Fast, cheap, and accurate: Detecting CO2 with a fluorescent twist

ScienceDaily (Sep. 4, 2011) — Detecting specific gases in the air is possible using a number of different existing technologies, but typically all of these suffer from one or more drawbacks including high energy cost, large size, slow detection speed, and sensitivity to humidity.

Overcoming these deficiencies with a unique approach, a team based at Kyoto University has designed an inexpensive new material capable of quick and accurate detection of a specific gas under a wide variety of circumstances. Moreover, in addition to being reusable, the compound gives off variable degrees of visible light in correspondence with different gas concentrations, providing for development of easy to use monitoring devices.

The findings, published in a recent issue of Nature Materials, describe the use of a flexible crystalline material (porous coordination polymer, or PCP) that transforms according to changes in the environment. When infused with a fluorescent reporter molecule (distyrylbenzene, or DSB), the composite becomes sensitive specifically to carbon dioxide gas, glowing with varying intensity based on changing concentrations of the gas. Lead author for the paper was Dr. Nobuhiro Yanai of the university's Graduate School of Engineering.

"The real test for us was to see whether the composite could differentiate between carbon dioxide and acetylene, which have similar physiochemical properties," explains Assoc. Prof. Takashi Uemura, also of the Graduate School of Engineering. "Our findings clearly show that this PCP-DSB combination reacts very differently to the two gases, making accurate CO2 detection possible in a wide variety of applications."

In its natural state, DSB is a long, flat molecule, which emits a blue light. When adsorbed by the PCP framework, DSB molecules twist, causing the entire PCP structure to also become skewed. In this condition, the glow of DSB diminishes significantly.

"On this occasion we observed that the presence of CO2 causes the DSB molecules to revert to their flat, brightly fluorescent form, while also returning the PCP grid to its usual state," adds Professor and deputy director Susumu Kitagawa of the university's Institute for Integrated Cell-Material Sciences (iCeMS). "And importantly, these steps can be reversed without causing any significant changes to the composite, making possible the development of a wide variety of specific, inexpensive, reusable gas detectors."

This work was supported by the Murata Science Foundation, ERATO-JST, a Grant-in-Aid for Young Scientists (A), and a Grant-in-Aid for Scientific Research on Innovative Area "Emergence in Chemistry" from MEXT.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Institute for Integrated Cell-Material Sciences, Kyoto University.

Journal Reference:

Nobuhiro Yanai, Koji Kitayama, Yuh Hijikata, Hiroshi Sato, Ryotaro Matsuda, Yoshiki Kubota, Masaki Takata, Motohiro Mizuno, Takashi Uemura, Susumu Kitagawa. Gas detection by structural variations of fluorescent guest molecules in a flexible porous coordination polymer. Nature Materials, 2011; DOI: 10.1038/nmat3104

Manufacturing method paves way for commercially viable quantum dot-based LEDs

University of Florida researchers may help resolve the public debate over our future light source of choice: Edison's incandescent bulb or the more energy efficient compact fluorescent lamp.

It could be neither.

Instead, our future lighting needs may be supplied by a new breed of light emitting diode, or LED, that conjures light from the invisible world of quantum dots. According to an article in the current online issue of the journal Nature Photonics, moving a QD LED from the lab to market is a step closer to reality thanks to a new manufacturing process pioneered by two research teams in UF's department of materials science and engineering.

"Our work paves the way to manufacture efficient and stable quantum dot-based LEDs with really low cost, which is very important if we want to see wide-spread commercial use of these LEDs in large-area, full-color flat-panel displays or as solid-state lighting sources to replace the existing incandescent and fluorescent lights," said Jiangeng Xue, the research leader and an associate professor of material science and engineering "Manufacturing costs will be significantly reduced for these solution-processed devices, compared to the conventional way of making semiconductor LED devices."

A significant part of the research carried out by Xue's team focused on improving existing organic LEDs. These semiconductors are multilayered structures made up of paper thin organic materials, such as polymer plastics, used to light up display systems in computer monitors, television screens, as well as smaller devices such as MP3 players, mobile phones, watches, and other handheld electronic devices. OLEDs are also becoming more popular with manufacturers because they use less power and generate crisper, brighter images than those produced by conventional LCDs (liquid crystal displays). Ultra-thin OLED panels are also used as replacements for traditional light bulbs and may be the next big thing in 3-D imaging.

Complementing Xue's team is another headed by Paul Holloway, distinguished professor of materials science and engineering at UF, which delved into quantum dots, or QDs. These nano-particles are tiny crystals just a few nanometers (billionths of a meter) wide, composed of a combination of sulfur, zinc, selenium and cadmium atoms. When excited by electricity, QDs emit an array of colored light. The individual colors vary depending on the size of the dots. Tuning, or "adjusting," the colors is achieved by controlling the size of the QDs during the synthetic process.

By integrating the work of both teams, researchers created a high-performance hybrid LED, composed of both organic and QD-based layers. Until recently, however, engineers at UF and elsewhere have been vexed by a manufacturing problem that hindered commercial development. An industrial process known as vacuum deposition is the common way to put the necessary organic molecules in place to carry electricity into the QDs. However, a different manufacturing process called spin-coating, is used to create a very thin layer of QDs. Having to use two separate processes slows down production and drives up manufacturing costs.

According to the Nature Photonics article, UF researchers overcame this obstacle with a patented device structure that allows for depositing all the particles and molecules needed onto the LED entirely with spin-coating. Such a device structure also yields significantly improved device efficiency and lifetime compared to previously reported QD-based LED devices.

Spin-coating may not be the final manufacturing solution, however.

"In terms of actual product manufacturing, there are many other high through-put, continuous "roll-to-roll" printing or coating processes that we could use to fabricate large area displays or lighting devices," Xue said. "That will remain as a future research and development topic for the university and a start-up company, NanoPhotonica, that has licensed the technology and is in the midst of a technology development program to capitalize on the manufacturing breakthrough."

Other co-authors of this article are Lei Qian and Ying Zheng, two postdoctoral fellows who worked with the professors on this research. The UF research teams received funding from the Army Research Office, the U.S. Department of Energy, and the Florida Energy Systems Consortium.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by University of Florida. The original article was written by John Dunn.

Journal Reference:

Lei Qian, Ying Zheng, Jiangeng Xue, Paul H. Holloway. Stable and efficient quantum-dot light-emitting diodes based on solution-processed multilayer structures. Nature Photonics, 2011; 5 (9): 543 DOI: 10.1038/nphoton.2011.171

Down to the wire: Inexpensive technique for making high quality nanowire solar cells

Solar or photovoltaic cells represent one of the best possible technologies for providing an absolutely clean and virtually inexhaustible source of energy to power our civilization. However, for this dream to be realized, solar cells need to be made from inexpensive elements using low-cost, less energy-intensive processing chemistry, and they need to efficiently and cost-competitively convert sunlight into electricity.

A team of researchers with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) has now demonstrated two out of three of these requirements with a promising start on the third.

Peidong Yang, a chemist with Berkeley Lab's Materials Sciences Division, led the development of a solution-based technique for fabricating core/shell nanowire solar cells using the semiconductors cadmium sulfide for the core and copper sulfide for the shell. These inexpensive and easy-to-make nanowire solar cells boasted open-circuit voltage and fill factor values superior to conventional planar solar cells. Together, the open-circuit voltage and fill factor determine the maximum energy that a solar cell can produce. In addition, the new nanowires also demonstrated an energy conversion efficiency of 5.4-percent, which is comparable to planar solar cells.

"This is the first time a solution based cation-exchange chemistry technique has been used for the production of high quality single-crystalline cadmium sulfide/copper sulfide core/shell nanowires," Yang says. "Our achievement, together with the increased light absorption we have previously demonstrated in nanowire arrays through light trapping, indicates that core/shell nanowires are truly promising for future solar cell technology."

Yang, who holds a joint appointment with the University of California (UC) Berkeley, is the corresponding author of a paper reporting this research that appears in the journal Nature Nanotechnology. The paper is titled "Solution-processed core-shell nanowires for efficient photovoltaic cells." Co-authoring this paper with Yang were Jinyao Tang, Ziyang Huo, Sarah Brittman and Hanwei Gao.

Typical solar cells today are made from ultra-pure single crystal silicon wafers that require about 100 micrometers in thickness of this very expensive material to absorb enough solar light. Furthermore, the high-level of crystal purification required makes the fabrication of even the simplest silicon-based planar solar cell a complex, energy-intensive and costly process.

A highly promising alternative would be semiconductor nanowires -- one-dimensional strips of materials whose width measures only one-thousandth that of a human hair but whose length may stretch up to the millimeter scale. Solar cells made from nanowires offer a number of advantages over conventional planar solar cells, including better charge separation and collection capabilities, plus they can be made from Earth abundant materials rather than highly processed silicon. To date, however, the lower efficiencies of nanowire-based solar cells have outweighed their benefits.

"Nanowire solar cells in the past have demonstrated fill factors and open-circuit voltages far inferior to those of their planar counterparts," Yang says. "Possible reasons for this poor performance include surface recombination and poor control over the quality of the p-n junctions when high-temperature doping processes are used."

At the heart of all solar cells are two separate layers of material, one with an abundance of electrons that function as a negative pole, and one with an abundance of electron holes (positively-charged energy spaces) that function as a positive pole. When photons from the sun are absorbed, their energy is used to create electron-hole pairs, which are then separated at the p-n junction -- the interface between the two layers -- and collected as electricity.

About a year ago, working with silicon, Yang and members of his research group developed a relatively inexpensive way to replace the planar p-n junctions of conventional solar cells with a radial p-n junction, in which a layer of n-type silicon formed a shell around a p-type silicon nanowire core. This geometry effectively turned each individual nanowire into a photovoltaic cell and greatly improved the light-trapping capabilities of silicon-based photovoltaic thin films.

Now they have applied this strategy to the fabrication of core/shell nanowires using cadmium sulfide and copper sulfide, but this time using solution chemistry. These core/shell nanowires were prepared using a solution-based cation (negative ion) exchange reaction that was originally developed by chemist Paul Alivisatos and his research group to make quantum dots and nanorods. Alivisatos is now the director of Berkeley Lab, and UC Berkeley's Larry and Diane Bock Professor of Nanotechnology.

"The initial cadmium sulfide nanowires were synthesized by physical vapor transport using a vapor-liquid-solid (VLS) mechanism rather than wet chemistry, which gave us better quality material and greater physical length, but certainly they can also be made using solution process" Yang says. "The as-grown single-crystalline cadmium sulfide nanowires have diameters of between 100 and 400 nanometers and lengths up to 50 millimeters."

The cadmium sulfide nanowires were then dipped into a solution of copper chloride at a temperature of 50 degrees Celsius and kept there for 5 to 10 seconds. The cation exchange reaction converted the surface layer of the cadmium sulfide into a copper sulfide shell.

"The solution-based cation exchange reaction provides us with an easy, low-cost method to prepare high-quality hetero-epitaxial nanomaterials," Yang says. "Furthermore, it circumvents the difficulties of high-temperature doping and deposition for typical vapor phase production methods, which suggests much lower fabrication costs and better reproducibility. All we really need are beakers and flasks for this solution-based process. There's none of the high fabrication costs associated with gas-phase epitaxial chemical vapor deposition and molecular beam epitaxy, the techniques most used today to fabricate semiconductor nanowires."

Yang and his colleagues believe they can improve the energy conversion efficiency of their solar cell nanowires by increasing the amount of copper sulfide shell material. For their technology to be commercially viable, they need to reach an energy conversion efficiency of at least ten-percent.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by DOE/Lawrence Berkeley National Laboratory.

Journal Reference:

Jinyao Tang, Ziyang Huo, Sarah Brittman, Hanwei Gao, Peidong Yang. Solution-processed core–shell nanowires for efficient photovoltaic cells. Nature Nanotechnology, 2011; DOI: 10.1038/nnano.2011.139

'Plastic bottle' solution for arsenic-contaminated water threatening 100 million people

ScienceDaily (Sep. 1, 2011) — With almost 100 million people in developing countries exposed to dangerously high levels of arsenic in their drinking water, and unable to afford complex purification technology, scientists have now described a simple, inexpensive method for removing arsenic based on chopped up pieces of ordinary plastic beverage bottles coated with a nutrient found in many foods and dietary supplements.

The report was part of the 242nd National Meeting & Exposition of the American Chemical Society (ACS), a major scientific meeting with 7,500 technical papers, being held in Denver Colorado the week of August 29.

"Dealing with arsenic contamination of drinking water in the developing world requires simple technology based on locally available materials," said study leader Tsanangurayi Tongesayi, Ph.D., professor of analytical and environmental chemistry at Monmouth University, West Long Branch, N.J. "Our process uses pieces of plastic water, soda pop and other beverage bottles. Coat the pieces with cysteine -- that's an amino acid found in dietary supplements and foods -- and stir the plastic in arsenic-contaminated water. This works like a magnet. The cysteine binds up the arsenic. Remove the plastic and you have drinkable water."

Tongesayi described laboratory tests of the plastic bottle arsenic removal method on water containing 20 parts per billion (ppb) of arsenic, which is two times the safe standard set by the U.S. Environmental Protection Agency for drinking water. It produced drinkable water with 0.2 ppb of arsenic that more than meets the federal standard.

The technology is so straight-forward that people without technical skills can use it, Tongesayi said, citing that as one of its advantages over some of the existing arsenic-removal technologies. It can use discarded plastic bottles available locally, and the application of cysteine does not require complicated technology. Tongesayi is seeking funding or a commercial partner, which he said is the key to moving the arsenic-removing process into use in a relatively short time. The technology also has the potential for removing other potentially toxic heavy metals from drinking water.

Odorless, tasteless and colorless, arsenic enters drinking water supplies from natural deposits in soil and rock that occur in some parts of the world, including parts of the United States, and from agricultural and industrial sources. Symptoms of arsenic poisoning include thickening and discoloration of the skin; stomach pain, nausea, vomiting and diarrhea; vision loss; and numbness in hands and feet. Arsenic also has been linked to cancer of the bladder, lungs, skin, kidney, nasal passages, liver and prostate.

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Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by American Chemical Society.

Note: If no author is given, the source is cited instead.

Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of ScienceDaily or its staff.

Insect gut microbe with a molecular iron reservoir: Researchers analyze the structure of an iron storage protein

Iron plays an important role in almost every life form. Low iron can lead to deficiency symptoms and reduced growth, whereas too much iron may harm biomolecules like DNA. Max Planck researchers from Jena and Tuebingen have now elucidated the spatial structure of a bacterial enzyme in Microbacterium arborescens which is able to accumulate several hundred iron ions in its center -- depending on the iron supply situation in its environment: for example in the larval gut of the beet armyworm Spodoptera exigua.

With its additional peroxidase activity, the enzyme inhibits the occurrence of cell-damaging oxygen radicals. Moreover, it catalyzes the hydrolysis and formation of N-acyl glutamines (conjugates of the amino acid glutamine with fatty acids). The plant recognizes the larval pest with the help of these conjugates and initiates its chemical defense against invader. Structurally related enzymes are produced by other bacteria and are collectively termed as DNA protecting proteins under starvation (DPS).

The research is reported in the Journal of Biological Chemistry.

Microbes are omnipresent on Earth. They are found as free-living microorganisms as well as in communities with other higher organisms. Thanks to modern biological techniques we are now able to address the complex communities and study the role of individual microorganisms and enzymes in more detail.

Microbacterium arborescens is a bacterium, which can be found in the guts of herbivorous caterpillars. The Department of Bioorganic Chemistry at the Max Planck Institute for Chemical Ecology studies interactions between insects and microorganisms which live in their digestive system. What is the advantage for both, insects and microbes? How strongly do they depend on each other? Do microbes play a role in mediating interactions between herbivorous insects and host plants?

In the course of the experiments to answer these questions the scientists came across an enzyme they had isolated from M. arborescens, a resident in the gut of the Beet Armyworm Spodoptera exigua. It was called N-acyl amino acid hydrolase (AAH) because of its catalytic function: it catalyzes the synthesis and hydrolysis of conjugates of the amino acid glutamine with fatty acids. The N-acyl glutamines enter the infested plant via oral secretions and intestinal contents of the larvae and trigger the plant's defense responses. After cloning and sequencing the AAH encoding gene the scientists discovered an interesting result: AAH is closely related to proteins from other microorganisms: the "DNA protection during starvation (DPS)" proteins, which bind to DNA molecules and protect them by crystallization or by removal of dangerous OH• radicals.

Jelena Pesek, PhD student in the Department of Bioorganic Chemistry at the institute, was surprised that the enzyme AAH from M. arborescens differs from DPS enzymes in other microbes to the effect that it additionally regulates the concentration of N-acyl glutamine (conjugates of glutamic acid with fatty acids) in the gut, which are important for molecular plant-insect interactions. Moreover, the enzyme is able to store Fe(III)ions in its center. If free Fe(II) is present, hydrogen peroxide (H2O2), which is synthesized by the insect's intestinal cells to fend off microorganisms, is converted to highly reactive hydroxyl radicals. The process is known as Fenton's Reaction:

Fe2+ + H2O2 › Fe3+ + OH- + •HO

The highly reactive hydroxyl radical •HO damages especially the DNA and thus causes dangerous mutations of the genetic material. In cooperation with Kornelius Zeth from the Max Planck Institute for Developmental Biology in Tuebingen the researchers succeeded in analyzing the iron transport mechanisms by means of crystallization and X-ray structure determination.The protein consists of 12 identical subunits and has a molecular mass of 204 kDa -- a considerable size for a single enzyme. The homo-oligomer is round and hollow inside. It can store up to 500 iron atoms as ferric iron (usually in the form of Fe2O3) in the hollow cavity. The iron transport into the cavity is unique: The spherical protein has four selective pores which provide access only to ferrous iron ions along with their hydration shells (six water molecules). At catalytic ferroxidase centers inside the cavity the Fe(II) is oxidized to Fe(III) with simultaneous reduction of the dangerous H2O2 to water (H2O). The scientists assume that AAH ensures survival of M. arborescens in the larval gut, where conditions may be harsh and constantly changing depending on food quality. The enzyme is protective against oxidative stress, reducing the concentration of free Fe(II) by storing it and simultaneously neutralizing H2O2 as a source for cell damaging radicals.

The evolutionary context of these processes as well as the formation and hydrolysis of N-acyl glutamines which are also catalyzed by AAH are still unknown. Because of their detergent character these compounds may help the larvae to better digest the plant food. In the course of evolution, attacked host plants may have "learned" to exploit the conjugates which enter the leaves during herbivory as a chemical alarm signal in order to activate their defense against the insect pest efficiently.

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Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by Max Planck Institute for Chemical Ecology.

Journal Reference:

J. Pasek, R. Buechler, R. Albrecht, W. Boland, K. Zeth. Structure and mechanism of iron translocation by a DPS protein from Microbacterium arborescens. Journal of Biological Chemistry, 2011; DOI: 10.1074/jbc.M111.246108