Habitable regions of Europa may include a subsurface ocean and transient
liquid environments within its icy shell. Ocean-surface communication
may occur on 1–2 million-year (My) timescales or even more rapidly in
chaos regions. Any ice-entombed organisms could remain viable at
near-surface depths (10–100 cm) over 1–10 ky. The proposed Europa
Lander will target samples at depths >10 cm, potentially
enabling recovery of viable organisms if sampling conditions are ideal.
Any life there would likely represent a separate genesis event from
Earth life. Life detection approaches should therefore not only target
life as we know it (contamination, common physicochemistry), but also as
we don’t know it, to lower the risk of false negatives. We propose to
target prebiotic, ancient, or extant life using a novel fully-electronic
single-molecule detection strategy. Now in early development (PICASSO),
the Electronic Life-detection Instrument for Enceladus/Europa (ELIE)
instrument will utilize quantum electron tunneling between nanogap
electrodes to interrogate the electronic structure of single molecules.
Nanogaps are formed by breaking a gold nanowire embedded on a silicon
chip. Bending is then used to control the gap size in the sub-nanometer
regime. A molecule can be identified by its characteristic conductance
and interaction time as a function of gap size. This technology can
detect and distinguish among amino acids, and detect RNA and DNA bases
and short base sequences. The extrapolated limit of detection for single
amino acids is ~200 ppt after 5 min of sampling
(~1 pMol/g). Integrating upfront separation methods will
enhance specificity and sensitivity. Our lab-bench prototype integrates
a nanogap chip, low-noise amplifier, and a laptop for data processing.
We target a ~1 kg flight instrument mass. ELIE will be
able to measure two key biosignatures: the amino acid complexity
distribution, and charged informational polymers, through to be
universal for aqueous based life.