Pico-droplet dispensing control in digital microfluidic systems

Generating and manipulating pL to μL droplets reproducibly in droplet-based (digital) microfluidic chips requires advanced application of control systems. The most common approach of droplet dispensing controllers combines capacitance measurements with calculations of the optical footprint of the droplet on the chip. This technique does not provide the precision and accuracy required for many applications, and it is difficult to apply for wide range of conductive to nonconductive (insulating) liquids. This paper presents a novel technique for measuring the droplet volume using a model reference adaptive control technique. The controller can be used to dispense both conductive and nonconductive liquids. A model of the digital microfluidic system has been developed to control the droplet volume on the electrodes. Simulations of droplet dispensing volume control for conductive and nonconductive liquids demonstrate the method provides an accurate control approach.