A Low-Cost Portable Dynamic Droplet Sensing System for Digital Microfluidics Applications

A simple and low-cost open electrowetting on dielectric (EWOD)-based dynamic droplet sensing system has been designed and fabricated to measure the droplet parameters. The system has the capability of monitoring and controlling the droplet position by using electrical and optical methods. The droplet position is measured electrically by sensing the capacitance between the bottom electrode and top ground wire with a capacitance input range of +/- 8 pF and resolution of 24 bit. A high-voltage control unit (5-400 VDC) is designed for actuation of voltage on different electrode pads. The printed circuit board (PCB) technology is used for the cost-effective open EWOD device fabrication, whereas polypropylene (PP) is used as a dielectric as well as a hydrophobic layer. Open source computer vision (OpenCV) libraries are used in the optical method for processing of the droplet images. The speed of droplet movement at 300 VDC is 7.1 mm/s. Because of its portability, automation, and low cost, the dynamic sensing system has the potential to be useful in many of the existing lab-on-chip (LOC) applications.