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What's New in Nanotechnology?

August 29, 2013

Two vials in a Rice University lab show gold nanoparticles in saline water. At left, the nanoparticles have been stabilized in bovine serum albumin and are dispersed in the solution. At right, without albumin, the nanoparticles clump together and sink to the bottom. (Image Credit: Rice University; Photo by Sergio Dominguez-Medina/Link Research Group)

A protein from cow blood has the remarkable ability to keep gold nanoparticles from clumping in a solution. The discovery could lead to improved biomedical applications and contribute to projects that use nanoparticles in harsh environments. Bovine serum albumin (BSA) forms a protein “corona” around gold nanoparticles that keeps them from aggregating, particularly in high-salt environments like seawater. The new research was conducted by Rice University chemists Stephan Link and Christy Landes. Link’s primary interest is in the plasmonic properties of nanoparticles. Landes’ work incorporates protein binding and molecular transport. The BSA research combines their unique talents with those of Sergio Dominguez-Medina, a graduate student in Link’s lab who studied to be a physicist at Monterrey Tech and was drawn to this interdisciplinary project during an undergraduate fellowship at Link’s Rice lab. IInitially, we wanted to look at nanoparticles in solution with something they would encounter frequently in blood: serum albumin,” Landes said. “In our first experiments, Sergio reported the very efficient, reasonably fast and irreversible binding the moment he put nanoparticles into a solution that contained serum albumin.” “It turned out the salt is actually driving this binding,” Dominguez-Medina said. Without BSA, gold nanoparticles in a salty solution quickly aggregate and fall to the bottom. “That by itself is undesirable for biomedical or industrial applications, because it could lead to toxicity issues,” he said. “The nanoparticles get more hydrophobic because in the presence of salts, the excess charges on the surface (which discourage clumping) are actually removed.” But if BSA is present, the proteins are drawn to the nanoparticles faster than the particles are drawn to each other. “Once the protein is bound, it gives a super protection against any type of salt-induced aggregation. We think this could be used for the stabilization of nanoparticles in environments where, right now, it hasn’t been achieved,” Dominguez-Medina said. He said the discovery also offers the possibility that nanoparticles might be made more compatible for treating humans by using a patient’s own albumin. “Albumin is really easy to purify and the process is well-established,” he said.

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August 22, 2013

(a) Device structures, (b) J−V characteristics, and (c) EQE of PTB7:PC70BM-based PSCs with type I and type II architectures (Top)(a) Device structures and (b) reflectance spectra of PTB7:PC70BM-based PSCs with different spatial locations of Ag@SiO2 (Bottom) (Image credit: Ulsan National Institute of Science and Technology)

Researchers from Ulsan National Institute of Science and Technology (UNIST) have demonstrated high-performance polymer solar cells (PSCs) with a power conversion efficiency (PCE) of 8.92% --the highest values reported to date for plasmonic PSCs using metal nanoparticles (NPs). A polymer solar cell is a type of thin film solar cells made with polymers that produce electricity from sunlight by the photovoltaic effect. Most current commercial solar cells are made from a highly purified silicon crystal. The high cost of these silicon solar cells and their complex production process has generated interest in developing alternative photovoltaic technologies. Compared to silicon-based devices, PSCs are lightweight (which is important for small autonomous sensors), solution processability (potentially disposable), inexpensive to fabricate (sometimes using printed electronics), flexible, and customizable on the molecular level, and they have lower potential for negative environmental impact. Polymer solar cells have attracted a lot of interest due to these many advantages. But PSCs currently suffer from a lack of enough efficiency for large scale applications and stability problems -- but their promise of extremely cheap production and eventually high efficiency values has led them to be one of the most popular fields in solar cell research. The research team employed the surface plasmon resonance (SPR) effect via multi-positional silica-coated silver NPs (Ag@SiO2) to increase light absorption. The silica shell in Ag@SiO2 preserves the SPR effect of the Ag NPs by preventing oxidation of the Ag core under ambient conditions and also eliminates the concern about exciton quenching by avoiding direct contact between Ag cores and the active layer.

Categories : University News
August 15, 2013

Vikas Berry, William H. Honstead professor of chemical engineering, and his research team are using graphene quantum dots to improve electron tunneling-based sensing devices. (Image credit: Kansas State Universitiy)

The latest research from a Kansas State University chemical engineer may help improve humidity and pressure sensors, particularly those used in outer space. Vikas Berry, William H. Honstead professor of chemical engineering, and his research team are using graphene quantum dots to improve sensing devices in a twofold project. The first part involves producing the graphene quantum dots, which are ultrasmall pieces of graphene. Graphene is a single-atom thick sheet of carbon atoms and has superior electrical, mechanical and optical properties. The second part of the project involves incorporating these quantum dots into electron-tunneling based sensing devices. To create the graphene quantum dots, the researchers used nanoscale cutting of graphite to produce graphene nanoribbons. T.S. Sreeprasad, a postdoctoral researcher in Berry's group, chemically cleaved these ribbons into 100 nanometers lateral dimensions. The scientists assembled the quantum dots into a network on a hydroscopic microfiber that was attached to electrodes on its two sides. They placed the assembled quantum dots less than a nanometer apart so they were not completely connected. The assembling of dots is similar to a corn on the cob structure -- the corn kernels are nanoscale quantum dots and the cob is the microfiber. Several researchers applied a potential across the fiber and controlled the distance between the quantum dots by adjusting the local humidity, which changes the current flowing through the dots. "If you reduce the humidity around this device, the water held by this fiber is lost," Berry said. "As a result, the fiber shrinks and the graphenic components residing atop come close to one another in nanometer scale. This increases the electron transport from one dot to the next. Just by reading the currents one can tell the humidity in the environment."

Categories : University News
August 08, 2013

Quantum Dots doped with copper. (Image credit: University of Illinois at Chicago)

Quantum dots are tiny nanocrystals with extraordinary optical and electrical properties with possible uses in dye production, bioimaging, and solar energy production. Researchers at the University of Illinois at Chicago have developed a way to introduce precisely four copper ions into each and every quantum dot. The introduction of these “guest” ions, called doping, opens up possibilities for fine-tuning the optical properties of the quantum dots and producing spectacular colors. “When the crystallinity is perfect, the quantum dots do something that no one expected–they become very emissive and end up being the world’s best dye,” says Preston Snee, assistant professor of chemistry at UIC and principal investigator on the study. Incorporating guest ions into the crystal lattice can be very challenging, says UIC graduate student Ali Jawaid, first author of the paper. Controlling the number of ions in each quantum dot is tricky. Merely targeting an average number of guest ions will not produce quantum dots with optimal electrical and optical properties. Jawaid developed a procedure that reliably produces perfect quantum dots, each doped with exactly four copper ions. Snee believes the method will enable them to substitute other guest ions with the same consistent results. “This opens up the opportunity to study a wide array of doped quantum dot systems,” he said.

Categories : University News
August 01, 2013

Qiaoqiang Gan, University at Buffalo assistant professor of electrical engineering. (Image credit: University at Buffalo)

Most Americans want the U.S. to place more emphasis on developing solar power, recent polls suggest. A major impediment, however, is the cost to manufacture, install and maintain solar panels. Simply put, most people and businesses cannot afford to place them on their rooftops. Fortunately, that is changing because researchers such as Qiaoqiang Gan, University at Buffalo assistant professor of electrical engineering, are helping develop a new generation of photovoltaic cells that produce more power and cost less to manufacture than what’s available today. One of the more promising efforts, which Gan is working on, involves the use of plasmonic-enhanced organic photovoltaic materials. These devices don’t match traditional solar cells in terms of energy production but they are less expensive and - because they are made (or processed) in liquid form - can be applied to a greater variety of surfaces.  Currently, solar power is produced with either thick polycrystalline silicon wafers or thin-film solar cells made up of inorganic materials such as amorphous silicon or cadmium telluride. Both are expensive to manufacture, Gan said. His research involves thin-film solar cells, too, but unlike what’s on the market he is using organic materials such as polymers and small molecules that are carbon-based and less expensive. “Compared with their inorganic counterparts, organic photovoltaics can be fabricated over large areas on rigid or flexible substrates potentially becoming as inexpensive as paint,” Gan said. The reference to paint does not include a price point but rather the idea that photovoltaic cells could one day be applied to surfaces as easily as paint is to walls, he said.

Categories : University News
July 25, 2013

(Image credit: MIT)

Many industrial plants depend on water vapor condensing on metal plates: In power plants, the resulting water is then returned to a boiler to be vaporized again; in desalination plants, it yields a supply of clean water. The efficiency of such plants depends crucially on how easily droplets of water can form on these metal plates, or condensers, and how easily they fall away, leaving room for more droplets to form. The key to improving the efficiency of such plants is to increase the condensers’ heat-transfer coefficient — a measure of how readily heat can be transferred away from those surfaces, explains Nenad Miljkovic, a doctoral student in mechanical engineering at MIT. As part of his thesis research, he and colleagues have done just that: designing, making and testing a coated surface with nanostructured patterns that greatly increase the heat-transfer coefficient. On a typical, flat-plate condenser, water vapor condenses to form a liquid film on the surface, drastically reducing the condenser’s ability to collect more water until gravity drains the film. “It acts as a barrier to heat transfer,” Miljkovic says. He and other researchers have focused on ways of encouraging water to bead up into droplets that then fall away from the surface, allowing more rapid water removal.

Categories : University News
July 18, 2013

In this reconstruction by Matthew Landry, nanoparticles (blue spheres) travel through a nanochannel (red) similar in dimensions to what will be used in the space-bound experiments. (Image credit: Methodist Hospital Research Institute)

A microgravity experiment designed at The Methodist Hospital Research Institute will be funded by The Center for the Advancement of Science in Space (CASIS) to fly aboard the International Space Station U.S. National Laboratory. The proposal to study the diffusion of drug-like particles will receive about $200,000 from CASIS, which is directed by Congress to manage, promote, and broker research for the orbiting U.S. National Laboratory. If all goes well on Earth, the experiment will go to the International Space Station as early as 2014. Principal investigator Alessandro Grattoni, Ph.D., and a team of scientists from Methodist, BioServe Space Technologies at the University of Colorado at Boulder, and NASA Glenn Research Center in Cleveland, Ohio, will study the movement of drug-like particles through tiny channels. The scientists' ultimate goal is improving implantable devices that release pharmaceutical drugs at a steady rate. Nearly all drugs taken orally spike in concentration, decay quickly, and are only at their peak effectiveness for a short period of time. Grattoni and co-PI Mauro Ferrari, Ph.D., have been working on a solution -- nanocapsules implanted beneath the skin that release pharmaceutical drugs through a nanochannel membrane and into the body at a sustained, steady rate. To design better nanochannels for a given drug, Grattoni says he and others need to improve their understanding of the underlying physics. Grattoni's group will look at two things they believe play a major role in how particles move through channels -- the relative size of particle to channel, as well as charge (plus/minus) interactions between the particle and channel. The fluorescent silicon particles will diffuse into an empty chamber through a long series of narrow channels. Photographs taken periodically with a fluorescent microscope will show the scientists how -- and how quickly -- the particles move, how charge gradients affect the particles, and the effects of size constraints. The experiment will be performed over three months.

July 11, 2013

Hexagon-shaped nanoplates arranged themselves into different crystal patterns, depending on the length of the sides of the hexagons. Long hexagons fit together in a grid like a stretched honeycomb, but researchers were surprised that hexagons whose sides were all the same lengths ended up in a herringbone pattern. University of Michigan engineering researchers helped figure out why, and the work could lead to a new tool to control how nanoparticles arrange themselves. (Image credit: Xingchen Ye, University of Pennsylvania)

Leading nanoscientists created beautiful, tiled patterns with flat nanocrystals, but they were left with a mystery: Why did some sets of crystals arrange themselves in an alternating, herringbone style? To find out, they turned to experts in computer simulation at the University of Michigan and the Massachusetts Institute of Technology. The result gives nanotechnology researchers a new tool for controlling how objects one-millionth the size of a grain of sand arrange themselves into useful materials—and a means to discover the rest of the tool chest. "The excitement in this is not in the herringbone pattern, it's about the coupling of experiment and modeling, and how that approach lets us take on a very hard problem," said Christopher Murray, the Richard Perry University Professor and professor of chemistry at the University of Pennsylvania. Ultimately, researchers want to modify patches on nanoparticles in different ways to coax them into more complex patterns. The goal is a method that will allow people to imagine what they would like to do and then design a material with the right properties for the job. "By engineering interactions at the nanoscale, we can begin to assemble target structures of great complexity and functionality on the macroscale," said U-M's Sharon Glotzer, the Stuart W. Churchill Collegiate Professor of Chemical Engineering. Glotzer introduced the concept of nanoparticle "patchiness" in 2004. Her group uses computer simulations to understand and design the patches. Recently, Murray's team made patterns with flat nanocrystals made of heavy metals, known to chemists as lanthanides, and fluorine atoms. Lanthanides have valuable properties for solar energy and medical imaging, such as the ability to convert between high- and low-energy light.

Categories : University News
July 04, 2013

Electron pumps made from graphene work ten times faster than similar pumps made from conventional three-dimensional materials and can be used to generate larger currents. (Image credit: Malcolm Connolly, NPL/Cambridge)

A new joint innovation by the National Physical Laboratory (NPL) and the University of Cambridge could pave the way for redefining the ampere in terms of fundamental constants of physics. The world's first graphene single-electron pump (SEP) provides the speed of electron flow needed to create a new standard for electrical current based on electron charge. A good SEP pumps precisely one electron at a time to ensure accuracy, and pumps them quickly to generate a sufficiently large current. Up to now the development of a practical electron pump has been a two-horse race. Tuneable barrier pumps use traditional semiconductors and have the advantage of speed, while the hybrid turnstile utilises superconductivity and has the advantage that many can be put in parallel. Traditional metallic pumps, thought to be not worth pursuing, have been given a new lease of life by fabricating them out of the world's most famous super-material - graphene. Previous metallic SEPs made of aluminium are very accurate, but pump electrons too slowly for making a practical current standard. Graphene's unique semi-metallic two-dimensional structure has just the right properties to let electrons on and off the quantum dot very quickly, creating a fast enough electron flow - at near gigahertz frequency - to create a current standard. The Achilles' heel of metallic pumps, slow pumping speed, has thus been overcome by exploiting the unique properties of graphene.

June 27, 2013

Nanoparticles (purple) carrying melittin (green) fuse with HIV (small circles with spiked outer ring), destroying the virus’s protective envelope. Molecular bumpers (small red ovals) prevent the nanoparticles from harming the body’s normal cells, which are much larger in size. (Image credit: Washington University in St. Louis)

Nanoparticles carrying a toxin found in bee venom can destroy human immunodeficiency virus (HIV) while leaving surrounding cells unharmed, researchers at Washington University School of Medicine in St. Louis have shown. The finding is an important step toward developing a gel that may prevent the spread of HIV, the virus that causes AIDS. “Our hope is that in places where HIV is running rampant, people could use this gel as a preventive measure to stop the initial infection,” says Joshua L. Hood, MD, PhD, a research instructor in medicine. Bee venom contains a potent toxin called melittin that can poke holes in the protective envelope that surrounds HIV, and other viruses. Large amounts of free melittin can cause a lot of damage. Indeed, in addition to anti-viral therapy, the paper’s senior author, Samuel A. Wickline, MD, the J. Russell Hornsby Professor of Biomedical Sciences, has shown melittin-loaded nanoparticles to be effective in killing tumor cells. The new study shows that melittin loaded onto these nanoparticles does not harm normal cells. That’s because Hood added protective bumpers to the nanoparticle surface. When the nanoparticles come into contact with normal cells, which are much larger in size, the particles simply bounce off. HIV, on the other hand, is even smaller than the nanoparticle, so HIV fits between the bumpers and makes contact with the surface of the nanoparticle, where the bee toxin awaits. “Melittin on the nanoparticles fuses with the viral envelope,” Hood says. “The melittin forms little pore-like attack complexes and ruptures the envelope, stripping it off the virus.” According to Hood, an advantage of this approach is that the nanoparticle attacks an essential part of the virus’ structure. In contrast, most anti-HIV drugs inhibit the virus’s ability to replicate. But this anti-replication strategy does nothing to stop initial infection, and some strains of the virus have found ways around these drugs and reproduce anyway.

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