BackgroundEngineered nanomaterials display unique properties that may have impact on human health, and thus require a reliable evaluation of their potential toxicity. Here, we performed a standardized in vitro screening of 23 engineered nanomaterials. We thoroughly characterized the physicochemical properties of the nanomaterials and adapted three classical in vitro toxicity assays to eliminate nanomaterial interference. Nanomaterial toxicity was assessed in ten representative cell lines.ResultsSix nanomaterials induced oxidative cell stress while only a single nanomaterial reduced cellular metabolic activity and none of the particles affected cell viability. Results from heterogeneous and chemically identical particles suggested that surface chemistry, surface coating and chemical composition are likely determinants of nanomaterial toxicity. Individual cell lines differed significantly in their response, dependent on the particle type and the toxicity endpoint measured.ConclusionIn vitro toxicity of the analyzed engineered nanomaterials cannot be attributed to a defined physicochemical property. Therefore, the accurate identification of nanomaterial cytotoxicity requires a matrix based on a set of sensitive cell lines and in vitro assays measuring different cytotoxicity endpoints.

Experimental approaches for analyzing the chemical composition of animal cells with spatial resolution are important for many fields of biomedical research. The analysis of threedimensional microstructures by time-of-flight secondary-ion mass spectrometry (TOF-SIMS) is an emerging technique to make the molecular architecture of biological samples accessible. In SIMS the sample surface is bombarded by primary ions. A fraction of the energy transported in the socalled collision cascade is directed back to the sample surface and causes the desorption of neutral and charged chemical species (secondary ions) from the uppermost molecular layer. These are subsequently collected and analyzed with respect to their mass/charge ratio.[1] Today, most state-of-the-art instruments for organic applications use TOF analyzers for mass determination of the desorbed secondary ions.[2] TOF-SIMS allows the detection of all elements as well as small organic molecules in parallel and has a sensitivity down to the ppm/ femtomole range.[3] Scanning the sample surface with the primary-ion beam provides a 2D image of the chemical surface composition. Moreover, prolonged ion bombardment of the sample at a constant position leads to sputter erosion. Mass analysis of the sputtered material then reveals the vertical composition of the sample.[1] The lateral distribution of organic material can be imaged with a resolution of about 150-400 nm, [4][5][6] whereas the vertical resolution in organic polymer films was shown to be better than 30 nm. [7] Application to biological samples like cells and tissues, however, has so far been hindered by the limited signal intensities obtained from organic materials and the fact that the collision cascade destroys organic molecules and, thus, molecular information. The low signal intensities in surface analysis and the loss of molecular information in sputter depth profiling have been improved by the use of polyatomic primary ions like Au 3 + and Bi 3 + . [3,8] Moreover, buckminsterfullerenes have become available as a new ion source for sputter erosion.[9] The impact of C 60 + ions was found to be less destructive to organic samples than the common sputter ions O 2 + and Cs + .[10] Even intact organic molecules survive the sputter process.[11] Thus, it was the objective of this study to reconstruct the molecular composition of animal cells in three dimensions by applying repeated cycles of SIMS analysis of the sample surface followed by sputter erosion that exposes a deeper layer of the sample to the next round of SIMS analysis (TOF-SIMS 3D microarea analysis). In a dual-beam setup Bi 3 + primary ions were used to determine the chemical composition of the surface, and C 60 + ions were used for intermittent sputter erosion. [12] Six confluent layers of normal rat kidney (NRK) cells, grown on cover slips under ordinary cell-culture conditions, were analyzed by TOF-SIMS 3D microarea analysis after the cells had been stabilized by chemical fixation. Chemical fixation is a routine procedure to preserve the struct...

Many interferometry-based quantitative phase contrast imaging techniques require a separately generated coherent reference wave. This results in a low phase stability and the demand for a precise adjustment of the intensity ratio between object and reference wave. To overcome these problems, the performance of a Michelson interferometer approach for digital holographic microscopy was analyzed that avoids a separately generated reference wave by superposition of different image areas. It is shown that this simplified arrangement yields improved phase stability. Furthermore, results from time-lapse investigations on living pancreas tumor cells demonstrate the capability of the method for reliable quantitative phase contrast imaging.

Electrochemical oxidation of 2,4‐dimethylphenol directly provides pentacyclic systems being generated by an oxidative trimerization. The major pentacyclic scaffold is exclusively formed as a single diastereoisomer and is easily isolated. Three further pentacyclic compounds which occur in minor quantities were also fully characterized including their solid‐state structures. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Substituted phenols were anodically coupled to the corresponding 2,2'-biphenols via tetraphenoxy borate derivatives. This electrochemical method is particularly useful for methyl-substituted substrates, such as 2,4-dimethyl phenol. The selective ortho-coupling reaction can be easily performed on a multikilogram scale.