Fluorescent-Labeling of Amino Acids with Dry 5-Carboxyfluorescein Succinimidyl Ester for In-Situ Analysis of Future Missions to Ocean Worlds

Ocean worlds, such as Europa and Enceladus, are compelling cases in the search forextraterrestrial life due to the presence of liquid water, a key component for life to arise. Aminoacids provide three biosignatures that could help distinguish the biotic or abiotic origin of a sample.Capillary electrophoresis coupled to a laser-induced fluorescence detector is the ideal approach forin-situ analysis of chiral amino acids originating from ocean worlds based on sample compatibility,high resolution, and enhanced sensitivity. However, one limitation of this approach is thenecessary step of derivatizing amino acids with a fluorescent tag. The expected long duration offuture missions to ocean worlds dictates that any reagent needed must be stored in a way to avoidpossible degradation. In the case of fluorescent dyes, the best approach is to store the dyes as ananhydrous powder. However, the general procedure for derivatization with such dyes involves theuse of dye in liquid form, as a solution of a known concentration. The efficiency of labeling from2dry dye has never been demonstrated. Here, we demonstrate that using dried CFSE dye (the onlyform stable for long-term storage under mission conditions) to label chiral amino acids havesimilar labeling efficiencies compared to previously published labeling methods using the dye insolution