Pressure-driven sample injection with quantitative liquid dispensing for on-chip electrophoresis.

A novel pressure-driven sample injection method was developed as an alternative to electrokinetic injection, and electrophoretic separation was carried out on a microfabricated device employing this method. This method enables a defined volume of liquid dispensing, followed by instantaneous injection driven by pneumatic pressure, greatly simplifying the injection procedure. A particular microstructure, called a "metering chamber", has been designed for the quantitative dispensing of an ultra-low volume of sample liquid; a "hydrophobic passive valve" equipped with an air vent channel is employed for injecting a dispensed sample into the separation channel. The reproducibility of dispensing was 3.3% (n = 15), expressed by the variation of dispensed volumes. The electrophoretic separation of DNA fragments was performed using this injection method, varying the injection volumes from 0.45 to 4.0 nL, and the separation efficiencies were compared. This precise injection method, easily variable in injection volumes, is highly suitable for quantitative as well as qualitative electrophoretic analyses.