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Abstract: The local and systemic dissemination of implant-related derivatives into the body is of great interest to human health. Biological exposures of metal micro/nano-particles, complexes and soluble ions, generated as a consequence of in-service degradation of metallic prosthetics, can result in severe adverse tissues reactions. However, individual reactions are highly variable and are not easily predicted, due to in part a lack of understanding of the properties of the metalstimuli which dictates cellular interactions and toxicity. However, interrogating ultra-dilute metals within fragile, hydrated biological tissues without influencing the native physical and/or chemical composition is challenging. Therefore, a drive for more advanced characterisation techniques of the exogenous metallic particles is required. Here, synchrotron-based X-ray fluorescence spectroscopy (XRF) and X-ray absorption near edge structure (XANES) were deployed to investigate the quantitative spatial distribution and local chemistry of implant-related metal particles within soft tissues. Analytical and experimental steps were outlined and improved when using XRF for greater accuracy in quantification. This included the implications of the matrix composition, the effects of saturation and how the instability in the flux and beam profile affected the measurement. Two post-analytical algorithms were generated to reduce the effects of image artefacts observed frequently in micro-focus XRF images. These methodological advances will have significant positive impact on quantitative XRF. Specifically, the quantitative XRF imaging displayed within this thesis, combined in a multi-institution research effort, influenced the future use of specific metallic implants. The chemistry of exogenous implant-related particles was also investigated, for the first time, using a XANES mapping approach. This enabled twodimensional chemical imaging at a high spatial resolution, allowing superior chemical discrimination of small, isolated, heterogenous features. This method highlighted the unreported variability in metal chemistry associated with orthopaedic implants, which may alter the perceived toxicity of implant derivatives. The results shown within this thesis outline the advantages of using a XANES mapping approach over conventional spectroscopy methods and should be considered when interrogating chemical species of metals in biological environments. Finally, a novel approach to co-locative analysis between exogenous metal particles and the underlying cellular content was developed using a lanthanide-antibody conjugate with XRF. This allowed simultaneous imaging of the native elemental distributions and biological epitopes. The development of this imaging modality is promising for understanding spatial relationships between such components. Collectively, advances within these interrogation methods applied to implant- related products will ultimately help our understanding of associated immunological responses and will generate more appropriate biological exposure models. Additionally, the advantages reported from the development of these techniques can be applied to an array of samples types in many areas of science.

Open Access

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Abstract: Background: Chemical imaging of the human brain has great potential for diagnostic and monitoring purposes. The heterogeneity of human brain iron distribution, and alterations to this distribution in Alzheimer’s disease, indicate iron as a potential endogenous marker. The influence of iron on certain magnetic resonance imaging (MRI) parameters increases with magnetic field, but is under-explored in human brain tissues above 7 T. New Method: Magnetic resonance microscopy at 9.4 T is used to calculate parametric images of chemically-unfixed post-mortem tissue from Alzheimer’s cases (n = 3) and healthy controls (n = 2). Iron-rich regions including caudate nucleus, putamen, globus pallidus and substantia nigra are analysed prior to imaging of total iron distribution with synchrotron X-ray fluorescence mapping. Iron fluorescence calibration is achieved with adjacent tissue blocks, analysed by inductively coupled plasma mass spectrometry or graphite furnace atomic absorption spectroscopy. Results: Correlated MR images and fluorescence maps indicate linear dependence of R2, R2* and R2’ on iron at 9.4 T, for both disease and control, as follows: [R2(s−1) = 0.072[Fe] + 20]; [R2*(s−1) = 0.34[Fe] + 37]; [R2’(s−1) = 0.26[Fe] + 16] for Fe in μg/g tissue (wet weight). Comparison with Existing Methods: This method permits simultaneous non-destructive imaging of most bioavailable elements. Iron is the focus of the present study as it offers strong scope for clinical evaluation; the approach may be used more widely to evaluate the impact of chemical elements on clinical imaging parameters. Conclusion: The results at 9.4 T are in excellent quantitative agreement with predictions from experiments performed at lower magnetic fields.

Open Access

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Abstract: We have determined the chemical speciation of dissolved sulfur and the sulfur concentration at fixed oxygen and sulfur fugacities for a wide range of silicate melt compositions (from Fe-rich basalt to dacite). Each melt was equilibrated at 1300 °C and 1-atmosphere pressure at oxygen fugacities (fO2) between −1.67 and +1.6 log units relative to the Fayalite–Magnetite–Quartz (FMQ) buffer and absolute sulfur fugacities between −5.1 and −1.2 log units. The fO2 and fS2 of the experiments were controlled by using gas mixtures of CO–CO2–SO2. The speciation of sulfur in the quenched glasses was determined using both X-ray Absorption Near-Edge Spectroscopy (XANES), and from the dependence of equilibrium sulfur concentration on the fS2/fO2 ratio measured by secondary-ion mass spectrometry (SIMS) and electron microprobe. The speciation of dissolved sulfur in each melt undergoes an abrupt transformation from S2− to S6+ with increasing fO2, and this transition is shifted ∼0.5 log units higher in fO2 as melt FeO concentration increases from ∼5 wt% to ∼18 wt%. Since sulfide concentrations at constant fO2 and fS2 are consistently greater for more FeO-rich melts, the compositional effect on speciation may be explained by the well-known sensitivity of the sulfide capacity ( CS2− ) of the melt to FeO concentration. S6+/S2− ratios for the glasses exhibit a linear relationship with Fe3+/Fe2+, indicating that the redox couples for iron and sulfur can be directly related to one another. We used thermodynamic data to model the interrelationship between Fe and S oxidation states in terms of the equilibrium FeS+8FeO1.5=8FeO+FeSO4 Fitting the data to our experiments at 1300 °C we obtained the following expression for the temperature-dependence of speciation: log⁡(S6+S2−)=8log⁡(Fe3+Fe2+)+8.7436×106T2−27703T+20.273 This equation fits the data for all our compositions and is also consistent with earlier results at 1050 °C and 950 °C. We used the interdependence of S and Fe oxidation states to infer electron transfer between Fe2+ and S6+ during quenching of glasses from Mauna Kea, Hawaii. The effect is sufficient to cause significant overestimation of equilibrium Fe3+/ΣFe in natural glasses and corresponding overestimate of fO2 by about 0.8 log units. Glasses equilibrated under the most oxidizing conditions (containing S6+ only) have equilibrium S concentrations that are negatively correlated with their mole fractions of tetrahedral (Si + Ti) cations.

Open Access

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Abstract: This study aims to highlight discrepancies between experimental and simulation linked to the mechanisms of Mo and V adsorption onto ferrihydrite (FHY) nanoparticles. We have measured adsorption capacities and uptake efficiencies and then fitted and compared these with outputs from various geochemical and adsorption models that were run as a function of pH, surface area (SA) and ferrihydrite particles size distributions. Our results revealed that the experimental data for the Mo system could be fitted very well, but this was not the case for the V system, when a model default value for the SA of FHY of 600 m2 g−1 was used. The discrepancy in the results for the V system can be explained by the lack of specific V species and/or associated constants in databases and variation in software versions, which change the outputted chemical species. Our comparative results also confirm that any experimental variables used as modelling inputs need to be checked carefully prior to any modelling exercises.

Open Access

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Abstract: We report the fabrication of low-loss, low temperature deposited polysilicon waveguides via laser crystallization. The process involves pre-patterning amorphous silicon films to confine the thermal energy during the crystallization phase, which helps to control the grain growth and reduce the heat transfer to the surrounding media, making it compatible with CMOS integration. Micro-Raman spectroscopy, Secco etching and X-ray diffraction measurements reveal the high crystalline quality of the processed waveguides with the formation of millimeter long crystal grains. Optical losses as low as 5.3 dB/cm have been measured, indicating their suitability for the development of high-density integrated circuits.