Electrochemically actuated passive stop-go microvalves for flow control in microfluidic systems

Flow manipulation is a critical expected capacity for integrated microsystems. One way to realize low cost devices is to take advantage of capillary forces for fluid movement. In such systems, flow manipulation should be achieved with easily operated, effortlessly integrated valves. One advantageous method to operate sensors and actuators in microsystems is electrochemistry. Here, the design, fabrication and implementation of low voltage electrochemically actuated passive stop-go microvalves for on-off fluidic manipulations in microfluidic systems are reported. Two closely spaced electrodes (one of which has superhydrophobic surface) were fabricated by screen printing followed by surface structuring in a microchannel. The fabrication of the superhydrophobic surface (water contact angle (CA) 152^o) was performed by selective and controlled solvent-etching of a naturally hydrophobic (CA=105^o) screen printed carbon surface. The process increased the roughness and porosity of the surface that caused the superhydrophobic effect. The superhydrophobic surface of the carbon electrode, in addition to functioning as passive stop valve (PSV), facilitates the flow actuation using low applied voltage avoiding observable electrochemical reactions in aqueous solutions. When a low voltage (~1V) was applied at the carbon electrode against a silver electrode, the flow of such solutions (e.g. 0.01M phosphate buffer saline solution) that was stopped at the PSV, resumed, crossing the 1mm pitch of hydrophobic barrier of the PSV in 1s and reestablishing capillary flow downstream. The low cost and flexibility of fabrication, facile integration and miniaturization, and reproducible performance of such on/off valves make this configuration promising for the development of low cost microfluidic devices for point-of-care diagnostics, food analysis, and environmental monitoring.