3-D Printer Can Build Synthetic Tissues

3-D Printer Can Build Synthetic Tissues

  4:26:00 PM    Science Lover

---

A custom-built programmable 3D printer can create materials with several of the properties of living tissues, Oxford University scientists have demonstrated.

A custom-built programmable 3D printer can create materials with several of the properties of living tissues, Oxford University scientists have demonstrated: Droplet network c.500 microns across with electrically conductive pathway between electrodes mimicking nerve. (Credit: Oxford University/G Villar)

The new type of material consists of thousands of connected water droplets, encapsulated within lipid films, which can perform some of the functions of the cells inside our bodies.

These printed 'droplet networks' could be the building blocks of a new kind of technology for delivering drugs to places where they are needed and potentially one day replacing or interfacing with damaged human tissues. Because droplet networks are entirely synthetic, have no genome and do not replicate, they avoid some of the problems associated with other approaches to creating artificial tissues -- such as those that use stem cells.

The team report their findings in this week's Science.

'We aren't trying to make materials that faithfully resemble tissues but rather structures that can carry out the functions of tissues,' said Professor Hagan Bayley of Oxford University's Department of Chemistry, who led the research. 'We've shown that it is possible to create networks of tens of thousands connected droplets. The droplets can be printed with protein pores to form pathways through the network that mimic nerves and are able to transmit electrical signals from one side of a network to the other.'

Each droplet is an aqueous compartment about 50 microns in diameter. Although this is around five times larger than living cells the researchers believe there is no reason why they could not be made smaller. The networks remain stable for weeks.

'Conventional 3D printers aren't up to the job of creating these droplet networks, so we custom built one in our Oxford lab to do it,' said Professor Bayley. 'At the moment we've created networks of up to 35,000 droplets but the size of network we can make is really only limited by time and money. For our experiments we used two different types of droplet, but there's no reason why you couldn't use 50 or more different kinds.'

The unique 3D printer was built by Gabriel Villar, a DPhil student in Professor Bayley's group and the lead author of the paper.

The droplet networks can be designed to fold themselves into different shapes after printing -- so, for example, a flat shape that resembles the petals of a flower is 'programmed' to fold itself into a hollow ball, which cannot be obtained by direct printing. The folding, which resembles muscle movement, is powered by osmolarity differences that generate water transfer between droplets.

Gabriel Villar of Oxford University's Department of Chemistry said: 'We have created a scalable way of producing a new type of soft material. The printed structures could in principle employ much of the biological machinery that enables the sophisticated behaviour of living cells and tissues.'

Read More

Self-Assembling Nanocubes for Lenses

Self-Assembling Nanocubes for Lenses

  8:39:00 PM    Science Lover

---

Researchers at the University of California, San Diego Jacobs School of Engineering have developed a technique that enables metallic nanocrystals to self-assemble into larger, complex materials for next-generation antennas and lenses. The metal nanocrystals are cube-shaped and, like bricks or Tetris blocks, spontaneously organize themselves into larger-scale structures with precise orientations relative to one another.

UC San Diego nanoengineers have developed a 
technique that enables silver nanocubes to 
self-assemble into larger-scale structures for use in 
new optical chemical and biological sensors, and 
optical circuitry. (Credit: Image courtesy of 
University of California - San Diego)

Their findings were published online June 10 in the journal Nature Nanotechnology.

This research is in the new field of nanoplasmonics, where researchers are developing materials that can manipulate light using structures that are smaller than the wavelength of light itself. The nanocubes used in this study were less than 0.1 microns; by comparison, the breadth of a human hair is 100 microns. Precise orientation is necessary so that the cubes can confine light (for a nanoscale antenna) or focus light (for a nanoscale lens) at different wavelengths.

"Our findings could have important implications in developing new optical chemical and biological sensors, where light interacts with molecules, and in optical circuitry, where light can be used to deliver information," said Andrea Tao, a professor in the Department of NanoEngineering at the Jacobs School. Tao collaborated with nanoengineering professor Gaurav Arya and post-doctoral researcher Bo Gao.

To construct objects like antennas and lenses, Tao's team is using chemically synthesized metal nanocrystals. The nanocrystals can be synthesized into different shapes to build these structures; in this study, Tao's team created tiny cubes composed of crystalline silver that can confine light when organized into multi-particle groupings. Confining light into ultra-small volumes could allow optical sensors that are extremely sensitive and that could allow researchers to monitor how a single molecule moves, reacts, and changes with time.

To control how the cubes organize, Tao and her colleagues developed a method to graft polymer chains to the silver cube surfaces that modify how the cubes interact with each other. Normally when objects like cubes stack, they pack side-by-side like Tetris blocks. Using simulations, Tao's team predicted that placing short polymer chains on the cube surface would cause them to stack normally, while placing long polymer chains would cause the cubes to stack edge-to-edge. The approach is simple, robust, and versatile.

In demonstrating their technique, the researchers created macroscopic films of nanocubes with these two different orientations and showed that the films reflected and transmitted different wavelengths of light.

The research was supported by the National Science Foundation, the Hellman Foundation, and Jacobs School of Engineering at UC San Diego.

Read More

Biofuel Research Boosted by Discovery of How Cyanobacteria Make Energy

Biofuel Research Boosted by Discovery of How Cyanobacteria Make Energy

  10:14:00 AM    Science Lover

---

A generally accepted, 44-year-old assumption about how certain kinds of bacteria make energy and synthesize cell materials has been shown to be incorrect by a team of scientists led by Donald Bryant, the Ernest C. Pollard Professor of Biotechnology at Penn State and a research professor in the Department of Chemistry and Biochemistry at Montana State University. The research, which will be published in the journal Science on Dec. 16, is expected to help scientists discover new ways of genetically engineering bacteria to manufacture biofuels -- energy-rich compounds derived from biological sources. Many textbooks, which cite the 44-year-old interpretation as fact, likely will be revised as a result of the new discovery.

Penn State scientists have scoured this cyanobacterium's
genome to discover genes that could make alternative
energy-cycle enzymes for biofuels and plastics.
(Credit: Bryant lab, Penn State)

Bryant explained that, in 1967, two groups of researchers concluded that an important energy-making cycle was incomplete in cyanobacteria -- photosynthetic bacteria formerly known as blue-green algae. This energy-producing cycle -- known as the tricarboxylic acid (TCA) cycle or the Krebs cycle -- includes a series of chemical reactions that are used for metabolism by most forms of life, including bacteria, molds, protozoa and animals. This series of chemical reactions eventually leads to the production of ATP -- molecules responsible for providing energy for cell metabolism.

"During studies 44 years ago, researchers concluded that cyanobacteria were missing an essential enzyme of the metabolic pathway that is found in most other life forms," Bryant explained. "They concluded that cyanobacteria lacked the ability to make one enzyme, called 2-oxoglutarate dehydrogenase, and that this missing enzyme rendered the bacteria unable to produce a compound -- called succinyl-coenzyme A -- for the next step in the TCA cycle. The absence of this reaction was assumed to render the organisms unable to oxidize metabolites for energy production, although they could still use the remaining TCA-cycle reactions to produce substrates for biosynthetic reactions. As it turns out, the researchers just weren't looking hard enough, so there was more work to be done."

Bryant suspected that the decades-old finding needed to be re-evaluated with a fresh set of eyes and new scientific tools. He explained that, after researchers in the 1960s concluded that cyanobacteria had an incomplete TCA cycle, that false assumption was compounded by later researchers who used modern genomics-research methods to confirm it.

"One idea we had was that the 1967 hypothesis never was corrected because modern genome-annotation methods were partly to blame," Bryant said. "Computer algorithms are used to search for strings of genetic code to identify genes. Sometimes important genes simply can be missed because of matching errors, which occur when very similar genes have very different functions. So if researchers don't use biochemical methods to validate computer-identified gene functions, they run the risk of making premature and often incorrect conclusions about what's there and what's not there."

To re-test the 1967 hypothesis, the team performed new biochemical and genetic analyses on a cyanobacterium called Synechococcus sp. PCC 7002, scouring its genome for genes that might be responsible for making alternative energy-cycle enzymes. The scientists discovered that Synechococcus indeed had genes that coded for one important alternative enzyme, succinic semialdehyde dehydrogenase, and that adjacent to the gene for this enzyme was a misidentified gene that subsequently was shown to encode a novel enzyme, 2-oxo-glutarate decarboxylase.

"As it turns out, these two enzymes work together to complete the TCA cycle in a slightly different way," Bryant said. "That is, rather than making 2-oxoglutarate dehydrogenase, these bacteria produce both 2-oxoglutarate decarboxylase and succinic semialdehyde dehydrogenase. That combination of enzymes allows these organisms to move to the next intermediate -- succinate -- and to complete the TCA cycle." Bryant also said that his team found that the genes coding for the two enzymes are present in all cyanobacterial genomes except those of a few marine species. Bryant's co-author on the Science paper is Shuyi Zhang, a graduate student in the Department of Biochemistry and Molecular Biology at Penn State.

Bryant hopes to use the findings of his research to investigate new ways of producing biofuels. "Now that we understand better how cyanobacteria make energy, it might be possible to genetically engineer a cyanobacterial strain to synthesize 1,3-butanediol -- an organic compound that is the precursor for making not just biofuels but also plastics," Bryant said.

Bryant also said that his team's discoveries about cyanobacteria show how science is an ever-evolving process, and that firm conclusions never should be drawn from studies with negative results.

"Sadly, the conclusion that cyanobacteria have an incomplete TCA cycle is written into many textbooks as fact, simply because the research teams in 1967 misinterpreted their failure to find a particular enzyme," Bryant said. "But in science there is never really an end. There always is something new to discover."

The research was supported by the Air Force Office of Scientific Research and the Genomic Science Program of the U.S. Department of Energy.

Read More

Design Rules Will Enable Scientists to Use DNA to Build Nanomaterials With Desired Properties

Design Rules Will Enable Scientists to Use DNA to Build Nanomaterials With Desired Properties

  12:35:00 AM    Science Lover

---

Nature is a master builder. Using a bottom-up approach, nature takes tiny atoms and, through chemical bonding, makes crystalline materials, like diamonds, silicon and even table salt. In all of them, the properties of the crystals depend upon the type and arrangement of atoms within the crystalline lattice.

Abstract rendering of a DNA strand.
(Credit: iStockphoto/Johan Swanepoel)

Now, a team of Northwestern University scientists has learned how to top nature by building crystalline materials from nanoparticles and DNA, the same material that defines the genetic code for all living organisms.

Using nanoparticles as "atoms" and DNA as "bonds," the scientists have learned how to create crystals with the particles arranged in the same types of atomic lattice configurations as some found in nature, but they also have built completely new structures that have no naturally occurring mineral counterpart.

The basic design rules the Northwestern scientists have established for this approach to nanoparticle assembly promise the possibility of creating a variety of new materials that could be useful in catalysis, electronics, optics, biomedicine and energy generation, storage and conversion technologies.

The new method and design rules for making crystalline materials from nanostructures and DNA will be published Oct. 14 by the journal Science.

"We are building a new periodic table of sorts," said Professor Chad A. Mirkin, who led the research. "Using these new design rules and nanoparticles as 'artificial atoms,' we have developed modes of controlled crystallization that are, in many respects, more powerful than the way nature and chemists make crystalline materials from atoms. By controlling the size, shape, type and location of nanoparticles within a given lattice, we can make completely new materials and arrangements of particles, not just what nature dictates."

Mirkin is the George B. Rathmann Professor of Chemistry in the Weinberg College of Arts and Sciences and professor of medicine, chemical and biological engineering, biomedical engineering and materials science and engineering and director of Northwestern's International Institute for Nanotechnology (IIN).

"Once we have a certain type of lattice," Mirkin said, "the particles can be moved closer together or farther apart by changing the length of the interconnecting DNA, thereby providing near-infinite tunability."

"This work resulted from an interdisciplinary collaboration that coupled synthetic chemistry with theoretical model building," said coauthor George C. Schatz, a theoretician and the Charles E. and Emma H. Morrison Professor of Chemistry at Northwestern. "It was the back and forth between synthesis and theory that was crucial to the development of the design rules. Collaboration is a special aspect of research at Northwestern, and it worked very effectively for this project."



In the study, the researchers start with two solutions of nanoparticles coated with single-stranded DNA. They then add DNA strands that bind to these DNA-functionalized particles, which then present a large number of DNA "sticky ends" at a controlled distance from the particle surface; these sticky ends then bind to the sticky ends of adjacent particles, forming a macroscopic arrangement of nanoparticles.

Different crystal structures are achieved by using different combinations of nanoparticles (with varying sizes) and DNA linker strands (with controllable lengths). After a process of mixing and heating, the assembled particles transition from an initially disordered state to one where every particle is precisely located according to a crystal lattice structure. The process is analogous to how ordered atomic crystals are formed.

The researchers report six design rules that can be used to predict the relative stability of different structures for a given set of nanoparticle sizes and DNA lengths. In the paper, they use these rules to prepare 41 different crystal structures with nine distinct crystal symmetries. However, the design rules outline a strategy to independently adjust each of the relevant crystallographic parameters, including particle size (varied from 5 to 60 nanometers), crystal symmetry and lattice parameters (which can range from 20 to 150 nanometers). This means that these 41 crystals are just a small example of the near infinite number of lattices that could be created using different nanoparticles and DNA strands.

Mirkin and his team used gold nanoparticles in their work but note that their method also can be applied to nanoparticles of other chemical compositions. Both the type of nanoparticle assembled and the symmetry of the assembled structure contribute to the properties of a lattice, making this method an ideal means to create materials with predictable and controllable physical properties.

Mirkin believes that, one day soon, software will be created that allows scientists to pick the particle and DNA pairs required to make almost any structure on demand.

The Air Force Office of Scientific Research, the U.S. Department of Energy Office of Basic Energy Sciences and the National Science Foundation supported the research.

Read More

Inexpensive catalyst that makes hydrogen gas 10 times faster than natural enzyme

Inexpensive catalyst that makes hydrogen gas 10 times faster than natural enzyme

  10:14:00 AM    Science Lover

---

Looking to nature for their muse, researchers have used a common protein to guide the design of a material that can make energy-storing hydrogen gas. The synthetic material works 10 times faster than the original protein found in water-dwelling microbes, the researchers report in the August 12 issue of the journal Science, clocking in at 100,000 molecules of hydrogen gas every second.

The part of the catalyst that cranks out 100,000
molecules of hydrogen gas a second packs electrons
into chemical bonds between hydrogen atoms, possibly
hijacked from water. Credit: PNNL

This step is just one part of a series of reactions to split water and make hydrogen gas, but the researchers say the result shows they can learn from nature how to control those reactions to make durable synthetic catalysts for energy storage, such as in fuel cells.

In addition, the natural protein, an enzyme, uses inexpensive, abundant metals in its design, which the team copied. Currently, these materials -- called catalysts, because they spur reactions along -- rely on expensive metals such as platinum.

"This nickel-based catalyst is really very fast," said coauthor Morris Bullock of the Department of Energy's Pacific Northwest National Laboratory. "It's about a hundred times faster than the previous catalyst record holder. And from nature, we knew it could be done with abundant and inexpensive nickel or iron."

Stuffing Bonds

Electrical energy is nothing more than electrons. These same electrons are what tie atoms together when they are chemically bound to each other in molecules such as hydrogen gas. Stuffing electrons into chemical bonds is one way to store electrical energy, which is particularly important for renewable, sustainable energy sources like solar or wind power. Converting the chemical bonds back into flowing electricity when the sun isn't shining or the wind isn't blowing allows the use of the stored energy, such as in a fuel cell that runs on hydrogen.

Electrons are often stored in batteries, but Bullock and his colleagues want to take advantage of the closer packing available in chemicals.

"We want to store energy as densely as possible. Chemical bonds can store a huge amount of energy in a small amount of physical space," said Bullock, director of the Center for Molecular Electrocatalysis at PNNL, one of DOE's Energy Frontier Research Centers. The team also included visiting researcher Monte Helm from Fort Lewis College in Durango, Colo.

Biology stores energy densely all the time. Plants use photosynthesis to store the sun's energy in chemical bonds, which people use when they eat food. And a common microbe stores energy in the bonds of hydrogen gas with the help of a protein called a hydrogenase.

Because the hydrogenases found in nature don't last as long as ones that are built out of tougher chemicals (think paper versus plastic), the researchers wanted to pull out the active portion of the biological hydrogenase and redesign it with a stable chemical backbone.

Two Plus Two Equals One

In this study, the researchers looked at only one small part of splitting water into hydrogen gas, like fast-forwarding to the end of a movie. Of the many steps, there's a part at the end when the catalyst has a hold of two hydrogen atoms that it has stolen from water and snaps the two together.

The catalyst does this by completely dismantling some hydrogen atoms from a source such as water and moving the pieces around. Due to the simplicity of hydrogen atoms, those pieces are positively charged protons and negatively charged electrons. The catalyst arranges those pieces into just the right position so they can be put together correctly. "Two protons plus two electrons equals one molecule of hydrogen gas," says Bullock.



In real life, the protons would come from water, but since the team only examined a portion of the reaction, the researchers used water stand-ins such as acids to test their catalyst.

"We looked at the hydrogenase and asked what is the important part of this?" said Bullock. "The hydrogenase moves the protons around in what we call a proton relay. Where the protons go, the electrons will follow."

A Bauble for Energy

Based on the hydrogenase's proton relay, the experimental catalyst contained regions that dangled off the main structure and attracted protons, called "pendant amines." A pendant amine moves a proton into position on the edge of the catalyst, while a nickel atom in the middle of the catalyst offers a hydrogen atom with an extra electron (that's a proton and two electrons for those counting).

The pendant amine's proton is positive, while the nickel atom is holding on to a negatively charged hydrogen. Positioned close to each other, the opposites attract and the conglomerate solidifies into a molecule, forming hydrogen gas.

With that plan in mind, the team built potential catalysts and tested them. On their first try, they put a bunch of pendant amines around the nickel center, thinking more would be better. Testing their catalyst, they found it didn't work very fast. An analysis of how the catalyst was moving protons and electrons around suggested too many pendant amines got in the way of the perfect reaction. An overabundance of protons made for a sticky catalyst, which pinched it and slowed the hydrogen-gas-forming reaction down.

Like good gardeners, the team trimmed a few pendant amines off their catalyst, leaving only enough to make the protons stand out, ready to accept a negatively charged hydrogen atom.

Fastest Cat in the West

Testing the trimmed catalyst, the team found it performed much better than anticipated. At first they used conditions in which no water was present (remember, they used water stand-ins), and the catalyst could create hydrogen gas at a rate of about 33,000 molecules per second. That's much faster than their natural inspiration, which clocks in at around 10,000 per second.

However, most real-life applications will have water around, so they added water to the reaction to see how it would perform. The catalyst ran three times as fast, creating more than 100,000 hydrogen molecules every second. The researchers think the water might help by moving protons to a more advantageous spot on the pendant amine, but they are still studying the details.

Their catalyst has a drawback, however. It's fast, but it's not efficient. The catalyst runs on electricity -- after all, it needs those electrons to stuff into the chemical bonds -- but it requires more electricity than practical, a characteristic called the overpotential.

Bullock says the team has some ideas on how to reduce the inefficiency. Also, future work will require assembling a catalyst that splits water in addition to making hydrogen gas. Even with a high overpotential, the researchers see high potential for this catalyst.

More information: Monte L. Helm, Michael P. Stewart, R. Morris Bullock, M. Rakowski DuBois, Daniel L. DuBois, A Synthetic Nickel Electrocatalyst With a Turnover Frequency Above 100,000 s-1 for H2 Production, Science, August 12, 2011, DOI:10.1126/science.1205864

Provided by Pacific Northwest National Laboratory

Read More

A better way to photo gray: New technology allows lenses to change color rapidly

A better way to photo gray: New technology allows lenses to change color rapidly

  8:37:00 PM    Science Lover

---

A University of Connecticut scientist has perfected a method for creating quick-changing, variable colors in films and displays, such as sunglasses, that could lead to the next hot fashion accessory.

The new technology also has captured the interest of the U.S. military as a way to assist soldiers who need to be able to see clearly in rapidly changing environments.

The process for creating the lenses, for which a patent is pending, also is less expensive and less wasteful to manufacturers than previous methods. The findings were published July 7 in the Journal of Materials Chemistry.

"This is the next big thing for transition lenses," says Greg Sotzing, a professor of chemistry in UConn's College of Liberal Arts and Sciences and a member of UConn's Polymer Program.

The typical material behind a transition lens is what's called a photochromic film, or a sheet of polymers that change color when light hits them. Sotzing's new technology does things slightly differently – his electrochromic lenses are controlled by an electric current passing through them when triggered by a stimulus, such as light.

"They're like double pane windows with a gap between them," explains Sotzing. He and his colleagues squirt a mixture of polymers – or as he calls it, "goop" – in between the layers, creating the lens as it hardens. The mixture of polymers used in this lens, says Sotzing, creates less waste and is less expensive to produce than previous mixtures.

"The lifetime of sunglasses is usually very short," says Sotzing, who points out that people often misplace them. So by making the manufacturing less expensive, he says, commercial retailers will be able to produce more of them.



Another benefit of this material is that it can change colors as quickly as electricity passes through it – which is virtually instantaneously. This process could be very useful for the military, Sotzing says. For example, if a person emerges from a dark passageway and into the desert, a lens that would alter its color instantly to complement the surroundings could mean life or death for some soldiers.

"Right now, soldiers have to physically change the lenses in their goggles," Sotzing says. "This will eliminate that need." Sotzing will begin a one-year sabbatical at the Air Force Academy in August, where he hopes to develop some of these ideas.

In November 2010, partially based on work supported by the Center for Science and Technology Commercialization's Prototype Fund, the UConn R&D Corporation started a company, called Alphachromics Inc., with Sotzing and colleague Michael Invernale, now a post-doctoral researcher at MIT, as founders. The university has a patent pending for this new technology, which is currently under option to the company. Alphachromics is also testing applications of these polymer systems for energy-saving windows and custom fabrics.

Currently in talks with sunglass manufacturers, Sotzing says that the world of Hollywood could have a market for this technology. He describes applications he calls "freaky," including colors that move back and forth across the glasses, evoking styles like those sported by Lady Gaga.

But Sotzing stresses that the best thing about this technology is the creation of business in Connecticut. Although the glasses won't be made here, the technology will be licensed out of the state and, he hopes, Alphachromics will continue to expand.

"We don't make the sunglasses," he says. "We make the formulation of what goes inside them."

Sotzing's collaborators on the paper are Invernale and Ph.D. students Yujie Ding, Donna Mamangun and Amrita Kumar. The research was funded by the tech/textile company ITP-GmbH.

More information: Paper online: http://pubs.rsc.or … m/c1jm11141h

Read More

Transparent Conductive Material Could Lead to Power-Generating Windows

Transparent Conductive Material Could Lead to Power-Generating Windows

  1:18:00 PM    Science Lover

---

Scientists at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory and Los Alamos National Laboratory have fabricated transparent thin films capable of absorbing light and generating electric charge over a relatively large area. The material, described in the journal Chemistry of Materials, could be used to develop transparent solar panels or even windows that absorb solar energy to generate electricity.

Top: Scanning electron microscopy image and zoom 
of conjugated polymer (PPV) honeycomb. Bottom 
(left-to-right): Confocal fluorescence lifetime images of 
conjugated honeycomb, of polymer/fullerene honeycomb 
double layer and of polymer/fullerene honeycomb blend. 
Efficient charge transfer within the whole framework is 
observed in the case of polymer/fullerene honeycomb 
blend as a dramatic reduction in the fluorescence lifetime. 
(Credit: Image courtesy of DOE/Brookhaven National 
Laboratory)

The material consists of a semiconducting polymer doped with carbon-rich fullerenes. Under carefully controlled conditions, the material self-assembles to form a reproducible pattern of micron-size hexagon-shaped cells over a relatively large area (up to several millimeters).

"Though such honeycomb-patterned thin films have previously been made using conventional polymers like polystyrene, this is the first report of such a material that blends semiconductors and fullerenes to absorb light and efficiently generate charge and charge separation," said lead scientist Mircea Cotlet, a physical chemist at Brookhaven's Center for Functional Nanomaterials (CFN).

Furthermore, the material remains largely transparent because the polymer chains pack densely only at the edges of the hexagons, while remaining loosely packed and spread very thin across the centers. "The densely packed edges strongly absorb light and may also facilitate conducting electricity," Cotlet explained, "while the centers do not absorb much light and are relatively transparent."

"Combining these traits and achieving large-scale patterning could enable a wide range of practical applications, such as energy-generating solar windows, transparent solar panels, and new kinds of optical displays," said co-author Zhihua Xu, a materials scientist at the CFN.

"Imagine a house with windows made of this kind of material, which, combined with a solar roof, would cut its electricity costs significantly. This is pretty exciting," Cotlet said.

The scientists fabricated the honeycomb thin films by creating a flow of micrometer-size water droplets across a thin layer of the polymer/fullerene blend solution. These water droplets self-assembled into large arrays within the polymer solution. As the solvent completely evaporates, the polymer forms a hexagonal honeycomb pattern over a large area.

"This is a cost-effective method, with potential to be scaled up from the laboratory to industrial-scale production," Xu said.

The scientists verified the uniformity of the honeycomb structure with various scanning probe and electron microscopy techniques, and tested the optical properties and charge generation at various parts of the honeycomb structure (edges, centers, and nodes where individual cells connect) using time-resolved confocal fluorescence microscopy.

The scientists also found that the degree of polymer packing was determined by the rate of solvent evaporation, which in turn determines the rate of charge transport through the material.

"The slower the solvent evaporates, the more tightly packed the polymer, and the better the charge transport," Cotlet said.

"Our work provides a deeper understanding of the optical properties of the honeycomb structure. The next step will be to use these honeycomb thin films to fabricate transparent and flexible organic solar cells and other devices," he said.

The research was supported at Los Alamos by the DOE Office of Science. The work was also carried out in part at the CFN and the Center for Integrated Nanotechnologies Gateway to Los Alamos facility. The Brookhaven team included Mircea Cotlet, Zhihua Xu, and Ranjith Krishna Pai. Collaborators from Los Alamos include Hsing-Lin Wang and Hsinhan Tsai, who are both users of the CFN facilities at Brookhaven, Andrew Dattelbaum from the Center for Integrated Nanotechnologies Gateway to Los Alamos facility, and project leader Andrew Shreve of the Materials Physics and Applications Division.

Read More

2010 Nobel Prize in Chemistry: Creating Complex Carbon-Based Molecules Using Palladium

2010 Nobel Prize in Chemistry: Creating Complex Carbon-Based Molecules Using Palladium

  12:06:00 AM    Science Lover

---

The Royal Swedish Academy of Sciences has awarded the Nobel Prize in Chemistry for 2010 to Richard F. Heck, Ei-ichi Negishi and Akira Suzuki for developing new ways of linking carbon atoms together that has allowed scientists to make medicines and better electronics.

New ways of linking carbon atoms together has allowed scientists to make medicines and better electronics. (Credit: iStockphoto/Liang Zhang)

American citizen Richard F. Heck, 79, of the University of Delaware in Newark, Delaware, Japanese citizens Akira Suzuki, 80, of Hokkaido University in Sapporo, Japan, and Ei-Ichi Negishi, 75, of Purdue University in West Lafayette, Indiana, will share the 10 million Swedish crowns ($1.5 million) award for their development of "palladium-catalyzed cross couplings in organic systems."

Carbon, the atom that is the backbone of molecules in living organisms, is usually very stable and it can be difficult in the laboratory chemically to synthesize large molecules containing carbon. In the Heck reaction, Negishi reaction and Suzuki reaction, carbon atoms meet on a palladium atom, which acts as a catalyst. The carbon atoms attach to the palladium atom and are thus positioned close enough to each other for chemical reactions to start. This allows chemists to synthesize large, complex carbon-containing molecules.

The Academy said it's a "precise and efficient" tool that is used by researchers worldwide, "as well as in the commercial production of for example pharmaceuticals and molecules used in the electronics industry."

Great art in a test tube

Organic chemistry has developed into an art form where scientists produce marvelous chemical creations in their test tubes. Humankind benefits from this in the form of medicines, ever-more precise electronics and advanced technological materials. The Nobel Prize in Chemistry 2010 awards one of the most sophisticated tools available to chemists today.

This year's Nobel Prize in Chemistry is awarded to Richard F. Heck, Ei-ichi Negishi and Akira Suzuki for the development of palladium-catalyzed cross coupling. This chemical tool has vastly improved the possibilities for chemists to create sophisticated chemicals -- for example, carbon-based molecules as complex as those created by nature itself.

Carbon-based (organic) chemistry is the basis of life and is responsible for numerous fascinating natural phenomena: colour in flowers, snake poison and bacteria killing substances such as penicillin. Organic chemistry has allowed man to build on nature's chemistry; making use of carbon's ability to provide a stable skeleton for functional molecules. This has yielded new medicines and revolutionary materials such as plastics.

In order to create these complex chemicals, chemists need to be able to join carbon atoms together. However, carbon is stable and carbon atoms do not easily react with one another. The first methods used by chemists to bind carbon atoms together were therefore based upon various techniques for rendering carbon more reactive. Such methods worked when creating simple molecules, but when synthesizing more complex molecules chemists ended up with too many unwanted by-products in their test tubes.

Palladium-catalyzed cross coupling solved that problem and provided chemists with a more precise and efficient tool to work with. In the Heck reaction, Negishi reaction and Suzuki reaction, carbon atoms meet on a palladium atom, whereupon their proximity to one another kick-starts the chemical reaction.

Palladium-catalyzed cross coupling is used in research worldwide, as well as in the commercial production of for example pharmaceuticals and molecules used in the electronics industry.

Read More

Edible Nanostructures: Compounds Made from Renewable Materials Could Be Used for Gas Storage, Food Technologies

Edible Nanostructures: Compounds Made from Renewable Materials Could Be Used for Gas Storage, Food Technologies

  12:40:00 AM    Science Lover

---

Sugar, salt, alcohol and a little serendipity led a Northwestern University research team to discover a new class of nanostructures that could be used for gas storage and food and medical technologies. And the compounds are edible.

Sugar, salt, alcohol and a little serendipity led a Northwestern University research team to discover a new class of nanostructures that could be used for gas storage and food and medical technologies. And the compounds are edible. (Credit: Image courtesy of Northwestern University)

The porous crystals are the first known all-natural metal-organic frameworks (MOFs) that are simple to make. Most other MOFs are made from petroleum-based ingredients, but the Northwestern MOFs you can pop into your mouth and eat, and the researchers have.

"They taste kind of bitter, like a Saltine cracker, starchy and bland," said Ronald A. Smaldone, a postdoctoral fellow at Northwestern. "But the beauty is that all the starting materials are nontoxic, biorenewable and widely available, offering a green approach to storing hydrogen to power vehicles."

Smaldone is co-first author of a paper about the edible MOFs published by Angewandte Chemie. The study is slated to appear on the cover of one of the journal's November issues.

"With our accidental discovery, chemistry in the kitchen has taken on a whole new meaning," said Sir Fraser Stoddart, Board of Trustees Professor of Chemistry in the Weinberg College of Arts and Sciences at Northwestern. The implications of what Sir Fraser refers to as "Bob's your uncle chemistry" go all the way from cleaner air to healthier living, and it all comes from a product that can be washed down the sink.

Stoddart led the research group that included a trio of postdoctoral fellows in chemistry at Northwestern and colleagues from the University of California, Los Angeles (UCLA) and the University of St. Andrews in the U.K.

Metal-organic frameworks are well-ordered, lattice-like crystals. The nodes of the lattices are metals (such as copper, zinc, nickel or cobalt), and organic molecules connect the nodes. Within their very roomy pores, MOFs can effectively store gases such as hydrogen or carbon dioxide, making the nanostructures of special interest to engineers as well as scientists.

"Using natural products as building blocks provides a new direction for an old technology," said Jeremiah J. Gassensmith, a postdoctoral fellow in Stoddart's lab and an author of the paper.

"The metal-organic framework technology has been around since 1999 and relies on chemicals that come from crude oil," explained Ross S. Forgan, also a postdoctoral fellow in Stoddart's lab and co-first author of the paper. "Our main constituent is a starch molecule that is a leftover from corn production."

For their edible MOFs, the researchers use not ordinary table sugar but gamma-cyclodextrin, an eight-membered sugar ring produced from biorenewable cornstarch. The salts can be potassium chloride, a common salt substitute, or potassium benzoate, a commercial food preservative, and the alcohol is the grain spirit Everclear.

With these ingredients in hand, the researchers actually had set out to make new molecular architectures based on gamma-cyclodextrin. Their work produced crystals. Upon examining the crystals' structures using X-rays, the researchers were surprised to discover they had created metal-organic frameworks -- not an easy feat using natural products.

"Symmetry is very important in metal-organic frameworks," Stoddart said. "The problem is that natural building blocks are generally not symmetrical, which seems to prevent them from crystallizing as highly ordered, porous frameworks."

It turns out gamma-cyclodextrin solves the problem: it comprises eight asymmetrical glucose residues arranged in a ring, which is itself symmetrical. The gamma-cyclodextrin and potassium salt are dissolved in water and then crystallized by vapor diffusion with alcohol.

The resulting arrangement -- crystals consisting of cubes made from six gamma-cyclodextrin molecules linked in three-dimensions by potassium ions -- was previously unknown. The research team believes this strategy of marrying symmetry with asymmetry will carry over to other materials.

The cubes form a porous framework with easily accessible pores, perfect for capturing gases and small molecules. The pore volume encompasses 54 percent of the solid body.

"We achieved this level of porosity quickly and using simple ingredients," Smaldone said. "Creating metal-organic frameworks using petroleum-based materials, on the other hand, can be expensive and very time consuming."

Stoddart added, "It is both uplifting and humbling to come to terms with the fact that a piece of serendipity could have far-reaching consequences for energy storage and environmental remediation on the one hand and food quality control and health care on the other."

The National Science Foundation and the Engineering and Physical Sciences Research Council (U.K.) supported the research.

Read More

DNA Puts Chemists on Scent of Better Artificial Nose

DNA Puts Chemists on Scent of Better Artificial Nose

  10:53:00 PM    Science Lover

---

A new approach to building an "artificial nose" -- using fluorescent compounds and DNA -- could accelerate the use of sniffing sensors into the realm of mass production and widespread use, say Stanford chemists. If their method lives up to its promise, it could one day detect everything from incipiently souring milk to high explosives.

Florent Samain displays a fluorescence microscope image showing how the fluorescent sensors change color in the presence of organic vapors. (Credit: Linda Cicero, Stanford University News Service)

By sticking fluorescent compounds onto short strands of the molecules that form the backbone of DNA, the researchers have produced tiny sensor molecules that change color when they detect certain substances. The sensors were made using existing technology for synthesizing DNA, and are viewed with a fluorescence microscope.

The color changes enable the new sensors to convey far more information than most other existing optical sensors, which typically just detect one specific molecule, said Eric Kool, professor of chemistry and senior author of a paper published online this week in the German journal Angewandte Chemie.

"We were blown away by how strong the color changes were," Kool said. "One of the surprising findings was that we could tell the difference between four different organic vapors with just one sensor, because it would turn different colors with different vapors."

The key to Kool's versatile sensor molecules lies in the structure of DNA, the famous double helix that encodes the genetic blueprint for life, often described as looking like a twisted ladder. Two long parallel chains of sugar and phosphate molecules constitute the rails of the ladder, with the rungs made of pairs of molecules called bases. The arrangement of the bases, of which there are only four types, encodes the genetic data.

Kool's team of researchers developed a new set of fluorescent replacements for the DNA bases -- seven different ones they could choose from -- to attach to the DNA backbone of the new sensor in place of the usual four. They used only a single helix, so the bases project out from a single twisted pole, ready to detect organic vapors.

Florent Samain, a postdoctoral researcher in chemistry and lead author on the Angewandte Chemie paper, used DNA synthesis techniques to generate a library of all 2,401 possible ways that the seven substitute molecules could be combined in a string of four units.

The team then screened all the possible combinations for sensitivity to four different test substances -- as vapors -- that differed significantly in their structural and electronic properties.

One substance was commonly used as an aquatic herbicide, another as a solvent in research and industrial applications, another as an inhibitor of mold and bacteria in food and the fourth as an ingredient in products ranging from shoe polish to pesticides, as well as in the preparation of explosives.

The researchers found multiple sensors that showed marked fluorescent responses when exposed to the four test substances. "This is our first try with vapors and it ended up working really well," Kool said.

"What makes these sensors work exceptionally well is that the bases in DNA are stacked on one another, physically touching each other," he said. "DNA bases talk to one another, electronically."

That close physical contact also allows the compounds that Kool's group attaches to the DNA backbone to communicate with each other, which is crucial to their functionality.

What is also crucial, the researchers found out, is the order of the compounds along the DNA backbone. Like the sequence of natural DNA, which varies among different animals, the different sequences of the artificial DNA sensors gave different color changes.

"We saw a couple of examples where we had the same components, but in a different order and got a different response," Kool said. "So clearly they are talking to one another and whoever is next to someone else, it makes a difference."

"One of our long-term goals is to now build up a set of sensors for a much more complex range of possible substances for analysis," Kool said. "Because we get such a diversity of responses -- even one molecule can tell the difference among four different things -- we could have a set of 10 or 20, or 100 sensors, which would give a vast array of responses to many different kinds of molecules."

Having a large number of sensors available in a single device could broaden the application of the sensors from pure organic molecules such as the ones used in the tests to the many mixtures of molecules often encountered outside the laboratory.

Outside the lab is where the researchers see the DNA sensors being used most effectively. They hope to eventually pair their sensors with some type of portable device that would contain an inexpensive fluorescence microscope, which Kool says a number of other laboratories are already working on. One example -- called the "CellScope" -- was recently developed at the University of California-Berkeley.

The researchers still need to determine how small a quantity of any given substance the DNA sensors can detect.

"Another of our long-term goals is to print these sensors on plastic, and if the spots were big enough to see, you could see the color changes," Kool said. "You could hold a black light over the sensor and read the response. Then you could match up the color of the sensor with a key of some sort and say, 'Ah, this sensor best compares with this color on the key -- this milk is about to go sour.'"

Kool said it might even be possible, with more research, to use the DNA sensors in liquids.

"To me, the most intriguing possibility is smelling differences that are biologically important," Kool said. "It could be smelling differences in cells that are related to disease or sensing toxins in the environment. Those are probably the most likely applications in the near future.

"We want to sense everything," Kool said. "That is our ultimate goal."

Samantak Ghosh and Yin Nah Teo, both of whom recently graduated with PhD degrees in chemistry, also worked on the study and are coauthors of the paper in Angewandte Chemie. Kool is the George A. and Hilda M. Daubert Professor in Chemistry at Stanford.

Read More

Nanoscale DNA Sequencing Could Spur Revolution in Personal Health Care

Nanoscale DNA Sequencing Could Spur Revolution in Personal Health Care

  2:22:00 PM    Science Lover

---

In experiments with potentially broad health care implications, a research team led by a University of Washington physicist has devised a method that works at a very small scale to sequence DNA quickly and relatively inexpensively.

This illustration depicts a single strand of DNA moving through a nanopore that is being used to sequence the DNA. (Credit: Image courtesy of University of Washington)

That could open the door for more effective individualized medicine, for example providing blueprints of genetic predispositions for specific conditions and diseases such as cancer, diabetes or addiction.

"The hope is that in 10 years people will have all their DNA sequenced, and this will lead to personalized, predictive medicine," said Jens Gundlach, a UW physics professor and lead author of a paper describing the new technique published the week of Aug. 16 in the Proceedings of the National Academy of Sciences.

The technique creates a DNA reader that combines biology and nanotechnology using a nanopore taken from Mycobacterium smegmatis porin A. The nanopore has an opening 1 billionth of a meter in size, just large enough to measure a single strand of DNA as it passes through.

The scientists placed the pore in a membrane surrounded by potassium-chloride solution. A small voltage was applied to create an ion current flowing through the nanopore, and the current's electrical signature changed depending on the nucleotides traveling through the nanopore. Each of the nucleotides that are the essence of DNA -- cytosine, guanine, adenine and thymine -- produced a distinctive signature.

The team had to solve two major problems. One was to create a short and narrow opening just large enough to allow a single strand of DNA to pass through the nanopore and for only a single DNA molecule to be in the opening at any time. Michael Niederweis at the University of Alabama at Birmingham modified the M. smegmatis bacterium to produce a suitable pore.

The second problem, Gundlach said, was that the nucleotides flowed through the nanopore at a rate of one every millionth of a second, far too fast to sort out the signal from each DNA molecule. To compensate, the researchers attached a section of double-stranded DNA between each nucleotide they wanted to measure. The second strand would briefly catch on the edge of the nanopore, halting the flow of DNA long enough for the single nucleotide to be held within the nanopore DNA reader. After a few milliseconds, the double-stranded section would separate and the DNA flow continued until another double strand was encountered, allowing the next nucleotide to be read.

The delay, though measured in thousandths of a second, is long enough to read the electrical signals from the target nucleotides, Gundlach said.

"We can practically read the DNA sequence from an oscilloscope trace," he said.

Besides Gundlach and Niederweiss, other authors are Ian Derrington, Tom Butler, Elizabeth Manrao and Marcus Collins of the UW; and Mikhail Pavlenok at Alabama-Birmingham.

The work was funded by the National Institutes of Health and its National Human Genome Research Institute as part of a program to create technology to sequence a human genome for $1,000 or less. That program began in 2004, when it cost on the order of $10 million to sequence a human-sized genome.

The new research is a major step toward achieving DNA sequencing at a cost of $1,000 or less.

"Our experiments outline a novel and fundamentally very simple sequencing technology that we hope can now be expanded into a mechanized process," Gundlach said.

Read More

Breakthrough in Blinking Molecules Phenomenon

Breakthrough in Blinking Molecules Phenomenon

  10:22:00 AM    Science Lover

---

A new paper by University of Notre Dame physicist Boldizsár Jankó and colleagues offers an important new understanding of an enduring mystery in chemical physics.

Fluorescence intensity measured by a single-molecule microscope sees sharp peaks at quantum dot locations. (Credit: Boldizsár Jankó / University of Notre Dame)

More than a century ago, at the dawn of modern quantum mechanics, the Noble Prize-winning physicist Neils Bohr predicted so-called "quantum jumps." He predicted that these jumps would be due to electrons making transitions between discrete energy levels of individual atoms and molecules. Although controversial in Bohr's time, such quantum jumps were experimentally observed, and his prediction verified, in the 1980s. More recently, with the development of single molecule imaging techniques in the early 1990s, it has been possible to observe similar jumps in individual molecules.

Experimentally, these quantum jumps translate to discrete interruptions of the continuous emission from single molecules, revealing a phenomenon known as fluorescent intermittency or "blinking."

However, while certain instances of blinking can be directly ascribed to Bohr's original quantum jumps, many more cases exist where the observed fluorescence intermittency does not follow his predictions. Specifically, in systems as diverse as fluorescent proteins, single molecules and light harvesting complexes, single organic fluorophores, and, most recently, individual inorganic nanostructures, clear deviations from Bohr's predictions occur.

As a consequence, virtually all known fluorophores, including fluorescent quantum dots, rods and wires, exhibit unexplainable episodes of intermittent blinking in their emission.

The prevailing wisdom in the field of quantum mechanics was that the on and off blinking episodes were not correlated. However, at a 2007 conference on the phenomenon sponsored by Notre Dame's Institute for Theoretical Sciences, which Jankó directs, Fernando Stefani of the University of Buenos Aires presented research suggesting that there was, in fact, correlation between these on and off events. No theoretical model available at that time was able to explain these correlations.

In a 2008 Nature Physics paper, Jankó and a group of researchers that included Notre Dame chemistry professor Ken Kuno, physics visiting assistant professor Pavel Frantsuzov and Nobel Laureate Rudolph Marcus suggested that the on- and off-time intervals of intermittent nanocrystal quantum dots follow universal power law distributions. The discovery provided Jankó and other researchers in the field with the first hints for developing a deeper insight into the physical mechanism behind the vast range of on- and off-times in the intermittency.

In a new paper appearing in the journal Nano Letters, Jankó, Frantsuzov and Notre Dame graduate student Sándor Volkán-Kascó reveal that they have developed a model for the blinking phenomena that confirms what Stefani observed experimentally. The finding is important confirmation that strong correlation exists between the on and off phenomenon.

If the blinking process could be controlled, quantum dots could, for example, provide better, more stable imaging of cancer cells; provide researcher with real-time images of a viral infection, such as HIV, within a cell; lead to the development of a new generation of brighter display screens for computers, cell phones and other electronic applications; and even improved lighting fixtures for homes and offices.

The Nano Letters paper represents another important step in understanding the origins of the blinking phenomenon and identifying ways to control the process.

Read More