title: Identification of beta-carotene in an evaporitic matrix--evaluation of Raman spectroscopic analysis for astrobiological research on Mars.
abstract: Since evaporitic rocks on the Martian surface could (or still can) serve as potential habitats for microbial life on Mars, there is a reasonable possibility that these rocks may sustain molecular remnants as evidence for the presence of extinct or extant living organisms on Mars and that beta-carotene could be a suitable biomarker. In this paper, Raman microspectrometry was tested as a nondestructive method of determining the lowest detectable beta-carotene content in experimentally prepared evaporitic matrices--namely, gypsum, halite and epsomite. Two excitation wavelengths were compared--514.5 nm, because of the resonance Raman enhancement in the carotenoid analysis, and 785 nm, as a more universal wavelength now much used in the detection of biomolecules terrestrially. Mixtures were measured directly as well as with a laser beam penetrating the crystals of gypsum and epsomite. We have obtained beta-carotene signals at the 0.1 to 10 mg kg(-1) level--the number of registered beta-carotene Raman bands differed depending on the particular mineral matrix and the excitation wavelength. Concentrations of beta-carotene of about one order of magnitude higher were identified when analysed through single crystals of gypsum and epsomite, respectively.
authors.affiliation: Institute of Geochemistry, Mineralogy and Mineral Resources, Charles University in Prague, Albertov 6, 128 43, Prague 2, Czech Republic.
authors.forename: Petr
authors.initials: P
authors.lastname: Vítek
authors.forename: Jan
authors.initials: J
authors.lastname: Jehlicka
authors.forename: Howell G M
authors.initials: HG
authors.lastname: Edwards
authors.forename: Katerina
authors.initials: K
authors.lastname: Osterrothová
mesh_terms: D018559:Exobiology / Q000379:methods*; D005118:Extraterrestrial Environment / Q000737:chemistry*; D018535:Mars; D015203:Reproducibility of Results; D012106:Research; D013059:Spectrum Analysis, Raman / Q000379:methods*; D019207:beta Carotene / Q000032:analysis*
chemical_list: D019207:beta Carotene