Channel shapes split microdrops

One important component of labs-on-a-chip is the capability of handling tiny volumes of liquid precisely. Researchers from Harvard University have come up with a method for breaking larger drops into daughter drops of specific volumes.

The method is passive; it uses the pressure-driven flow of liquid through microscale channels containing T-shaped junctions or isolated obstacles to create the daughter drops.

The method could be used in future labs-on-a-chip to, for example, break off a portion of a reaction that is taking place in a droplet in order to analyze the reaction at that point.

The researchers used a 30-micron-wide channel that led to a T-junction. Under pressure each droplet is halved at the intersection. The researchers were able to create unevenly split droplets by changing the shape of the T. When they made the arms different lengths, the shorter arm had faster flowing fluid and ended up with a larger fraction of each water droplet.

The researchers also used a series T-junctions to break up a droplet into a sequence of smaller droplets. The researchers also showed that it was possible to break up droplets by putting a square obstacle either in the center or on one side of a channel.

The method could be used in practical applications in two to five years, according to the researchers. The work is slated to appear in an upcoming issue of Physical Review Letters.