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

TLDR

The authors employ an electrowetting‑on‑dielectric (EWOD) platform with a parallel‑plate channel, theoretically analyze the channel gap, droplet size, and contact‑angle change to derive a cutting criterion, and experimentally confirm this criterion. They demonstrate that electrowetting can perform creating, transporting, cutting, and merging droplets, and identify a material‑dependent design limit beyond which droplets cannot be cut.

Abstract

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 (μTAS): 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.