REPOSITORY > RESULTS

Abstract

The application of magnetic nanoparticles in biomedicine dictates the preparation of properly arranged nanoparticles. The preparation of a stable colloidal suspension of nanoparticles in complex biological media is a prerequisite for all types of applications. Depending on the type of application, the proper coating, functionalization and (bio)conjugation of the nanoparticles should be chosen.
The presented work describes the synthesis of silica coatings on nanoparticles' surfaces, the functionalization of silica-coated nanoparticles and the (bio)conjugation of functionalized nanoparticles.
The superparamagnetic maghemite nanoparticles were synthesized by the coprecipitation of Fe2+ and Fe3+ ions from an aqueous solution. Next, a stable colloidal suspension of nanoparticles was prepared using citric acid as a surfactant and this electrostatically stabilized suspension was further used for the synthesis of silica coatings.
The nanoparticles with adsorbed citric acid exhibited a highly negative surface charge in an alkaline medium, which ensures an adequate stability of the colloidal suspension. Therefore, the reactions of the silica coatings were performed at alkaline pH values. The relevant parameters influencing the quality of the thin silica coatings were systematically studied. The optimal selection of parameters ensuring the homogeneous silica coatings was determined.
Various amino silanes were bonded onto the surfaces of silica-coated nanoparticles. Silanes form strong siloxane bonds with silica surfaces and they provide free terminal amino groups onto the surfaces at the same time. These amino groups enable the successful bonding of biologically interesting molecules in physiologically acceptable reaction conditions. Among the four amino silanes only one was selected. This enabled precisely controlled bonding onto the silica surfaces. The possibility of controlling the surface concentration of bound silane molecules ensures well-defined products, which are the basis for further bioconjugations.
Part of the introduced surface amino groups was bonded with fluorescent molecules, which ensured the tracking of fluorescent nanoparticles with optical methods.
The preparation of multifunctional nanoparticles, where the various types of molecules were bonded to the nanoparticles' surfaces in a desired ratio, required good understanding of the surface chemistry involved as well as the ability to adjust the ratio between various surface functional groups. A special method was developed for this purpose providing good control over the ratio between the surface amino and carboxyl groups. Succinic anhydride was bonded onto the amino-functionalized nanoparticles, introducing surface carboxyl groups onto the nanoparticle surfaces.
Furthermore, the effect of various surface charges of fluorescent nanoparticles on their cellular uptake was intensively studied. For this purpose the amino-functionalized and carboxyl-functionalized nanoparticles were prepared due to their differences in zeta-potential values.
Finally, five different types of bioconjugates designed to actively target specific A431 cells were synthesized. For this purpose, the epidermal growth factor (EGF) was chosen as an affinity ligand. Since EGF shows an affinity for the EGF receptor over-expressed at
the targeted A431 cells the targeting specificity toward the A431 cells was also intensively studied.