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    RAMAN AND ATR-FTIR SPECTROSCOPY TOWARDS CLASSIFICATION OF WET BLUE BOVINE LEATHER USING RATIOMETRIC AND CHEMOMETRIC ANALYSIS
    (BioMed Central Ltd, 2020-12) Mehta M; Naffa R; Maidment C; Holmes G; Waterland M
    There is a substantial loss of value in bovine leather every year due to a leather quality defect known as “looseness”. Data show that 7% of domestic hide production is affected to some degree, with a loss of $35 m in export returns. This investigation is devoted to gaining a better understanding of tight and loose wet blue leather based on vibrational spectroscopy observations of its structural variations caused by physical and chemical changes that also affect the tensile and tear strength. Several regions from the wet blue leather were selected for analysis. Samples of wet blue bovine leather were collected and studied in the sliced form using Raman spectroscopy (using 532 nm excitation laser) and Attenuated Total Reflectance - Fourier Transform InfraRed (ATR-FTIR) spectroscopy. The purpose of this study was to use ATR-FTIR and Raman spectra to classify distal axilla (DA) and official sampling position (OSP) leather samples and then employ univariate or multivariate analysis or both. For univariate analysis, the 1448 cm− 1 (CH2 deformation) band and the 1669 cm− 1 (Amide I) band were used for evaluating the lipid-to-protein ratio from OSP and DA Raman and IR spectra as indicators of leather quality. Curve-fitting by the sums-of-Gaussians method was used to calculate the peak area ratios of 1448 and 1669 cm− 1 band. The ratio values obtained for DA and OSP are 0.57 ± 0.099, 0.73 ± 0.063 for Raman and 0.40 ± 0.06 and 0.50 ± 0.09 for ATR-FTIR. The results provide significant insight into how these regions can be classified. Further, to identify the spectral changes in the secondary structures of collagen, the Amide I region (1600–1700 cm− 1) was investigated and curve-fitted-area ratios were calculated. The 1648:1681 cm− 1 (non-reducing: reducing collagen types) band area ratios were used for Raman and 1632:1650 cm− 1 (triple helix: α-like helix collagen) for IR. The ratios show a significant difference between the two classes. To support this qualitative analysis, logistic regression was performed on the univariate data to classify the samples quantitatively into one of the two groups. Accuracy for Raman data was 90% and for ATR-FTIR data 100%. Both Raman and ATR-FTIR complemented each other very well in differentiating the two groups. As a comparison, and to reconfirm the classification, multivariate analysis was performed using Principal Component Analysis (PCA) and Linear Discriminant Analysis (LDA). The results obtained indicate good classification between the two leather groups based on protein and lipid content. Principal component score 2 (PC2) distinguishes OSP and DA by symmetrically grouping samples at positive and negative extremes. The study demonstrates an excellent model for wider research on vibrational spectroscopy for early and rapid diagnosis of leather quality.
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    Validity and reliability of Raman spectroscopy for carotenoid assessment in cattle skin
    (Elsevier BV, 2021-09) Mehta M; Naffa R; Zhang W; Schreurs NM; Waterland M; Cooper S; Holmes G
    Carotenoids are powerful antioxidants capable of helping to protect the skin from the damaging effects of exposure to sun by reducing the free radicals in skin produced by exposure to ultraviolet radiation, and they may also have a physical protective effect in human skin. Since carotenoids are lipophilic molecules which can be ingested with the diet, they can accumulate in significant quantities in the skin. Several studies on humans have been conducted to evaluate the protective function of carotenoids against various diseases, but there is very limited published information available to understand the mechanism of carotenoid bioavailability in animals. The current study was conducted to investigate the skin carotenoid level (SCL) in two cattle skin sets - weaners with an unknown feeding regime and New Generation Beef (NGB) cattle with monitored feed at three different ages. Rapid analytical and sensitive Raman spectroscopy has been shown to be of interest as a powerful technique for the detection of carotenoids in cattle skin due to the strong resonance enhancement with 532 nm laser excitation. The spectral difference of both types of skin were measured and quantified using univariate and linear discriminant analysis. SCL was higher in NGB cattle than weaners and there is a perfect classification accuracy between weaners and NGB cattle skin using carotenoid markers as a basis. Further work carried out on carotenoid rich NGB cattle skin of 8, 12 and 24 months of age identified an increasing trend in SCL with age. The present work validated the ability of Raman spectroscopy to determine the skin carotenoid level in cattle by comparing it with established HPLC methods. There is an excellent correlation of R2 = 0.96 between the two methods that could serve as a model for future application for larger population studies.
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    Monitoring the mode of action of synthetic and natural biocides against Aeromonas hydrophila by Raman spectroscopy and chemometrics
    (BioMed Central Ltd, 2021-12) Mehta M; Liu Y; Waterland M; Holmes G
    We have investigated the mode of action of synthetic biocides, (2-(thiocyanomethylthio) benzothiazole(TCMTB), dichlorophen, (commonly used in leather industry for preservation) and natural biocides, oregano and eucalyptus oils, on Aeromonas hydrophila using Raman spectroscopy in collaboration with multivariate analysis and 2D correlation spectroscopy to evaluate whether Raman spectra acquired contained valuable information to study the action of biocides on bacterial cells. The growth of A. hydrophila in clear and outer edge zone of inhibition differ in their reaction with different biocides, which allows us to highlight the differences as a characteristic of two kinds of bacteria. Such classification helps identify oregano oil as the most effective biocide by altering clear and outer edge zone of bacteria. Standard disk diffusion assay method was used for screening biocide bacteria interactions and later analysed by Raman spectroscopy. The paper also presents the introduction of TCMTB and oregano oil into leather processing stages to examine and determine the antimicrobial effect as an application to real-world setting. Therefore, we conclude that Raman spectroscopy with appropriate computational tools constitutes a powerful approach for screening biocides, which provide solutions to all the industries using biocides including leather industry, considering the potentially harmful effect of biocides to humans and the environment.
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    The defect modes of MoS₂ : indirect double resonance Raman spectroscopy in transition metal dichalcogenides : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Nanoscience at Massey University, Manawatū, New Zealand
    (Massey University, 2022) Brooke, Samuel James
    Molybdenum disulfide (MoS₂) is a layered two-dimensional (2D) semiconducting crystal which has been a focal point of 2D materials research since the isolation and characterisation of graphene in 2005, owing to its relative abundance and a wide range of potential applications in thin film electronics, photovoltaics, information storage, and catalysis to name a few. It has unique layer-dependent electronic properties, demonstrating intense photoluminescence in single-layers and tightly-bound excitons at room temperature. The excitonic properties of MoS₂ lead to an optical phenomenon known as double resonance Raman (DRR), whereby the excited state charge carriers of excitons can interact with lattice vibrations (phonons) to scatter throughout the Brillouin zone during optical absorption and Raman spectroscopy measurements. These processes reveal signatures of electron and hole scattering dynamics that govern the complex electronic and physical properties of the material. At the nanoscale, the edges of MoS₂ have significant influence over the material’s properties, altering the electronic structure and contributing to doping effects for semiconductor performance and photoluminescence tuning. In addition, these edges (and defects) are also the sites of catalytic reactions, leading to intense efforts in literature to optimise MoS₂ as a catalyst for the production of clean hydrogen fuels. Consequently, understanding the edges of these materials is of great interest. This work demonstrates the design of a home-built low-frequency scanning Raman microscope, used to probe DRR features in MoS₂, revealing for the first time a defect-mediated indirect DRR mechanism which allows the quantification of defects and determination of zigzag and armchair edge structures in MoS₂ materials. This mechanism reveals indirect scattering pathways in the Brillouin zone, and appears to be applicable to similar materials in the family of transition metal dichalcogenides (TMDs). This indirect resonance mechanism has immediate application in facilitating the development of catalytic materials and novel nanomaterial architectures, as well as potential applications in the characterisation of exotic TMD materials and next-generation spin-valley coupled information storage devices.
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    Surface-enhanced Raman spectroscopy for environmental and biological analysis : a dissertation presented for the Doctor of Philosophy in Nanoscience, Massey University, Manawatu, New Zealand
    (Massey University, 2019) Mehta, Megha
    In recent years, extended efforts have been made to protect the environment, public and animal health from toxic chemicals that create a threat to the society. Either it is rodenticides affecting the entire forest food chain or toxicity of certain drugs on animals and humans. All such outbreaks require a faster and readily available detection method as a solution. There are numerous techniques for such toxic contaminant detection, but all require specific instrumentation and tedious sample preparation procedures. Due to the growing popularity of Surfaceenhanced Raman spectroscopy (SERS), detection becomes a simpler, easier, faster and inexpensive for multiplex detection of environmental, chemical or biological contaminants. Here, we explored a variety of SERS substrates (e.g., etched silicon, silver dendrites, and silver colloidal nanoparticles) for such detection. Our results demonstrate that colloidal nanoparticles combined with an omniphobic substrate, known as slippery infused porous substrate (SLIPSERS) has the potential for detection of rodenticides and anesthetic drugs in simple and complex biological matrices. This research explores the diversity of this method as well as how it behaves differently in different environments responsible for surface enhancement by substrate characterisation. An initial experiment was performed on Rhodamine 6G as a test analyte using SLIPSERS which give an excellent limit of detection down to picomolar level concentration. Therefore, the method was further applied for the detection of rodenticides – brodifacoum and sodium monofluoroacetate in aqueous solution and milk and lidocaine hydrochloride in aqueous and deer antler velvet. The results indicate that SLIPSERS and SERS are capable of highly sensitive detection, characterisation, and quantification of toxic analytes in the environment that pose a threat to society. Moreover, for the first time, the SLIPSERS method has been used for detection and quantification of such analytes quickly and accurately.
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    The Raman spectroscopy of ionic liquids : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Chemical Physics at Massey University, New Zealand
    (Massey University, 2007) Swanson, Adam James
    Raman and infrared spectra were recorded for the ionic liquids [CH3N(C4H8)Bu]+[(F3CSO2)2N]-, [Et3NH]+[(octyl)PO2H]-, [Bu4N]+[(hexyl)PO2H]-, and [Bu4P]+[(octyl)2PO2]- and was compared to spectra calculated by Gaussian 03 using the density functional theory method B3LYP. The experimental and calculated spectra were found to be very similar, indicating that no underlying anomalous effects were perturbing the vibrational modes. The peaks of the experimental and calculated Raman and infrared spectra were found to be broad and intertwined, because of the close proximity of numerous vibrational bands. The differential and absolute scattering cross sections of selected bands of the ionic liquids were determined using a method of comparing the area of the ionic liquid’s peak to standards of known cross section (cyclohexane, carbon tetrachloride, benzene, dichloromethane, and acetonitrile). Differential and absolute cross sections were determined experimentally at wavelengths 416 nm, 487 nm, 514 nm, 532 nm and 633 nm. A-term plots were constructed with these results to obtain the coupling constant and the effective excited state energy. These parameters allowed the calculation of the differential and absolute scattering cross sections at any wavelength. This project is the first in a series of investigations to determine the electron transfer rate of ionic liquids and determine their suitability as materials in new devices.
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    The synthesis and spectroscopy of dipyrrins and their metal complexes : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Chemistry, Massey University
    (Massey University, 2012) McLean, Tracey Maree
    Dipyrrin ligands can be considered as ‘half-porphyrins’. They absorb light in the visible region due to a strongly allowed π-π* transition. With the energy crisis being one of the most important issues of our time, the strong absorption in the visible region endows dipyrrinato complexes with promise in solar energy conversion applications. The focus of this project was to undertake some fundamental synthesis and spectroscopy of dipyrrin ligands and dipyrrinato complexes for their applications in photochemical devices. The well-known characteristics of Ru(II)-bipyridine chemistry were combined with the light absorbing properties and synthetic versatility of dipyrrin ligands to prepare and test a range of Ru(II)-dipyrrinato-bipyridine complexes as dyes for applications in dye-sensitised solar cells. The preliminary results of the solar cell measurements show evidence that the Ru(II)-dipyrrinato-bipyridine complexes show promise as light harvesters in solar energy conversion applications. A series of Re(I)-dipyrrinato complexes has also been designed and prepared for potential applications as catalysts in carbon dioxide reduction. Metallodipyrrin complexes also exhibit strong exciton coupling. A library of transition metal dipyrrinato complexes has been prepared to investigate the exciton interactions in dipyrrin systems. Understanding the exciton interactions in dipyrrin systems and the ability to control the exciton interactions are desirable for improving the solar energy conversion efficiency of dye-sensitised solar cells containing Ru(II)-dipyrrinato-bipyridine complexes as the dye. Raman spectroscopy and more specifically resonance Raman, as a technique for probing the excited state of dipyrrinato complexes, has largely been overlooked in the literature. Therefore the spectroscopy aspect of this thesis has a central focus on the Raman spectroscopy of dipyrrins, including the first full characterisation of dipyrrin ligands by Raman spectroscopy at a variety of wavelengths (visible and near infrared). Strong resonance enhancement was observed for the dipyrrin ligands, which lays the foundation for fundamental single-molecule SERS studies but also for a broad range of bioanalytical applications.