Controlling the physical and biological properties of highly fluorescent aqueous quantum dots using block copolymers of different size and shape.

The phase transfer of fluorescent CdSe based quantum dots (QDs) while retaining their properties and offering some advantages concerning the stability and functionalization characteristics is an important and intensively investigated field of research. Here we report how to tune and control the properties of CdSe/CdS/ZnS core-shell-shell QDs in water, using poly(isoprene-block-ethylene oxide) (PI-b-PEO) as a versatile system of amphiphilic diblock copolymers for the micellular encapsulation of nanoparticles (NPs). We show the synthesis of a novel PI-b-(PEO)2 miktoarm star polymer and how this different architecture besides the variation of the polymers' molecular weight gives us the opportunity to control the size of the built constructs in water between 24 and 53 nm. Because of this size control, an upper limit of the construct's diameter for the cellular uptake could be determined by a systemic study with human alveolar epithelial cells (A549) and murine macrophage leukemia cell (RAW-264.7). Furthermore, fluorescence quenching experiments with copper(II) and iron(III) ions show a strong influence of the used polymer on the shielding against these ions. This enables us to control the permeability of the polymer shell from very porous shells, which allow an almost complete cation exchange up to very dense shells. These even offer the possibility to perform copper(I) catalyzed click reactions while keeping the fluorescence of the QDs. All these results underline the huge variability and controllability of the PI-b-PEO diblock copolymer system for the encapsulation and functionalization of nanoparticles for biological applications. As a general trend, it can be stated that those coatings, which were most stable against quenchers, also showed the best resistivity with respect to unspecific cellular uptake.

Amphiphilic, cross-linkable diblock copolymers for multifunctionalized nanoparticles as biological probes.

Nanoparticles (NPs) play an increasingly important role in biological labeling and imaging applications. However, preserving their useful properties in an aqueous biological environment remains challenging, even more as NPs therein have to be long-time stable, biocompatible and nontoxic. For in vivo applications, size control is crucial in order to route excretion pathways, e.g. renal clearance vs. hepato-biliary accumulation. Equally necessary, cellular and tissue specific targeting demands suitable linker chemistry for surface functionalization with affinity molecules, like peptides, proteins, carbohydrates and nucleotides. Herein, we report a three stage encapsulation process for NPs comprised of (1) a partial ligand exchange by a multidentate polyolefinic amine ligand, PI-N3, (2) micellar encapsulation with a precisely tuned amphiphilic diblock PI-b-PEG copolymer, in which the PI chains intercalate to the PI-N3 prepolymer and (3) radical cross-linking of the adjacent alkenyl bonds. As a result, water-soluble NPs were obtained, which virtually maintained their primal physical properties and were exceptionally stable in biological media. PEG-terminal functionalization of the diblock PI-b-PEG copolymer with numerous functional groups was mostly straightforward by chain termination of the living anionic polymerization (LAP) with the respective reagents. More complex affinity ligands, e.g. carbohydrates or biotin, were introduced in a two-step process, prior to micellar encapsulation. Advantageously, this pre-assembly approach opens up rapid access to precisely tuned multifunctional NPs, just by using mixtures of diverse functional PI-b-PEG polymers in a combinatorial manner. All constructs showed no toxicity from 0.001 to 1 µM (particle concentration) in standard WST and LDH assays on A549 cells, as well as only marginal unspecific cellular uptake, even in serum-free medium.

Tailor-made quantum dot and iron oxide based contrast agents for in vitro and in vivo tumor imaging.

The biofunctionalization of CdSe/CdS/ZnS quantum dots and Fe(3)O(4) nanocrystals using a novel ligand system based on polyisoprene-block-poly(ethylene oxide) ligands is described. The synthesis includes a partial ligand exchange of the hydrophobic nanocrystals with amino-functionalized polyisoprene ligands, followed by seeded micelle formation of the diblock-copolymers in water. The resulting water-soluble quantum dots showed fluorescence quantum efficiencies in the 40 to 50% range and extraordinary fluorescence stability in the biological environment after cross-linking of the polyisoprene moiety of the ligand shell. No toxicity was detected by water-soluble tetrazolium (WST8) and lactate dehydrogenase (LDH) assays, even at very high nanoparticle concentrations, and almost no nonspecific cell adhesion was detected. The ligand shell was further coupled to the antigen-related cell adhesion molecule (CEACAM) specific monoclonal antibody T84.1. The so-conjugated Fe(3)O(4) nanocrystals allowed in vitro and in vivo tumor targeting by magnetic resonance imaging.

Plasmon-exciton interactions on single thermoresponsive platforms demonstrated by optical tweezers.

Optical and hydrodynamic-size studies on single bare thermo-responsive microspheres, and microspheres covered either with Au nanoparticles, CdSe/CdS quantum dots, or a combination of both have been performed by optical tweezers. The photothermal heating of water in the focal region boosts the shrinkage of the microspheres, an effect that is intensified in the presence of Au nanoparticles. In contrast, bigger microspheres are measured when they are covered with quantum dots. Plasmon-exciton interactions are observable in the trap in the combined Au and quantum dots hybrid systems.