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Procedia Engineering
ProcediaProcedia Engineering 00 (2011) 000–000 Engineering 25 (2011) 132 – 135 www.elsevier.com/locate/procedia
Proc. Eurosensors XXV, September 4-7, 2011, Athens, Greece
Flexible Microfluidic Devices for Both Generation and Absorption of Carbon Dioxide Gas and Liquid Perfusion Po Ki Yuen* and Michael E. DeRosa Science & Technology, Corning Incorporated, Corning, New York, 14831-0001, USA
Abstract We present a method of fabrication and applications of flexible microfluidic devices with three-dimensional (3D) interconnected microporous walls based on treatment using a solvent/non-solvent mixture at room temperature. The complete fabrication process from device design concept to working device can be completed in less than an hour in a regular laboratory setting without the need of expensive equipment. Microfluidic devices were used to demonstrate gas generation and absorption reactions by acidifying water with carbon dioxide (CO2) gas. By selectively treating the microporous structures with oxygen plasma, acidification of water by acetic acid (distilled white vinegar) perfusion was also demonstrated with the same device design.
© 2011 Published by Elsevier Ltd. Keywords: Flexible microfluidic device; Three-dimensional interconnnected microporous; polystyrene film; Carbon dioxide; Acidification of water
1. Introduction The demand has increased for methods of fabricating low-cost prototype microfluidic devices rapidly with compatible materials and novel functional attributes. One attractive feature that can be incorporated into microfluidic devices is a porous membrane or porous channel wall [1]. Devices with such features can potentially be used for multiphase catalytic reactions in chemical and pharmaceutical applications similar to the gas-liquid-solid hydrogenation reactions reported by Kobayahi et al. [2] or gas-liquid syntheses by Park and Kim [3].
* Corresponding author. Tel.: +1-607-974-9680; fax: +1-607-974-5957. E-mail address:
[email protected]
1877-7058 © 2011 Published by Elsevier Ltd. doi:10.1016/j.proeng.2011.12.033
Po 2500(2011) 132 – 135 PoKiKiYuen Yuenand andMichael MichaelE.E.DeRosa DeRosa/ Procedia / ProcediaEngineering Engineering (2011) 000–000
Several groups have demonstrated the potential of using microfluidic devices with porous channel walls for multiphase analytical and synthetic applications. For example, Hisamoto et al. demonstrated permeation of ammonia species through an inner-channel nylon membrane [4]. Vogelaar et al. [5] and de Jong et al. [6] reported a replication method based on phase separation micro molding (PSµM) of a polymer solution to produce thin polymeric microfluidic devices with tunable porosity. de Jong et al. demonstrated that they could acidify water by diffusing CO2 gas through the porous channel walls of a multi-layer porous microfluidic device [6]. However, they did not show the possibility of transporting liquid through the porous channel walls. We present a simple, low-cost fabrication method and applications of flexible microfluidic devices with 3D interconnected microporous channel walls. Unlike PSµM, a microstructured mold is not required and the complete process from design concept to working device can be completed quickly and inexpensively in a regular laboratory setting. Since masking techniques and oxygen plasma treatment can be used to create selected hydrophilic regions on the patterned microporous structures to control their wettability for transporting liquid through the microporous structures, the microfluidic devices that we fabricated were used for both CO2 gas generation and absorption reactions by acidifying water with CO2 gas, and acidification of water by acetic acid (distilled white vinegar) perfusion with the same device design.
Fig. 1 Device fabrication. (a) White vinyl self-adhesive sheet was cut and adhered to polystyrene film as protective mask. Backside of the film was also protected by transparent self-adhesive tapes. (b) After 20 s dipped into tetrahydrofuran (THF)/isopropanol (IPA) solvent mixture (40/60 v/v %) at room temperature and blown dry with nitrogen. (c) Removal of protective masks revealing 3D raised interconnected microporous structures. (d) Cut double-sided PSA tape. (e) Completely assembled microfluidic device with inlet and outlet holes. Assembly from (c), (d) and laser printer transparency film. (f) Flexibility demonstration of device.
2. Device fabrication and assembly A customized microfluidic device design mask was first cut out from a white vinyl self-adhesive sheet using a desktop digital craft cutter [7]. The cut vinyl sheet was then adhered to one side of a 3 mil thick polystyrene film as a protective mask (Fig. 1a). The backside of the polystyrene film was also protected by transparent self-adhesive tapes. Next, the masked polystyrene film was dipped into a tetrahydrofuran (THF)/isopropanol (IPA) solvent mixture (40/60 v/v %) for 10 s – 20 s at room temperature. The film was then removed from the solvent mixture bath and immediately blown dry with nitrogen gas for 2 – 3 minutes to ensure that the solvent mixture was evaporated (Fig. 1b). Then, the protective masks were removed from the patterned polystyrene film to reveal the 3D raised interconnected microporous structures on the unprotected polystyrene film surfaces (Fig. 1c and 2).
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Ki Yuen and Michael E. DeRosa / Procedia Engineering 25 (2011) 132 – 135 Po KiPo Yuen and Michael E. DeRosa / Procedia Engineering 00 (20111) 000–000
Fig. 2 Scanning electron microscopy (SEM) images of microporous structures. (a) 50 × magnification depicting the top view of the area within the red box of the insert image. (b) 1000 × magnification of the same area depicted in (a). (c) 50 × magnification depicting the area within the red box of the inserted image at a 45 o tilt angle. (d) 500 × magnification of the same area depicted in (c).
After polystyrene film patterning, the matching microfluidic device design was cut out from a doublesided pressure sensitive adhesive (PSA) tape using a desktop digital craft cutter (Fig. 1d). After inlet and outlet holes were punched through the patterned polystyrene film, the cut double-sided PSA tape with the top and bottom protective layers removed was manually aligned and sandwiched between the patterned polystyrene film and the laser printer transparency film (Fig. 1e and 1f). For applications that required liquid perfusion, we selectively oxygen plasma treated the patterned microporous structures to create selected hydrophilic regions to control their wettability for transporting liquid through the microporous structures before assembling the final devices (Fig. 3). Finally, leak free inlet and outlet connections were attached to the inlet and outlet holes as described previously [7].
Fig. 3 One half of the microporous structures was exposed to oxygen plasma at 30 W for 60 s while the other half was protected. The dotted line depicts the boundary between the two sides. (a) A transparent self-adhesive tape was adhered across the oxygen plasma treated and untreated sides and a droplet of red colored food dye was separately pipetted onto the two sides. (b) 90 days after oxygen plasma treatment, a droplet of distilled white vinegar was separately pipetted onto the treated and untreated sides.
3. Acidification of water by CO2 gas and by acetic acid perfusion Carbon dioxide gas was used in the first two sets of experiment to demonstrate gas permeability in the microfluidic devices. In the first set of the experiment, CO2 gas was generated inside a glass bubbler by dissolving dry ice in water. The generated CO2 gas was directed from the bubbler through Tygon® tubing into the inner circular chamber of the device without any other pumping means (Fig. 4a – 4c). In the second set of the experiment, we generated CO2 gas within the device by mixing a saturated aqueous solution of sodium bicarbonate with household distilled white vinegar (5 % acetic acid). When the two solutions mixed, they generated CO2 gas and became aqueous solution of sodium acetate (Fig. 4d – 4f). As water absorbed CO2 gas, it reacted with the CO2 gas to form carbonic acid. Thus, the pH indicator
Po 2500(2011) 132 – 135 PoKiKiYuen Yuenand andMichael MichaelE.E.DeRosa DeRosa/ Procedia / ProcediaEngineering Engineering (2011) 000–000
solution would turn from blue to green to yellow depending on the amount of CO2 was absorbed. In the final set of experiment, acidification of water by acetic acid perfusion experiment was performed inside the microfluidic device by introducing distilled white vinegar into the inner circular chamber of the device. The pH indicator solution inside the outer circular channel would turn from blue to yellow as vinegar perfused through the hydrophilic (oxygen plasma treated) microporous structures (Fig. 4g – 4i).
Fig. 4 Time lapse images. Bromothymol blue pH indicator solution became blue at pH > 7.6, green at pH ~ 6.5 – 7.0, and yellow at a pH < 6.0. (a) – (c) CO 2 gas absorption experiment. (d) – (f) CO 2 gas generation and absorption experiment. Saturated sodium bicarbonate solution and distilled white vinegar were introduced into microfluidic device via syringe pump at flow rate of 10 µl/min to generate CO2 gas. (g) – (i) Acetic acid (white distilled vinegar) perfusion experiment. Distilled white vinegar was introduced into microfluidic device via syringe pump at flow rate of 5 µl/min.
Acknowledgements We would like to thank Vasudha Ravichandran, Allison J. Tanner, Natalya M. Isachkina, Earl J. Sanford, Todd L. Heck, Sara J. Sick, Vasiliy N. Goral and Mircea S. Despa for their support on this work. References [1] de Jong J, Lammertink RGH and Wessling M, Membranes and microfluidics: a review, Lab on a Chip 2006, 6, 1125-1139. [2] Kobayashi J, Mori Y, Okamoto K, Akiyama R, Ueno M, Kitamori T and Kobayshi S, A microfluidic device for conducting gas-liquid-solid hydrogenation reactions, Science 2004, 304, 1305-1308. [3] Park CP and Kim D-P, Dual-channel microreactor for gas-liquid syntheses, Journal of the American Chemical Society 2010, 132, 10102-10106. [4] Hisamoto H, Shimizu Y, Uchiyama K, Tokeshi M, Kikutani Y, Hibara A and Kitamori T, Chemicofunctional membrane for integrated chemical processes on a microchip, Analytical Chemistry 2003, 75, 350-354. [5] Vogelaar L, Lammertink RGH, Barsema JN, Nijdam W, Bolhuis-Versteeg LAM, van Rijn CJMand Wessling M, Phase separation micromolding: a new generic approach for microstructuring various materials, Small 2005, 1, 645-655. [6] de Jong J, Ankoné B, Lammertink RGH and Wessling M, New replication technique for the fabrication of thin polymeric microfluidic devices with tunable porosity, Lab on a Chip 2005, 5, 1240-1247. [7] Yuen PK and Goral VN, Low-cost rapid prototyping of flexible microfluidic devices using a desktop digital craft cutter, Lab on a Chip 2010, 10, 384-387.
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