Hybrid organic-inorganic nanostructures and interfaces: from fundamental studies of low dimensional systems to biomedical applications

Abstract

This thesis reports some studies of interfacial systems for biomedical applications. Nanosystems for Self Lighting Photo Dynamic Therapy (SLPDT) of cancer have been characterized from the growth steps up to the in vitro tests. At the same time, from a more fundamental point of view, aggregation and spontaneous fluctuation dynamics in interfacial model systems has been investigated. Several complementary techniques are employed for a comprehensive characterization of nanostructures (i.e. SEM, TEM, AFM) and for the study of their optical properties (i.e. microfluorescence, epifluorescence). Farther, for this cutting-edge research, state-of-the-art techniques have been employed: for instance, i) singlet oxygen production was excited by irradiation with a 6 MeV Linac; ii) mechanical properties of delicate Langmuir monolayers have been measured by ad-hoc developed techniques; iii) spontaneous fluctuation dynamics was characterized by synchrotron X-ray photon correlation spectroscopy (XPCS). The thesis begins reporting investigations on molecular layers of porphyrins deposited by Supersonic Molecular Beam Deposition (SuMBD) as idealized interfaces to comprehend the more complex nanosystem i.e. porphyrinated core-shell nanowires constituted by a silica coating around a silicon carbide core. The latter are developed and studied for SLPDT applications. SLPDT is the evolution of the standard PDT to the treatment of deep tumors; the porphyrins locally activated by nanowires -suitably excited by X-rays- react with the oxygen molecules present in tissues, generating cytotoxic singlet oxygen. In this framework, besides nanowires, other nanostructures have been synthesized to pursue the maximum efficiency i.e. core-shell nanoparticles based on CeF3 surrounded by an oxide cladding. CeF3 is a very efficient scintillator converting X-ray photons in visible light while the oxide cladding allows many easy functionalization processes for biocompatibility and targeting. At the same time, some model interfacial systems have been investigated: firstly, a Langmuir network of hydrophobic gold nanoparticles at air/water interface to understand aggregation processes and to study the evolution of the dynamics at nanoscopic scale. Furthermore, a Langmuir mixed monolayer of lipid and silica nanoparticles has been investigated as a model system for the interactions between hydrophilic nanoparticles and a simple model of cell membrane. It is expected that studies like those presented here shall prove useful to understand the behavior of nanostructures in interaction with bio-interfaces and shall pave the way for novel applications.