Biochip moves liquids with heat

Researchers from Princeton University have made a microscopic device that uses heat to move, mix and split droplets of liquid. The device could be used in small, battery-operated chemical sensors and hand-held medical testers.

The device consists of an interconnected network of hydrophilic stripes on an otherwise hydrophobic, or water-repelling surface. The droplets are confined to the hydrophilic stripes much like a train is confined to a train track.

When the droplets are warmed up by embedded heating elements, the surface tension of the liquid changes, and the droplets move in the direction of cooler surface temperatures. Temperature changes can happen as quickly as two tenths of a second. The right surface tension changes at the right times allow the researchers to control the direction, timing and flow rate of the droplets.

The Princeton droplet manipulator could also be used to test new materials and chemical compounds.

The device could be used in practical applications in two to five years, according to the researchers. The work appeared in the January 27, 2003 issue of Applied Physics Letters.