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Dry and Wet Surface Enhanced Raman Scattering Substrates
- Author / Creator
- Mahmoud, Ahmed
In the past few decades, surface enhanced Raman scattering (SERS) has been evolving as a powerful analytical technique for the detection of a wide of chemical and biological molecules. The technique can reach a sensitivity of single molecule detection, which triggered plenty of ongoing research. In addition, technological advancements in photonics and nanoscience have resulted in the advent of portable and handheld Raman systems. These devices help SERS analysis move from expensive heavy-equipped research labs to low cost field deployable-research. The development of efficient SERS substrates that can provide signal enhancement by many orders of magnitude is a core component for SERS. The SERS substrates market and research are generally dominated by rigid solid substrates that are fabricated mostly by micro/nanofabrication techniques. Although these methods can provide reproducible substrates, they suffer from usability constraints because of their high cost of fabrication.
The work presented in this thesis explored cost-effective approaches to develop and optimize SERS substrates. The substrates investigated are divided into two main categories, membrane-based SERS substrates and in-solution SERS substrates. The membrane-based SERS substrates were fabricated by equipment-free methods. In these deviceless methods, gold and silver nanostructures were incorporated in-situ within the micropores of polyvinylidene fluoride (PVDF) membranes by seed mediated and seedless protocols, respectively. The SERS performance of these substrates was investigated and optimized by controlling the loading of plasmonic nanostructures. These flexible inexpensive substrates have the advantages of being easy to fabricate and to use. In addition, the variation in the SERS performance of these substrate was less than 20% within the same substrate and from substrate-to-substrate, which reflects acceptable reproducibility. Analytical applications of these substrates were demonstrated using a Raman microscope as well as a handheld Raman spectrometer.
The second category of the SERS substrates studied was based on the optimization of gold nanostars and graphene–silver nanocomposites for water dispersible SERS measurements. In-solution SERS platforms are not used as commonly as solid-based substrates; however, these wet platforms can provide some advantages over the dried-based ones in terms of cost, reproducibility, and analysis time. The SERS performance of gold nanostars with different branch lengths was optimized based on the type of Good’s buffer, the ratio of buffer to gold concentration, and their aggregation. Our results were counterintuitive in that the gold nanostars with the shorter branches provided the largest in-solution SERS intensity. These findings can be attributed to higher surface coverage of the Raman probe rather than enhanced electromagnetic effects. Graphene–silver nanocomposites were investigated also as in-solution SERS substrates with a large 2D surface area. The SERS behavior of these nanocomposites were studied using graphene, a thiolated Raman probe, and a dye labelled ssDNA to simulate different possible interactions. The SERS and plasmonic performance of these nanocomposites can be tuned by the size of silver nanoparticles on these substrates. The nanocomposites were more stable and showed superior SERS performance when compared to commercial silver nanoparticles. The contributions of this work can pave the way for flexible membrane-based and in-solution SERS substrates to be accompanied with a handheld Raman device for field-deployable SERS measurements.
- Graduation date
- Spring 2020
- Type of Item
- Doctor of Philosophy
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