The non-destructive separation of diverse astrobiologically relevant organic molecules by customizable capillary zone electrophoresis and monolithic capillary electrochromatography

Abstract

The in situ detection of organic molecules in space is key to understanding the variety and the distribution of the building blocks of life, and possibly the detection of extraterrestrial life itself. Gas chromatography mass spectrometry (GC-MS) has been the most sensitive analytical strategy for organic analyses in flight, and was used on missions from NASA's Viking, Phoenix, Curiosity missions to ESA's Rosetta space probe. While pyrolysis GC-MS revealed the first organics on Mars, this step alters or degrades certain fragile molecules that are excellent biosignatures including polypeptides, oligonucleotides and polysaccharides, rendering the intact precursors undetectable. We have identified a solution tailored to the detection of biopolymers and other biomarkers by the use of liquid-based capillary electrophoresis and electrochromatography. In this study, we show that a capillary electrochromatography approach using monolithic stationary phases with tailor-made surface chemistry can separate and identify various polycyclic aromatic hydrocarbons, nucleobases and aromatic acids that could be formed under astrophysically relevant conditions. In order to simulate flyby organic sample capture, we conducted hypervelocity impact experiments which consisted of accelerating peptide-soaked montmorillonite particles to a speed of 5.6 km s−1, and capturing them in an amorphous silica aerogel of 10 mg cm−3 bulk density. Bulk peptide extraction from aerogel followed by capillary zone electrophoresis led to the detection of only two stereoisomeric peptide peaks. The recovery rates of each step of the extraction procedure after the hypervelocity impact suggest that major peptide loss occurred during the impact. Our study provides initial exploration of feasibility of this approach for capturing intact peptides, and subsequently detecting candidate biomolecules during flight missions that would be missed by GC-MS alone. As the monolith-based electrochromatography technology could be customized to detect specific classes of compounds as well as miniaturized, these results demonstrate the potential of the instrumentation for future astrobiology-related spaceflight missions.

Method for detecting and quantitating capture of organic molecules in hypervelocity impacts

“…Fujishima et al. performed terrestrial hypervelocity impacts on ultra-low-density silica aerogel using peptide-rich particles to assess the capture and survival of short peptides post impact [21] . While trace organic molecules and cometary amino acids [22] , [23] , [24] were detected, aerogels are extremely hard to work with for trace organic analysis [25] , [26] , [27] .…”

In situ organic biosignature detection techniques for space applications

“…ME for in situ analysis in space applications has almost exclusively been developed with laserinduced fluorescence (LIF) detection, and consequently, much attention has been given to optimizing labeling protocols for various target analytes. Examples of CE-LIF and ME-LIF include chiral and achiral separation of amino acids (Skelley and Mathies, 2003;Stockton et al, 2009a;Chiesl et al, 2009;Creamer et al, 2017;Fujishima et al, 2019), peptides (Fujishima et al, 2019), amines (Skelley et al, 2006;Stockton et al, 2009a;Cable et al, 2013;Cable et al, 2014a), aldehydes and ketones (Stockton et al, 2010), nucleobases (Skelley et al, 2006;Fujishima et al, 2019), carboxylic acids (Stockton et al, 2011;Cable et al, 2014b), thiols (Mora et al, 2015), and PAHs (Stockton et al, 2009b). The instrument LODs are typically in the µg/L range (see Table 2), where the most high-performance methods targeting amino acids have LODs in the range from 5 nM to 750 nM (~0.4 μg/ L up to 100 μg/L; Creamer et al, 2017), except for valine that could be detected as low as 75 pM (9 ng/L; Chiesl et al, 2009).…”

Capillary zone electrophoresis method for quantification of therapeutic peptide glatiramer acetate

“…Capillary zone electrophoresis (CZE) serves as a tool that could achieve these targets. CZE separates compounds based on their various electrophoretic mobilities, such as their charge/molecular mass ratio [10]. CZE holds the potential to provide high efficiency and resolution for macromolecules (e.g., peptides and proteins) with good repeatability, minimal reagent consumption, reduced lead times, and costs, along with operation automation [11].…”