Detection of Biosignatures by Geomatrix-Assisted Laser Desorption/Ionization (GALDI) Mass Spectrometry

Abstract

Identification of mineral-associated biosignatures is of significance for retrieving biochemical information from geological records here on Earth and for detecting signs of life on other planets, such as Mars. An investigation using laser desorption Fourier transform mass spectrometry was conducted to determine whether geomatrix-assisted laser desorption/ionization (GALDI) can be used to detect amino acids (e.g., histidine, threonine, and cysteine) and small proteins (e.g., gramicidin S) associated with mineral phases and whether the geomatrix impacts detection. Iron oxide (Fe 2 O 3 ) and sodium chloride (NaCl) were investigated as clean chemical analogues of hematite and halite, respectively, which have both been detected on the surface of Mars. Samples were prepared by 2 methods: (1) application of analyte solution to the geomatrix surface with subsequent drying; and (2) physical mixing of analyte and geomatrix. Amino acids incorporated within NaCl by physical mixing yielded a better signal-to-noise ratio than those that were applied to the surface of a NaCl pellet. The composition of the geomatrix had an influence on the detection of biomolecules. Peaks corresponding to the cation-attached biomolecular ions were observed for the NaCl prepared samples. However, no biomolecular ion species were observed in samples using Fe 2 O 3 as geomatrix. Instead, only minor peaks that may correspond to ions derived from fragments of the biomolecules were obtained.

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).…”

“…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.…”

“…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). The properties of biomarkers affect detection and fragmentation and may complicate their identification (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).…”

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.…”