The Physics of Microdroplets

Chapter 10

Digital Microfluidics

10.1 Abstract

From its beginning, digital microfluidics has been developed for biotechnological applications, with the aim to manipulate extremely small volumes of sample liquid. Volumes smaller than 60 nl can be manipulated in such microsystems and used to transport biologic targets. In parallel, digital microfluidics has seen many applications in the field of optofluidics, such as tunable lenses and electronic display screens.

Digital microfluidics consists of moving, merging, separating, and mixing droplets on a locally planar surface. The actuation force can be of two types: electric or acoustic. In the first case, the droplets are moved on a substrate paved with electrodes; this technique is called electrowetting. In the second case, droplets are actuated by acoustic surface waves (SAW) directionally guided. Although some interesting applications have been developed using acoustic methods [1–3], we will only present here electrowetting, and its practical form called “electrowetting on dielectric” (EWOD). The theory of electrowetting is presented first, then the different mechanisms for droplet manipulation are analyzed, and finally some applications in the fields of biotechnology and optofluidics are given.

10.2 Electrowetting and EWOD

In this section, we present the Berge-Lippmann-Young law, which is the basis for the practical developments of digital microfluidics, and we investigate the potentialities of EWOD by analyzing its physical limits. ...