Title: The HOMO-LUMO Gap of Amino Acids as a Marker of Genetic Code Selection and a Biosignature for Life Detection

Date, time, location: Wednesday, July 8th, 2026, 1 pm, Ford ES&T L1255

Names of committee members: Dr. Christopher Carr (Advisor), Dr. James Wray, Dr. Amanda Stockton, Dr. David Sherrill, and Dr. Bernd Moosmann

Abstract: Identifying signs of life beyond Earth remains one of the defining quests in the field of astrobiology. Amino acids, the building blocks of proteins, are among the most promising biosignature targets due to their universal role in life as we know it, their stability over geologic timescales, and their detectability with existing instrumentation. However, amino acids also form through abiotic chemistry throughout the solar system, and existing methods for distinguishing biotic from abiotic origins are limited by overlapping signatures between the two, or by degradation of the biotic signature under environmental conditions. This dissertation explores the HOMO-LUMO gap, a chemical property reflecting molecular electron reactivity, as a biosignature capable of overcoming these limitations. Three lines of work support this investigation: (i) demonstrating that this property can be measured directly using single-molecule nanogap instrumentation, including a flight-validated prototype tested under space-analog conditions; (ii) characterizing how pH, temperature, and solvent polarity influence this property across a broad set of amino acids, and evaluating its stability under the geochemical conditions predicted for Enceladus, Europa, and Mars; and (iii) constructing a quantitative framework that applies this property to distinguish biotic from abiotic amino acid samples with high accuracy. Taken together, this dissertation establishes a biosignature framework grounded in the fundamental electronic chemistry of life. It further finds that the electronic landscape of amino acids reflects the biochemical stages proposed for early genetic code diversification, consistent with environmental selection shaping life's amino acid repertoire, and offering an insight into the chemical logic underlying life as we know it. The developed framework is also measurable with flight-ready instrumentation, and applicable to current and future missions in the search for life across the solar system.