Electrochemically actuated passive stop–go microvalves for flow control in microfluidic systems Alemayehu Paulos Washe, Pablo Lozano-Sánchez 1 , Diego Bejarano-Nosas, Bruno Teixeira-Dias, Ioanis Katakis ⇑ Bioengineering and Bioelectrochemistry Group, Department of Chemical Engineering, Universitat Rovira i Virgili, Avinguda Països Catalans 26, 43007 Tarragona, Spain article info Article history: Available online xxxx Keywords: Microfluidics Fluid control Passive microvalve Electrochemically actuated Superhydrophobic abstract 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 manipula- tion 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 micro- channel. The fabrication of the superhydrophobic surface (water contact angle (CA) 152°) was performed by selective and controlled solvent-etching of a naturally hydrophobic (CA = 105°) screen printed carbon surface. The process increased the roughness and porosity of the surface that caused the superhydropho- bic 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 electro- chemical reactions in aqueous solutions. When a low voltage (1 V) was applied at the carbon electrode against a silver electrode, the flow of such solutions (e.g. 0.01 M phosphate buffer saline solution) that was stopped at the PSV, resumed, crossing the 1 mm pitch of hydrophobic barrier of the PSV in 1 s 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 prom- ising for the development of low cost microfluidic devices for point-of-care diagnostics, food analysis, and environmental monitoring. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction For more than ten years the microfluidics community is antic- ipating an impressive market domination of lab-on-a-chip (LOC) devices in sectors such as point of care (POC) diagnostics, food and environmental analysis. Expectations of market volumes in ex- cess of several billion dollars have not materialized in part due to the high manufacturing costs of the disposables with many current production processes. One possible enabling development for LOC devices is to break down their overall performance in simpler ‘‘unit operations’’ and use simple fluid manipulation and sensing princi- ples lowering manufacturing costs and simplifying operation. The simplest such process consists of the movement of a fluid in a microchannel where simple operations take place (for example, dilution, and dissolution of solids, metering, and detection). The ability to precisely control flow in such a simplistic microchannel could prove crucial for many LOC applications, particularly in bio- analytical applications where an analytical response depends on the dissolution of previously deposited reagents, the kinetics of biological affinity and enzymatic reactions, and mass transport of products to a transducer [1]. A miniaturized microfluidic immuno- assay, for instance as reported in Ref. [2], involves an immuno- chemical previously deposited in the microchannel which, as the solution containing the analyte is introduced, undergoes–dissolu- tion, mixing, and reaction with the analyte yielding an immuno- complex that is detected at the detector located downstream. Therefore the success of detection depends critically on the extent of dissolution, mixing, and immunoaffinity binding, all of which re- quire enough residence time due to the laminar nature of micro- scale flow. To this end, two key on-chip fluidic operations are required: stopping the flow at the vicinity of the probe zone in the microchannel and a fast and reliable flow actuation mecha- nism. Such operations can be performed in the microchannels using microvalves. 0167-9317/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.mee.2013.04.022 ⇑ Corresponding author. Tel.: +34 977 55 96 55; fax: +34 977 55 96 21. E-mail address: ioanis.katakis@urv.cat (I. Katakis). 1 Present address: Integrated Microsystems for the Quality of Life S.L., C/del Ferro 6, Nave 7, 43006 Tarragona, Spain. Microelectronic Engineering xxx (2013) xxx–xxx Contents lists available at SciVerse ScienceDirect Microelectronic Engineering journal homepage: www.elsevier.com/locate/mee Please cite this article in press as: A.P. Washe et al., Microelectron. Eng. (2013), http://dx.doi.org/10.1016/j.mee.2013.04.022