Microfabricated Capillarity-driven Stop Valve and Sample Injector

This paper presents the design, fabrication, and testing of passive plastic microfluidic valves and active injectors driven by capillary forces. The passive valves stop the flow of a liquid inside a capillary using a capillary pressure barrier that develops when the channel cross section changes abruptly. Two types of valves with vertical and horizontal neck regions were fabricated yielding pressure barriers ranging from 1-6 kPa. Introducting asymmetry in the neck region, unidirectional valving action was achieved. The passive valving devices were used in combination with two electrodes to implement a sample injector. The injector uses an electrolytically-generated bubble that raises the liquid pressure beyond the barrier thus reestablishing flow with as little as 150 W of electrical power.