Nano technique: fossilized liquid assembly

GAITHERSBURG, Md. - Researchers at the National Institute of Standards and Technology (NIST) have developed a novel platform for the self-assembly of experimental hierarchical surfaces in a fluid. Their work offers diverse industries a new way to generate and measure self-assembly at the nano-scale.

Creating topologically complex, self-assembled surfaces has been a challenge. If the components are mixed on a surface, that substrate affects how they assemble; if mixed in a solvent and dried, the drying process similarly distorts the results.

An optical microscope image (lower plane) shows spheres at multiple size scales self-arranging in complex “super-assemblies” in NIST’s hierarchical topology modeling system. Atomic-force microscopy (detail) shows the textured surface formed by the spheres. Image courtesy of NIST
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In a paper published in the journal Macromolecular Rapid Communications, the NIST team detailed a much simpler and faster system they dubbed “fossilized liquid assembly” to create models of hierarchical topologies in which the components are allowed to mix and assemble freely in a fluid, and then quickly “frozen” in place. The key is the use of solutions of water and a special monomer that polymerizes when exposed to ultraviolet light. Like an oil-water mixture, the fluid forms liquid interfaces that can be manipulated to create a desired hierarchical structure and then suddenly solidified with a burst of UV light.

Lead researcher and physicist Alamgir Karim estimates that it takes about five minutes to make a sample of self-assembling particles using NIST’s approach. Other methods, he notes, not only are more complicated and costly, but also do not allow the structures to form as freely. With the new technique, engineers also will be able to build complex dynamic structures and freeze them into solid form, studying self-assembly under the microscope.

SEMATECH North team pushes immersion lithography to 45 nm features

ALBANY, N.Y. - A team of engineers and technicians at International SEMATECH North have successfully used 193 nm immersion technology to pattern features narrower than 45 nm half-pitch in multiple orientations simultaneously. SEMATECH North is part of the Albany NanoTech complex within the College of Nanoscale Science and Engineering of the University at Albany, N.Y. The team used 193 nm immersion at 1.3 numerical aperture (NA) with azimuthal polarization, a technique which allows for aggressive imaging of arbitrary circuit features beyond simple line-and-space test patterns.

The team used an Exitech immersion projection microstepper with 1.3 NA in combination with optical proximity correction and other resolution enhancement techniques to simultaneously image sub-45 nm linewidths along X and Y axes within the same field. The resulting “pitch,” or width of a single line and its adjoining space, was 84 nm.

Motorola, Arizona State advance carbon nanotube sensing capabilities

TEMPE, Ariz. - Motorola Labs, the applied research arm of Motorola Inc., and Arizona State University announced a key advancement in the use of single-wall carbon nanotubes (SWNTs) in field effect transistors (FETs) to sense biological and chemical agents.

Together, the research teams have developed a method to functionalize SWNTs with peptides to produce low-power SWNT-FETs that are highly sensitive and can selectively detect heavy metal ions down to the parts-per-trillion level.

Researchers have successfully tuned SWNT-FETs to sense specific agents by applying a peptide-functionalized polymer coating that does not affect their ability to transmit electrical signals. This developing sensor technology could be used to monitor a host of environmental and health issues including air and water quality, industrial chemicals and biological agents.

The work was published in a paper coauthored by Arizona State University and Motorola titled “Tuning the Chemical Selectivity of SWNT-FETs for Detection of Heavy-Metal Ions” in the journal Small.

Researchers harness DNA to direct gold nanoparticle assembly

UPTON, N.Y. - The speed of nanoparticle assembly can be accelerated with the assistance of DNA, a team of researchers at the U.S. Department of Energy’s Brookhaven National Laboratory recently found.

The interdisciplinary team, composed of scientists from Brookhaven’s new Center for Functional Nanomaterials and the biology department, found a way to control the assembly of gold nanoparticles using rigid, double-stranded DNA. Their technique takes advantage of the molecule’s natural tendency to pair up components called bases, known by the code letters A, T, G and C.

The synthetic DNA used in the laboratory is capped onto individual gold nanoparticles and customized to recognize and bind to complementary DNA located on other particles. The process forms clusters, or aggregates, of gold particles.

Researchers, standing, Oleg Gang (left) and Daniel van der Lelie and, sitting, Mathew Maye (left) and Dmytro Nykypanchuk have capped synthetic DNA onto gold nanoparticles to direct nanoparticle assembly. Photo courtesy of Brookhaven National Laboratory
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“It’s really by design,” said Mathew Maye, a Brookhaven chemist and the study’s lead author, in a prepared statement. “We can sit down with a piece of paper, write out a DNA sequence, and control how these nanoparticles will assemble.”

One limitation to the assembly process is the use of single-stranded DNA, which can bend backward and attach to the particle’s gold surface instead of binding with surrounding nanoparticles. This flexibility, along with the existence of multiple forms of single-stranded DNA, can greatly slow the assembly process.

In the Brookhaven study, researchers introduced partially rigid, double-stranded DNA, which forces interacting linker segments of DNA to extend away from the gold surface, allowing for more efficient assembly.

UD scientists use carbon nanotube networks to detect composite defects

NEWARK, Del. - Two University of Delaware researchers discovered a means to detect and identify damage within advanced composite materials by using a network of carbon nanotubes which act in much the same manner as human nerves.

The discovery has important implications both in the laboratory, where the scientists hope to better predict the life span of various composite materials, and in everyday applications, where it could become an important tool in monitoring the health of composite materials used in the construction of a variety of essential products, including commercial airliners.

The research is the work of Tsu-Wei Chou, Pierre S. du Pont chair of engineering, and Erik Thostenson, assistant professor of mechanical engineering, and was published in the journal Advanced Materials.

Composite materials are generally laminates, sheets of high-performance fibers, such as carbon, glass or Kevlar, embedded in a polymer resin matrix. Chou said that the traditional composite materials have inherent weaknesses because the matrix materials - plastics - surrounding the fibers are “strong, but far less strong than the fibers.”

This results in weak spots in composites in the interface areas in the matrix materials, particularly where there are pockets of resin, Chou said. As a result, defects, including tiny microcracks, can occur. Over time, those microcracks can threaten the integrity of the composite.

The carbon nanotubes can be used to detect defects at onset by embedding them uniformly throughout the composite material as a network capable of monitoring the health of the composite structures. Because the carbon nanotubes conduct electricity, they create a nanoscale network of sensors that work like the nerves in the human body.

The researchers can pass an electrical current through the network and if there is a microcrack, it breaks the pathway of the sensors and the response can be measured. Chou said the carbon nanotubes are minimally invasive and just 0.15 percent of the total composite volume.

The research is supported by funding from the Air Force Office of Scientific Research and the National Science Foundation.

Clemson researchers develop nanotubes to fight anthrax

CLEMSON, N.C. - Clemson University chemist Ya-Ping Sun and his research team have developed a countermeasure strategy to weaponized anthrax. The Clemson team’s findings were published online in the Journal of the American Chemical Society.

“For anthrax to be effective, it has to be made into a fine powder that can easily enter the lungs when inhaled. That is what makes it lethal,” said Sun in a prepared statement. “What we have done is come up with an agent that clings to the anthrax spores to make their inhalation into the lungs difficult.”

Anthrax spores gather in clusters on sugar coated carbon nanotubes. Images courtesy of Clemson University
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Anthrax spores are covered with carbohydrates, or simple sugars, that are used to communicate with or attract other biological species. The Clemson team used carbon nanotubes as a platform or scaffolding for displaying sugar molecules that would attract the anthrax spores. When sugar coated, the carbon nanotubes bind with the anthrax spores, creating clusters that are too large to be inhaled -- stopping their infection and destruction.

Sun said a similar approach using sugar-coated carbon nanotubes to stop the spread of E. coli bacteria was tested successfully in 2004. He sees this new method potentially as a way for first responders to contain anthrax in an office or mailroom setting using a water-based gel, foam or aerosol spray, and he thinks it has potential application on the battlefield in larger quantities.

55,000 tiny T.J’s show power of DPN

EVANSTON, Ill. - Northwestern University researchers have developed a 55,000-pen, two-dimensional array that allows them to simultaneously create 55,000 identical patterns drawn with tiny dots of molecular ink on substrates of gold or glass. Each structure is only a single molecule tall.

The recent advance of dip-pen nanolithography (DPN), which was invented at Northwestern in 1999 and is being commercialized by local startup NanoInk, was published online by the journal Angewandte Chemie.

To demonstrate the technique’s power, the researchers reproduced the face of Thomas Jefferson from a five-cent coin 55,000 times, which took only 30 minutes. Each identical nickel image is 12 micrometers wide - about twice the diameter of a red blood cell - and is made up of 8,773 dots, each 80 nanometers in diameter.

The parallel process paves the way for making DPN competitive with other optical and stamping lithographic methods used for patterning large areas on metal and semiconductor substrates, including silicon wafers. The advantage of DPN, which is a maskless lithography, is that it can be used to deliver many different types of inks simultaneously to a surface in any configuration one desires. Mask-based lithographies and stamping protocols are extremely limited in this regard.

In addition to Professor Chad Mirkin, other authors on the paper are Khalid Salaita (lead author), Yuhuang Wang and Rafael A. Vega, from Northwestern; Joseph Fragala, from NanoInk, Inc.; and Chang Liu, from the University of Illinois at Urbana-Champaign.

The research was supported by the National Institutes of Health, the Defense Advanced Research Projects Agency, the Air Force Office of Scientific Research and the National Science Foundation.

Brown engineers build a better battery - with plastic

PROVIDENCE, R.I. - Brown University engineers have created a new battery that uses plastic, not metal, to conduct electrical current. The hybrid device is intended to marry the power of a capacitor with the storage capacity of a battery.

“Batteries have limits,” said Tayhas Palmore, an associate professor in Brown’s division of engineering, in a prepared statement. “They have to be recharged. They can be expensive. Most of all, they don’t deliver a lot of power. Another option is capacitors. These components, found in electronic devices, can deliver that big blast of power. But they don’t have much storage capacity. So what if you combined elements of both a battery and a capacitor?”

That’s the question Palmore set out to answer with Hyun-Kon Song, a former postdoctoral research associate at Brown who now works as a researcher at LG Chem Ltd. They began to experiment with a new energy storage system using a substance called polypyrrole, a chemical compound that carries an electrical current.

A prototype battery created at Brown University combines elements of both a capacitor and a battery. Photo courtesy of Brown University
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In their experiments, Palmore and Song took a thin strip of gold-coated plastic film and covered the tip with polypyrrole and a substance that alters its conductive properties. The process was repeated, this time using another kind of conduction-altering chemical. The result: two strips with different polymer tips. The plastic strips were then stuck together, separated by a papery membrane to prevent a short circuit.

The result is a hybrid. Like a capacitor, the battery can be rapidly charged then discharged to deliver power. Like a battery, it can store and deliver that charge over long periods of time. During performance testing, the new battery performed like a hybrid, too. It had twice the storage capacity of an electric double-layer capacitor. And it delivered more than 100 times the power of a standard alkaline battery.

Palmore said some performance problems - such as decreased storage capacity after repeated recharging - must be overcome before the device is marketable. But she expects strong interest since battery makers are always looking for new ways to more efficiently store and deliver power. NASA and the U.S. Air Force are also exploring polymer-based batteries. A description of the prototype was published in Advanced Materials.