Sensors and Actuators B 177 (2013) 668–675 Contents lists available at SciVerse ScienceDirect Sensors and Actuators B: Chemical journa l h o me pa ge: www.elsevier.com/locate/snb Design rules and operational optimization for rapid, contamination-free microfluidic transfer using monolithic membrane valves Amanda M. Stockton, Maria F. Mora, Morgan L. Cable, Peter A. Willis ∗ Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA a r t i c l e i n f o Article history: Received 8 June 2012 Received in revised form 9 November 2012 Accepted 14 November 2012 Available online 28 November 2012 Keywords: Normally-closed monolithic membrane microvalves Peristaltic micropump Rapid microfluidic transfer Spaceflight applications a b s t r a c t Networks of monolithic membrane microvalves integrated into microdevices enable complete automa- tion of liquid-based chemical analyses necessary for fully automated applications, such as spaceflight. Although individual pumping devices and operational routines have been characterized, to date there has been no rigorous evaluation of microvalve layout and its effect on fluidic transfer. Here, we eval- uate two microdevices at opposite extremes of fluidic resistance and evaluate three pumping routines on each device. Delay times between operational steps are optimized for fastest fluidic transfer. A 3- valve double-chamber routine enables fastest pumping rates on both devices. On low fluidic resistance devices, a 2-valve (bivalve) pumping routine enables faster fluidic transfer than a 3-valve single-chamber pumping routine. Additionally, low fluidic resistance devices enable significantly faster fluidic transfer (4–6 fold) than their higher resistance counterparts. Back-contamination is qualitatively characterized for the optimized routines; higher fluidic resistance between the pumping architecture and the fluidic output reservoir is the most essential feature for preventing back-contamination. We use these results to suggest design rules to guide future pumping architectures to enable the rapid, contamination-free fluidic transfer that will be necessary in spaceflight applications. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Ultra portable, fully automated, highly sensitive instrumenta- tion is essential in the search for organic chemical signatures of extraterrestrial life. Microchip capillary electrophoresis (CE) cou- pled to laser-induced fluorescence (LIF) detection is extremely attractive in this regard, and offers low mass, power, volume and reagent consumption [1,2]. This technique provides a liquid-based analysis of a broad range of compound classes with ultra-low lim- its of detection, including amines and amino acids (∼70 pM) [3], aldehydes and ketones (∼70 pM) [4], carboxylic acids (∼6 nM) [5], polycyclic aromatic hydrocarbons (∼1 nM) [6], and thiols (∼1 nM) [7]. Because we cannot expect life that has evolved under dif- ferent redox and thermodynamic conditions to choose the same set of organic molecules for its biochemistry as terrestrial life, this broad coverage is essential when looking for signs of life on other planets. Additionally, because of the anticipated low levels of these molecules on astrobiologically relevant targets (e.g. Mars, Europa, Enceladus) whether life ever evolved there or not, the ultra- low limits of detection provided by this method may be crucial ∗ Corresponding author at: Mail Stop 302-231, 4800 Oak Grove Dr., Pasadena, CA 91109, USA. Tel.: +1 818 354 1297; fax: +1 818 393 4773. E-mail address: peter.a.willis@jpl.nasa.gov (P.A. Willis). in achieving meaningful results. Additionally, CE is well-suited for integration with other microfabricated components including heaters [8,9], resistive temperature detectors [8,9], pH sensitive electrodes [10], membrane microvalves [11–13], etc., on a sin- gle device. The integration of networks of monolithic membrane microvalves, in particular, has enabled the automation required for spaceflight-ready liquid-based organic chemical analyses [1,14]. In order to minimize the time required for these analyses, pre- vent on-chip cross-contamination during operation, and inform us of the next generation of spaceflight-compatible microfluidic sample handling systems, we undertook the study we report here. Monolithic membrane microvalves are constructed of two etched glass layers with a polymeric membrane layer sandwiched between their etched faces (Fig. 1A) [1,11–14]. A fluidic layer contains a discontinuous channel opposite a displacement cham- ber etched in a pneumatic layer. When vacuum is applied to the pneumatic displacement chamber, the membrane deflects and enables fluidic flow across the discontinuity (Fig. 1B). A closing pressure is utilized in the pneumatic layer to seal the microvalve against fluidic pressures. Multiple valves in series (Fig. 1C) actu- ated sequentially form a peristaltic pump that drives fluidic flow (Fig. 2) [2,12–14]. Microfluidic networks of these valves have been used to autonomously dispense and retrieve liquid samples [1], route multiple fluids to individually addressable CE channels [2], 0925-4005/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.snb.2012.11.039