Cytotoxicity of CdSe and CdSe/ZnS nanoparticles has been investigated for different surface modifications such as coating with mercaptopropionic acid, silanization, and polymer coating. For all cases, quantitative values for the onset of cytotoxic effects in serum-free culture media are given. These values are correlated with microscope images in which the uptake of the particles by the cells has been investigated. Our data suggest that in addition to the release of toxic Cd(2+) ions from the particles also their surface chemistry, in particular their stability toward aggregation, plays an important role for cytotoxic effects. Additional patch clamp experiments investigate effects of the particles on currents through ion channels.

The fluorescence quantum yield of Cy5 molecules attached to gold nanoparticles via ssDNA spacers is measured for Cy5-nanoparticle distances between 2 and 16 nm. Different numbers of ssDNA per nanoparticle allow to fine-tune the distance. The change of the radiative and nonradiative molecular decay rates with distance is determined using time-resolved photoluminescence spectroscopy. Remarkably, the distance dependent quantum efficiency is almost exclusively governed by the radiative rate.

Escape route: The laser‐initiated release of fluorescently labeled polymers from polyelectrolyte‐multilayer microcapsules is demonstrated inside living cancer cells. A polymer is incorporated in capsules with metal nanoparticles in their walls, which serve as light‐absorbing centers. The capsules are internalized by cells and near‐infrared light ruptures the walls of the capsules, thus releasing the content into the cells.

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In this Review, we describe the synthesis of high-quality colloidal nanoparticles in organic solvents, the mechanisms by which they can be transferred into aqueous solution, and some of their applications in biology. In particular, we will place emphasis on the creation of multifunctional nanoparticles or nanoparticle assemblies.

Fluchtweg: Die Laser‐initiierte Freisetzung von fluoreszenzmarkierten Polymeren aus Polyelektrolytmultischicht‐Mikrokapseln in lebenden Krebszellen wird vorgestellt. Ein Polymer wird in Kapseln eingeschlossen, die als Lichtabsorptionszentren fungierende Metallnanopartikel in den Wänden enthalten. Die Kapseln werden von Zellen aufgenommen, und Nah‐Infrarotlicht bricht die Kapselwände auf, sodass der Inhalt in die Zellen gelangt.

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A flow-cytometry-based assay is presented with which the uptake of polyelectrolyte capsules can be quantified. The cavity of the capsules is loaded with the pH-sensitive dye SNARF, which emits in the red and green in alkaline and acidic environments, respectively. By recording the fluorescence intensities in the red and green channels, the localization of capsules associated with cells can be determined. Capsules adherent to the outer cell membrane fluoresce in the red due to the alkaline pH of the cell medium, whereas capsules internalized by cells fluoresce in the green due to the acidic pH in the endosomal/lysosomal/phagosomal compartments in which incorporated capsules are located. Adding the SNARF readout to the scattering signal typically derived with flow cytometry analysis allows for a more detailed quantitative analysis of particle uptake, which can also distinguish between adherent and ingested particles.