Showing papers on "Electrowetting published in 2003"

Creating, transporting, cutting, and merging liquid droplets by electrowetting-based actuation for digital microfluidic circuits

Abstract: Reports the completion of four fundamental fluidic operations considered essential to build digital microfluidic circuits, which can be used for lab-on-a-chip or micro total analysis system (/spl mu/TAS): 1) creating, 2) transporting, 3) cutting, and 4) merging liquid droplets, all by electrowetting, i.e., controlling the wetting property of the surface through electric potential. The surface used in this report is, more specifically, an electrode covered with dielectrics, hence, called electrowetting-on-dielectric (EWOD). All the fluidic movement is confined between two plates, which we call parallel-plate channel, rather than through closed channels or on open surfaces. While transporting and merging droplets are easily verified, we discover that there exists a design criterion for a given set of materials beyond which the droplet simply cannot be cut by EWOD mechanism. The condition for successful cutting is theoretically analyzed by examining the channel gap, the droplet size and the degree of contact angle change by electrowetting on dielectric (EWOD). A series of experiments is run and verifies the criterion.

Video-speed electronic paper based on electrowetting

Abstract: In recent years, a number of different technologies have been proposed for use in reflective displays1,2,3. One of the most appealing applications of a reflective display is electronic paper, which combines the desirable viewing characteristics of conventional printed paper with the ability to manipulate the displayed information electronically. Electronic paper based on the electrophoretic motion of particles inside small capsules has been demonstrated1 and commercialized; but the response speed of such a system is rather slow, limited by the velocity of the particles. Recently, we have demonstrated that electrowetting is an attractive technology for the rapid manipulation of liquids on a micrometre scale4. Here we show that electrowetting can also be used to form the basis of a reflective display that is significantly faster than electrophoretic displays, so that video content can be displayed. Our display principle utilizes the voltage-controlled movement of a coloured oil film adjacent to a white substrate. The reflectivity and contrast of our system approach those of paper. In addition, we demonstrate a colour concept, which is intrinsically four times brighter than reflective liquid-crystal displays5 and twice as bright as other emerging technologies1,2,3. The principle of microfluidic motion at low voltages is applicable in a wide range of electro-optic devices.

Electrowetting-based droplet mixers for microfluidic systems

Abstract: Mixing of analytes and reagents is a critical step in realizing a lab-on-a-chip. However, mixing of liquids is very difficult in continuous flow microfluidics due to laminar flow conditions. An alternative mixing strategy is presented based on the discretization of liquids into droplets and further manipulation of those droplets by electrowetting. The interfacial tensions of the droplets are controlled with the application of voltage. The droplets act as virtual mixing chambers, and mixing occurs by transporting the droplet across an electrode array. We also present an improved method for visualization of mixing where the top and side views of mixing are simultaneously observed. Microliters of liquid droplets are mixed in less than five seconds, which is an order of magnitude improvement in reported mixing times of droplets. Flow reversibility hinders the process of mixing during linear droplet motion. This mixing process is not physically confined and can be dynamically reconfigured to any location on the chip to improve the throughput of the lab-on-a-chip.

Methods and apparatus for manipulating droplets by electrowetting-based techniques

Abstract: An apparatus is provided for manipulating droplets The apparatus is a single-sided electrode design in which all conductive elements are contained on one surface on which droplets are manipulated An additional surface can be provided parallel with the first surface for the purpose of containing the droplets to be manipulated Droplets are manipulated by performing electrowetting-based techniques in which electrodes contained on or embedded in the first surface are sequentially energized and de-energized in a controlled manner The apparatus enables a number of droplet manipulation processes, including merging and mixing two droplets together, splitting a droplet into two or more droplets, sampling a continuous liquid flow by forming from the flow individually controllable droplets, and iterative binary or digital mixing of droplets to obtain a desired mixing ratio

Light actuation of liquid by optoelectrowetting

Abstract: Optical actuation of liquid droplets has been experimentally demonstrated for the first time using a novel optoelectrowetting (OEW) principle. The optoelectrowetting surface is realized by integrating a photoconductive material underneath a two-dimensional array of electrowetting electrodes. Contact angle change as large as 308 has been achieved when illuminated by a light beam with an intensity of 65 mW/cm 2 . A micro-liter droplet of deionized water has been successfully transported by a 4 mW laser beam across a 1 cm � 1 cm OEW surface. The droplet speed is measured to be 7 mm/s. Light actuation enables complex microfluidic functions to be performed on a single chip without encountering the wiring bottleneck of two-dimensional array of electrowetting electrodes. Published by Elsevier Science B.V.

Preventing Biomolecular Adsorption in Electrowetting-Based Biofluidic Chips.

Abstract: Electrowetting-on-dielectric (EWOD) is a new method for moving liquids in biofluidic chips through electrical modification of the surface hydrophobicity. EWOD-based devices are reconfigurable, have low power requirements, and can handle neutral and charged analytes, as well as particulates. We show that biomolecular adsorption in EWOD is minimized by limiting the time during which no potential is applied and through choice of solution pH and electrode polarity. The same approach may be useful for controlling biomolecular adsorption in other applications of hydrophobic dielectric materials. These results demonstrate the feasibility of implementing EWOD for fluid actuation in biofluidic chips.

Electrowetting-based on-chip sample processing for integrated microfluidics

Abstract: In this work, results and data are reported on key aspects of sample processing protocols performed on-chip in a digital microfluidic lab-on-a-chip We report the results of experiments on aspects of sample processing, including on-chip preconcentration and dilution, on-chip sample injection or dispensing, and sample mixing It is shown that high speed transport and mixing of analytes and reagents can be performed using biological solutions without system contamination

Frequency-Based Relationship of Electrowetting and Dielectrophoretic Liquid Microactuation

Abstract: Electrowetting and dielectrophoretic actuation are potentially important microfluidic mechanisms for the transport, dispensing, and manipulation of liquid using simple electrode structures patterned on a substrate. These two mechanisms are, respectively, the low- and high-frequency limits of the electromechanical response of an aqueous liquid to an electric field. The Maxwell stress tensor and an RC circuit model are used to develop a simple predictive model for these electromechanics. The model is tested by measuring electric-field-induced pressure changes within an aqueous droplet trapped between two parallel, disk-shaped electrodes immersed in a bath of immiscible, insulating oil. The experiment is an adaptation of Quincke's original bubble method for measuring the dielectric constant of a liquid. For AC voltages lower than ∼100 V-rms, the pressure data largely conform to the square-law predictions of the model. At higher voltages, this square-law behavior is no longer evident, a result consistent with...

Cooling of integrated circuits using droplet-based microfluidics

Abstract: Decreasing feature sizes and increasing package densities are making thermal issues extremely important in IC design. Uneven thermal maps and hot spots in ICs cause physical stress and performance degradation. Many MEMS and microfluidics-based solutions were proposed in the past. We present a cooling method based on high-speed electrowetting manipulation of discrete sub-microliter droplets under voltage control with volume flow rates in excess of 10 mL/min. We also propose a flow-rate feedback control where the hot areas get increased supply of droplets without the need for external sensors and electrothermocapillary control where hot areas attract droplets due to thermocapillarity and are returned to their reservoirs by electrowetting resulting in a self-contained and a self-regulated system.

Influence of the Electrical Double Layer in Electrowetting

Abstract: Electrowetting (wetting under the influence of an applied electric field) of three fluoropolymer surfaces (amorphous Teflon, DuPont) by electrolyte solutions was studied with the sessile drop method. The electrowetting curve (contact angle/potential) is analogous to the electrocapillary curve (surface tension/potential) and may be described by a combination of the Young and Lippmann equations. The influence of the electrical double layer at the polymer/solution interface has been neglected in the past because the overall interfacial capacitance is mainly determined by the capacitance of the insulating polymer layer. We demonstrate that for some surfaces a systematic deviation occurs at positive potentials. This departure from the constant capacitance regime is attributed to double layer effects, namely, the adsorption of hydroxide and halide anions. The pH, ionic strength, and polymer composition can all influence electrowetting behavior.

Systems and methods for optical actuation of microfluidics based on opto-electrowetting

Abstract: The invention is related to methods and apparatus that manipulate droplets in a microfluidic environment. Advantageously, embodiments of the invention manipulate droplets by controlling the electro-wetting characteristics of a surface with light, thereby inducing a gradient in the surface tension of a droplet. The gradient in the surface tension propels the droplet by capillary force. A variety of operations, such as transporting, joining, cutting, and creating can be performed. Advantageously, embodiments of the invention obviate the need to create a relatively large and complex control electrode array. A plurality of photoconductive cells or a layer of a photoconductive material selectively couples an electrode carrying an electrical bias to otherwise floating conductive cells in response to a beam of light. The electrical bias applied to the conductive cell generates a localized electric field, which can change the contact angle of the droplet, thereby permitting the droplet to be propelled.

Manipulation of multiple droplets on N/spl times/M grid by cross-reference EWOD driving scheme and pressure-contact packaging

Abstract: This paper reports two recent breakthroughs in our development of EWOD-based (ElectroWetting On Dielectric) digital (droplet) microfluidic circuits: a driving scheme and a packaging scheme, both of which greatly simplify fabrication and make large-array chips a reality. This paper will explain (1) the concept of cross-reference driving, which allows single-layer electrode fabrication, including the techniques to allow simultaneous driving of multiple droplets and (2) pressure-contact connection, which greatly simplifies packaging and assembly for high-density EWOD devices. The efficacy of the driving concept is demonstrated by transporting four droplets simultaneously, each along its own path, on a 9/spl times/9 grid and performing essential fluidic functions such as creation, cutting, merging, and mixing of droplets.

Apparatus for forming variable fluid meniscus configurations

Abstract: Apparatus for providing a fluid meniscus with variable configurations by means of electrowetting. A fluid chamber (5) holds two different fluids (A, B) separated by a meniscus (14) of which the edge, having different sides, is constrained by the fluid chamber. A first electrowetting electrode (2a) is arranged to act on a first side of the meniscus edge and a second electrowetting electrode (2a') is arranged to act separately on a second side of the meniscus edge. Selected meniscus configurations can be formed by providing selected voltages to the first and second electrowetting electrodes respectively.

Fabrication of biological microarrays using microcantilevers

Abstract: Arrays of silicon-based microcantilevers with properly designed passivated aluminum electrodes have been used to generate microarrays by depositing microspots of biological samples using a direct contact deposition technique. The approach proposed here can be compared to the dip-pen technique but with the noticeable difference that electrostatic fields are generated onto the cantilevers to increase the height of liquid rise on the cantilever surface when dipping them into the liquid to be deposited. Both electrowetting through the reduction of the contact angle and dielectrophoresis through electrostatic forces can be used to favor the loading efficiency. These phenomena are particularly pronounced on the microscale due to the fact that physical scaling laws favor electrostatic forces. Moreover, at this scale, conductive heat dissipation is enhanced and therefore joule heating can be minimized. Using this approach, with a single loading, arrays of more than a hundred spots, from the femtoliter to the picoliter range, containing fluorescent-labeled oligonucleotides and proteins were directly patterned on a glass slide.

Reversible switching of high-speed air-liquid two-phase flows using electrowetting-assisted flow-pattern change.

Abstract: This work is the first demonstration of electrical modulation of surface energy to reversibly switch dynamic high-speed gas−liquid two-phase microfluidic flow patterns. Manipulation of dynamic two-phase systems with continuous high-speed flows is complex and interesting due to the multiple types of forces that need to be considered. Here, distinct stable flow patterns are formed through a multipronged approach: both surface tension forces generated by surface chemistry modulation as well as viscous and inertial forces produced by fluid flows are employed. The novel fluidic actuation mechanism provides insights into better understanding microscale two-phase flow dynamics and offers new opportunities for the development of two-phase biochemical microsystems that are mechanically simple and operational at high speeds.

3-d imaging of moving droplets for microfluidics using optical coherence tomography

Abstract: VVe present the use of optical coherence tomography (OCT), an interferometric 3-D imaging technique, to visualize microdroplets in an electrowetting-based microfluidic device. Vertical cross-sectional images of stationary and moving microdroplets are obtained using this technique, to provide information on static and dynamic contact angle changes and flow profiles inside the microdroplet during transport. The initial results are encouraging and OCT appears to be a promising method to study fundamental, yet poorly understood electrowetting phenomena such as contact angle saturation and contact angle hysteresis. OCT can also be used in visualizing 3-D flow profiles in droplet-based microfluidics.

Tunable microfluidic optical-fiber devices based on electrowetting pumps and plastic microchannels

Abstract: This letter introduces a class of tunable microfluidic fiber device that uses molded plastic microchannels and electrowetting pumps. It demonstrates the application of this type of system to dynamically adjustable narrow-band and wide-band all-fiber filters. Compact size, low-cost fabrication procedures, low-power (<1 mW) consumption, nonmechanical operation, and good optical characteristics are among the attractive features of these devices. They have many attributes that could make them useful for certain applications in photonics.

Wetting Tension Due to Coulombic Interaction in Charge-Related Wetting Phenomena

Abstract: The influence of Coulombic interaction on wetting is elucidated within the framework of electromechanics. The Maxwell stress and osmotic pressure acting on a meniscus are integrated to obtain a concise analytical expression for the Coulombic contribution to wetting tension. The results are verified alternatively by using a thermodynamic approach. The method is applied to three important charge-related wetting configurations in which droplets are placed on a solid substrate. First, when the constant-potential boundary condition is applied at the substrate surface, only the electrocapillary term which represents the electrostatic free energy of the electrical double layer contributes to the wetting tension. Second, in the case of the constant-charge condition, the wetting tension includes an additional edge-effect term. It is found that the wetting tension in this case is dependent on the interface profile near the three-phase contact line. Third, in the case of electrowetting on dielectrics, the wetting tension also includes the edge-effect term. The wetting-tension term appearing in the Lippmann-Young equation is recovered as a special case of the third case.

Particle separation and concentration control for digital microfluidic systems

Abstract: This paper proposes a concept of separation and concentration control of particles in droplets for eventual digital microfluidic systems. The concept is confirmed by facilitating electrophoresis of particles within droplets that are driven by electrowetting on dielectric (EWOD) and is aimed to take advantage of the simplicity of digital operation for complex systems.

Electrowetting optical switch

Abstract: A switchable optical element having a first discrete state and a different, second discrete state. The element comprises a fluid system including a first fluid (44) and a different, second fluid (46), a wavefront modifier (26) having a face (28); and a fluid system switch for acting on the fluid system to switch between the first and second discrete states of the element. When the element is in the first discrete state, the face (28) of the wavefront modifier (26) is substantially covered by the first fluid (44). When the element is in the second discrete state, the face of the wavefront modifier is substantially covered by the second fluid (46). The fluid system switch comprises a configuration of electrodes arranged to act on the fluid system by the application of electrowetting forces and a voltage control system arranged to control voltages applied to the configuration of electrodes to switch between the first and second discrete states of the element.

Digitally tunable microfluidic optical fiber devices

Abstract: This communication introduces a digital design for tunable microfluidic optical fiber devices. In these systems, multiple, independently controlled microfluidic plugs are pumped into or out of overlap with a fiber structure to modulate its transmission characteristics. The devices described here use eight plugs, eight electrowetting pumps and a corresponding set of molded planar recirculating microchannels to control the depth of the narrowband loss feature associated with a long period fiber grating. Optical measurements illustrate the digital and relatively fast operation of this type of microfluidic fiber device.

Investigation of electrowetting-based microfluidics for real-time pcr api’lications

Abstract: An investigation was conducted to determine the suitability of electrowetting-based droplet actuation for microfluidic PCR applications. We experimentally verified that droplets containing standard PCR reagents could be microactuated with the same facility previously demonstrated for droplets of deionized water or salt solution. We further verified that the manipulations and the environment inside the electrowetting chip did not inhibit PCR and we were able to successfully perform real-time PCR assays in 300 nL droplets within the electrowetting chip.

Optimal strategies for moving droplets in digital microfluidic systems

Abstract: In digital microfluidic systems, analyte droplets (volume typically c 1~1) are transported on a planar electrode array by dielectrophoretic and electrowetting effects. While recent work has demonstrated feasibility mainly with single droplets on small arrays, these systems hold promise for commercial-scale applications by simultaneously moving many droplets on large arrays. This paper introduces a broadly applicable approach to optimally control digital microfluidic systems, i.e., software algorithms that generate a sequence of control signals for moving one or many droplets from start to goal positions in the shortest number of steps, subject to constraints such as minimum required separation between droplets, obstacles on the array surface, and limitations in the control circuitry.

Self-excited oscillatory dynamics of capillary bridges in electric fields

Abstract: We studied the stability of capillary bridges between flat, parallel, and dielectrically coated electrodes as a function of the voltage applied between them. The stability limits of the capillary bridge state and the state consisting of two separated droplets are shifted with respect to ordinary capillary hysteresis at zero voltage. Surprisingly, we found that the system can oscillate periodically between the two states within a certain range of applied voltage and electrode separation. These oscillations could be applied to promote mixing in electrowetting-based microfluidic devices. We present a model based on the balance between interfacial and electrostatic energies, which explains the experimental findings quantitatively.

Modification of Drop Shape Controlled by Electrowetting

Abstract: Wetting defects were created thanks to electrowetting: the effective surface tension between brine and an insulating solid is independently monitored, via an external electrical field, on two complementary areas (defect and background). This article describes the bicapacitor substrates that allow such a zone differentiation when connected to an adequate high-tension setup. Observations of the deformation of a drop on a stripe-shaped defect showed that it is possible to scan an appreciable range of wetting contrasts between the defect and the background with a unique sample. Theoretical calculations suggest an order of magnitude for electrostatic edge effects characteristic of these "virtual" wetting defects.

Soft printing of droplets digitized by electrowetting

Abstract: This paper describes a new way of printing, enabled by electric control and geometric utilization of surface tension. The printing is performed by contact between liquid droplets and a solid printing surface (e.g. a glass plate), with neither solid-solid contact nor droplet ejection. The droplets are formed prior to the printing by electrowetting-on-dielectric (EWOD) so that the droplet volume is not affected by the printing surface or environment. Micromachining processes have been developed to accommodate active liquid digitization and passive droplet transfer in the testing device. Successful printings of water and diluted DNA solution droplets (/spl sim/100 nl) were demonstrated. Incorporated with EWOD, this printing mechanism is capable of programming the sizes and positions of printed spots using multiple nozzles and various droplet volumes.

Electrowetting optical switch

Abstract: Switchable optical element having a first state of separation, and a further second state of separation. This element has a fluid system including a first fluid (44) and another of the second fluid (46), the wavefront modulation material having a first surface (28) and (26), and a fluid system switch the fluid system switch acts on the fluid system to switch between first and second states of the element. Element when in a first state of separation, the surface of the wavefront modulation material (26) (28) is covered substantially over the first fluid (44). Element when in the second state of separation, the surface of the wavefront modulation material is covered substantially to the second fluid (46). Fluid system switch has an electrode structure and voltage control system, the electrode structure is disposed so as to act on the fluid system by electrowetting forces, the voltage control system is installed for controlling the voltage applied to the electrode structure, switching between first and second separation state of the element.

Optical beamsplitter with electro-wetting actuation

Abstract: A tunable optical beamsplitter is disclosed that uses electrowetting techniques to vary the propagation characteristics of one or more light beams. Specifically, electrowetting principles are applied to a region of fluid enclosed within an enclosure to form a plurality of liquid lenses. When a light beam is incident upon the plurality of lenses, the plurality of lenses transforms portions of the light beam in corresponding plurality of output split beams. The region of fluid is controllably moved within the enclosure to modify at least a first optical characteristic of at least a first lens in said plurality of lenses in order to change the propagation characteristics of at least one of the split beams.

Modeling of electrowetted surface tension for addressable microfluidic systems: dominant physical effects, material dependences, and limiting phenomena

Abstract: This paper describes the equilibrium shape of a liquid drop under applied fields such as gravity and electrical fields, taking into account material properties such as dielectric constants, resistivities, and surface tension coefficients. The analysis is based on an energy minimization framework, scaling arguments, and on solutions of Maxwell's electrostatic equations. A rigorous and exact link is provided between the energy function corresponding to any given physical phenomena, and the resulting shape and size dependent force term in the (modified) Young's equation. It is shown that a dielectric solid and a perfectly conducting liquid is all that is needed to exactly recover the Young-Lippmann equation. A dielectric liquid on a conducting solid gives rise to line tension terms. Finally, a slightly resistive liquid on top of a dielectric, highly resistive solid gives rise to contact angle saturation and accurately predicts the experimental data that we observe in our electrowetting devices.