Traveling wave dielectrophoresis

Traveling-wave dielectrophoresis — A special case of -> dielectrophoresis where particles can be moved along an extended array of electrodes. The translational force is created by energizing the electrodes with poly-phase voltages to create an electrical traveling wave, as depicted below. 

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 4. Diagram showing an interdigitated electrode array used to induce travelling wave dielectrophoresis. The cells move over the electrodes along the channel in the direction opposite to that of the travelling field. Cells on the left-hand (right-hand) side of the channel rotate in a clockwise (anti-clockwise) sense while moving.

Individual cells can be identified on the basis of differences in size and dielectric properties using electrical techniques that are non-invasive and label-free. Characterization of the dielectric properties of biological cells is generally performed in two ways, with AC electrokinetics or impedance analysis. AC electrokinetic techniques are used to study of the behavior of particles (movement and/or rotation) and fluids subjected to an AC electric field. The electrical forces act on both the particles and the suspending fluid and have their origin in the charge and electric field distribution in the system. They are the basis of phenomena such as dielectrophoresis [10-14], travelling wave dielectrophoresis [15, 16], electrorotation [17, 18] and electroorientation [19]. 

Masuda et al. (1987) introduced the use of a traveling wave configuration for the manipulation of particles. The frequency used was originally relatively low, so that electrophoresis rather than dielectrophoresis was predominant. The teehnique was later improved by, among others, by Fuhr et al. (1991) and Talary et al. (1996), who used higher frequencies where dielectrophoresis dominates. Talary et al. (1996) used traveling wave dielectrophoresis to separate viable from nonviable yeast eells and the same group have used the teehnique to separate erythroeytes from white blood eells (Burt et al., 1998). 

The major application of dielectrophoresis in micro- and nanofluidic systems continues to be the manipulation of particles and cells. Popular applications include particle trapping, dielectrophoretic microsystems, traveling wave dielectrophoresis, and determination of cell dielectric properties. The specific dielectrophoretic techniques used in existing applications are too numerous to cover in this entry. This entry does provide a brief overview of some of the established manipulation techniques. 

Dielectrophoretic Motion of Particles and Cells, Fig. 7 Traveling wave dielectrophoresis... 

Traveling wave dielectrophoresis is simply a linear application of electrorotation. An AC electric wave is produced by applying an electric field that travels linearly along a series of electrodes. 

An example of a traveling wave dielectrophoresis system with a 90° phase shift between electrodes is shown in Fig. 7. The expression for the traveling wave dielectrophoresis force for a homogeneous spherical particle is given by... 

AC Dielectrophoresis Lab-on-ChIp Devices, Rgure 2 DIelectrophoretIc manipulation techniques (a) electrorotation, (b) electro-orientation, (c) particle trapping and (d) traveling wave dielectrophoresis... 

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