Surface Modification and Functionalization of Colloidal Nanoparticles

The principle focus of this dissertation is the synthesis of multifunctional nanoparticles, their surface modification and functionalization for biological applications. Colloidal nanoparticles possess unique size dependent physical and chemical properties that can be controlled in a manner that is not possible in bulk size materials. Multi modal molecular imaging is the synergistic combination of two or more detection techniques, enabled by multi modal probes and imaging agents and ensures enhanced visualization of biological materials. Some prototypical probes based on multimodal nanoparticles have been developed. Colloidal nanoparticles composed of an inorganic corematerial and a polymer shell have been synthesized. Both, the core and the polymer shell can be fluorescent, magnetic, or radioactive for appropriate imaging / detection. The polymer contains carboxylic groups that stabilize the particles by electrostatic repulsion and moreover provide anchor groups for further chemical functionalization. Hydrophobic nanoparticles (CdSe/ZnS, Fe2O3 or Gold-198) have been transferred to an aqueous phase by means of modified polymers (with Gadolinium, Organic fluorophores or Indium-111). For the study of sensors based on nanoparticles, a FRET geometry has been introduced, in which the organic dye (ATTO-590) as an acceptor is directly incorporated into the polymer shell used to provide colloidal stability for the CdSe/ZnS quantum dot donor. For the detection of protons,gold nanoparticles coated with negatively or positively charged polymers have been modified with an ion sensitive dye (SNARF). It has been demonstrated that sensor read-out should be thus not determined by the bulk ion concentration, but by the local ion concentration in the “nano”- environment of the nanoparticles surface. In a collaborative work it was moreover demonstrated that nanoparticles cores combined with the polymer shells are responsible for the induction of proinflammatory effects and not the shells alone. It is concluded that the uptake behavior and the proinflammatory response upon particle exposure are dependent on the time, cell type, and cell culture. In addition gold nanoparticles with and without PEG modification have been investigated in “rainbow trout gill” cell line RTGill-W and it was observed that the PEG modified goldnanoparticles were found to be less toxic to the alga compared to the non PEG modified particles.