Micro/nano liter droplet formation and dispensing by capacitance metering and electrowetting actuation

In this work, a method is presented for dispensing droplets. The method exploits the built-in capacitance of an electrowetting device to meter the droplet volume and control the dispensing process dynamically. A fully automated droplet dispensing device is developed and used to load liquid samples or couple continuous flow to electro-wetting droplet handling. The reproducibility of the dispensing process is tested against dispensing parameters including dispensing volume, production rate, fluid viscosity, channel geometry and needle diameter. The relative independence of the reproducibility on those parameters indicates the wide applicability of the device in biological and chemical sample dispensing. Meanwhile, as low as 1.2% error in reproducibility is demonstrated and up to 120 droplets per minute production rate is possible. The dispensing process has been demonstrated for droplet volumes between 60 nl and 1900 nl or above while maintain reproducibility in an acceptable range of 10%.