Nanogap Solid-State Single-Molecule Detection at Mars, Europa, and Microgravity Conditions
Solid-state nanogap systems are an emerging technology for in-situ life detection due to their single-molecule resolution of a wide range of biomolecules, including amino acids and informational polymers, at the parts per billion to trillion level. By targeting the abundance distributions of organic molecules, this technology is a candidate for detecting ancient and extant life and discriminating between biotic and abiotic organics on future planetary missions to Mars and icy moons such as Enceladus and Europa. A benchtop system developed at Osaka University has a proven ability to detect and discriminate among single amino acids, RNA, and DNA using nanogap chips. The Electronic Life-detection Instrument for Enceladus/Europa (ELIE) prototype was subsequently developed to make this technology viable for space instrumentation through the simplification of electronics, reduction of size and weight, and automation of gap formation. Initial ground testing using a manually formed nanogap with the first ELIE prototype detected the amino acid L-proline. However, this manual adjustment approach posed limitations in maintaining a consistent gap size. To address this challenge, we integrated an automated piezo actuator to enable real-time gap control, permitting single-molecule identification of a target amino acid, L-proline, under reduced gravity (g), including Mars (g = 0.378), Europa or Lunar (g = 0.166), and microgravity conditions (g = 0.03-0.06), as validated through parabolic flight testing. Power supply noise and experimental constraints of the experiment design limited data collection to short segments of good-quality data. Nevertheless, the subsequent analysis of detected events within these segments revealed a consistent system performance and a controlled gap size across the different accelerations. This finding highlights the systems resilience to physical vibrations. Future goals are to progress the instrument towards technology readiness level 4 with further reductions of size and mass, lower noise, and additional system automation. With further development, ELIE has the potential to be an autonomous and sensitive single-molecule detection instrument for deployment throughout the solar system.