Dielectrophoresis DEP

DEP has been employed to trap or manipulate cells such as HL-60 [871], lurkat cells [872], mouse fibroblast (3T3 cells) [873], and rabbit heart cells [234]. 

In one report, DEP was used for the separation of biological warfare bacterial simulants in a laminated device (five layers including polyimide). For instance, 

FIGURE 8.28 Latex particles (15-uni ), have been confined from a particle jet from the left by DEP. The high field was provided by 10 V (1 MHz) across a 20-pm electrode gap, or 0.5 MV/m [869]. Reprinted with permission from the American Chemical Society. 

Bacillus cereus, E. coli, and Listeria monocytogenes were separated from human blood cells. All separations were run with an AC voltage (10 Vpp at 10 kHz). Bacteria are collected at the electric field maxima by positive DEP forces and blood cells (RBC and WBC) are collected at field minima by negative DEP forces. By applying a suitable fluid flow, the blood cells are swept away, but the bacterial cells are retained [874], In another report, spores of Bacillus globigii were trapped on a DEP chip [486], 

To achieve DEP over a large region, a large-area traveling wave DEP was developed. This was conducted on a glass chip consisting of 1000 electrodes. In the DEP separation of rabbit blood cells, it was observed that rabbit erythrocytes traveled faster than leukocytes [266]. 

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Introduction Dielectrophoresis (DEP) is defined as the motion of neutral, polarizable matter produced by a nonimiform electric (ac or dc) field. DEP should be distinguished from electrophoresis, which is the motion of charged particles in a uniform electric field (Fig. 22-30). 

Gambari R, Borgatti M, Altomare L, et al. Applications to cancer research of lab-on-a-chip devices based on dielectrophoresis (DEP). Technol Cancer Res Treat 2003 2(1) 31 10. 

This dielectrophoresis (DEP) mixer, specially designed for mixing of dielectric particles was made with a rectangular chamber having one inlet and outlet [48], Pairs of micromachined electrodes generate the electric field. 

Cell retention, manipulation, and subsequent cellular analysis can be all achieved on-chip. Cell retention can be achieved by using slit- or weir-type filters, or by cell adhesion. In addition, fluid flow optical trapping and dielectrophoresis (DEP) have been exploited to manipulate and retain cells. 

In the presence of non-uniform AC electric field, colloidal particles suspended in an aqueous medium experience electrokinetic forces including electrophoresis (EP), dielectrophoresis (DEP), and hydrodynamic drag force due... 

Figure 13. Basic electrokinetic effects. (According to Atkins et al. [242].) (a) Electroosmotic flow (EOF), (b) electrophoresis (EP), (c) dielectrophoresis (DEP).

AC electric fields and includes dielectrophoresis (DEP), travelling wave dielectrophoresis (twDEP) and electrorotation (ROT). Generally, non-uniform electric fields are used in AC electrokinetics. The assumption that the uniform field solution for the dipole moment is valid, is referred to as the dipole moment approximation, and is sufficient if the size of the particle is small compared to the scale of the electric field non-uniformity, which is true for most cases. In this chapter, we describe the forces on particles due to the action of AC fields, and discuss applications for manipulation of particles. We finish with a discussion of scaling effects. 

Figure 3. Diagram showing the principle of dielectrophoresis (DEP), which only occurs in a non-homogeneous electric field, (a) Particle more polarizable than the medium positive dielectrophoresis (pDEP) (b) particle less polarizable than the medium negative dielectrophoresis (nDEP).

Field flow fraction (FFF) describes a method for separating particles based on combining a deterministic force with hydrodynamic separation. A typical configuration is shown in Fig. 11. The system consists of a channel with interdigitated microelectrodes patterned on the bottom substrate. Particles are introduced into the system and when the field is switched on they experience nDEP, moving to equilibrium positions which are defined according to the balance of dielectrophoresis (DEP) and gravity (buoyancy). Different types of particles move to different equilibrium positions in the... 

The most common digital microfluidic fluid actuation techniques utilize a combination of strategically placed electrodes and changes in contact angle induced by one of two principles electrowetting on dielectric (EWOD) or dielectrophoresis (DEP). EWOD and DEP can be considered as the low- and high-frequency cases, respectively, of the application of a sufficient electric field to polarizable liquids along the correct axes.7... 

Fig. 2 (a) Microelectroporation device for cell lysis, (b) Device at various steps of the fabrication process after metallization and electrode-mold formation (left) and after electroplating right). (c) Dielectrophoresis (DEP) effect observed in the flow channels top). Saw-tooth microelectrodes acting as a DEP device for focusing intracellular materials after electroporation bottom). Reproduced from [23] with permission... 

The motion that results from the action of a nonuniform electric field upon a neutral is called dielectrophoresis (DEP) from the Greek word phoresis meaning motion. It is to be distinguished from that motion caused by the response of a free charge to an external electric field. The latter is known as electrophoresis. 

In the late 1990s, Ramos et al. discovered steady electroosmotic flow over a pair of microelectrodes applying an AC voltage and dubbed the effect AC electroosmosis [1]. Around the same time, Ajdari predicted ACEO flow over periodic electrode arrays and showed how the effect could be used for long-range pumping [2]. As the performance of ACEO pumps has advanced [3, 4], ACEO has also been exploited, in conjunction with dielectrophoresis (DEP), in different geometries to manipulate particles and cells in microfluidic devices [5-7]. 

An alternative method is electrokinetic focusing, which uses a direct current electric field (at high voltages of 1 kV) to focus particles and Uquids into a narrow stream. Typically, the sample fluid stream is driven along the central channel of a cross-shaped channel. As the sample enters the intersection, three fluid streams meet and the sample stream is focused into narrow stream. Dielectrophoresis (DEP) can also be used for sample focusing. DEP is the movement of polarized particles in a nonuniform electric field. This phenomenon is explained further in the next section. The main advantage of this... 

For mechanical lysis, nanostructured filter-Uke contractions are employed in microfluidic channels with pressure-driven cell flow. Prinz et al. utilized rapid diffusive mixing to lyse Escherichia coli cells and trap the released chromosome via dielectrophoresis (DEP). Kim et al. developed a microfluidic compact disk platform for mechanical lysis of cells using spherical particles with an efficiency of approximately 65 % however, this method is difficult to be apphed for single-cell analysis. Lee et al. fabricated nanoscale barbs in a microfluidic chip for mechanical cell lysis by shear and frictional forces. Munce et al. reported a device to lyse individual cells by electromechanical shear force at the entrance of 10 mm separation channels. The contents of individual cells were simultaneously injected into parallel channels for electrophoretic separation, which can be recorded by laser-induced fluorescence OLIF) of the labeled cellular contents. The use of individual separation channels for each cell separation eliminated possible cross-contamination from multiple cell separations in a single channel. 

Direct current (DC) dielectrophoresis (DEP) is an efficient means to move and thus separate particles or cells with the force of a stationary electric field. This is accomplished with a spatially nonuniform electric field shaped around insulative objects as obstacles in the path of the DC field. DC-DEP is then the induced motion of polarizable, dielectric objects of micron and smaller size, in a DC electric field that is modified by lab-on-a-chip geometry (or other means) to be spatially nonuniform. 

Dielectrophoresis (DEP) is the motion observed of a dielectric particle polarized in a nonuniform... 

A DHT configuration on a planar surface is shown in Fig. 2 where droplets are actuated via electrowetting on a dielectric (EWOD) or dielectrophoresis (DEP). In both these actuation methods, electrodes are patterned onto a substrate using microfabrication techniques and then covered with a dielectric layer that also functions as a hydrophobic layer. If a voltage is applied to an electrode near the interface of a droplet, the... 

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