Tuesday, March 1, 2011

Liquid metal key to simpler creation of electrodes for microfluidic devices

Researchers from North Carolina State University have developed a faster, easier way to create microelectrodes, for use in microfluidic devices, by using liquid metal. Microfluidic devices manipulate small amounts of fluid and have a wide variety of applications, from testing minute blood samples to performing advanced chemical research.

"By making it easier to incorporate electrodes into microfluidic devices, we hope to facilitate research and development into new technologies that utilize those devices, such as biomedical tools," says Dr. Michael Dickey, an assistant professor of chemical and biomolecular engineering at NC State and co-author of a paper describing the research.

Traditionally, microfluidic devices have incorporated solid metal electrodes that serve as sensors, pumps, antennas or other functions. However, these solid electrodes can be problematic, because they need to be physically aligned to a channel that runs through the device. The channel serves as the entry point for whatever fluid the device is designed to manipulate. Aligning the electrodes is tricky because the electrodes are only tens to hundreds of microns in diameter, as is the channel itself. It is difficult to manipulate objects of that size -- a micron is one-millionth of a meter, and a human hair is approximately 100 microns in diameter.

The NC State team has addressed the problem by designing microfluidic devices that incorporate three channels, with the central channel separated from the other two by a series of closely set posts. The researchers inject the two outer channels with a liquid metal alloy composed of gallium and indium. The alloy fills the outer channels completely, but forms an oxidized "skin" that spans the space between the posts -- leaving the central channel free to receive other fluids.

"This approach allows you to create perfectly aligned electrodes in a single step," Dickey says. "The channels are built into the device, so the electrodes are inherently aligned -- we get the metal to go exactly where we want it. This means creating these devices is easier and faster."

In addition, this approach allows for the creation of electrodes in useful configurations that were previously difficult or impossible to achieve. This can be done by changing the shape of the channels that will be injected with the liquid metal. These configurations would create more uniform electric fields, for use in manipulating fluids and particles.

The paper, "Inherently aligned microfluidic electrodes composed of liquid metal," was co-authored by Dickey and NC State Ph.D. student Ju-Hee So. The paper is forthcoming from the Royal Society of Chemistry's journal Lab on a Chip. The research was supported, in part, by the National Science Foundation.

NC State's Department of Chemical and Biomolecular Engineering is part of the university's College of Engineering.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by North Carolina State University.

Journal Reference:

Ju-Hee So, Michael D. Dickey. Inherently aligned microfluidic electrodes composed of liquid metal. Lab on a Chip, 2011; 11 (5): 905 DOI: 10.1039/c0lc00501k

New way to design metal nanoparticle catalysts

Tiny metal nanoparticles are used as catalysts in many reactions, from refining chemicals to producing polymers and biofuels. How well these nanoparticles perform as catalysts for these reactions depend on which of their crystal faces are exposed.

But previous attempts to design these nanoparticles by changing their shape have failed because the structures are unstable and will revert back to their equilibrium shape.

Now, researchers at Northwestern University's Institute for Catalysis in Energy Processing have discovered a new strategy for fabricating metal nanoparticles in catalysts that promises to enhance the selectivity and yield for a wide range of structure-sensitive catalytic reactions. The team, led by Laurence D. Marks, professor of materials science and engineering at the McCormick School of Engineering and Applied Science, discovered that they could design nanoparticles by designing the particle's support structure.

"Instead of trying to engineer the nanoparticles, we've engineered the substrate that the nanoparticle sits on," Marks said. "That changes what faces are exposed." Their results were published in February in the journal Nano Letters.

This solution was a bit of a discovery: the team created the nanoparticle samples, discovered that they didn't change their shape (as the laws of thermodynamics caused previously designed nanoparticles to do), then set out figuring how it worked. It turns out that epitaxy -- the relationship between the position of the atoms in the nanoparticle and the position of the atoms on the substrate -- was more important to design than previously thought.

The team is currently testing the nanoparticles in a catalytic reactor, and early results look promising, Marks says. The nanoparticles appear to be stable enough to survive the rigors of long-term use as catalysts.

"It opens the door to designing better catalysts," Marks said. "This method could be used with a variety of different metal nanoparticles. It's a new strategy, and it could have a very big impact.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Northwestern University.

Journal Reference:

James A. Enterkin, Kenneth R. Poeppelmeier, Laurence D. Marks. Oriented Catalytic Platinum Nanoparticles on High Surface Area Strontium Titanate Nanocuboids. Nano Letters, 2011; : 110202144738042 DOI: 10.1021/nl104263j

More than 4,000 components of blood chemistry listed

ScienceDaily (Feb. 24, 2011) — After three years of exhaustive analysis led by a University of Alberta researcher, the list of known compounds in human blood has exploded from just a handful to more than 4,000.

"Right now a medical doctor analyzing the blood of an ailing patient looks at something like 10 to 20 chemicals," said U of A biochemist David Wishart. "We've identified 4,229 blood chemicals that doctors can potentially look at to diagnose and treat health problems."

Blood chemicals, or metabolites, are routinely analyzed by doctors to diagnose conditions like diabetes and kidney failure. Wishart says the new research opens up the possibility of diagnosing hundreds of other diseases that are characterized by an imbalance in blood chemistry.

Wishart led more than 20 researchers at six different institutions using modern technology to validate past research, and the team also conducted its own lab experiments to break new ground on the content of human-blood chemistry.

"This is the most complete chemical characterization of blood ever done," said Wishart. "We now know the normal values of all the detectable chemicals in blood. Doctors can use these measurements as a reference point for monitoring a patient's current and even future health."

Wishart says blood chemicals are the "canary in the coal mine," for catching the first signs of an oncoming medical problem. "The blood chemistry is the first thing to change when a person is developing a dangerous condition like high cholesterol."

The database created by Wishart and his team is open access, meaning anyone can log on and find the expanded list of blood chemicals. Wishart says doctors can now tap into the collected wisdom of hundreds of blood-research projects done in the past by researchers all over the world. "With this new database doctors can now link a specific abnormality in hundreds of different blood chemicals with a patient's specific medical problem," said Wishart.

Wishart believes the adoption of his research will happen slowly, with hospitals incorporating new search protocols and equipment for a few hundred of the more than 4,000 blood-chemistry markers identified by Wishart and his colleagues.

"People have being studying blood for more than 100 years," said Wishart. "By combining research from the past with our new findings we have moved the science of blood chemistry from a keyhole view of the world to a giant picture window."

The research was published last week in the journal PLoS One.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Alberta.

Journal Reference:

Nikolaos Psychogios, David D. Hau, Jun Peng, An Chi Guo, Rupasri Mandal, Souhaila Bouatra, Igor Sinelnikov, Ramanarayan Krishnamurthy, Roman Eisner, Bijaya Gautam, Nelson Young, Jianguo Xia, Craig Knox, Edison Dong, Paul Huang, Zsuzsanna Hollander, Theresa L. Pedersen, Steven R. Smith, Fiona Bamforth, Russ Greiner, Bruce McManus, John W. Newman, Theodore Goodfriend, David S. Wishart. The Human Serum Metabolome. PLoS ONE, 2011; 6 (2): e16957 DOI: 10.1371/journal.pone.0016957

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

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

New stretchable solar cells will power artificial electronic 'super skin'

"Super skin" is what Stanford researcher Zhenan Bao wants to create. She's already developed a flexible sensor that is so sensitive to pressure it can feel a fly touch down. Now she's working to add the ability to detect chemicals and sense various kinds of biological molecules. She's also making the skin self-powering, using polymer solar cells to generate electricity. And the new solar cells are not just flexible, but stretchable -- they can be stretched up to 30 percent beyond their original length and snap back without any damage or loss of power.

Super skin, indeed.

"With artificial skin, we can basically incorporate any function we desire," said Bao, a professor of chemical engineering. "That is why I call our skin 'super skin.' It is much more than what we think of as normal skin."

The foundation for the artificial skin is a flexible organic transistor, made with flexible polymers and carbon-based materials. To allow touch sensing, the transistor contains a thin, highly elastic rubber layer, molded into a grid of tiny inverted pyramids. When pressed, this layer changes thickness, which changes the current flow through the transistor. The sensors have from several hundred thousand to 25 million pyramids per square centimeter, corresponding to the desired level of sensitivity.

To sense a particular biological molecule, the surface of the transistor has to be coated with another molecule to which the first one will bind when it comes into contact. The coating layer only needs to be a nanometer or two thick.

"Depending on what kind of material we put on the sensors and how we modify the semiconducting material in the transistor, we can adjust the sensors to sense chemicals or biological material," she said.

Bao's team has successfully demonstrated the concept by detecting a certain kind of DNA. The researchers are now working on extending the technique to detect proteins, which could prove useful for medical diagnostics purposes.

"For any particular disease, there are usually one or more specific proteins associated with it -- called biomarkers -- that are akin to a 'smoking gun,' and detecting those protein biomarkers will allow us to diagnose the disease," Bao said.

The same approach would allow the sensors to detect chemicals, she said. By adjusting aspects of the transistor structure, the super skin can detect chemical substances in either vapor or liquid environments.

Regardless of what the sensors are detecting, they have to transmit electronic signals to get their data to the processing center, whether it is a human brain or a computer.

Having the sensors run on the sun's energy makes generating the needed power simpler than using batteries or hooking up to the electrical grid, allowing the sensors to be lighter and more mobile. And having solar cells that are stretchable opens up other applications.

A recent research paper by Bao, describing the stretchable solar cells, will appear in an upcoming issue of Advanced Materials. The paper details the ability of the cells to be stretched in one direction, but she said her group has since demonstrated that the cells can be designed to stretch along two axes.

The cells have a wavy microstructure that extends like an accordion when stretched. A liquid metal electrode conforms to the wavy surface of the device in both its relaxed and stretched states.

"One of the applications where stretchable solar cells would be useful is in fabrics for uniforms and other clothes," said Darren Lipomi, a graduate student in chemical engineering in Bao's lab and lead author of the paper.

"There are parts of the body, at the elbow for example, where movement stretches the skin and clothes," he said. "A device that was only flexible, not stretchable, would crack if bonded to parts of machines or of the body that extend when moved." Stretchability would be useful in bonding solar cells to curved surfaces without cracking or wrinkling, such as the exteriors of cars, lenses and architectural elements.

The solar cells continue to generate electricity while they are stretched out, producing a continuous flow of electricity for data transmission from the sensors.

Bao said she sees the super skin as much more than a super mimic of human skin; it could allow robots or other devices to perform functions beyond what human skin can do.

"You can imagine a robot hand that can be used to touch some liquid and detect certain markers or a certain protein that is associated with some kind of disease and the robot will be able to effectively say, 'Oh, this person has that disease,'" she said. "Or the robot might touch the sweat from somebody and be able to say, 'Oh, this person is drunk.'"

Finally, Bao has figured out how to replace the materials used in earlier versions of the transistor with biodegradable materials. Now, not only will the super skin be more versatile and powerful, it will also be more eco-friendly.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Stanford University. The original article was written by Louis Bergeron.

Journal Reference:

Christopher J. Bettinger, Hector A. Becerril, Do Hwan Kim, Bang-Lin Lee, Sangyoon Lee, Zhenan Bao. Microfluidic Arrays for Rapid Characterization of Organic Thin-Film Transistor Performance. Advanced Materials, 2011; DOI: 10.1002/adma.201003815


Low-energy remediation with patented microbes: Naturally occurring microbes break down chlorinated solvents

Using funding provided under the American Reinvestment and Recovery Act, the U.S. Department of Energy's Savannah River National Laboratory has launched a demonstration project near one of the Savannah River Site's former production reactor sites to clean up chemically contaminated groundwater, naturally.

A portion of the subsurface at the Site's P Area has become contaminated with chlorinated volatile organic compounds that are essentially like dry-cleaning fluid. SRNL and Clemson University have patented a consortium of microbes that have an appetite for that kind of material.

"If they are as effective as we expect in cleaning up the chemical contamination in the groundwater, it will be far cheaper than energy-intensive types of cleanup, such as pump-and-treat techniques or soil heating," said Mark Amidon, SRNL's project manager for the demonstration.

The mixture of microbes was found occurring naturally at SRS, where they were feeding on the same kind of chemical that was in groundwater seeping into an SRS creek. SRNL and Clemson University worked together on the discovery and characterization of the microbes. The mixture is called MicroCED, for "microbiological-based chlorinated ethene destruction," and when injected into the subsurface can completely transform lethal chlorinated ethenes to safe, nontoxic end products.

In P Area, the first step was to make groundwater conditions better for the microbes. "In late summer we injected more than 5,000 gallons of emulsified soybean oil, buffering agents and amendments and 108,000 gallons of water to get the dissolved oxygen and acidity right," Amidon said. "Once the conditions were right, we started injecting the store of microbes we've been culturing." An initial application of 18 gallons of the microbes was recently injected to get things started. By the end of the demonstration, approximately 1,500 gallons of the microbes could be injected into the demonstration site.

Amidon estimated that it would take a year or more to see appreciable results. "You can't rush Mother Nature." The current test site is about 100 by 120 feet at the surface and 85 to 100 feet below ground, and will be used to determine whether this approach should be used for full-scale treatment of the area. "If we were to go full-scale, there would be a 'biowall' about 1,000 feet long and between 50 and 145 feet below ground," Amidon said.

SRNL has been working in bioremediation for many years, using existing microorganisms as part of the strategy. The difference here is the culturing and injection of quantities of a specific mixture of microbes for use on chlorinated solvents. (Another SRNL invention, BioTiger™, is a consortium of microbes used on petroleum contamination.)

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by DOE/Savannah River National Laboratory, via EurekAlert!, a service of AAAS.

New form of sulfur discovered in geological fluids

 Sulfur is the sixth most abundant element on Earth and plays a key role in many geological and biological processes. A French-German team including CNRS1 and the Universit√© Paul Sabatier has identified, on the basis of laboratory measurements, a novel form of sulfur present in geological fluids: the S3- ion. The discovery calls existing theories about the geological transport of sulfur into question, and could provide ways of identifying new deposits of precious metals such as gold and copper.

These findings are published in the Feb. 25, 2011 issue of the journal Science.

Until now, geochemists believed that inside Earth, only two forms of molecules contained sulfur: sulfides (based on H2S or S2-) and sulfates (based on H2SO4 or SO42-). Yet they had no way of directly plunging a probe into the hydrothermal fluids2 that flow through rocks to verify this theory. To get round this problem and test their hypothesis, the French-German team first created fluids similar to those in Earth's crust and mantle, i.e. aqueous solutions containing elementary sulfur (S) and thiosulfates (molecules containing the S2O32- ion). They then used a diamond anvil cell to bring the fluids to the temperatures and pressures found at depths of several kilometers (several hundred degrees and tens of thousands of atmospheres).

The researchers used an optical method known as Raman spectroscopy to identify the chemical species, and they were astounded to discover not two, but three forms of sulfur, the third being the trisulfur ion S3-. This was a double surprise: although S3- was already known to chemists (it is found in sulfur-containing silicate glass and ultramarine pigments for instance), it had never been observed in an aqueous solution.

The detection of S3- during these experiments means that sulfur must be considerably more mobile in hydrothermal fluids in Earth's crust than was previously thought. This is because, unlike sulfides and sulfates, which attach to minerals as soon as they appear in fluids, S3- proves to be extremely stable in the aqueous phase. In other words, below ground these ions must flow for long distances in dissolved form, taking with them the noble metals to which they may be bound. This chemical species may therefore be the main metal transporting agent in two major types of gold and copper deposits: Archaean greenstone belts3 and subduction zone magmas.

This discovery could provide additional indicators in the search for new deposits, by helping geologists to identify the pathways along which metals travel prior to forming veins. In addition, the presence of S3- in hydrothermal fluids could affect sulfur isotope fractionation models (a sort of equivalent to the carbon-14 dating technique), which until now have taken no account of this chemical species. These new findings could for instance help scientists to find out more about the geological conditions in  Earth's crust and on its surface shortly after the appearance of life.


Laboratoire 'G√©osciences Environnement Toulouse' (CNRS/Universit√© Paul Sabatier/IRD) and Bayerisches Geoinstitut/University of Bayreuth.A hydrothermal fluid is a natural hot, aqueous fluid whose temperature usually exceeds 100°C.These rocks formed during the Archaean era, between -4 and -2.5 billion years ago.

Story Source:

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

Journal Reference:

G. S. Pokrovski, L. S. Dubrovinsky. The S3- Ion Is Stable in Geological Fluids at Elevated Temperatures and Pressures. Science, 2011; 331 (6020): 1052 DOI: 10.1126/science.1199911

Making a point: Method prints nanostructures using hard, sharp 'pen' tips floating on soft polymer springs

Northwestern University researchers have developed a new technique for rapidly prototyping nanoscale devices and structures that is so inexpensive the "print head" can be thrown away when done.

Hard-tip, soft-spring lithography (HSL) rolls into one method the best of scanning-probe lithography -- high resolution -- and the best of polymer pen lithography -- low cost and easy implementation.

HSL could be used in the areas of electronics (electronic circuits), medical diagnostics (gene chips and arrays of biomolecules) and pharmaceuticals (arrays for screening drug candidates), among others.

To demonstrate the method's capabilities, the researchers duplicated the pyramid on the U.S. one-dollar bill and the surrounding words approximately 19,000 times at 855 million dots per square inch. Each image consists of 6,982 dots. (They reproduced a bitmap representation of the pyramid, including the "Eye of Providence.") This exercise highlights the sub-50-nanometer resolution and the scalability of the method.

The results will be published Jan. 27 by the journal Nature.

"Hard-tip, soft-spring lithography is to scanning-probe lithography what the disposable razor is to the razor industry," said Chad A. Mirkin, the paper's senior author. "This is a major step forward in the realization of desktop fabrication that will allow researchers in academia and industry to create and study nanostructure prototypes on the fly."

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.

Micro- and nanolithographic techniques are used to create patterns and build surface architectures of materials on a small scale.

Scanning probe lithography, with its high resolution and registration accuracy, currently is a popular method for building nanostructures. The method is, however, difficult to scale up and produce multiple copies of a device or structure at low cost.

Scanning probe lithographies typically rely on the use of cantilevers as the printing device components. Cantilevers are microscopic levers with tips, typically used to deposit materials on surfaces in a printing experiment. They are fragile, expensive, cumbersome and difficult to implement in an array-based experiment.

"Scaling cantilever-based architectures at low cost is not trivial and often leads to devices that are difficult to operate and limited with respect to the scope of application," Mirkin said.

Hard-tip, soft-spring lithography uses a soft polymer backing that supports sharp silicon tips as its "print head." The spring polymer backing allows all of the tips to come in contact with the surface in a uniform manner and eliminates the need to use cantilevers. Essentially, hard tips are floating on soft polymeric springs, allowing either materials or energy to be delivered to a surface.

HSL offers a method that quickly and inexpensively produces patterns of high quality and with high resolution and density. The prototype arrays containing 4,750 tips can be fabricated for the cost of a single cantilever-based tip and made in mass, Mirkin said.

Mirkin and his team demonstrated an array of 4,750 ultra-sharp silicon tips aligned over an area of one square centimeter, with larger arrays possible. Patterns of features with sub-50-nanometer resolution can be made with feature size controlled by tip contact time with the substrate.

They produced patterns "writing" with molecules and showed that as the tips push against the substrate the flexible backing compresses, indicating the tips are in contact with the surface and writing is occurring. (The silicon tips do not deform under pressure.)

"Eventually we should be able to build arrays with millions of pens, where each pen is independently actuated," Mirkin said.

The researchers also demonstrated the ability to use hard-tip, soft-spring lithography to transfer mechanical and electrical energy to a surface.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Northwestern University. The original article was written by Megan Fellman.

Journal Reference:

Wooyoung Shim, Adam B. Braunschweig, Xing Liao, Jinan Chai, Jong Kuk Lim, Gengfeng Zheng, Chad A. Mirkin. Hard-tip, soft-spring lithography. Nature, 2011; 469 (7331): 516 DOI: 10.1038/nature09697