Particle Sorting Research Articles

Inertia-Induced Breakdown of Acoustic Sorting Efficiency at High Flow Rates

The clinical utility of microfluidic techniques is often hampered by an unsatisfying sample throughput. Here, the effect of inertial forces on acoustofluidic particle sorting at high sample throughputs is investigated experimentally and theoretically. Polystyrene particles are acoustically prefocused to obtain precise trajectories. At increased flow rates it is observed that the particle stream is displaced towards the channel center, and above specific flow settings the particles spill over into the center outlet. This effect, coined the spillover effect, illustrates the complex interplay of viscous and inertial forces inside the microchannel. The effect is due to increased bending of the separatrices at the inlet and outlets and not due to the wall-lift force. The impact of the spillover effect on the separation of two different-sized particles is subsequently studied. Efficient sorting is done for subcritical splitting ratios and flow rates, but for close to critical settings or beyond, there is a breakdown of the acoustofluidic separation.

Anaerobic single-cell dispensing facilitates the cultivation of human gut bacteria.

Cultivation via classical agar plate (CAP) approaches is widely used to study microbial communities, but they are time-consuming. An alternative approach is the application of single-cell dispensing (SCD), which allows high-throughput, label-free sorting of microscopic particles. We aimed to develop a new anaerobic SCD workflow to cultivate human gut bacteria and compared it with CAP using faecal communities on three rich culture media. We found that the SCD approach significantly decreased the experimental time to obtain pure cultures from 17± 4 to 5± 0 days, while the isolate diversity and relative abundance coverage were comparable for both approaches. We further tested the total captured fraction by sequencing the sorted bacteria directly after growth as bulk biomass from 2400 dispensed single cells without downstream identification of individual strains. In this approach, the cultured fraction increased from 35.2% to 52.2% for SCD, highlighting the potential for deeper cultivation projects from single samples. SCD-based cultivation also captured species not detected by sequencing (16± 5 per sample, including seven novel taxa). From this work, 82 human gut bacterial species across five phyla (Actinobacteriota, Bacteroidota, Desulfobacterota, Firmicutes and Proteobacteria) and 24 families were obtained, including the first cultured member of 11 novel genera and 10 novel species that were fully characterized taxonomically.

Application of a 3D printed miniaturized hydrocyclone in biopharmaceutical industry-numerical and experimental studies of yeast separation from fermentation culture media

Various industries ranging from water purification to pharmaceutical production have experienced multi separation steps that impose more process time and contamination possibility by batch operation. We propose a developed microfluidic particle sorter (miniaturized hydrocyclone) that adopts centrifugal force as it has ability to decline the number of separation steps and the risk of extrinsic contamination in continuous process. While biological industries have not relied on mini hydrocyclones considerably because of low efficiency and microfabrication difficulties, current work has been planned to conquer these obstacles. In this research, biomass separation from fermentation broth by 3 mm hydrocyclones was investigated. The effect of apex size, feed flow rate, hydrocyclone geometry were analyzed numerically in four mini-hydrocyclones. The most efficient mini-hydrocyclone was chosen to be made by elegant additive manufacturing technology and studied experimentally. The separation efficiency was achieved up to 90% while the concentration ratio of heavy stream (apex) to dilute stream (vortex finder) was reached more than twofold. The mini hydrocyclone performance in view of energy target was studied by Euler-Reynolds-Efficiency plots. The 4 μm cut size was achieved that is promising high throughput separation for biological particles.

Using computed tomography (CT) to reconstruct depositional processes and products in the subaqueous glaciogenic Champlain Sea basin, Ottawa, Canada

In this study, depositional conditions in the glaciogenic Champlain Sea basin were inferred solely from evidence of computed tomography (CT). CT-scan images and Hounsfield unit (HU) profiles of two continuous cores in Ottawa, Canada, provided the data to identify five lithologically distinct, mud-dominated stratal units. Distinctively, all strata exhibit a repeating pattern of HU values. The upward increase and then decrease in HU values within each bed suggests upward increasing and then decreasing silt content, which collectively, is interpreted to reflect the consistent waxing followed by waning flow conditions during a single cycle of glaciogenic meltwater discharge. Mud rhythmites at the base of the succession (Unit 1) and beds of well-stratified mud at the top (Unit 4a) exhibit well-developed parallel-stratification in the lower part of each bed; they are characterized by a range of ~250–350 HU. This wide range in HU values reflects the effective partitioning of silt-rich and clay-rich parts in each bed, and therefore bed-surface and near-bed transport processes that sorted sediment mostly by grain size, followed by low-energy sediment fallout. The silt-rich part of each bed was deposited by glaciogenic meltwater-sourced hyperpycnal flows, which due to the freshwater composition of the basin, or at least in the upper part of the water column, were able to plunge to the basin floor and sort particles along the bed. In comparison, beds of bioturbated mud (Unit 2), banded mud (Unit 3), and diffusely stratified or structureless mud (Unit 4a) have a narrower range of ~50–120 HU, indicative of poorer particle sorting. These conditions, most clearly illustrated by the bioturbation, indicate a change to a seawater basin that caused meltwater inflows to instead form buoyant, sediment-laden hypopycnal flows, which aided by clay-silt particle flocculation and/or settling-driven convection, resulted in sediment deposition directly from suspension. In addition to characteristic sedimentary structures and textures, beds within each unit also exhibit similar thickness, which often doubles or triples in the abrupt transition from one unit to the next. These changes most probably reflect abrupt and systemic changes in deglacial dynamics and its control on sediment supply that often coincide with equally abrupt changes in salinity in the Champlain Sea basin.

In-situ transfer vat photopolymerization for transparent microfluidic device fabrication

While vat photopolymerization has many advantages over soft lithography in fabricating microfluidic devices, including efficiency and shape complexity, it has difficulty achieving well-controlled micrometer-sized (smaller than 100 μm) channels in the layer building direction. The considerable light penetration depth of transparent resin leads to over-curing that inevitably cures the residual resin inside flow channels, causing clogs. In this paper, a 3D printing process — in-situ transfer vat photopolymerization is reported to solve this critical over-curing issue in fabricating microfluidic devices. We demonstrate microchannels with high Z-resolution (within 10 μm level) and high accuracy (within 2 μm level) using a general method with no requirements on liquid resins such as reduced transparency nor leads to a reduced fabrication speed. Compared with all other vat photopolymerization-based techniques specialized for microfluidic channel fabrication, our universal approach is compatible with commonly used 405 nm light sources and commercial photocurable resins. The process has been verified by multifunctional devices, including 3D serpentine microfluidic channels, microfluidic valves, and particle sorting devices. This work solves a critical barrier in 3D printing microfluidic channels using the high-speed vat photopolymerization process and broadens the material options. It also significantly advances vat photopolymerization’s use in applications requiring small gaps with high accuracy in the Z-direction.

Particle-Induced Electrostatic Repulsion within an Electric Curtain Operating below the Paschen Limit.

The electric curtain is a platform developed to lift and transport charged particles in air. Its premise is the manipulation of charged particles; however, fewer investigations isolate dielectric forces that are observed at lower voltages (i.e., less than the Paschen limit). This work focuses on observations of simultaneous dielectrophoretic and electrostatic forces. The electric curtain was a printed circuit board with interdigitated electrodes (0.020 inch width and spacing) coated with a layer of polypropylene, where a standing wave or travelling wave AC signal was applied (50 Hz) to produce an electric field below the Paschen limit. Soda lime glass beads (180–212 µm) demonstrated oscillatory rolling via dielectrophoretic forces. In addition, several particles simultaneously experienced rapid projectile repulsion, a behavior consistent with electrostatic phenomena. This second result is discussed as a particle-induced local increase in the electric field, with simulations demonstrating that a particle in close proximity to the curtain’s surface produces a local field enhancement of over 2.5 times. The significance of this is that individual particles themselves can trigger electrostatic repulsion in an otherwise dielectric system. These results could be used for advanced applications where particles themselves provided triggered responses, perhaps for selective sorting of micrometer particles in air.

Insights into a deterministic lateral displacement sorting chip with new cross-section micropillars

Microfluidic technology has great advantages in the precise manipulation of micro and nanoparticles, and the separation method based on deterministic lateral displacement separation technology has attracted much attention due to its high resolution, high throughput, and strong size dependence. In this paper, starting from the principle of deterministic lateral displacement sorting and taking control of the flow velocity distribution and pressure difference in the gap as the key points, a new shape of inverted heart-shaped micro-columns with a smaller critical size was designed to separate white blood cells and red blood cells. Under the premise of considering the two-way coupling, the trajectory of the particles was simulated, the critical size of the array was determined, and the influence of the flow velocity particle sorting was discussed. Finally, the separation process of the two kinds of cells was simulated, and the separation of the two kinds of cells was successfully realized. This work has laid a certain theoretical foundation for the rapid diagnosis of diseases in practical applications.

Continuous 3D particles manipulation based on cooling thermal convection

Techniques that can dexterously manipulate particles/cells are significant for biological detection, analytical chemistry, and material synthesis applications. Although there are many methods to realize the 3D manipulation in a static condition, there is a lack of sufficient 3D manipulating strategies in a continuous flow. We develop an integrated microsystem with a cooling system based on thermal convection to realize 3D manipulation in continuous flow. Theoretical modeling and experiments demonstrate that with increasing the temperature of a microheater, the moving direction of particles transfers from the y-axis to the z-axis. Based on the principle, focusing flow and single particles are manipulated in the y-axis and z-axis. Besides, five outlets in different z-axis are fabricated to demonstrate the application of particle sorting. This novel strategy offers a new direction for particle manipulation vertically and benefits to reveal the heat transfer in micro-scale, which can pave a path for generating the next integrated microfluidic system for particles/cells sorting.

Deterministic Lateral Displacement Using Hexagonally Arranged, Bottom-Up-Inspired Micropost Arrays.

Size-based separation of particles in microfluidic devices can be achieved using arrays of micro- or nanoscale posts using a technique known as deterministic lateral displacement (DLD). To date, DLD arrays have been limited to parallelogram or rotated-square arrangements of posts, with various post shapes having been explored in these two principal arrangements. This work examines a new DLD geometry based on patterning obtainable through self-assembly of single-layer nanospheres, which we call hexagonally arranged triangle (HAT) geometry. Finite element simulations are used to characterize the DLD separation properties of the HAT geometry. The relationship between the array angle, the gap spacing, and the critical diameter for separation is derived for the HAT geometry and expressed in a similar mathematical form as conventional parallelogram and rotated-square DLD arrays. At array angles <7°, HAT structures demonstrate smaller particle sorting capability (smaller critical diameter-to-gap spacing ratio) compared to published experimental results for parallelogram-type DLD arrays with circular posts. Experimental validation of DLD separation confirms the separation ability of the HAT array geometry. It is envisioned that this work will provide the first step toward future implementation of nanoscale DLD arrays fabricated by low-cost, bottom-up self-assembly approaches.

Neuronal subtype-specific growth cone and soma purification from mammalian CNS via fractionation and fluorescent sorting for subcellular analyses and spatial mapping of local transcriptomes and proteomes.

During neuronal development, growth cones (GCs) of projection neurons navigate complex extracellular environments to reach distant targets, thereby generating extraordinarily complex circuitry. These dynamic structures located at the tips of axonal projections respond to substrate-bound as well as diffusible guidance cues in a neuronal subtype- and stage-specific manner to construct highly specific and functional circuitry. In vitro studies of the past decade indicate that subcellular localization of specific molecular machinery in GCs underlies the precise navigational control that occurs during circuit 'wiring'. Our laboratory has recently developed integrated experimental and analytical approaches enabling high-depth, quantitative proteomic and transcriptomic investigation of subtype- and stage-specific GC molecular machinery directly from the rodent central nervous system (CNS) in vivo. By using these approaches, a pure population of GCs and paired somata can be isolated from any neuronal subtype of the CNS that can be fluorescently labeled. GCs are dissociated from parent axons using fluid shear forces, and a bulk GC fraction is isolated by buoyancy ultracentrifugation. Subtype-specific GCs and somata are purified by recently developed fluorescent small particle sorting and established FACS of neurons and are suitable for downstream analyses of proteins and RNAs, including small RNAs. The isolation of subtype-specific GCs and parent somata takes ~3 h, plus sorting time, and ~1-2 h for subsequent extraction of molecular contents. RNA library preparation and sequencing can take several days to weeks, depending on the turnaround time of the core facility involved.

Continuous Particle Separation Driven by 3D Ag-PDMS Electrodes with Dielectric Electrophoretic Force Coupled with Inertia Force.

Cell separation has become @important in biological and medical applications. Dielectrophoresis (DEP) is widely used due to the advantages it offers, such as the lack of a requirement for biological markers and the fact that it involves no damage to cells or particles. This study aimed to report a novel approach combining 3D sidewall electrodes and contraction/expansion (CEA) structures to separate three kinds of particles with different sizes or dielectric properties continuously. The separation was achieved through the interaction between electrophoretic forces and inertia forces. The CEA channel was capable of sorting particles with different sizes due to inertial forces, and also enhanced the nonuniformity of the electric field. The 3D electrodes generated a non-uniform electric field at the same height as the channels, which increased the action range of the DEP force. Finite element simulations using the commercial software, COMSOL Multiphysics 5.4, were performed to determine the flow field distributions, electric field distributions, and particle trajectories. The separation experiments were assessed by separating 4 µm polystyrene (PS) particles from 20 µm PS particles at different flow rates by experiencing positive and negative DEP. Subsequently, the sorting performances of the 4 µm PS particles, 20 µm PS particles, and 4 µm silica particles with different solution conductivities were observed. Both the numerical simulations and the practical particle separation displayed high separating efficiency (separation of 4 µm PS particles, 94.2%; separation of 20 µm PS particles, 92.1%; separation of 4 µm Silica particles, 95.3%). The proposed approach is expected to open a new approach to cell sorting and separating.

Potential of on‐chip analysis and engineering techniques for extracellular vesicle bioproduction for therapeutics

AbstractThe clinical interest around extracellular vesicles (EVs) started during the year 2000s, now leading to new clinical diagnostic and therapeutic strategies. Due to their outstanding properties as biogenic drug delivery systems and as alternatives to cell therapy, the need to produce EVs with sufficiently high yield and quality for clinical use expedited the development of analytical techniques and dedicated bioproduction methods. Though preclinical studies revealed the potential of EVs to become next generation subcellular therapies that could lead to major breakthroughs in current therapeutics possibilities, they remain complex objects on both a physicochemical and biological level. Here, we review the capacity of microfluidic technologies to match EV‐based therapeutics need for clinical translation via standardized and intensified bioproduction methods. Indeed, some of the current routine tools used in bioproduction are already achieved on chips such as micromixers or particle sorting and analysis using field flow fraction or nanoparticle tracking analyzer. Also, microfluidics communities have developed a wide set of new techniques to isolate and quantify EVs, but the few that are adopted in a bioproduction workflow are well‐established since the 1990s. We first review the different EV generation and loading methods embedded on chip. We focus on EVs preparation methods, from purification to in‐line separative techniques. We finally describe the on‐chip analytical tools to analyze physicochemistry and phenotypes of EVs.

From Exosomes to Circulating Tumor Cells: Using Microfluidics to Detect High Predictive Cancer Biomarkers.

Early cancer screening and effective diagnosis is the most effective form to diminish the number of cancer-related deaths. Liquid biopsy constitutes an attractive alternative to tumor biopsy due to its non-invasive nature and sample accessibility, which permits effective screening and patient monitoring. Within the plethora of biomarkers present in circulation, liquid biopsy has mainly been performed by analyzing circulating tumor cells, and more recently, extracellular vesicles. Tracking these biological particles could provide valuable insights into cancer origin, progression, treatment efficacy, and patient prognosis. Microfluidic devices have emerged as viable solutions for point-of-care cancer screening and monitoring due to their user-friendly operation, low operation costs, and capability of processing, quantifying, and analyzing these bioparticles in a single device. However, the size difference between cells and exosomes (micrometer vs nanometer) requires an adaptation of microfluidic isolation approaches, particularly in label-free methodologies governed by particle and fluid mechanics. This chapter will explore the theory behind particle isolation and sorting in different microfluidic techniques necessary to guide researchers into the design and development of such devices.

Active Graphene Plasmonic Tweezers: Size Based Nanoparticle Trapping and Sorting

In this article, a novel graphene based Optical tweezer (OT) and size based particle sorter is proposed and numerically investigated by finite difference time domain (FDTD) method and Maxwells stress tensor (MST) analysis. Each unit cell of the structure is composed of a graphene layer on top a metallic nano-ring which is embedded in SiO2. Strong hotspots with field enhancements reaching values as high as 140 are obtained inside the rings with no need to sharp edges conventional in plasmonic structures. Size based trapping can be achieved by controlling the fermi energy of the graphene through a gate. By cascading several unit cells, each operating at a different gate voltage, a particle size based sorter is designed which can effectively sort Polystyrene particles with their diameter in the range of smaller than 10 nm to 100 nm. The structure is illuminated by a laser beam in the mid-IR frequency range of 4-8 m and its wavelength and intensity are kept constant even for sorting functionality. Instead, tunable plasmonic characteristics of graphene is utilized for active particle sorting. The fermi level-particle size-gate voltage relationship of the proposed OT is fully investigated at the article. Moreover, it is shown that the proposed structure is capable of sorting particles according to their refractive indices as well.

Particle Sorting Technique Using Microfluidic Devices with Integrated Dielectrophoresis Electrodes

Micro-order particle sorting technology is essential for research applications in the chemical, environmental, and biomedical fields, as well as in various industrial sectors. Many microfluidic devices have been proposed to sort and collect microparticles in the liquid phase. On the other hand, there are not many microfluidic devices for sorting and collecting particles in the gas phase, such as PM2.5 and other dust particles. In our previous study, we successfully developed an electrostatic precipitation technique that uses dielectrophoretic forces to retain microbeads in the gas phase. In this study, we will integrate the dielectrophoresis electrodes into a microfluidic device and apply them as a particulate sorting and selection.

LES two-phase modelling of suspended sediment transport using a two-way coupled Euler–Lagrange approach

Sediment plume development was modelled using an Euler–Lagrangian two-way coupled large eddy simulation. Momentum exchange was calculated based on interaction forces in the Maxey–Riley equation. Validation showed good agreement with experimental data from literature. For analysis of interaction between sediment and fluid 6,859 particles were released into turbulent fluid flow. In order to ensure independence of the results from arbitrary turbulent velocity fluctuations in the initial fluid velocity field, 41 simulations of the test case starting from different initial flow fields were analysed. Results of these simulations are normally distributed. Mean values indicate three phases of the development of the sediment plume: (i) acceleration phase, (ii) transport phase and (iii) deposition phase. Significant slow down of fluid flow and particle sorting turned out to be relevant processes in the initial development of the sediment plume which are not accounted for in one-way coupled models.

Refining of Particulates at Stimuli‐Responsive Interfaces: Label‐Free Sorting and Isolation

AbstractThe mechanism of separation methods, for example, liquid chromatography, is realized through rapid multiple adsorption‐desorption steps leading to the dynamic equilibrium state in a mixture of molecules with different partition coefficients. Sorting of colloidal particles, including protein complexes, cells, and viruses, is limited due to a high energy barrier, up to millions kT, required to detach particles from the interface, which is in dramatic contrast to a few kT for small molecules. Such a strong interaction renders particle adsorption quasi‐irreversible. The dynamic adsorption‐desorption equilibrium is approached very slowly, if ever attainable. This limitation is alleviated with a local oscillating repulsive mechanical force generated at the microstructured stimuli‐responsive polymer interface to switch between adsorption and mechanical‐force‐facilitated desorption of the particles. Such a dynamic regime enables the separation of colloidal mixtures based on the particle‐polymer interface affinity, and it could find use in research, diagnostics, and industrial‐scale label‐free sorting of highly asymmetric mixtures of colloids and cells.

Refining of Particulates at Stimuli-Responsive Interfaces: Label-Free Sorting and Isolation.

The mechanism of separation methods, for example, liquid chromatography, is realized through rapid multiple adsorption-desorption steps leading to the dynamic equilibrium state in a mixture of molecules with different partition coefficients. Sorting of colloidal particles, including protein complexes, cells, and viruses, is limited due to a high energy barrier, up to millions kT, required to detach particles from the interface, which is in dramatic contrast to a few kT for small molecules. Such a strong interaction renders particle adsorption quasi-irreversible. The dynamic adsorption-desorption equilibrium is approached very slowly, if ever attainable. This limitation is alleviated with a local oscillating repulsive mechanical force generated at the microstructured stimuli-responsive polymer interface to switch between adsorption and mechanical-force-facilitated desorption of the particles. Such a dynamic regime enables the separation of colloidal mixtures based on the particle-polymer interface affinity, and it could find use in research, diagnostics, and industrial-scale label-free sorting of highly asymmetric mixtures of colloids and cells.

Tunable particle/cell separation across aqueous two-phase system interface by electric pulse in microfluidics

HypothesisSeparations of particles and cells are indispensable in many microfluidic systems and have numerous applications in chemistry and biomedicine. The interface of aqueous two-phase system (ATPS) can act as a liquid filter. Under electric field stimuli, the selective transfer of targets across the liquid–liquid interface are expected for particles and cells separation. ExperimentsThe separations of particles and cells based on ATPS electrophoresis in a microfluidic chip were investigated. A systematical study of the mechanism of ATPS electrophoresis was performed first by employing polystyrene (PS) particles. Subsequently, the separations of particles and microalgae cells were demonstrated. FindingsThe electrophoretic transfer of particles across the interface of ATPS is determined by multi-parameters, including the strength of electric pulse, particle size, zeta potential, and hydrophobicity of the particle. The continuous separations of particles/cells can be achieved through the controllable transfer of target particles/cells across the interface under electric pulses in a microfluidic chip. By simply turning the magnitude of the applied electric pulse, the technique is suitable for different purposes, for example, the separations of particles and cells, purification of cells, and viability identification of cells. This tunable separation approach opens opportunities in multidimensional particle and cell sorting for the fields of seed selection of microorganisms, environmental assessment, and biomedical research.

Single-particle trapping and dynamic manipulation with holographic optical surface-wave tweezers

Optical surface waves have widely been used in optical tweezers systems for trapping particles sized from the nano- to microscale, with specific importance and needs in applications of super-resolved detection and imaging if a single particle can be trapped and manipulated accurately. However, it is difficult to achieve such trapping with high precision in conventional optical surface-wave tweezers. Here, we propose and experimentally demonstrate a new method to accurately trap and dynamically manipulate a single particle or a desired number of particles in holographic optical surface-wave tweezers. By tailoring the optical potential wells formed by surface waves, we achieved trapping of the targeted single particle while pushing away all surrounding particles and further dynamically controlling the particle by a holographic tweezers beam. We also prove that different particle samples, including gold particles and biological cells, can be applied in our system. This method can be used for different-type optical surface-wave tweezers, with significant potential applications in single-particle spectroscopy, particle sorting, nano-assembly, and others.