The conformational energy differences have been determined for ethylene glycol, 2- chloroethanol, and 2,2- dichloroethanol in the neat liquid, DMSO, and H20 with Raman spectroscopy. Spectra in the 0-H valence region were utilized to determine the energy difference between interand intramolecularly hydrogen bonded species. It was found that the solvent effect on the relative stabilities of the gauche and trans rotamers of the alcohols differ significantly. The results also indicate that, unlike ethylene glycol, there is significant intramolecular hydrogen bond formation in the halogenated alcohols in the neat liquid phase. Stronger intramolecular hydrogen bond formation was observed in dichloroethanol than in 2-chloroethanol.

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Benzoyl peroxide (BPO) is a common bleaching agent used in wheat flour. Due to its ability to damage existing nutrients in food and potential adverse effect to health, BPO have been strictly banned as a food additive in several countries and regions, such as China and Europe. However, the United States specifies that BPO is generally recognized as safe (GRAS). So, the WHO/FAO created a Codex Alimentarius Commission (CAC) to regulate the international BPO usage standard. According to the CAC, it is restricted at 75 mg/kg or parts per million (ppm). BPO is very unstable and easily converts to benzoic acid (BA), which places the analytical challenge for accurate BPO quantification. The objective of this study is to develop a reliable method for BPO quantification in flour. Raman spectroscopy was first explored to detect BPO and BA on an aluminum foil slide. The result showed BPO and BA produced distinct Raman peaks that can be discriminated against. However, the sensitivity was not satisfactory to reach the regulation limit. To improve sensitivity, surface-enhanced Raman spectroscopy (SERS) was applied using silver nanoparticles as the substrate. Although the signals did enhance significantly using SERS, the characteristic peaks of BPO disappeared as BPO converted to BA during the sample preparation. We then went back to Raman spectroscopy but focused on optimizing the sample preparation to enhance the signal intensity. Using a hydrophobic surface (i.e., parafilm) which can hold the droplet and minimize the spread, the Raman signal was enhanced significantly after repeating multiple droplets on the same surface. A standard curve was created for BPO from 25 ppm to 250 ppm and for BA from 250 ppm to 1000 ppm, respectively. To detect BPO in wheat flour, we applied a more advanced Raman imaging instrument and focused on the analysis of Raman maps instead of spectra for the analysis of effect flour matrix to BPO extraction and detection. We firstly tried an in situ method, which scanned the pellet of flour spiked with different amounts of BPO without extraction. However, we could not detect BPO at 0.1% or lower in flour samples. We then tried an extraction method using acetonitrile as the solvent, which showed a lower detection limit compared to the in situ method. However, this extraction method yielded inconsistent results for BPO that is under 0.05% in flour. The extraction method developed was further improved with an evaporating step and a C18 solid phase extraction (SPE) spin column. This improved the extraction efficacy and provided a roughly 60% recovery percentage for detecting BPO in wheat flour without decomposing into BA. In conclusion, we developed a simple sample preparation protocol coupled with Raman spectroscopy to quantify BPO in flour without converting to BA, which would meet the regulation requirement. This method also shortened the experiment time including both sample preparation and detection time compared to current methods.

Droplets are ubiquitous microscopic systems - ranging in size from several nanometers to ~100 micrometers – that undergo abundant environmental interactions. Researchers have shown that droplets can impact both earth climate and air quality through physical and chemical processes. Droplets released from the human respiratory system, either suspended in air or deposited on surfaces, can carry pathogens (e.g., influenza viruses, the SARS-CoV-2 virus), and are thus important for disease transmission. The need to understand the role of droplets in environmental processes requires appropriate tools for droplet characterization. We used Raman and surface-enhanced Raman spectroscopy (SERS) based imaging as such tools due to their capacity for simultaneous collection of abundant molecular information inside droplets and their potential to collect detailed images of droplet component distributions. We imaged pH and chemical moiety distributions inside droplets over a wide range of: 1) droplet compositions; 2) surrounding environmental conditions (relative humidity, temperature); and 3) droplet morphologies. This dissertation describes measurement of droplet pH in droplets containing mixtures of phosphate buffer (PB), one of the most commonly used biological solvents, and ammonium sulfate (AS), arguably the most abundant chemical species in atmospheric droplets, at room temperature. We observed a pH gradient inside PB droplets while a homogeneous pH distribution was found inside AS droplets, thus showing a significant pH effect due to droplet composition. We attributed the contrasting pH distribution in the two droplet systems to different ionic interactions at the air-water interface. In addition, we obtained AS droplet images at 223K to investigate ice nucleation upon freezing. We observed variable nucleation behavior in AS droplets as a function of concentration, a finding with implications for atmospheric cloud nucleation. We also investigated virus deposition during sessile droplet evaporation using gold nanoparticles. SERS imaging enabled development of correlations between virus viability and droplet deposition pattern and related them in terms of the coffee-ring effect. Suppression of the coffee-ring effect can reduce virus infectivity on surfaces during droplet evaporation. These works collectively exhibit the potential of Raman and SERS imaging for droplet characterization. / Doctor of Philosophy / Droplets are ubiquitous in the environment. Small droplets can form clouds and fogs, and are often micro- to nano-scale in size. Droplets can either grow or shrink in the environment when they absorb or lose water. Similarly, reactions may happen when droplets contain various species. Droplets in human breath exhalate may contain pathogens, such as the SARS-CoV-2 virus that is the cause of the COVID-19 pandemic. If the virus stays viable in droplets, no matter where the droplets are located, the virus will remain infectious and may be transmitted to others through contact. The studies in this dissertation were conducted to determine the distributions of soluble and insoluble components inside droplets and to elucidate how the observed distributions correlate with important droplet properties and environmental processes. We used two methods to observe droplets: Raman spectroscopy and surface-enhanced Raman spectroscopy (SERS). Molecules are constantly vibrating, these vibrations result in characteristic Raman signals that can be monitored. Both Raman and SERS provide such measurements, except that SERS has greater sensitivity due to the signal enhancement provided by gold or silver nanoparticles. In this dissertation, we obtained images of droplets with variable compositions at both room temperature and -50 °C. We also examined virus survival inside droplets during droplet drying. Using the collected images, we related the component distribution inside a droplet to its acidity, and evaluated virus survival in terms of droplet drying patterns. The images demonstrate that Raman and SERS imaging are promising tools for the study of droplets.

Raman spectroscopy is a powerful tool in the field of biomedicine for disease diagnosis owing to its potential to provide the molecular fingerprint of biological samples. However due to the inherent weak nature of the Raman process, there is a constant quest for enhancing the sensitivity of this technique for enhanced diagnostic efficiency. This thesis focuses on achieving this goal by integrating advanced methods with Raman spectroscopy. Firstly this thesis explores the applicability of a laser based fluorescence suppression technique – Wavelength Modulated Raman Spectroscopy (WMRS) - for suppressing the broad luminescence background which often obscure the Raman peaks. The WMRS technique was optimized for its applications in single cell studies and tissue studies for enhanced sensing without compromising the throughput. It has been demonstrated that the optimized parameter would help to chemically profile single cell within 6 s. A two fold enhancement in SNR of Raman bands was demonstrated when WMRS was implemented in fiber Raman based systems for tissue analysis. The suitability of WMRS on highly sensitive single molecule detection techniques such as Surface Enhanced Raman Spectroscopy (SERS) and Surface Enhanced Resonance Raman Spectroscopy (SERRS) was also explored. Further this optimized technique was successfully used to address an important biological problem in the field of immunology. This involved label-free identification of major immune cell subsets from human blood. Later part of this thesis explores a multimodal approach where Raman spectroscopy was combined with Optical Coherence Tomography (OCT) for enhanced diagnostic sensitivity (>10%). This approach was used to successfully discriminate between ex-vivo adenocarcinoma tissues and normal colon tissues. Finally this thesis explores the design and implementation of a specialized fiber Raman probe that is compatible with surgical environments. This probe was originally developed to be compatible with Magnetic Resonance Imaging (MRI) environment. It has the potential to be used for performing minimally invasive optical biopsy during interventional MRI procedures.

Over 70% of the Earth s economically recoverable nickel (Ni) resides in laterite ore deposits, however they account for less than half of the current global nickel production. During laterization, nickel and other soluble ions are taken into solution before re-precipitating within iron oxide minerals in the limonite zone, or as serpentines and other phyllosilicates in the layers below this zone. It is these laterite deposits that show the greatest potential for low energy, environmentally conscious processing. The major host of nickel in the limonite zone is the iron-oxyhydroxide mineral goethite, α-FeOOH, where up to 4 mol% Ni has been reported in natural specimens, and even higher levels in synthetic samples (5.5 mol%). The Ni is assumed to be incorporated in the crystal structure of the goethite, but previous characterisation work only demonstrated a weak to moderate correlation of mineral structure change with the nickel content in goethite. Mining companies working on the extraction and recovery of nickel from the limonite zone of lateritic deposits have noticed that the ease with which nickel can be extracted varies greatly; goethite rich ores that appear to have similar mineralogies/geologies can display extreme variation in their leachability. It is not clear why the ores behave in this way, but in order for extraction techniques and subsequent recovery of nickel to be improved, the reasons behind this variability need to be understood. The lateritic ore materials from which nickel is extracted are generally made up of a number of different mineral phases. The multiphase nature of the samples means that characterisation of the goethite-type phases from these materials is challenging. To simplify the system and allow the association of Ni into goethite and/or other iron oxyhydroxide phases to be studied in a controlled environment, a synthetic study was carried out. Ni-bearing goethites have been synthesised at a series of different temperatures and characterised by a range of analytical techniques including PXRD, IR, Raman, TGA, ICP-OES, SEM and TEM. It was found that a second phase, ferrihydrite, co-existed with the goethites, the proportion of which increased at lower synthesis temperatures and with increasing amounts of Ni. Ferrihydrite is known to be a precursor phase in the formation of goethite, but its poorly crystalline nature makes it difficult to identify using standard characterisation techniques such as PXRD. The introduction of Ni to the system increases the stability of the ferrihydrite phase, inhibiting its transformation to goethite. It is believed that some of the Ni thought to be incorporated into goethite could actually reside in an undetected ferrihydrite phase, which could account for the differences observed in the leachability of natural materials. Characterisation techniques were investigated to try and determine a simple way to identify ferrihydrite in these systems, which could ideally be used in the field to identify the presence of ferrihydrite in goethite rich ore materials. Thermal analysis proved to be particularly promising as a technique which could be used to identify ferrihydrite rich deposits before extraction, enabling the most efficient and environmentally conscious metal recovery process for each deposit to be identified. In order to investigate the way in which Ni partitions itself between structural incorporation into goethite and association with a secondary ferrihydrite phase, a new washing technique was developed using EDTA, which is capable of selectively removing the ferrihydrite phase whilst leaving the goethite intact. This investigation suggests that a maximum of ~2.5 mol% of Ni is structurally incorporated into goethite, regardless of how much is added during the synthesis. Any excess nickel, above that which is substituted into the goethite structure, was found to be associated with the poorly crystalline ferrihydrite phase. Despite being considered a metastable phase, the increased stability of ferrihydrite resulting from the presence of Ni suggests that it may persist in laterite deposits within geological systems. If ferrihydrite is indeed present in nickeliferous laterites, it may be a significant host for Ni, and potentially many other critical elements. Based on the methodology developed whilst studying synthetic samples, a characterisation program for materials from lateritic ore deposits was conducted to investigate the presence of ferrihydrite in natural systems. From the research presented and discussed in this thesis, proof of the presence or absence of ferrihydrite in laterite systems, causing variations in the leachability of the ore materials, could not be conclusively established. The thermal analysis technique developed here successfully identified and quantified ferrihydrite in the presence of goethite in synthetic systems, and showed great potential when used to characterise the lateritic goethite samples, certainly suggesting that ferrihydrite could be present in these natural ore materials. With further refinement of the methodology, to enable a larger range of sample types to be accurately analysed, TGA is a technique which could be used as a screening tool for laterite ores.

Single-walled carbon nanotubes (SWNTs) exhibit extraordinary properties: mechanical, thermal, optical and, possibly the most interesting, electrical. These all-carbon cylindrical structures can be metallic or semi-conducting depending on their precise structure. They have the potential to allow faster transistor switching speeds and smaller, more closely-packed interconnects in microelectronics. However, such applications are hindered by the difficulties of positioning the correct type of SWNT in a spatially precise location and orientation. In addition, greater understanding of the fundamental limits of SWNTs, such as the limit of current density, is needed for optimum operation in applications. The primary aim of this project was to increase the understanding of current density limitation by using in situ plasmonically enhanced Raman spectroscopy during electrical transport. The use of plasmonic metal nanostructures to enhance the Raman scattering should allow the acquisition of informative spectra from SWNTs away from their intrinsic resonance conditions. To achieve this aim, SWNTs must be integrated with plasmonic metal structures as well as electrical connections. This thesis presents two approaches for the integration of SWNTs with other nanometre-scaled features, in particular plasmonic nanoparticles. Fountain pen nanolithography uses a hollow nanopipette in place of the probe tip in an atomic force microscope (AFM), through which material can be delivered to a spatially precise position on a surface. Aqueous SWNT dispersion was delivered to chemically-functionalised silicon in this way, through pulled quartz pipettes with aperture diameters of 50 nm, 100 nm and 150 nm. The heights, widths and continuity of lines drawn on the surface by the nanopipette depended on the size, setpoint and lateral speed of the tip. A small bias voltage applied between the SWNT dispersion inside the pipette and the substrate allowed the deposition to be switched on or off depending on the polarity of the voltage, through the action of electroosmotic effects within the quartz capillary. The quality and density of the SWNT dispersion was found to be important for successful deposition to occur, since too low a concentration results in the lines deposited from the pipette being only surfactant but too high a concentration of bundles would quickly block the small tip of the pipette. Polarised Raman spectroscopy on SWNT deposited by fountain pen nanolithography showed that they had a high level of alignment parallel to the direction in which the pipette moved. Spherical gold nanoparticles with plasmonic properties suitable for enhancing Raman scattering were dropped onto samples containing individual SWNTs supported on a Si/SiO2 surface. Nanomanipulation with an atomic force microscope was used to push the gold nanoparticles onto the SWNTs. Raman spectra measured with and without the gold particles showed that the gold nanoparticles gave local enhancement factors of 24 for a single 150 nm nanoshell and 130 for a small cluster of 150 nm nanoshells. Polarised Raman studies on the cluster showed that the angle dependence deviated significantly from that expected of a bare SWNT. Electrical transport experiments with in situ plasmonically enhanced Raman spectroscopy may be performed on samples prepared from the methods described here. Such experiments would increase understanding of the electrical properties of SWNTs and how they relate to the vibrational and optical properties.

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Detecting lung cancer is di cult as it is hidden in the body, and current clinical methods are not elective at an early stage; the one-year survival rate after diagnosis in the World is just 29-33%. Acetyl amantadine (AcAm) is recognised as an exogeneous cancer biomarker because it is the product of a metabolic process known to be significantly up-regulated in cancerous cells. After ingestion, the an-tiparkinson and antiviral drug amantadine is acetylated in the body by the enzyme spermidine/spermine N1 acetyltransferase to give AcAm, which can be detected in patient’s urine. However, techniques previously used to quantify AcAm in urine, such as liquid chromatography-mass spectrometry (LC-MS), are undesirable for clin- ical adoption due to high costs and long run times. Further costs and delays result from the requirement for solid phase extraction (SPE). Therefore, it is highly desired to lower the costs and delays in processing by exploring different quantification approaches, ideally without the need for SPE processing. In this thesis, I investigate the use of surface enhanced Raman spectroscopy (SERS) to quantify AcAm in urinalysis. I prepare two kinds of Raman substrates with hydrophobic pocket surface capture agents beta -cyclodextrin (beta -CD) that work to extract the AcAm from the urine, followed by the surface enhanced Raman measurement using two kinds of Raman systems. The detection strategy is more economical than the currently used LC-MS approach, and enables development of an easy-to-use point-of-care tool that should provide a more rapid turnaround to the health care provider. The next step will be to use real samples. If it is achieved, it will be a promising step in early cancer diagnostics. / Graduate

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