Microfabricated valveless pump for delivering nonpulsatile flow

Over the past decade, there has been tremendous interest in developing miniaturized chemical analysis systems using microfabrication techniques. Microfluidic components such as pumps and valves form an integral part of such microsystems. Emerging biological assays like single molecule studies of DNA and cell adhesion analyses demand a robust pumping system that can deliver non-pulsatile flows at extremely low velocities. Several types of valved and valve-less pumps have been constructed on both silicon and glass substrates. However, most of the valved pumps involve moving parts and deliver pulsatile flow, while the valveless pumps employ high electric fields. In this paper, we describe the design, construction and operation of a microfabricated valveless micropump, for continuous pumping of reagents at controlled, ultra low flow velocities in the range of 50 micrometers /s. This novel pumping concept is based on pinning a liquid meniscus inside a microchannel by selective hydrophobic patterning and controlling the evaporation rate of the liquid at the meniscus. The resulting pumping action delivers non- pulsatile, low velocity flows that can find applications in a variety of biological assays involving single molecules.