High-aspect ratio ZnO nanowires have become one of the most promising products in the nanosciences within the past few years with a multitude of applications at the interface of optics and electronics. The interaction of zinc with cells and organisms is complex, with both deficiency and excess causing severe effects. The emerging significance of zinc for many cellular processes makes it imperative to investigate the biological safety of ZnO nanowires in order to guarantee their safe economic exploitation. In this study, ZnO nanowires were found to be toxic to human monocyte macrophages (HMMs) at similar concentrations as ZnCl(2). Confocal microscopy on live cells confirmed a rise in intracellular Zn(2+) concentrations prior to cell death. In vitro, ZnO nanowires dissolved very rapidly in a simulated body fluid of lysosomal pH, whereas they were comparatively stable at extracellular pH. Bright-field transmission electron microscopy (TEM) showed a rapid macrophage uptake of ZnO nanowire aggregates by phagocytosis. Nanowire dissolution occurred within membrane-bound compartments, triggered by the acidic pH of the lysosomes. ZnO nanowire dissolution was confirmed by scanning electron microscopy/energy-dispersive X-ray spectrometry. Deposition of electron-dense material throughout the ZnO nanowire structures observed by TEM could indicate adsorption of cellular components onto the wires or localized zinc-induced protein precipitation. Our study demonstrates that ZnO nanowire toxicity in HMMs is due to pH-triggered, intracellular release of ionic Zn(2+) rather than the high-aspect nature of the wires. Cell death had features of necrosis as well as apoptosis, with mitochondria displaying severe structural changes. The implications of these findings for the application of ZnO nanowires are discussed.

The development of semiconductor nanowires has recently been the focus of extensive research as these structures may play an important role in the next generation of nanoscale devices. Using semiconductor nanowires as building blocks, a number of high performance electronic devices have been fabricated. In this review, we discuss synthetic methodologies and electrical characteristics of Si, Ge, and Ge/Si core/shell nanowires. In particular the fabrication and electrical properties of a variety of nanowire-based field effect transistors (FETs) are discussed. Although the bottom-up approach has the potential to go far beyond the limits of top-down technology, new techniques need to be developed to realize precise control of structural parameters, such as size uniformity, growth direction, and dopant distribution within nanowires to produce nanowire-based electronics on a large scale.

We report an observation of room temperature ferromagnetism in Ge nanowires doped with Mn. Highdensity arrays of Ge 1−x Mn x ͑x =1% -5%͒ nanowires with the smallest diameter of 35 nm have been synthesized within the pores of anodized aluminium oxide membranes using a supercritical fluid inclusion-phase technique. Structural analysis of the nanowires proved the existence of a highly crystalline germanium host lattice containing discrete manganese atoms. All of the nanowires studied displayed ferromagnetic properties at room temperature. Ferromagnetic ordering reaches a maximum at intermediate Mn concentrations. The magnetic properties of the nanowires can be understood by considering the influence of co-dopant nonmagnetic impurities and nanowire/membrane interfaces.