AC electrokinetics

Electrochemical investigations are found in the areas of molecular electronics and nanotechnology. Electrochemistry can be used to produce and characterize clean surfaces (e.g., electrochemical cleaning of metals). It can direct the assembly and structure of supramolecular assemblies (e.g., by using self-assembled or spontaneously adsorbed 

An application of AC electrokinetic phenomena is the preconcentration of a target molecule within a small volume. Crooks and coworkers (88) have achieved enrichment factors for DNA exceeding 100 using channels that are 5 mm in length, require only a single homogeneous analyte phase, and avoid complex microfluidic designs. The approach 

Wilhams, J. V. Macpherson, in Comprehensive Chemical Kinetics, R. G Compton, G Hancock, Eds., Elsevier Amsterdam, 1999, pp. 369-438. 

Sugimura, T. Uchida, N. Kitamura, H. Masuhara, AppZ. Phys. Lett. 63, 1288 (1993). 

Michaelis, S. Kudelka, in New Trends in Electrochemical Technology Series, Gordon and Breach London, 2001, Vol. 2, p. 160. 

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Lynntech, Inc. s (Lynntech s), electrokinetic remediation of contaminated soil technology is an in situ soil decontamination method that uses an electric current to transport soil contaminants. According to Lynntech, this technology uses both direct current (DC) and alternating current (AC) electrokinetic techniques (dielectrophoresis) to decontaminate soil containing heavy metals and organic contaminants. A non homogeneous electric field is applied between electrodes positioned in the soil. The field induces electrokinetic processes that cause the controlled, horizontal, and/or vertical removal of contaminants from soils of variable hydraulic permeabilities and moisture contents. 

In the following, we present a simple particle displacement analysis for various AC electrokinetic effects. Assuming co-planar parallel interdigitated electrodes, the electric field between two electrodes can be assumed as half-circular lines near the electrode surface. Various electrokinetic forces can be represented in simple analytical forms using this simplified electric field distribution. 

H. Morgan, N. G. Green, AC Electrokinetics colloids and nanoparticles Research Stndies Press Hertfordshire, (2003). 

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. 

AC electrokinetic techniques, particularly DEP, have been used for the manipulation, separation, focusing, trapping and handling of latex spheres [31-34], viruses [35-39], bacteria [40-45] and cells [46-50], Many different electrode geometries have been used to perform DEP. 

T. Sun, H. Morgan and N. G. Green, Analytical solutions of ac electrokinetics in interdigitated electrode arrays electric field, dielectrophoretic and travelling-wave dielectrophoretic forces, Phys. Rev. E., 76, 046610 (2007). 

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]. 

Figure 4. Selective concentration of microparticles using frequency-dependency of ac electrokinetics in lab-on-a-display. (Reproduced with permission from Ref. [17] Copyright 2009, The Royal Society of Chemistry.)...

The principles behind eleetrorotation, dieleetrophoresis, and other electrokinetic effects are described in Section 2.5. A good basic understanding of the various AC-electrokinetic effects is also provided by Gimsa (2012). The direetion and rate of movement of bioparticles and cells due to these meehanisms depend on the dieleetrie properties of, for example, the cell. These dielectric properties may to some extent refleet the type of eeU or the condition of the eell and there is eonsequently a significant potential in the use of these techniques for cell sorting or eharaeterization. 

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