Deterministic splitting of fluid volumes in electrowetting microfluidics

Conventional droplet generation approaches in digital microfluidics show ~10% variation in droplet volumes and are restricted to creating only small volumes. In this work, we demonstrate a new approach for splitting sample volumes precisely by gradually ramping down voltage, in place of abruptly switching off electrodes. This allows us to eliminate hydrodynamic instabilities responsible for variations in droplet volume. A simple visual method was developed for measuring sample volumes created on-chip. Our results show that generating and measuring arbitrary sample volumes accurately, with < 1% variation, is possible in electrowetting devices. The approach can be easily extended to existing digital microfluidic systems, and can potentially improve performance of applications requiring precise sample metering, such as immunoassays or DNA amplification.