Exploring Biosignatures Associated with Thenardite by Geomatrix-Assisted Laser Desorption/Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (GALDI-FTICR-MS)

Abstract

Geomatrix-assisted laser desorption/ionization (GALDI) in conjunction with a Fourier transform ion cyclotron resonance mass spectrometer (FTICR-MS) has been employed to determine how effectively bio/organic molecules associated with the mineral thenardite (Na 2 SO 4 ) can be detected. GALDI is based on the ability of the mineral host to assist desorption and ionization of bio/organic molecules without additional sample preparation. When glycine was mixed with thenardite, glycine was deprotonated to produce C 2 H 4 NO − 2 at m/z 74.025. The combination of stearic acid with thenardite produced a complex cluster ion at m/z 390.258 in the negative mode, which was assigned a composition of C 18 H 39 O 7 Na − . A natural sample of thenardite from Searles Lake in California also produced a peak at m/z 390.260. The bio/organic signatures in both the laboratory-based and natural samples were heterogeneously dispersed as revealed by chemical imaging. The detection limits for the stearic acid and thenardite combination were estimated to be 3 parts per trillion or ∼7 zeptomoles (10 −21 ) per laser spot. Attempts to improve the signal-to-noise ratio by co-adding FTICR-MS data predetermined to contain the biosignatures of interest revealed problems due to a lack of phase coherence between data sets.

The Significance of Microbe-Mineral-Biomarker Interactions in the Detection of Life on Mars and Beyond

“…The minerals impact detection; desorption and ionization of the biomarker is dependent on the energy of the laser absorbed by the mineral matrix and converted to heat. Evaporates like halite and jarosite yielded a signal, but hematite did not (Yan et al, 2007;Kotler et al, 2008;Richardson et al, 2008). Amino acids incorporated within halite yielded a better signalto-noise ratio than those applied to its surface (Yan et al, 2007).…”

“…MALDI itself is not effective when biomarkers are strongly adsorbed to minerals, as dissolution of biomarkers in MALDI solvents is required for detection (Yan et al, 2007). Biomarkers were also not detectable when directly exposed to LDI, without a matrix (Yan et al, 2007;Richardson et al, 2008).…”

“…Amino acids incorporated within halite yielded a better signalto-noise ratio than those applied to its surface (Yan et al, 2007). The properties of biomarkers affect detection and fragmentation and may complicate their identification (Yan et al, 2007;Richardson et al, 2008). MALDI itself is not effective when biomarkers are strongly adsorbed to minerals, as dissolution of biomarkers in MALDI solvents is required for detection (Yan et al, 2007).…”

“…However, a systematic evaluation of LDI efficiency in extracting biomarkers appears to be lacking. A few studies have addressed how minerals may act as a geological matrix that aids desorption and ionization of amino acids, fatty acids, and small proteins by a laser, comparable to matrixassisted laser desorption/ionization (MALDI) (Yan et al, 2007;Kotler et al, 2008;Richardson et al, 2008). The minerals impact detection; desorption and ionization of the biomarker is dependent on the energy of the laser absorbed by the mineral matrix and converted to heat.…”

Astrobiology and habitability studies in preparation for future Mars missions: trends from investigating minerals, organics and biota

“…The Urey instrument, an advanced in situ organic and oxidant detector, originally proposed for the Exomars mission, developed a sub-critical water extraction system to separate and concentrate the organic compounds from the mineral matrix (Aubrey et al 2008). Due to the potential difficulty of extracting organic matter from mineral matrices because of adsorption and/or potential substitution within the mineral structure (Kotler et al 2009), direct laser desorption and ionization techniques (such as those being explored for the Exomars mission) and related techniques for sample return missions (Yan et al 2007;Kotler et al 2008;Richardson et al 2008) may provide the needed methods to release and detect potential biosignatures.…”