Practical Device For Controlling Ultrasmall Volume Flow

As research in certain chemical and bio-chemical fields advance, so does research in analytical techniques. Often, samples to be analyzed or otherwise manipulated are exceedingly tiny. One commonplace application that comes to mind is in the analysis of biological samples where sample sizes may be in micro-liter or pico-liter quantities. In order to effectively manipulate and/or analyze such samples, whole new and innovative techniques must be developed. Additionally, the use of microchips to perform analytical testing is a significant and emerging field of research. Consequently, there is a need to develop methods whereby liquid samples can be analyzed and manipulated on a micro scaleMovement of fluids on microchips has been accomplished by a number of methods. Most notably by pneumatic pressure and electroosmosis. Pressure-induced flow generally requires physical valves to be fabricated and placed in the flow stream. This must be done to control the variety of fluid movements needed on complex microdevices. These valves are difficult to design and fabricate, and exhibit poor back-pressure and leakage performance. Also, the valves have not been fabricated on the micron to submicron scale that are required for future generations of microdevices. Even if these physical structures could be fabricated reliably with good performance characteristics, pressure-induced flow does not scale down to narrow passages and ultrasmall volumes very well. The back pressure generated by these minute passages is immense and the size of the valve structures lead to dead volume and time delays in flow between volume elements.Researchers at Arizona State University have devised a unique combination of technologies, materials and designs to form a flow control mechanism in extremely small-volume environments. For a practical means of flow control several issues are addressed, including the physical dimensions of the channels (or tubes), the physical dimensions of the channel walls, the surface properties at the solution/wall interface, the materials making up the wall, methods to monitor flow and operational parameters.