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This artistic rendering depicts fluid-filled nanotubes changing with time. Caltech researchers used four-dimensional electron microscopy to visualize and monitor the flow of molten lead within single zinc oxide nanotubes in real time and space. (Image credit: Caltech)

At the nanoscale, where objects are measured in billionths of meters and events transpire in trillionths of seconds, things do not always behave as our experiences with the macro-world might lead us to expect. Water, for example, seems to flow much faster within carbon nanotubes than classical physics says should be possible. Now imagine trying to capture movies of these almost imperceptibly small nanoscale movements. Researchers at Caltech now have done just that by applying a new imaging technique called four-dimensional (4D) electron microscopy to the nanofluid dynamics problem. The researchers describe how they visualized and monitored the flow of molten lead within a single zinc oxide nanotube in real time and space. The 4D microscopy technique was developed in the Physical Biology Center for Ultrafast Science and Technology at Caltech, created and directed to advance understanding of the fundamental physics of chemical and biological behavior.

In 4D microscopy, a stream of ultra-fast-moving electrons bombards a sample in a carefully timed manner. Each electron scatters off the sample, producing a still image that represents a single moment, just a femtosecond—or a millionth of a billionth of a second—in duration. Millions of the still images can then be stitched together to produce a digital movie of nanoscale motion. In the new work, single laser pulses were used to melt the lead cores of individual zinc oxide nanotubes and then, using 4D microscopy, captured how the hot pressurized liquid moved within the tubes—sometimes splitting into multiple segments, producing tiny droplets on the outside of the tube, or causing the tubes to break.

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(Image Credit: Moscow Institute of Physics and Technology)

A group of researchers from Russia, Belarus and Spain, including Moscow Institute of Physics and Technology professor Yury Lozovik, have developed a microscopic force sensor based on carbon nanotubes. The scientists proposed using two nanotubes, one of which is a long cylinder with double walls one atom thick. These tubes are placed so that their open ends are opposite to each other. Voltage is then applied to them, and a current of about 10nAflows through the circuit. Carbon tube walls are good conductors, and along the gap between the ends of the nanotubes the current flows thanks to the tunnel effect, which is a quantum phenomenon where electrons pass through a barrier that is considered insurmountable in classical mechanics. This current is called tunneling current and is widely used in practice. There are, for example, tunnel diodes, wherein current flows through the potential barrier of the p-n junction. The researchers used the relationship between the tunneling current and the distance between the ends of the nanotubes to determine the relative position of the carbon nanotubes and thus to find the magnitude of the external force exerted on them. The new sensor allows the position of coaxial cylinders in two-layer nanotubes to be controlled quite accurately. As a result, it is possible to determine the stretch of an n-scale object, to which electrodes are attached. Calculations made by the researchers showed the possibility of recording forces of a few tenths of a nN(10-10newtons). To make it clearer, a single bacterium weighs about 10-14newtons on average, and a mosquito weighs a few dozen mcN (10-5 N).However, the device developed by the physicists may find application beyond micro scales.

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Stanford engineers have developed an improved process for making flexible circuits that use carbon nanotube transistors, a development that paves the way for a new generation of bendable electronic devices. (Bao Lab / Stanford University)

Engineers would love to create flexible electronic devices, such as e-readers that could be folded to fit into a pocket. One approach involves designing circuits based on electronic fibers, known as carbon nanotubes (CNTs), instead of rigid silicon chips. But reliability is essential. Most silicon chips are based on a type of circuit design that allows them to function flawlessly even when the device experiences power fluctuations. However, it is much more challenging to do so with CNT circuits. But now a team at Stanford University has developed a process to create flexible chips that can tolerate power fluctuations in much the same way as silicon circuitry. "This is the first time anyone has designed flexible CNT circuits that have both high immunity to electrical noise and low power consumption, " said Zhenan Bao, a professor of chemical engineering at Stanford. In principle, CNTs should be ideal for making flexible electronic circuitry. These ultra-thin carbon filaments have the physical strength to take the wear and tear of bending and the electrical conductivity to perform any electronic task. But until this recent work from the Stanford team, flexible CNT circuits didn't have the reliability and power-efficiency of rigid silicon chips.

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An electron microscope image shows carbon black nanoparticles modified by adding polyvinyl alcohol for downhole detection of hydrogen sulfide in oil and gas wells. The nanoreporters were created at Rice University. (Credit: Tour Group/Rice University)

Scientists at Rice University have created a nanoscale detector that checks for and reports on the presence of hydrogen sulfide in crude oil and natural gas while they’re still in the ground. The nanoreporter is based on nanometer-sized carbon material developed by a consortium of Rice labs led by chemist James Tour. Limited exposure to hydrogen sulfide causes sore throats, shortness of breath and dizziness, according to the researchers. The human nose quickly becomes desensitized to hydrogen sulfide, leading to an inability to detect higher concentrations. That can be fatal, they said. On the flip side, hydrogen sulfide is also a biologically important signaling molecule in processes that include pain and inflammation. Tour said chemists have synthesized fluorescent probes to detect it in the body. The Rice team capitalized on that work by using the probes to create downhole detectors for oil fields. Crude oil and natural gas inherently contain hydrogen sulfide, which gives off a “rotten egg” smell. Even a 1 percent trace of sulfur turns oil into what’s known as “sour crude,” which is toxic and corrodes pipelines and transportation vessels, Tour said. The extra steps required to turn the sour into “sweet” crude are costly. So it’s important to know the content of what you’re pumping out of the ground, and the earlier the better,” Tour said. Led by Rice professors Tour, Michael Wong and Mason Tomson and researcher Amy Kan, the university has pioneered efforts to gather information from oil fields through the use of nanoreporters. The nanoreporters were designed to detect and report on the presence and amount of oil in a well that might otherwise be hard to assess. Now the same team, joined by chemist Angel Martí, is employing thermally stable, soluble, highly mobile, carbon black-based nanoreporters modified to look for hydrogen sulfide and report results immediately upon their return to the surface.

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Scientists at New York University and the University of Melbourne have developed a method using DNA origami to turn one-dimensional nano materials into two dimensions. Their breakthrough offers the potential to enhance fiber optics and electronic devices by reducing their size and increasing their speed. DNA origami employs approximately two hundred short DNA strands to direct longer strands in forming specific shapes. In their work, the scientists sought to create, and then manipulate the shape of, amyloid fibrils—rods of aggregated proteins, or peptides, that match the strength of spider’s silk. To do so, they engineered a collection of 20 DNA double helices to form a nanotube big enough (15 to 20 nanometers—just over one-billionth of a meter—in diameter) to house the fibrils. The platform builds the fibrils by combining the properties of the nanotube with a synthetic peptide fragment that is placed inside the cylinder. The resulting fibril-filled nanotubes can then be organized into two-dimensional structures through a series of DNA-DNA hybridization interactions.

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Professor Jonathan Coleman, AMBER. (Image Credit: AMBER)

Researchers in AMBER, the Science Foundation Ireland funded materials science centre headquartered at Trinity College Dublin have, for the first time, developed a new method of producing industrial quantities of high quality graphene. Described as a wonder material, graphene is a single-atom thick sheet of carbon. It is extremely light and stronger than steel, yet incredibly flexible and extremely electrically conductive. The discovery will change the way many consumer and industrial products are manufactured. The materials will have a multitude of potential applications including advanced food packaging; high strength plastics; foldable touch screens for mobile phones and laptops; super-protective coatings for wind turbines and ships; faster broadband and batteries with dramatically higher capacity than anything available today. Until now, researchers have been unable to produce graphene of high quality in large enough quantities. The subject of on-going international research, the research undertaken by AMBER is the first to perfect a large-scale production of pristine graphene materials and has been highlighted by the highly prestigious Nature Materials publication as a global breakthrough. Professor Coleman and his team used a simple method for transforming flakes of graphite into defect-free graphene using commercially available tools, such as high-shear mixers. They demonstrated that not only could graphene-containing liquids be produced in standard lab-scale quantities of a few 100 millilitres, but the process could be scaled up to produce 100s of litres and beyond.

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The particles were designed to release doxorubicin when exposed to ultraviolet light. Here, ovarian cancer cells turn red as the doxorubicin is released over time. (Image Source: MIT; Image courtesy of Erik Dreaden and Kevin Shopsowitz)

Delivering chemotherapy drugs in nanoparticle form could help reduce side effects by targeting the drugs directly to the tumors. In recent years, scientists have developed nanoparticles that deliver one or two chemotherapy drugs, but it has been difficult to design particles that can carry any more than that in a precise ratio. Now MIT chemists have devised a new way to build such nanoparticles, making it much easier to include three or more different drugs. The researchers showed that they could load their particles with three drugs commonly used to treat ovarian cancer. “We think it’s the first example of a nanoparticle that carries a precise ratio of three drugs and can release those drugs in response to three distinct triggering mechanisms,” says Jeremiah Johnson, an assistant professor of chemistry at MIT. Such particles could be designed to carry even more drugs, allowing researchers to develop new treatment regimens that could better kill cancer cells while avoiding the side effects of traditional chemotherapy. Johnson and colleagues demonstrated that the triple-threat nanoparticles could kill ovarian cancer cells more effectively than particles carrying only one or two drugs, and they have begun testing the particles against tumors in animals.

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ORNL and UT researchers have invented a method to merge different 2-dimensional materials into a seamless layer. This colorized scanning tunneling microscope image shows a single-atom sheet composed of graphene (seen in blue) combined with hexagonal boron nitride (seen in yellow).Image Credit: Oak Ridge National Laboratory

Researchers at the Department of Energy’s Oak Ridge National Laboratory and the University of Tennessee, Knoxville have pioneered a new technique for forming a two-dimensional, single-atom sheet of two different materials with a seamless boundary. The study could enable the use of new types of 2-D hybrid materials in technological applications and fundamental research. By rethinking a traditional method of growing materials, the researchers combined two compounds -- graphene and boron nitride -- into a single layer only one atom thick. Graphene, which consists of carbon atoms arranged in hexagonal, honeycomb-like rings, has attracted waves of attention because of its high strength and electronic properties. “People call graphene a wonder material that could revolutionize the landscape of nanotechnology and electronics,” ORNL’s An-Ping Li said. “Indeed, graphene has a lot of potential, but it has limits. To make use of graphene in applications or devices, we need to integrate graphene with other materials.” The researchers first grew graphene on a copper foil, etched the graphene to create clean edges, and then grew boron nitride through chemical vapor deposition. Instead of conforming to the structure of the copper base layer as in conventional epitaxy, the boron nitride atoms took on the crystallography of the graphene.

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Roy’s team used an imprinting technology that works like a cookie cutter but on the nanoscale. Drugs are mixed with a polymer solution and dispensed on a silicon wafer. Then a shape is imprinted onto the polymer-drug mixture using a quartz template. The material is then solidified using UV light. Whatever the cookie cutter’s template – triangle, rod, disc – a nanoparticle with that shape is produced.Image Source: Georgia Tech, Image Credit: Rob Felt

For years scientists have been working to fundamentally understand how nanoparticles move throughout the human body. One big unanswered question is how the shape of nanoparticles affects their entry into cells. Now researchers have discovered that under typical culture conditions, mammalian cells prefer disc-shaped nanoparticles over those shaped like rods. Understanding how the shape of nanoparticles affects their transport into cells could be a major boost for the field of nanomedicine by helping scientists to design better therapies for various diseases, such as improving the efficacy and reducing side effects of cancer drugs. In addition to nanoparticle geometry, the researchers also discovered that different types of cells have different mechanisms to pull in nanoparticles of different sizes, which was previously unknown. The research team also used theoretical models to identify the physical parameters that cells use when taking in nanoparticles. “This research identified some very novel yet fundamental aspects in which cells interact with the shape of nanoparticles,” said Krishnendu Roy of Department of Biomedical Engineering at Georgia Tech and Emory University. He conducted this research at The University of Texas at Austin in collaboration with Profs. S. V. Sreenivasan and Li Shi, but is continuing the work at Georgia Tech. Roy’s team used a unique approach to making the differently shaped nanoparticles. The researchers adapted an imprinting technology used in the semiconductor industry and rigged it to work with biological molecules, Roy said. This imprinting technique, which they developed at UT-Austin, works like a cookie cutter but on the nanoscale. Drugs are mixed with a polymer solution and dispensed on a silicon wafer. Then a shape is imprinted onto the polymer-drug mixture using a quartz template. The material is then solidified using UV light. Whatever the cookie cutter’s template – triangle, rod, disc – a nanoparticle with that shape is produced.

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Physicists Kevin Twedt (left), who is visually impaired, and Vladimir Aksyuk (right) led a two day educational program to introduce a group of blind and visually impaired high school students to nanotechnology. Image Credit: NIST

In July 2013, 45 blind and visually impaired high school students from around the country gathered at Towson University for a weeklong event designed to expose them to science careers long believed to be impossible for the blind. Twenty of those students participated in an exciting educational program on nanoscale science led by NIST Center for Nanoscale Science and Technology (CNST) Project Leader Vladimir Aksyuk, who has participated in this event for the last three years, and CNST/University of Maryland Postdoctoral Researcher Kevin Twedt, who is visually impaired.  During six hours of hands-on activities spread over two days, the students learned the basics of size and scale, the metric system, and received an introduction to the nanoscale. They then learned the techniques scientists use to create and measure nanoscale structures. By probing canes against floor models of different shapes and sizes, they were exposed to how an atomic force microscope probe senses topographic changes on a surface. Using plastic models, they explored the structural relationships between carbon atoms forming either planar graphene or three-dimensional carbon nanotubes. Finally, by scanning a laser pointer across black shapes on white paper and using a photodiode with an audio output that got louder in white regions and quieter in dark regions, the students learned how a scanning electron microscope creates images by scanning a beam of electrons across a surface.  “Most of these students had never really considered careers in science or knew that they are possible for blind people,” says Twedt, who has had 20/200 vision since birth. “In a few days, the students gained an appreciation for the work scientists do and perhaps some will consider going into science later on.”  The science, technology, engineering, and math (STEM) program, known as the STEM-X program was sponsored by National Federation of the Blind, under the auspices of its National Center for Blind Youth in Science.

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