, and receivers, among other applications. In addition, the ability to remotely tune soft capacitors, resistors, and inductors is important for applications in which the device is not accessible. In this paper, a uniform method of remotely tuning the characteristic properties of soft electronic units (i.e. inductance, capacitance, and resistance) is presented. In this method, magnetically actuated ferrofluid mixed with iron powder is dragged in a soft fluidic channel made of polydimethylsiloxane (PDMS) to tune the electrical properties of the component. The effects of position and quantity of the ferrofluid and iron powder are studied over a range of frequencies, and the changes in inductance, capacitance, resistance, quality factor, and self-resonance frequency are reported accordingly. The position plays a bigger role in changing inductance, capacitance, and resistance. With the proposed design, the inductance can be changed by 20.9% from 3.31 μH for planar inductors and 23% from 0.44 μH for axial inductors. In addition, the capacitance of capacitors and impedance of resistors can be changed by 12.7% from 2.854 pF and 185.3% from 0.353 kΩ, respectively. Furthermore, the changes in the inductance, capacitance, and resistance follow "quasi-linear profiles" with the input during position and quantity effect experiments.

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.

Perpetual sedimentation for the continuous delivery of particulate suspensions

Particle sedimentation is deleterious to a tremendous variety of microfluidic applications. Using an open instrumentation approach we show that syringe rotation retains particles in a suspended state, providing a universal solution for the continuous delivery of particulate samples to microfluidic processors.

Low-cost multi-core inertial microfluidic centrifuge for high-throughput cell concentration

We developed a low-cost multi-core inertial microfluidic centrifuge (IM-centrifuge) to achieve a continuous-flow cell/particle concentration at a throughput of up to 20 mL/min. To lower the cost of our IM-centrifuge, we clamped a disposable multilayer film-based inertial microfluidic (MFIM) chip with two reusable plastic housings. The key MFIM chip was fabricated in low-cost materials by stacking different polymer-film channel layers and double-sided tape. To increase processing throughput, multiplexing spiral inertial microfluidic channels were integrated within an all-in-one MFIM chip, and a novel sample distribution strategy was employed to equally distribute the sample into each channel layer. Then, we characterized the focusing performance in the MFIM chip over a wide flow-rate range. The experimental results showed that our IM-centrifuge was able to focus various-sized particles/cells to achieve volume reduction. The sample distribution strategy also effectively ensured identical focusing and concentration performances in different cores. Finally, our IM-centrifuge was successfully applied to concentrate microalgae cells with irregular shapes and highly polydisperse sizes. Thus, our IM-centrifuge holds the potential to be employed as a low-cost, high-throughput centrifuge for disposable use in low-resource settings.

Shaping and transporting diamagnetic sessile drops

Electromagnetic fields are commonly used to control small quantities of fluids in microfluidics and digital microfluidics. Magnetic control techniques are less well studied than their electric counterparts, with only a few investigations into liquid diamagnetism. The ratio of magnetic to surface energy (magnetic Bond number B m ) is an order of magnitude smaller for diamagnetic drops ( B m ≈ - 0.3 at 1.2 T applied field) than for paramagnetic drops ( B m ≈ 9.0 at 1.2 T applied field). This weaker interaction between the magnetic field and the diamagnetic drop has led to the phenomenon being overlooked in digital microfluidics. Here, we investigate shaping and transport of diamagnetic drops using magnetostatic fields. Our findings highlight how diamagnetic fluids can be used as a novel tool in the toolbox of microfluidics and digital microfluidics.

Recent Advances in Continuous-Flow Particle Manipulations Using Magnetic Fluids

Magnetic field-induced particle manipulation is simple and economic as compared to other techniques (e.g., electric, acoustic, and optical) for lab-on-a-chip applications. However, traditional magnetic controls require the particles to be manipulated being magnetizable, which renders it necessary to magnetically label particles that are almost exclusively diamagnetic in nature. In the past decade, magnetic fluids including paramagnetic solutions and ferrofluids have been increasingly used in microfluidic devices to implement label-free manipulations of various types of particles (both synthetic and biological). We review herein the recent advances in this field with focus upon the continuous-flow particle manipulations. Specifically, we review the reported studies on the negative magnetophoresis-induced deflection, focusing, enrichment, separation, and medium exchange of diamagnetic particles in the continuous flow of magnetic fluids through microchannels.

Characterizing the Process Physics of Ultrasound-Assisted Bioprinting

3D bioprinting has been evolving as an important strategy for the fabrication of engineered tissues for clinical, diagnostic, and research applications. A major advantage of bioprinting is the ability to recapitulate the patient-specific tissue macro-architecture using cellular bioinks. The effectiveness of bioprinting can be significantly enhanced by incorporating the ability to preferentially organize cellular constituents within 3D constructs to mimic the intrinsic micro-architectural characteristics of native tissues. Accordingly, this work focuses on a new non-contact and label-free approach called ultrasound-assisted bioprinting (UAB) that utilizes acoustophoresis principle to align cells within bioprinted constructs. We describe the underlying process physics and develop and validate computational models to determine the effects of ultrasound process parameters (excitation mode, excitation time, frequency, voltage amplitude) on the relevant temperature, pressure distribution, and alignment time characteristics. Using knowledge from the computational models, we experimentally investigate the effect of selected process parameters (frequency, voltage amplitude) on the critical quality attributes (cellular strand width, inter-strand spacing, and viability) of MG63 cells in alginate as a model bioink system. Finally, we demonstrate the UAB of bilayered constructs with parallel (0°-0°) and orthogonal (0°-90°) cellular alignment across layers. Results of this work highlight the key interplay between the UAB process design and characteristics of aligned cellular constructs, and represent an important next step in our ability to create biomimetic engineered tissues.

Self-assembly of colloids based on microfluidics

Self-assembly of colloids provides a powerful way for the construction of complex multi-scale materials. Microfluidic techniques possess great potential to precisely control the assembly of micro- and nano-scale building blocks via the rational design of various microfluidic environments. In this review, we first discuss the self-assembly of colloids without templates by using the laminar microfluidic technique. The self-assembly of colloids based on a droplet as a template was subsequently summarized and discussed via droplet microfluidic technique. Moreover, the evaporation-driven self-assembly of colloids in microfluidic channels has been discussed and analysed. Finally, the representative applications in this field have been pointed out. The aim of this review is to summarize the state-of-art on the self-assembly of colloids based on various microfluidic techniques, exhibit their representative applications, and point out the current challenges in this field, hoping to inspire and guide future work.

Self-Sustained Coalescence-Breakup Cycles of Ferrodrops under a Magnetic Field

The self-sustained coalescence-breakup cycles of ferrodrops were investigated for the first time by a high-speed camera under various magnetic fields. Under an axial magnetic field, the upper ferrodrop would deform into a conic shape before coalescing with the bottom ferropeak. Within 0.2 ms after coalescence, the minimum width of the expanding neck obeys a power-law relationship with time, while the exponents increase with the magnetic field and deviate with a decreasing trend in the later coalescence. The cone angle of the upper ferrodrop before coalescence gradually decreases while it increases before breakup with the magnetic field. A critical magnetic field around 35 mT was reported, above which the ferrofluid column undergoes the periodic phenomenon of coalescence and breakup. The frequency for the whole coalescence-breakup cycle increases exponentially with the applied magnetic field. A simplified force balance allows capturing the periodic mechanism involved in this driven harmonic oscillator.

Liquid-Infused Surfaces: A Review of Theory, Design, and Applications

Due to inspiration from the Nepenthes pitcher plant, a frontier of devices has emerged with unmatched capabilities. Liquid-infused surfaces (LISs), particularly known for their liquid-repelling behavior under low tilting angles (<5°), have demonstrated a plethora of applications in medical, marine, energy, industrial, and environmental materials. This review presents recent developments of LIS technology and its prospective to define the future direction of this technology in solving tomorrow's real-life challenges. First, an introduction to the different models explaining the physical phenomena of these surfaces, their wettability, and viscous-dependent frictional forces is discussed. Then, an outline of different emerging strategies required to fabricate a stable liquid-infused interface is presented, including different substrates, lubricants, surface chemistries, and design parameters which can be tuned depending on the application. Furthermore, applications of LIS coatings in the areas of anticorrosion, antifouling, anti-icing, self-healing, droplet manipulation, and biomedical devices will be presented followed by the limitations and future direction of this technology.

Is small smarter? Nanomaterial-based detection and elimination of circulating tumor cells: current knowledge and perspectives

Circulating tumor cells (CTCs) are disseminated cancer cells. The occurrence and circulation of CTCs seem key for metastasis, still the major cause of cancer-associated deaths. As such, CTCs are investigated as predictive biomarkers. However, due to their rarity and heterogeneous biology, CTCs’ practical use has not made it into the clinical routine. Clearly, methods for the effective isolation and reliable detection of CTCs are urgently needed. With the development of nanotechnology, various nanosystems for CTC isolation and enrichment and CTC-targeted cancer therapy have been designed. Here, we summarize the relationship between CTCs and tumor metastasis, and describe CTCs’ unique properties hampering their effective enrichment. We comment on nanotechnology-based systems for CTC isolation and recent achievements in microfluidics and lab-on-a-chip technologies. We discuss recent advances in CTC-targeted cancer therapy exploiting the unique properties of nanomaterials. We conclude by introducing developments in CTC-directed nanosystems and other advanced technologies currently in (pre)clinical research.

Interaction pressure tensor on high-order lattice Boltzmann models for nonideal fluids

In this work we address the application of pseudopotentials directly on high-order lattice Boltzmann models. We derive a general expression for the pressure tensor on high-order lattices considering all nonideal interactions, including intra- and intermolecular interactions, following the discrete lattice theory introduced by X. Shan [Phys. Rev. E 77, 066702 (2008)PLEEE81539-375510.1103/PhysRevE.77.066702]. From the derived expression, a generalized continuum approximation, truncated at fourth-order isotropy, is obtained that is readily applicable to high-order lattices. With this, we demonstrate that high-order lattice models with pseudopotentials can satisfy thermodynamic consistency. The derived generalized expression and continuum approximation are validated for the case of a flat interface and compared against the standard definition available from the literature. The generalized expression is also shown to accurately reproduce the Laplace experiment for a variety of high-order lattice structures. This work sets the preliminary steps towards the application of high-order lattice models for simulating nonideal fluid mixtures.

Tumor antigen-independent and cell size variation-inclusive enrichment of viable circulating tumor cells

Isolation of circulating tumor cells (CTCs) from blood provides a minimally-invasive alternative for basic understanding, diagnosis, and prognosis of metastatic cancer. The roles and clinical values of CTCs are under intensive investigation, yet most studies are limited by technical challenges in the comprehensive enrichment of intact and viable CTCs with minimal white blood cell (WBC) contamination. Here, we report a novel method based on contrast of cell magnetization in biocompatible ferrofluids (a colloidal magnetic nanoparticle suspension), termed as integrated ferrohydrodynamic cell separation (iFCS), that enriches CTCs in a tumor antigen-independent and cell size variation-inclusive manner, achieves a high throughput (12 mL h-1), high recovery rate (99.08% at down to ∼10 cells per mL spike ratio), and low WBC contamination (533 cells for every one milliliter blood processed) and is biocompatible. This method will enable large cohort research to define the clinical and diagnostic value of CTC subtypes.

Numerical Analysis of Bead Magnetophoresis from Flowing Blood in a Continuous-Flow Microchannel: Implications to the Bead-Fluid Interactions

In this work, we report a numerical flow-focused study of bead magnetophoresis inside a continuous-flow microchannel in order to provide a detailed analysis of bead motion and its effect on fluid flow. The numerical model involves a Lagrangian approach and predicts the bead separation from blood and their collection into a flowing buffer by the application of a magnetic field generated by a permanent magnet. The following scenarios are modelled: (i) one-way coupling wherein momentum is transferred from the fluid to beads, which are treated as point particles, (ii) two-way coupling wherein the beads are treated as point particles and momentum is transferred from the bead to the fluid and vice versa, and (iii) two-way coupling taking into account the effects of bead volume in fluid displacement. The results indicate that although there is little difference in the bead trajectories for the three scenarios, there is significant variation in the flow fields, especially when high magnetic forces are applied on the beads. Therefore, an accurate full flow-focused model that takes into account the effects of the bead motion and volume on the flow field should be solved when high magnetic forces are employed. Nonetheless, when the beads are subjected to medium or low magnetic forces, computationally inexpensive models can be safely employed to model magnetophoresis.

Ephemeral states in protein folding under force captured with a magnetic tweezers design

Magnetic tape heads are ubiquitously used to read and record on magnetic tapes in technologies as diverse as old VHS tapes, modern hard-drive disks, or magnetic bands on credit cards. Their design highlights the ability to convert electric signals into fluctuations of the magnetic field at very high frequencies, which is essential for the high-density storage demanded nowadays. Here, we twist this conventional use of tape heads to implement one in a magnetic tweezers design, which offers the unique capability of changing the force with a bandwidth of ∼10 kHz. We calibrate our instrument by developing an analytical expression that predicts the magnetic force acting on a superparamagnetic bead based on the Karlqvist approximation of the magnetic field created by a tape head. This theory is validated by measuring the force dependence of protein L unfolding/folding step sizes and the folding properties of the R3 talin domain. We demonstrate the potential of our instrument by carrying out millisecond-long quenches to capture the formation of the ephemeral molten globule state in protein L, which has never been observed before. Our instrument provides the capability of interrogating individual molecules under fast-changing forces with a control and resolution below a fraction of a piconewton, opening a range of force spectroscopy protocols to study protein dynamics under force.

Potential utility of graphene-based nano spinel ferrites as adsorbent and photocatalyst for removing organic/inorganic contaminants from aqueous solutions: A mini review

Toxic substances such as heavy metals or persistent organic pollutants raise global environmental concerns. Thus, diverse water decontamination approaches using nano-adsorbents and/or photocatalysts based on nanotechnology are being developed. Particularly, many studies have examined the removal of organic and inorganic contaminants with novel graphene-based nano spinel ferrites (GNSFs) as potential cost-effective alternatives to traditionally used materials, owing to their enhanced physical and chemical properties. The introduction of magnetic spinel ferrites into 2-D graphene-family nanomaterials to form GNSFs brings various benefits such as inhibited particle agglomeration, enhanced active surface area, and easier magnetic separation for reuse, making the GNSFs highly efficient and eco-friendly materials. Here, we present a short review on the state-of-the-art progresses on developments of GNSFs, as well as their potential application for removing several recalcitrant contaminants including organic dyes, antibiotics, and heavy metal ions. Particularly, the mechanisms involved in the adsorptive and photocatalytic degradation are thoroughly reviewed, and the reusability of the GNSFs is also highlighted. This review concludes that the GNSFs hold great potential in remediating contaminated aquatic environments. Further studies are needed for their practical and large-scale applications.

µLAS: Sizing of expanded trinucleotide repeats with femtomolar sensitivity in less than 5 minutes

We present µLAS, a lab-on-chip system that concentrates, separates, and detects DNA fragments in a single module. µLAS speeds up DNA size analysis in minutes using femtomolar amounts of amplified DNA. Here we tested the relevance of µLAS for sizing expanded trinucleotide repeats, which cause over 20 different neurological and neuromuscular disorders. Because the length of trinucleotide repeats correlates with the severity of the diseases, it is crucial to be able to size repeat tract length accurately and efficiently. Expanded trinucleotide repeats are however genetically unstable and difficult to amplify. Thus, the amount of amplified material to work with is often limited, making its analysis labor-intensive. We report the detection of heterogeneous allele lengths in 8 samples from myotonic dystrophy type 1 and Huntington disease patients with up to 750 CAG/CTG repeats in five minutes or less. The high sensitivity of the method allowed us to minimize the number of amplification cycles and thus reduce amplification artefacts without compromising the detection of the expanded allele. These results suggest that µLAS can speed up routine molecular biology applications of repetitive sequences and may improve the molecular diagnostic of expanded repeat disorders.

Development of a microfluidic platform for size-based hydrodynamic enrichment and PSMA-targeted immunomagnetic isolation of circulating tumour cells in prostate cancer

Efforts to further improve the clinical management of prostate cancer (PCa) are hindered by delays in diagnosis of tumours and treatment deficiencies, as well as inaccurate prognoses that lead to unnecessary or inefficient treatments. The quantitative and qualitative analysis of circulating tumour cells (CTCs) may address these issues and could facilitate the selection of effective treatment courses and the discovery of new therapeutic targets. Therefore, there is much interest in isolation of elusive CTCs from blood. We introduce a microfluidic platform composed of a multiorifice flow fractionation (MOFF) filter cascaded to an integrated microfluidic magnetic (IMM) chip. The MOFF filter is primarily employed to enrich immunomagnetically labeled blood samples by size-based hydrodynamic removal of free magnetic beads that must originally be added to samples at disproportionately high concentrations to ensure the efficient immunomagnetic labeling of target cancer cells. The IMM chip is then utilized to capture prostate-specific membrane antigen-immunomagnetically labeled cancer cells from enriched samples. Our preclinical studies showed that the proposed method can selectively capture up to 75% of blood-borne PCa cells at clinically-relevant low concentrations (as low as 5 cells/ml), with the IMM chip showing up to 100% magnetic capture capability.

Effect of moderate magnetic fields on the surface tension of aqueous liquids: a reliable assessment

We precisely measure the effect of moderate magnetic field intensity on the surface tension of liquids, by placing pendant drops inside uniform fields where bulk forces due to gradients are eliminated. The surface tension of water is unaffected while that of paramagnetic salt solutions slightly decreases with increasing field strength.

A novel setup measures the effect of magnetic field intensities on the surface tension of liquids placed inside uniform fields.

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.

Microfluidic diamagnetic water-in-water droplets: a biocompatible cell encapsulation and manipulation platform

Droplet microfluidics enables cellular encapsulation for biomedical applications such as single-cell analysis, which is an important tool used by biologists to study cells on a single-cell level, and understand cellular heterogeneity in cell populations. However, most cell encapsulation strategies in microfluidics rely on random encapsulation processes, resulting in large numbers of empty droplets. Therefore, post-sorting of droplets is necessary to obtain samples of purely cell-encapsulating droplets. With the recent advent of aqueous two-phase systems (ATPS) as a biocompatible alternative of the conventional water-in-oil droplet systems for cellular encapsulation, there has also been a focus on integrating ATPS with droplet microfluidics. In this paper, we describe a new technique that combines ATPS-based water-in-water droplets with diamagnetic manipulation to isolate single-cell encapsulating water-in-water droplets, and achieve a purity of 100% in a single pass. We exploit the selective partitioning of ferrofluid in an ATPS of polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymer (PEG-PPG-PEG) and dextran (DEX), to achieve diamagnetic manipulation of water-in-water droplets. A cell-triggered Rayleigh-Plateau instability in the dispersed phase thread results in a size distinction between the cell-encapsulating and empty droplets, enabling diamagnetic separation and sorting of the cell-encapsulating droplets from empty droplets. This is a simple and biocompatible all-aqueous platform for single-cell encapsulation and droplet manipulation, with applications in single-cell analysis.

Magnetic Biohybrid Vesicles Transported by an Internal Propulsion Mechanism

Some biological microorganisms can crawl or swim due to coordinated motions of their cytoskeleton or the flagella located inside their bodies, which push the cells forward through intracellular forces. To date, there is no demonstration of synthetic systems propelling at low Reynolds number via the precise actuation of the material confined within an enclosing lipid membrane. Here, we report lipid vesicles and other more complex self-assembled biohybrid structures able to propel due to the advection flows generated by the actuated rotation of the superparamagnetic particles they contain. The proposed swimming and release strategies, based on cooperative hydrodynamic mechanisms and near-infrared laser pulse-triggered destabilization of the phospholipid membranes, open new possibilities for the on-command transport of minute quantities of drugs, fluid or nano-objects. The lipid membranes protect the confined substances from the outside environment during transportation, thus enabling them to work in physiological conditions.

A Hierarchical 3D Nanostructured Microfluidic Device for Sensitive Detection of Pathogenic Bacteria

Efficient capture and rapid detection of pathogenic bacteria from body fluids lead to early diagnostics of bacterial infections and significantly enhance the survival rate. We propose a universal nano/microfluidic device integrated with a 3D nanostructured detection platform for sensitive and quantifiable detection of pathogenic bacteria. Surface characterization of the nanostructured detection platform confirms a uniform distribution of hierarchical 3D nano-/microisland (NMI) structures with spatial orientation and nanorough protrusions. The hierarchical 3D NMI is the unique characteristic of the integrated device, which enables enhanced capture and quantifiable detection of bacteria via both a probe-free and immunoaffinity detection method. As a proof of principle, we demonstrate probe-free capture of pathogenic Escherichia coli (E. coli) and immunocapture of methicillin-resistant-Staphylococcus aureus (MRSA). Our device demonstrates a linear range between 50 and 10⁴ CFU mL^-1 , with average efficiency of 93% and 85% for probe-free detection of E. coli and immunoaffinity detection of MRSA, respectively. It is successfully demonstrated that the spatial orientation of 3D NMIs contributes in quantifiable detection of fluorescently labeled bacteria, while the nanorough protrusions contribute in probe-free capture of bacteria. The ease of fabrication, integration, and implementation can inspire future point-of-care devices based on nanomaterial interfaces for sensitive and high-throughput optical detection.

Magnetophoretic Sorting of Single Catalyst Particles

A better understanding of the deactivation processes taking place within solid catalysts is vital to design better ones. However, since inter-particle heterogeneities are more a rule than an exception, particle sorting is crucial to analyse single catalyst particles in detail. Microfluidics offers new possibilities to sort catalysts at the single particle level. Herein, we report a first-of-its-kind 3D printed magnetophoretic chip able to sort catalyst particles by their magnetic moment. Fluid catalytic cracking (FCC) particles were separated based on their Fe content. Magnetophoretic sorting shows that large Fe aggregates exist within 20 % of the FCC particles with the highest Fe content. The availability of Brønsted acid sites decreases with increasing Fe content. This work paves the way towards a high-throughput catalyst diagnostics platform to determine why specific catalyst particles perform better than others.

Multifunctional ferrofluid-infused surfaces with reconfigurable multiscale topography

Developing adaptive materials with geometries that change in response to external stimuli provides fundamental insights into the links between the physical forces involved and the resultant morphologies and creates a foundation for technologically relevant dynamic systems^1,2. In particular, reconfigurable surface topography as a means to control interfacial properties³ has recently been explored using responsive gels⁴, shape-memory polymers⁵, liquid crystals^6-8 and hybrid composites^9-14, including magnetically active slippery surfaces^12-14. However, these designs exhibit a limited range of topographical changes and thus a restricted scope of function. Here we introduce a hierarchical magneto-responsive composite surface, made by infiltrating a ferrofluid into a microstructured matrix (termed ferrofluid-containing liquid-infused porous surfaces, or FLIPS). We demonstrate various topographical reconfigurations at multiple length scales and a broad range of associated emergent behaviours. An applied magnetic-field gradient induces the movement of magnetic nanoparticles suspended in the ferrofluid, which leads to microscale flow of the ferrofluid first above and then within the microstructured surface. This redistribution changes the initially smooth surface of the ferrofluid (which is immobilized by the porous matrix through capillary forces) into various multiscale hierarchical topographies shaped by the size, arrangement and orientation of the confining microstructures in the magnetic field. We analyse the spatial and temporal dynamics of these reconfigurations theoretically and experimentally as a function of the balance between capillary and magnetic pressures^15-19 and of the geometric anisotropy of the FLIPS system. Several interesting functions at three different length scales are demonstrated: self-assembly of colloidal particles at the micrometre scale; regulated flow of liquid droplets at the millimetre scale; and switchable adhesion and friction, liquid pumping and removal of biofilms at the centimetre scale. We envision that FLIPS could be used as part of integrated control systems for the manipulation and transport of matter, thermal management, microfluidics and fouling-release materials.

Prozone-like phenomenon found in chemiluminescent enzyme immunoassay using magnetic particles for measurement of serum anti-single stranded DNA antibody titers: Definition and management

BACKGROUND

Serum anti-single stranded DNA antibody (anti-ssDNAab) is used as a marker for systemic lupus erythematosus. We found a 'prozone-like phenomenon,' which was different from an original prozone phenomenon, in chemiluminescent enzyme immunoassay using magnetic particles for the measurement of serum anti-ssDNAab titers. We investigated mechanisms of the prozone-like phenomenon and countermeasures to prevent it from being overlooked.

METHODS

This study examined 679 samples from patients tested for anti-ssDNAab titer at our hospital. In addition, the BF photometry OD value 2 (OD2), an index of optical density, was monitored simultaneously.

RESULTS

The undiluted samples with a prozone-like phenomenon showed extremely lower OD2. Those samples were able to be distinguished from other samples by setting OD2 criteria based on the 95% prediction interval. Significant differences (p < 0.05) were found in the titer ratios (ten-fold diluted against undiluted) between groups with >1.5 and other groups with <1.5 for the ratios of OD2.

CONCLUSIONS

We proposed two valuable methods to find a prozone-like phenomenon: one by setting OD2 criteria based on the 95% prediction interval and the other by analyzing the ratios both in titers and OD2 between undiluted and 10-fold diluted samples.

Computational modeling and fluorescence microscopy characterization of a two-phase magnetophoretic microsystem for continuous-flow blood detoxification

Magnetic beads can be functionalized to capture and separate target pathogens from blood for extracorporeal detoxification. The beads can be magnetically separated from a blood stream and collected into a coflowing buffer solution using a two-phase liquid-liquid continuous-flow microfluidic device in the presence of an external field. However, device design and process optimization, i.e. high bead recovery with minimum blood loss or dilution remain a substantial technological challenge. We introduce a CFD-based Eulerian-Lagrangian computational model that enables the rational design and optimization of such systems. The model takes into account dominant magnetic and hydrodynamic forces on the beads as well as coupled bead-fluid interactions. Fluid flow (Navier-Stokes equations) and mass transfer (Fick's law) between the coflowing fluids are solved numerically, while the magnetic force on the beads is predicted using analytical methods. The model is demonstrated via application to a prototype device and used to predict key performance metrics; degree of bead separation, flow patterns, and mass transfer, i.e. blood diffusion to the buffer phase. The impact of different process variables and parameters - flow rates, bead and magnet dimensions and fluid viscosities - on both bead recovery and blood loss or dilution is quantified for the first time. The performance of the prototype device is characterized using fluorescence microscopy and the experimental results are found to match theoretical predictions within an absolute error of 15%. While the model is demonstrated here for analysis of a detoxification device, it can be readily adapted to a broad range of magnetically-enabled microfluidic applications, e.g. bioseparation, sorting and sensing.

Biofabrication of in situ Self Assembled 3D Cell Cultures in a Weightlessness Environment Generated using Magnetic Levitation

Magnetic levitation though negative magnetophoresis is a novel technology to simulate weightlessness and has recently found applications in material and biological sciences. Yet little is known about the ability of the magnetic levitation system to facilitate biofabrication of in situ three dimensional (3D) cellular structures. Here, we optimized a magnetic levitation though negative magnetophoresis protocol appropriate for long term levitated cell culture and developed an in situ 3D cellular assembly model with controlled cluster size and cellular pattern under simulated weightlessness. The developed strategy outlines a potential basis for the study of weightlessness on 3D living structures and with the opportunity for real-time imaging that is not possible with current ground-based simulated weightlessness techniques. The low-cost technique presented here may offer a wide range of biomedical applications in several research fields, including mechanobiology, drug discovery and developmental biology.

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.

Integration of Magnetic Bead-Based Cell Selection into Complex Isolations

Magnetic bead-based analyte capture has emerged as a ubiquitous method in cell isolation, enabling the highly specific capture of target populations through simple magnetic manipulation. To date, no "one-size fits all" magnetic bead has been widely adopted leading to an overwhelming number of commercial beads. Ultimately, the ideal bead is one that not only facilitates cell isolation but also proves compatible with the widest range of downstream applications and analytic endpoints. Despite the diverse offering of sizes, coatings, and conjugation chemistries, few studies exist to benchmark the performance characteristics of different commercially available beads; importantly, these bead characteristics ultimately determine the ability of a bead to integrate into the user's assay. In this report, we evaluate bead-based cell isolation considerations, approaches, and results across a subset of commercially available magnetic beads (Dynabeads FlowComps, Dynabeads CELLection, GE Healthcare Sera-Mag SpeedBeads streptavidin-blocked magnetic particles, Dynabeads M-270s, Dynabeads M-280s) to compare and contrast both capture-specific traits (i.e., purity, capture efficacy, and contaminant isolations) and endpoint compatibility (i.e., protein localization, fluorescence imaging, and nucleic acid extraction). We identify specific advantages and contexts of use in which distinct bead products may facilitate experimental goals and integrate into downstream applications.

Particle-Based Microfluidic Quartz Crystal Microbalance (QCM) Biosensing Utilizing Mass Amplification and Magnetic Bead Convection

Microfluidic quartz crystal microbalances (QCM) can be used as powerful biosensors that not only allow quantifying a target analyte, but also provide kinetic information about the surface processes of binding and release. Nevertheless, their practical use as point-of-care devices is restricted by a limit of detection (LoD) of some ng/cm². It prohibits the measurement of small molecules in low concentrations within the initial sample. Here, two concepts based on superparamagnetic particles are presented that allow enhancing the LoD of a QCM. First, a particle-enhanced C-reactive protein (CRP) measurement on a QCM is shown. The signal response could be increased by a factor of up to five by utilizing the particles for mass amplification. Further, a scheme for sample pre-preparation utilizing convective up-concentration involving magnetic bead manipulation is investigated. These experiments are carried out with a glass device that is fabricated by utilizing a femtosecond laser. Operation regimes for the magnetic manipulation of particles within the microfluidic channel with integrated pole pieces that are activated by external permanent magnets are described. Finally, the potential combination of the concepts of mass amplification and up-concentration within an integrated lab-on-a chip device is discussed.