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(2021)ThesisImpedance cellular biosensors are amongst a promising type of label-free technologies in providing ongoing insights into physiological function of cells over a period ranging from several minutes to several days. However, detection of a highly specific biomolecular event using traditional impedance assays is technically challenging. The nature of impedance signal relies on the changes in the local ionic environment at the interface, providing many biochemical events at once lacking biomolecular specificity. The next decade is then likely to witness an interest in using developed impedance assays. Impedance-quartz crystal microbalance (QCM), impedance-surface plasmon resonance spectroscopy (SPR), and impedance-optical microscopy are the hybrid approaches that have been employed in the field. Integrating impedance biosensors to another sensing method, in particular new microscopies that enable identification of cellular structures and processes with a high degree of specificity, enhances the potential of traditional assays by providing additional relevant information. Herein an effective approach for accurate interpretation of impedance signal is presented. By development of optical/electrical multi-electrode chips, light was utilized for direct visualization of cell structures and processes on the surface of the microelectrode. It was essential to achieve both high throughput electrical results and high-resolution microscopy images to detect the transient changes inside the cells. Therefore, the strategy of simultaneous dual sensing was developed in three main steps. For the establishment of a reliable dual sensing readout, it was essential to use a commercial biosensing device (known as xCELLigence) in the first step. This approach enabled to compare the electrical results of developed dual biosensing device and a commercial device (as a high throughput assay for electrical measurement of subtle changes within the cell monolayer). The highly sensitive measurement of commercial device also made it possible to investigate the ongoing mechanism behind receptor/ligand activation. The signalling pathway was determined by using different pharmacological inhibitors. In a separate parallel experiment, fluorescence microscopy was used to visualise the specificity of histamine/HeLa cell interaction which was coupled to intracellular calcium rise. While it is assumed these two processes are connected, this could not be determined definitively by the sole biosensing device application. In the second step it was necessary to develop a setup with the capability of data acquisition in both the high throughput electrical setup and high-resolution fluorescence microscopy on a single platform. The first material of choice for the fabrication of this biosensor was ITO because of its electrical conductivity and optical transparency. It was shown that contribution of cells to the overall signal on the surface of ITO depends on the parameters including sensing area and width of microfingers. Furthermore, comparing the ITO results with the identical gold microelectrode revealed the ITO severely lacked sensitivity compared to gold. This was due to a better penetration of the electric field within the cell layer on the gold surface. The addition of a viewing window made a dual sensing readout possible on the gold microelectrode. Finally, the finding were used to maximize the system efficiency and precision for the detection of minute change of cells to the drug. The reduction of the microfingers down to the single cell level led to a more efficient distribution of electric field within cell monolayer. A high density of gold electrode arrays also increased the chance of individual cells blocking the current which was desirable. The added value of the developed biosensor was illustrated by studying GPCR activation in a more thorough manner using simultaneous fluorescence microscopy. The simultaneous optical/electrical experiment was performed as a powerful approach to translate specific intracellular biomolecular event contributing to the morphological changes in cell/drug interaction.
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(2020)ThesisClassification methods capable of identifying signals or groups of samples, whose geochemical composition is affected by dispersion from mineralisation, are critical in regional and local scale mineral exploration projects. This study compares various population and spatial fractal classification models with several new models to identify populations associated with VMS-style mineralisation in regional till geochemical data from Sweden and both Cyprus-style VMS deposits and anthropogenic contamination in soil data from Cyprus. The new models include concentration-distance from centroids (C-DC), concentration-concentration (C-C), and simulated-based and category-based fractal models applied to representative and simulated samples (CF-R and CF-S). The precision (stability) of the models and spatial uncertainty were tested using Monte Carlo and sequential Gaussian simulations, as well as the effects of pre-processing of the geochemical data. In the Sweden till data, CF-R, spectrum-area (S-A) and the related simulated (SS-A) approach proved more effective in delineating known VMS mineralisation in some regions than single element patterns for mineralisation-related metals such as Cu. In Cyprus, both established and new fractal approaches were marginally more effective at separating areas of known mineralisation (including the major deposits) against a backdrop of generally elevated levels of VMS-related elements in the pillow basalts and underlying sheeted dyke complex. The C-C and C-DC approaches define a contiguous zone whose multivariate patterns are closely linked to either geogenic dispersion or anthropogenic contamination including historical contamination that cuts across current land use zoning. Population or spatial features in geochemical data delineated by different fractal approaches are dependent on the mathematical basis of specific fractal models. Application of a wide range of fractal methods, along with assessment of uncertainty in sample classification and stability of spatial patterns, provides a firmer basis for quantifying the processes and features that control element distributions in regional geochemical data. It also provides criteria for selection of the most effective combination of data pre-processing and fractal modelling to extract desired features or signals in the data.
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(2021)ThesisLead-based perovskites have been one of the hottest research topics due to its excellent optoelectronic performance, such as outstanding absorption coefficients, tuneable bandgap≈1.6 eV, long carrier diffusion length, high defect tolerance, convenient solution processability, and good charge carrier mobility. It has been widely studied to be applied on solar cells, photodetector, and light emitting diode. However, there are still some challenges on widely applying lead halide perovskites: nature toxicity of lead, unreliability in moisture and light environment, poor stability to heat and oxygen, and the existed self-degradation pathway. To overcome these problems, we fabricated lead-free perovskites Cs2CuBr4 single crystals and characterized the perovskites from structure, optical properties, and electrical device performance. The solution-evaporated method was introduced to grow Cs2CuBr4 single crystals. The prepared perovskites exhibit 2D orthorhombic structure and blue-green luminescence with the PL peak at 460nm. The bandgap is ~1.74 eV, which is relatively ideal for optoelectronic devices. Moreover, the resistive switching devices based on Cs2CuBr4 single crystals thin films were also fabricated, showing the excellent reversible threshold switching behaviour and robustness of 2D Cs2CuBr4 material. We believe this thesis significantly demonstrated that lead-free Cs2CuBr4 perovskites have potential to play an important role in the next-generation optoelectronic devices.
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(2021)ThesisImprovements in liquid lithium-ion battery electrolytes using of metal organic frameworks (MOFs) as a functional decoration on polymer membrane separators were investigated using a combination of experimental and theoretical methods. Zirconium-based MOF UiO-66 was introduced to the polymer support using the mixed matrix membrane (MMM) method. The method allowed the one-step manufacture of a robust, mechanically pliable polymer-MOF membrane composite of high MOF loading. MOF-MMMs imparted improved electrochemical behaviours such as a widened potential operating window, near-unity transference number, and increased presence of solid electrolyte interphase (SEI) components crucial to battery performance. Density functional theory (DFT) calculations were also performed to provide insights regarding electrolyte solvation in the presence of MOF. A simple dip-coating technique was utilised to modify the surface of the MOF-MMMs with polydopamine (PDA) for further improvement of the electrochemical properties. Increased transference numbers, as well as stability during rate cycling, were observed with the resulting PDA-MMM owing to the improved electrode/electrolyte interface. However, surface analyses using x-ray photoelectron spectroscopy (XPS) showed that there are reduced amounts vital SEI components compared to the original MOF-MMM support. The last section further explores the versatility of UiO-66 and tackled the preparation of gel polymer electrolytes (GPEs) decorated with UiO-66 via phase inversion technique. Using the phase inversion method, the fabricated GPE contained pores from both polymer substrate and the intrinsic pores of the 3D nanomaterial for improvement of electrochemical properties. It was demonstrated in this work that the MOF GPE is equally inert and suitable in ether or carbonate-based electrolytes. Overall, this study demonstrated the versatility of UiO-66 metal organic frameworks for use as a functional nanofiller for electrolyte membranes. With the use of inexpensive membrane fabrication methods, the composites obtained are viable for lithium-metal battery applications. Similarly, insights drawn can provide a springboard towards future study of MOF-based electrolytes.
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(2021)ThesisParental warmth/affection (e.g., terms of endearment, physical affection) is an essential component of healthy, securely attached parent-child relationships. Strong parent-child relationships serve as buffers against psychosocial stressors and facilitate healthy empathy development in children. In particular, warmth/affection is thought to promote affective empathy development (i.e., being able to feel what others feel) via the modelling of emotional expressions and prosocial behaviour. Lower levels of parental warmth have been linked with a host of negative outcomes for children and in some cases contribute to the development and worsening of severe psychopathology (e.g., Conduct Problems with co-occurring Callous-Unemotional traits in children). Given these outcomes, parental warmth/affection is increasingly being incorporated as a treatment target among emerging interventions. It is therefore critical that there are reliable and valid ways to measure warmth/affection. However, the availability of comprehensive and ecologically valid methods that are designed for in-vivo clinical use are limited. The Warmth/Affection Coding System (WACS) was explicitly developed to have clinical utility as a novel observational coding system to assess both verbal and non-verbal warmth/affection in real time. The present study sought to establish the preliminary reliability and validity of the WACS in a sample of 172 mothers and their young children (M = 3.7 years, SD = 1.23) referred for externalising problems to two outpatient clinics in Sydney, Australia. This program of research: i) provides a conceptual overview of warmth/affection and limitations of current assessment approaches (Part I), ii) chronicles the development and refinement of the WACS (Part II), and iii) outlines the preliminary reliability and validity of this coding system (Part III). Results provided support for the reliability of WACS scores and adds to the few existing coding systems that capture both microsocial and global assessments of verbal and non-verbal warmth/affection. The validity of non-verbal WACS scores was supported, while verbal WACS scores largely did not correlate as expected with other measures. These findings have implications for advancing methods for assessing parental warmth/affection and provide an important first step in establishing the preliminary reliability and validity of the WACS. Future directions for the refinement of the WACS are also discussed.
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(2021)ThesisTitanium oxide (TiO2) is one of the most widely studied dioxides as its specific surface properties, which makes it an ideal candidate for pollutant reducing and water splitting. TiO2 thin film has gained an increasing concern for transparent electrodes, photovoltaic application and resistive switching memory devices. Research for the highly reduced TiO2 thin film for transparent electrodes has been conducted in some research groups; however, the cost and technology present a challenge to the widespread use of TiO2 transparent electrodes. As an n-type semiconductor, TiO2 has been recognized as an ideal switching interlayer in resistive switching memory. The new challenge derived from Moore’s crisis and von Neuman architecture present obstacles to the further improvement of computer performance. Memristor, as its in-memory computing, can be applied in the next generation computer to reduce the cost and increase operational efficiency. Furthermore, till now, fabrication freestanding TiO2 with a near 100% stable (001) anatase surface is still a challenge. In this research thesis, I firstly reported a convenient way to produce highly conductive TiO2 thin film that can be used to replace ITO and FTO for the transparent electrode application. Subsequently, a TiO2/Nb: STO memristor was fabricated to realize the high-density data storage, arithmetic logical operation and neuromorphic computing, and then a state-of-the-art method was introduced to fabricate freestanding anatase TiO2 thin film with near 100% (001) surface.
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(2021)ThesisThe expression levels of immune checkpoint inhibitor biomarkers including programmed death-ligand 1 (PD‐L1), cytokine lymphocyte antigen 4 (CTLA-4) and B7-homolog3 (B7-H3) can be used to identify the presence of diseases, and also show a good correlation with therapeutic outcomes. Invasive solid biopsies are used to achieve samples with immunohistochemistry assays being the detection method of choice to identify the expression levels of these biomarkers in clinical practice. These assays are qualitative or semi-quantitative due to biopsy heterogeneity. There is an unmet clinical need for quantitative detection methods that are less invasive, to improve the efficacy of treatments that are closely associated with PD-L1, CTLA-4 and B7-H3 expression levels. The detection of PD-L1, CTLA-4 and B7-H3 in whole blood is an attractive pathway for the early detection, prediction and evaluation of cancer treatment response because of its simplicity but remains almost completely unexplored. The challenge is that a limit of detection of less than picomolar must be achieved for a detection technology to satisfy the requirements of the unmet need. The purpose of this work is firstly to address the unmet need for improved conventional immune checkpoint inhibitor biomarkers detection techniques by designing an ultrasensitive quantitative biosensor based on gold-coated magnetic nanoparticles, referred to as dispersible electrodes. The research demonstrates the ultrasensitive, selective and rapid electrochemical detection of PD-L1, CTLA-4 and B7-H3 directly in whole blood. These dispersible electrodes selectively capture analytes within biofluids and upon application of a magnet, they are reassembled into a macroelectrode for electrochemical detection of the target antigen using a classic sandwich immunoassay with a detection range of nanomolar to attomolar and a response time of only 15 min. The research then focuses on how this system is capable of detecting these species in whole blood without being completely fouled by proteins. Investigations show that ‘soft protein corona’ layer forms around the antibody-modified particles, which can be resulted in lower signal intensity and greater uncertainties of dispersible electrodes but does not completely suppress electrochemistry.
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(2021)ThesisThere is currently limited theoretical understanding of the mechanisms driving Repetitive Negative Thinking (RNT) transdiagnostically, as most research has examined RNT with a disorder-specific focus (e.g., rumination in depression, worry in generalised anxiety disorder). The Impaired Disengagement Hypothesis (IDH; Koster et al., 2011) proposed a role for impaired attention-shifting in depressive rumination. However, only one published study has examined the relationship between internally-focused attention-shifting from verbal material and RNT; notably, RNT was indexed with disorder-specific measures (Beckwé et al., 2014). That is, no study has examined the link between attention-shifting and RNT assessed by a transdiagnostic measure (not contaminated by disorder-specific features). This thesis aimed to: (i) investigate whether internal verbal attention-shifting biases are related to RNT transdiagnostically, and (ii) determine the content-specificity of any such biases. Study 1 assessed RNT with disorder-specific and transdiagnostic measures, and found no evidence for a reliable relationship between RNT and slowed internal verbal attention-shifting. This study highlighted the need for validated RNT-relevant stimuli; Studies 2a and 2b developed and validated such stimuli. Study 3 used these stimuli to investigate the relationship between verbal RNT and attention-shifting performance; Bayes Factors provided evidence that elevated RNT was not associated with attention-shifting from negative RNT-relevant stimuli. Study 4 aimed to investigate whether this finding was due to modality (i.e., verbal vs. visual) mediating the relationship between attention-shifting and RNT. Given the exploratory nature of this study, its scope was reduced to depressive rumination to allow for the development of a novel in vivo measure of RNT severity across modalities. Data collection was terminated during the pilot phase owing to COVID-19. Overall, the findings of this thesis suggest that the shifting of internal verbal attention is unlikely to play a role in the maintenance of verbal RNT. However, the relationship between visual attention-shifting and imagery-based RNT remains unclear. The thesis highlights the need for precision when investigating the cognitive mechanisms of RNT, and made steps towards this by developing validated RNT-relevant stimuli and an in vivo measure of RNT.
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(2021)ThesisConcern about falling is a common and serious health concern for older people. However, older people's participation in proven interventions for reducing concern about falling remains low. Health literacy could be influential to older people’s long-term participation in health programs for concern about falling. This thesis aimed to understand the relationship between health literacy and concern about falling in community-living older people. Six studies were conducted: (i) proposed a multicomponent theoretical model on health literacy and concern about falling; (ii) conducted a systematic review and meta-analysis exploring the relationship between health literacy and physical activity; (iii) developed and validated the Falls Health Literacy Scale (FHLS), a health literacy instrument specific to falls; (iv) developed cut-points for the 30-item and 10-item Iconographical Falls Efficacy Scales (IconFES) and evaluated their construct and predictive validity to falls and reduced physical activity; (v) assessed the effectiveness of a six-week online cognitive behavioural therapy (CBT) program for reducing concern about falling; (vi) explored how health literacy affects adherence to a home-based exercise program. The main findings were: (i) health literacy is closely related to many determinants of concern about falling and greater efforts are needed to clarify the impact of health literacy on intervention adherence and decision-making of older people with concern about falling; (ii) older people with inadequate health literacy are less likely to engage in physical activity on ≥5 days per week than those with adequate health literacy; (iii) the FHLS is sensitive to levels of fall-related health literacy, with good validity in an older population; (iv) the developed IconFES cut-points were sensitive to variables associated with concern about falling and predicted fall incidence and physical activity restriction after one year; (v) online CBT is a feasible treatment method for older people, and a targeted program with a well-integrated psychoeducation module on concern about falling seems warranted to boost the therapeutic effects; (vi) education, history of falls, anxiety and neuroticism moderate the relationship between health literacy and adherence of older people to a home-based exercise program. The thesis findings elucidate key aspects of the relationship between health literacy and concern about falling in older people.
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(2021)ThesisPlanetary waves play a role in a large variety of oceanic and climate dynamics. In particular, Kelvin waves can provide rapid teleconnections from large-scale climate and weather events to remote regions of the globe. Kelvin waves may be partially responsible for linking climatic changes in Southern Ocean winds to increases in subsurface warming around Antarctica that can lead to glacial ice-melt and increases in global sea level rise. Kelvin waves may also link changes in Southern Ocean winds to increases in North Atlantic Deep Water (NADW) formation and an enhancement of the Atlantic Meridional Overturning Circulation (AMOC), which is responsible for circulating a vast amount of the ocean’s heat and nutrient content. However, the exact role of Kelvin waves in these processes is unclear. This thesis aims to further clarify the role that Kelvin waves play in these high-latitude climate processes. First, we use a suite of idealized models in order to better understand the dynamics of barotropic Kelvin waves around Antarctica. We find that super-inertial (high frequency) barotropic Kelvin waves are nearly completely scattered away from the Antarctic coastline due to a combination of coastal geometry and bathymetry. Sub-inertial (low frequency) barotropic Kelvin waves are mostly scattered away from the Antarctic coastline due to bathymetry, however a significant amount of barotropic Kelvin wave energy remains at the Antarctic coastline after one circumnavigation of the continent, enabling a gradual build-up of energy along the coast and the ability to sustain a barotropic Kelvin wave signal around Antarctica over time. Secondly, we perform a diagnostic study using theory and a range of varying resolution model simulations to quantify the amount of subsurface warming along the West Antarctic Peninsula caused by barotropic Kelvin waves via an induced bottom Ekman flow that advects warm Circumpolar Deep Water onto the Antarctic continental shelf. We find that barotropic Kelvin waves can account for a substantial amount of warming within one year, depending on the background temperature gradients and thickness of the bottom Ekman layer. Lastly, we explore the role of Kelvin waves in linking Southern Ocean wind-stress to NADW formation and the AMOC by analysing ensemble simulations from a fully-coupled ocean-sea-ice model at 1/4 degree horizontal resolution (50 vertical levels). We find first mode baroclinic Kelvin waves to propagate along a global coastal and equatorial waveguide from the Southern Ocean forcing region to the North Atlantic, where downwelling waves initiate an enhancement of the AMOC by making surface waters denser.