From hydrophilic to hydrophobic metal nanoparticles: the role of surface functionality on chemical properties

This PhD thesis provides a comprehensive investigation into the synthesis, characterization, and application of metal nanoparticles (MNPs), with particular emphasis on gold nanoparticles (AuNPs) and the role of the thiol ligands on the gold surface and how they influence the application potential of nanoparticles. The nanoparticles were synthesised via chemical reduction methods, yielding spherical nanoparticles with controlled diameters predominantly below 10 nm. The research is structured into two main parts. The first focused on hydrophilic AuNPs for biomedical applications, in this respect, a highly stable and reproducible system was developed using a mixed thiols ligand layer (sodium 3-mercapto-1-propanesulfonate, 3MPS, and 2-(diethylamino)ethanethiol hydrochloride, DEA). These nanoparticles were thoroughly characterized, including with the innovative μ-liquid jet XPS technique at the SOLEIL Synchrotron, which can investigate the structural and chemical properties of free thiols in solution and thiol-capped on gold surface in the native colloidal state of AuNPs. Thanks to the small size (ca. 10 nm) and high stability, this AuNPs system has been successfully used as versatile drug delivery platform of an anticancer drug (Methotrexate) and a therapeutic antibody (Trastuzumab); in both cases, the AuNPs platform significantly enhanced the therapeutic effect compared to the free drug, proving its potential in nanomedicine. The second part of the thesis explored hydrophobic nanoparticles for materials science and sensing applications. Here, the precise control over surface chemistry enabled the creation of "smart" systems, responsive to external stimuli. By functionalizing AuNPs with dodecanethiol (DDT) and 4-aminothiophenol (Ani) in mixture, three distinct self-assemblies were achieved: supramolecular, covalent, and transient covalent self-assembly. Furthermore, the use of rigid, bifunctional π-conjugated ligands allowed for the construction of covalent networks of AuNPs, AgNPs, and PdNPs with tunable interparticle distances, opening perspectives for optoelectronics. Fine-tuning the 2D/3D arrangement of AuNPs networks is possible using a monofunctional ligand in mixture with the bifunctional ligands yielding promising preliminary results as chemiresistive sensors for volatile organic compounds like benzene and toluene. Finally, hydrophobic and interconnected AuNPs were incorporated into different polymer matrices (poly(phenylacetylene), PPA; poly(3-hexylthiophene-2,5-diyl), P3HT; polylactic acid, PLA) to create hybrid organic-inorganic nanocomposites. These blends consistently demonstrated significant enhancements in electrical conductivity, showing a synergistic effect between the nanoparticles and the polymers. The thesis concludes with a preliminary study into chirality, functionalizing AuNPs with enantiopure [2.2]paracyclophane synthetic derivatives, laying the foundations for future studies on chiral plasmonics