Ανάπτυξη υβριδικών φωτονικών υλικών για εφαρμογές σε οπτικούς αισθητήρες

Abstract

In the present study the synthesis of hybrid materials consisting of metal nanoparticles incorporated into organic and inorganic matrices is presented. The synthesized materials can be divided into two categories; the first one consists of Au and Ag nanoparticles incorporated into polymeric matrices, while the second one consists of Au, Ag and NiCl2 nanoparticles incorporated into inorganic matrices. The thesis was focused on the synthesis and the spectroscopic study of these materials. Meanwhile, the optical and photonic properties of these materials were exploited. Moreover, the biological applications of the synthesized hybrid materials were investigated. In more detail, the larger part of this work focuses on the in situ synthesis of Au and Ag nanoparticles either inside the core or on the corona of di- and triblock copolymers and random copolymers. More specifically, the synthesis protocol requires three steps. First, the proper solvent must be chosen, which should be selective for one of the blocks of the amphiphilic copolymer, in order for micelles to be formed, consisting of a dense core and a solubilized corona. Then the metal precursor is added, which is preferentially dissolved into the core or is coordinated on the periphery of the corona block, depending on the chemical affinity that each block displays toward the metal compound. Finally, the metal ions are reduced in metal nanoparticles either by the addition of a reducing agent or by the coordinating block of the copolymer. The second category of the materials involves the synthesis of Au, Ag and NiCl2 nanoparticles inside inorganic matrices such as SiO2 and TiO2. Solutions containing SiO2 and TiO2 precursors were mixed with metal salts and the standard sol-gel methods were followed for the in situ synthesis of the hybrid materials. Thermal treatment and ageing were the two main parameters that influenced the size and the degree of aggregation of the metal nanoparticles, as well as the porosity of the final material. The non-linear optical properties of the synthesized hybrid materials were studied using the OKE and Z-scan techniques. All the materials studied displayed nonlinear refraction which was proportional to the ratio between the metal nanoparticles and the polymer. The composition of the block copolymer itself played also an important role. The hybrid nano materials were also evaluated as active components in potential photonic sensors. In the presence of methanol and ammonia, morphological changes on the surface of the materials were noticed. These changes were recorded as a signal modulation in respect to the reference signal. Finally, some of the synthesized hybrid materials displayed biocompatibility and their ability to coordinate with proteins and DNA molecules was examined, toward their utilization in bioanalytical devices.