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.

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The chemical instability of the gallium arsenide surface poses a serious limitation to its use under ambient conditions, such as in air or aqueous solution. It is shown that both bare GaAs and GaAs coated with self‐assembled monolayers of organic alkanethiols are continuously etched in aqueous environments, which limits their use as biosensor devices in physiological environments. A corrosion protection material having long‐term stability (“chemical passivation”) and biocompatibility (“biological passivation”) with the GaAs surface was found to be interfacial layers of polymerized organic mercaptosilanes a few tens of nanometers thick. The mercaptosilanes not only provided a nearly perfect corrosion protection of GaAs in water, but they also have the potential to introduce chemical groups that allow easy, further surface functionalization. Characterization of the interfacial polymer layer and its protective role was done by atomic force microscopy (AFM), ellipsometry, contact angle measurements, and atomic absorption spectroscopy (AAS). The interfacial polymer layers fully suppressed the release of arsenic into the electrolyte buffer and also provided an adhesion‐promoting interface, which allowed the cultivation of electrically excitable cells, normal rat kidney (NRK) fibroblasts, on GaAs. The electrical performance of GaAs and GaAs/InGaAs heterostructures in water was monitored via cyclic voltammetry and the IU characteristics of field‐effect channels. GaAs was significantly stabilized by the insulating polymeric surface coatings, even under moderate electrochemical loads. These findings are promising for, e.g., the implementation of GaAs technology in future cell–semiconductor hybrids.