Anal. Chem. 2007, 79, 371-377
Measurements of Surface Tension of Organic Solvents Using a Simple Microfabricated Chip Jiangjiang Liu, Haifang Li, and Jin-Ming Lin*
The Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology, Department of Chemistry, Tsinghua University, Beijing, 100084, China
Measurement of the surface tension of organic solvents using a simple microfabricated chip was developed based on the principle of differential capillary rise. The theory, design, fabrication, and characterization of the chip were described. A two-step etching technique was used to fabricate a number of microchannels with different dimensions on the glass substrate. Capillarity was used to introduce liquid samples, which requires no power supply or actuator to be applied in the experiment. Liquid in different microchannels generated capillary rise with different heights, by which surface tension maybe calculated. Seven common organic solvents, ethanol, acetone, acetonitrile, dichloromethane, hexane, methanol, and toluene, were tested at room temperature. The surface tension of ethanol at different temperatures was measured over the range of 5-45 °C. Relative standard deviation for seven replicate measurements at each temperature is 0.20-0.74%. The results showed good reproducibility and acceptable precision compared with traditional methods. Very low reagent consumptions and short analysis time were achieved using this simple method. Over the past few years, the area of micro total analysis systems (µTAS) has been growing rapidly and a large number of applications have been developed based on that concept.1-4 µTAS shows a capability for high-throughput screening, short analysis time, and low reagent consumption in both analytical chemistry and biological research,5 such as electrophoresis,6,7 DNA analysis,8,9 cell analysis,10-12 immunoassay,13-16 and many other biologi* To whom correspondence should be addressed. E-mail: jmlin@ mail.tsinghua.edu.cn. Tel: (86)10-62792343. Fax: (86)10-62841953. (1) Reyes, D. R.; Iossifidis, D.; Auroux, P.; Manz, A. Anal. Chem. 2002, 74, 2623-2636. (2) Auroux, P.; Iossifidis, D.; Reyes, D. R.; Manz, A. Anal. Chem. 2002, 74, 2637-2652. (3) Vilkner, T.; Janasek, D.; Manz, A. Anal. Chem. 2004, 76, 3373-3386. (4) Dittrich, P. S.; Tachikawa, K.; Manz, A. Anal. Chem. 2006, 78, 38873908. (5) Delamarche, E.; Juncker, D.; Schmid, H. Adv. Mater. 2005, 17, 29112933. (6) Aborn, J. H.; El-Difrawy, S. A.; Novotny, M.; Gismondi, E. A.; Lam, R.; Matsudaira, P.; Mckenna, B. K.; O’Neil, T.; Streechon, P.; Ehrlich, D. J. Lab Chip 2005, 5, 669-674. (7) Tabuchi, M.; Kuramitsu, Y.; Nakamura, K.; Baba, Y. Anal. Chem. 2003, 75, 3799-3805. (8) Legendre, L. A.; Bienvenue, J. M.; Roper, M. G.; Ferrance, J. P.; Landers, J. P. Anal. Chem. 2006, 78, 1444-1451. (9) Huang, L. R.; Tegenfeldt, J. O.; Kraeft, J. J.; Sturm, J. C.; Austin, R. H.; Cox, E. C. Nat. Biotechnol. 2002, 20, 1048-1051. 10.1021/ac061401l CCC: $37.00 Published on Web 11/18/2006
© 2007 American Chemical Society
cal applications.17-20 At the micrometer to millimeter scale, surface tension plays a critical role in µTAS, due to the very high surfaceto-volume ratio in microfabricated devices. The phenomenon can be easily observed that liquid may be driven and controlled in microchannels by capillarity rather than gravity or inertia. Such a principle is widely used in µTAS for microvalve,21,22 liquid transport,23,24 sample introduction,25-28 surface modification,29 and interface formation.30,31 Surface tension is an essential thermodynamic property of organic solvents, surfactant solutions, and many other liquids from both scientific and industrial perspectives. In scientific research, it is a useful tool to investigate the kinetics and mechanisms of the adsorption of molecules in aqueous solutions by monitoring the dynamic surface tension.32,33 Meanwhile, the measurement of surface tension is fundamental to the study of interfacial phenomena during agricultural and industrial processes. For example, (10) Lee, P. J.; Hung, P. J.; Shaw, R.; Jan, L.; Lee, L. P. Appl. Phys. Lett. 2005, 86, 223902. (11) Mao, H.; Cremer, P. S.; Manson, M. D. Proc. Natl. Acad. Sci. U.S.A. 2003, 100, 5449-5454. (12) Carlo, D. D.; Ionescu-Zanetti, C.; Zhang, Y.; Hung, P.; Lee, L. P. Lab Chip 2005, 5, 171-178. (13) Delamarche, E.; Bernard, A.; Schmid, H.; Michel, B.; Biebuyck, H. Science 1997, 276, 779-781. (14) Hosokawa, K.; Omata, M.; Sato, K.; Maeda, M. Lab Chip 2006, 6, 236241. (15) Sia, S. K.; Linder, V.; Parviz, B. A.; Siegel, A.; Whitesides, G. M. Angew. Chem., Int. Ed. 2004, 43, 498-502. (16) Cesaro-Tadic, S.; Dernick, G.; Juncker, D.; Buurman, G.; Kropshofer, H.; Michel, B.; Fattinger, C.; Delamarche, E. Lab Chip 2004, 4, 563-569. (17) Cai, L.; Friedman, N.; Xie, X. S. Nature 2006, 440, 358-362. (18) Lipman, E. A.; Schuler, B.; Bakajin, O.; Eaton, W. A. Science 2003, 301, 1233-1235. (19) DeMello, A. J. Nature 2003, 422, 28-29. (20) Rondelez, Y.; Tresset, G.; Tabata, K. V.; Arata, H.; Fujita, H.; Takeuchi, S.; Noji, H. Nat. Biotechnol. 2005, 23, 361-365. (21) Melin, J.; Roxhed, N.; Gimenez, G.; Griss, P.; van der Wijngaart, W.; Stemme, G. Proceedings of Transducers 03, 12th, 2003; pp 1562-1555. (22) Leu, T.; Chang, P. Sens. Actuators, A 2004, 115, 508-515. (23) Chung, K. H.; Lee, D. S.; Yang, H.; Kim, S. J.; Pyo, H. B. Proc. SPIE Int. Soc. Opt. Eng. 2005, 204-213. (24) Juncker, D.; Schmid, H.; Drechsler, U.; Wolf, H.; Wolf, M.; Michel, B.; de Rooij, N.; Delamarche, E. Anal. Chem. 2002, 74, 6139-6144. (25) Ito, T.; Inoue, A.; Sato, K.; Hosokawa, K.; Maeda, M. Anal. Chem. 2005, 77, 4759-4764. (26) Yamada, M.; Seki, M. Anal. Chem. 2004, 76, 895-899. (27) Handique, K.; Burke, D. T.; Mastrangelo, C. H.; Burns, M. A. Anal. Chem. 2000, 72, 4100-4109. (28) Hosokawa, K.; Fujii, T.; Endo, I. Anal. Chem. 1999, 71, 4781-4785. (29) Hibara, A.; Iwayama, S.; Matsuoka, S.; Ueno, M.; Kikutani, Y.; Tokeshi, M.; Kitamori, T. Anal. Chem. 2005, 77, 943-947. (30) Atencia1, J.; Beebe, D. J. Nature 2005, 437, 648-655. (31) Zhao, B.; Moore, J. S.; Beebe, D. J. Science 2001, 291, 1023-1026.
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Figure 1. Schematic illustration of the procedure for chip fabrication. (a) Pattern printed on mask is transferred to a glass plate coated with chromium and photoresist under the UV light source; 5-min exposure. (b) After exposure, the photoresist layer and chromium layer confined in the exposed area were removed using 0.5% NaOH solution and chromium etchant. (c) Application of 10% HF solution to etch the glass chip for 30 min to fabricate eight uniform microchannels; microchannel depth controlled by etching time. (d) Three deeper microchannels were obtained by further etching for 40 min. During further etching, the other five microchannels were covered by adhesive tape to prevent etching. Two microchannels with different dimensions were fabricated during this simple procedure. (e) Assemblage of the polyester transparent film, glass slide and etched glass plate using clamps to form closed microchannels.
aqueous agricultural pesticide sprays with low surface tension can spread more easily on leaves for a better insecticidal effect.34 In textile, paper, metal, water treatment, and petroleum industries, surface tension influences the wetting, foaming, and solubility of liquids and should be monitored for quality control of products.33 A number of methods to measure surface tension have been developed over the last hundred years. of both static and dynamic types, including Du Nou¨y ring, Wilhelmy plate, pendent drop, spinning drop, sessile drop, growing drop, maximum bubble pressure, capillary rise, and drop volume method.32 These methods have been widely applied in many different areas. However, they also have some disadvantages, e.g.: (i) pendent drop, spinning drop, and sessile drop methods require expensive optical devices and image systems; (ii) Du Nou¨y ring, Wilhelmy plate, and maximum bubble pressure methods require equipment incorporating accurate measurement of pressure and force; (iii) maximum bubble pressure and capillary rise methods often suffer from the influence of temperature; and (iv) the drop volume method requires long analysis time (several minutes per trial). Hudson and co-workers35,36 developed a microfluidic instrument to rapidly measure the interfacial tension of multicomponent immiscible liquids. Such a microfluidic instrument provides fast real-time measurements with very small sample volumes (∼10 µL). However, this approach still required optical microscope, syringe pumps, and computer for data acquisitions and analysis, (32) Eastoe, J.; Dalton, J. S. Adv. Colloid Interface Sci. 2000, 85, 103-144. (33) Chang, C.; Franses, E. I. Colloids Surf. A 1995, 100, l-45. (34) Knoche, M.; Tamura, H.; Bukovac, M. J. J. Agric. Food Chem. l991, 39, 202-206. (35) Hudson, S. D.; Cabral, J. T.; Goodrum, Jr., W. J.; Beers, K. L.; Amis, E. J. Appl. Phys. Lett. 2005, 87, 081905. (36) Cabral, J. T.; Hudson, S. D. Lab Chip 2006, 6, 427-436.
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leading to a large volume of apparatus discarding the benefit of µTAS. In the present work, the differential capillary rise method was applied and performed on a microfabricated chip. A simple and reliable method is illustrated to measure surface tension of organic solvents on the microfabricated chip, with a simple fabrication process and easy measurement procedure. The design, fabrication, and characterization of this microfabricated chip are discussed. Very low reagent consumption (∼15 µL) and short analysis time (
