Scientists searching for clues of extraterrestrial life may soon have a new way to examine one of biology’s most revealing chemical characteristics: living organisms’ preference for certain molecules over their nearly identical mirror images.
An international research team has developed an electrical sensor that can identify individual amino acid molecules and distinguish between their left- and right-handed forms.
The technology uses tiny gold electrodes and machine learning to recognize subtle differences in electrical signals produced as molecules pass through a gap smaller than a billionth of a meter.
The researchers also tested the system on material from the Murchison meteorite and soil collected in Chile’s Atacama Desert, demonstrating its power to examine the kinds of chemically complex samples prospective missions might encounter on Mars or other worlds.
The findings, published in Nature Communications, could provide a foundation for instruments intended to search for possible signs of life without relying on bulky optical equipment or complex chemical processing.
“Detecting enantiomeric excess among molecules of biological interest has therefore been proposed as a potential biosignature for life beyond Earth,” the researchers write. “Here we show that quantum tunneling currents electrically distinguish individual L- and D-amino acids and quantify their ratios at the single-molecule level without optical measurements or chiral recognition molecules.”
Life’s Preference for One Side of a Molecule
Many molecules exist in two forms that contain the same atoms but are arranged as mirror images of one another. Known as enantiomers, these molecular pairs resemble left and right hands: structurally similar, but impossible to superimpose perfectly.
This property, called chirality, is especially important in biology.
Living organisms on Earth overwhelmingly use left-handed, or L-form, amino acids to construct proteins. By contrast, nonbiological chemical processes generally produce roughly equal quantities of left- and right-handed molecules.
Scientists have consequently proposed that an unusually strong preference for one molecular orientation, known as enantiomeric excess, could serve as a likely biosignature.
However, identifying that imbalance in extraterrestrial material is challenging. Amino acids can form without life, and some nonbiological processes can also produce unequal proportions of their mirror-image forms.
Determining whether a sample contains amino acids is therefore only part of the problem. Researchers must also establish which forms are present, their relative abundances, and whether the results can be explained by contamination or nonbiological chemistry.
Reading Molecules With Electricity
The new sensor approaches that problem by measuring electrical current as individual amino acids interact with two sharply pointed gold electrodes.
Separated by a gap approximately 0.54 to 0.58 nanometers wide, the electrodes allow electrons to move through a quantum mechanical process known as tunneling.
When an amino acid enters the gap, it produces a brief change in electrical current. The resulting signal contains information about the molecule and its interactions with the electrodes.
Researchers trained machine-learning algorithms to recognize those patterns, including differences that conventional measurements of signal strength or duration alone could miss.
The team tested 39 molecular forms representing the 20 standard amino acids. Nineteen have distinct left- and right-handed versions, while one, glycine, has no handedness.
When distinguishing between the left- and right-handed forms of individual amino acids, the system attained an average F1 score of approximately 0.876 on a scale from 0 to 1, where 1 represents perfect performance.
Unlike a simple accuracy percentage, the F1 score accounts for both how often the system correctly identifies a molecule and how often it misses or incorrectly classifies one. The result indicates that the sensor performed well at distinguishing between the two molecular forms, although it was not error-free.
Finding both the amino acid and its molecular orientation across all 39 possibilities proved more difficult, producing an F1 score of approximately 0.49. Nevertheless, that performance was substantially better than the roughly 0.026 expected from random guessing.
The sensor also detected tryptophan, an essential amino acid that living organisms use to build proteins, at concentrations as low as 0.03 nanomolar at controlled laboratory conditions. That level of sensitivity is especially important for the search for alien life, where amino acids may exist in only trace amounts.
It suggests the technology could potentially identify extremely small quantities of biologically important molecules in samples collected from other worlds. However, researchers caution that its sensitivity in chemically complex environmental samples remains to be established.
Testing a Meteorite and Earth’s Mars-Like Desert
To investigate whether the technology could work beyond prepared laboratory solutions, the team analyzed amino acid extracts from the Murchison meteorite and two locations in the Atacama Desert.
The meteorite provided an extraterrestrial source of organic compounds, while the desert samples offered a challenging terrestrial environment relevant to astrobiological research.
Using a targeted panel of 11 amino acid forms, the researchers compared their sensor’s measurements with results from liquid chromatography–mass spectrometry, an established laboratory technique.
In the Murchison extract, the electrical measurements identified glycine as the most abundant amino acid in the selected analysis, accounting for 47.9% of high-confidence assignments. Alanine followed at 16.9%, with glutamic acid and serine accounting for 12.0% and 11.7%, respectively.
These results captured several major compositional features observed using conventional analysis, although differences remained between the techniques.
Importantly, the system also rejected many uncertain signals rather than automatically assigning every electrical event to a known amino acid.
For upcoming planetary missions, the ability to filter out uncertain signals could be especially valuable when testing samples containing soil, minerals, contaminants, and unfamiliar organic compounds that might otherwise be mistaken for evidence of biological activity.
A New Tool for Searching for Life Outside Our Planet
The technology currently remains experimental. Its accuracy varies with molecular composition, and further work is needed to establish accurate performance in complex samples and understand precisely how the electrode surfaces distinguish molecular handedness.
Still, the findings suggest that quantum tunneling could offer a relatively compact electrical approach to analyzing molecular chirality, conceivably reducing the need for optical components in future instruments.
For scientists investigating Mars, icy moons, or extraterrestrial samples returned to Earth, that ability could help address a question more revealing than whether life’s chemical ingredients are present.
Ultimately, finding the ingredients of life on another world would be remarkable. Discovering that those ingredients favor one molecular hand over the other could tell scientists something far more revealing about their origins.
Study: Ohshiro, T., et al. “Chiral discrimination of amino acids in meteorite and desert soil extracts via single-molecule nanogap conductance.” Nature Communications, (2026).
Tim McMillan is a retired law enforcement executive, investigative reporter and co-founder of The Debrief. His writing typically focuses on defense, national security, the Intelligence Community and topics related to psychology. You can follow Tim on Twitter: @LtTimMcMillan. Tim can be reached by email: tim@thedebrief.org or through encrypted email: LtTimMcMillan@protonmail.com