Anal. Chem. 2010, 82, 2372–2379
Multichannel Capillary Electrophoresis Microdevice and Instrumentation for in Situ Planetary Analysis of Organic Molecules and Biomarkers Merwan Benhabib,† Thomas N. Chiesl, Amanda M. Stockton, James R. Scherer, and Richard A. Mathies* Department of Chemistry, University of California at Berkeley, Berkeley, California 94720 The Multichannel Mars Organic Analyzer (McMOA), a portable instrument for the sensitive microchip capillary electrophoresis (CE) analysis of organic compounds such as amino acid biomarkers and polycyclic aromatic hydrocarbons (PAHs), is developed. The instrument uses a four-layer microchip, containing eight CE analysis systems integrated with a microfluidic network for autonomous fluidic processing. The McMOA has improved optical components that integrate 405 nm laser excitation with a linear-scanning optical system capable of multichannel real-time fluorescence spectroscopic analysis. The instrumental limit of detection is 6 pM (glycine). Microfluidic programs are executed to perform the automated sequential analysis of an amine-containing sample in each channel as well as eight consecutive analyses of alternating samples on the same channel, demonstrating less than 1% cross-contamination. The McMOA is used to identify the unique fluorescence spectra of nine components in a PAH standard and then applied to the analysis of a sediment sample from Lake Erie. The presence of benzo[a]pyrene and perylene in this sample is confirmed, and a peak coeluting with anthanthrene is disqualified based on spectral analysis. The McMOA exploits lab-on-a-chip technologies to fully integrate complex autonomous operations demonstrating the facile engineering of microchipCE platforms for the analysis of a wide variety of organic compounds in planetary exploration. A key goal of planetary exploration is to search for signs of past or present extraterrestrial life.1-3 Several indicators point to an environment on Mars that might have supported life, including the presence of jarosite, a sulfate-rich mineral associated with * To whom correspondence should be addressed. E-mail: ramathies@ berkeley.edu. Phone: 510-642-4192. Fax: 510-642-3599. † Department of Mechanical Engineering, University of California at Berkeley. (1) Bada, J. L.; Sephton, M. A.; Ehrenfreund, P.; Mathies, R. A.; Skelley, A. M.; Grunthaner, F. J.; Zent, A. P.; Quinn, R. C.; Josset, J. L.; Robert, F.; Botta, O.; Glavin, D. P. Astron. Geophys. 2005, 46, 26–27. (2) Dick, S. J. Endeavour 2006, 30, 71–75. (3) McKay, C. P.; Grunthaner, F. J.; Lane, A. L.; Herring, M.; Bartman, R. K.; Ksendzov, A.; Manning, C. M.; Lamb, J. L.; Williams, R. M.; Ricco, A. J.; Butler, M. A.; Murray, B. C.; Quinn, R. C.; Zent, A. P.; Klein, H. P.; Levin, G. V. Planet. Space Sci. 1998, 46, 769–777.
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liquid water,4 images of outcroppings attributed to aqueous seeps,5-7 recent measurements of water ice at the Martian north pole by Phoenix,8,9 and measurements by Phoenix-MECA showing a high concentration of evaporative salts indicative of ancient oceans.8 Additionally, regions of the Martian atmosphere exhibit a seasonal source of methane which may or may not be biological in origin.10 However, in situ detection of organic material has yet to be accomplished on Mars. Since the level of organics on Mars is unknown, only the most sensitive instrumentation will enable a meaningful result.11 Of the possible organic biomarkers, amino acids are expected to have a relatively long lifetime under the conditions found on the surface of Mars and are hence excellent targets for detecting the presence of extant or extinct life.11,12 A sample containing a restricted subset of 10-20 homochiral amino acids (L or D) would indicate the presence of active life while a larger subset of ∼50-100 racemic amino acids would indicate abiotic sample origins.13 Additionally, samples with significant enantiomeric excess would indicate extinct life.14 Studies of Martian meteorites have revealed the presence of amino acids at parts per billion (ppb) concentrations; however, potential terrestrial contamination has made it difficult to draw definitive conclusions about the origin of these amino acids.15,16 This important caveat at least in part is resolved by in situ chemical analysis. (4) Levy, J. S.; Head, J. W.; Marchant, D. R. Geophys. Res. Lett. 2009, 36. (5) Clifford, S. M. J. Geophys. Res., [Planets] 1993, 98, 10973–11016. (6) Perron, J. T.; Mitrovica, J. X.; Manga, M.; Matsuyama, I.; Richards, M. A. Nature 2007, 447, 840–843. (7) Squyres, S. W.; Grotzinger, J. P.; Arvidson, R. E.; Bell, J. F.; Calvin, W.; Christensen, P. R.; Clark, B. C.; Crisp, J. A.; Farrand, W. H.; Herkenhoff, K. E.; Johnson, J. R.; Klingelhofer, G.; Knoll, A. H.; McLennan, S. M.; McSween, H. Y.; Morris, R. V.; Rice, J. W.; Rieder, R.; Soderblom, L. A. Science 2004, 306, 1709–1714. (8) Malin, M. C.; Edgett, K. S. Science 2003, 302, 1931–1934. (9) Renno, N. O.; Bos, B. J.; Catling, D.; Clark, B. C.; Drube, L.; Fisher, D.; Goetz, W.; Hviid, S. F.; Keller, H. U.; Kok, J. F.; Kounaves, S. P.; Leer, K.; Lemmon, M.; Madsen, M. B.; Markiewicz, W. J.; Marshall, J.; McKay, C.; Mehta, M.; Smith, M.; Zorzano, M. P.; Smith, P. H.; Stoker, C.; Young, S. M. M. J. Geophys. Res., [Planets] 2009, 114. (10) Geminale, A.; Formisano, V.; Giuranna, M. Planet. Space Sci. 2008, 56, 1194–1203. (11) ten Kate, I. L.; Garry, J. R. C.; Peeters, Z.; Foing, B.; Ehrenfreund, P. Planet. Space Sci. 2006, 54, 296–302. (12) Bada, J. L.; McDonald, G. D. Icarus 1995, 114, 139–143. (13) Bada, J. L. Science 1997, 275, 942–943. (14) Lu, Y.; Freeland, S. Genome Biol. 2006, 7. (15) Bada, J. L.; Glavin, D. P.; McDonald, G. D.; Becker, L. Science 1998, 279, 362–365. 10.1021/ac9025994 2010 American Chemical Society Published on Web 02/12/2010
Microchip capillary electrophoresis is a compact and very attractive format for in situ analysis of amino acids and a wide variety of other organic compounds. The sample and analysis volumes are miniscule (
