Disposable capacitive electrical droplet measurement (DisC-EDM) based on a film-chip technique

Abstract

For droplet-based microfluidics, a simple and easy-to-use method to measure the size and number of droplets in real-time is required to generate droplets with high uniformity, stability, and throughput. This study introduces a disposable capacitive electrical droplet measurement (DisC-EDM) technique that consists of a disposable microchannel superstrate and a reusable sensing substrate, which can be assembled and disassembled by vacuum pressure. Because the disposable microchannel superstrates can be fabricated easily and cost-effectively with an ultrathin polymer film, it can be replaced after a single use to prevent biological contamination and can also be used to detect the droplet size with a high sensitivity. Meanwhile, the sensing substrate can be continuously reused to achieve cost reduction and ease of use. Owing to three interdigitated electrode configurations, the amplitude of the output signal is linearly proportional to the size of the droplets. Consequently, the need for a complex calculation algorithm or expensive equipment to determine the droplet size is eliminated. Furthermore, because the sensing principle of the DisC-EDM is based on a capacitive detection method, its sensitivity remains constant, even for changes in the conductivity and velocity of the droplets. To demonstrate the effectiveness of the DisC-EDM, it was used to evaluate and compare the performance of a pressure-driven pump and a screw-driven syringe pump in droplet generation. As a cost-effective, reliable, and easy-to-use technique, the DisC-EDM can be used to control the size and uniformity of the droplets in a variety of droplet-based applications.