Solid-Supported Gold Nanorods for Antibacterial Applications

Abstract

Biomaterials are essential in modern medicine, ensuring the quality of life of the individual by providing functions for diagnostic, therapeutic, and prosthetic purposes. However, when the surface of a biomaterial is colonised by bacteria, hard-to-treat infections can arise. The severity of biomaterial-associated infections (BAIs) stems from the ability of biofilm-growing bacteria to evade our bodies’ immune response and their high tolerance to antibiotics. The increasing incidence of antimicrobial resistant bacteria and the insufficient development rate of new antimicrobial agents are further limiting the options available for combatting these infections. In response to the pressing need for new approaches to combat BAIs, the development of antibacterial modification strategies for biomaterials has emerged as a promising alternative. This thesis explores materials based on solid-supported gold nanorods and their application as an antibacterial modification strategy utilising the nanoparticles’ photothermal heating. Material preparation protocols were developed for the surface-attachment of gold nanorods on glass and titanium, as well as for the preparation of gold nanorod gradient surfaces. The photothermal properties of the solid-supported gold nanorods were studied as a function of near-infrared (NIR) light intensity and nanoparticle surface coverage. An in vitro method for studying the antibacterial activity of the solid-supported gold nanorods under NIR irradiation was developed. The antibacterial activity evaluation was focused on the influence of the support material, the dependency on the NIR light intensity, and the effect in combination with an antimicrobial peptide (AMP).    The material preparation protocols facilitated surface-attachment of gold nanorods in a well-dispersed manner, with retained plasmon resonance characteristics on glass. By monitoring the lattice thermal expansion of the solid-supported gold nanorods with in situ X-ray diffraction, and supporting the findings with Vis-NIR spectroscopy and electron microscopy characterisation, a relationship between the NIR light intensity, the gold nanorod temperature, and the onset of heating-induced morphology transformations was established. Furthermore, studying the gold nanorod gradient surfaces provided insight into how the optical and photothermal properties were affected by the nanoparticle surface coverage. The antibacterial activity of the solid-supported gold nanorods was influenced by the support material, and on glass, a NIR light intensity dependent bactericidal effect caused by the photothermal heating of the nanorods was attained. Additionally, an enhanced antibacterial efficacy was demonstrated when combining the solid-supported gold nanorods with an AMP. The findings of this thesis elucidate the characteristics of solid-supported gold nanorods, highlight ways of tuning their properties, and show the potential of using these materials for antibacterial applications.