Nanoflow valve for the removal of trapped air in microfluidic structures

Lab-on-a-chip applications rely on the ability to deliver and manipulate pico/nanoliter volumes of liquid. The presence of air bubbles interferes with the stable operation of microfluidic devices leading potentially to catastrophic failures. In this work, we describe a microfabricated structure that facilitates the elimination of trapped air bubbles from microfluidic chips. The structure consists of a few microchannels that intersect zones on the chip prone to trapping bubbles, and was tested for the elimination of air from aqueous and aqueous/organic solvents that are frequently used in bioanalytical applications. Due to its large hydraulic resistance, the structure also acts as a “nanoflow valve,” minimizing the loss of liquid flow. The nanoflow valve was integrated into glass microfluidic chips fabricated by wet chemical etching, and evaluated for flow loss, ability to maintain stable flow and effectiveness for removing trapped air. With proper dimensioning of the microfluidic channels, the flow loss through the nanoflow valve was less than 18% and flow stability could be maintained with a relative standard deviation (RSD) <1.5%. Trapped air was completely removed prior to analysis. The newly designed microfluidic device was demonstrated for the analysis of peptide samples by mass spectrometry detection. The simple design and straightforward fabrication is conducive, however, to incorporation in any bioanalytical applications that rely on the use of lab-on-a-chip technologies.