Electrowetting on dielectrics

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]. 

Electrowetting-on-dielectric (EWD) microfluidics is based on the actuation of droplet volumes up to several microliters using the principle of modulating the interfacial tension between a liquid and an electrode coated with a dielectric layer [1]. An electric field established in the dielectric layer creates an imbalance of interfacial tension if the electric field is applied to only one portion of the droplet, which forces the droplet to move [2]. Droplets are usually sandwiched between two parallel plates - the bottom... 

R.-F. Yue, J.-G. Wu, X.F. Zeng, M. Kang, and L.T. Liu, Demonstration of four fundamental operations of liquid droplets for digital microfluidic systems based on an electrowetting-on-dielectric actuator. Chin. Phys. Lett. 23, 2303-2306 (2006). 

L. Malic, T. Veres and M. Tabrizian, Two-dimensional droplet-based surface plasmon resonance imaging using electrowetting-on-dielectric microfluidics, Lab Chip, 9, 473M75 (2009). 

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.

F. Mugele and J. C. Baret, Electrowetting From basics to applications, Journal of Physics-Condensed Matter, vol. 17, no. 28, p. R705-R774, July 2005. J. Lee, H. Moon, J. Fowler, T. Schoellhammer, and C. J. Kim, Electrowetting and electrowetting-on-dielectric for microscale liquid handling, Sensors and Actuators A-Physical, vol. 95, no. 2-3, pp. 259-268, Jan. 2002. 

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... 

T-junction and flow-focusing design/device (FFD) are the two main and traditional methods of droplet formation in microfluidic applications. Other emerging methods include dielectrophoresis and electrowetting on dielectric [42]. 

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... 

Lee J, Momr H, Fowler J, Schoellhatruner T, Kim CJ (2002) Electrowetting and electrowetting-on-dielectric for microscale liquid handling. Sens Actuators A 95 259-268... 

Fig. 3 The arrangement for electrowetting on dielectrics of a liquid droplet. The right hand diagram is a simpler schematic illustration...

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

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