AC Electric-Field-Induced Fluid Flow in Microelectrodes

Ramos, António; Morgan, Hywel; Green, Nicolas G.; Castellanos, A.

doi:10.1006/jcis.1999.6346

Cited by 465 publications

(463 citation statements)

References 8 publications

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“…This type of particle aggregation was concluded to not arise from positive DEP, but possibly to be influenced by electrophoretic effects. However, Green and Morgan 80 and Ramos et al 81 correctly interpreted this effect in terms of a hydrodynamic fluid flow induced by electro-osmotic stress arising from the interaction of the electric field and the electrical double layer on an electrode surface. Anomalous frequency effects, not explainable by DEP forces alone, were also observed by Voldman et al 67 for particles held in traps, and this was also attributed to electrohydrodynamic flow.…”

Section: Technologymentioning

confidence: 99%

Review Article—Dielectrophoresis: Status of the theory, technology, and applications

2010

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A review is presented of the present status of the theory, the developed technology and the current applications of dielectrophoresis ͑DEP͒. Over the past 10 years around 2000 publications have addressed these three aspects, and current trends suggest that the theory and technology have matured sufficiently for most effort to now be directed towards applying DEP to unmet needs in such areas as biosensors, cell therapeutics, drug discovery, medical diagnostics, microfluidics, nanoassembly, and particle filtration. The dipole approximation to describe the DEP force acting on a particle subjected to a nonuniform electric field has evolved to include multipole contributions, the perturbing effects arising from interactions with other cells and boundary surfaces, and the influence of electrical double-layer polarizations that must be considered for nanoparticles. Theoretical modelling of the electric field gradients generated by different electrode designs has also reached an advanced state. Advances in the technology include the development of sophisticated electrode designs, along with the introduction of new materials ͑e.g., silicone polymers, dry film resist͒ and methods for fabricating the electrodes and microfluidics of DEP devices ͑photo and electron beam lithography, laser ablation, thin film techniques, CMOS technology͒. Around three-quarters of the 300 or so scientific publications now being published each year on DEP are directed towards practical applications, and this is matched with an increasing number of patent applications. A summary of the US patents granted since January 2005 is given, along with an outline of the small number of perceived industrial applications ͑e.g., mineral separation, micropolishing, manipulation and dispensing of fluid droplets, manipulation and assembly of micro components͒. The technology has also advanced sufficiently for DEP to be used as a tool to manipulate nanoparticles ͑e.g., carbon nanotubes, nano wires, gold and metal oxide nanoparticles͒ for the fabrication of devices and sensors. Most efforts are now being directed towards biomedical applications, such as the spatial manipulation and selective separation/enrichment of target cells or bacteria, high-throughput molecular screening, biosensors, immunoassays, and the artificial engineering of three-dimensional cell constructs. DEP is able to manipulate and sort cells without the need for biochemical labels or other bioengineered tags, and without contact to any surfaces. This opens up potentially important applications of DEP as a tool to address an unmet need in stem cell research and therapy.

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Section: Technologymentioning

confidence: 99%

Review Article—Dielectrophoresis: Status of the theory, technology, and applications

2010

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“…Induced-charge electro-osmotic flows driven by applied AC fields can thus persist only in a certain band of driving frequencies, τ −1 e ≤ ω ≤ τ −1 c , unless Faradaic reactions occur at the electrodes to maintain the bulk field. In AC electro-osmosis at adjacent surface electrodes (Ramos et al (1999)) or AC pumping at an asymmetric electrode array (Ajdari (2000)), the inducing surfaces are the electrodes, and so the two time scales coincide to yield a single characteristic frequency ω c = 1/τ e . (Note that Ramos et al (1999) and Gonzalez et al (2000) use the equivalent form ω ∼ σλ D /ε w L.) Table 2 presents typical values for ICEO flow velocities and charging time scales for some reasonable microfluidic parameters.…”

Section: Double-layer Relaxation At Electrodesmentioning

confidence: 99%

Induced-charge electro-osmosis

2004

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We describe the general phenomenon of 'induced-charge electro-osmosis' (ICEO) -the nonlinear electro-osmotic slip that occurs when an applied field acts on the ionic charge it induces around a polarizable surface. Motivated by a simple physical picture, we calculate ICEO flows around conducting cylinders in steady (DC), oscillatory (AC), and suddenly-applied electric fields. This picture, and these systems, represent perhaps the clearest example of nonlinear electrokinetic phenomena. We complement and verify this physically-motivated approach using a matched asymptotic expansion to the electrokinetic equations in the thin double-layer and low potential limits. ICEO slip velocities vary like u s ∝ E 2 0 L, where E 0 is the field strength and L is a geometric length scale, and are set up on a time scale τ c = λ D L/D, where λ D is the screening length and D is the ionic diffusion constant. We propose and analyze ICEO microfluidic pumps and mixers that operate without moving parts under low applied potentials. Similar flows around metallic colloids with fixed total charge have been described in the Russian literature (largely unnoticed in the West). ICEO flows around conductors with fixed potential, on the other hand, have no colloidal analog and offer further possibilities for microfluidic applications.

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“…Although ICEO flows have been observed in diverse settings [1,5,8,9], ICEP motion of colloids is largely unexplored. In what may be the only prior experimental work, Murtsovkin and Mantrov [10] observed that the motion of quartz particles of irregular shapes varies with the square of the applied field, but did not provide a theory.…”

mentioning

confidence: 99%

Induced-Charge Electrophoresis of Metallodielectric Particles

et al. 2008

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The application of AC electric fields in aqueous suspensions of anisotropic particles leads to unbalanced liquid flows and nonlinear, induced-charge electrophoretic (ICEP) motion. We report experimental observations of the motion of "Janus" microparticles with one dielectric and one metal-coated hemisphere induced by uniform fields of frequency 100 Hz -10 kHz in NaCl solutions. The motion is perpendicular to the field axis and persists after particles are attracted to a glass wall. This phenomenon may find applications in microactuators, microsensors, and microfluidic devices.Nonlinear electrokinetic phenomena are widely used to manipulate colloids and drive flows in microfluidic devices. The liquid and particle velocities typically depend on the strength of the applied field squared and are commonly driven by alternating current (AC) to avoid Faradaic reactions. The classical example is dielectrophoresis (DEP), where a net electrostatic force causes particle motion in a non-uniform AC field. Polarization of the ionic double layers can also lead to nonlinear electro-osmotic flows at low frequencies (kHz), as first described by Murtsovkin and coworkers [1,2]. Bazant and Squires [3,4] conceptually unified this phenomenon with AC electro-osmosis at electrodes, first described by Ramos et al. [5] and Ajdari [6], and suggested the term "induced-charge electro-osmosis" (ICEO) to describe all flows resulting from the action of an applied electric field on its own induced diffuse charge near a polarizable surface. They also predicted how broken symmetries could cause polarizable particles to move in electric fields by "induced-charge electrophoresis" (ICEP) [3,7].

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AC Electric-Field-Induced Fluid Flow in Microelectrodes

Cited by 465 publications

References 8 publications

Review Article—Dielectrophoresis: Status of the theory, technology, and applications

Review Article—Dielectrophoresis: Status of the theory, technology, and applications

Induced-charge electro-osmosis

Induced-Charge Electrophoresis of Metallodielectric Particles

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