DEP actuated nanoliter droplet dispensing using feedback control.

Dielectrophoretic (DEP) droplet dispensing using dielectric-coated coplanar electrode structures provides an ideal platform for testing smart control systems for high-speed microfluidic devices. Open-loop control of DEP droplet dispensing is not sufficiently robust for precision droplet dispensing because unavoidable surface property variations of the substrates and other parameters such as liquid viscosity introduce uncertainty in the motion. Closed-loop systems employing distributed optical sensors and feedback provide flexibility, sensitivity, and reliability. In this new scheme, an array of distributed optical sensors detects fluid motion and, through a programmable control module, triggers application of AC voltage bursts of appropriate magnitude, duration, and frequency to control liquid motion and droplet formation. Reconfiguring the module connections and reprogramming the control module permits testing of a variety of control strategies.