Thin-Film Phase Plates for Transmission Electron Microscopy Fabricated from Metallic Glasses.

Thin-film phase plates (PPs) have become an interesting tool to enhance the contrast of weak-phase objects in transmission electron microscopy (TEM). The thin film usually consists of amorphous carbon, which suffers from quick degeneration under the intense electron-beam illumination. Recent investigations have focused on the search for alternative materials with an improved material stability. This work presents thin-film PPs fabricated from metallic glass alloys, which are characterized by a high electrical conductivity and an amorphous structure. Thin films of the zirconium-based alloy Zr65.0Al7.5Cu27.5 (ZAC) were fabricated and their phase-shifting properties were evaluated. The ZAC film was investigated by different TEM techniques, which reveal beneficial properties compared with amorphous carbon PPs. Particularly favorable is the small probability for inelastic plasmon scattering, which results from the combined effect of a moderate inelastic mean free path and a reduced film thickness due to a high mean inner potential. Small probability plasmon scattering improves contrast transfer at high spatial frequencies, which makes the ZAC alloy a promising material for PP fabrication.

One-pot synthesis of near-infrared fluorescent gold clusters for cellular fluorescence lifetime imaging.

A facile strategy to synthesize water-soluble fluorescent gold nanoclusters (Au NCs) stabilized with the bidentate ligand dihydrolipoic acid (DHLA) is reported. The DHLA-capped Au NCs are characterized by UV-vis absorption spectroscopy, fluorescence spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The Au NCs possess many attractive features including ultrasmall size, bright near-infrared luminescence, high colloidal stability, and good biocompatibility, making them promising imaging agents for biomedical and cellular imaging applications. Moreover, their long fluorescence lifetime (>100 ns) makes them attractive as labels in fluorescence lifetime imaging (FLIM) applications. As an example, the internalization of Au NCs by live HeLa cells is visualized using the FLIM technique.

Cellular uptake of platinum nanoparticles in human colon carcinoma cells and their impact on cellular redox systems and DNA integrity.

Supercritical fluid reactive deposition was used for the deposition of highly dispersed platinum nanoparticles with controllable metal content and particle size distribution on beta-cyclodextrin. The average particle size and size distribution were steered by the precursor reduction conditions, resulting in particle preparations <20, <100, and >100 nm as characterized by transmission electron microscopy and scanning electron microscopy (SEM). These particle preparations of different size distributions were used to address the question as to whether metallic platinum particles are able to invade cells of the gastrointestinal tract as exemplified for the human colon carcinoma cell line HT29 and thus affect the cellular redox status and DNA integrity. Combined focused ion beam and SEM demonstrated that platinum nanoparticles were taken up into HT29 cells in their particulate form. The chemical composition of the particles within the cells was confirmed by energy-dispersive X-ray spectroscopy. The potential influence of platinum nanoparticles on cellular redoxsystems was determined in the DCF assay, on the translocation of Nrf-2 and by monitoring the intracellular glutathione (GSH) levels. The impact on DNA integrity was investigated by single cell gel electrophoresis (comet assay) including the formation of sites sensitive to formamidopyrimidine-DNA-glycosylase. Platinum nanoparticles were found to decrease the cellular GSH level and to impair DNA integrity with a maximal effect at 1 ng/cm(2). These effects were correlated with the particle size in an inverse manner and were enhanced with increasing incubation time but appeared not to be based on the formation of reactive oxygen species.