Merino Becomes Noble: A study of nanogold, wool and nanogold–wool composites

Our research group, led by Professor J. H. Johnston, has developed a novel approach for dyeing merino wool with nanogold [gold nanoparticles (AuNPs)] by coupling the chemistry of gold with that of wool fibres. This utilises the plasmonic properties of nanogold to create attractive fabric colours ranging from pink to purple to grey. The newly created fabric benefits from the synergistic effect of the unique properties of strong merino wool and valuable gold, i.e. the innovative product is intensely coloured, colour fast, naturally hydrophobic, anti-microbial, anti-static as well as having first-rate wearing comfort. This innovation has attracted substantial interest from industry resulting in the collaboration of our research group with leading fabric manufacturers and designers. However, the colour range of this unique high-value product is limited. It was desirable to enlarge the colour range by developing new strategies to create wash fast nanogold–wool composites with a broad colour spectrum. Thus my research aimed to identify and understand the fundamental principles that govern the formation of nanogold–wool composites. Based on the derived knowledge, it was aimed to develop a methodology to covalently link pre-synthesised AuNPs of various colours to the surface of New Zealand merino wool fibres in order to obtain wash fast nanogold–wool composites with a broad colour spectrum. This involved the synthesis, functionalisation and characterisation of colloidal AuNPs, and their application as colourants for wool. The methodology followed three general steps: (1) synthesis of colloidal gold, (2) preparation of the wool surface for the colouring processes, and (3) production of nanogold–wool composites. Each work stage was accompanied by thorough analysis and characterisation of the intermediate and final products. Studying colloidal gold systems and nanogold–wool composites which were previously reported provided the insights that were necessary to develop new methodologies to strongly link AuNPs to wool. For instance, nanogold stabilised by oleylamine produces especially bright pink nanogold–wool composites; however, the AuNP–wool bond is relatively weak. Hence, several AuNP–wool bond types were intensively studied, and as a result of combining the knowledge gained, two approaches were developed to provide a proof-of-concept for the creation of wash fast nanogold–wool composites. These approaches involved a specifically designed, in-house-synthesised capping agent for AuNPs as well as a crosslinker that binds functionalised AuNPs to the reactive sites of wool. In addition to achieving the project aims, my work produced three new systems of colloidal gold in aqueous medium which stand out due to their properties. Specifically, these properties were: (1) being stable without significant electrostatic or steric stabilisation, (2) having a unique surface functionalisation allowing for selective chemistry, and (3) having an intense blue colour as a result of controlling the AuNP shape during synthesis. All three systems show application potential for wool colouration, ligand exchange reactions, surface-enhanced Raman spectroscopy (SERS), and in the field of biomedicine.