Closed portable electrowetting-on-dielectric system for actuation of water droplets

We describe the design and performance of a portable closed electrowetting-on-dielectric (EWOD) system for digital microfluidics applications. The system is cost-effective and is capable of controlling the motion of one or more droplets under the influence of an asymmetric electric field. Using polypropylene (commercial cello tape) as a dielectric layer with Glaco (TM) spray to create a hydrophobic surface lowers device fabrication cost. For the first time, a superhydrophobic Glaco (TM) layer (equilibrium contact angle similar to 150 degrees) is used for the EWOD device fabrication. The device has four modules that are designed to provide a high actuation voltage in the range of 5-300 V-DC over the array of electrode pads. Given a large enough electrode array over the lower surface, the effect of the applied potential of the top electrode on droplet motion is studied via numerical simulation and is shown to be insignificant. This result further helps in simplifying the fabrication process. The user-friendly interface that defines droplet motion is designed using Qt, a cross-platform framework that is used as a graphical toolkit and an open-source image processing software in Raspberry Pi. Two types of closed EWOD configurations are developed to demonstrate their features in terms of moving and merging multiple droplets. For the designs implemented, the greatest speed of droplet movement at 295 V-DC was measured to be 60 mm/s. Additional features of the device include calculation of the real-time mixing index and a thermal management module for temperature control. The simplicity of design and low-cost makes the device attractive for studying electrically induced drop motion on one end to a biomedical diagnostic test kit, on the other.