Dissertation
Non-thiolated intermolecular and interfacial interactions near gold nanostars and their effect on SERS
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Autumn 2024
DOI: 10.25820/etd.007651
Abstract
Vibrational spectroscopy utilizes vibrational and rotational motion to detect molecules and discern information about chemical bonds. One type of vibrational spectroscopy, Raman scattering, relies on the presence, location, and shape of spectral features to identify molecules and study individual chemical bonds. Surface-enhanced Raman scattering (SERS) is an analytical technique utilizing chemical and electromagnetic enhancements, of Raman scattering, generated near a nanoparticle surface to detect molecular vibrations with high sensitivity. SERS enables molecular detection of concentrations approaching pico- and femtomolar by enhancing Raman intensities from 1 to 13 orders of magnitude. Though SERS has significant advantages, the challenges associated with this technique are equally large in certain scenarios because the nature and design of nanoparticles limits the number and types of molecules detectable through SERS. This thesis explores and addresses a few of the current challenges associated with SERS by further expanding the technical applications through discerning new methods of detection for two different analytes aspirin and Δ9 -tetrahydrocannabinol in solution. The subsequent sections of this study cover the recent advances in SERS before discussing co-solvent effects on non-thiolated molecular detection and the application to saliva samples involving drug-induced impairment.
This thesis first provides a detailed overview of vibrational spectroscopy, SERS, and recent advances in new applications that overcome challenges with, enable better usage of, or further the understanding of the technique. SERS is discussed beginning with the fundamentals of Raman scattering and ending with the recent applications before describing SERS, as a technique, in detail. The SERS enhancement mechanisms are explained with a focus on electromagnetic enhancement and the relationship with group theory surface selection rules. After discussing enhancement mechanisms, the chapter discusses challenges inherent to solution-phase nanoparticles including iii nanoparticle design, nanoparticle composition, analyte surface affinity, solvent presence, and surface-stabilizing agent presence.
Next, an inherent problem of mono-disperse, solution-phase nanoparticles is addressed by combining surface-activation and co-solvents to enable the detection of non-thiolated molecules on gold nanoparticle surface. This problem stems from the nanoparticle surface-stabilizing agents and analytes with relatively weak surface affinities like non-thiolated molecules where nonthiolated analytes cannot readily replace the surface-stabilizing agents to approach sufficiently close to the surface to enable SERS detection. The results show that tetrahydrofuran, as a cosolvent in water, facilitates aspirin detection with SERS by forming a hydrogen-bonded complex with aspirin allowing the complex to reach and interact with the surface through π-orbital overlap with the aromatic ring.
Lastly, the thesis covers a novel method of detection for Δ9 -tetrahydrocannabinol (THC) in human saliva that correlates observed signal with cannabis-induced euphoria at a given time after THC inhalation. This method utilizes monodisperse, gold nanostars to detect a primary THC metabolite, 11-nor-9-carboxy-Δ 9 -tetrahydrocannabinol (THC-COOH), within saliva from participants post THC inhalation without a separation mechanism. This method further supports the possibility of identifying whether a person is impaired by THC using SERS.
Overall, SERS is a qualitative and quantitative technique for molecular detection and analysis that yields information about the environment surrounding a molecule. This thesis works to minimize the disadvantages of SERS and improve the versatility of the technique, enabling SERS to be powerful tool for understanding complex molecular systems and the mechanisms behind various chemical phenomena. Furthermore, a few selected future directions are discussed pertaining to each study.
Details
- Title: Subtitle
- Non-thiolated intermolecular and interfacial interactions near gold nanostars and their effect on SERS
- Creators
- Ryan D. Norton
- Contributors
- Alexei V. Tivanski (Advisor)Ned B. Bowden (Committee Member)Claudio J. Margulis (Committee Member)Florence J. Williams (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Chemistry
- Date degree season
- Autumn 2024
- DOI
- 10.25820/etd.007651
- Publisher
- University of Iowa
- Number of pages
- xii, 105 pages
- Copyright
- Copyright 2024 Ryan D. Norton
- Language
- English
- Date submitted
- 12/05/2024
- Description illustrations
- Illustrations, tables, graphs, charts
- Description bibliographic
- Includes bibliographical references (pages 95-105).
- Public Abstract (ETD)
How low amounts of molecules in solution vibrate are studied by mixing them with metal nanoparticles (sizes below 100 nanometers) and exposing the solution to a laser. Each molecule vibrates at a specific frequency allowing us to identify what molecules are present and how they interact with each other. This thesis first provides an overview of molecular vibration near nanoparticle surfaces and how these are utilized to study vibrations of molecules. The overview explains how vibrational signal is enhanced near a nanoparticle surface while identifying the current advantages and disadvantages of the technique. Next, nanoparticles are exploited to determine how tetrahydrofuran, a common organic solvent, affects the detection and vibration of aspirin, a common drug, near a gold surface. Tetrahydrofuran is shown to facilitate aspirin reaching the nanoparticle surface, enabling detection, by interacting and moving with aspirin in solution. Lastly, the molecular vibrations near a gold surface allow the metabolism of Δ9-tetrahydrocannabinol (THC) to be tracked through saliva and associated with how “high” a person feels at a given time after THC inhalation. Molecular vibration further supports that a long-lasting metabolite of THC is detected in saliva with the possibility of identifying whether a person is impaired by THC at a given time. Overall, this thesis discusses our progress towards minimizing the disadvantages of using molecular vibrations to understand what is around us and how it works.
- Academic Unit
- Chemistry
- Record Identifier
- 9984774665002771
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