Microfluidic Chromatography for Enhanced Amino Acid Detection at Ocean Worlds

Abstract

Increasing interest in the detection of biogenic signatures, such as amino acids, on icy moons and bodies within our solar system has led to the development of compact in situ instruments. Given the expected dilute biosignatures and high salinities of these extreme environments, purification of icy samples before analysis enables increased detection sensitivity. Herein, we outline a novel compact cation exchange method to desalinate proteinogenic amino acids in solution, independent of the type and concentration of salts in the sample. Using a modular microfluidic device, initial experiments explored operational limits of binding capacity with phenylalanine and three model cations, Na + , Mg 2+ , and Ca 2+ . Phenylalanine recovery (94–17%) with reduced conductivity (30–200 times) was seen at high salt-to-amino-acid ratios between 25:1 and 500:1. Later experiments tested competition between mixtures of 17 amino acids and other chemistries present in a terrestrial ocean sample. Recoveries ranged from 11% to 85% depending on side chain chemistry and cation competition, with concentration shown for select high affinity amino acids. This work outlines a nondestructive amino acid purification device capable of coupling to multiple downstream analytical techniques for improved characterization of icy samples at remote ocean worlds.

Testing of Ion Exchange Solid Phase Extraction Media for Extraterrestrial In Situ Sample Preparation on Liquid Samples

“…To further test the multianalyte extraction, the 1 μM solution was diluted 1 in 10 in IO before extraction on Oasis MCX columns; this is 1000× lower concentrations than previous mixed amino acids extractions from ocean water. 31 To concentrate the analytes for the subsequent LC-MS analysis, the fractions were vacuum-dried after collection and reconstituted in 50 μL, providing a 10× concentration factor for the analysis. To avoid a high concentration of NaOH in these reconstituted fractions, elutions were performed using NH 4 OH solutions for both the pre-elute and elution steps.…”

“…Another major issue is the salt to amino acid ratios used for the extractions. The work by Van Volkenburg et al only achieved 17% recovery of phenylalanine as the salt:AA ratio increased to 500:1. Low recovery is due to analytes not being captured from the load solution, loss during the wash step, or failure to elute, but the underlying issues were not fully explored in this work.…”

“…This means that simply changing the pH of the solution passing through the column can make these analytes less likely to interact with the charge on the column or even be repelled by the column charge, allowing them to be eluted, while the salt ions are retained on the column. This technique has been used since the early reports − as well as in more recent work, − and this type of cation exchange method was directly proposed for application with Ocean World samples by Van Volkenburg et al Abrahamsson et al also proposed extraction of analytes from Ocean World samples, utilizing a cation exchange column directly coupled with a LC column for amino acid analysis, but required subcritical water as the solvent.…”

“…In addition, these studies utilized amino acids in salt solutions normally containing only a single mono- or divalent cation and chloride ions as the anion, which does not represent what is likely to be encountered in actual samples. Sodium and potassium ions are known to be present on Enceladus, along with both Mg and Ca in the μM to mM range. , Van Volkenburg et al did test recovery of a 17 amino acid mixture from a terrestrial ocean sample as a potential mimic for ocean world brines but used 100 μM amino acid concentrations, with no indication that endogenous amino acids in the collected ocean sample were accounted for in their analysis. If the reported method did not recover endogenous amino acid analytes from an Earth ocean sample, where we know life exists, it is unlikely to be useful in looking for life detection molecules on other Ocean Worlds.…”

In situ organic biosignature detection techniques for space applications

“…Examples of applications for planetary science applications include desalting of samples containing amino acids on a microchip (Craft et al, 2020;Volkenburg et al, 2022), on-line preconcentration of amino acids before chromatographic analysis (Abrahamsson et al, 2021), and refocusing of extracted analytes for on-line extraction and chromatography (Abrahamsson et al, 2019).…”