Home > What's New in Nanotechnology?

What's New in Nanotechnology?

June 20, 2013

This false-color image (left) depicts the core lattice in blue, where drugs can be placed in compartment pores for targeting in the body. In the hexagon-shaped cylinder branches, other types of drugs may be place for delivery. Simultaneous delivery of pharmaceuticals can thus be optimized for each drug separately. The accompanying illustration (right) offers a clear vision of the left image. (Image credit: Cornell University)

Ulrich Wiesner, the Spencer T. Olin Professor of Materials Science and Engineering, and first authors, Cornell researcher Teeraporn Suteewong and graduate student Hiroaki Sai, have tweaked familiar “sol-gel” chemistry used to self-assemble porous silica particles, making the assembly shift gears partway through to create what amounts to two or more different nanoparticles joined together, while controlling how one particle grows out of another, a process referred to as epitaxial growth. “It’s the first time I’m aware of that the shapes of porous silica nanoparticles have been controlled via epitaxy,” Wiesner said. “The cubic lattice and the hexagonal lattice have a well-defined relationship.” The products so far are fairly simple particles with two or three compartments, but the methods might be extended to create much more complex structures, he said. The discovery was partly serendipitous. While making ordinary nanoparticles, the scientists saw a small fraction with hexagonally structured porous branches growing out of a cubic core particle. “We set out to understand what controls that,” Wiesner said. The starter for the process is a mixture of organosilanes, molecules built around carbon and silicon atoms, and surfactants. Surfactants, of which the prime example is soap, have one end that likes water and another “oily” end that tries to stay away from it. So in water surfactants form micelles, tiny spherical bundles with the water-loving end out and the oily part tucked away in the center. In the sol-gel process the micelles act as cages around which silica from the orgaosilanes forms, building particles about a hundred nanometers in diameter. When the micelles are washed away what remains is a porous silica structure with pores two to three nanometers in size.

Categories : University News
June 13, 2013

Graphene-coated ribbons of vanadium oxide, seen in a scanning electron microscope image, might be the best electrode for lithium-ion batteries yet tested, according to researchers at Rice University. (Credit: Ajayan Group/Rice University)

Hybrid ribbons of vanadium oxide (VO2) and graphene may accelerate the development of high-power lithium-ion batteries suitable for electric cars and other demanding applications. The Rice University lab of materials scientist Pulickel Ajayan determined that the well-studied material is a superior cathode for batteries that could supply both high energy density and significant power density. The ribbons created at Rice are thousands of times thinner than a sheet of paper, yet have potential that far outweighs current materials for their ability to charge and discharge very quickly. Cathodes built into half-cells for testing at Rice fully charged and discharged in 20 seconds and retained more than 90 percent of their initial capacity after more than 1,000 cycles. “This is the direction battery research is going, not only for something with high energy density but also high power density,” Ajayan said. “It’s somewhere between a battery and a supercapacitor.” The ribbons also have the advantage of using relatively abundant and cheap materials. “This is done through a very simple hydrothermal process, and I think it would be easily scalable to large quantities,” he said.

Categories : University News
June 06, 2013

(Image credit: McGill University)

As demand for computing and communication capacity surges, the global communication infrastructure struggles to keep pace since the light signals transmitted through fiber-optic lines must still be processed electronically, which creates a bottleneck in telecommunications networks. While the idea of developing an optical transistor to get around this problem is alluring to scientists and engineers, it has also remained an elusive vision, despite years of experiments with various approaches. Now, McGill University researchers have taken a significant, early step toward this goal by showing a new way to control light in the semiconductor nanocrystals known as “quantum dots.” In results published online recently, PhD candidate Jonathan Saari, Prof. Patanjali (Pat) Kambhampati and colleagues in McGill’s Department of Chemistry show that all-optical modulation and basic Boolean logic functionality – key steps in the processing and generation of signals – can be achieved by using laser-pulse inputs to manipulate the quantum mechanical state of a semiconductor nanocrystal. “Our findings show that these nanocrystals can form a completely new platform for optical logic,” says Saari. “We’re still at the nascent stages, but this could mark a significant step toward optical transistors.” Quantum dots already are used in applications ranging from photovoltaics, to light-emitting diodes and lasers, to biological imaging. The Kambhampati group’s latest findings point toward an important new area of potential impact, based on the ability of these nanocrystals to modulate light in an optical gating scheme.

Categories : University News
May 30, 2013

An illustration of a silicon AFM tip sliding over a diamond surface, with a TEM image of the tip inset. (Image Source: University of Pennsylvania; Art: Felice Macera)

Wear is a fact of life. As surfaces rub against one another, they break down and lose their original shape. With less material to start with and functionality that often depends critically on shape and surface structure, wear affects nanoscale objects more strongly than it does their macroscale counterparts.  Worse, the mechanisms behind wear processes are better understood for things like car engines than nanotech devices. But now, researchers at the University of Pennsylvania’s School of Engineering and Applied Science have experimentally demonstrated one of the mechanisms behind wear at the smallest scale: the transfer of material, atom by atom, from one surface to another.  On the nanoscale, wear is mainly understood through two processes, fracture and plastic deformation. Fracture is where large pieces of a surface break off at once, like when the point of a pencil snaps off in the middle of a sentence. Plastic deformation is what happens when the surface changes shape or compresses without breaking, like when the edge of knife gets dull or bent.  These mechanisms typically affect thousands or millions of atoms at a time, whereas nanoscale wear often proceeds through a much more gradual process. Determining the mechanisms behind this more gradual process is key to improving such devices.  The Penn team’s breakthrough was to conduct AFM-style wear experiments inside of a transmission electron microscope, or TEM, which passes a beam of electrons through a sample (in this case, the nanoscale tip) to generate an image of the sample, magnified more than 100,000 times.  By modifying a commercial mechanical testing instrument that works inside a TEM, the researchers were able to slide a flat diamond surface against the silicon tip of an AFM probe. By putting the probe-cantilever assembly inside the TEM and running the wear experiment there, they were able to simultaneously measure the distance the tip slid, the force with which it contacted the diamond and the volume of atoms removed in each sliding interval.

Categories : University News
May 23, 2013

An optical signal, represented by the red arrow, comes into contact with the metamaterial and interprets the ultrasound waves, resulting in an altered optical signal that is processed to produce a high-quality image. Image Credit: Texas A&M University.

Ultrasound technology could soon experience a significant upgrade that would enable it to produce high-quality, high-resolution images thanks to the development of a new key material by a team of researchers that includes a professor in Texas A&M University’s Department of Biomedical Engineering. The material, which converts ultrasound waves into optical signals that can be used to produce an image, is the result of a collaborative effort by Texas A&M Professor Vladislav Yakovlev and researchers from King’s College London, The Queen’s University of Belfast and the University of Massachusetts Lowell. The engineered material, known as a “metamaterial,” offers significant advantages over conventional ultrasound technology, which generates images by converting ultrasound waves into electrical signals, Yakovlev explains. The material, he notes, consists of golden nanorods embedded in a polymer known as polypyrolle. An optical signal is sent into this material where it interacts with and is altered by incoming ultrasound waves before passing through the material. A detection device would then read the altered optical signal, analyzing the changes in its optical properties to process a higher resolution image.

Categories : University News
May 16, 2013

Illustration: Rod-shaped chemotherapy drug nanoparticles bind more efficiently to receptors on cancer cells. Image Source: UC Santa Barbara, Credit: Peter Allen

Bioengineering researchers at University of California, Santa Barbara have found that changing the shape of chemotherapy drug nanoparticles from spherical to rod-shaped made them up to 10,000 times more effective at specifically targeting and delivering anti-cancer drugs to breast cancer cells. Their findings could have a game-changing impact on the effectiveness of anti-cancer therapies and reducing the side effects of chemotherapy, according to the researchers. “Conventional anti-cancer drugs accumulate in the liver, lungs and spleen instead of the cancer cell site due to inefficient interactions with the cancer cell membrane,” explained Samir Mitragotri , professor of chemical engineering and Director of the Center for BioEngineering at UCSB. “We have found our strategy greatly enhances the specificity of anti-cancer drugs to cancer cells.”  To engineer these high-specificity drugs, scientists formed rod-shaped nanoparticles from a chemotherapeutic drug, camptothecin, and coated them with an antibody called trastuzumab that is selective for certain types of cancer cells, including breast cancer. The antibody-coated camptothecin nanorods were 10,000-fold more effective than tratsuzumab alone and 10-fold more effective than camptothecin alone at inhibiting breast cancer cell growth.

Categories : University News
May 09, 2013

Solar cells are just like leaves, capturing the sunlight and turning it into energy. It’s fitting that they can now be made partially from trees. Georgia Institute of Technology and Purdue University researchers have developed efficient solar cells using natural substrates derived from plants such as trees. Just as importantly, by fabricating them on cellulose nanocrystal (CNC) substrates, the solar cells can be quickly recycled in water at the end of their lifecycle. The researchers report that the organic solar cells reach a power conversion efficiency of 2.7 percent, an unprecedented figure for cells on substrates derived from renewable raw materials. The CNC substrates on which the solar cells are fabricated are optically transparent, enabling light to pass through them before being absorbed by a very thin layer of an organic semiconductor. During the recycling process, the solar cells are simply immersed in water at room temperature. Within only minutes, the CNC substrate dissolves and the solar cell can be separated easily into its major components. Georgia Tech College of Engineering Professor Bernard Kippelen says his team’s project opens the door for a truly recyclable, sustainable and renewable solar cell technology.

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May 02, 2013

New work by theorists at Rice and Tsinghua universities shows defects in polycrystalline forms of graphene will sap its strength. The illustration from a simulation at left shows a junction of grain boundaries where three domains of graphene meet with a strained bond in the center. At right, the calculated stress buildup at the tip of a finite-length grain boundary. (Credit: Zhiping Xu/Tsinghua University)

Graphene, the single-atom-thick form of carbon, has become famous for its extraordinary strength. But less-than-perfect sheets of the material show unexpected weakness, according to researchers at Rice University in the U.S. and Tsinghua University in China. The kryptonite to this Superman of materials is in the form of a seven-atom ring that inevitably occurs at the junctions of grain boundaries in graphene, where the regular array of hexagonal units is interrupted. At these points, under tension, polycrystalline graphene has about half the strength of pristine samples of the material. Calculations by the Rice team of theoretical physicist Boris Yakobson and his colleagues in China could be important to materials scientists using graphene in applications where its intrinsic strength is a key feature, like composite materials and stretchable or flexible electronics. Graphene sheets grown in a lab, often via chemical vapor deposition, are almost never perfect arrays of hexagons, Yakobson said. Domains of graphene that start to grow on a substrate are not necessarily lined up with each other, and when these islands merge, they look like quilts, with patterns going in every direction.

Categories : University News
April 25, 2013

Sometimes the best discoveries come by accident. A team of researchers at Washington University in St. Louis, headed by Srikanth Singamaneni, PhD, assistant professor of mechanical engineering & materials science, unexpectedly found the mechanism by which tiny single molecules spontaneously grow into centimeter-long microtubes by leaving a dish for a different experiment in the refrigerator. Once Singamaneni and his research team, including Abdennour Abbas, PhD, a former postdoctoral researcher at Washington University, Andrew Brimer, a senior undergraduate majoring in mechanical engineering, and Limei Tian, a fourth-year graduate student, saw that these molecules had become microtubes, they set out to find out how.  To do so, they spent about six months investigating the process at various length scales (nano to micro) using various microscopy and spectroscopy techniques.  “What we showed was that we can actually watch the self-assembly of small molecules across multiple length scales, and for the first time, stitched these length scales to show the complete picture,” Singamaneni says. “This hierarchical self-organization of molecular building blocks is unprecedented since it is initiated from a single molecular crystal and is driven by vesiclular dynamics in water.” Self-assembly, a process in which a disordered collection of components arrange themselves into an ordered structure, is of growing interest as a new paradigm in creating micro- and nanoscale structures and functional systems and subsystems. This novel approach of making nano- and microstructures and devices is expected to have numerous applications in electronics, optics and biomedical applications.

Video Caption: A team of researchers at Washington University in St. Louis, headed by Srikanth Singamaneni, PhD, assistant professor of mechanical engineering & materials science, unexpectedly found the mechanism by which tiny single molecules spontaneously grow into centimeter-long microtubes by leaving a dish for a different experiment in the refrigerator.

Categories : University News
April 18, 2013

This scanning electron microscope (SEM) image shows a nanobeam probe, including a large part of the handle tip, inserted in a typical cell. (Image Credit: Stanford University)

If engineers at Stanford University have their way, biological research may soon be transformed by a new class of light-emitting probes small enough to be injected into individual cells without harm to the host. Welcome to biophotonics, a discipline at the confluence of engineering, biology and medicine in which light-based devices – lasers and light-emitting diodes (LEDs) – are opening up new avenues in the study and influence of living cells.  The team’s work is the first study to demonstrate that tiny, sophisticated devices known as light resonators can be inserted inside cells without damaging the cell. Even with a resonator embedded inside, a cell is able to function, migrate and reproduce as normal. The researchers call their device a "nanobeam," because it resembles a steel I-beam with a series of round holes etched through the center. This beam, however, is not massive, but measure only a few microns in length and just a few hundred nanometers in width and thickness. It looks a bit like a piece from an erector set of old. The holes through the beam act like a nanoscale hall of mirrors, focusing and amplifying light at the center of the beam in what are known as photonic cavities. These are the building blocks for nanoscale lasers and LEDs. "Devices like the photonic cavities we have built are quite possibly the most diverse and customizable ingredients in photonics," said the paper's senior author, Jelena Vuckovic, a professor of electrical engineering. "Applications span from fundamental physics to nanolasers and biosensors that could have profound impact on biological research." At the cellular level, a nanobeam acts like a needle able to penetrate cell walls without injury. Once inserted, the beam emits light, yielding a remarkable array of research applications and implications. While other groups have shown that it is possible to insert simple nanotubes and electrical nanowires into cells, nobody had yet realized such complicated optical components inside biological cells.

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