Sensing area-variable electrode for wide-range droplet size detection.

Microfluidic droplets of various sizes are applied in a broad spectrum of biological and chemical processes and require high uniformity for reliable outcomes. Although various droplet detection methods have been employed to achieve monodisperse droplets, the capacitive method stands out for its ease of use and rapid response, enabling real-time feedback control. However, this method has limitations in terms of significantly altering the droplet size, resulting in increased continuous phase consumption and the need for microchannel and sensing component replacements. In response, we present the Sensing Area-Variable Electrode (SAVE), which is designed to produce monodisperse droplets across a broad size range without excessive continuous phase consumption and without requiring the frequent replacement of sensing components. The experimental results demonstrate that using the SAVE electrode enables the generation of monodisperse 0.2, 0.4, and 1.0 nL droplets by simply replacing the disposable microchannel while reusing the sensing components. Moreover, the adaptable number of droplets achieved by microchannel replacement allows the SAVE electrode to be effectively utilized in droplet digital polymerase chain reaction (ddPCR) assays, providing a balance between sensitivity and throughput. Consequently, the SAVE electrode addresses the limitations of the capacitive detection method and offers a versatile solution for various droplet-based biological and chemical processes, including ddPCR assays. • SAVE electrode (Sensing Area-Variable Electrode) for optimized droplet detection with minimized oil consumption. • Real-time electrical capacitive method for droplet detection and control. • Simple and cost-effective hybrid microfluidic device combining disposable microchannels with a reusable sensing substrate. • Sensing a wide range of droplet sizes (0.2−1.0 nL) using a single SAVE electrode. • Applied to droplet digital PCR with customized sensitivity and throughput. [ABSTRACT FROM AUTHOR]