Focusing and continuous separation of microparticles by insulator-based dielectrophoresis (iDEP) in stair-shaped microchannel

Numerical study of a double-stair-shaped dielectrophoresis channel for continuous on-chip cell separation and lysis using finite element method

Prognostication of numerous chronic diseases are in need of identifying circulating tumor cells (CTCs), afterwards, separating and reviving contaminated samples are required. Conventional methods of separating blood cells, namely cytometry or magnetically activated cell sorting, in many cases lose their functionality, or efficiency under different conditions. Hence microfluidic methods of separation have been implemented. Herein, an innovative integrated double stair-shaped microchannel is designed and optimized, capable of 'separation', and 'chemical lysis' simultaneously in which the lysis reagent concentration can be controlled to tune the lysis intensity. The method of insulator-based dielectrophoresis (iDEP), which is the main physics in this device, is utilized yielding maximum separation. Pivotal features of the applied voltage, the voltage difference, the angles and the number of stairs, and the width of the throat in the microchannel have been numerically explored in order to optimize the channel in terms of separation and the lysis buffer concentration. The overall state of optimum case for the voltage difference (ΔV) of 10 owns the following features: the number of stairs is 2, the angle of stairs is 110°, the width of throat is 140 μm, and the inlet voltages are 30 V and 40 V. Also, the overall state of optimum cases for delta possess the following features: the number of stairs is 2, the angle of stairs is 110°, the width of throat is 140 μm, and the inlet voltages are 30 V and 35 V.

Focusing particles by induced charge electrokinetic flow in a microchannel

A novel method of sheathless particle focusing by induced charge electrokinetic flow in a microchannel is presented in this paper. By placing a pair of metal plates on the opposite walls of the channel and applying an electrical field, particle focusing is achieved due to the two pairs of vortex that constrain the flow of the particle solution. As an example, the trajectories of particles under different electrical fields with only one metal plate on one side channel wall were numerically simulated and experimentally validated. Other flow focusing effects, such as the focused width ratio (focused width/channel width) and length ratio (focused length/half-length of metal plate) of the sample solution, were also numerically studied. The results show that the particle firstly passes through the gaps between the upstream vortices and the channel walls. Afterwards, the particle is focused to pass through the gap between the two downstream vortices that determine the focused particle position. Numerical simulations show that the focused particle stream becomes thin with the increases in the applied electrical field and the length of the metal plates. As regards to the focused length ratio of the focused stream, however, it slightly increases with the increase in the applied electrical field and almost keeps constant with the increase in the length of the metal plate. The size of the focused sample solution, therefore, can be easily adjusted by controlling the applied electrical field and the sizes of the metal plates.

Insulator-based dielectrophoretic diagnostic tool for babesiosis

Babesia species are obligate intraerythrocytic tick-borne protozoan parasites that are the etiologic agents of babesiosis, a potentially life-threatening, malaria-like illness in humans and animals. Babesia-infected people have been known to suffer from complications including liver problems, severe hemolytic anemia, and kidney failure. As reported by the Food and Drug Administration, 38% of mortality cases observed in transfusion recipients were associated with transfusion transmitted diseases of which babesiosis is the chief culprit. As of now, no tests have been licensed yet for screening blood donors for babesiosis. Current diagnostic tools for babesiosis including enzyme-linked immunosorbent assay, fluorescence in situ hybridization, and polymerase chain reaction are expensive and burdened with multifarious shortcomings. In this research, a low-cost, high-specificity, quick, and easy-to-use insulator-based dielectrophoretic diagnostic tool is developed for characterizing and concentrating Babesia-infected cells in their homogenous mixture with healthy cell population. In this work, a mixture of Babesia-infected (varying parasitemia) and healthy red blood cells (RBCs or erythrocytes) was exposed to non-uniform electric fields in a fabricated microfluidic platform to manipulate and sort the Babesia-infected cells within a minute. At DC voltage configurations of 10 V and 0/6 V in the inlet and the two outlet channels, respectively, the diseased cells were seen to flow in a direction different from the healthy RBCs. Bright field and fluorescence microscopy were utilized to present qualitative differentiation of the healthy erythrocytes from the infected cells. The proposed micro device platform was able to enrich RBCs from 0.1% to ∼70% parasitemia. This device, when finally developed into a point-of-care diagnostic chip, would enhance the detection of Babesia-infected erythrocytes and as well serve as a precursor to babesiosis vaccine development.

Filter-less submicron hydrodynamic size sorting

We propose a simple microfluidic device able to separate submicron particles (critical size ∼0.1 μm) from a complex sample with no filter (minimum channel dimension being 5 μm) by hydrodynamic filtration. A model taking into account the actual velocity profile and hydrodynamic resistances enables prediction of the chip sorting properties for any geometry. Two design families are studied to obtain (i) small sizes within minutes (low-aspect ratio, two-level chip) and (ii) micron-sized sorting with a μL flow rate (3D architecture based on lamination). We obtain quantitative agreement of sorting performances both with experiments and with numerical solving, and determine the limits of the approach. We therefore demonstrate a passive, filter-less sub-micron size sorting with a simple, robust, and easy to fabricate design.

Microparticles manipulation and enhancement of their separation in pinched flow fractionation by insulator-based dielectrophoresis

The separation and manipulation of microparticles in lab on a chip devices have importance in point of care diagnostic tools and analytical applications. The separation and sorting of particles from biological and clinical samples can be performed using active and passive techniques. In passive techniques, no external force is applied while in active techniques by applying external force (e.g. electrical), higher separation efficiency is obtained. In this article, passive (pinched flow fractionation) and active (insulator-based dielectrophoresis) methods were combined to increase the separation efficiency at lower voltages. First by simulation, appropriate values of geometry and applied voltages for better focusing, separation, and lower Joule heating were obtained. Separation of 1.5 and 6 μm polystyrene microparticles was experimentally obtained at optimized geometry and low total applied voltage (25 V). Also, the trajectory of 1.5 μm microparticles was controlled by adjusting the total applied voltage.