Surface Modification and Functionalization of Colloidal Nanoparticles

Subject of this cumulative dissertation is the surface modification, functionalization and bioconjugation of inorganic colloidal nanoparticles. Such particles have a diameter of about 1 – 100 nm and consist of an inorganic, crystalline core that is commonly covered by a shell of organic ligand molecules. These ligand molecules control the growth of the particles during synthesis and also stabilize the particles in solution against aggregation. Besides the core material, the particle surface determines the properties of the particles, as to their interaction with the surrounding medium and to chemical and biological functionality that can be modified by reactive groups and biomolecules. This work aimed to functionalize the surface of colloidal nanoparticles in a controlled fashion and to modify the particles with molecules that provide stability in biological relevant, aqueous environment and that possibly also provide specific interaction with biological systems. First hydrophobic nanoparticles, e.g. made of gold or CdSe/ZnS, were transferred from organic to the aqueous phase by means of an amphiphilic polymer. The polymer consists of carboxylic groups that stabilize the particles by electrostatic repulsion and provide anchor groups for further chemical functionalization. Besides the direct functionalization of the amphiphilic polymer in organic solution, different molecules could be bound to the polymer shell in aqueous solution, regardless to the core material. By means of poly(ethylene glycol), PEG, an inert linear polymer, the particles could be sterically stabilized. Bifunctional PEG with different functional groups allows for modification of the particles with new chemical functions. By means of sufficiently large PEG molecules, a separation of particles with exactly one or two reactive functional groups could be achieved by gel electrophoresis. For the size characterization of nanoparticles, different complementary methods were compared. The system was applied to particles of different core materials and different functional molecules. Complementary to this, citrate-stabilized gold nanoparticles were modified by thiol-modified DNA and characterized by gel electrophoresis which provided information about the DNA conformation. In a collaborative work it was demonstrated that such DNA-modified particles can be used for the detection of DNA oligomers by laser-induced melting of nanoparticle aggregates