Ultrasensitive SERS detection of organophosphorus compounds via surface modified silver nanostructures : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Chemistry, School of Natural Sciences, Massey University, New Zealand
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2022
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Massey University
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The detection of target analytes with high specificity and sensitivity within fluids or on substrates is essential in many analytical applications. Surface-enhanced Raman spectroscopy (SERS) is a variation on vibrational Raman spectroscopy which uses plasmonic nanostructures or nanoparticles to amplify the Raman signal of various molecules via the formation of surface plasmons; concentrated areas of surface plasmons are known as 'hot spots', often influenced by the morphology of the chosen nanostructure. SERS can be attractive because it can provide greatly improved sensitivity and selective identification of an analyte in a mixture without separation, despite having different selection rules to normal Raman scattering. A variation of this technique, the slippery liquid-infused porous substrate (SLIPS) method, has also been shown to increase SERS signal enhancement considerably, allowing the detection of certain compounds at even lower initial concentrations. SLIPS-SERS involves the use of a Teflon-based microporous filter coated with a polyfluorinated oil to dry a drop of nanoparticles to a single condensed spot, which increases the likelihood of hotspot interactions with analytes. Despite increasing the overall sensitivity of SERS, some analytes still pose a challenge in SLIPS-SERS. One way to overcome this is modifying the surfaces of chosen nanoparticles, in the case of this research, this is done with a thin outer layer of SiO₂ or TiO₂ (ideally less than 5 nm thick). This is known as Shell-isolated Nanoparticle Enhanced Raman Spectroscopy (SHINERS), which can increase sensitivity by another order of magnitude than normal SERS, decreases particle agglomeration and the oxidation of the plasmonic core. In this research, we combine known SERS techniques: SLIPS-SERS, SHINERS and utilizing various nanoparticle shapes to greatly increase the sensitivity and detection of organophosphorus compounds.
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Figure 1.6 is reproduced with permission.