title: Defining Multiple Characteristic Raman Bands of α-Amino Acids as Biomarkers for Planetary Missions Using a Statistical Method.
abstract: Biomarker molecules, such as amino acids, are key to discovering whether life exists elsewhere in the Solar System. Raman spectroscopy, a technique capable of detecting biomarkers, will be on board future planetary missions including the ExoMars rover. Generally, the position of the strongest band in the spectra of amino acids is reported as the identifying band. However, for an unknown sample, it is desirable to define multiple characteristic bands for molecules to avoid any ambiguous identification. To date, there has been no definition of multiple characteristic bands for amino acids of interest to astrobiology. This study examined L-alanine, L-aspartic acid, L-cysteine, L-glutamine and glycine and defined several Raman bands per molecule for reference as characteristic identifiers. Per amino acid, 240 spectra were recorded and compared using established statistical tests including ANOVA. The number of characteristic bands defined were 10, 12, 12, 14 and 19 for L-alanine (strongest intensity band: 832 cm(-1)), L-aspartic acid (938 cm(-1)), L-cysteine (679 cm(-1)), L-glutamine (1090 cm(-1)) and glycine (875 cm(-1)), respectively. The intensity of bands differed by up to six times when several points on the crystal sample were rotated through 360 °; to reduce this effect when defining characteristic bands for other molecules, we find that spectra should be recorded at a statistically significant number of points per sample to remove the effect of sample rotation. It is crucial that sets of characteristic Raman bands are defined for biomarkers that are targets for future planetary missions to ensure a positive identification can be made.
authors.affiliation: Planetary and Space Sciences, Department of Physical Sciences, The Open University, Robert Hooke Building, Walton Hall, Milton Keynes, MK7 6AA, UK. samantha.rolfe@open.ac.uk.
authors.forename: S M
authors.initials: SM
authors.lastname: Rolfe
authors.affiliation: Planetary and Space Sciences, Department of Physical Sciences, The Open University, Robert Hooke Building, Walton Hall, Milton Keynes, MK7 6AA, UK.|Space Science and Technology Department, STFC Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, OX11 0QX, UK.
authors.forename: M R
authors.initials: MR
authors.lastname: Patel
authors.affiliation: Planetary and Space Sciences, Department of Physical Sciences, The Open University, Robert Hooke Building, Walton Hall, Milton Keynes, MK7 6AA, UK.
authors.forename: I
authors.initials: I
authors.lastname: Gilmour
authors.affiliation: Department of Environment, Earth and Ecosystems, The Open University, Milton Keynes, MK7 6AA, UK.
authors.forename: K
authors.initials: K
authors.lastname: Olsson-Francis
authors.affiliation: Planetary and Space Sciences, Department of Physical Sciences, The Open University, Robert Hooke Building, Walton Hall, Milton Keynes, MK7 6AA, UK.
authors.forename: T J
authors.initials: TJ
authors.lastname: Ringrose
mesh_terms: D000409:Alanine / Q000737:chemistry; D001224:Aspartic Acid / Q000737:chemistry; D001272:Atmosphere / Q000032:analysis*; D003545:Cysteine / Q000737:chemistry; D018534:Earth, Planet; D018559:Exobiology; D005118:Extraterrestrial Environment; D005973:Glutamine / Q000737:chemistry; D005998:Glycine / Q000737:chemistry; D006801:Humans; D018535:Mars; D015233:Models, Statistical; D018561:Space Simulation; D018531:Spacecraft; D013059:Spectrum Analysis, Raman
chemical_list: D005973:Glutamine; D001224:Aspartic Acid; D003545:Cysteine; D000409:Alanine; D005998:Glycine
keywords: Amino acids; Astrobiology; Biomarker; ExoMars; Mars; Raman spectroscopy