Electrochemistry for Life Detection on Ocean Worlds

All forms of terrestrial life include cellular machinery to transform and regulate chemical energy flow through electron‐transfer pathways reliant upon key classes of biological redox molecules; life that evolved elsewhere, presumably, would possess a similar possibly overlapping set of energy‐management molecules. A second set of universal processes in terrestrial biology encompasses enzymatic change to add or remove functional groups, such as phosphate moieties, to biomolecules for a variety of purposes, from managing energy flow to tuning protein function; electrochemical assays can detect such enzymes. Thus, measurement of biological redox activity is a promising means to search for two major classes of life indicators as a component of future exploration missions to the “ocean worlds” of our solar system, those bodies that support substantial liquid oceans. Here, we assay a representative set of life‐critical redox molecules in synthetic seawater (SW) using electrochemical techniques. We also appropriate a well‐developed electrochemical assay that indicates the presence of phosphatase(s) by comparing the redox signatures of a substrate for, and the product of, the enzymatic process. We report measured limits of detection in SW as low as 10 nM for naturally occurring redox molecules and 3.1 aM for alkaline phosphatase over a 60‐minute period, demonstrating the promise and sensitivity of electrochemical sensors as effective life‐detection tools for future ocean worlds missions. Moon life: Electrochemical instrumentation played a key role in the exploration of Mars, and now seems a powerful candidate for missions aimed at the ocean worlds Europa and Enceladus. This study describes the use of electrochemical sensors for in situ life detection of key molecular indicators of life in an ocean world context.