Researchers discover a new path for light through metal

Helping bridge the gap between photonics and electronics, researchers from Purdue University have coaxed a thin film of titanium nitride into transporting plasmons, tiny electron excitations coupled to light that can direct and manipulate optical signals on the nanoscale. Titanium nitride's addition to the short list of surface-plasmon-supporting materials, formerly composed only of metals, could point the way to a new class of optoelectronic devices with unprecedented speed and efficiency.

"We have found that titanium nitride is a promising candidate for an entirely new class of technologies based on plasmonics and metamaterials," said Alexandra Boltasseva, a researcher at Purdue and an author on a paper published March 27 in the Optical Society's (OSA) open-access journal Optical Materials Express. "This is particularly compelling because surface plasmons resolve a basic mismatch between wavelength-scale optical devices and the much smaller components of integrated electronic circuits."

Value of Plasmons

Metals carry electricity with ease, but normally do nothing to transmit light waves. Surface plasmons, unusual light-coupled oscillations that form on the surface of metallic materials, are the exception to that rule. When excited on the surface of metals by light waves of specific frequencies, plasmons are able to retain that same frequency, but with wavelengths that are orders-of-magnitude smaller, cramming visible and near-infrared light into the realm of the nanoscale.

In the world of electronics and optics, that 100-fold contraction is a boon. Circuits that direct the paths of electrons operate on a much smaller scale than optical light waves, so engineers must either rely on small but relatively sluggish electrons for information processing or bulk up to accommodate the zippy photons. Plasmons represent the best of both worlds and are already at the heart of a number of optoelectronic devices. They have not had widespread use, however, due to the dearth of materials that readily generate them and the fact that metals, in most cases, cannot be integrated with semiconductor devices.

Plasmonic Materials

Until now, the best candidates for plasmonic materials were gold and silver. These noble metals, however, are not compatible with standard silicon manufacturing technologies, limiting their use in commercial products. Silver is the metal with the best optical and surface plasmon properties, but it forms grainy, or semi-continuous, thin films. Silver also easily degrades in air, which causes loss of optical signal, making it a less-attractive material in plasmon technologies.

In an effort to overcome these drawbacks, Boltasseva and her team chose to study titanium nitride- a ceramic material that is commonly used as a barrier metal in microelectronics and to coat metal surfaces such as medical implants or machine tooling parts- because they could manipulate its properties in the manufacturing process. It also could be easily integrated into silicon products, and grown crystal-by-crystal, forming highly uniform, ultrathin films- properties that metals do not share.

To test its plasmonic capabilities, the researchers deposited a very thin, very even film of titanium nitride on a sapphire surface. They were able to confirm that titanium nitride supported the propagation of surface plasmons almost as efficiently as gold. Silver, under perfect conditions, was still more efficient for plasmonic applications, but its acknowledged signal loss limited its practical applications.

To further improve the performance of titanium nitride, the researchers are now looking into a manufacturing method known as molecular beam epitaxy, which would enable them to grow the films and layered structures known as superlattices crystal-by-crystal.

Technologies and Potential Applications

In addition to plasmonics, the researchers also speculate that titanium nitride may have applications in metamaterials, which are engineered materials that can be tailored for almost any application because of their extraordinary response to electromagnetic, acoustic, and thermal waves. Recently proposed applications of metamaterials include invisibility cloaks, optical black holes, nanoscale optics, data storage, and quantum information processing.

The search for alternatives to noble metals with improved optical properties, easier fabrication and integration capabilities could ultimately lead to real-life applications for plasmonics and metamaterials.

"Plasmonics is an important technology for nanoscale optical circuits, sensing, and data storage because it can focus light down to nanoscale," notes Boltasseva. "Titanium nitride is a promising candidate in the near-infrared and visible wavelength ranges. Unlike gold and silver, titanium nitride is compatible with standard semiconductor manufacturing technology and provides many advantages in its nanofabrication and integration."

According to the researchers, titanium nitride-based devices could provide nearly the same performance for some plasmonic applications. While noble metals like silver would still be the best choice for specific applications like negative index metamaterials, titanium nitride could outperform noble metals in other metamaterial and transformation optics devices, such as those based on hyperbolic metamaterials.

Story Source:

The above story is reprinted from materials provided by Optical Society of America.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Gururaj V. Naik, Jeremy L. Schroeder, Xingjie Ni, Alexander V. Kildishev, Timothy D. Sands, Alexandra Boltasseva. Titanium nitride as a plasmonic material for visible and near-infrared wavelengths. Optical Materials Express, 2012; 2 (4): 478 DOI: 10.1364/OME.2.000478

3D structure opens new avenue for drug discovery

The enzyme SHIP2, which plays a major role in cell signalling, has attracted particular attention due to its role in the negative regulation of insulin signalling and is thought to be involved in type-2 diabetes, obesity and cancer. Previous attempts to crystallise the enzyme with its natural substrate were unsuccessful, so scientists at Bath designed a new synthetic inhibitor as a mimic and with their European colleagues solved the X-ray crystal structure of a key fragment of SHIP2 bound to this compound.

The research, recently published in the leading international journal ACS Chemical Biology, was a collaborative project carried out by an international group of scientists based at the Karolinska Institutet in Stockholm Sweden, Nanyang University Singapore, the Université Libre de Bruxelles in Belgium and the University of Bath.

The scientists also undertook computational molecular dynamics on the complex, and discovered a flexible loop region of the protein that may close over the compound during binding. The researchers hope that targeting such a closed complex could provide a new strategy for the design of small-molecule drugs against SHIP2.

Professor Barry Potter, who led the enterprise together with his Wellcome Trust–funded Bath colleagues Drs Steve Mills, Andrew Riley, Gyles Cozier and Mark Thomas, said: “Such interdisciplinary collaboration represents a real route to early progress in drug discovery at a time when the global pharmaceutical industry is restructuring and looking more than ever towards academic-industry partnerships for early stage drug discovery, rather than in-house R&D.

“These data further reinforce use of a new class of synthetic molecule that we have pioneered at Bath for several years, for co-crystallisation studies.

“This work emphasises the strength of Medicinal Chemistry at the University of Bath and demonstrates that academic scientists can play a key role in drug discovery, particularly at early and innovative stages.”

The next step will be to design in silico related, but more drug-like, compounds that might bind to the closed complex of the SHIP2 enzyme. The researchers hope that others will use their work as a starting point to design such novel drug candidates.

More information: http://pubs.acs.or … 21/cb200494d

Provided by University of Bath (news : web)

Better analysis methods for vitamin D

As featured in a three-part series in the March 2012 issue of Agricultural Research magazine, the Beltsville center's Food Composition and Methods Development Laboratory is using new spectrometry methods to discover compounds in foods that have never before been documented.

Accurate data on the amount of vitamins and minerals in the U.S. food supply is critical to accurately assessing the intakes of these nutrients in the U.S. population. At the Beltsville center, chemist Craig Byrdwell has pioneered new, highly precise methods for analyzing vitamin D in foods and dietary supplements.

Byrdwell found that there are many ways in which multiple instruments that measure molecules can be used in parallel to provide much more information about food samples than single instruments used alone. These molecular mass-measuring instruments are called "mass spectrometers." One of Byrdwell's techniques is "triple-parallel mass spectrometry," in which three mass spectrometers, operating in different modes, are used in parallel.

Byrdwell's experiments also have shown that two systems for separating molecules (liquid chromatographs) can be used in combination to analyze complex food samples for vitamin D and its metabolites. Byrdwell authored a book chapter describing his vitamin D analysis methods, which appears in Extreme Chromatography, published by AOCS Press in Champaign, Ill. Byrdwell is also a coeditor of the book, which was published in May 2011.

Read more about the ARS national program for human nutrition monitoring in Agricultural Research magazine's March 2012 issue.

Provided by USDA Agricultural Research Service

Capsule for removing radioactive contamination from milk, fruit juices, other beverages

Amid concerns about possible terrorist attacks with nuclear materials, and fresh memories of environmental contamination from the 2011 Fukushima Daiichi nuclear disaster in Japan, scientists have described the development of a capsule that can be dropped into water, milk, fruit juices and other foods to remove more than a dozen radioactive substances.

In a presentation at the 243rd National Meeting & Exposition of the American Chemical Society (ACS), they said the technology could be used on a large scale by food processors or packaged into a small capsule that consumers at the home-kitchen level could pop into beverage containers to make them safe for consumption.

"We repurposed and repackaged for radioactive decontamination of water and beverages a tried-and-true process that originally was developed to mine the oceans for uranium and remove uranium and heavy metals from heavily contaminated water," said Allen Apblett, Ph.D., who led the research team. "The accident at the Fukushima nuclear plant in Japan and ongoing concerns about possible terrorist use of nuclear materials that may contaminate food and water led us to shift the focus of this technology."

The technology also can remove arsenic, lead, cadmium and other heavy metals from water and fruit juices, Apblett said, adding that higher-than-expected levels of some of those metals have been reported in the past in certain juices. He is with Oklahoma State University in Stillwater.

Nanoparticles composed of metal oxides, various metals combined with oxygen, are the key ingredients in the process. The particles, so small that hundreds would fit on the period at the end of this sentence, react with radioactive materials and other unwanted substances and pull them out of solution. The particles can absorb all 15 of the so-called "actinide" chemical elements on the periodic table of the elements, as well as non-actinide radioactive metals (e.g., strontium), lead, arsenic and other non-radioactive elements.

The actinides all are radioactive metals, and they include some of the most dangerous substances associated with nuclear weapons and commercial nuclear power plant accidents like Fukushima. Among them are plutonium, actinium, curium and uranium.

In the simplest packaging of the technology, the metal-oxide nanoparticles would be packed inside a capsule similar to a medicine capsule, and then stirred around in a container of contaminated water or fruit juice. Radioactive metals would exit the liquid and concentrate inside the capsule. The capsule would be removed, leaving the beverage safe for consumption. In laboratory tests, it reduced the concentrations of these metals to levels that could not be detected, Apblett noted.

The technology is moving toward commercialization, with the first uses probably in purifying calcium dietary supplements to remove any traces of lead, cadmium and radiostrontium. Apblett said the capsule version could have appeal beyond protection against terrorist attacks or nuclear accidents, among consumers in areas with heavy metals in their water or food supplies, for instance.

The scientists acknowledged funding from the Oklahoma Economic Development Generating Excellence Program.

Story Source:

The above story is reprinted from materials provided by American Chemical Society (ACS), via Newswise.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Preserving arson evidence with triclosan

The preservative, triclosan, would be the first evidence preservative for traces of gasoline and other ignitable fluids, or flame "accelerants," commonly used in arson, according to John V. Goodpaster, Ph.D., an international expert who reported on evidence of triclosan's effectiveness.

"We may finally have a substance that enables crime scene investigators to preserve traces of gasoline and other fire starters in the charred remains of buildings long enough to determine whether a fire was arson," Goodpaster said. "It could not only help law enforcement officials catch criminals, but also reveal the true scope of the arson problem."

Estimates already rank arson, the intentional starting of a fire, as the leading cause of fires in the U.S. Arson is involved in an estimated 267,000 fires each year; causes 475 deaths and 2,000 injuries and almost $1.5 billion in property damage. Those figures, however, may be an underestimate, Goodpaster said.

"Because of the huge backlog in law enforcement labs today, evidence often sits on a shelf for weeks or months until a laboratory technician has time to analyze it," he explained. "By then, any traces of gasoline or other accelerants may disappear due to the action of soil microbes that break down those materials. Currently, the only way to preserve this evidence is to freeze it, but freezer space in crime labs often is limited."

Goodpaster, who is with Indiana University-Purdue University Indianapolis, traces the idea for enlisting antimicrobials as arson fighters to concerns expressed by staff at the Indiana State Police Laboratory in Indianapolis. They knew that microbes were degrading suspected arson samples and could tell that gasoline was probably in a particular sample. But the gasoline was so degraded that they couldn't draw a definitive conclusion.

Searching for a solution to the problem, Goodpaster and graduate student Dee Ann Turner began testing various antimicrobial agents as preservatives. Those agents ranged from household chlorine bleach to iodine to hydrogen peroxide. Finally, they tested triclosan, which is in many consumer products, such as antibacterial hand soaps, toothpaste and even furniture and toys.

"We decided to try it, and lo and behold, it was tremendously effective," said Goodpaster.

Under the supervision of the Indianapolis Fire Department, Goodpaster and Turner threw Molotov cocktails — bottles of gasoline that shatter on impact in a ball of flame. They then collected soil samples just like an arson investigator would do at a fire scene. Unlike some other research, the sampling was done in real-world conditions, rather than laboratory settings that differ from the outdoor environment. Turner and Goodpaster stored the samples for 60 days to simulate a typical timeframe that evidence would sit in a crime lab due to a backlog. Then they did standard analyses for gasoline.

"The results with triclosan were amazing," Goodpaster said. "It worked quite well, preserving the gasoline so that it showed up in the analysis."

Goodpaster said that using triclosan is easy. It involves just pouring triclosan onto suspected arson samples until the material is soaked. Arson investigators could start adding triclosan right now. But Goodpaster's lab is looking into development of a commercial triclosan solution custom-tailored for crime labs.

More information:
Abstract
Fire debris evidence often sits for months before analysis, wherein the ignitable liquid residue (ILR) potentially suffers degradation by hydrocarbon-metabolizing bacteria, complicating identification and classification. Degradation severity depends on bacterial populations, soil type, and season. The goal of this research is to develop a chemical method applicable in the field to stop microbial degradation and preserve fire debris evidence.
Degradation studies were conducted during two seasons with two soil types to track degradation over 60 days in samples from incendiary devices containing gasoline. A preservation study was conducted to test the efficacy of Triclosan in preserving ILRs. ILR extraction was performed via passive headspace GC-MS.
Statistical analysis of the data yielded trends among different soil types and seasons. The soil studies described above demonstrate that bacteria selectively degrade aromatic and/or n-alkane compounds readily. However, the addition of Triclosan to fire debris upon collection is an effective method for evidence preservation.