Electrowetting-on-dielectric EWOD

One of the requirements in MALDI-MS analysis is the use of a liquid matrix. The electrowetting-on-dielectric (EWOD) method has been used to move and mix droplets containing proteins and peptides with the liquid matrix, all of which were situated at specific locations on an array of electrodes. With this method, insulin (1.75 pM), insulin chain B (2 pM), cytochrome c (1.85 pM), and myoglobin (1.45 pM) have been analyzed [518]. 

Figure 15. The electrowetting effect. (According to Mugele et al. [260].) (a) If a voltage V is applied between a liquid and an electrode separated by an insulating layer, the contact angle of the liquid-solid interface is decreased and the droplet flattens , (b) Hydrophobic surfaces enhance the effect of electro wetting. For electrowetting on dielectrics (EWOD) several individual addressable control electrodes (here on the bottom) and a large counter-electrode are used. The droplet is pulled to the charged electrodes.

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... 

Electrowetting-on-dielectric (EWOD) is a new method for moving liquids in biofluidic chips through electrical modification of the surface hydrophobicity (Fig. 5) [3]. We have demonstrated prevention of protein and DNA adsorption by minimizing hydrophobic... 

In electrowetting-on-dielectric (EWOD) systems, the overall goal is precise and robust control of liquid motion. The following results are taken from [17, 19, 20]. 

Walker S, Shapiro B (2006) Modeling the fluid dynamics of electrowetting on dielectric (EWOD). J MEMS 15 986-1000... 

Electrocapillary effect Electrowetting on dielectric (EWOD) Electrowetting on insulator-coated electrodes (EICE) Electrowetting on line electrodes (ELE)... 

Electrowetting, Fig. 3 Typical contact angle/voltage response in electrowetting-on-dielectric (EWOD) experiments. This particular set of experimental data corresponds to a 75% aqueous glycerol drop sitting above a 100 pm poly(tetrafluoroethylene) dielectric layer under an applied AC field [5]... 

An industrial batch reactor has neither an inflow nor an outflow of reactants or products while the reaction is being carried out. Batch reactions can be carried out in droplet microreactors, where nanoliters of fluid are individually manipulated using techniques such as electrowetting on dielectric (EWOD) and surface tension control. Semibatch reactors are used in cases where a by-product needs to be removed continuously and to cany out exothermic batch reactions where a reactant has to be added slowly. Microfluidics allows precise control of concentration and temperature, which allows batch and semibatch reactions to be carried out in a continuous manner. Figure 1 shows the general components of a simple industrial-reactor semp, compared with a laboratory-scale setup to carry out a reaction with microfluidic chips. 

Cho SK, Moon H (2008) Electrowetting on dielectric (EWOD) new tool for bio/micro fluids handling. Biochip J 2(2) 79-96... 

Disadvantages of conventional microchips include resistance to hydrodynamic flow (backpressure), adsorption of some biomolecules on walls, and limited robustness (e.g., clogging narrow channels). Digital microfluidic systems overcome the problems with mixing reagents, which are normally associated with conventional microfluidic devices that use laminar hydrodynamic flow. Such microscale platforms are normally based on the electrowetting-on-dielectric (EWOD) principle [66]. In these digital microchips. 

A third t) e of electrocapillary principle is known as electrowetting on dielectrics (EWOD), in which the liquid and the electrodes are separated by a thin dielectric layer (refer to Fig. 3). Major advantages of such an arrangement lie... 

Strictly, the term electrocapillarity therefore refers to the change in the solid or liquid metal-electrolyte interfacial tension, as shown in Eig. la. Eor the principle to be practical, however, it was necessary to avoid electrolysis of the aqueous solution. This was later overcome by coating the electrode surface with a thin dielectric layer (e. g., polymer substrate) several microns to millimeters in thickness, from which the term electrowetting-on-dielectric (EWOD) or electrowetting on insulator coated electrodes (EICE) arises [1], as shown in Figs, lb and Ic. In cases where the insulating layer is not hydrophobic (e. g., parylene), a very thin hydrophobic layer such as a fluoropolymer of order nanometers in thickness, is coated onto the insulator. 

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