Electrowetting on liquid-infused membrane for flexible and reliable digital droplet manipulation and application

Droplet manipulation is a critical step for microfluidic applications. We present digital microfluidic devices based on electrowetting-on-dielectric (EWOD) for reliable and repeatable droplet manipulation. The EWOD device consists of two flexible conducive films as top and bottom electrodes, and one flexible liquid-infused membrane (LIM) as the hydrophobic insulating layer. LIMs made by infusing various fluids (air, fluorocarbon, silicone and hydrocarbon oils) into polytetrafluoroethylene (PTFE) membranes are evaluated by electrowetting performance of a sessile water droplet. Silicone oil is selected as the filling insulating oil according to its excellent electrowetting performance in good reversibility, low contact angle hysteresis, and negligible volatility. Fast (85 mm.s(-1)), repeatable ( > 5000 times without obvious decay) and continuous droplet (designed routes) moving, merging, mixing and positioning have been demonstrated. The factors affecting droplet transport velocity are investigated, including the infused oil viscosity, the conducive volume and the top-to-bottom gap distance. Both the conducive film and LIM are replaceable and robust, showing reliable and long-term stability. Quantitative chromogenic reactions and a flexible EWOD device are demonstrated. These devices are easy-to-fabricate, replaceable-in-material and robust-in-performance, showing high potential for applications in sample preparation, and flexible sensing and display devices.