Immunological detection of small organic molecules in the presence ofperchlorates: relevance to the life marker chip and life detection on Mars.

摘要

The proposed ExoMars mission, due to launch in 2018, aims to look for evidenceof extant and extinct life in martian rocks and regolith. Previous attempts todetect organic molecules of biological or abiotic origin on Mars have beenunsuccessful, which may be attributable to destruction of these molecules byperchlorate salts during pyrolysis sample extraction techniques. Organicmolecules can also be extracted and measured with solvent-based systems. TheExoMars payload includes the Life Marker Chip (LMC) instrument, capable ofdetecting biomarker molecules of extant and extinct Earth-like life in liquidextracts of martian samples with an antibody microarray assay. The aim of thework reported here was to investigate whether the presence of perchlorate salts,at levels similar to those at the NASA Phoenix landing site, would compromisethe LMC extraction and detection method. To test this, we implemented an LMC-representative sample extraction process with an LMC-representative antibodyassay and used these to extract and analyze a model sample that consisted of aMars analog sample matrix (JSC Mars-1) spiked with a representative organicmolecular target (pyrene, an example of abiotic meteoritic infall targets) inthe presence of perchlorate salts. We found no significant change in immunoassayfunction when using pyrene standards with added perchlorate salts. When modelsamples spiked with perchlorate salts were subjected to an LMC-representativeliquid extraction, immunoassays functioned in a liquid extract and detectedextracted pyrene. For the same model sample matrix without perchlorate salts, weobserved anomalous assay signals that coincided with yellow coloration of theextracts. This unexpected observation is being studied further. This initialstudy indicates that the presence of perchlorate salts, at levels similar tothose detected at the NASA Phoenix landing site, is unlikely to prevent the LMCfrom extracting and detecting organic molecules from martian samples.