Flow control for microfluidic system with liquid nitrogen valve

To achieve multiple functions of microfluidic systems, microvalves are indispensable units to control fluid paths, close/open specific sections, and measure reagent volumes. Although various valves have been developed, and shown good properties on microchips, not only the design but also the fabrication are relatively complex. In this work, a novel liquid nitrogen valve was designed and applied in microfluidic chip for flow control, according to the fast freezing and thawing properties of liquid nitrogen. By dropping liquid nitrogen on microchip surface, fluid in microchannels was frozen, and thus the flow stopped flowing by closing the valve. After heating by an electric blower, the frozen fluid was thawed, and with valve open, fluid began to remove. Our experimental results show that the time required to open and close the valve is 3.7 s and 1.1 s, respectively, and the RSDs of the open/close time in five consecutive operation are 5.4% and 7.5%, respectively. Furthermore, the valve could resist pressures up to 33 MPa. All these results demonstrated the facile valve could be successfully used on microfluidic chips for flow control. In addition, the valve is an green valve, without any pollution to environment. Therefore, such liquid nitrogen valves are of the advantages including fast switching, good endurance to high pressure, simple, green and low cost, making it promising for flow control in microfluidic systems.