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Title: RF sputter deposited silver/silver oxide biomaterial thin films with antimicrobial and bio-photonic enhancing properties
Author: Tsendzughul, Nathaniel Terver
ISNI:       0000 0004 9352 1779
Awarding Body: University of the West of Scotland
Current Institution: University of the West of Scotland
Date of Award: 2018
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Research at the frontiers of knowledge aimed at producing viable, efficient and stable visible light activated photocatalyst with many potential applications has been ongoing. Some possible areas of applications of photocatalysts include antimicrobial and surface enhanced bio-photonic bacterial component identification. Cutting edge microbiology requires rapid bacteria component identification for prevention and early commencement of infection management. Recently, microbial resistance to multiple antibiotic therapies and the emergence of superbugs has been a significant challenge in the prevention and control of infection. Titanium dioxide the most researched and utilised photocatalyst has many advantages but is activated using visible light. Researchers have made several attempts to activate titanium dioxide in the visible such as dye sensitisation, doping and composite formation using metals, metal oxides and non-metals. Surface enhancement for Raman bacteria component identification such as surface-enhanced Raman spectroscopy (SERS), tip-enhanced Raman spectroscopy (TERS), and oblique angle deposition (OAD) is both expensive and complicated. Radiofrequency magnetron sputtering has been used to produce visible light activated transparent silver/silver oxide biomaterial thin films with very high antimicrobial efficacy and bio-photonic properties. The bandgap and film morphology were tuned using the oxygen flow rate and forward deposition power. Structural characterisation conducted using x-ray diffraction (XRD) and radial distribution function (RDF) reveals that the thin films are a mixture of silver oxides having Ag, AgO, Ag2O and Ag4O4 in the microstructure and are polycrystalline with crystallite sizes ranging from 2.45 to 31.30nm and have high nanoparticle clusters within small radii. Silver ion release on the films monitored in water and saline solutions indicated a sustained release of silver ions for up to 24hours with the ion release higher in water (maximum of 16.1ppm) compared to saline solution (maximum of 3.79ppm). Scanning electron microscopy of the thin films revealed a columnar growth mode. Optical characterisation confirmed optical bandgaps ranging between 2.35 to 3.15eV indicating that the silver oxides are activated in the visible spectrum of the electromagnetic radiation. A transmission of up to 83% of incident light, absorption between 420 to 650nm wavelength of light incident on the films showing the occurrence of surface plasmon resonance and a variation in refractive index in the wavelength range covered, confirming surface enhancement on the thin films which has been used to identify components of gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) bacteria. The x-ray photoelectron spectroscopy (XPS), high-resolution spectra of the films, indicated the presence of Ag3d3/2 and Ag3d5/2 binding energies for AgO at about 367.4eV and Ag2O at about 367.6eV respectively and silver Ag at a binding energy of 373.6eV. Oxygen O1s, high resolution spectra, indicated the presence of binding energies at 528.84eV and 528.36eV corresponding to AgO and Ag2O respectively and hydroxyl (531.25eV), superoxides (531.94eV) and atmospheric oxygen (530.52eV) which are products of photocatalysis. The research confirmed 100% microbial cell deaths of two gram-negative (Escherichia coli, Pseudomonas aeruginosa) and two gram-positive (Staphylococcus epidermidis and Staphylococcus aureus) bacteria within 5 and 25 minutes respectively on exposure to silver oxide films using killing curve measurements more efficient than copper and its compounds reported of 99.9% contact killing of bacteria within 2hours. The current finding opens the door to further the development of visible light-activated antimicrobial surfaces and rapid bacteria component identification. This research has produced a monolithic visible light activated transparent antimicrobial and bio-photonic biomaterial photocatalyst
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available