Synthesis and characterization of bismuth oxide based and c-dots hybrid materials for teragnostic applications

Synthesis and characterization of bismuth oxide based and c-dots hybrid materials for teragnostic applications. The aim of this thesis work is to synthesize and subsequently to conjugate carbon dots (C-Dots) with microparticles of Bismuth Oxide. C-Dots are composed by sp^2 and sp^3 hybridized carbon structures with size of few nanometers. Since their discovery, C-Dots have attracted a great attention on the due to their simple synthesis, solubility, photoluminescence, biocompatibility and presence of surface functional groups acting as anchoring points for a variety of drugs. The bottom-up approach has been used for the C-Dots synthesis through citric acid (AC) and p-Phenylendiamine (DPA), in order to promote polymerization, and subsequent purification by means of two different methods. The first one includes carbonization by thermal treatment at different temperatures (250°, 350° and 450°) and centrifugation. The second purification process is performed by dialysis with two different types of membrane cutoff. It can be hypothesized that in both cases the C-Dots are random cross-linked polymeric structures organized in parallel planes with external functional groups. Comparing two results with IR spectroscopy it arise that the heat treatment produces more heterogeneous and functionalizable structure. The dialyzed one has more compact¸ less flexible so more aromatic structure. The C-Dots synthesis has been repeated adding polyethyleneglycol (PEG) as a reagent (in 1:1, 0.5:1 and 0.1:1 proportions w.r. to AC) and then purified with both methods. PEG acts as a separator which avoids the C-Dots aggregation, favors the aromatic compounds condensation and reacting with its functional groups maximizes the subsequent conjugation. Basing on the applications of C-Dots, it is possible to choose the most suitable method. Bismuth Oxide microparticles, thanks to their radiopacity, are applicable in the teragnostic and diagnostic purposes. They are insoluble, but it is possible to bring them in suspension in water by surrounding them with C-Dots. These particles can cause inflammatory phenomena, oxidative stress and cytotoxicity in some cells, so they must be big enough to not cross the cell membrane, but at the same time, small enough to remain suspended be C-Dots. Bismuth Oxide microparticles has been prepared by hydrothermal synthesis (using Bismuth Nitrate and Nitric Acid as precursors in acidic environment with and without active surfactants (sodium lauryl sulphate, lauric acid, polyethylene glycol and polyvinylpyrrolidone) which direct the planes’ growth) and by solid state synthesis (using Bismuth Nithate without solvent at different calcinations temperatures to promote the thermal decomposition). Analyzing FESEM images for the first set of synthesis¸ more regular structures are observed for SLS and PEG, instead in other cases the irregular structures and no preferential growth directions are present. The conjugation has been performed by mixing the solid state synthesized particles with different types of purified C-Dots for 48h and subsequently centrifuging the product in order to separate the soluble part and residue, which contains the Bismuth Oxide microparticles conjugated with C-Dots through the weak surface interactions of π-d type. Also the direct synthesis of microparticles and their conjugation with C-Dots has been performed with a satisfying result by repeating all steps of the hydrothermal synthesis adding C-Dots in the solution.