Degree

Doctor of Philosophy (PhD)

Department

Cain Department of Chemical Engineering

Document Type

Dissertation

Abstract

The far- (λ < 250 nm) ultraviolet (UV) chiroptical response from protein secondary structures can aid in understanding protein interactions for drug discovery. Chiral metasurfaces have attracted attention to enhance the intrinsically weak biomolecular optical activity for improved structural biology characterization. However, due to materials and fabrication challenges, current metasurfaces mostly operate in the visible and near-infrared regimes with limited, if any, response in far-UV. The large spectral mismatch between metasurface and biomolecular resonances limits the chiral enhancement factor. In this work, we study aluminum planar metamaterials which display optical activity in the UV region. In the first part of this work, we experimentally and computationally investigate the resonant plasmonic-biomolecular interactions in the far-UV. To the best of our knowledge, our work is the first to experimentally explore these resonant interactions in the biologically relevant far-UV regime. We demonstrate experimentally and computationally enhanced chiral sensing of sub-10 nm amino acid films. We develop a full-wave computational model of a biomolecular film on an aluminum gammadion array using experimentally derived chiral parameters (κ) for L- and DTyrosine films. Our model shows that detectable enhancements in the circular dichroism (CD) and birefringence (CB) signals from small amounts of biomolecules are only possible when tight spectral overlap exists between the plasmonic and biomolecular chiroptical signals. We support this conclusion experimentally by fabricating aluminum gammadion arrays on fused silica substrates and sublimating ultrathin racemic, L- and D- Tyrosine films on the arrays. Complete Mueller matrix analysis of the resonant plasmonic-biomolecular system agrees with our computational results and demonstrates the importance of using far-UV active metasurfaces for enhancing natural optical activity. In the second part of this work, we study hybrid aluminum reflective metasurfaces, which leverage both local and propagating surface plasmons (PSP). These materials display strong bi-anisotropy with rich polarization conversion properties. We explore several geometries and verify how their symmetry properties affect their far-field response. Our observations provide an opportunity for researchers to improve the chiral response of plasmonic metasurfaces, especially in the challenging ultraviolet regime.

Date

8-6-2022

Committee Chair

McPeak, Kevin M.

Available for download on Sunday, July 27, 2025

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