The amorphization of crystalline silicon by ball milling.

The transformation of crystalline silicon to amorphous silicon during ball milling was quantitatively measured by x-ray diffraction and electrochemical methods. Amorphous silicon was found to form rapidly from the very initial stages of ball milling. Simultaneously, the grain size of the crystalline silicon phase decreased. Under extended milling times it was found that a maximum of 86 % of the silicon became amorphous. Similarly, the grain size of the crystalline silicon phase could not be reduced below 6 nm. This transformation followed an Avrami kinetic model, which is consistent with a system which reaches a steady state. These observations suggest a mechanism in which ball milling generates defects, resulting in silicon amorphization and grain size reduction, where the degree of amorphization is limited in extent because there exists a limiting silicon grain size below which defects are no longer formed.

Facile synthesis of antibiotic-functionalized gold nanoparticles for colorimetric bacterial detection.

The development of quick and efficient methods for the detection of pathogenic bacteria is urgently needed for the diagnosis of infectious diseases and the control of microbiological contamination in global waterways, potable water sources and the food industry. This contribution will describe the synthesis of gold nanoparticles and their conjugation to broad spectrum, polypeptide and ß-lactam antibiotics that function as both reducing agents and surface protectants (ATB@AuNP). Nanoparticle colloids examined using transmission electron microscopy are generally spherical in shape and range from 2-50 nm in size. Dynamic light scattering and infrared spectroscopy were also used to confirm encapsulation of the AuNP surface by antibiotic molecules. ATB@AuNP were then used to detect 3 common pathogenic bacterial species: Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli. The colour of the AuNP colloid was monitored visually and using UV-visible spectroscopy. A red shift of the UV visible absorbance and a visible colour change following introduction of each pathogen is indicative of ATB binding to the bacteria surface, ascribed to AuNP agglomeration. This work demonstrates that ATB@AuNP may be an efficient and high throughput tool for the rapid detection of common bacterial contaminants.

Nanoparticulate-specific effects of silver on teleost cardiac contractility.

Silver nanoparticles (nAg), due to their biocidal properties, are common in medical applications and are used in more consumer products than any other engineered nanomaterial. This growing abundance, combined with their ability to translocate across the epithelium and bioaccumulate, suggests that internalized nAg may present a risk of toxicity to many organisms in the future. However, little experimentation has been devoted to cardiac responses to acute nAg exposure, even though nAg is known to disrupt ion channels even when ionic Ag+ does not. In this study, we examined the cardiac response to nAg exposure relative to a sham and an ionic AgNO3 control across cardiomyocyte survival and homeostasis, ventricular contractility, and intrinsic pacing rates of whole hearts. Our results suggest that nAg, but not Ag+ alone, inhibits force production by the myocardium, that Ag in any form disrupts normal pacing of cardiac contractions, and that these responses are likely not due to cytotoxicity. This evidence of nanoparticle-specific effects on physiology should encourage further research into nAg cardiotoxicity and other potential sublethal effects.

Environmentally relevant concentrations of amine-functionalized copper nanoparticles exhibit different mechanisms of bioactivity in Fundulus Heteroclitus in fresh and brackish water.

The bioavailability of engineered nanomaterials should be limited in marine environments, but uptake and toxicity has been noted in marine fish and invertebrates, albeit at exposure doses far exceeding predicted environmental levels. We examined the bioactivity of amine functionalized copper nanoparticles (nCu; 5-10 nm core diameter) to the euryhaline killifish, Fundulus heteroclitus, in fresh (FW) and brackish water (BW). Free copper dissolution was undetectable in either water type and nCu remained relatively well dispersed in BW, despite the high ionic strength. Exposure to an environmentally relevant concentration of nCu (10 µg L-1) for 48 h significantly increased the maximum rate of oxygen consumption and aerobic scope in BW killifish. This effect was associated with gill remodeling which likely increased surface area and scope for oxygen uptake. In contrast, nCu exposure had no effect on oxygen consumption in FW killifish, but gill Na+/K+-ATPase activity was reduced by >40%, an effect not seen in BW. Osmotic and ionic homeostasis were protected and no indications of physiological or oxidative stress were observed in either FW and BW exposure groups. The results show that functionalized nCu formulations can exhibit bioactivity in both FW and BW and that the underlying mechanisms are different between water types.

Voronoi-Tessellated Graphite Produced by Low-Temperature Catalytic Graphitization from Renewable Resources.

A highly crystalline graphite powder was prepared from the low temperature (800-1000 °C) graphitization of renewable hard carbon precursors using a magnesium catalyst. The resulting graphite particles are composed of Voronoi-tessellated regions comprising irregular sheets; each Voronoi-tessellated region having a small "seed" particle located near their centroid on the surface. This suggests nucleated outward growth of graphitic carbon, which has not been previously observed. Each seed particle consists of a spheroidal graphite shell on the inside of which hexagonal graphite platelets are perpendicularly affixed. This results in a unique high surface area graphite with a high degree of graphitization that is made with renewable feedstocks at temperatures far below that conventionally used for artificial graphites.

Promoting DNA loading on magnetic nanoparticles using a DNA condensation strategy.

Maximizing DNA loading on magnetic nanoparticles (MNPs) is crucial for their successful utilization in gene transfer, DNA isolation, and bio-analytical applications. This enhancement is typically achieved by altering particle size and surfaces as well as charge density and ionic strength. We demonstrate a novel route for promoting DNA loading on amino-modified silica-coated magnetic nanoparticles (ASMNPs) by prior condensation of elongated DNA to a compact globule before adsorption. The enhanced DNA-loading capacity, as demonstrated by a reduction in the number of ASMNPs needed to achieve complexation, was presumably due to the elimination of DNA wrapping around nanoparticles and substantially reduced electrostatic interactions of DNA with nanoparticles because the compacted DNA globule conformation decreases its exposed surface charge. The maximum loading capacity of ASMNPs for condensed DNA was 4.4 times greater than that for elongated coiled DNA, achieving the highest ever reported value of 385 µg mg(-1). Practical applications for plasmid DNA isolation from cleared lysate confirmed the reliability of the proposed method.

Structural phase transition and related electronic properties in quasi-one-dimensional (NbSe4)(10/3)I.

The real crystal structure of the (NbSe4)(10/3)I charge density wave (CDW) compound is studied by simulation of the X-ray diffuse scattering. The average structure of the low-temperature twinned phase is determined and the phase transition is attributed to the formation of a CDW. The diffuse streaking, present in X-ray diffraction patterns above and below the transition at T = 282 K, is shown to be a projection of diffuse concentric rings perpendicular to the c* direction. The simulated patterns, based on a mismatch model between infinite NbSe4 chains, correlated by I atoms, are in good accordance with the experimental patterns. In addition to the experiments, the electronic properties of the high- and the low-temperature phases are calculated with the extended Hückel tight-binding method. The Fermi surfaces of the average structures above and below the phase transition appear very similar. Their shapes support a nesting instability and a CDW formation. The weak incommensurate CDW satellites, present below the phase transition, are at 100 K properly described by a modulation wavevector q = [0.06 (1), 0, 0.55 (1)].