Nanoliter liquid metering in microchannels using hydrophobic patterns

Nanoliter-sized liquid drops can be accurately metered inside hydrophilic m icrochannels using a combination of hydrophobic surface treatment and air p ressure. The technique involves spontaneously filling the microchannels up to a hydrophobic region and splitting a liquid drop bq injecting air throug h a hydrophobic side channel. The hydrophobic regions are fabricated by usi ng a patterned metal mask on a substrate. The patterned substrate is immers ed in an isooctane solution containing 1H,1H,- 2H,2H-per-fluorodecyltrichlo rosilane to form hydrophobic patches on the exposed surface. Stripping the metal mask leaves the hydrophobic patches and restores the hydrophilic subs trate surface. Precise and accurate liquid volumes, ranging from 0.5 to 125 nanoliters, have been metered using this technique. Theoretical prediction s of the pressure needed to meter drops compare well with the experimental values.