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

Abstract

Abstract-This paper 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 ( 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. A smaller channel gap, a larger droplet size and a larger change in the contact angle enhance the necking of the droplet, helping the completion of the cutting process. Creating droplets from a pool of liquid is highly related to cutting, but much more challenging. Although droplets may be created by simply pulling liquid out of a reservoir, the location of cutting is sensitive to initial conditions and turns out unpredictable. This problem of an inconsistent cutting location is overcome by introducing side electrodes, which pull the liquid perpendicularly to the main fluid path before activating the cutting. All four operations are carried out in air environment at 25 V dc applied voltage.[862]Index Terms-Contact angle, electrowetting, electrowetting on dielectric (EWOD), lab-on-a-chip, microfluidics, micro total analysis system ( TAS), surface tension.

Electrode-assisted trapping and release of droplets on hydrophilic patches in a hydrophobic microchannel

“…One thing must be noted: by using protocols involving individual droplets that have to perform complicated tasks, a manipulation method is required. Many methods have been developed (Chen and Jiang 2012;Cho et al 2003;Pit et al 2015b). For combination with SPR, pneumatic membrane valves (Luo et al 2008) and electrowetting-on-dielectric (EWOD) (Malic et al 2009(Malic et al , 2011 have been used.…”

Annealing Effect of High Dielectric Material for Low Voltage Electrowetting on Dielectric (EWOD)

“…Many studies have used SiO 2 with a low dielectric-constant of about 3.8 as the insulating layer, leading to a large operating voltage of several tens of volts (Smith, Abeysinghe, Haus, & Heikenfeld, 2006;Papathanasiou, Papaioannou, & Boudouvis, 2008;Cho, Fan, Moon, & Kim, 2002;Cho, Moon, & Kim, 2003). The larger operating voltage will cause electrical breakdown and reliability.…”

Theory, fabrication and applications of microfluidic and nanofluidic biosensors

“…species) actuation and consequently biosensors based on electrokinetic flow have also been developed. In the so-called 'digital based microfluidics' based on electro-osmosis [67,68], electrically controlled surface tension is used to drive liquid droplets [54,55]. Direct manipulation of electro-osmosis through chemical modification of surfaces to preferentially direct flows has also been demonstrated [53] thus eliminating the need for valves and pumps.…”