Pressure barrier of capillary stop valves in micro sample separators

This paper presents a simple and accurate method for characterizing pressure barrier of capillary stop valves inside micro sample separators based on active CD-like microfluidics platforms. The capillary stop valves and micro sample separator were fabricated on polycarbonate (PC) substrates by using hot embossing techniques. The capillary valves stop the flow of liquid inside the microfluidic devices using a capillary pressure barrier when the channel geometry changes abruptly. Experiments are performed by rotating micro sample separator on a platform. The liquid sample stopped inside the micro sample separator is expected to be segmented by using density gradient centrifugation. Various density segments of samples required for an analysis can be separated by simply rotating at different speeds. Design parameters of the capillary valves used in micro sample separator have been analyzed theoretically. It is shown that the pressure barrier of capillary valve design can be better predicted by using current modified 3-D meniscus model. Detailed theoretical analyses of valve behavior is presented and compared with experimental measurement. A model for the valve is then extracted that characterizes the valve performance for various parameters of capillary stop valves. (C) 2004 Elsevier B.V. All rights reserved.