SYNTHESIS AND FUNCTIONALIZATION OF HYBRID MAGNETIC NANOPARTICLE COMPOSITES FOR ENERGY CONVERSION, LIGHT HARVESTING AND OPTICAL AND BIOMEDICAL APPLICATIONS

Abstract

The primary objective of this dissertation was to develop and prepare hybrid multifunctional engineered composite contrast agent nanoparticles for applications in energy conversion, light harvesting in optical and biomedical systems. In this work, superparamagnetic iron oxide nanoparticles were the most common components in the preparation of synthesized nanocomposites. These nanoparticles were used as a core to add reactive moieties such as alkoxysilanes derivatives and polymers to introduce functional ligands including amino, epoxy and aldehyde groups. The most relevant working hypothesis in this dissertation is based on the concept that modified magnetic nanoparticles with semiconductor materials, specifically in this work, with titania thin films shells, provide a suitable surface for protein immobilization. Core-shell hybrid magnetic composites of an iron oxide core and a titania oxide shell were prepared by introducing a new method of synthesis that involves low temperature treatments, inexpensive precursors and with no special reaction conditions required. Magnetic derivatives modified with the linker, 3-Aminopropyltriethoxysilane (APTES) were used successfully to coat the nanoparticles with fluorescent dyes. The amino groups of the APTES moieties were further reacted with glutaraldehyde as a linker to attach amino group derivatives that included proteins (e.g., (enzymes, antibodies) and fluorescent dyes. Other nanostructures prepared in this work included hybrid materials with a core of iron oxide coated with intermediate layers of gold followed by an outer shell of titania oxide that can be used for further modifications. These systems provide properties of photo-corrosion resistance and protection from aggregation. Magnetic nanoparticles derivatives with specific applications in magnetic resonance imaging (MRI) were prepared with coatings of dextran that after further activation with reducing agents the surface was modified via amino moieties. The successful synthesis was demonstrated with 7

the attachment of the enzyme trypsin on different magnetic nanoparticle derivatives and the effective evaluation of the enzyme kinetic parameters. Based on these results it seems feasible to obtain similar effective attachment of any other protein, enzymes or antibodies. The nanoparticle magnetic derivatives coated with dextran provide a stable, water compatible without aggregation and thus suitable for diverse medical applications. Other nanoparticle derivatives produced in this work include quantum dots of different compositions, particularly simple methods to produce carbon dots for light harvesting applications. Silver and gold nanoparticles were produced as materials to promote synthesis of magnetic core and titania shell hybrids. Additionally, silver nanoparticles were used as seeds to deposit gold shells on the silver surface that after a galvanization process created hollow gold nanoparticles derivatives that are being used as photothermal agents to study their thermal ablation properties, technique with promising future in cancer therapy. The characterization of the nanoparticles was performed with SEM/TEM imaging for nanoparticle morphology and size. For optical properties, UV-vis spectroscopy has been used. EDS and XRD have been used to verify element composition. For functional groups analysis, we used FTIR. We used mathematical modeling, particularly, Mie theory to predict the behavior of light behavior and energy conversion of certain nanocomposites. Thus, this work has particularly focused in the synthesis of hybrid magnetic engineered composite contrast agents (MECCA) nanoparticles with biomolecules, particularly with an enzyme as a system for applications at the interface between materials science, biotechnology, and medicine. Nanoparticle derivative of silver, gold and carbon dots were prepared that could be