Science

Publication Search Results

Now showing 1 - 10 of 102
  • (2021) Arman, Seyedyousef
    Thesis
    Impedance 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.

  • (2020) Sadeghi, Behnam
    Thesis
    Classification 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.

  • (2021) Yao, Yuchen
    Thesis
    Lead-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.

  • (2021) Chua, Stephanie
    Thesis
    Improvements 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.

  • (2021) Prasad, Ashneeta
    Thesis
    Parental 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.

  • (2021) Yang, Ni
    Thesis
    Titanium 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.

  • (2021) Moazzam, Parisa
    Thesis
    The 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.

  • (2021) Alosaimi, Ghaida
    Thesis
    Perovskite-based photovoltaic (PV) devices are promising candidates for next-generation PV applications. However, defects that cause poor stability in hybrid perovskites create a manufacturing bottleneck. Recently, grain boundary (GBs) defects have shown dual impacts: detrimental or benign. Therefore, exploring nanoscale charge dynamics will allow us to understand these defects' physical properties to optimize device performance and long-term stability. Scanning probe microscopy (SPM) is an effective instrument for studying micro- and nano-sized structures and electronic properties. This thesis used SPM to study the photoelectric properties of three-dimensional (3D) and quasi-two-dimensional (2D) halide perovskite. Morphology-dependent charge transport is investigated with a new approach using directional illumination and SPM characterization. The nanoscale optoelectronic behaviour of 3D caesium formamidinium lead iodide (FAPbI3) and methylammonium lead bromide (MAPbBr3) with various electron transport layers (ETLs); (SnO2), (c-TiO2), and phenyl-C61-butyric acid methyl ester (PCBM)/SnO2, under indoor light is explored. The implications of perovskite GB defects and perovskite/ETL interfacial defects on the charge transport properties are identified by varying illumination direction and wavelength. The findings demonstrate that the interface and GB defects dominate device performance under indoor lighting conditions. Perovskite/SnO2 is recommended as an efficient indoor PV device. The nanoscale electronic effects of triplet state management in quasi-2D FAPbBr3 is studied. The photoelectrical properties are investigated under laser illumination and bias application. The findings indicate that the quasi-2D perovskite with naphthyl methyl ammonium (NMA+) mitigates the ion migration and enhances the charge transport through GBs. SPM results offer new insight into the physical properties of defects in layered quasi-2D perovskite for optimizing device performance. Moisture-dependent SPM characterizations are performed on open and compressed GB structures of wide bandgap (FAPbI3)0.3(FAPbBr3)0.7 perovskites. The structural and surface electrical properties are examined. The findings demonstrate that the compact-GB sample has a higher photocurrent, lower current hysteresis, and lower trap states under 60% relative humidity for 24 hours than the open-GB sample. Therefore, controlling GB structure and humidity level enhances a material’s optoelectronic properties. The SPM results shed light on microscopic observations of perovskite (PV) devices to optimize efficiency and long-term stability.

  • (2022) Nguyen, Robert
    Thesis
    Data-driven decision making is everywhere in the modern sporting world. The most well-known example of this is the Moneyball movement in Major League Baseball (MLB), which built on research by Sherri Nichols in the 1980s, but sport analytics has also driven major changes in strategy in basketball, the National Football League, and soccer. In Australia, sports analytics has not had quite the same influence in its major domestic codes. In this thesis, we develop tools to assist the analytics community in two major Australian commercial sports. For Australian Rules Football, the largest commercial sport in Australia, data was not readily accessible for the national competition, the Australian Football League (AFL). Data access is fundamental to data analysis, so this has been a major constraint on the capacity of the AFL analytics community to grow. In this thesis, this issued is solved by making AFL data readily accessible through the R package fitzRoy. This package has already proven to be quite successful and has seen uptake from the media, fans, and club analysts. Expected points models are widely used across sports to inform tactical decision making, but as currently implemented, they confound the effects of decisions on points scored and the situations that the decisions tend to be made in. In Chapter 3, a new expected points approach is proposed, which conditions on match situation when estimating the effect of decisions on expected points. Hence we call this a conditional Expected Points (cEP) model. Our cEP model is used to provide new insight into fourth Down (NFL) decision-making in the National Football League, and decision-making when awarded a penalty in Rugby League. The National Rugby League (NRL) is the leading competition of Australia’s second largest commercial sport it is played on a pitch that is 100m long and 70m wide, and the NRL have provided us with detailed event data from the previous five seasons, used in academic research for the first time in this thesis. We found that NRL teams should kick for goal from penalties much more often than is currently the case. In Chapter 4 we develop a live probability model for predicting the winner of a Rugby League game using data that is collected live. This model could be used by the National Rugby League during broadcasts to enhance their coverage by reporting live win probabilities. While most live probability models are constructed using scores only, the availability of live event data meant we could investigate whether models constructed using event data have better predictive performance. We were able to show that in addition to score differential that the addition of covariates such as missed tackles can improve the prediction. Clubs use their own domain knowledge to test their own live win probability theories with the R scripts that are provided to the NRL

  • (2022) Gautam, Shreedhar
    Thesis
    Extracellular vesicles (EVs) are phospholipid membrane bound sacs (vesicles) produced from almost all types of cells. They are found in circulation and contain the cargo biomolecules such as nucleic acids, proteins, lipids, and amino acids. EVs are involved in trafficking these biomolecules between cells and as such have the role in physiological and pathological processes. EVs are heterogenous and revealing their heterogeneity is crucial to understand their explicit physiological and pathological roles. Current isolation techniques cannot sort EVs based on their biogenesis and provides average information instead of each EVs subtype. Thus, single EVs analysis was popular and many surface protein characterization techniques are developed. But there are no techniques available for internal cargo analysis of individual EVs. The overall aim was to develop a technique to analyse internal microRNA cargo content, if possible, for single EVs, if not from the minimum number of EVs. To achieve that goal, light activated electrochemistry, a technique where focused light beam was illuminated on the semiconductor surface and make it electrochemically active was used. The surface was protected against oxidation during electrochemical reactions by grafting self-assembled monolayer of 1,8-nonadiyne. Then, silicon-based surface was patterned with polymers, antibodies, and cells using the light patterns. As a result, the first milestone to prepare light-assisted patterned semiconductor surface was achieved for our overall aim of analysing content of individual EVs. The size range of EVs is 30 to 200 nm, still very low compared to 30 µm which is the best spatial resolution achieved for light activated electrochemistry using crystalline silicon. Thus, chapter 4 developed a technique to improve the spatial resolution of light activated electrochemistry using amorphous silicon. Amorphous silicon has short diffusion length of charge carriers compared to crystalline silicon due to the defect states in band gap called as localized states. So, charge carriers are frequently trapped in these localized states leading to 60 times improvement in spatial resolution to 500 nm. But even this spatial resolution was not enough to analyse individual EVs. So, microRNA content from pool of EVs were detected using the screen-printed electrodes in a high throughput manner instead of single EVs.