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This research-microscope image shows the increasing density at the bone-crack site during a 40-minute test of particles carrying the bone-healing medication. The particles were treated with a red-glowing fluorescent dye. Image Credit: Sen laboratory/Penn State University.

A novel method for finding and delivering healing drugs to newly formed microcracks in bones has been invented by a team of chemists and bioengineers at Penn State University and Boston University. The method involves the targeted delivery of the drugs, directly to the cracks, on the backs of tiny self-powered nanoparticles. The energy that revs the motors of the nanoparticles and sends them rushing toward the crack comes from a surprising source -- the crack itself. "When a crack occurs in a bone, it disrupts the minerals in the bone, which leach out as charged particles -- as ions -- that create an electric field, which pulls the negatively charged nanoparticles toward the crack," said Penn State Professor of Chemistry Ayusman Sen, a co-leader of the research team. "Our experiments have shown that a biocompatible particle can quickly and naturally deliver an osteoporosis drug directly to a newly cracked bone." Sen said that the formation of this kind of an electric field is a well-known phenomenon, but other scientists previously had not used it as both a power source and a homing beacon to actively deliver bone-healing medications to the sites most at risk for fracture or active deterioration. "It is a novel way to detect cracks and deliver medicines to them," said team co-leader and Boston University Professor Mark Grinstaff. The method is more-energetic and more-targeted than current methods, in which medications ride passively on the circulating bloodstream, where they may or may not arrive at microcracks in a high-enough dosage to initiate healing. The new method holds the promise of treating -- as soon as they form -- the microcracks that lead to broken bones in patients with osteoporosis and other medical conditions.

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A DNA cage (at left), with lipid-like molecules (in blue). The lipids come together in a ‘handshake’ within the cage (center image) to encapsulate small-molecule drugs (purple). The molecules are released (at right) in response to the presence of a specific nucleic acid. Image Credit: Thomas Edwardson/McGill University.

Nanoscale “cages” made from strands of DNA can encapsulate small-molecule drugs and release them in response to a specific stimulus, McGill University researchers report in a new study. The research marks a step toward the use of biological nanostructures to deliver drugs to diseased cells in patients. The findings could also open up new possibilities for designing DNA-based nanomaterials. “This research is important for drug delivery, but also for fundamental structural biology and nanotechnology,” says McGill Chemistry professor Hanadi Sleiman, who led the research team. DNA carries the genetic information of all living organisms from one generation to the next. But strands of the material can also be used to build nanometre-scale structures. (A nanometre is one billionth of a metre – roughly one-100,000th the diameter of a human hair.) In their experiments, the McGill researchers first created DNA cubes using short DNA strands, and modified them with lipid-like molecules. The lipids can act like sticky patches that come together and engage in a “handshake” inside the DNA cube, creating a core that can hold cargo such as drug molecules. The McGill researchers also found that when the sticky patches were placed on one of the outside faces of the DNA cubes, two cubes could attach together. This new mode of assembly has similarities to the way that proteins fold into their functional structures, Sleiman notes.  “It opens up a range of new possibilities for designing DNA-based nanomaterials.”

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Work by a research team at Penn State and Rice University could lead to the development of flexible solar cells. The engineers' technique centers on control of the nanostructure and morphology to create organic solar cells made of block polymers. Image Credit: Penn State/Curtis Chan.

Work by a team of chemical engineers at Penn State and Rice University may lead to a new class of inexpensive organic solar cells. "Imagine if you could make solar cells as easily as you can print posters or newspapers -- you could make sheets of this," said Enrique Gomez, assistant professor of chemical engineering. Most solar cells today are inorganic and made of crystalline silicon. The problem with these, Gomez explained, is that inorganic solar cells tend to be expensive, rigid and relatively inefficient when it comes to converting sunlight into electricity. But organic solar cells offer an intriguing alternative that's flexible and potentially less expensive. The problem is that the bulk of organic solar cells employ fullerene acceptors -- a carbon-based molecule that's extremely difficult to scale up for mass production. Gomez's approach skips the fullerene acceptor altogether and seeks to combine molecules in a solution. He says, "It's like trying to mix oil and water." The issue is that weak intermolecular interactions and disorder at junctions of different organic materials limited the performance and stability of previous organic solar cells. But by controlling the nanostructure and morphology, the team essentially redesigned the molecules to link together in a better way. The engineers were able to control the donor-acceptor heterojunctions through microphase-separated conjugated block copolymers. The result is an organic solar cell made of block copolymers that's three percent efficient. Though the team's prototype is not as efficient as some solar cells that are commercially available, Gomez explained the work shows flexible organic solar cells are indeed possible.

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Palladium nanocrystals. Image Credit: Vanderbilt University/Rizia Bardhan.

More efficient catalytic converters on autos, improved batteries and more sensitive gas sensors are some of the potential benefits of a new system that can directly measure the manner in which nanocrystals adsorb and release hydrogen and other gases. The technique was developed by Vanderbilt University Assistant Professor of Chemical and Biomolecular Engineering Rizia Bardhan. In the last 30 years, there has been a tremendous amount of research studying nanocrystals – tiny crystals sized between one to 100 nanometers in size (a nanometer is to an inch what an inch is to 400 miles) – because of the expectation that they have unique physical and chemical properties that can be used in a broad range of applications. One class of applications depends on nanocrystals’ ability to grab specific molecules and particles out the air, hold on to them and then release them: a process called adsorption and desorption. Progress in this area has been hindered by limitations in existing methods for measuring the physical and chemical changes that take place in individual nanocrystals during the process. As a result, advances have been achieved by trial-and-error and have been limited to engineered samples and specific geometries. “Our technique is simple, direct and uses off-the shelf instruments so other researchers should have no difficulty using it,” said Bardhan. The method is based on a standard procedure called fluorescence spectroscopy. A laser beam is focused on the target nanocrystals, causing them to fluoresce. As the nanocrystals adsorb the gas molecules, the strength of their fluorescent dims and as they release the gas molecules, it recovers.

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Georgia Tech researchers have created the "Mini Lisa" on a substrate surface approximately 30 microns in width. The image demonstrates a technique that could potentially be used to achieve nano-manufacturing of devices because the team was able to vary the surface concentration of molecules on such short length scales. Image credit: Georgia Institute of Technology.

The world’s most famous painting has now been created on the world’s smallest canvas. Researchers at the Georgia Institute of Technology have “painted” the Mona Lisa on a substrate surface approximately 30 microns in width – or one-third the width of a human hair. The team’s creation, the “Mini Lisa,” demonstrates a technique that could potentially be used to achieve nanomanufacturing of devices because the team was able to vary the surface concentration of molecules on such short-length scales. The image was created with an atomic force microscope and a process called ThermoChemical NanoLithography (TCNL). Going pixel by pixel, the Georgia Tech team positioned a heated cantilever at the substrate surface to create a series of confined nanoscale chemical reactions. By varying only the heat at each location, Ph.D. Candidate Keith Carroll controlled the number of new molecules that were created. The greater the heat, the greater the local concentration. More heat produced the lighter shades of gray, as seen on the Mini Lisa’s forehead and hands. Less heat produced the darker shades in her dress and hair seen when the molecular canvas is visualized using fluorescent dye. Each pixel is spaced by 125 nanometers. “By tuning the temperature, our team manipulated chemical reactions to yield variations in the molecular concentrations on the nanoscale,” said Jennifer Curtis, an associate professor in the School of Physics. “We envision TCNL will be capable of patterning gradients of other physical or chemical properties, such as conductivity of graphene,” Curtis added. “This technique should enable a wide range of previously inaccessible experiments and applications in fields as diverse as nanoelectronics, optoelectronics and bioengineering.”

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The researchers show photoluminescence from an optically levitated nano diamond. Image Credit: J. Adam Fenster/University of Rochester.

Researchers at the University of Rochester have measured for the first time light emitted by photoluminescence from a nanodiamond levitating in free space. The team used a laser to trap nanodiamonds in space, and – using another laser – caused the diamonds to emit light at given frequencies. The experiment, led by Nick Vamivakas, an assistant professor of optics, demonstrates that it is possible to levitate diamonds as small as 100 nanometers (approximately one-thousandth the diameter of a human hair) in free space, by using a technique known as laser trapping. "Now that we have shown we can levitate nanodiamonds and measure photoluminescence from defects inside the diamonds, we can start considering systems that could have applications in the field of quantum information and computing," said Vamivakas. He said an example of such a system would be an optomechanical resonator. Vamivakas explained that optomechanical resonators are structures in which the vibrations of the system, in this case the trapped nanodiamond, can be controlled by light. "We are yet to explore this, but in theory we could encode information in the vibrations of the diamonds and extract it using the light they emit."

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Move over, silicon. In a breakthrough in the quest for the next generation of computers and materials, researchers at USC have solved a long-standing challenge with carbon nanotubes: how to actually build them with specific, predictable atomic structures. If this is an age built on silicon, then the next one may be built on carbon nanotubes, which have shown promise in everything from optics to energy storage to touch screens. Not only are nanotubes transparent, but this research discovery on how to control the atomic structure of nanotubes will pave the way for computers that are smaller, faster and more energy efficient than those reliant on silicon transistors. Until now, scientists were unable to “grow” carbon nanotubes with specific attributes — say metallic rather than semiconducting — instead getting mixed, random batches and then sorting them. The sorting process also shortened the nanotubes significantly, making the material less practical for many applications. For more than three years, the USC team has been working on the idea of using these short, sorted nanotubes as “seeds” to grow longer nanotubes, extending them at high temperatures to get the desired atomic structure.

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Scanning electron micrograph of BCNU-loaded microspheres (black and white background) with 3d rendered images of brain cancers cells (yellow) and released BCNU (purple). Image Credit: Penn State/Mohammad Reza Abidian Lab

Consistently uniform, easily manufactured microcapsules containing a brain cancer drug may simplify treatment and provide more tightly controlled therapy, according to Penn State researchers. "Brain tumors are one of the world's deadliest diseases," said Mohammad Reza Abidian, assistant professor of bioengineering, chemical engineering and materials science and engineering. "Typically doctors resect the tumors, do radiation therapy and then chemotherapy." The majority of chemotherapy is done intravenously, but, because the drugs are very toxic and are not targeted, they have a lot of side effects. Another problem with intravenous drugs is that they go everywhere in the bloodstream and do not easily cross the blood brain barrier so little gets to the target tumors. To counteract this, high doses are necessary. "We are trying to develop a new method of drug delivery," said Abidian. "Not intravenous delivery,  but localized directly into the tumor site." Current treatment already includes leaving wafers infused with the anti-tumor agent BCNU in the brain after surgery, but when the drugs in these wafers run out, repeating invasive placement is not generally recommended. "BCNU has a half life in the body of 15 minutes," said Abidian. "The drug needs protection because of the short half life. Encapsulation inside biodegradable polymers can solve that problem." Encapsulation of BCNU in microspheres has been tried before, but the resulting product did not have uniform size and drug distribution or high drug-encapsulation efficiency. With uniform spheres, manufacturers can design the microcapsules to precisely control the time of drug release by altering polymer composition. The tiny spheres are also injectable through the skull, obviating the need for more surgery.

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An X-ray image of unlabeled mesenchymal stem cells in test tubes shows the dramatic difference between those tagged with nanotubes that don't include bismuth (left) and those that do (right). The technique developed at Rice University shows promise for tracking live stem cells in the body. Image Credit: Eladio Rivera/Rice University.

Scientists at Rice University have trapped bismuth in a nanotube cage to tag stem cells for X-ray tracking. Bismuth is probably best known as the active element in a popular stomach-settling elixir and is also used in cosmetics and medical applications. Rice chemist Lon Wilson and his colleagues are inserting bismuth compounds into single-walled carbon nanotubes to make a more effective contrast agent for computed tomography (CT) scanners. This is not the first time bismuth has been tested for CT scans, and Wilson’s lab has been experimenting for years with nanotube-based contrast agents for magnetic resonance imaging (MRI) scanners. But this is the first time anyone has combined bismuth with nanotubes to image individual cells, he said. “At some point, we realized no one has ever tracked stem cells, or any other cells that we can find, by CT,” Wilson said. “CT is much faster, cheaper and more convenient, and the instrumentation is much more widespread (than MRI). So we thought if we put bismuth inside the nanotubes and the nanotubes inside stem cells, we might be able to track them in vivo in real time.”

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Graduate student Pinshane Huang and Professor David Muller with a model that depicts the atomic structure of glass. They were the first to directly image the world's thinnest sheet of glass. Image Credit: Cornell University Jason Koski/University Photography

At just a molecule thick, it’s a new record: The world’s thinnest sheet of glass, a serendipitous discovery by scientists at Cornell University and Germany’s University of Ulm, is recorded for posterity in the Guinness Book of World Records. The “pane” of glass, so impossibly thin that its individual silicon and oxygen atoms are clearly visible via electron microscopy, was identified in the lab of David A. Muller, professor of applied and engineering physics and director of the Kavli Institute at Cornell for Nanoscale Science. Just two atoms in thickness, making it literally two-dimensional, the glass was an accidental discovery, Muller said. The scientists had been making graphene, a two-dimensional sheet of carbon atoms in a chicken wire crystal formation, on copper foils in a quartz furnace. They noticed some “muck” on the graphene, and upon further inspection, found it to be composed of the elements of everyday glass – silicon and oxygen. They concluded that an air leak had caused the copper to react with the quartz, also made of silicon and oxygen. This produced the glass layer on the would-be pure graphene.

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