- Japanese researchers develop new electrical method to aid search for signs of extraterrestrial life.
- New method counts amino acids one by one, without optical measurements or chemical reagents.
- First distinction of amino acid chirality at single-molecule level, with significant implications.
- Practical application to space missions requires further validation and testing.
Japanese researchers have developed an electrical method capable of distinguishing the mirror-image forms of amino acids molecule by molecule, a step toward a future compact instrument that could help search for signs of life beyond Earth. The research, from Osaka University, combines nanoscale gaps between gold electrodes with artificial intelligence.
Amino acids, the building blocks of proteins, exist in two mirror-image forms known as L and D. Living organisms almost exclusively use L-form amino acids, while their sugars are D-form. Non-biological chemical and physical processes produce both forms in equal amounts, making the L/D ratio a potential biosignature. The researchers emphasize this is only one clue and should be considered alongside other evidence. They note that reported excesses of L-form amino acids in meteorites have often been attributed to terrestrial contamination, and that sample-return missions by the U.S. National Aeronautics and Space Administration (NASA) and the Japan Aerospace Exploration Agency (JAXA) have not found significant excesses.
Technical features of the new method
Where traditional methods analyze bulk molecules, the new method counts them one by one. When a molecule passes through a gap roughly half a nanometer wide between two gold nanowires, it generates a tunneling current. Each amino acid form produces a distinct current waveform, which is then classified by machine learning. The method requires no optical measurements or chemical reagents, and the researchers say electrical detection can simplify instrument design and reduce sensitivity to vibration. Lead author Daiki Oshiro said: "By combining our nanogap tunneling technology with artificial intelligence, we are able to distinguish L- and D-form amino acids with over 80% accuracy.
This is the first time amino acid chirality has been distinguished at the single-molecule level, constituting a fundamental advance in chemical sensing."
Experimental results and applications
In meteorite and desert tests, blind measurements of 39 forms covering the L and D versions of 19 chiral amino acids, plus non-chiral glycine, achieved identification accuracy above 50%, far higher than random chance. Quantitative accuracy for mixtures of four amino acids with different chiral compositions exceeded 66%. Because samples of interest typically contain large numbers of molecules, the team analyzed soil extracts from the Murchison meteorite and two sites in Chile's Atacama Desert. Senior author Masateru Taniguchi said: "Our method is comparable to conventional methods because both capture the main features of amino acid composition."
The paper describes a targeted approach rather than a comprehensive profiling, focusing on a pre-selected 11 forms of six amino acids. In the desert samples, glutamic acid was not reliably identified. Unlike comparisons with liquid chromatography-mass spectrometry, the aspartic acid ratio in the Murchison sample matched well, but the ratios for alanine and valine differed.
The authors say practical application to space missions will require further validation, including contamination-controlled testing and software trained against common contaminants. In calibration tests, the sensor detected tryptophan at a concentration of 0.03 nanomolar, below the roughly 1 nanomolar target for life-detection measurements, though they caution this figure does not reflect performance in complex samples. The chip withstands temperatures above 572 degrees Fahrenheit (300 degrees Celsius), so it can operate on a spacecraft without cooling. The research was published Oct. 5 in Nature Communications.
Potential of new technology in search for extraterrestrial life
The development of this new technology provides a novel direction for the search for extraterrestrial life. By analyzing the chirality of amino acids molecule by molecule, researchers can more precisely identify potential biosignatures. Because the distribution of amino acid mirror-image forms in living organisms is specific, this technology could become a key tool for future space exploration. However, practical application still faces challenges such as contamination and sample complexity, and further validation will be an important step in advancing this research.