Infrared Action Spectroscopy of Biomolecules for Planetary Science Applications

Author: Nguyen, Tyler Minh-Hung

Year: 2026

Degree: Dissertation (Ph.D.)

Advisor: Okumura, Mitchio

Committee Members: Blake, Geoffrey A.; Okumura, Mitchio; Mayo, Stephen L.; Brown, Michael E.; Nemchick, Deacon J.

Option: Chemistry

Abstract

The search for extraterrestrial life in our solar system requires the development of novel in situ instrumentation capable of detecting biosignatures in planetary environments and biological samples. This thesis applies infrared (IR) action spectroscopy of mass-selected ions toward this goal, demonstrating the ability to unambiguously characterize planetary-relevant biomolecules in liquid samples for various test cases. Action spectra are generated by plotting a photodissociation yield for biomolecular ions of interest as a function of IR frequency. In Chapter II, I describe the setup and operating procedures of an action spectrometer that uses a quantum cascade laser (QCL) (1000-1600 cm^-1) and a Cr:ZnSe/S laser (3300-3800 cm^-1), as well as describe general data processing procedures. In Chapter III, I describe the initial demonstration of the relatively compact, QCL-based action spectrometer, highlighting its ability to record action spectra of room temperature, water-tagged amino acids and discern amino acid isomers in mixtures. In Chapter IV, I record the action spectra of planetary-relevant, water-tagged amino acid isomers using the QCL-based instrument. I distinguish between the isomers using a combination of spectrum matching and machine learning methods. In Chapter V, I use the Cr:ZnSe/S laser-based action spectrometer to record multiplexed action spectra of protonated amino acids and nucleosides from bacterial samples, with some trials at lower laser output power than contemporary methods. In Chapter VI, I show progress towards differentiating amino acid enantiomers by recording action spectra of non-covalent chiral tag-amino acid complexes using the Cr:ZnSe/S laser-based action spectrometer. In Chapter VII, I recorded action spectra of additional biomolecules, including small molecules, carbohydrates, and a pigment. Overall, this thesis will aid future development of in situ instruments for astrobiology missions and general analytical applications.