Precise droplet volume measurement and electrode-based volume metering in digital microfluidics

In this work, for the first time, we demonstrate nanoscale droplet generation from a continuous electrowetting microchannel using a simple and precise image-based droplet volume metering technique. One of the most popular ways of droplet generation in electrowetting devices is to split a droplet from a preloaded volume as a fluid reservoir. This method is effective, but lowers volume consistency after multiple droplets are generated. Impedance- and capacitance-based methods of volume metering have been successfully used in digital microfluidics, but require complex circuitry and feedback signal processing. In this work, we demonstrate nanoliter droplet generation from a continuous electrowetting channel used as a replenishable fluid reservoir which compensates for the loss of reservoir volume as droplets are sequentially split. This improves volume consistency especially for applications requiring multi-droplet generation. Based on the area of the electrode, the volume of each droplet split from the electrowetting channel can be obtained by a simple and precise image processing technique with no need for additional hardware and measurement errors of ±0.05 %. This simple technique can be used in a wide range of applications that require precise volume metering, such as immunoassay.