Centrifugo-pneumatic Valve for Metering of Highly Wetting Liquids on Centrifugal Microfluidic Platforms

We designed and experimentally validated a new type of passive valve for centrifugal microfluidic platforms. A liquid column entering an unvented receiving chamber is stopped by the counter-pressure of compressed air. This valve opens under defined conditions at high centrifugal frequencies at which the interface between liquid and air becomes unstable and enables a phase exchange, forwarding the liquid. Burst frequencies of the valve were determined for liquids typically used in biochemical assays: pure water, water with detergent concentrations between 0.01 and 10%, and pure ethanol. Burst frequencies between 8.5 +/- 0.6 and 27.9 +/- 2.0 Hz were measured for different surface tensions. The burst frequencies can be tuned by simple geometrical changes in the valving structure. The valve does not require ultra-precise structures or local surface modifications and is therefore ideal for low-cost microfluidic polymer disks. Potential applications are in the field of multiparameter and panel analysis, such as PCR-genotyping.