This thesis examines the need for new antibacterial materials to treat small colony variants
(SCVs) of Staphylococcus (S.) aureus bacteria and their parental strains. While ZnO-based
nanoparticles (NPs) activated by ultraviolet (UV) and short wavelength visible light have been
researched for their antibacterial properties, the potential benefits of incorporating UCNPs to
allow activation by near-infrared (NIR) light have been overlooked. This study aims to fill this
research gap by comprehensively investigating the synthesis and performance of ZnO-coated
lanthanide-doped upconversion nanoparticle (UCNP) composites activated by NIR light
against S. aureus SCVs and parental strains.
Furthermore, this research addresses the limited understanding of the potential risks associated
with UV emission from UCNPs used as fluorescent probes in super-resolution microscopy
(SRM). Despite extensive research on the usage of UCNPs as fluorescent probes for SRMs,
the potential cytotoxic effects of UV emission from UCNPs have not been thoroughly studied.
To advance cellular imaging techniques and ensure cellular viability, a comprehensive
investigation of UV emission from UCNPs is necessary. This thesis aims to identify and
quantify UV emission by UCNPs used in SRM and develop strategies to minimise UV
emission and mitigate potential cytotoxic effects.
These two main aims are addressed in three results chapters. The first aim, the focus of chapters
2 and 3, focuses on the synthesis UCNP@ZnO composites that can be activated by NIR light
for antimicrobial photodynamic therapy (aPDT) applications against S. aureus SCVs and
parental strains. Chapter 2 reports the synthesis and performance of these composites, showing
these materials to be effective antibacterial therapies against S. aureus SCVs, while chapter 3
improves upon the performance of these composites by careful tuning of the UCNP core and
provides enhancements to the ZnO shell composition to improve reactive oxygen species
generation and add a second mode of action in the form of silver nanoparticles. The second
aim of this research is covered in chapter 4, which reports an investigation into the UV emission
from UCNPs used as fluorescent probes in SRM. The work posits the need to understand the
UV emission properties of these UCNPs as knowledge of these and the potential for cytotoxic
effects are crucial for optimizing cellular imaging experiments and ensuring accurate and
reliable results. Chapter 4 identifies design features and compositions that can limit UV
emission, thereby minimizing the risk of phototoxicity and advancing the field of cellular
imaging.
Overall, the findings from this research have the potential to contribute to the development of
safer and more effective targeted antibacterial therapies and enhance the understanding of UV
emissions in cellular imaging techniques.Thesis (Ph.D.) -- University of Adelaide, School of Chemical Engineering, 202
