Electrowetting-based actuation of droplets for integrated microfluidicsElectronic supplementary information (ESI) available: six videos showing droplet flow, droplet dispensing and electrowetting. See http://www.rsc.org/suppdata/lc/b1/b110474h/

Abstract

The serviceability of microfluidics-based instrumentation including 'lab-on-a-chip' systems critically depends on control of fluid motion. We are reporting here an alternative approach to microfluidics based upon the micromanipulation of discrete droplets of aqueous electrolyte by electrowetting. Using a simple open structure, consisting of two sets of opposing planar electrodes fabricated on glass substrates, positional and formational control of microdroplets ranging in size from several nanoliters to several microliters has been demonstrated at voltages between 15-100 V. Since there are no permanent channels or structures between the plates, the system is highly flexible and reconfigurable. Droplet transport is rapid and efficient with average velocities exceeding 10 cm s(-1) having been observed. The dependence of the velocity on voltage is roughly independent of the droplet size within certain limits, thus the smallest droplets studied (approximately 3 nl) could be transported over 1000 times their length per second. Formation, mixing, and splitting of microdroplets was also demonstrated using the same microactuator structures. Thus, electrowetting provides a means to achieve high levels of functional integration and flexibility for microfluidic systems.

Water-oil core-shell droplets for electrowetting-based digital microfluidic devices

“…1, 6 Additionally, the electrowetting effect can transport the droplets at high speeds (>10 cm s −1 ) and is very energy efficient. 1, 4 EWOD-based devices have thus attracted a considerable attention recently and have been used for a wide variety of applications including: clinical diagnostic, 20,21 polymerase chain reaction, 22 DNA sequencing, 8 proteomics, 11-14 airborne particle sampler, 23 on-chip cooling, 34 micro-viscometer, 35 micro-conveyor, 36 micro-motor, 37 electronic paper, 38 etc.…”

Local Heating of Discrete Droplets Using Magnetic Porous Silicon-Based Photonic Crystals

“…10 A number of techniques have been described for the actuation of droplets on solid surfaces including the use of thermocapillary effects, 14 photochemical effects, 15 electrochemical gradients, 16 surface tension gradients, 17 temperature gradients, 18 air pressure, 19 structured surfaces, 20 dielectrophoresis, 21 and electrostatic methods. 8 An extension of this approach is a liquid-liquid microfluidic system for manipulating freely suspended microliter or nanoliter droplets. Only few such systems have been reported to date and new manipulation methods continue to emerge.…”

Controlling Drop Size and Polydispersity Using Chemically Patterned Surfaces

“…[17,18,19,20,21,22,23,24,25,26,27,28,29,30] and the references therein. We explore numerically two ways in which this might be possible.…”