Date of Award
Doctor of Philosophy in Chemistry
Jason R Dwyer
The aim of this dissertation was to explore and develop tools for marine sensing by surface-enhanced Raman spectroscopy (SERS). The first chapter focuses on the development of a real-time signal processing program to deal with background removal in different spectroscopic techniques such as UV/Vis, SERS and XPS. Background removal by a dual-tree complex wavelet transform with an iterative algorithm (DTCWT-IA) was compared to different background removal methods such as: linear, spline, Tougaard, Shirley, and unspecified proprietary methods from the instrument software companies. Unlike the more conventional methods, DTCWT-IA more resembled the presumed background shape and was generalizable across different spectroscopic spectra covering UV/Vis, SERS, and XPS. With minimal need for user input or spectrum-specific parameter adjustment, DTCWT-IA is compatible with batch processing to handle large amounts of data that would come with real-time signal processing. The method is therefore a useful candidate in processing real-time data from sources such as marine sensors using a variety of different spectroscopic techniques. The next chapter investigates the use of a non-contact cleaning procedure for commercially available SERS substrates. The genesis for this work was the apparent contamination of commercial SERS substrates upon removal from their shipping containers. Not only was this procedure proven to remove hydrocarbon contaminants on the surface, but it also improved the sensitivity of the SERS substrates. The plasma-cleaning procedure is not limited to removing packaging contamination but could also be useful for biofouling removal in marine sensing and extending the lifetime of sensors. This chapter thus also presents an exploration of the reusability of SERS substrates after plasma cleaning to remove analyte. While the presence of unwanted substances on the surface of a SERS substrate can be detrimental, judiciously chosen organic monolayers can serve a variety of useful functions. In a marine environment, the stability and ease for formation of such a monolayer are of paramount importance. The final chapter of the dissertation explores the use of N-heterocyclic carbenes (NHCs) as candidates for self-assembled monolayers (SAMs) on gold surfaces. Unlike thiols which are well-known for the reliable formation of SAMs onto gold surfaces, but can have limited stability, NHC monolayers have been shown to withstand a range of harsh conditions and could be more suitable for marine sensing. Various different approaches and formulations had been proposed for NHC monolayer formation, with procedures less established than for thiol SAMs. We found that various different NHC preparations acted as gold etchants. The removal of gold has dire consequences for the performance of a gold-coated SERS substrate, so that care in the preparation of NHC monolayers is necessary. We investigated the role of solvent, concentration, and species, in order to establish various parameter bounds to be controlled. The final chapter presents this systematic study for the perspective of benchmarking a new class of gold etchant
Chevalier, Robert, "CHEMICALLY TUNED SERS SENSORS AND SIGNAL PROCESSING FOR MARINE SENSING" (2022). Open Access Dissertations. Paper 1483.
Available for download on Sunday, January 12, 2025