DEVELOPMENT OF GOLD BASED NANO-SYSTEMS FOR BIOMEDICAL APPLICATIONS

Gold nanoparticles (Au NPs) always fascinated the scientific community, demonstrating several applications in nano-medicine, due to the peculiar properties of this metal at the nano-metric scale. First of all, gold is characterized by a strong inert nature, resisting to the air oxidation and corrosion. This chemical non-reactivity is correlated to a bio-inert nature of the metal that makes it an outstanding candidate for the development of in vitro and in vivo devices. Despite this great inertness, Au can form stable bonds with sulphur containing compounds, like thiols or disulfides. Exploiting this kind of chemistry is possible to easy and robustly functionalize Au NPs with different types of polymers, bio-molecules or targeting moieties. Moreover, Au NPs possess fascinating optical properties like localized surface plasmon resonance (LSPR), photoluminescence, enhancement of Raman signals and elevated X-rays attenuation. By tuning the Au NPs size, shape, coating, labelling and active targeting it is possible to obtain designed platforms acting as therapeutic, diagnostic or theranostic agents. In the present thesis are investigated three fundamental aspects correlated with the employment of gold nanoparticles in biomedicine. Au NPs, thanks to the high density and atomic number, present an elevated X-ray absorption coefficient. These NPs, if properly functionalized, can act as effective CT contrast agent and can be easily visualized by mean of in vivo micro-CT analysis. Here in is reported a methodology for the synthesis of highly stable and functionalized Au. The presented method allowed us to tune the surface coatings and the morphology of the Au NPs, designing a “one-pot” synthesis of engineered isotropic and anisotropic nanoparticles. The present study is devoted to elucidate the major factors involved in the in vivo biodistribution of PEGylated Au NPs. The effects of NPs structural parameters (eg. charge, shape and dimension) on the circulation time in the blood pool were analysed. From this study, we derived interesting information, generally applicable to the design of different types nano-structured contrast agents. Furthermore, other two fundamental topics involved in the design of effective nano-structured contrast agents has been investigate: the nanoparticles renal clearance and the active targeting toward inflamed tissues. Moreover, in the present thesis is investigated the interaction of surface functionalized Au NPs with the biological matter. When nanoparticles come in contact with biological materials, bio-molecules are adsorbed on their surface. This phenomenon causes a modification the identity of the systems and an uncontrolled aggregation of the NPs. The investigation of this phenomenon is fundamental to understand both the intracellular dynamics and the physiological behaviour of the nanoparticles. It is essential to consider these factors in the design of nano-systems effectively applicable in the biomedical field. In particular, in the present study, Fluorescence Correlation Spectroscopy (FCS) has been exploited to acquire information on the diffusion times of surface functionalized Au NPs, both in protein solution and in living cells. In the last chapter is investigated a more technical issue, related to the nanoparticles synthesis. In order to think to a reliable application of the nanotechnologies in the biomedical field, innovative synthetic procedure needs to be identified, to ensure a scale up and higher reproducibility of the production. A fluidic manufacturing method for the production of structurally controlled Au NPs was developed. Fluidic chemistry is a promising technology that can address to the scale up and reproducibility issues that affect the nano-materials production. The presented manufacturing method demonstrated to be strongly versatile, allowing the one-pot production of nano-materials with controlled shape, and engineered surface, readily applicable in a vast number of fields.