Dissertation
Elucidating temporal plasmonic and surface-enhanced Raman scattering enhancements using kinetic and potential energy arguments for nanosensor development
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Summer 2020
DOI: 10.17077/etd.005503
Abstract
Surface-enhanced Raman scattering (SERS) is a highly sensitive technique that can be used to detect trace amounts of target molecules based on enhanced signals of vibrational motions in molecules using plasmonic nanoparticles. To achieve the largest enhancements where molecular signals are increased by 2−9 orders of magnitude, direct interactions of molecules with metal surfaces are required. This, however, causes stabilizing agents to be disrupted, which leads to cluster formation when solution-phase nanoparticles are used. Because the optical properties of nanoparticle clusters are heterogeneous, the reproducibility of SERS measurements decreases. This thesis addresses this challenge in several ways. First, nanoparticle stability is defined in terms of aggregation, core composition, shape, size, and surface chemistry so that changes in structure-function relationships can be better communicated. Next, the influence of the kinetics and dynamics associated with cluster formation under diffusion-limited conditions on time-dependent SERS responses is investigated. These kinetics are found to be directly correlated to the dynamics of gold nanosphere aggregation but limited by both sedimentation and plasmonic losses due to scattering and reabsorption. Additionally, solution-phase nanosphere concentration and size are considered as a function of SERS enhancement and reproducibility. Microporous silica membranes are then used to encapsulate gold-coated silver nanoparticles to improve their optical integrity while also providing reproducible pH-sensitive SERS signals of 4-mercaptobenzoic acid. This study reveals the impacts of intermolecular interactions arising from molecular protonation on SERS detectability. Fourth, these same nanostructures are modified with 3-mercaptopropionate to detect uranyl in solution. The presence of microporous silica membranes promotes the SERS detection of uranyl in a wide range of solution pHs, ionic strengths, and temperatures. The kinetics of uranyl coordination depends on uranyl concentration and MPA protonation, variables that depend on pH. Fifth, the spatial distribution of gold nanostars on SERS detection of uranyl on amidoximated polymers are explored. An inverted drop coating geometry was utilized to reduce the deposition of gold nanostar aggregates on active sensing regions thus promoting uniform measurements with low, less than 10% relative standard deviations in relevant sensing zones. This is accomplished using spatially resolved LSPR and SERS measurements to facilitate correlated nanostar optical density and uranyl quantification measurements. These important improvements in analytical figures of merit and reduction in sampling biases are critical for the development of a user-friendly SERS-based sensor for uranyl and other small molecules. All in all, by considering and employing plasmonically stable nanoparticles, quantitative SERS measurements are realized thus improving molecular detection using this technique.
Details
- Title: Subtitle
- Elucidating temporal plasmonic and surface-enhanced Raman scattering enhancements using kinetic and potential energy arguments for nanosensor development
- Creators
- Hoa Tri Phan
- Contributors
- Amanda J. Haes (Advisor)Ned B. Bowden (Committee Member)Edward G. Gillan (Committee Member)Claudio J. Margulis (Committee Member)Alexei V. Tivanski (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Chemistry
- Date degree season
- Summer 2020
- DOI
- 10.17077/etd.005503
- Publisher
- University of Iowa
- Number of pages
- xix, 155 pages
- Copyright
- Copyright 2020 Hoa Tri Phan
- Comment
- This thesis has been optimized for improved web viewing. If you require the original version, contact the University Archives at the University of Iowa: https://www.lib.uiowa.edu/sc/contact/
- Language
- English
- Description illustrations
- color illustrations
- Description bibliographic
- Includes bibliographical references (pages 138-155).
- Public Abstract (ETD)
Nanosensors combine nanotechnology and sensing capabilities to improve our daily lives especially as related to medical diagnosis and quality control of everyday products. Today, these small sensors identify and quantify chemicals and physical changes such as pH or temperature. All sensors including nanosensors must be reliable and reproducible for everyday use. This is a major challenge for scientists because nanosensor operation depends on the physical and chemical properties of nanostructures such as their size, shape, composition, and surface chemistry. Because of their small dimensions, these materials are energetically unstable so methods to improve their utility is of utmost importance. As such, this thesis focuses on understanding the stabilization mechanisms of nanoparticles including silver core-gold shell nanospheres and gold nanostars, and manipulating their surface chemistry to promote nanoparticle stability and sensing capabilities. The charge of the nanoparticles induced by surface chemistry is impacted by local environment. Consequently, this thesis also investigates how local environmental parameters facilitate quantitative and reproducible nanosensor responses. In the future, nanoparticle design and surface molecule selection could be optimized to further improve the detectability and selectivity of biological and chemical nanosensors thereby positively impacting the environment and human beings.
- Academic Unit
- Chemistry
- Record Identifier
- 9983987795002771
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