# A Novel EWOD Platform for Freely Transporting Droplets in Double and Single-Plate Structures

## TL;DR

A new EWOD platform allows droplet transport in both double and single-plate structures, enabling precise control and mixing.

## Contribution

A novel EWOD platform with a curved surface connection structure enables droplet pull-out and precise volume control.

## Key findings

- The EWOD platform successfully achieves droplet pull-out from parallel to single-plate structures.
- Coplanar electrodes generate sufficient driving force for DI water, PC, and PEGDA buffer droplets.
- Droplet volume error is controlled within 0.1% to 2% for precise sample handling.

## Abstract

This study developed a novel dielectric wetting microfluidic operation platform combining parallel-plate and coplanar-plate regions with a curved surface structure as the connection structure. With the new electrowetting on dielectric (EWOD) platform, “droplet pull-out” has been successfully achieved and viewed as an essential new operation for microfluidics with the dielectric wetting technique. The EWOD system is divided into a PDMS substrate top plate and an indium tin oxide (ITO) glass substrate as a bottom layer on this chip. In the parallel-plate region, the droplets can be generated and transported through the square parallel electrodes; in the single-plate area, the droplets can be pulled out from the parallel structure, transported and mixed through the common grounded coplanar electrodes. In dielectric wetting performance testing, coplanar electrodes can apply a maximum driving force of 31.22 µN to DI water and 13.38 µN to propylene carbonate (PC). This driving force is sufficient to detach the sample from the top cover and pull the sub-droplet from the parallel plate structure for DI water, PC and polyethylene glycol diacrylate (PEGDA) buffer. The novel EWOD system also possesses the advantage of precise volume control for liquid samples; the volume error of the generated droplet can be controlled within 0.1% to 2%.