Biogenic production of Gold and Silver Nanoparticles using extracts from indigenous Australian plants: Their synthesis, optimisation, characterisation and antibacterial activities

Today, the primary focus of nanotechnology is the creation of nanometre scale materials, techniques and applications. The main driver for this intense nanotechnologybased research is the unique material properties that occur at the nanometre scale which are significantly different to those at the bulk scale. Importantly, because of their size nanoparticles can act as bridge between bulk materials and molecular structures. Therefore, an important aspect of nanotechnology is the synthesis of nanoparticles of different compositions and the ability to directly control particle parameters such as size, shape and size distribution. Since the material composition and related material parameters will ultimately determine the overall properties of the nanoparticles. Furthermore, there is also a need to develop reliable, sustainable and eco-friendly protocols for manufacturing nanoparticles. In recent years there has been a convergence between biological based technologies, green chemistry and nanotechnology. This convergence has the potential to produce clean technologies that can significantly reduce environmental and human health risks resulting from toxic chemicals and solvents generally used in conventional nanoparticle manufacturing processes. The biogenic synthesis of nanoparticles via plant extracts has the potential to significantly reduce or eliminate the use of hazardous substances. Worldwide, alternative eco-friendly green chemistry based techniques for biosynthesising metal nanoparticles using various plant species has been actively investigated in recent years. However, finding suitable plant species and developing effective protocols to biosynthesis metal nanoparticles with predetermined physiochemical properties still remains a challenge. Taking up the challenge, this thesis for the first time examines the biogenic properties of three indigenous Australian plant species to produce (Au) gold and (Ag) silver nanoparticles. Plant species studied were Eucalyptus macrocarpa (rose of the west), Xanthorrhoea glauca (grass tree) and Anigozanthos manglesii (red and green kangaroo paw). The thesis is composed of five case studies that deal with the discovery, biosynthesis optimisation & particle characterisation, and identification of Ag nanoparticle/plant antimicrobial properties. The studies reveal all three plant species were effective bio-factories capable of manufacturing of Ag and Au nanoparticles. Subsequent antimicrobial studies using Ag nanoparticles biosynthesised using Xanthorrhoea glauca and Anigozanthos manglesii were found to be effective agents against bacterial pathogens such as Deinococcus, Escherichia coli and Staphylococcus Epidermis. The research for the first time has demonstrated that three indigenous Australian plant species are capable of producing nanoparticles with unique physiochemical properties and the nanoparticles have the potential to be used in antibacterial pharmaceuticals