title: Eletrochemically actuated stop-go valves for capillary force-operated diagnostic microsystems.
abstract: Lateral-flow immunosensing devices continue to be the most successful commercial realization of analytical microdevices. They owe their success to their simplicity, which significantly depends on the capillary-driven flow and versatile technological platform that lends itself to fast and low-cost product development. To compete with such a convenient product, microsystems can benefit from simple-to-operate fluid manipulation. We show that the capillary-driven flow in microchannels can be manipulated with electrochemically activated valves with no moving parts. These valves consist of screen-printed electrode pairs that are transversal to the flow. One of the electrodes is solvent-etched to produce a superhydrophobic surface that provides passive stopping and facilitates low-voltage (~1 V) actuation of the flow via electrowetting. The operation of such valves in the stop-go mode, with a response time between 2 and 45 sec depending on the type and concentration of salt, is demonstrated. Mechanistic investigations indicated that the response depends on at least three phenomena that contribute to electrocapillarity: the electrochemical double-layer capacitance, specific counterion adsorption, and possible electrohydrodynamic effects.
authors.affiliation: Bioengineering and Bioelectrochemistry Group, Department of Chemical Engineering, Universitat Rovira i Virgili, Avinguda Països Catalans, 26, 43007, Tarragona, Spain.
authors.forename: Alemayehu P
authors.initials: AP
authors.lastname: Washe
authors.forename: Pablo
authors.initials: P
authors.lastname: Lozano
authors.forename: Diego
authors.initials: D
authors.lastname: Bejarano
authors.forename: Ioanis
authors.initials: I
authors.lastname: Katakis
mesh_terms: D019719:Diagnostic Equipment; D055664:Electrochemical Techniques / Q000295:instrumentation; D004566:Electrodes; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation; D010316:Particle Size; D019095:Point-of-Care Systems; D013499:Surface Properties
keywords: electrochemistry; graphite; ion effects; microsystems; stop-go valve