Chiral discrimination of amino acids in meteorite and desert soil extracts via single-molecule nanogap conductance

Life on Earth uses L-amino acids and D-sugars, whereas abiotic processes produce equal abundances of both enantiomers. Detecting enantiomeric excess among molecules of biological interest has therefore been proposed as a potential biosignature for life beyond Earth. However, robust electrical methods for determining the L/D ratios of amino acids and sugars at low concentrations, particularly in chemically complex samples, remain limited. 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. Individual enantiomers are distinguished with over 80% accuracy, and a blind test of 39 amino acids identifies both molecular identity and chirality with >50% accuracy, well above random chance. Mixtures containing four amino acids with different chiral compositions are quantified with >66% accuracy. Murchison meteorite and Atacama Desert extracts are analyzed using a targeted panel of 11 amino acids. Confidence-based filtering distinguishes high-confidence target assignments from low-confidence events, and the resulting compositions capture major compositional features observed by LC–MS while highlighting the effects of background and low-abundance signals. These results establish a targeted single-molecule electrical approach for chiral amino acid analysis and provide a foundation for future applications to study chemically complex samples, including those relevant to astrobiological research. Chiral amino acids are important biomarkers in the search for life beyond Earth, but their analysis remains challenging. Here, the authors demonstrate single-molecule electrical identification of amino acid chirality and apply it to Murchison meteorite and Atacama Desert samples.