Synthesis and Characterization of Gold Nanostructures for Healthcare Applications

Functionalized gold nanostructures with well-defined geometry and controlled optical properties can potentially play an important role in healthcare applications such as biosensing, photocatalysis, drug delivery, photothermal therapy and imaging due to their unique properties. This thesis aims to develop a novel Au nanostructure for healthcare applications, using an effective synthesis protocol in order to produce a suitable Au nanostructure with NIR absorption, high thermal stability and low toxicity. Well-controlled, reproducible Au nanostructures with NIR absorption spectra, including gold nanoparticles (NPs), nanorods (NRs), nanobipyramids (NBPs) and nanotriangles (NTs) have been synthesised using a wet-chemical synthesis approach and characterized using dynamic light scattering and transmission electron microscopy. The optical and plasmonic properties of the Au nanostructures were investigated using uv-vis spectroscopy, finite element modelling (FEM) and STEM/low-loss EELS analysis was employed. EELS results exhibited good agreement with uv-vis spectra and FEM modeling and revealed the size- and shape-dependent plasmonic properties and showed that NIR absorption can be altered by increasing the curvature of particles. The thermal stability of Au nanostructures, which is important for photothermal therapy applications, was investigated using in-situ TEM heating. It was found that the thermal stability of Au nanostructures decreased in the order : AuNPs > AuNTs > AuNBPs > AuNRs. The proposed useful temperature ranges whereby heating does not significantly affect the optical properties were up to 100ºC, 200ºC, 800ºC, for CTAB-capped AuNRs, CTAB-capped AuNBPs and CTAC-stabilized AuNTs, respectively. The thermal stability of particles was increased by surface functionalization of the NPs from a CTAB coating, through a PSS coating and finally to a silica coating. Thermal deformation arose from curvature-driven surface diffusion. Finally, the biocompatibility of Au nanostructures, in terms of the effect of size, morphology, and surface coating, was investigated by their electrochemical interaction with a model membrane based on DOPC on an Hg/Pt electrode. Only smaller Au nanostructures with a diameter of ca. 20 nm exhibited a significant interaction. However, the effect of the surface coating was found to be a more significant effect with the order of interaction with the model membrane ranging from CTAB > PSS > CTAC > citrate coated Au nanostructures. Thus overall, potential biocompatible candidates for healthcare applications are proposed to be citrate-, PSS- or silica-coated gold nanostructures with NIR absorption and dimensions larger than approximately 20-25 nm.

Influences of Ga3+ doping content on microstructure and interfacial polarization in colossal permittivity GayNb0.025Ti0.975-yO2 ceramics

Colossal permittivity (CP) materials, particularly co–doped TiO2 ceramics, have garnered significant attention for their potential in high–performance ceramic capacitors. However, understanding the origin of CP remains a challenge, with the role of doping ratios between acceptor and donor ions largely underexplored. This study addresses this gap by systematically investigating the effects of Ga3+ concentrations on the microstructure and CP of GayNb0.025Ti0.975-yO2, prepared via the solid–state reaction method. The sintered ceramics exhibited a dense rutile TiO2 phase with increasing grain sizes and oxygen vacancies. Notably, CP values as high as 105 were achieved at Ga3+/Nb5+ ratio  1.0 eV. Ceramics with 5% Ga3+ doping showed diminished CP due to the absence of semiconducting grains. The findings suggest that CP originates from the internal barrier layer capacitor. This study not only elucidates the crucial role of doping ratios in tailoring CP but also establishes a pathway for developing advanced dielectric materials with superior performance for ceramic capacitors

Sugarcane waste-derived carbon quantum dots–chlorophyll/bacterial cellulose composites for solar-driven antibiotic degradation

Abstract A bio-based CQDs–Chl/BC nanocomposite (NCs) was synthesized from sugarcane bagasse, sugarcane leaves, and bacterial cellulose (BC) via a green bio-construction strategy to enhance antibiotic removal through a synergistic adsorption–photocatalysis mechanism. CQDs were prepared by a microwave-assisted method, Chl was extracted from sugarcane leaves, and BC provided a renewable support matrix. The incorporation of CQDs and Chl broadened visible-light absorption and improved charge transfer, as confirmed by UV–Vis spectroscopy, FTIR, PL, TEM–EDS, and XPS analyses. Förster resonance energy transfer (FRET) and photoinduced electron transfer (PET) minimized charge recombination, while LC–MS spectra of degradation products identified transient intermediates of ciprofloxacin (CIP) and oxytetracycline (OTC), validating the proposed photocatalytic pathway. Under solar irradiation, the CQDs–Chl/BC NCs achieved near-complete degradation of CIP (98.83 ± 0.46%) and OTC (98.59 ± 0.50%) at 2 mg/L within 180 min, outperforming CQDs/BC (k = 0.01044 min−1) and Chl/BC (k = 0.01109 min−1), with a pseudo-first-order rate constant of 0.02642 min−1. The composite also exhibited strong adsorption capacity, excellent recyclability, and structural stability, retaining 67.7% efficiency after five cycles, with FTIR and XPS confirming integrity post-reuse. Biotoxicity assays revealed no intrinsic antibacterial activity, underscoring its environmental safety. The novelty of this study lies in the dual biomass valorization approach, where CQDs from sugarcane bagasse and Chl from sugarcane leaves were synergistically integrated with BC to couple adsorption, photosensitization, and advanced charge-transfer processes in one photocatalyst. These findings confirm the potential of CQDs–Chl/BC NCs as a sustainable solution for visible-light-driven wastewater treatment