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Accurate determination of the surface enhanced Raman scattering (SERS) enhancement factor (EF) is critically important for a fundamental understanding of the SERS phenomenon. Experimental quantification of SERS EFs is challenging. A series of instrument-, analyte-, and SERS-substrate related issues can affect the SERS intensity and thus compromise the reliability of the measured SERS EFs. This dissertation presents a series of computational and experimental studies that enhance the quantitative understanding of the SERS signal variation and identify ways to enhance the reliability of the SERS EF determination. Chapter I presents an overview of works described in this dissertation. The gold nanoparticle (AuNP) inner filter effect on SERS measurements is demonstrated in Chapter II. Using dithiopurine and ethanol as model analytes, we demonstrate that the nanoparticle will modify the analytes’ Raman signal through two competitive mechanisms: enhancing the Raman signal of the analyte on the nanoparticle surface through electromagnetic enhancement, and attenuating the analyte Raman signal through photon extinction. The significance of the AuNP inner filter effect is quantitatively evaluated using ethanol as the internal reference. A solvent internal reference method is presented in Chapter III for quantifying the SERS EFs of analytes adsorbed onto AuNPs and AgNPs. One of the key findings is that while an analyte’s SERS EF varies significantly as a function of nanoparticle aggregation, its peak SERS EF depends only on the types and sizes of nanoparticles, but not on experimental conditions including concentrations of analyte, nanoparticle, and aggregation reagent. Chapter IV presents a SERS internal reference method for the determination of the resonance Raman EFs in the SERS study of rhodamine 6G (R6G) adsorbed onto AuNPs and AgNPs. The most striking finding is that the AgNP binding reduces, instead of enhancing, the R6G resonance enhancement. Finally, the wavelength-dependent correlation between UV-vis intensities and SERS EFs of aggregated AuNPs and AgNPs were investigated under three fixed excitation wavelengths (532, 632, and 785 nm). The nanoparticle UV-vis intensity is an excellent indicator for identifying the optimal aggregation state for AgNP-based SERS acquisitions under each of the three excitation wavelengths and for the AuNP-based SERS under a 632 nm excitation.

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Inhaled corticosteroids (ICS) are used to address inflammatory illnesses including asthma and COPD, with delivery commonly achieved using pressurised metered dose inhalers (pMDI). Hydrofluoroalkanes (HFAs) have been introduced as an alternative propellant to chlorofluorocarbons (CFCs) to reduce their environmental impact. However, the thermodynamic properties of HFAs are poorly understood and are different to those of CFCs. It is essential, therefore, to characterise the drugs and excipients used in HFA inhalers in order to obtain a comprehensive understanding of the device performance and the therapeutic efficacy. This work has developed different analytical methods to study the complexation between ICS and CD which are added to enhance the solubility of inhaled drugs in pMDI propellant systems providing rational control of suspension vs. solution formulations and hence their dose uniformity and stability. The Nuclear Magnetic Resonance (NMR) method developed has shown weaker complexation between budesonide and the derivatised CDs DIMEB and TRIMEB in organic solvents compared to D2O with the strength of the complex formed being ranked as D2O > MeOD > CDCl3 > CD3CN. The derivatisation of the CD also shows a marked difference in complexation with budesonide with the strength of the association being ranked as DIMEB > βCD > TRIMEB. Studies of various ICS compounds with TRIMEB in the fluorinated propellant HPFP showed the association to be greatest in budesonide, followed by beclomethasone dipropionate, momestasone furoate and fluticasone propionate. Surface-enhanced Raman scattering (SERS) has been used for the detection of corticosteroids in water using thiol functionalised βCD as a complementary study to NMR. This has been utilised to evaluate the host-guest complexes formed and provides further insight into the complexation of the compounds by their inclusion into the CD cavity. The structural data obtained using the NMR and SERS approaches developed have provided a fundamental insight into the physical chemistry of these interactions at a molecular level.

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Cyanobacterial blooms are of great concern to the drinking water treatment industry due to their capacity to produce microcystins and other cyanotoxins that are deadly to humans, livestock, pets, and aquatic life at low doses. Unfortunately, the strategies currently employed for cyanotoxin detection involve laborious analyses requiring significant expertise or bioassay kits that are subject to numerous false positives and negatives. These methods are incapable of providing rapid, inexpensive, and robust information to differentiate between the >80 cyanotoxin variants potentially present in an aqueous sample. The use of Raman spectroscopy for identification and quantification of the ubiquitous cyanotoxin microcystin-LR (MC-LR) was examined. Raman spectra readily reflect minute changes in molecular structure, spectra can be collected through water or glass, portable Raman spectrometers are increasingly available, and through surface enhanced Raman spectroscopy (SERS) it is possible to achieve femto or picomolar detection limits for a variety of target species. Drop coating deposition Raman (DCDR) was successfully implemented for quantitation of 2-100 ng of MC-LR deposited in 2 ?L of aqueous sample, even without the use of a specifically designed DCDR substrate or Raman signal enhancements. Reproducible MC-LR Raman spectra were observed for both fresh and aged DCDR samples, and the MC-LR Raman spectrum remained identifiable through a matrix of >80% DOM by mass. DCDR methods show tremendous potential for the rapid, simple, and economical detection of cyanotoxins in environmental matricies at environmentally relevant concentrations. / Master of Science

Um dos principais desafios no sensoriamento químico e biológico se encontra na detecção de traços de uma dada substância (analito), podendo chegar ao regime de detecção de uma única molécula. Uma forma de se obter este regime de detecção é por meio de análises utilizando a técnica SERS (Surface-Enhanced Raman Spectroscopy) utilizando substratos contendo nanoestruturas metálicas. Neste contexto, um material compósito formado por nanopartículas de ouro localizadas abaixo da superfície de um polímero, o polimetilmetacrilato (PMMA), foi estudado para a utilização como substratos para SERS. Neste trabalho, as nanopartículas foram produzidas através da implantação iônica de baixa energia (49 eV) de ouro em filme fino de PMMA utilizando plasma de arco catódico. O diâmetro médio da nanopartícula para dose de 0,75 x 1016 átomos/cm2 é de (4,25 ± 0,02) nm. Verificou-se que, utilizando esta técnica, as nanopartículas são formadas a uma profundidade de 10 nm abaixo da superfície do polímero. Utilizando esse material como substrato SERS, análises com analito Rodamina 6G (R6G) foram realizadas, e como fonte de excitação, um laser com comprimento de onda de 633 nm. Desta forma, verificou-se a presença dos picos característicos da R6G com concentração de 10 M, nos espectros obtidos, o que não foi possível para um substrato de PMMA sem implantação de ouro. Neste trabalho, pôde-se verificar que a dose utilizada na implantação iônica influencia na intensidade do espectro, de forma que foi observado o aumento da intensidade do sinal SERS com o aumento da dose de implantação no intervalo de 0,64 a 1,02 x 1016 átomos/cm2. Outro efeito observado foi a ocorrência de uma maior intensidade do sinal SERS quando se mantém a camada de PMMA sobre a camada compósita, isto é, sem expor as nanopartículas através da remoção da camada de polímero acima delas. Este comportamento pode ser explicado pelo efeito do intumescimento d solução de R6G, que pode favorecer o aprisionamento das moléculas de R6G na camada de polímero sobre a camada compósita. O melhor resultado foi obtido ao aquecer os substratos a 150 °C por 6 horas. O aquecimento, ao contrário do que se imaginava, não aumenta o tamanho da nanopartícula, mas torna a distribuição de geometrias das nanopartículas mais homogênea, fato que é corroborado através das micrografias obtidas por microscopia eletrônica de transmissão e pelas análises estatísticas. Utilizando a técnica de Espectrofotometria na região Ultravioleta-Visível (UV-Vis) para análise dos substratos que passaram pelo aquecimento, verificou-se um deslocamento de aproximadamente 40 nm do pico de extinção, para a região do vermelho, no espectro do substrato sem a camada de PMMA sobre a camada compósita, além de uma diminuição da extinção. Este resultado indica que a camada de PMMA sobre as nanopartículas influencia as propriedades da camada de PMMA. Além disso os espectros UV-Vis obtidos após o aquecimento dos substratos também corroboram o fato de que há alteração na geometria das nanopartículas. / One of the main challenges in chemical and biological sensing lies in the detection of traces of a given substance (analyte) and can reach the detection regime of a single molecule. One way of obtaining this detection regime is through the Surface-Enhanced Raman Spectroscopy (SERS) technique using substrates containing metal nanostructures. In this context, a composite material formed by gold nanoparticles buried in the surface of a polymer, polymethylmethacrylate (PMMA) has been studied as substrates for SERS. In this work, the nanoparticles were produced by low energy gold ion implantation (49 eV), in thin film of PMMA, using cathodic arc plasma. We found that, using this technique, the nanoparticles are formed 10 nm below the surface of the polymer, with mean nanoparticle diameter of (4.25 ± 0.02) nm at a dose of 0.75 x 1016 atoms/cm2. Using this material as SERS substrate, we performed analyzes with analyte Rhodamine 6G (R6G), and as a source of excitation, a laser with wavelength of 633 nm. In this way, we verified the presence of the characteristic peaks of Rhodamine 6G, with concentration of 10 M, which was not possible for a PMMA substrate without gold implantation. In this work, it was verified that the dose used in the gold ion implantation influences the intensity of the spectrum, so that the increase of the SERS signal intensity was observed with the increase of the implantation dose in the range of 0.64 x 1016 to 1.02 x 1016 atoms/cm2. Another observed effect was the occurrence of a higher intensity of the SERS signal when the PMMA layer was maintained on the composite layer, i.e. without exposing the nanoparticles by removing the polymer layer above them. This behavior can be explained by the swelling effect, which may favor the entrapment of R6G molecules in the polymer layer above the composite layer. The best signal was obtained after annealing the substrates at 150 °C for 6 hours. The annealing does not increase the size of nanoparticles, but makes the distribution of geometries more homogeneous, a fact that is corroborated by the micrographs obtained by transmission electron microscopy and by the statistical analyzes. Using the Spectrophotometry technique in the Ultraviolet-Visible (UV-Vis) region, there was a redshift of approximately 40 nm of the extinction peak of the sample without the PMMA layer above the composite layer, in addition there was a decrease in the extinction. Also, the obtained UV-Vis spectra of the annealed sample corroborate to the fact that there is alteration in the nanoparticles geometry.