Light-Activated Antimicrobial Surfaces Containing Quantum Dots for the Prevention of Hospital-Acquired Infections

This thesis details the development of effective light-activated antimicrobial polymers for use in healthcare environments, with the aim of reducing hospital-acquired infections (HAIs). The overuse and misuse of antibiotics is the most important factor that has led to increased incidence of multi-drug resistant HAIs. In the hospital setting where there is an abundance of immunosuppressed patients and often hygiene protocols are not strictly followed, HAIs can spread quickly, leading to increased length of hospital stay, morbidity and mortality and high healthcare costs. Self-disinfecting surfaces can reduce the incidence of HAIs by reducing the levels of bacteria on frequently touched hospital surfaces that serve as bacterial reservoirs, thus reducing the risk of HAI transmission. Quantum dots (QDs), extremely small nanoparticles that exhibit unique size-dependent properties, combined with photosensitisers display potent strong bactericidal activity upon incorporation into polymer surfaces. When irradiated under ambient white light, polymer surfaces induce the lethal photosensitisation of a range of Gram-positive and Gram-negative bacteria through the production of reactive oxygen species (ROS). ROS cause irreversible damage leading to cell apoptosis and death by attacking bacterial cells in a non-specific fashion thus making the development of resistance unlikely. Polyurethane substrates were impregnated with QDs and photosensitiser dye (crystal violet) using a modified version of the simple and easily scalable dipping procedure known as the “swell-encapsulation-shrink” technique. Solely cadmium-free, indium-based QDs were used in this study, thereby circumventing issues regarding toxicity arising from the release of cadmium ions from traditional, commonly prepared QDs such CdTe, CdSe and CdS. Materials were characterised using techniques such as UV-Vis absorbance spectroscopy, fluorescence spectroscopy and transmission electron microscopy. The prepared polymer substrates were activated under white light conditions mimicking those used in the hospital (~500 – 6000 lux). In order to deduce the photochemical pathway responsible for light-activated antibacterial activity, whether Type I, Type II or both, the antimicrobial surfaces were tested in a series of microbiological assays using specific ROS inhibitors and quenchers. The surfaces were tested against a range of nosocomial pathogens including Escherichia coli, Staphylococcus aureus, epidemic methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa. The novel materials described in this thesis demonstrate very strong self-disinfecting properties even under low light levels, demonstrating their potential for use in hospitals to reduce HAIs without the use of antibiotics