Monolayer Protected Gold Nanoparticles: Application in Molecular Recognition

In the last years, a relevant attention has been paid to monolayer protected gold nanoparticles (AuNPs), which are nanometer-sized gold colloids coated with a monolayer of organic molecules. Indeed, they have several interesting features.The first one is the easiness to synthesize gold cores with various sizes. Second, the versatile chemistry of AuNPs allows the grafting of functional groups and co-factors onto their surface. Taking advantage of different kinds of non-covalent interactions (namely hydrophobic, ion pairing, and metal-ligand coordination), such functional groupscan in turn provide tailored binding sites for virtually any class of substrates. The variety of monolayers that can be potentially assembled endows a fine-tuning of these interactions not only in terms of selectivity, but also in terms of their strength. Therefore, AuNPs were emerging as great scaffolds for molecular recognition. In this thesis, chapter 1, the introductive chapter, will present the methods for the preparation of AuNPs, the recent progress of AuNPs as chemosensors and the approaches that have been developed to investigate the monolayer morphology of mixed AuNPs. In chapter 2, the aims and objectives of this thesis will be addressed. In chapter 3 and 4, a series of water soluble AuNPs were prepared and investigated as nanoreceptors and chemosensors using nuclear magnetic resonance (NMR) protocols. The results of chapter 3 indicated that by appropriate design of the coating ligands, the spontaneous formation of the sensing pockets in the monolayer of the gold nanoparticles can be achieved. The results in chapter 4 confirmed the possibility that the rational design of AuNPs with intrinsic binding cavities and controlled sensing ability can be aided by molecular dynamic (MD) simulations. In chapter 5, three kinds of positive charged AuNPs were prepared and they were able to detect and discriminate nonsteroidal anti-inflammatory drugs in a quantitative manner. In the field of molecular recognition, unique properties can also be obtained by the preparation of mixed AuNPs. Previous studies have already demonstrated that the morphology of the mixed monolayer is closely related to their properties. For this reason, in chapter 6, we will describe a method which combines NMR and electron paramagnetic resonance (EPR) techniques to investigate the morphology of mixed AuNPs. Furthermore, in chapter 7we demonstrated that the morphology of the mixed monolayer can be transformed when in the presence of proper interacting analytes.