Sampling from nanoliter plugs via asymmetrical splitting of segmented flow

A microfluidic device is developed to sample from oil-segmented fluid plugs of nanoliter volume by passive splitting. In the device, plugs are pumped into a loop where they split according to the flow resistance of each arm of the loop. The loop structure prevents changes in flow resistance over time, caused by accumulation of plugs in downstream collector capillaries, from interfering with the split ratio. To prevent plugs from recombining at the downstream junction of the loop, a series of posts is fabricated into the junction. This structure allows oil to cross, enabling pressure equalization, but not the aqueous plugs allowing them to be collected into separate capillaries or channels. The split ratio depended on both dimensions of the loop channels and frequency of plugs entering the loop. Split ratios from 1:1 to 34:1 were achieved for samples from 1.7 to 3.3 nL. Long-term stability was demonstrated by splitting over 7000 plugs with 6.3% relative standard deviation of the daughter plug size. The system will have application to high-throughput chemical analysis on a nanoliter scale by enabling several applications including performing multiple assays on a single sample, preserving sample while some is removed for analysis, and splitting reagents or test compounds for use in multiple assays.