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.

Institute of Geochemistry Mineralogy and Mineral Resources Charles University Prague Albertov 6 128 43 Prague 2 Czech Republic

References provided by Crossref.org

Microbial colonization of gypsum: from the fossil record to the present day

Detection of pigments of halophilic endoliths from gypsum: Raman portable instrument and European Space Agency's prototype analysis

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Raman spectroscopy in halophile research

The miniaturized Raman system and detection of traces of life in halite from the Atacama Desert: some considerations for the search for life signatures on Mars

Use of Raman spectroscopy for identification of compatible solutes in halophilic bacteria