Dye doped, core / shell silica nanoparticles: synthesis, characterization, & biotechnological applications

The aim of this thesis was to design, synthesize and develop a nanoparticle based system to be used as a chemosensor or as a label in bioanalytical applications. A versatile fluorescent functionalizable nanoarchitecture has been effectively produced based on the hydrolysis and condensation of TEOS in direct micelles of Pluronic® F 127, obtaining highly monodisperse silica - core / PEG - shell nanoparticles with a diameter of about 20 nm. Surface functionalized nanoparticles have been obtained in a one-pot procedure by chemical modification of the hydroxyl terminal groups of the surfactant. To make them fluorescent, a whole library of triethoxysilane fluorophores (mainly BODIPY based), encompassing the whole visible spectrum has been synthesized: this derivatization allows a high degree of doping, but the close proximity of the molecules inside the silica matrix leads to the development of self - quenching processes at high doping levels, with the concomitant fall of the fluorescence signal intensity. In order to bypass this parasite phenomenon, multichromophoric systems have been prepared, where highly efficient FRET processes occur, showing that this energy pathway is faster than self - quenching, recovering the fluorescence signal. The FRET efficiency remains very high even four dye nanoparticles, increasing the pseudo Stokes shift of the system, attractive feature for multiplexing analysis. These optimized nanoparticles have been successfully exploited in molecular imaging applications such as in vitro, in vivo and ex vivo imaging, proving themselves superior to conventional molecular fluorophores as signaling units.

Development of innovative catalysts for the hydrodechlorination to fluoroethers

In this work the hydrodechlorination of CF3OCFClCF2Cl to produce unsaturated CF3OCF=CF2 was studied over a series of supported metal catalysts. Currently this molecule is produced from the precursor CF3OCFClCF2Cl by dechlorination with zinc powder. An important cost on the economic and environmental balance is represents by the large amount of ZnCl2 produced and to be disposed of. A new approach, based on gas-phase hydrodechlorination over supported catalysts can lead to a new sustainable process. During the feasibility step of this project, substantially two kind of materials were studied: metals supported over activated carbon and Pd/Cu species supported over MCM-41 mesoporous silica. Observed catalytic performances were strongly dependent on the metal and support used. All carbon-supported Ru, Pd, and bimetallic catalysts are fairly active and yielded the target product CF3OCF=CF2, the higher selectivity being obtained with ruthenium- and palladium-based materials. Nevertheless, Ru-based catalysts showed poor stability and this deactivation may be attributed to the deposition of chlorinated organic species blocking the active sites. On the other hand, palladium-containing catalysts showed high stability. Ru/Pd and Pd/Cu bimetallic catalysts exhibited long-term selectivity and stability, highlighting the possibility for these materials to be employed in the CF3OCF=CF2 production process. During the second part of this thesis, a series of bimetallic meso-structured Pd/Cu MCM-41 catalysts were studies to overcome possible mass transfer limitations. The materials were obtained by different synthesis methods. The incorporation of Pd and Cu during MCM-41 synthesis, did not destroy the typical hexagonal array and ordered pore system of MCM-41. However, the calcination for the removal of the template provoked significant segregation of oxides. The impregnation leads to pore-occlusion and formation of Cu particles and large bimetallic PdCu species. Larger metal particles leads to lower CF3OCFClCF2Cl conversion, while the monometallic particles can decrease the selectivity to CF3OCF=CF2, fostering the dehalogenation to CF3OCH=CF2.

Silica-Supported Gold Nanoparticles: Synthesis, Characterization and Reactivity

The main aim of this work was the synthesis and applications of functionalized-silica-supported gold nanoparticles. The silica-anchored functionalities employed, e.g. amine, alkynyl carbamate and sulfide moieties, possess a notable affinity with gold, so that they could be able to capture the gold precursor, to spontaneously reduce it (possibly at room temperature), and to stabilize the resulting gold nanoparticles. These new materials, potentially suitable for heterogeneous catalysis applications, could represent a breakthrough among the “green” synthesis of supported gold nanoparticles, since they would circumvent the addition of extra reducing agent and stabilizers, also allowing concomitant absorption of the active catalyst particles on the support immediately after spontaneous formation of gold nanoparticles. In chapter 4 of this thesis is also presented the work developed during a seven-months Marco Polo fellowship stay at the University of Lille (France), regarding nanoparticles nucleation and growth inside a microfluidic system and the study of the corresponding mechanism by in situ XANES spectroscopy. Finally, studies regarding the reparation and reactivity of gold decorated nanodiamonds are also described. Various methods of characterization have been used, such as ultraviolet-visible spectroscopy (UV-Vis), Transmission Electron Microscopy (TEM), Dynamic Light Scattering (DLS), X-ray Fluorescence (XRF), Field Emission Gun Scanning Electron Microscopy (SEM-FEG), X-ray Photoionization (XPS), X ray Absorption Spectroscopy (XAS).

Design and Characterization of Luminescent Silica Nanoparticles

The aim of this thesis was to design, synthesize and characterize dye-doped silica nanoparticles (DDSNPs) to be used as chemosensors or labels in bioanalytical applications. DDSNPs represent one of the most versatile and useful components in nanomedicine displaying important features such as high colloid stability in water, low toxicity, one-pot inexpensive synthesis and tunable fluorescence emission. Starting from the one-pot and highly reproducible synthesis of “silica-core/PEG shell” DDSNPs based on the use of micelles of Pluronic F127, in which take place both hydrolysis and condensation of the silica precursor and of the dyes functionalized with a triethoxysilane group, we developed DDSNPs suitable for optical and optoacustic imaging, drug loading and chemical sensing obtaining very interesting results for the further development of nanomedicine.