Talukder Z. Jubery

Dielectrophoretic separation of bioparticles in microdevices: A review

In recent years, dielectrophoretic force has been used to manipulate colloids, inert particles, and biological microparticles, such as red blood cells, white blood cells, platelets, cancer cells, bacteria, yeast, microorganisms, proteins, DNA, etc. This specific electrokinetic technique has been used for trapping, sorting, focusing, filtration, patterning, assembly, and separating biological entities/particles suspended in a buffer medium. Dielectrophoretic forces acting on particles depend on various parameters, for example, charge of the particle, geometry of the device, dielectric constant of the medium and particle, and physiology of the particle. Therefore, to design an effective micro‐/nanofluidic separation platform, it is necessary to understand the role of the aforementioned parameters on particle motion. In this paper, we review studies particularly related to dielectrophoretic separation in microfluidic devices. Both experimental and theoretical works by several researchers are highlighted in this article covering AC and DC DEP. In addition, AC/DC DEP, which uses a combination of low frequency AC and DC voltage to manipulate bioparticles, has been discussed briefly. Contactless DEP, a variation of DC DEP in which electrodes do not come in contact with particles, has also been reviewed. Moreover, dielectrophoretic force‐based field flow fractionations are featured to demonstrate the bioparticle separation in microfluidic device. In numerical front, a comprehensive review is provided starting from the most simplified effective moment Stokes‐drag (EMSD) method to the most advanced interface resolved method. Unlike EMSD method, recently developed advanced numerical methods consider the size and shape of the particle in the electric and flow field calculations, and these methods provide much more accurate results than the EMSD method for microparticles.

Chemically modified solid state nanopores for high throughput nanoparticle separation

The separation of biomolecules and other nanoparticles is a vital step in several analytical and diagnostic techniques. Towards this end we present a solid state nanopore-based set-up as an efficient separation platform. The translocation of charged particles through a nanopore was first modeled mathematically using the multi-ion model and the surface charge density of the nanopore membrane was identified as a critical parameter that determines the selectivity of the membrane and the throughput of the separation process. Drawing from these simulations a single 150 nm pore was fabricated in a 50 nm thick free-standing silicon nitride membrane by focused-ion-beam milling and was chemically modified with (3-aminopropyl)triethoxysilane to change its surface charge density. This chemically modified membrane was then used to separate 22 and 58 nm polystyrene nanoparticles in solution. Once optimized, this approach can readily be scaled up to nanopore arrays which would function as a key component of next-generation nanosieving systems.

10 000-fold concentration increase of the biomarker cardiac troponin I in a reducing union microfluidic chip using cationic isotachophoresis

This paper describes the preconcentration of the biomarker cardiac troponin I (cTnI) and a fluorescent protein (R-phycoerythrin) using cationic isotachophoresis (ITP) in a 3.9 cm long poly(methyl methacrylate) (PMMA) microfluidic chip. The microfluidic chip includes a channel with a 5× reduction in depth and a 10× reduction in width. Thus, the overall cross-sectional area decreases by 50× from inlet (anode) to outlet (cathode). The concentration is inversely proportional to the cross-sectional area so that as proteins migrate through the reductions, the concentrations increase proportionally. In addition, the proteins gain additional concentration by ITP. We observe that by performing ITP in a cross-sectional area reducing microfluidic chip we can attain concentration factors greater than 10,000. The starting concentration of cTnI was 2.3 μg mL⁻¹ and the final concentration after ITP concentration in the microfluidic chip was 25.52 ± 1.25 mg mL⁻¹. To the authors knowledge this is the first attempt at concentrating the cardiac biomarker cTnI by ITP. This experimental approach could be coupled to an immunoassay based technique and has the potential to lower limits of detection, increase sensitivity, and quantify different isolated cTnI phosphorylation states.

10,000-fold concentration increase in proteins in a cascade microchip using anionic ITP by a 3-D numerical simulation with experimental results.

This paper describes both the experimental application and 3‐D numerical simulation of isotachophoresis (ITP) in a 3.2 cm long “cascade” poly(methyl methacrylate) (PMMA) microfluidic chip. The microchip includes 10× reductions in both the width and depth of the microchannel, which decreases the overall cross‐sectional area by a factor of 100 between the inlet (cathode) and outlet (anode). A 3‐D numerical simulation of ITP is outlined and is a first example of an ITP simulation in three dimensions. The 3‐D numerical simulation uses COMSOL Multiphysics v4.0a to concentrate two generic proteins and monitor protein migration through the microchannel. In performing an ITP simulation on this microchip platform, we observe an increase in concentration by over a factor of more than 10 000 due to the combination of ITP stacking and the reduction in cross‐sectional area. Two fluorescent proteins, green fluorescent protein and R‐phycoerythrin, were used to experimentally visualize ITP through the fabricated microfluidic chip. The initial concentration of each protein in the sample was 1.995 μg/mL and, after preconcentration by ITP, the final concentrations of the two fluorescent proteins were 32.57±3.63 and 22.81±4.61 mg/mL, respectively. Thus, experimentally the two fluorescent proteins were concentrated by over a factor of 10 000 and show good qualitative agreement with our simulation results.

Modeling and simulation of nanoparticle separation through a solid-state nanopore

Recent experimental studies show that electrokinetic phenomena such as electroosmosis and electrophoresis can be used to separate nanoparticles on the basis of their size and charge using nanopore‐based devices. However, the efficient separation through a nanopore depends on a number of factors such as externally applied voltage, size and charge density of particle, size and charge density of membrane pore, and the concentration of bulk electrolyte. To design an efficient nanopore‐based separation platform, a continuum‐based mathematical model is used for fluid. The model is based on Poisson–Nernst–Planck equations along with Navier–Stokes equations for fluid flow and on the Langevin equation for particle translocation. Our numerical study reveals that membrane pore surface charge density is a vital parameter in the separation through a nanopore. In this study, we have simulated high‐density lipoprotein (HDL) and low‐density lipoprotein (LDL) as the sample nanoparticles to demonstrate the capability of such a platform. Numerical results suggest that efficient separation of HDL from LDL in a 0.2 M KCL solution (resembling blood buffer) through a 150 nm pore is possible if the pore surface charge density is ∼ −4.0 mC/m2. Moreover, we observe that pore length and diameter are relatively less important in the nanoparticle separation process considered here.

A new design for efficient dielectrophoretic separation of cells in a microdevice

Effectiveness of a continuous biological cell separation device can be improved significantly by increasing the distance among different types of cells. To achieve this, most of the recent dielectrophoresis based continuous separation devices implement differential forces on cells either along the transverse direction or the vertical direction with respect to the bulk fluid flow motion. However, interparticle distance can be increased further by implementing forces along both transverse and vertical planes. In this article, a design for a microfluidic platform has been proposed where a new electrode configuration is identified to implement symmetric forces in both vertical and transverse directions. A numerical model, which considers presence of particles in the electric field and flow field, shows a much higher interparticle distance between red blood cells and plasmodium falciparum infected red blood cells in such a device than that in a conventional separation device. This configuration also reduces the possibility of particle trapping on the electrodes, which is a major bottleneck of dielectrophoresis.

A Fast Algorithm to Predict Cell Trajectories in Microdevices Using Dielectrophoresis

Prediction of accurate trajectories of biological particles is necessary for efficient design of microdevices for dielectrophoretic manipulation. Due to simplicity, a point-based method is generally used to simulate particle trajectory, but a point-based method provides significant distortion from the actual path when particle size is comparable to the device characteristic dimension. This article reports an efficient numerical model which can overcome these drawbacks of a point-based method and can be used for accurate predictions of particle trajectory. This model is formulated on a distributed Lagrange multiplier based fictitious domain (FD) approach for flow field and motion of particles, and the multi-domain method for electric potential. In this study, the dielectric forces are calculated from the Maxwell stress tensor. The accuracy of the proposed methods are validated separately with two test problems: terminal velocity of a particle in a stationary fluid while it is pulled with a constant force, and dielectrophoretic force acting on a particle when it is placed in between two planar electrodes. The capability of the proposed model is demonstrated by simulating trajectories of two biological particles (cells) of the same geometry and size but different dielectric properties in a microdevice. The effects of frequency, particle-particle initial separation distance, and particles’ relative position are investigated. Numerical results indicate that this model can capture the physics of particle manipulation better than the conventional point-based method. Moreover, this algorithm reduces the computational time significantly, which is a major bottleneck in 3-D simulation.

A new fabrication technique to form complex polymethylmethacrylate microchannel for bioseparation

Recent studies show that reduction in cross-sectional area can be used to improve the concentration factor in microscale bioseparations. Due to simplicity in fabrication process, a step reduction in cross-sectional area is generally implemented in microchip to increase the concentration factor. But the sudden change in cross-sectional area can introduce significant band dispersion and distortion. This paper reports a new fabrication technique to form a gradual reduction in cross-sectional area in polymethylmethacrylate (PMMA) microchannel for both anionic and cationic isotachophoresis (ITP). The fabrication technique is based on hot embossing and surface modification assisted bonding method. Both one-dimensional and two-dimensional gradual reduction in cross-sectional area microchannels were formed on PMMA with high fidelity using proposed techniques. ITP experiments were conducted to separate and preconcentrate fluorescent proteins in these microchips. Thousand fold and ten thousand fold increase in concentrations were obtained when 10 × and 100 × gradual reduction in cross-sectional area microchannels were used for ITP.

Preconcentration of Cardiac Proteins in a Cascade Microchip

Concentration of bio-molecules prior to detection is very critical in the development of an integrated, multifunctional lab-on-a chip device for detection of ultra trace molecules from complex biological fluids such as serum, urine, or saliva. In this work, the preconcentration of a clinically relevant biomarker, cardiac troponin I (cTnI), is demonstrated in a cascade microfluidic channel using cationic isotachophoresis (ITP). The cascade chip is formed on PMMA (poly methyl methacrylate) with gradual changes in size both in width and depth direction to achieve a 100× reduction in overall cross sectional area between inlet (anode) and outlet (cathode) sections. The ITP experiments were conducted with two fluorescent proteins, FITC (Fluorescein isothiocyanate-conjugated) albumin and cTnI labeled with Pacific Blue. Potassium ions were used as the leader and hydronium ions were used as the terminator for these cationic ITP experiments. The microchip ITP demonstrates that it is possible to increase the concentration of cTnI by 10,000 folds using a potential drop of 400 V across a 3.5 cm long microchannel. The reduction in cross sectional area facilitates additional concentration gain, as the proteins migrate through cascade microchannel under discontinuous electric field and stacked into nearly pure zones.Copyright

Modeling and Simulation of Translocation Phenomenon in a Solid State Nanopore for Nanoparticle Separation

Solid state nanopore is a potential candidate for separation of nanoparticles or biomolecules such as proteins, DNA, and RNA. However, efficient separation of particles through nanopores is a challenging task as a number of factors such as externally applied voltage, size and charge density of particle, size and charge density of membrane pore, and the concentration of bulk electrolyte influence the translocation behavior of nanoparticles through pores. This paper uses a mathematical model based on Poisson–Nernst–Plank equations along with Navier-Stokes equations to systematically study these factors. Membrane pore surface charge is found to be a vital parameter in this seperation process. Numerical results reveal that efficient separation of high density lipoprotein (HDL) from low density lipoprotein (LDL) in a 0.2 M KCL solution (resembling blood buffer) through a 150 nm pore is possible if the pore surface charge density is around −4.0 mC/m2 .Copyright