Browsing by Author "Sims, Mark R."

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    Extraction of polar and nonpolar biomarkers from the martian soil using aqueous surfactant solutions
    (Elsevier Science B.V., Amsterdam., 2012-12-31T00:00:00Z) Court, Richard W.; Rix, Catherine S.; Sims, Mark R.; Cullen, David C.; Sephton, Mark A.
    The Life Marker Chip intends to use an aqueous surfactant solution to extract both polar AND nonpolar biomarkers from the martian soil for transport to an antibody-based detection system. Currently, a solution of 1.5 g l-1 polysorbate 80 in 20:80 (vol:vol) methanol:water is being considered and appears to be suitable. However, should this solution be shown to be unsuitable for the LMC or the martian environment, it will be necessary to use a different surfactant. Here, we have investigated the ability of a range of other surfactant solutions to extract a suite of eight standards spiked on the surfaces of the martian soil simulant JSC Mars-1 and tested the compatibility of the best two surfactants with a representative antibody assay for the detection of pyrene. The results show that using 20:80 (vol:vol) methanol:water as the solvent leads to greater recoveries of standards than using water alone. The poloxamer surfactants Pluronic® F-68 and F-108 are not effective at extracting the standards from JSC Mars-1 at any of the concentrations tested here. The fluorosurfactant Zonyl® FS- 300 is able to extract the standards, but not as efficiently as polysorbate 80 solutions. Most successful of the alternative surfactants was the siloxane-based surfactant poly[dimethylsiloxane-co-[3-(2-(2- hydroxyethoxy)ethoxy)propyl]methylsiloxane] (PDMSHEPMS) which is able to extract the standards from JSC Mars-1 about as efficiently as polysorbate 80 solutions. Enhanced recovery of the standards using polysorbate 80 solutions can be achieved by increasing the concentration of polysorbate 80, from 1.5 g l-1 to 10 g l-1, leading to an increase in the recovery of standards of about 50%; a similar increase in effectiveness is also apparent for PDMSHEPMS. Polysorbate 80 at concentrations of 1.5 g l-1 and 10 g l-1 and Zonyl® FS-300 and PDMSHEPMS (both at a concentration of 10 g l-1) are also compatible with the representative pyrene antibody ass
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    Immunological detection of small organic molecules in the presence of perchlorates: relevance to the life marker chip and life detection on Mars.
    (Mary Ann Leibert, 2011-11-17T00:00:00Z) Rix, Catherine S.; Sims, Mark R.; Cullen, David C.
    The proposed ExoMars mission, due to launch in 2018, aims to look for evidence of extant and extinct life in martian rocks and regolith. Previous attempts to detect organic molecules of biological or abiotic origin on Mars have been unsuccessful, which may be attributable to destruction of these molecules by perchlorate salts during pyrolysis sample extraction techniques. Organic molecules can also be extracted and measured with solvent-based systems. The ExoMars payload includes the Life Marker Chip (LMC) instrument, capable of detecting biomarker molecules of extant and extinct Earth-like life in liquid extracts of martian samples with an antibody microarray assay. The aim of the work reported here was to investigate whether the presence of perchlorate salts, at levels similar to those at the NASA Phoenix landing site, would compromise the LMC extraction and detection method. To test this, we implemented an LMC- representative sample extraction process with an LMC-representative antibody assay and used these to extract and analyze a model sample that consisted of a Mars analog sample matrix (JSC Mars-1) spiked with a representative organic molecular target (pyrene, an example of abiotic meteoritic infall targets) in the presence of perchlorate salts. We found no significant change in immunoassay function when using pyrene standards with added perchlorate salts. When model samples spiked with perchlorate salts were subjected to an LMC-representative liquid extraction, immunoassays functioned in a liquid extract and detected extracted pyrene. For the same model sample matrix without perchlorate salts, we observed anomalous assay signals that coincided with yellow coloration of the extracts. This unexpected observation is being studied further. This initial study indicates that the presence of perchlorate salts, at levels similar to those detected at the NASA Phoenix landing site, is unlikely to prevent the LMC from extracting and detecting organic molecules from martian samples.
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    Novel solvent systems for in situ extraterrestrial sample analysis
    (Elsevier, 2010-09) Court, Richard W.; Baki, Alexander O.; Sims, Mark R.; Cullen, David C.; Sephton, Mark A.
    The life marker chip (LMC) is being designed to test for the chemical signature of life in the soil and rocks of Mars. It will use an antibody array as part of its detection and characterisation system and aims to detect both polar and non-polar molecules at the sub-ppm to tens of ppb level. It is necessary to use a solvent to transfer organic compounds from the Martian samples to the LMC itself, but organic solvents such as dichloromethane or hexane, commonly used to dissolve non-polar molecules, are incompatible with the LMC antibodies. Hence, an aqueous-based solvent capable of dissolving the biomarkers that might exist in the soil or rocks of Mars is required. Solvent extractions of a Martian soil analogue, JSC Mars-1, spiked with a range of standards show that a 20:80 (vol:vol) mixture of methanol and water is incapable of extracting compounds insoluble in water. However, addition of 1.5 mg ml−1 of the surfactant polysorbate 80 produces extraction efficiencies of the aliphatic standards, hexadecane and phytane, equal to 25–30% of those produced by the common organic solvent mixture 93:7 (vol:vol) dichloromethane:methanol. Extraction of squalene and stigmasterol using the polysorbate solution is less efficient but still successful, at 5–10% of the efficiency of 93:7 dichloromethane:methanol. Such aliphatic compounds with occasional functional groups represent the compound classes to which most fossil organic biomarkers belong. The polysorbate solution did not extract the aromatic compounds pyrene and anthracene with great efficiency. A solvent of 20:80 methanol:water with 1.5 mg ml−1 polysorbate 80 is therefore capable of selectively extracting aliphatic biomarkers from Martian samples and transferring them to the antibody sites on the life marker chip.