Gold Nanorod-Functionalised Surfaces for the Photothermal Elimination of Bacteria

Abstract

Implant-associated infections constitute a significant limitation to the use of medical implants, and the development of alternatives to conventional antibiotics for prevention and/or treatment of these infections would have a great impact on the future use of medical implants. In this thesis, a strategy for utilising gold nanorodfunctionalised surfaces that are irradiated with near-infrared (NIR) light in order to photothermally eliminate bacteria from the surfaces has been developed and evaluated. Gold nanorods were synthesised through a seed-mediated synthesis procedure, and subsequently surface assembled onto titanium and glass substrates via chemisorption using (3-mercaptopropyl)trimethoxysilane as a linker. The antimicrobial activity of the gold nanorod-functionalised surfaces upon irradiation with near-infrared light was evaluated through in vitro studies with Staphylococcus epidermidis as a representative bacterial species commonly causing implantassociated infections. From the in vitro study performed with the gold nanorodfunctionalised glass an evident antimicrobial activity was observed, where the gold nanorod-functionalised glass irradiated with NIR light exhibited 40-50% more dead bacteria than the control groups. The results highlight that the principle of using surface assembled gold nanorods to photothermally eliminate bacteria upon irradiation with NIR light is a possible alternative to conventional antibiotics in the fight against implant-associated infections. No evident antimicrobial activity could be observed from the in vitro studies performed with the gold nanorod-functionalised titanium upon exposure to NIR light. The lack of antimicrobial activity was attributed to two main factors; a red-shift occurring in the localised surface plasmon resonance frequency of the gold nanorods due to changes in refractive index of the local environment arising once assembled on titanium, and the titanium substrate having a plasmon damping effect on the gold nanorods. Based on the results from all the in vitro studies performed during the project, no apparent toxic effect of the gold nanorods themselves could be noticed, showing promise for potential future biological applications.