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.