Anal. Chem. 2005, 77, 7993-7997
Microchip Capillary Electrophoresis with Solid-State Electrochemiluminescence Detector Yan Du, Hui Wei, Jianzhen Kang, Jilin Yan, Xue-bo Yin, Xiurong Yang,* and Erkang Wang*
State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Graduate School of the Chinese Academy of Sciences, Changchun, Jilin, 130022, P. R. China
We report microchip capillary electrophoresis (CE) coupling to a solid-state electrochemiluminescence (ECL) detector. The solid-state ECL detector was fabricated by immobilizing tris(2,2′-bipyridyl)ruthenium(II) (TBR) into an Eastman AQ55D-silica-carbon nanotube composite thin film on an indium tin oxide (ITO) electrode. After being made by a photolithographic method, the surface of the ITO electrode was coated with a thin composite film through a micromolding in capillary (MIMIC) technique using a poly(dimethylsiloxane) (PDMS) microchannel with the same pattern as an ITO electrode. Then the TBR was immobilized via ion exchange by immersing the ITO electrode containing the thin film in TBR aqueous solution. The whole system was built by reversibly sealing the TBR-modified ITO electrode plate with a PDMS layer containing electrophoresis microchannels. The results indicated that the present solid-state ECL detector displayed good durability and stability in the microchip CEECL system. Proline was selected to perform the microchip device with a limit of detection of 2 µM (S/N ) 3) and a linear range from 25 to 1000 µM. Compared with the CE-ECL of TBR in aqueous solution, while the CE microchip with solid-state ECL detector system gave the same sensitivity of analysis, a much lower TBR consumption and a high integration of the whole system were obtained. The present system was also used for medicine analysis. Capillary electrophoresis (CE) microchips have received considerable interest in analytical chemistry recently due to their promising features such as short analysis time, efficient separation capabilities, minute consumption of samples and reagents, and portability.1,2 Among the detection methods employed on CE microchips the commonly used detection mode is laser-induced fluorescence (LIF)3,4 due primarily to the lowest concentration detection limits and high sensitivity. However, a LIF detector is * Corresponding author. Tel: +86-431-5262003. Fax: +86-431-5689711. Email:
[email protected]. (1) Reyes, D. R.; Iossifidis, D.; Auroux, P. A.; Manz, A. Anal. Chem. 2002, 74, 2623-2636. (2) Auroux, P. A.; Iossifidis, D.; Reyes, D. R.; Manz, A. Anal. Chem. 2002, 74, 2637-2652. (3) Roulet, J. C.; Volkel, R.; Herzig, H. P.; Verpoorte, E.; de Rooij, N. F.; Dandliker, R. Anal. Chem. 2002, 74, 3400-3407. (4) Qin, J. H.; Fung, Y. S.; Zhu, D. R.; Lin, B. C. J. Chromatogr., A 2004, 1027, 223-229. 10.1021/ac051369f CCC: $30.25 Published on Web 11/09/2005
© 2005 American Chemical Society
expensive, difficult to implement, and often requires derivatization of the sample with a fluorophore. Another alternative detection mode is mass spectrometry (MS).5 Although MS can provide more chemical information, it is nonportable, more costly, and less sensitive than LIF.6 During the past several years, electrochemical detection has received increased attention and has been demonstrated as an attractive detection mode, which can offer comparable sensitivity and high flexibility. Since electrochemiluminescence (ECL) based on tris(2,2′bipyridyl)ruthenium(II) (TBR) was first reported by Tokel and Bard,7 TBR ECL as a sensitive detection method has received considerable attention in chemical analysis because of its excellent stability and high efficiency in aqueous phase.8 Moreover, as TBR is regenerated during the ECL process, a reagentless ECL sensor can be constructed by immobilizing the TBR on an electrode surface.9 Compared with the solution-phase ECL procedure, the immobilization of the TBR reduces the consumption of expensive reagent and simplifies experimental design. So far, several different methods have been used to immobilize the TBR on an solid surface, including the Langmuir-Blodgett technique,10,11 selfassembled technique,12-14 and electrostatic attachment.15-17 Although so many techniques to immobilize TBR have been developed, the application of a solid-state ECL sensor is very limited. Our group18 first fabricated a solid-state ECL sensor for traditional capillary electrophoresis by immobilizing TBR in poly(p-styrenesulfonate)-silica-poly(vinyl alcohol) grafting 4-vinylpyridine copolymer films. Lee’s group19 reported that the sol-gelimmobilized TBR ECL sensor was applied to the reversed-phase (5) Benetton, S.; Kameoka, J.; Tan, A. M.; Wachs, T.; Craighead, H.; Henion, J. D. Anal. Chem. 2003, 75, 6430-6436. (6) Vandaveer IV W. R.; Pasas-Farmer, S. A.; Fischer, D. J.; Frankenfeld, C. N.; Lunte, S. M. Electrophoresis 2004, 25, 3528-3549. (7) Tokel, N. E.; Bard, A. J. J. Am. Chem. Soc. 1972, 94, 2862-2863. (8) Richter, M. M. Chem. Rev. 2004, 104, 3003-3036. (9) Yin, X. B.; Dong, S.; Wang, E. Trends Anal. Chem. 2004, 23, 432-441. (10) Zhang, Z.; Bard, A. J. J. Phys. Chem. 1988, 92, 5566-5569. (11) Miller, C. J.; McCord, P.; Bard, A. J. Langmuir 1991, 7, 2781-2787. (12) Guo, Z.; Shen, Y.; Wang, M.; Zhao, F.; Dong, S. Anal. Chem. 2004, 76, 184-191. (13) Zhou, Y. L.; Li, Z.; Hu, N. F.; Zeng, Y. H.; Rusling, J. T. Langmuir 2002, 18, 8537-8579. (14) Salditt, T.; Schubert, U. S. Rev. Mol. Biotechnol. 2002, 90, 55-70. (15) Wang, H.; Xu, G.; Dong, S. Anal. Chim. Acta 2003, 480, 285-290. (16) Wang, H.; Xu, G.; Dong, S. Analyst 2001, 126, 1095-1099. (17) Khramov, A. N.; Collinson, M. M. Anal. Chem. 2000, 72, 2943-2948. (18) Cao, W.; Jia, J.; Yang, X.; Dong, S.; Wang, E. Electrophoresis 2002, 23, 36923698. (19) Choi, H.; Cho, S.; Park, Y.; Lee, D.; Lee, W. Anal. Chim. Acta 2005, 541, 49-56.
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high-performance liquid chromatography determination of phenothiazine derivatives. Recently, Chen’s group20 developed TBRzirconia-Nafion composite films as solid-state ECL detector for CE. Ju’s group21 detected heroin by flow injection ECL with immobilized TBR in a zeolite Y-modified carbon paste electrode. To our knowledge, the immobilizing TBR used as a solid-state ECL sensor has never been applied to a CE microchip mainly because most of the electrodes presently used to attach TBR are not transparent, such as platinum,18 graphite electrode,20 and glassy carbon electrode,15,16,22 which makes the operation process complex and time-consuming. Moreover, once the microchip CE is combined with solid-state ECL detection, the whole system is further integrated together and simplified. In this work, we proposed a novel microchip CE using solidstate ECL detection based on immobilizing TBR into the Eastman AQ55D-silica-carbon nanotube composite thin film on an indium tin oxide (ITO) electrode. While the ITO electrode allowed electrochemical current, its transparency did not affect the emission detection. The thin composite film was just coated on the ITO electrode with the help of a poly(dimethylsiloxame) (PDMS) microchannel stamp. The incorporation of TBR took place only at the area of the thin film, and thus, the TBR-modified ITO microelectrode of the pattern was formed. The PDMS layer containing separation and injection channel was reversely sealed with the ITO-coated glass slide to form the whole system. Proline was selected as test analyte to validate this solid-state CE-ECL microchip system in the experiments. And the present system was also used to detect ofloxacin and 4-(dimethylamino)butyric acid (DMBA). EXPERIMENTAL SECTION Chemicals and Materials. Tris(2,2′-bipyridyl)ruthenium(II) chloride hexahydrate was purchased from Aldrich (Milwaukee, WI). Sylgard 184 silicone elastomer and curing agent were obtained from Dow Corning (Midland, MI). RZJ-390 photoresist (for TN/ STN ITO) was purchased from Suzhou Ruihong Electronic Chemicals Co., Ltd. (Suzhou, China). Proline was obtained from Shanghai Biochemical Co., Ltd. Ofloxacin and DMBA were purchased from Sigma-Aldrich (St. Louis, MO). Other reagents and chemicals were at least analytical reagent grade. ITO-coated (150 nm thick and resistance of
