Chemical methods for the preparation of gold particles based nanostructures and nanocomposites

In this thesis, the potential functional interactions of gold nanoparticles with organic, hybrid, inorganic and biological systems have been investigated. Nanoparticles with varying sizes have been synthesized following different preparation methods. Molecular-like (D < 2 nm), highly fluorescent few-atoms clusters were prepared by a slow reduction of gold salts in organic solvent, yielding a colloidal solution that can be easily redispersed in a variety of solvents and matrices, including sol-gel silica and a hybrid copolymer. The emission wavelength has a lifetime in the ns and can be tuned from the near UV to the whole visible range by adjusting the reaction parameters, and the luminescence is stable for months both in intensity and wavelength. Use of alternative precursors and solvents, influence of reaction temperature and purification methods are all currently being investigated, together with potential application as biolabels and sensitizers for rare-earth-based optical amplifiers. Uncapped nanoparticles with 3 nm < D < 10 nm were obtained in situ in fluorinated polyimides via thermal reduction-precipitation with the concurrent matrix imidization. The doping profile, monitored with RBS analyses, can be easily varied both for thick (30 mm) and thin (< 1 mm) film samples. The selective permeability properties that are typical of polyimides suggest potential employment as both optical and electic gas sensors, and the first measurements are now underway. Eventually, 10 nm nanoparticles were synthesized with the traditional Turkevich citrate method, capped with streptavidin and used to functionalize DNA origami structures. Liquid cell AFM technique allows to image the effectiveness of the proposed method for positioning nanoscopic objects with nm resolution thanks to the peculiar design features of these DNA-based structures. The specific interest is here related to the possibility of using them as lego-like building blocks for nanoelectronics, and the focus is at present centered on the self-induced or externally directed organization of the functionalized origami on substrates. At present, self-assembly on patterned surfaces is being studied together with AFM electrophoresis, but new interesting strategies are being proposed on a daily basis as further interesting origami peculiarities emerge.