Passive Generation of Droplets in Mini and Microchannels

Microfluidic systems generating droplets by oil and aqueous solutions have shown great promise in biochemical and chemical applications, each drop acting as a micro reaction vessel. A popular approach utilizes dual flow of immiscible fluids in microchannels, producing droplets by shear forces at the liquid interfaces. These systems require precise, computer controlled flow, and the resulting drops continue to move, and so are hard to localize. We have developed a unique method to generate an array of precision microdroplets on a plate that does not require careful fluid control and places the drops at specific, predetermined locations. The method utilizes geometric design of a channel to introduce instabilities in a column of water at predetermined locations with predetermined volumes ranging from a few nanoliters to microliters. Droplets form as a result of channel design, not as a result of fluid flow. Different drops can be set up at different locations and volume, then fused together to initiate a reaction. These micro-droplet arrays can be set up by hand in under one minute and can be used for high throughput or combinatorial experiments.