Surface Enhanced Raman Spectroscopy for Environmental Analysis: Metal Sensing and Solvent Effect
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Raman spectroscopy is a form of molecular spectroscopy that can provide structural information on analyte molecules based on the scattering of incident light. However, Raman scattering is intrinsically weak which makes Raman spectroscopy unable to detect analytes at low concentrations. Surface-enhanced Raman Spectroscopy (SERS) can amplify the Raman signals of analytes by several orders of magnitude when the analyte adsorbs on a rough metal surface. Because of this, SERS has become a promising technique for quantitative and qualitative detection of very low concentrations of molecules in aqueous environmental samples, with both high specificity and sensitivity. With advances in nanotechnology and materials sciences, the sensitivity of this technique has been significantly improved. A variety of SERS sensors have developed and widely applied for environmental analysis, including the detection of heavy metals. Although many factors that can affect SERS detection have been investigated, a comprehensive review of this literature related to heavy metal was identified as a gap. There are many opportunities to improve SERS sensors. For example, the solvent effect on SERS detection has not been systematically studied. This thesis comprehensively reviewed the current SERS metal sensors, with an emphasis on signal generation mechanisms, sensitivity improvement, and the quantitation challenges with real environmental samples. This review provides a systematic overview of the field and gives the insight into the current limitations and future opportunities for development of SERS metal sensors. The second component of the thesis explored how solvents with different dielectric constants alters the SERS detection. SERS detection in low dielectric constant organic solvents (i.e. Methylene chloride, ɛ=9.93) can increase the technique’s sensitivity by ~10^9-10^10 times, allowing detection of analytes at zeptamolar concentrations. Computational modeling results were consistent with experimental observations, which supports that stronger electromagnetic enhancement of SERS substrates occurs in organic solvents through plasmon coupling. The use of this solvent effect on SERS yields fresh insights into SERS enhancement mechanisms and may facilitate additional future applications for environmental analysis.
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Dongchang Yang (2021). Surface Enhanced Raman Spectroscopy for Environmental Analysis: Metal Sensing and Solvent Effect. UWSpace. http://hdl.handle.net/10012/17281