Date of Award
Doctor of Philosophy in Ocean Engineering
Detection of anionic environmental pollutants such as nitrate in seawater is essential to monitoring and maintaining water quality in coastal ecosystems. Current on-site methods for nutrient detection often require extensive sample preparation and have detection limits above concentration thresholds associated with nutrient limited conditions where small variations in concentration can lead to sudden ecological events, such as toxic algae blooms.
Surface Enhanced Raman Spectroscopy (SERS) is based on the enhancement of otherwise weak Raman scattering in the presence of nanostructured metal surfaces where analytes are within approximately 2 nm of the surface. For in situ measurements in an aqueous phase, pre-concentration methods relying on surface functionalization with ligands or electrokinetic preconcentration can be used to increase the total number of target molecules within the SERS active region.
In this dissertation we show several ways to achieve detection of charged anionic species through the means of SERS as well as modelling of surface interactions to further the understanding of the occurring phenomena and inform further pathways to enhanced detection. We began this work by in situ measurements of nitrate dissolved in ultra-pure water with non- functionalized SERS substrates. By utilization of various normalization techniques, principal component analysis and application of image charge theory we were able to explain the observed adsorption behavior of the nitrate anions and were able to achieve a limit of detection for nitrate of LOD = 64 nM.
Building upon these results we investigated the combination of preconcentration measures for the detection of another charged environmental pollutant, namely 5(6)- carboxyfluorescein (5(6)-FAM). By combining surface charge through functionalization of the previously used substrates with cysteamine and application of an external electric field we were able to obtain a synergistic effect, meaning that the overall preconcentration is stronger than using functionalized substrates, or external electric fields alone, which we attributed to a combination of analyte capture, electrokinetic preconcentration and charge transfer.
Lastly, we show that cationic self-assembled cysteamine monolayers (SAM) can be utilized for the direct in situ detection of nitrate anions at micromolar concentrations, and for indirect detection at nanomolar concentrations based on nitrate interactions with the cationic ligands. We show that surface charge induction through SAM formation enables continuous in situ SERS measurements and that the detection mechanism varies based on the protonation state of the cationic SAM.
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This work is licensed under a Creative Commons Attribution 4.0 License.
Küster, Timo, "MEASURING THE NEEDLE IN THE HAYSTACK: SURFACE ENHANCED RAMAN SPECTROSCOPY (SERS) DETECTION OF ANIONIC ENVIRONMENTAL POLLUTANTS" (2023). Open Access Dissertations. Paper 1616.
Available for download on Monday, January 19, 2026