A three-dimensional dielectrophoretic particle focusing channel for microcytometry applications

In this paper, we have designed and fabricated a microfluidic channel to focus biological cells using dielectrophoresis for cytometry applications. The device consists of an elliptic-like channel fabricated by isotropic etching of soda lime glass wafers and a subsequent wafer-bonding process. Microelectrodes are patterned on the circumference of the channel to generate ac fringing fields that result in negative dielectrophoretic forces directing cells from all directions to the center of the channel. An analysis using a thin shell model and experiments with microbeads and human leukemia HL60 cells indicate that biological cells can be focused using an ac voltage of an amplitude up to 15 V/sub p-p/ and a frequency below 100 kHz, respectively. This design eliminates the sheath flow and the fluid control system that makes conventional cytometers bulky, complicated, and difficult to operate, and offers the advantages of a portable module that could potentially be integrated with on-chip impedance or optical sensors into a micro total analysis system.     

Centrifugo-magnetophoretic particle separation

There has been a recent surge of research output on magnetophoretic lab-on-a-chip systems due to their prospective use in a range of applications in the life sciences and clinical diagnostics. Manifold applications for batch-mode or continuous-flow magnetophoretic separations of cells, proteins, and nucleic acids are found in bioanalytics, cell biology, and clinical diagnostics. To ensure stable hydrodynamic conditions and thus reproducible separation, state-of-the-art magnetophoretic lab-on-a-chip systems have been based on pressure-driven flow (Gijs in Microfluid Nanofluid 1:22–40, 2004; Pamme and Manz in Anal Chem 76:7250–7256, 2004; Pamme in Lab Chip 7:1644–1659, 2007; Karle et al. in Lab Chip 10:3284–3290, 2010), which involves rather bulky and costly instrumentation. In a flow-based system, suspended particles are following the liquid phase as a result of the Stokes drag, thus being fully exposed to divergent flow lines around obstacles and pump-induced pressure fluctuations. To eventually achieve more stable hydrodynamic conditions, improved control of magnetic particles, a more compact instrumentation footprint, and integration of high-performance upstream sample preparation, this work introduces a novel two-dimensional particle separation principle by combining magnetic deflection with centrifugal sedimentation in a stopped-flow mode (i.e., mere particle sedimentation). The experimental parameters governing our centrifugo-magnetophoretic system are the strength and orientation of the co-rotating magnetic field, the rotationally induced centrifugal field, and the size-dependent Stokes drag of the various particles with respect to the (residual) liquid phase. In this work, the following set of basic functional modes is demonstrated as proof-of-concept: separation of magnetic from non-magnetic particles, routing of magnetic particles based on control of the spin speed, and size separation of various magnetic particles. Finally, a biomimetic application involving the separation of particles representing healthy cells from a very small concentration of magnetic particles of a similar size, mass and magnetization as a immuno-magnetically tagged target cell, for instance mimicking a circulating tumor cell.     

Time separation technique for large databases

International Journal of Parallel Programming - A time decomposition technique is suggested for large-database (DB) models. The problem of network aggregation is studied and the results used to...     

A multilayer lateral-flow microfluidic device for particle separation

Particle separation technology plays an important role in a wide range of applications as a critical sample preprocessing step for analysis. In this work, we proposed and fabricated a multilayer lateral-flow particle filtration and separation device based on polydimethylsiloxane molding and transfer bonding techniques. Particle separation capability was demonstrated by 4.5-um polystyrene bead filtration and cancer cell (SK-BR-3) retrieving. This device exhibits higher throughput compared with most active particle separation methods and is less vulnerable to membrane clogging problem. This novel multilayer particle filtration and separation device is expected to find applications in biomedical, environmental and microanalysis fields.     

Inertial particle focusing and spacing control in microfluidic devices

Focusing particles into a tight stream is usually a necessary step prior to counting, detecting and sorting them. Meanwhile, particle spacing control in microfluidic devices could also be applied in the field of accurate cell detection, material synthesis and chemical reaction. To achieve simultaneous particle focusing and spacing control, a novel microchannel composed by Dean and sheath flow section was proposed and fabricated according to the elaborated design principle with its manipulating performance in situ visualized. Using microspheres with a few microns as a template, the trajectory of the particles was discovered to follow lateral migration and reach certain equilibrium positions at the end of the designed Dean section. After being focused, the streamline was further concentrated and centralized with a controllable interparticle distance in sheath flow section. For sheath flow section, the angle between symmetrical tributaries and the mainstream channel and abrupt constriction/expansion structure of mainstream channel as important channel geometric features were investigated to minimize the focusing streamline width and optimize spacing control. An modified analytical model for sheath flow with different tributary angles was derived and proved to well describe the microsphere spacing control process.     

Diamagnetic particle focusing using ferromicrofluidics with a single magnet

Focusing particles into a tight stream is critical to many applications such as microfluidic flow cytometry and particle sorting. Current magnetic field-induced particle focusing techniques rely on the use of a pair of repulsive magnets, which makes the device integration and operation difficult. We develop herein a new approach to focusing nonmagnetic particles in ferrofluid flow through a T-microchannel using a single permanent magnet. Particles are deflected across the suspending ferrofluid by negative magnetophoresis and confined by a water flow to the center plane of the microchannel, leading to a focused particle stream flowing near the bottom channel wall. Such three-dimensional diamagnetic particle focusing is demonstrated in a sufficiently diluted ferrofluid through both the top and side views of the microchannel. As the suspended particles can be visualized in bright field, this magnetic focusing method is expected to find applications to label-free (i.e., no magnetic or fluorescent labeling) cellular focusing in lab-on-a-chip devices.     

Sheathless microfluidic particle focusing technique using slanted microstructure array

This paper proposes a microfluidic channel for particle focusing that uses a microstructure on the bottom of the channel. Particles can be effectively focused in channels with bottom structures because of microvortex induced by the structure. Microchannels with top structures (top type) and bottom structures (bottom type) were fabricated. The focusing ratios in the focusing region (one-eighth of the channel width) were 86 % in top type and 89 % in bottom type at a flow rate of 1 μl/min. When the flow rate was increased to 5 μl/min, particles in top type were barely focused, whereas particles in bottom type were focused with a focusing ratio of approximately 80 %. We also evaluated the effect of a slanted angle for the microstructures. The comparative experiment was conducted with microstructures fabricated at slanted angle intervals of 20° (20°, 40°, 60°, and 80°) and 10°. The results indicated that the slanted angle (20°) required a small number of microstructures to direct the sample to the focusing region. For microstructures with a 20° slanted angle, the sample was focused after passing through 20 microstructures (10 mm). However, microstructures with an angle of 80° needed over 70 microstructures (over 23 mm) to direct the particle. In this sense, a microchannel with microstructures slanted at 20° is applicable to miniaturized devices. These results show that the microchannel with bottom structures slanted 20° can be used to effectively focus samples with advantages of applying various ranges of flow rates and miniaturizing devices.     

Intra-droplet acoustic particle focusing: simulations and experimental observations

The aim of this paper is to study resonance conditions for acoustic particle focusing inside droplets in two-phase microfluidic systems. A bulk acoustic wave microfluidic chip was designed and fabricated for focusing microparticles inside aqueous droplets (plugs) surrounded by a continuous oil phase in a 380-μm-wide channel. The quality of the acoustic particle focusing was investigated by considering the influence of the acoustic properties of the continuous phase in relation to the dispersed phase. To simulate the system and study the acoustic radiation force on the particles inside droplets, a simplified 3D model was used. The resonance conditions and focusing quality were studied for two different cases: (1) the dispersed and continuous phases were acoustically mismatched (water droplets in fluorinated oil) and (2) the dispersed and continuous phases were acoustically matched (water droplets in olive oil). Experimentally, we observed poor acoustic particle focusing inside droplets surrounded by fluorinated oil while good focusing was observed in droplets surrounded by olive oil. The experimental results are supported qualitatively by our simulations. These show that the acoustic properties (density and compressibility) of the dispersed and continuous phases must be matched to generate a strong and homogeneous acoustic field inside the droplet that is suitable for high-quality intra-droplet acoustic particle focusing.     

Inertial particle focusing dynamics in a trapezoidal straight microchannel: application to particle filtration

Inertial microfluidics has emerged recently as a promising tool for high-throughput manipulation of particles and cells for a wide range of flow cytometric tasks including cell separation/filtration, cell counting, and mechanical phenotyping. Inertial focusing is profoundly reliant on the cross-sectional shape of channel and its impacts on not only the shear field but also the wall-effect lift force near the wall region. In this study, particle focusing dynamics inside trapezoidal straight microchannels was first studied systematically for a broad range of channel Re number (20 < Re < 800). The altered axial velocity profile and consequently new shear force arrangement led to a cross-lateral movement of equilibration toward the longer side wall when the rectangular straight channel was changed to a trapezoid; however, the lateral focusing started to move backward toward the middle and the shorter side wall, depending on particle clogging ratio, channel aspect ratio, and slope of slanted wall, as the channel Reynolds number further increased (Re > 50). Remarkably, an almost complete transition of major focusing from the longer side wall to the shorter side wall was found for large-sized particles of clogging ratio K ~ 0.9 (K = a/H_min) when Re increased noticeably to ~ 650. Finally, based on our findings, a trapezoidal straight channel along with a bifurcation was designed and applied for continuous filtration of a broad range of particle size (0.3 < K < 1) exiting through the longer wall outlet with ~ 99% efficiency (Re < 100).     

Spiral microchannel with stair-like cross section for size-based particle separation

Particle separation has a variety of applications in biology, chemistry and industry. Among them, circulating tumor cells (CTCs) separation has drawn significant attention to itself due to its high impact on both cancer diagnosis and therapeutics. In recent years, there has been growing interest in using inertial microfluidics to separate micro/nano particles based on their sizes. This technique offers label-free, high-throughput and efficient separation and can be easily fabricated. However, further improvements are needed for potential clinical applications. In this study, a novel inertial separation technique using spiral microchannel having stair-like cross section is introduced. The design fundamental concepts, design criteria and efficacy are investigated thoroughly using a robust numerical model; moreover, it is experimentally tested on the fabricated spiral microchannel. Based on the results, in contrast to conventional spiral microchannels, in which the flow vortices are located latitudinal, the two vortices are uniquely placed longitudinally in the stair-like cross section. The numerical and experimental results indicate that there is a size-dependent volume flow rate threshold defined for each particle size determining which vortices become equilibrated and consequently facilitate their separation. According to the results, using stair-like cross section, the separation throughput and resolution, as the two important design criteria in CTCs’ separation techniques, are significantly improved compared to the conventional spiral microchannels.     

Particle swarm optimization with selective particle regeneration for data clustering

This paper presents selective regeneration particle swarm optimization (SRPSO), a novel algorithm developed based on particle swarm optimization (PSO). It contains two new features, unbalanced parameter setting and particle regeneration operation. The unbalanced parameter setting enables fast convergence of the algorithm and the particle regeneration operation allows the search to escape from local optima and explore for better solutions. This algorithm is applied to data clustering problems for performance evaluation and a hybrid algorithm (KSRPSO) of K-means clustering method and SRPSO is developed. In the conducted numerical experiments, SRPSO and KSRPSO are compared to the original PSO algorithm, K-means, as well as, other methods proposed by other studies. The results demonstrate that SRPSO and KSRPSO are efficient, accurate, and robust methods for data clustering problems.     

Assessment of cross-type optical particle separation system

This paper describes the optical and hydrodynamic characteristics of particle motion in a cross-type optical particle separator. The retention distance modulated by the optical force on a particle was measured in three dimensions for various vertical and horizontal positions via ??-defocusing digital particle image velocimetry. The experimental data showed that the actual retention distance was smaller than the predicted retention distance under the assumption that the approaching velocity was constant through the cross-section of a microfluidic channel. The retention distance was shown to increase as the injection position of the particle shifted toward the channel side wall at a given vertical position due to a higher residence time within the region of influence of the laser beam. In contrast, the retention distance decreased as the injection position shifted toward the channel top/bottom walls at a given horizontal position. A theoretical modeling study was conducted to support and interpret the experimental measurements. The resolution of the particle separation procedure, which did not require adjusting the flow rate, laser power, or working fluid properties, was studied.     

Inertially focused diamagnetic particle separation in ferrofluids

Continuous flow separation of target particles from a mixture is essential to many chemical and biomedical applications. There has recently been an increasing interest in the integration of active and passive particle separation techniques for enhanced sensitivity and flexibility. We demonstrate herein the proof-of-concept of a ferrofluid-based hybrid microfluidic technique that combines passive inertial focusing with active magnetic deflection to separate diamagnetic particles by size. The two operations take place in series in a continuous flow through a straight rectangular microchannel with a nearby permanent magnet. We also develop a three-dimensional numerical model to simulate the transport of diamagnetic particles during their inertial focusing and magnetic separation processes in the entire microchannel. The predicted particle trajectories are found to be approximately consistent with the experimental observations at different ferrofluid flow rates and ferrofluid concentrations.     

High-throughput,single-stream microparticle focusing using a microchannel with asymmetric sharp corners

A new microfluidic device for fast and high-throughput particle focusing is reported. The particle focusing is based on the combination of inertial lift force effect and centrifugal force effect generated in a microchannel with a series of repeated asymmetric sharp corners on one side of the channel wall. The inertial lift force induces two focused particle streams in the microchannel, and the centrifugal force generated at the sharp corner structures tends to drive the particles laterally away from the corner. With the use of a series of repeated asymmetric sharp corner structures, a single and highly focused particle stream was achieved near the straight channel wall at a wide range of flow rate. In comparison with other hydrodynamic particle focusing methods, this method is less sensitive to the flow rate and can work at a higher flow rate (up to 700 μL/min) and Reynolds number (Re = 129.5). With its simple structure and operation, and high throughput, this method can be potentially used in particle focusing processes in a variety of lab-on-a-chip applications.     

A microfluidic system combining acoustic and dielectrophoretic particle preconcentration and focusing

Microfabricated systems have recently become useful for routing particles to precise locations in microfluidic channels. In this paper we discuss the modeling, fabrication and characterization of such a platform that combines acoustic forces and ac dielectrophoresis (DEP). This system integrates a bulk lead zirconate titanate (PZT) slab with substrate patterned microelectrodes for DEP manipulation of particles. Moreover, a one-dimensional transmission line model is presented to understand the coupling of the acoustic and dielectrophoretic transducers with the microdevice. While the acoustic model does not predict the lateral coupling in the system, it does provide some insight into axial (thickness-mode) frequencies of operation. Experiments are also conducted in which particles were routed into a large (0.75 mm wide) microchannel and preconcentrated and focused into coarse bundles by coupling an acoustic wave into the channel. Subsequently, particles are further focused into single file particle streams using interdigitated DEP electrodes. This system can be used for high throughput assays for which it is necessary to isolate and investigate small bundles of particles and single particles.     

Three-dimensional hydrodynamic flow and particle focusing using four vortices Dean flow

We present a three-dimensional (3D) hydrodynamic focusing device built on a single-layer platform using single sheath flow. Despite the simple structure and operation, the device not only achieves narrow focusing of a sample fluid or particles but also switches the cross-sectional size and lateral position of the sample stream. The focusing mechanism utilizes four Dean vortices generated in a high-speed flow through a curved channel. Theoretical calculations, numerical simulations, and an experimental study demonstrated that the device could focus microparticles that resemble human platelets in terms of particle size and density in a single-stream manner. Further simulation study suggested that the device could focus most cell sizes used in flow cytometry with a throughput of 200,000 cells s^?1. In addition, the device can function as a 3D liquid-core/liquid-cladding (L2) optical waveguide by introducing a core liquid with a refractive index higher than that of the cladding.     

Fabrication and integration of microscale permanent magnets for particle separation in microfluidics

Microfluidic magnetophoresis is an effective technique to separate magnetically labeled bioconjugates in lab-on-a-chip applications. However, it is challenging and expensive to fabricate and integrate microscale permanent magnets into microfluidic devices with conventional methods that use thin-film deposition and lithography. Here, we propose and demonstrate a simple and low-cost technique to fabricate microscale permanent magnetic microstructures and integrate them into microfluidic devices. In this method, microstructure channels were fabricated next to a microfluidic channel and were injected with a liquid mixture of neodymium (NdFeB) powders and polydimethylsiloxane (PDMS). After the mixture was cured, the resulted solid NdFeB–PDMS microstructure was permanently magnetized to form microscale magnets. The microscale magnets generate strong magnetic forces capable of separating magnetic particles in microfluidic channels. Systematic experiments and numerical simulations were conducted to study the geometric effects of the microscale magnets. It was found that rectangular microscale magnets generate larger \(({\mathbf {H}}\cdot \nabla ) {\mathbf {H}}\) which is proportional to magnetic force and have a wider range of influence than the semicircle or triangle magnets. For multiple connected rectangular microscale magnet, additional geometric parameters, including separation distance, height and width of the individual elements, further influence the particle separation and were characterized experimentally. With an optimal size combination, complete separation of yeast cells and magnetic microparticles of similar sizes (\(4\;\upmu \hbox {m}\)) was demonstrated with the multi-rectangular magnet microfluidic device.     

Fabrication of microfluidic device channel using a photopolymer for colloidal particle separation

We have developed a method of fabricating microfluidic device channels for bio-nanoelectronics system by using high performance epoxy based dry photopolymer films or dry film resists (DFRs). The DFR used was with a trademark name Ordyl SY355 from Elga Europe. The developing and exposing processes as well as the time taken in making the channels are recorded. Finally from those recorded methods, the accurate procedures and time taken for DFR development and exposure have been found and ultimately been consistently used in fabricating our channels. These channels were patterned and sandwiched in between two glass substrates. In our advance, the channel was formed for the colloidal particle separation system. They can be used for handling continuous fluid flow and particle repositioning maneuver using dielectrophoresis that have showed successful results in the separation.