Anal. Chem. 2004, 76, 6792-6796
Technical Notes
Cationic Starch Derivatives as Dynamic Coating Additives for Analysis of Amino Acids and Peptides Using Poly(methyl methacrylate) Microfluidic Devices Masaru Kato,†,‡ Yukari Gyoten,† Kumiko Sakai-Kato,† Tohru Nakajima,§ and Toshimasa Toyo’oka*,†
Department of Analytical Chemistry, School of Pharmaceutical Sciences and COE Program in the 21st Century, University of Shizuoka, 52-1 Yada Shizuoka, Shizuoka, 422-8526, Japan, PRESTO, Japan Science and Technology Agency (JST), Saitama, Japan, and Nippon Starch Chemical Company, Ltd., 3-29, Mitsuyakita 3-chome, Yodogawa-ku, Osaka, 532-0032, Japan
Plastic microchips are very promising analytical devices because they are less fragile and are suitable for mass production. However, due to their hydrophobicity, the surface strongly interacts with nonpolar analytes or species containing hydrophobic domains, resulting in significant uncontrolled adsorption on channel walls. This paper describes the poly(methyl methacrylate) surface treatment by dynamic coating additives that considerably decreases adsorption of analytes to channel walls. Among the additives studied, quaternary ammonium starch derivatives suppressed the adsorption of fluorescently labeled amino acids and peptides most effectively. The effect was valid over the wide pH range from 2.5 to 8.0. Using a 10 mM phosphate buffer (pH 7.0) with 3% (w/v) quaternary ammonium starch as the running buffer, Asp and Glu, respectively, migrated at 54.6 and 57.6 s with efficiencies of 380 000 and 370 000 plates/m. In addition, this cationic starch derivative was found to possess good solubility and low viscosity. In the past decade, there have been an explosion of interest in the fields of microfluidic systems.1-15 Microfabricated fluidic * To whom correspondence should be addressed. E-mail: toyooka@ ys2.u-shizuoka-ken.ac.jp. Fax: +81-54-264-5593. Tel: +81-54-264-5656. † University of Shizuoka. ‡ PRESTO. § Nippon Starch Chemical Co., Ltd. (1) Harrison, D. J.; Manz, A.; Fan, Z.; Lu ¨ di, H.; Widmer, H. M. Anal. Chem. 1992, 64, 1926-1932. (2) Harrison, D. J.; Fluki, F.; Seiler, K.; Fan, Z.; Effenhauser, C. S.; Manz, A. Science 1993, 261, 895-897. (3) Verpoorte, E. Electrophoresis 2002, 23, 677-712. (4) Salimi-Momosavi, H.; Tang, T.; Harrison, D. J. J. Am. Chem. Soc. 1997, 119, 8716-8717. (5) Kopp, M. U.; de Mello, A. J.; Manz, A. Science 1998, 280, 1046-1048. (6) Schilling, E. A.; Kamholz, E.; Yager, P. Anal. Chem. 2002, 74, 1798-1804. (7) Olsen, K. G.; Ross, D. J.; Tarlov, M. J. Anal. Chem. 2002, 74, 1436-1441. (8) Hadd, A. G.; Jacobson, S. C.; Ramsey, J. M. Anal. Chem. 1999, 71, 52065212. (9) Wang, C.; Oleschuk, R.; Ouchen, F.; Li, J.; Thibault, P.; Harrison, D. J. Rapid Commun. Mass Spectrom. 2000, 14, 1377-1383.
6792 Analytical Chemistry, Vol. 76, No. 22, November 15, 2004
devices are potentially powerful tools for chemical or biological assays. These devices offer rapid analysis and reduced sample consumption and cost.4-7 Two types of substrates have been typically used for the fabrication of microfabricated devices. The first one is glass.1,2 In most devices, the pumping, valving, and mixing of fluids are achieved via electroosmotic flow (EOF). Therefore, the excellent properties of EOF generation in glass are very suitable for the separation channel. More recently, several plastic substrates have been used.16-23 Among those, poly(dimethylsiloxane)18,19 as a soft plastic and poly(methyl methacrylate) (PMMA)20-23 as a hard plastic are most popular. Because microfluidic devices using these substrates are less fragile and more suitable for mass production, they are more cost effective. Despite these advantages, plastic microfluidic device exhibited poor separation efficiencies that must be overcome before plastic can be considered as the material of (10) Tanaka, Y.; Slyadnev, M. N.; Hibara, A.; Tokeshi, M.; Kitamori, T. J. Chromatogr., A 2000, 894, 45-51. (11) Chiem, N. H.; Harrison, D. J. Clin. Chem. 1998, 44, 591-598. (12) Sato, K.; Tokeshi, M.; Odake, T.; Kimura, H.; Ooi, T.; Nakao, M.; Kitamori, T. Anal. Chem. 2000, 72, 1144-1147. (13) Murakami, Y.; Takeuchi, T.; Yokoyama, K.; Tamiya, E.; Karube, I.; Suda, M. Anal. Chem. 1993, 65, 2731-2735. (14) Reyes, D. R.; Iossifidis, D.; Auroux, P.-A.; Manz, A. Anal. Chem. 2002, 74, 2623-2636. (15) Auroux, P.-A.; Iossifidis, D.; Reyes, D. R.; Manz, A. Anal. Chem. 2002, 74, 2637-2652. (16) Soper, S. A.; Ford, S. M.; Qi, Shize, McCarley, R. L.; Kelly, Kevin, Murphy, M. C. Anal. Chem. 2000, 643A-651A. (17) Boone, T. D.; Hugh Fan, Z.; Hooper, H. H.; Ricco, A. J.; Tan, H.; Williams, S. J. Anal. Chem. 2002, 78A-86A. (18) Effenhauser, C. S.; Bruin, G. J. M.; Paulus, A. Anal. Chem. 1997, 69, 34513457. (19) Duffy, D. C.; McDonald, J. C.; Schueller, O. J. A.; Whitesides, G. M. Anal. Chem. 1998, 70, 4974-4984. (20) Ford, S. M.; Kar, B.; McWhorter, S.; Davies, J.; Soper, S. A.; Klopf, M.; Calderon, G.; Saile, V. J. Microcolumn Sep. 1998, 10, 413-422. (21) Henry, A. C.; Tutt, T. J.; Galloway, M.; Davidson, Y. Y.; McWhorter, C. S.; Soper, S. A.; McCarley, R. L. Anal. Chem. 2000, 72, 5331-5337. (22) McCormick, R. M.; Nelson, R. J.; Alonso-Amigo, M. G.; Benvegnu, D. J.; Hooper, H. H. Anal. Chem. 1997, 69, 2626-2630. (23) Sassi, A. P.; Paulus, A.; Cruzado, I. D.; Bjornson, T.; Hooper, H. H.J. Chromatogr., A 2000, 894, 203-217. 10.1021/ac049545s CCC: $27.50
© 2004 American Chemical Society Published on Web 10/15/2004
choice for microsystems employing electrophoresis. The major source of the peak broadening is believed to be the adsorption of hydrophobic analytes to the polymer surface. A commonly reported solution to this unfavorable separation performance is covalent24 or dynamic coating25-31 modification of the polymer surface. Most of the dynamic coating additives, including SDS,29 CTAB,30 and methyl cellulose (MC),31 have originally been used for the analysis of proteins or DNA in capillary electrophoresis. The goal of this work is to find new dynamic coating additives for suppressing the adsorption of analytes on the plastic microchips. In this report, we developed a simple separation procedure of fluorescently labeled amino acids and peptides using the PMMA microchip by adding cationic starch derivatives in the buffer solution. EXPERIMENTAL SECTION Materials and Chemicals. 4-Fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) was purchased from Tokyo Kasei (Tokyo, Japan). Amino acids, MC 400 (MW 41 000), MC 4000 (MW 88 000), AspSer-Asp-Pro-Arg, and Gly-Gly-Gly-Gly-Gly were purchased from Sigma-Aldrich (Milwaukee, WI). Diethylamine was purchased from Wako Pure Chemicals (Osaka, Japan). All starch derivatives, which were commercially available, were supplied by Nippon Starch Chemical Co., Ltd. (Osaka, Japan): 2-(diethylamino)ethyl ether (1L) f starch, 2-(diethylamino)ethyl ether (1L), 2-(diethylamino)ethyl, 2-hydroxypropyl ether (1H) f starch, 2-(diethylamino)ethyl, 2-hydroxypropyl ether (1H) 2-hydroxy-3-(trimethylammonio)propyl ether, chloride (2L) f starch, 2-hydroxy-3-(trimethylammonio)propyl ether, chloride (2L) 2-hydroxy-3-(trimethylammonio)propyl ether, chloride, 2-hydroxypropyl ether (2H) f starch, 2-hydroxy-3-(trimethylammonio)propyl ether, chloride, 2-hydroxypropyl ether (2H). The tertiary ammonium 1L and 1H or quaternary ammonium 2L and 2H were different with each other in the modification ratio by the ammonium groups. The nitrogen contents of starches 1L, 1H, 2L, and 2H determined by elemental analysis were 0.33, 0.45, 0.23, and 0.6%, respectively. Water was purified by Milli-Q apparatus (Millipore, Bedford, MA). Apparatus. The PMMA chip, i-chip 3 DNA (Hitachi, Tokyo, Japan), was used.29-34 The diagram of the chip is shown in Supporting Information. This microchip has dimensions of 85 mm × 50 mm with three simple cross channels of 100 µm in (24) Slentz, B. E.; Penner, N. A.; Lugowska, E.; Regnier, F. Electrophoresis 2001, 22, 3736-3743. (25) Hu, S. W.; Ren, X. Q.; Bachman, M.; Sims, C. E.; Li, G. P.; Allbritton, N. Anal. Chem, 2002, 74, 4117-4123. (26) Liu, Y.; Fanguy, J. C.; Bledsoe, J. M.; Henry, C. S. Anal. Chem. 2000, 72, 5939-5944. (27) Barker, S. L. R.; Ross, D.; Tarlov, M. J.; Gaitan, M.; Locascio, L. E. Anal. Chem. 2000, 72, 5925-5929. (28) Barker, S. L. R.; Tarlov, M. J.; Canavan, H.; Hickman, J. J.; Locascio, L. E. Anal. Chem. 2000, 72, 4899-4903. (29) Kato, M.; Gyoten, Y.; Sakai-Kato, K.; Toyo’oka, T. J. Chromatogr., A 2003, 1013, 183-189. (30) Wang, S. C.; Perso, C. E.; Morris, M. D. Anal. Chem. 2000, 72, 17041706. (31) Dang, F.; Zhang, L.; Jabasini, M.; Kaji, N.; Baba, Y. Anal. Chem. 2003, 75, 2433-2439. (32) Tabuchi, M.; Kuramitsu, Y.; Nakamura, K.; Baba, Y. Anal. Chem. 2003, 75, 3799-3805. (33) Sakai-Kato, K.; Kato, M.; Toyo’oka, T. Anal. Chem. 2003, 75, 388-393. (34) Dang, F.; Zhang, L.; Hagiwara, Y.; Mishina, Y.; Baba, Y. Electrophoresis 2003, 24, 714-721.
width and 30 µm in depth. The distance between the sample reservoir (SR) and the sample waste (SW) was 10 mm, whereas the distance from the buffer reservoir (BR) to the buffer waste (BW) was 44 mm. All experiments were performed using a Hitachi SV1100 microchip electrophoresis instrument (Tokyo, Japan).34 The instrument used a blue light-emitting diode (LED) (maximum wavelength 473 nm) as the excitation source. The LED light beam passed through a filter (transmission
