Thursday, September 30, 2010

Edible nanostructures

Compounds made from renewable materials could be used for gas storage, food technologies

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.

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."

Edible nanostructures

This simple recipe can be followed to make all-natural metal-organic frameworks.
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 title of the paper is "Metal–Organic Frameworks from Edible Natural Products." In addition to Stoddart, Smaldone, Forgan and Gassensmith, other authors of the paper are Hiroyasu Furukawa and Omar M. Yaghi, from UCLA, and Alexandra M. Z. Slawin, from the University of St. Andrews.

Contact: Megan Fellman is the science and engineering editor. fellman@northwestern.edu 847-491-3115 Northwestern University

Tuesday, September 28, 2010

Silicon oxide circuits break barrier

Nanocrystal conductors could lead to massive, robust 3-D storage

Rice University scientists have created the first two-terminal memory chips that use only silicon, one of the most common substances on the planet, in a way that should be easily adaptable to nanoelectronic manufacturing techniques and promises to extend the limits of miniaturization subject to Moore's Law.

Last year, researchers in the lab of Rice Professor James Tour showed how electrical current could repeatedly break and reconnect 10-nanometer strips of graphite, a form of carbon, to create a robust, reliable memory "bit." At the time, they didn't fully understand why it worked so well.

Now, they do. A new collaboration by the Rice labs of professors Tour, Douglas Natelson and Lin Zhong proved the circuit doesn't need the carbon at all.

silicon oxide memory

CAPTION: A 1k silicon oxide memory has been assembled by Rice and a commercial partner as a proof-of-concept. Silicon nanowire forms when charge is pumped through the silicon oxide, creating a two-terminal resistive switch. (Images courtesy Jun Yao/Rice University)
Jun Yao, a graduate student in Tour's lab and primary author of the paper to appear in the online edition of Nano Letters, confirmed his breakthrough idea when he sandwiched a layer of silicon oxide, an insulator, between semiconducting sheets of polycrystalline silicon that served as the top and bottom electrodes.

Applying a charge to the electrodes created a conductive pathway by stripping oxygen atoms from the silicon oxide and forming a chain of nano-sized silicon crystals. Once formed, the chain can be repeatedly broken and reconnected by applying a pulse of varying voltage.
The nanocrystal wires are as small as 5 nanometers (billionths of a meter) wide, far smaller than circuitry in even the most advanced computers and electronic devices.

"The beauty of it is its simplicity," said Tour, Rice's T.T. and W.F. Chao Chair in Chemistry as well as a professor of mechanical engineering and materials science and of computer science. That, he said, will be key to the technology's scalability. Silicon oxide switches or memory locations require only two terminals, not three (as in flash memory), because the physical process doesn't require the device to hold a charge.

It also means layers of silicon-oxide memory can be stacked in tiny but capacious three-dimensional arrays. "I've been told by industry that if you're not in the 3-D memory business in four years, you're not going to be in the memory business. This is perfectly suited for that," Tour said.

Silicon-oxide memories are compatible with conventional transistor manufacturing technology, said Tour, who recently attended a workshop by the National Science Foundation and IBM on breaking the barriers to Moore's Law, which states the number of devices on a circuit doubles every 18 to 24 months.

"Manufacturers feel they can get pathways down to 10 nanometers. Flash memory is going to hit a brick wall at about 20 nanometers. But how do we get beyond that? Well, our technique is perfectly suited for sub-10-nanometer circuits," he said.

Austin tech design company PrivaTran is already bench testing a silicon-oxide chip with 1,000 memory elements built in collaboration with the Tour lab. "We're real excited about where the data is going here," said PrivaTran CEO Glenn Mortland, who is using the technology in several projects supported by the Army Research Office, National Science Foundation, Air Force Office of Scientific Research, and the Navy Space and Naval Warfare Systems Command Small Business Innovation Research (SBIR) and Small Business Technology Transfer programs.

"Our original customer funding was geared toward more high-density memories," Mortland said. "That's where most of the paying customers see this going. I think, along the way, there will be side applications in various nonvolatile configurations."

Yao had a hard time convincing his colleagues that silicon oxide alone could make a circuit. "Other group members didn't believe him," said Tour, who added that nobody recognized silicon oxide's potential, even though it's "the most-studied material in human history."

"Most people, when they saw this effect, would say, 'Oh, we had silicon-oxide breakdown,' and they throw it out," he said. "It was just sitting there waiting to be exploited."

In other words, what used to be a bug turned out to be a feature.

Yao went to the mat for his idea. He first substituted a variety of materials for graphite and found none of them changed the circuit's performance. Then he dropped the carbon and metal entirely and sandwiched silicon oxide between silicon terminals. It worked.

"It was a really difficult time for me, because people didn't believe it," Yao said. Finally, as a proof of concept, he cut a carbon nanotube to localize the switching site, sliced out a very thin piece of silicon oxide by focused ion beam and identified a nanoscale silicon pathway under a transmission electron microscope.

"This is research," Yao said. "If you do something and everyone nods their heads, then it's probably not that big. But if you do something and everyone shakes their heads, then you prove it, it could be big.

"It doesn't matter how many people don't believe it. What matters is whether it's true or not."

Silicon-oxide circuits carry all the benefits of the previously reported graphite device. They feature high on-off ratios, excellent endurance and fast switching (below 100 nanoseconds).

They will also be resistant to radiation, which should make them suitable for military and NASA applications. "It's clear there are lots of radiation-hardened uses for this technology," Mortland said.

Silicon oxide also works in reprogrammable gate arrays being built by NuPGA, a company formed last year through collaborative patents with Rice University. NuPGA's devices will assist in the design of computer circuitry based on vertical arrays of silicon oxide embedded in "vias," the holes in integrated circuits that connect layers of circuitry. Such rewritable gate arrays could drastically cut the cost of designing complex electronic devices. ###

Zhengzong Sun, a graduate student in Tour's lab, was co-author of the paper with Yao; Tour; Natelson, a Rice professor of physics and astronomy; and Zhong, assistant professor of electrical and computer engineering.

The David and Lucille Packard Foundation, the Texas Instruments Leadership University Fund, the National Science Foundation, PrivaTran and the Army Research Office SBIR supported the research.

Contact: David Ruth druth@rice.edu 713-348-6327 Rice University

Monday, September 27, 2010

High-speed filter uses electrified nanostructures to purify water at low cost

By dipping plain cotton cloth in a high-tech broth full of silver nanowires and carbon nanotubes, Stanford researchers have developed a new high-speed, low-cost filter that could easily be implemented to purify water in the developing world.

Instead of physically trapping bacteria as most existing filters do, the new filter lets them flow on through with the water. But by the time the pathogens have passed through, they have also passed on, because the device kills them with an electrical field that runs through the highly conductive "nano-coated" cotton.

In lab tests, over 98 percent of Escherichia coli bacteria that were exposed to 20 volts of electricity in the filter for several seconds were killed. Multiple layers of fabric were used to make the filter 2.5 inches thick.

Nanowires on Cotton

Caption: This scanning electron microscope image shows the silver nanowires in which the cotton is dipped during the process of constructing a filter. The large fibers are cotton.

Credit: Courtesy of Yi Cui, Stanford University. Usage Restrictions: None.
"This really provides a new water treatment method to kill pathogens," said Yi Cui, an associate professor of materials science and engineering. "It can easily be used in remote areas where people don't have access to chemical treatments such as chlorine."

Cholera, typhoid and hepatitis are among the waterborne diseases that are a continuing problem in the developing world. Cui said the new filter could be used in water purification systems from cities to small villages.

Faster filtering by letting bacteria through.
Filters that physically trap bacteria must have pore spaces small enough to keep the pathogens from slipping through, but that restricts the filters' flow rate.

Since the new filter doesn't trap bacteria, it can have much larger pores, allowing water to speed through at a more rapid rate.

"Our filter is about 80,000 times faster than filters that trap bacteria," Cui said. He is the senior author of a paper describing the research that will be published in an upcoming issue of Nano Letters. The paper is available online now.

The larger pore spaces in Cui's filter also keep it from getting clogged, which is a problem with filters that physically pull bacteria out of the water.

Cui's research group teamed with that of Sarah Heilshorn, an assistant professor of materials science and engineering, whose group brought its bioengineering expertise to bear on designing the filters.

Silver has long been known to have chemical properties that kill bacteria. "In the days before pasteurization and refrigeration, people would sometimes drop silver dollars into milk bottles to combat bacteria, or even swallow it," Heilshorn said.

Cui's group knew from previous projects that carbon nanotubes were good electrical conductors, so the researchers reasoned the two materials in concert would be effective against bacteria. "This approach really takes silver out of the folk remedy realm and into a high-tech setting, where it is much more effective," Heilshorn said.

Using the commonplace keeps costs down

But the scientists also wanted to design the filters to be as inexpensive as possible. The amount of silver used for the nanowires was so small the cost was negligible, Cui said. Still, they needed a foundation material that was "cheap, widely available and chemically and mechanically robust." So they went with ordinary woven cotton fabric.

"We got it at Wal-mart," Cui said.

To turn their discount store cotton into a filter, they dipped it into a solution of carbon nanotubes, let it dry, then dipped it into the silver nanowire solution. They also tried mixing both nanomaterials together and doing a single dunk, which also worked. They let the cotton soak for at least a few minutes, sometimes up to 20, but that was all it took.

The big advantage of the nanomaterials is that their small size makes it easier for them to stick to the cotton, Cui said. The nanowires range from 40 to 100 billionths of a meter in diameter and up to 10 millionths of a meter in length. The nanotubes were only a few millionths of a meter long and as narrow as a single billionth of a meter. Because the nanomaterials stick so well, the nanotubes create a smooth, continuous surface on the cotton fibers. The longer nanowires generally have one end attached with the nanotubes and the other end branching off, poking into the void space between cotton fibers.

"With a continuous structure along the length, you can move the electrons very efficiently and really make the filter very conducting," he said. "That means the filter requires less voltage."

Minimal electricity required

The electrical current that helps do the killing is only a few milliamperes strong – barely enough to cause a tingling sensation in a person and easily supplied by a small solar panel or a couple 12-volt car batteries. The electrical current can also be generated from a stationary bicycle or by a hand-cranked device.

The low electricity requirement of the new filter is another advantage over those that physically filter bacteria, which use electric pumps to force water through their tiny pores. Those pumps take a lot of electricity to operate, Cui said.

In some of the lab tests of the nano-filter, the electricity needed to run current through the filter was only a fifth of what a filtration pump would have needed to filter a comparable amount of water.

The pores in the nano-filter are large enough that no pumping is needed – the force of gravity is enough to send the water speeding through.

Although the new filter is designed to let bacteria pass through, an added advantage of using the silver nanowire is that if any bacteria were to linger, the silver would likely kill it. This avoids biofouling, in which bacteria form a film on a filter. Biofouling is a common problem in filters that use small pores to filter out bacteria.

Cui said the electricity passing through the conducting filter may also be altering the pH of the water near the filter surface, which could add to its lethality toward the bacteria.

Cui said the next steps in the research are to try the filter on different types of bacteria and to run tests using several successive filters.

"With one filter, we can kill 98 percent of the bacteria," Cui said. "For drinking water, you don't want any live bacteria in the water, so we will have to use multiple filter stages."

Cui's research group has gained attention recently for using nanomaterials to build batteries from paper and cloth. ###

David Schoen and Alia Schoen were both graduate students in Materials Science and Engineering when the water-filter research was conducted and are co–lead authors of the paper in Nano Letters. David Schoen is now a postdoctoral researcher at Stanford.

Liangbing Hu, a postdoctoral researcher in Materials Science and Engineering, and Han Sun Kim, a graduate student in Materials Science and Engineering at the time the research was conducted, also contributed to the research and are co-authors of the paper.

Contact: Louis Bergeron louisb3@stanford.edu 650-725-1944 Stanford University

Sunday, September 26, 2010

IU chemists develop new 'light switch' chloride binder

BLOOMINGTON, Ind. -- Chemists at Indiana University Bloomington have designed a molecule that binds chloride ions -- but can be conveniently compelled to release the ions in the presence of ultraviolet light.

Reporting in the Journal of the American Chemical Society today (online), IU Bloomington chemist Amar Flood and Ph.D. student Yuran Hua explain how they designed the molecule, how it works and, just as importantly, how they know it works.

"One of the things we like most about this system is that the mechanism is predictable -- and it functions in the way we propose," said Flood, who led the project.

Chloride is a relatively common element on Earth, ubiquitous in seawater and in the bodies of living organisms.

Chloride Receptor

Caption: When azobenzene units (blue) at the ends of the receptor are struck with UV light, the receptor unfolds the helix and releases the chloride ion (green)

Credit: Amar Flood. Usage Restrictions: None
"We have two main goals with this research," Flood said. "The first is to design an effective and flexible system for the removal of toxic, negatively charged ions from the environment or industrial waste. The second goal is to develop scientific and even medical applications. If a molecule similar to ours could be made water soluble and non-toxic, it could, say, benefit people with cystic fibrosis, who have a problem with chloride ions accumulating outside of certain cells."
Many organic molecules exist that can bind positively charged ions, or cations, and this has much to do with the fact that it is easy to synthesize organic molecules with negatively charged parts. Synthesizing organic molecules that bind negatively charged ions, or anions, like chloride, presents special challenges.

The binding molecule or "foldamer" Flood and Hua designed is both a folding molecule and a (small) polymer, meaning the foldamer's constituent parts can be synthesized with relative ease. Under visible light of 436 nanometers (nm), the foldamer prefers a tight spiral structure that allows specially configured residues to interact with each other, which improves stability, and creates an attractive pocket for chloride. In the presence of ultraviolet light (365 nm), the foldamer absorbs energy and the tight spiral is destabilized, weakening the chloride binding pocket and freeing chloride to re-enter the solution.

The "light switch" properties of the foldamer could make it an invaluable tool to biochemists and molecular biologists who seek to adjust the availability of chloride in their experiments by simply turning a UV light emitter on or off.

The foldamer is not quite ready for that, however. It can only be dissolved at present in organic (fatty) solutions, whereas living systems operate mostly in water-based solutions.

"That's the direction we're headed," Flood said. "It actually wouldn't be that difficult to modify the molecule so that it is water soluble. But first we need to make sure it does all the things we want it to do."

In their JACS paper, Flood said he and Hua wanted to bring sythentic chemistry together with modern diagnostic approaches to demonstrate the efficacy of their foldamer.

"A lot of the ideas in our paper have been floating around for some time," Flood said. "The idea of a foldamer that binds anions, the idea of a foldamer that you can isomerize with light, the idea of receptor that can bind anions ... But none of the prior work uses conductivity to show that the chloride concentrations actually go up and down as intended. What's new is that we've put all these things together. We think we have something here that allows us to raise our heads to the great research that's preceded us."

Flood and Hua used an electrical conductivity test to show that when voltage is applied to the solution containing chloride ions and the binding molecule, electricity flows more freely in the presence of UV light, when the binder is relaxed and chloride is disassociated from it. That was proof, Flood said, that the foldamer was working as intended.

"My training is in building molecular machines," Flood said. "I create machines that do what we want them to do -- and to show what's possible in chemical and biological laboratory science."

The binding molecule Flood and Hua describe is an improvement on a previous binder developed by Flood and then-postdoctoral fellow Yongjun Li that was also an oligomer of sorts but did not fold. This previous iteration of the chloride binder was closed and donut-shaped, using space restrictions and strategically placed atoms to yield a binding pocket with a special affinity for chloride. ###

Funding and support for this research were provided by the U.S. Department of Energy's Office of Science and the Camille Dreyfus Teacher-Scholar Award.

To speak with Flood, please contact David Bricker, University Communications, at 812-856-9035 or brickerd@indiana.edu.

Contact: David Bricker brickerd@indiana.edu 812-856-9035 Indiana University

Thursday, September 23, 2010

Trouble with sputter? Blame giant nanoparticles

Particle pile-up explains decades-old industrial problem.

When you tear open a bag of potato chips or pop in a DVD, you're probably putting your hand on sputter deposition. No, don't run for the soap.

Sputter deposition is an industrial process used since the 1970s to spray -- sputter, that is -- thin films onto various backings, like the metallic coating on potato chip bags, the reflective surface on DVDs, or the electronics on computer chips.

Mostly, the process works very well. In a vacuum chamber filled with an inert gas, like argon, high voltage is applied to a magnet. This energizes the argon, which, in turn, bumps particles of, say, tungsten metal from a source near the magnet out into the cloud of gas. Some of these extremely hot, charged tungsten particles zip at high speed through the argon and deposit onto the target, forming a thin film.

Lan Zhou and Randy Headrick, University of Vermont

Caption: University of Vermont graduate student Lan Zhou and professor Randy Headrick made a fundamental discovery in the physics of sputter deposition that may improve computer chips, solar panels, X-ray lenses and even your next pair of mirrored sunglasses.

Credit: Sally McCay, University of Vermont, 2010. Usage Restrictions: May be used with the credit information above, in stories reprinting or reporting on the UVM research described in the release.
But sometimes the coatings peel off or the product bends in on itself and cracks, as if the film was stretched tight before it was applied to the surface. Other times, the films are just too rough. For decades, scientists have been baffled -- and manufacturers frustrated -- about why these problems happen.

Now researchers at the University of Vermont and the Argonne National Laboratory near Chicago have an explanation: "it's nanoparticles," says Randy Headrick, professor of physics at UVM, "sticking and pulling together."

The discovery, led by Headrick's graduate student, Lan Zhou, was published August 10 in the journal Physical Review B.

Using high-powered x-rays, the team measured the size of tungsten particles depositing on a target and were amazed.
Above a critical pressure in the argon gas (eight one-millionths of an atmosphere), the size suddenly jumped. Instead of single atoms or several-atom molecules -- as would be expected in the high-heat, high-velocity environment of a sputter chamber -- they detected relatively gigantic blobs of hundreds of atoms: what the researchers call a "nanoparticle aggregation."

"It's a condensation, like clouds, like mist," says Headrick, "this is something we really didn't expect."

These nanoparticles pull together and fuse, drawing the film tight as tiny "nano-voids" between particles are eliminated. This can create stress in thin films strong enough to pull electronic wafers into a cup shape or roughness that distorts the delicate coatings of optical lenses.

"No one realized that in the gas phase you could produce a particle so large," says Al Macrander, a physicist at Argonne National Laboratory and a co-author on the article. "They're highly energized, so it's counter-intuitive that they would stick -- because of their velocity," he says. But stick they do.

In the sputter deposition chamber, "particles start off with temperatures of around ten thousand degrees," UVM's Randy Headrick explains. But even as they are moving in the gas, they cool slightly and "once they cool," he says, "they want to go back to being a solid."

"This has large implications," Macrander says, "for many industries, not only optics." For his part, the new findings are likely to help accelerate the creation of advanced x-ray lenses that he has been helping to develop.

So far, the efforts to make these lenses have not succeeded since the sputter deposition process has produced coatings that are still too rough with too much tension -- despite using state-of-the-art techniques.

"These lenses are intended to focus x-ray beams on smaller dimensions than have ever been achieved," he said, "down to one nanometer." To make these lenses requires more than a thousand layers of thin film. "Stress builds up and becomes a problem," he says.

The team's new insight into the basic physics of sputter deposition points the way toward a solution, but the equation is complex. "If you want to get real smooth surfaces, you have to deposit at lower argon pressures," says UVM's Lan Zhou. But at this very low pressure, the particles hit with such velocity that the thin films want to expand, creating the opposite problem by pulling films apart.

"Its still an open question: what do you do to make a film with zero stress and as smooth as possible?" says Headrick.

"At least now we understand what is happening," says Zhou, "so people can try to optimize the film deposition conditions, for structure and roughness."

Still, what are problems in one application might be a benefit in others. "There is a lot more to this finding than lens coatings," says Headrick, "there are many kinds of materials where you want to make nanoparticles, like some kinds of catalytic converters or solar cells. This could be a good way to make nanoparticles cheaply."

But the cost of figuring it out was steep. "This took years for us to understand," says Zhou, with the slightly worn smile that PhD students wear best, "it was hard to think of aggregate particles forming in the middle of a flux." ###

Contact: Joshua Brown joshua.e.brown@uvm.edu 802-656-3039 University of Vermont

Tuesday, September 21, 2010

SU research team uses nanobiotechnology-manipulated light particles to accelerate algae growth

Research may be a key to creating efficient biofuel production

Scientists and engineers seek to meet three goals in the production of biofuels from non-edible sources such as microalgae: efficiency, economical production and ecological sustainability. Syracuse University's Radhakrishna Sureshkumar, professor and chair of biomedical and chemical engineering in the L.C. Smith College of Engineering and Computer Science, and SU chemical engineering Ph.D. student Satvik Wani have uncovered a process that is a promising step toward accomplishing these three goals.

Sureshkumar and Wani have discovered a method to make algae, which can be used in the production of biofuels, grow faster by manipulating light particles through the use of nanobiotechnology. By creating accelerated photosynthesis, algae will grow faster with minimal change in the ecological resources required. This method is highlighted in the August 2010 issue of Nature Magazine.

algae growthThe SU team has developed a new bioreactor that can enhance algae growth. They accomplished this by utilizing nanoparticles that selectively scatter blue light, promoting algae metabolism. When the optimal combination of light and confined nanoparticle suspension configuration was used, the team was able to achieve growth enhancement of an algae sample of greater than 30 percent as compared to a control.
"Algae produce triglycerides, which consist of fatty acids and glycerin. The fatty acids can be turned into biodiesel while the glycerin is a valuable byproduct," says Sureshkumar. "Molecular biologists are actively seeking ways to engineer optimal algae strains for biofuel production. Enhancing the phototropic growth rate of such optimal organisms translates to increased productivity in harvesting the feedstock."

The process involved the creation of a miniature bioreactor that consisted of a petri dish of a strain of green algae (Chlamydomonas reinhardtii) on top of another dish containing a suspension of silver nanoparticles that served to backscatter blue light into the algae culture. Through model-guided experimentation, the team discovered that by varying the concentration and size of the nanoparticle solution they could manipulate the intensity and frequency of the light source, thereby achieving an optimal wavelength for algal growth.

"Implementation of easily tunable wavelength specific backscattering on larger scales still remains a challenge, but its realization will have a substantial impact on the efficient harvesting of phototrophic microorganisms and reducing parasitic growth," says Sureshkumar. "Devices that can convert light not utilized by the algae into the useful blue spectral regime can also be envisioned."

To date, this is one of the first explorations into utilizing nanobiotechnology to promote microalgal growth. The acceleration in the growth rate of algae also had numerous benefits outside the area of biofuel production. Sureshkumar and Wani will be looking to employ this discovery to further their research in creating environmental sensors for ecological warning systems. ###

Contact: Ariel DuChene adduchen@syr.edu 315-443-2546 Syracuse University

Monday, September 20, 2010

Good vibrations: New atom-scale products on horizon

Breakthrough discovery enables nanoscale manipulation of the piezoelectric effect.

The generation of an electric field by the compression and expansion of solid materials is known as the piezoelectric effect, and it has a wide range of applications ranging from everyday items such as watches, motion sensors and precise positioning systems. Researchers at McGill University's Department of Chemistry have now discovered how to control this effect in nanoscale semiconductors called "quantum dots," enabling the development of incredibly tiny new products.

Although the word "quantum" is used in everyday language to connote something very large, it actually means the smallest amount by which certain physical quantities can change. A quantum dot has a diameter of only 10 to 50 atoms, or less than 10 nanometres. By comparison, the diameter of the DNA double-helix is 2 nanometres. The McGill researchers have discovered a way to make individual charges reside on the surface of the dot, which produces a large electric field within the dot.

nanoscale manipulation of the piezoelectric effect

Caption: This is a laser in Dr. Kambhampati's lab that is used to shine light on quantum dots.

Credit: Credit: Dept. of Chemistry, McGill University. Usage Restrictions: None.
This electric field produces enormous piezoelectric forces causing large and rapid expansion and contraction of the dots within a trillionth of a second. Most importantly, the team is able to control the size of this vibration.

Cadmium Selenide quantum dots can be used in a wide range of technological applications. Solar power is one area that has been explored, but this new discovery has paved way for other nanoscale device applications for these dots. This discovery offers a way of controlling the speed and switching time of nanoelectronic devices, and possibly even developing nanoscale power supplies, whereby a small compression would produce a large voltage.

"The piezoelectric effect has never been manipulated at this scale before, so the range of possible applications is very exciting," explained Pooja Tyagi, a PhD researcher in Professor Patanjali Kambhampati's laboratory.
"For example, the vibrations of a material can be analyzed to calculate the pressure of the solvent they are in. With further development and research, maybe we could measure blood pressure non-invasively by injecting the dots, shining a laser on them, and analyzing their vibration to determine the pressure." Tyagi notes that Cadium Selenide is a toxic metal, and so one of the hurdles to overcome with regard to this particular example would be finding a replacement material. ###

The research was published in Nano Letters and received funding from the Canada Foundation for Innovation, the Natural Sciences and Engineering Research Council of Canada, and the Fonds Québécois de la Recherche sur la Nature et les Technologies.

For more information: kambhampati-group.mcgill.ca

Contact: William Raillant-Clark william.raillant-clark@mcgill.ca 514-398-2189 McGill University

Sunday, September 19, 2010

Extreme darkness: Carbon nanotube forest covers NIST's ultra-dark detector

Harnessing darkness for practical use, researchers at the National Institute of Standards and Technology (NIST) have developed a laser power detector coated with the world's darkest material‑a forest of carbon nanotubes that reflects almost no light across the visible and part of the infrared spectrum.

NIST will use the new ultra-dark detector, described in a new paper in Nano Letters,* to make precision laser power measurements for advanced technologies such as optical communications, laser-based manufacturing, solar energy conversion, and industrial and satellite-borne sensors.

Inspired by a 2008 paper by Rensselaer Polytechnic Institute (RPI) on "the darkest man-made material ever,"** the NIST team used a sparse array of fine nanotubes as a coating for a thermal detector, a device used to measure laser power. A co-author at Stony Brook University in New York grew the nanotube coating. The coating absorbs laser light and converts it to heat, which is registered in pyroelectric material (lithium tantalate in this case).

World's Darkest Material
Caption: This is a colorized micrograph of the world's darkest material -- a sparse "forest" of fine carbon nanotubes -- coating a NIST laser power detector. Image shows a region approximately 25 micrometers across.

Credit: Aric Sanders, NIST. Usage Restrictions: None.
The rise in temperature generates a current, which is measured to determine the power of the laser. The blacker the coating, the more efficiently it absorbs light instead of reflecting it, and the more accurate the measurements.

The new NIST detector uniformly reflects less than 0.1 percent of light at wavelengths from deep violet at 400 nanometers (nm) to near infrared at 4 micrometers (μm) and less than 1 percent of light in the infrared spectrum from 4 to 14 μm. The results are similar to those reported for the RPI material and in a 2009 paper by a Japanese group.
The NIST work is unique in that the nanotubes were grown on pyroelectric material, whereas the other groups grew them on silicon. NIST researchers plan to extend the calibrated operating range of their device to 50 or even 100 micrometer wavelengths, to perhaps provide a standard for terahertz radiation power.

NIST previously made detector coatings from a variety of materials, including flat nanotube mats. The new coating is a vertical forest of multiwalled nanotubes, each less than 10 nanometers in diameter and about 160 micrometers long. The deep hollows may help trap light, and the random pattern diffuses any reflected light in various directions. Measuring how much light was reflected across a broad spectrum was technically demanding; the NIST team spent hundreds of hours using five different methods to measure the vanishingly low reflectance with adequate precision. Three of the five methods involved comparisons of the nanotube-coated detector to a calibrated standard.

Carbon nanotubes offer ideal properties for thermal detector coatings, in part because they are efficient heat conductors. Nickel phosphorous, for example, reflects less light at some wavelengths, but does not conduct heat as well. The new carbon nanotube materials also are darker than NIST's various Standard Reference Materials for black color developed years ago to calibrate instruments. ###

* J. Lehman, A. Sanders, L. Hanssen, B. Wilthan and J. Zeng. 2010. A Very Black Infrared Detector from Vertically Aligned Carbon Nanotubes and Electric-field Poling of Lithium Tantalate. Nano Letters. Posted online Aug. 3, 2010.

** Z.P. Yang, L. Ci, J.A. Bur, S.Y. Lin and P.M. Ajayan. Experimental observation of an extremely dark material made by a low-density nanotube array. Nano Letters. Vol. 8, No. 2, 446-451.

Contact: Laura Ost laura.ost@nist.gov 303-497-4880 National Institute of Standards and Technology (NIST)

Saturday, September 18, 2010

Ho-hum to high performance: A boring material, when 'stretched,' could lead to electronics revolution

ITHACA, N.Y. — It's the Clark Kent of oxide compounds, and – on its own – it is pretty boring. But slice europium titanate nanometers thin and physically stretch it, and then it takes on super hero-like properties that could revolutionize electronics, according to new Cornell research. (Nature, Aug. 19, 2010.)

Researchers report that thin films of europium titanate become both ferroelectric (electrically polarized) and ferromagnetic (exhibiting a permanent magnetic field) when stretched across a substrate of dysprosium scandate, another type of oxide. The best simultaneously ferroelectric, ferromagnetic material to date pales in comparison by a factor of 1,000.

Simultaneous ferroelectricity and ferromagnetism is rare in nature and coveted by electronics visionaries. A material with this magical combination could form the basis for low-power, highly sensitive magnetic memory, magnetic sensors or highly tunable microwave devices.

europium titanate ferromagnetic

Cornell researchers made a thin film of europium titanate ferromagnetic and ferroelectric by "stretching" it. They did it by depositing the material on an underlying substrate with a larger spacing between its atoms.
The search for ferromagnetic ferroelectrics dates back to 1966, when the first such compound – a nickel boracite – was discovered. Since then, scientists have found a few additional ferromagnetic ferroelectrics, but none stronger than the nickel compound – that is, until now.

"Previous researchers were searching directly for a ferromagnetic ferroelectric – an extremely rare form of matter," said Darrell Schlom, Cornell professor of materials science and engineering, and an author on the paper.
"Our strategy is to use first-principles theory to look among materials that are neither ferromagnetic nor ferroelectric, of which there are many, and to identify candidates that, when squeezed or stretched, will take on these properties," said Craig Fennie, assistant professor of applied and engineering physics, and another author on the paper.

This fresh strategy, demonstrated using the europium titanate, opens the door to other ferromagnetic ferroelectrics that may work at even higher temperatures using the same materials-by-design strategy, the researchers said.

Other authors include David A. Muller, Cornell professor of applied and engineering physics; and first author June Hyuk Lee, a graduate student in Schlom's lab.

The researchers took an ultra-thin layer of the oxide and "stretched" it by placing it on top of the disprosium compound. The crystal structure of the europium titanate became strained because of its tendency to align itself with the underlying arrangement of atoms in the substrate.

Fennie's previous theoretical work had indicated that a different kind of material strain – more akin to squishing by compression – would also produce ferromagnetism and ferroelectricity. But the team discovered that the stretched europium compound displayed electrical properties 1,000 times better than the best-known ferroelectric/ferromagnetic material thus far, translating to thicker, higher-quality films.

This new approach to ferromagnetic ferroelectrics could prove a key step toward the development of next-generation memory storage, superb magnetic field sensors and many other applications long dreamed about. But commercial devices are a long way off; no devices have yet been made using this material. The Cornell experiment was conducted at an extremely cold temperature – about 4 degrees Kelvin (-452 Fahrenheit). The team is already working on materials that are predicted to show such properties at much higher temperatures. ###

The team includes researchers from Penn State University, Ohio State University and Argonne National Laboratory.

The research was supported by the Cornell Center for Materials Research, a National Science Foundation-funded Materials Research and Engineering Center (MRSEC), and corresponding MRSECs at Penn State and Ohio State.

Contact: Blaine Friedlander bpf2@cornell.edu 607-254-8093 Cornell University

Thursday, September 16, 2010

Breakthrough gene therapy prevents retinal degeneration

BOSTON — In one of only two studies of its kind, a study from researchers at Tufts University School of Medicine and the Sackler School of Graduate Biomedical Sciences at Tufts demonstrates that non-viral gene therapy can delay the onset of some forms of eye disease and preserve vision. The team developed nanoparticles to deliver therapeutic genes to the retina and found that treated mice temporarily retained more eyesight than controls. The study, published online in advance of print in Molecular Therapy, brings researchers closer to a non-viral gene therapy treatment for degenerative eye disorders.

"Our work shows that it is possible to attain therapeutic results using non-viral gene delivery methods, specifically, nanoparticles. Nanoparticles, which are small enough to penetrate cells and stable enough to protect DNA, are capable of preventing retinal cell death and preserving vision," said senior author Rajendra Kumar-Singh, PhD, associate professor of ophthalmology at Tufts University School of Medicine (TUSM) and member of the genetics; neuroscience; and cell, molecular, and developmental biology program faculties at the Sackler School of Graduate Biomedical Sciences at Tufts.

Nanoparticles Treatment

Caption: The image on left shows damage (pink) to the retina. The image on right shows that POD GDNF nanoparticles protected the retina from damage.

Credit: Image courtesy of Rajendra Kumar-Singh, Tufts University School of Medicine. Usage Restrictions: The image may only be used with appropriate caption or credit.
"The most common approach to gene therapy involves using a virus to deliver DNA to cells. While viruses are very efficient carriers, they can prompt immune responses that may lead to inflammation, cancer, or even death. Non-viral methods offer a safer alternative, but until now, efficiency has been a significant barrier," said Kumar-Singh.
In a model simulating the progression of human retinal degeneration, the researchers treated mice with nanoparticles carrying a gene for GDNF (Glial Cell Line-Derived Neurotrophic Factor), a protein known to protect the photoreceptor cells in the eye. Retinas treated with the GDNF-carrying nanoparticles showed significantly less photoreceptor cell death than controls. Preservation of these cells resulted in significantly better eyesight in the treatment group seven days after treatment, compared to controls.

The protection conferred by the GDNF-carrying nanoparticles was temporary, as tests fourteen days after treatment showed no difference in eyesight between treated mice and controls.

"The next step in this research is to prolong this protection by adding elements to the DNA that permit its retention in the cell. Bringing forth a more potent and enduring result will move us closer to clinical application of non-viral gene therapy," said Kumar-Singh.

AMD, which results in a loss of sharp, central vision, is the number one cause of visual impairment among Americans age 60 and older. Retinitis pigmentosa, an inherited condition characterized by night blindness and loss of peripheral vision, affects approximately 1 in 4,000 individuals in the United States. ###

Additional authors on the study are first author Sarah Parker Read, an MD/PhD candidate at TUSM and Sackler and member of Kumar-Singh's lab, and Siobhan Cashman, PhD, research assistant professor in the department of ophthalmology at TUSM and member of Kumar-Singh's lab.

In a previous study, this same team of researchers developed the gene delivery method used in this research. The researchers showed that a peptide called PEG-POD, which compacts DNA into nanoparticles, delivers genes to the retina more efficiently than other non-viral carriers.

This study was supported by grants from The Ellison Foundation; the National Eye Institute, part of the National Institutes of Health; the Virginia B. Smith Trust; and grants to the Department of Ophthalmology at Tufts University from the Lions Eye Foundation and Research to Prevent Blindness. Sarah Parker Read is part of the Sackler/TUSM Medical Scientist Training Program, which is funded by the National Institute of General Medical Sciences, part of the National Institutes of Health.

Read SP, Cashman SM, Kumar-Singh R. Molecular Therapy. "POD Nanoparticles Expressing GDNF Provide Structural and Functional Rescue of Light-Induced Retinal Degeneration in an Adult Mouse." Published online August 10, 2010, doi: 10.1038/mt.2010.167

About Tufts University School of Medicine and the Sackler School of Graduate Biomedical Sciences

Tufts University School of Medicine and the Sackler School of Graduate Biomedical Sciences at Tufts University are international leaders in innovative medical education and advanced research. The School of Medicine and the Sackler School are renowned for excellence in education in general medicine, biomedical sciences, special combined degree programs in business, health management, public health, bioengineering and international relations, as well as basic and clinical research at the cellular and molecular level. Ranked among the top in the nation, the School of Medicine is affiliated with six major teaching hospitals and more than 30 health care facilities. Tufts University School of Medicine and the Sackler School undertake research that is consistently rated among the highest in the nation for its effect on the advancement of medical science.

If you are a member of the media interested in learning more about this topic, or speaking with a faculty member at the Tufts University School of Medicine, the Sackler School of Graduate Biomedical Sciences, or another Tufts health sciences researcher, please contact Siobhan Gallagher at 617-636-6586 or, for this study, Lindsay Peterson at 617-636-2789.

Contact: Siobhan Gallagher 617-636-6586 Tufts University, Health Sciences

Wednesday, September 15, 2010

The nano world of Shrinky Dinks

Low-cost nanopatterning method utilizes popular shrinkable plastic

The magical world of Shrinky Dinks -- an arts and crafts material used by children since the 1970s -- has taken up residence in a Northwestern University laboratory. A team of nanoscientists is using the flexible plastic sheets as the backbone of a new inexpensive way to create, test and mass-produce large-area patterns on the nanoscale.

"Anyone needing access to large-area nanoscale patterns on the cheap could benefit from this method," said Teri W. Odom, associate professor of chemistry and Dow Chemical Company Research Professor in the Weinberg College of Arts and Sciences. Odom led the research. "It is a simple, low-cost and high-throughput nanopatterning method that can be done in any laboratory."

solvent-assisted nanoscale embossing

One programmable soft lithography recipe: (1) Start with a thermoplastic substrate. (2) Perform SANE. (3) Heat substrate. (4) Create different nanopatterns with same feature sizes. (5) Repeat.

Details of the solvent-assisted nanoscale embossing (SANE) method are published by the journal Nano Letters. The work also will appear as the cover story of the journal's February 2011 issue.

The method offers unprecedented opportunities to manipulate the electronic, photonic and magnetic properties of nanomaterials. It also easily controls a pattern's size and symmetry and can be used to produce millions of copies of the pattern over a large area. Potential applications include devices that take advantage of nanoscale patterns, such as solar cells, high-density displays, computers and chemical and biological sensors.

"No other existing nanopatterning method can both prototype arbitrary patterns with small separations and reproduce them over six-inch wafers for less than $100," Odom said.

Starting with a single master pattern, the simple yet potentially transformative method can be used to create new nanoscale masters with variable spacings and feature sizes. SANE can increase the spacing of patterns up to 100 percent as well as decrease them down to 50 percent in a single step, merely by stretching or heating (shrinking) the polymer substrate (the Shrinky Dinks material). Also, SANE can reduce critical feature sizes as small as 45 percent compared to the master by controlled swelling of patterned polymer molds with different solvents. SANE works from the nanoscale to the macroscale.

Biologists, chemists and physicists who are not familiar with nanopatterning now can use SANE for research at the nanoscale. Those working on solar energy, data storage and plasmonics will find the method particularly useful, Odom said.

For example, in a plasmonics application, Odom and her research team used the patterning capabilities to generate metal nanoparticle arrays with continuously variable separations on the same substrate.

SANE offers a way to meet three grand challenges in nanofabrication from the same -- and a single -- master pattern: (1) creating programmable array densities, (2) reducing critical feature sizes, and (3) designing different and reconfigurable lattice symmetries over large areas and in a massively parallel manner. ###

The title of the Nano Letters paper is "Programmable Soft Lithography: Solvent-Assisted Nanoscale Embossing." In addition to Odom, other authors of the paper are Min Hyung Lee, Mark D. Huntington, Wei Zhou and Jiun-Chan Yang, all from Northwestern. The paper is available at pubs.acs.org/doi/abs/.

Contact: Megan Fellman fellman@northwestern.edu 847-491-3115 Northwestern University

Tuesday, September 14, 2010

New nanoscale transistors allow sensitive probing inside cells

Bioprobes offer first intracellular measurements with a semiconductor device.

CAMBRIDGE, Mass. – Chemists and engineers at Harvard University have fashioned nanowires into a new type of V-shaped transistor small enough to be used for sensitive probing of the interior of cells.

The new device, described this week in the journal Science, is smaller than many viruses and about one-hundredth the width of the probes now used to take cellular measurements, which can be nearly as large as the cells themselves. Its slenderness is a marked improvement over these bulkier probes, which can damage cells upon insertion, reducing the accuracy or reliability of any data gained.

"Our use of these nanoscale field-effect transistors, or nanoFETs, represents the first totally new approach to intracellular studies in decades, as well as the first measurement of the inside of a cell with a semiconductor device," says senior author Charles M. Lieber, the Mark Hyman, Jr. Professor of Chemistry at Harvard.

Kinked-Nanowire Electronic Sensor

Caption: This is a to scale schematic of a kinked-nanowire electronic sensor probing the intracellular region of a cell. The two-terminal device has a three-dimensional and flexible structure with the key nanoscale transistor element synthetically-integrated at the tip of the acute-angle nanowire nanostructure. 3-D nanoprobes modified with phospholipid bilayers enter single cells in a minimally-invasive manner to allow robust recording of intracellular potential.

Credit: Courtesy of Charles Lieber, Harvard University. Usage Restrictions: None.
"The nanoFETs are the first new electrical measurement tool for intracellular studies since the 1960s, during which time electronics have advanced considerably."

Lieber and colleagues say nanoFETs could be used to measure ion flux or electrical signals in cells, particularly neurons. The devices could also be fitted with receptors or ligands to probe for the presence of individual biochemicals within a cell.

Human cells can range in size from about 10 microns (millionths of a meter) for nerve cells to 50 microns for cardiac cells. While current probes measure up to 5 microns in diameter, nanoFETs are several orders of magnitude smaller: less than 50 nanometers (billionths of a meter) in total size, with the nanowire probe itself measuring just 15 nanometers in diameter.

Aside from their small size, two features allow for easy insertion of nanoFETs into cells. First, Lieber and colleagues found that by coating the structures with a phospholipid bilayer – the same material cell membranes are made of – the devices are easily pulled into a cell via membrane fusion, a process related to that used to engulf viruses and bacteria.

"This eliminates the need to push the nanoFETs into a cell, since they are essentially fused with the cell membrane by the cell's own machinery," Lieber says. "This also means insertion of nanoFETs is not nearly as traumatic to the cell as current electrical probes. We found that nanoFETs can be inserted and removed from a cell multiple times without any discernible damage to the cell. We can even use them to measure continu-ously as the device enters and exits the cell."
Secondly, the current paper builds upon previous work by Lieber's group to introduce triangular "stereocenters" – essentially, fixed 120º joints – into nanowires, structures that had previously been rigidly linear. These stereocenters, analogous to the chemical hubs found in many complex organic molecules, introduce kinks into 1-D nanostructures, transforming them into more complex forms.

Lieber and his co-authors found that introducing two 120º angles into a nanowire in the proper cis orientation creates a single V-shaped 60º angle, perfect for a two-pronged nanoFET with a sensor at the tip of the V. The two arms can then be connected to wires to create a current through the nanoscale transistor. ###

Lieber's co-authors on the Science paper are Bozhi Tian, Tzahi Cohen-Karni, Quan Qing, Xiaojie Duan, and Ping Xie, all of Harvard's Department of Chemistry and Chemical Biology and School of Engineering and Applied Sciences. The work was sponsored by the National Institutes of Health and the McKnight Foundation for Neuroscience.

Contact: Michael Patrick Rutter mrutter@seas.harvard.edu 617-496-3815 Harvard University

Monday, September 13, 2010

New paper offers breakthrough on blinking molecules phenomenon

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.

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."

blinking molecules phenomena

blinking molecules phenomena
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. ###

Contact: Boldizsar Janko jano.2@nd.edu 574-850-9850 University of Notre Dame

Sunday, September 12, 2010

Scientists achieve highest-resolution MRI of a magnet

COLUMBUS, Ohio -- In a development that holds potential for both data storage and biomedical imaging, Ohio State University researchers have used a new technique to obtain the highest-ever resolution MRI scan of the inside of a magnet.

Chris Hammel, Ohio Eminent Scholar in Experimental Physics, and his colleagues took a tiny magnetic disk -- measuring only 2 micrometers (millionths of a meter) across and 40 nanometers (billionths of a meter) thick – and were able to obtain magnetic resonance images its interior.

The resulting image -- with each "pixel" one tenth the size of the disk itself -- is the highest-resolution image ever taken of the magnetic fields and interactions inside of a magnet.

Highest-Resolution MRI Of A Magnet

Caption: Researchers at Ohio State University have developed a new type of magnetic resonance that can see inside magnetic materials. Here, slight variations in the structure of a thin magnetic film are evident as variations in ferromagnetic resonance frequency, represented by changes in color. Above the film is a representation of a polarized magnetic tip that scans the material.

Credit: Image courtesy of Ohio State University. Usage Restrictions: News Media use only.
Why look inside magnets? Because studying the material's behavior at these tiny scales is key to incorporating them into computer chips and other electronic devices.

The researchers report their findings in the August 12 issue of the journal Nature.

In 2008, Hammel's team debuted a new kind of high-resolution scanning system that combines three different kinds of technology: MRI, ferromagnetic resonance, and atomic force microscopy.

Ferromagnets -- the type of magnet used in this study -- are magnets made of ferrous metal such as iron. Common household refrigerator magnets are ferromagnets.

Because ferromagnets retain a particular polarization once magnetized, they are already essential components in today's computers and other electronics, where they provide data storage alongside computer chips.
But smaller magnets built directly into a computer chip could do even more, Hammel explained.

"We know that shrinking these magnets to the nanoscale and building them directly inside electronics would enable these devices to do more, and with less power consumption," Hammel said. "But a key barrier has always been the difficulty of imaging and characterizing nanomagnets."

Typical MRI machines work by inducing a magnetic field inside non-magnetic objects, such as the body. Since ferromagnets are already magnetic, conventional MRI can't see inside them.

The combination technique that the Ohio State researchers invented is called "scanned probe ferromagnetic resonance imaging," or scanned probe FMRI, and it involves detecting a magnetic signal using a tiny silicon bar with an even tinier magnetic probe on its tip.

In Nature, they report a successful demonstration of the technique, as they imaged the inside of the magnetic disk 0.2 micrometers (200 nanometers) at a time. They used a thin film of a commercially available nickel-iron magnetic alloy called Permalloy for the disk.

"In essence, we were able to conduct ferromagnetic resonance measurements on a small fraction of the disk, then move our probe over a little bit and do magnetic resonance there, and so on," explained Denis Pelekhov, director of the ENCOMM NanoSystems Laboratory at Ohio State. "Using these results, we could see how the magnetic properties vary inside the disk."

Experts suspect that computer chips equipped with tiny magnets might one day provide high-density data storage. Computers with magnets in their central processing units (CPUs) would never have to boot up. The entire computer would be contained inside the CPU, making such devices even smaller and less power-hungry as well.

Hammel believes that the technique could one day be useful tool in biomedical research labs. Researchers could use it to study tissue samples of the plaques that form in brain tissues and arteries, and perhaps develop better ways of detecting them in the body. Knowing how these plaques form could advance studies of many diseases, including Alzheimer's and atherosclerosis. ###

Hammel and Pelekhov's co-authors on the paper include Inhee Lee, Yuri Obukhov, Gang Xiang,, Adam Hauser, Fengyuan Yang, and Palash Banerjee, all of the Department of Physics at Ohio State.

This research was funded by the Department of Energy.

Contact: Chris Hammel Hammel.7@osu.edu 614-247-6928 Ohio State University Denis Pelekhov (614) 292-9125; Pelekhov.1@osu.edu Written by Pam Frost Gorder, (614) 292-9475; Gorder.1@osu.edu

Saturday, September 11, 2010

Innovation could bring super-accurate sensors, crime forensics

WEST LAFAYETTE, Ind. - A new technology enabling tiny machines called micro electromechanical systems to "self-calibrate" could make possible super-accurate and precise sensors for crime-scene forensics, environmental testing and medical diagnostics.

The innovation might enable researchers to create a "nose-on-a-chip" for tracking criminal suspects, sensors for identifying hazardous solid or gaseous substances, as well as a new class of laboratory tools for specialists working in nanotechnology and biotechnology.

"In the everyday macroscopic world, we can accurately measure distance and mass because we have well-known standards such as rulers or weights that we use to calibrate devices that measure distances or forces," said Jason Vaughn Clark, an assistant professor of electrical and computer engineering and mechanical engineering. "But for the micro- or nanoscopic worlds, there have been no standards and no practical ways for measuring very small distances or forces."

Self-Calibratable MEMS

Caption: This image depicts a device that enables tiny micro electromechanical systems to "self-calibrate," an advance that could make possible super-accurate sensors, a "nose-on-a-chip" for law enforcement and a new class of laboratory tools for specialists working in nanotechnology and biotechnology.

Credit: Jason Vaughn Clark, Purdue University Birck Nanotechnology Center. Usage Restrictions: None.
The micro electromechanical systems, or MEMS, are promising for an array of high-tech applications.

Researchers previously have used various techniques to gauge the force and movement of tiny objects containing components so small they have to be measured on the scale of micrometers or nanometers, millionths or billionths of a meter, respectively. However, the accuracy of conventional techniques is typically off by 10 percent or more because of their inherent uncertainties, Clark said.

"And due to process variations within fabrication, no two microstructures have the same geometric and material properties," he said.

These small variations in microstructure geometry, stiffness and mass can significantly affect performance.
"A 10 percent change in width can cause a 100 percent change in a microstructure's stiffness," Clark said. "Process variations have made it difficult for researchers to accurately predict the performance of MEMS."

The new technology created by Clark, called electro micro metrology - or EMM - is enabling engineers to account for process variations by determining the precise movement and force that's being applied to, or sensed by, a MEMS device.

"For the first time, MEMS can now truly self-calibrate without any external references," Clark said. "That is, our MEMS are able to determine their unique mechanical performance properties. And in doing so, they become very accurate sensors or actuators."

Research findings were detailed in two papers presented in June during a meeting of the Society of Experimental Mechanics in Indianapolis and at the Nanotech 2010 Conference and Expo in Anaheim, Calif. The work is based at the Birck Nanotechnology Center in Purdue's Discovery Park.

MEMS accelerometers and gyroscopes currently are being used in commercial products, including the Nintendo Wii video game, the iPhone, walking robots and automotive airbags.

"Those MEMS work well because they don't need ultra-high precision or accuracy," Clark said. "It is difficult for conventional technology to accurately measure very small forces, such as van der Waals forces between molecules or a phenomenon called the Casimir effect that is due to particles popping in and out of existence everywhere in the universe."

These forces are measured in "piconewtons," a trillionth of the weight of a medium-size apple.

"If we are trying to investigate or exploit picoscale phenomena like Casimir forces, van der Waals forces, the hydrogen bond forces in DNA, high-density data storage or even nanoassembly, we need much higher precision and accuracy than conventional methods provide," Clark said. "With conventional tools, we know we are sensing something, but without accurate measurements it is difficult to fully understand the phenomena, repeat the experiments and create predictive models."

Self-calibration also is needed because microdevices might be exposed to harsh environments or remain dormant for long periods.

"Say you have a MEMS sensor in the environment or on a space probe," Clark said. "You want it to be able to wake up and recalibrate itself to account for changes resulting from temperature differences, changes in the gas or liquid ambient, or other conditions that might affect its properties. That's when self-calibration technology is needed."

EMM defines mechanical properties solely in terms of electrical measurements, which is different than conventional methods, he said.

For example, by measuring changes in an electronic property called capacitance, or the storage of electrical charge, Clark is able to obtain the microstructure's shape, stiffness, force or displacement with high accuracy and precision, he said.

"We can measure capacitance more precisely than we can measure any other quantity to date," he said. "That means we could potentially measure certain mechanical phenomena more precisely by using MEMS than we could by using conventional macroscale measurement tools."

The researcher will use the new approach to improve the accuracy of instruments called atomic force microscopes, which are used by nanotechnologists.

"The atomic force microscope, which jumpstarted the nanotechnology revolution, is often used to investigate small displacements and forces," Clark said. "But the operator of the tool cannot precisely say what distance or force is being sensed beyond one or two significant digits. And the typical operator knows even less about the true accuracy of their measurements."

Purdue operates about 30 atomic force microscopes, and Clark's research group is planning to teach users how to calibrate their instruments using the self-calibrating MEMS.

He also plans to use his new approach to create a miniature self-calibrating "AFM-on-a-chip," dramatically shrinking the size and cost of the laboratory instrument.

"Such an advent should open the door to the nanoworld to a much larger number of groups or individuals," he said.

Clark's research group has fabricated and tested the first generation of self-calibrating MEMS, and repeatable results have shown the presence of the Casimir and van der Waals forces. ###

The research is funded by the National Science Foundation.

Contact: Emil Venere venere@purdue.edu 765-494-4709 Purdue University

Source: Jason Vaughn Clark, (765) 494-3437, jvclark@purdue.edu

Thursday, September 09, 2010

Study of electron orbits in multilayer graphene finds unexpected energy gaps

Electron transport. Researchers have taken one more step toward understanding the unique and often unexpected properties of graphene, a two-dimensional carbon material that has attracted interest because of its potential applications in future generations of electronic devices.

In the Aug. 8 advance online edition of the journal Nature Physics, researchers from the Georgia Institute of Technology and the National Institute of Standards and Technology (NIST) describe for the first time how the orbits of electrons are distributed spatially by magnetic fields applied to layers of epitaxial graphene.

The research team also found that these electron orbits can interact with the substrate on which the graphene is grown, creating energy gaps that affect how electron waves move through the multilayer material. These energy gaps could have implications for the designers of certain graphene-based electronic devices.

Stacking of graphene sheets

Caption: Stacking of graphene sheets creates regions where the moiré alignment is of type AA (all atoms have neighbors in the layer below), AB (only A atoms have neighbors) or BA (only B atoms have neighbors). In the figure, AA regions are blue-white, while AB and BA regions are red and yellow, respectively.

Credit: Courtesy of Phillip First. Usage Restrictions: None.

Electron Orbits

Caption: This graphic shows electrons that move along an equipotential, while those that follow closed equipotentials (as in a potential-energy valley) become localized (right). The arrows denote the magnetic field, while hills and valleys are small potential fluctuations.

Credit: Courtesy of Phillip First. Usage Restrictions: None.
"The regular pattern of energy gaps in the graphene surface creates regions where electron transport is not allowed," said Phillip N. First, a professor in the Georgia Tech School of Physics and one of the paper's co-authors. "Electron waves would have to go around these regions, requiring new patterns of electron wave interference. Understanding such interference will be important for bi-layer graphene devices that have been proposed, and may be important for other lattice-matched substrates used to support graphene and graphene devices."

In a magnetic field, an electron moves in a circular trajectory – known as a cyclotron orbit – whose radius depends on the size of the magnetic field and the energy of electron. For a constant magnetic field, that's a little like rolling a marble around in a large bowl, First said.

"At high energy, the marble orbits high in the bowl, while for lower energies, the orbit size is smaller and lower in the bowl," he explained. "The cyclotron orbits in graphene also depend on the electron energy and the local electron potential – corresponding to the bowl – but until now, the orbits hadn't been imaged directly."

Placed in a magnetic field, these orbits normally drift along lines of nearly constant electric potential. But when a graphene sample has small fluctuations in the potential, these "drift states" can become trapped at a hill or valley in the material that has closed constant potential contours. Such trapping of charge carriers is important for the quantum Hall effect, in which precisely quantized resistance results from charge conduction solely through the orbits that skip along the edges of the material.

The study focused on one particular electron orbit: a zero-energy orbit that is unique to graphene. Because electrons are matter waves, interference within a material affects how their energy relates to the velocity of the wave – and reflected waves added to an incoming wave can combine to produce a slower composite wave. Electrons moving through the unique "chicken-wire" arrangement of carbon-carbon bonds in the graphene interfere in a way that leaves the wave velocity the same for all energy levels.

In addition to finding that energy states follow contours of constant electric potential, the researchers discovered specific areas on the graphene surface where the orbital energy of the electrons changes from one atom to the next. That creates an energy gap within isolated patches on the surface.
"By examining their distribution over the surface for different magnetic fields, we determined that the energy gap is due to a subtle interaction with the substrate, which consists of multilayer graphene grown on a silicon carbide wafer," First explained.

In multilayer epitaxial graphene, each layer's symmetrical sublattice is rotated slightly with respect to the next. In prior studies, researchers found that the rotations served to decouple the electronic properties of each graphene layer.

"Our findings hold the first indications of a small position-dependent interaction between the layers," said David L. Miller, the paper's first author and a graduate student in First's laboratory. "This interaction occurs only when the size of a cyclotron orbit – which shrinks as the magnetic field is increased – becomes smaller than the size of the observed patches."

The origin of the position dependent interaction is believed to be the "moiré pattern" of atomic alignments between two adjacent layers of graphene. In some regions, atoms of one layer lie atop atoms of the layer below, while in other regions, none of the atoms align with the atoms in the layer below. In still other regions, half of the atoms have neighbors in the underlayer, an instance in which the symmetry of the carbon atoms is broken and the Landau level – discrete energy level of the electrons – splits into two different energies.

Experimentally, the researchers examined a sample of epitaxial graphene grown at Georgia Tech in the laboratory of Professor Walt de Heer, using techniques developed by his research team over the past several years.

They used the tip of a custom-built scanning-tunneling microscope (STM) to probe the atomic-scale electronic structure of the graphene in a technique known as scanning tunneling spectroscopy. The tip was moved across the surface of a 100-square nanometer section of graphene, and spectroscopic data was acquired every 0.4 nanometers.

The measurements were done at 4.3 degrees Kelvin to take advantage of the fact that energy resolution is proportional to the temperature. The scanning-tunneling microscope, designed and built by Joseph Stroscio at NIST's Center for Nanoscale Science and Technology, used a superconducting magnet to provide the magnetic fields needed to study the orbits.

According to First, the study raises a number of questions for future research, including how the energy gaps will affect electron transport properties, how the observed effects may impact proposed bi-layer graphene coherent devices – and whether the new phenomenon can be controlled.

"This study is really a stepping stone in long path to understanding the subtleties of graphene's interesting properties," he said. "This material is different from anything we have worked with before in electronics." ###

In addition to those already mentioned, the study also included Walt de Heer, Kevin D. Kubista, Ming Ruan, and Markus Kinderman from Georgia Tech and Gregory M. Rutter from NIST. The research was supported by the National Science Foundation, the Semiconductor Research Corporation and the W.M. Keck Foundation. Additional assistance was provided by Georgia Tech's Materials Research Science and Engineering Center (MRSEC).

Contact: John Toon jtoon@gatech.edu 404-894-6986 Georgia Institute of Technology Research News

Wednesday, September 08, 2010

Researchers develop magnetic molecular machines to deliver drugs to unhealthy cells

New nanomaterial could improve therapeutics and imaging in cancer treatment.

Scientists from UCLA's California NanoSystems Institute and Korea's Yonsei University have developed an innovative method that enables nanomachines to release drugs inside living cancer cells when activated remotely by an oscillating magnetic field.

The new system — the first to utilize a class of porous nanomaterials driven by a magnetic core — has the potential to improve both targeted drug-delivery and magnetic resonance imaging in the treatment of cancer and other diseases.

The research appears in the July issue of the Journal of the American Chemical Society.

anticancer drug doxorubicin

Images of nanoparticles (green) taken up by breast cancer cells. In the control sample (left), the magnetic field is not turned on. For the sample exposed to the magnetic field (right), an anticancer drug doxorubicin (red) is released into the cells, and the cells are killed.
In recent years, cancer research has increasingly focused on developing therapies that, unlike chemotherapy, target only cancer cells while leaving healthy cells unharmed. To that end, scientists have created nanomachines that can trap and release drug molecules from pores directly into individual cancer cells in response to a stimulus.

While many methods have been created for controlling how and when pores load and unload their cargos, for therapeutic applications, an external and noninvasive method of activation is preferable for the most effective results.
The new method, developed by the research groups of Jeffrey Zink, a UCLA professor of chemistry and biochemistry, and Jinwoo Cheon, a professor of chemistry at Korea's Yonsei University, uses a material that combines a framework of mesoporous silica nanoparticles with magnetic zinc-doped iron oxide nanocrystals, along with attached nanovalves that help hold drug molecules in the pores. When a magnetic-field stimulus is applied, the valves open and release the drug molecules from the pores into the target cells.

"The hydrophobic nature of the interior of the pores, as well as the ability to functionalize the silica surface with hydrophilic functionalities, makes these particles attractive for anti-cancer drug delivery," Zink said. "Adding a magnetic core to the silica-based nanoparticles is of interest for its potential applications in magnetic resonance imaging, as addition of the magnetic core may make it useful as a contrast agent. "

For this study, nanoparticles carrying the anti-cancer drug doxorubicin were introduced to and endocytosed by breast cancer cells. When the cancer cells containing the nanoparticles were then exposed to an oscillating magnetic field, cell death occurred.

"The novel magnetic-core silica nanoparticles are effective in activating nanovalves which release anti-cancer drugs when they are exposed to an oscillating magnetic field," Zink said.

The magnetic-field oscillation causes the zinc-doped iron oxide nanocrystals to heat. This increased heat causes the molecular machines to activate, and the doxorubicin in the pores is delivered into the cells.

"Magnetic nanocrystals are important in biomedical applications because they can be used for both therapeutics and imaging," said Cheon, director of the National Creative Research Initiative Center for Evolutionary Nanoparticles and the H.G. Underwood Professor of Chemistry and division head of the Nano-Medical National Core Research Center at Yonsei University.

"The ability to deliver anti-cancer drugs only to the cancer cells without affecting healthy cells is of key importance," added Cheon who is also a visiting professor at UCLA's CNSI.

Experiments for the research project were performed by UCLA graduate students Courtney Thomas and Daniel Ferris and Yonsei University graduate students Je-Hyun Lee and Eunsook Kim, who are part of the research group of professor Jeon-Soo Shin. The research team also involved Fraser Stoddard, a professor of chemistry at Northwestern University who began his collaboration with Zink while he was a professor of chemistry at UCLA. During his UCLA tenure, Stoddart served as Fred Kavli Chair of Nanosystems Sciences and director of the CNSI, positions now held by distinguished professor of chemistry Paul S. Weiss.

The next step in the research will be to examine the effects in vivo and to determine if we can use this to offer precise control over location of delivered drugs. The ultimate goal would be to develop this system to have applicability in treatment of cancer patients.

The research received support from numerous sources including the UC Toxic Substances Training and Research Program, the National Science Foundation, the NanoMedical National Core Research Center, and the Creative Research Initiative Program of Korea.

The California NanoSystems Institute at UCLA is an integrated research center operating jointly at UCLA and UC Santa Barbara whose mission is to foster interdisciplinary collaborations for discoveries in nanosystems and nanotechnology; train the next generation of scientists, educators and technology leaders; and facilitate partnerships with industry, fueling economic development and the social well-being of California, the United States and the world. The CNSI was established in 2000 with $100 million from the state of California and an additional $250 million in federal research grants and industry funding. At the institute, scientists in the areas of biology, chemistry, biochemistry, physics, mathematics, computational science and engineering are measuring, modifying and manipulating the building blocks of our world — atoms and molecules. These scientists benefit from an integrated laboratory culture enabling them to conduct dynamic research at the nanoscale, leading to significant breakthroughs in the areas of health, energy, the environment and information technology.

Media Contacts Jennifer Marcus, 310-267-4839 jmarcus@cnsi.ucla.edu