Dancing droplets (w/video)

Just as the size of transistors continues to decrease, laboratories are also expected to shrink until they eventually fit on a chip. ETH Zurich researchers have developed a system of using sound waves to move, merge or sort minuscule droplets with reagents or cells in a controlled manner. Schema Chip With ultrasound, represented by curved red and blue lines, ETH Zurich researchers move micro-droplets for sorting and analysis. (Scheme: ETH Zurich / Ivo Leibacher) Laboratory experiments today tend to be wasteful. For example, in order to conduct diagnostic tests, liquids are mixed together in reaction vessels when all this task requires is a few nanolitres of liquids. With miniaturisation, it would be possible to have a higher throughput with less consumption of materials. When attempting to compress an entire experiment into the size of a chip, known as 'Lab on a Chip', there is one key question: how can minuscule amounts of liquid or individual cells be moved, merged and assessed in a controlled way? Ivo Leibacher and Peter Reichert, doctoral students at the Institute of Mechanical Systems, developed a system to move tiny droplets under the guidance of ETH Professor Jürg Dual. The concept is based on acoustophoresis, which uses a ultrasonic standing wave to move aqueous droplets through a carrier liquid of oil on a silicon-glass chip. The droplets, which have a diameter of 50 to 250 micrometres, cannot mix with the carrier liquid, nor can they evaporate. “On this scale, the droplets are very stable because they are held together by the surface tension,” Leibacher explains. lab on a chip On this small chip, researchers move droplets with the help of ultra sonic waves. (Photo: Ivo Leibacher / ETH Zürich) Toward the node When the ultrasonic standing waves are applied, the droplets move to the node of the wave. This means researchers can place two different droplets in both sides of the channel to merge them in a controlled manner. Changing the frequency, on the other hand, guides targeted drops with, for example, a light signal into a branched-off channel. By separating them in this way, they can be sorted and analysed after the conclusion of the experiment. "One of the advantages of our technology is its high biocompatibility and versatility," says Reichert. Previous methods in which researchers manipulated individual cells on a tiny scale resulted in cases of cells being damaged. This method can be used for cells as well as for DNA, reagents and chemicals.

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"We hope this technology will become a valuable part of laboratory equipment, allowing for experiments in high throughput with minimal consumption," said Leibacher. The researchers have filed a patent application for the method, which has been recently published in the journal ("Microfluidic droplet handling by bulk acoustic wave (BAW) acoustophoresis").
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Designing crack-resistant metals with nanoporous materials

Potential solutions to big problems continue to arise from research that is revealing how materials behave at the smallest scales. The results of a new study to understand the interactions of various metal alloys at the nanometer and atomic scales are likely to aid advances in methods of preventing the failure of systems critical to public and industrial infrastructure. High-Speed Metal Alloy Cracking The image shows corrosion of a silver-gold alloy spontaneously resulting in the formation of nanoscale porous structures that undergo high-speed cracking under the action of a tensile stress. It helps demonstrate a discovery by an Arizona State University research team about the stress-corrosion behavior of metals that threatens the mechanical integrity of engineered components and structures. (Provided by Karl Sieradzki/Arizona State University) Research led by Arizona State University materials science and engineering professor Karl Sieradzki is uncovering new knowledge about the causes of stress-corrosion cracking in alloys used in pipelines for transporting water, natural gas and fossil fuels -- as well as for components used in nuclear power generating stations and the framework of aircraft. Sieradzki is on the faculty of the School for Engineering of Matter, Transport and Energy, one of ASU's Ira A. Fulton Schools of Engineering. His research team's findings are detailed in an advance online publication on June 22 of the paper "Potential-dependent dynamic fracture of nanoporous gold" on the website of the journal ("Potential-dependent dynamic fracture of nanoporous gold"). Using advanced tools for ultra-high-speed photography and digital image correlation, the team has been able to closely observe the events triggering the origination of stress-corrosion fracture in a model silver-gold alloy and to track the speed at which cracking occurs. They measured cracks moving at speeds of 200 meters per second corresponding to about half of the shear wave sound velocity in the material. This is a remarkable result, Sieradzki said, given that typically only brittle materials such as glass will fracture in this manner and that gold alloys are among the most malleable metals. In the absence of a corrosive environment these gold alloys fail in the same manner as children's modeling clay, Sieradzki explained: Roll modeling clay into a cylindrical shape and you can stretch it by a by 100 percent before it slowly tears apart. In the presence of corrosive environments, silver is selectively dissolved from the alloy causing porosity to form (see photo). If this occurs while the alloy is stressed, then the material fails as if it were made of glass. These results provide a deeper understanding of the stress-corrosion behavior of metals such as aluminum alloys, brass and stainless steel that threatens the mechanical integrity of important engineered components and structures. The team's discoveries could provide a guide for "designing alloys with different microstructures so that the materials are resistant to this type of cracking," Sieradzki said.
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3D plasmonic antenna capable of focusing light into few nanometers

Professors Myung-Ki Kim and Yong-Hee Lee of the Physics Department at KAIST and their research teams developed a 3D gap-plasmon antenna which can focus light into a few nanometers wide space. Their research findings were published in ("Squeezing Photons into a Point-Like Space"). 3D Gap-Plasmon Antenna Structure and the Simulation Results Figure 1: 3D Gap-Plasmon Antenna Structure and the Simulation Results. (Image: KAIST) Focusing light into a point-like space is an active research field as it finds many applications. However, concentrating light into a smaller space than its wavelength is often hindered by diffraction. In order to tackle this problem, many researchers have utilized the plasmonic phenomenon in a metal where light can be confined to a greater extent by overcoming the diffraction limit. Many researchers focused on developing a two dimensional plasmonic antenna and were able to focus light under 5 nanometers. However, this two dimensional antenna reveals a challenge that the light disperses to the opposite end regardless of how small it was focused. For a solution, a three dimensional structure has to be employed in order to maximize the light intensity. Adopting the proximal focused-ion-beam milling technology, the KAIST research team developed a three dimensional 4 nanometer wide gap-plasmon antenna. By squeezing the photons into a three dimensional nano space of 4 x 10 x 10 nm3 size, the researchers were able to increase the intensity of light 400,000 times stronger than that of the incident light. Capitalizing on the enhanced intensity of light within the antenna, they intensified the second-harmonic signal and verified that the light was focused in the nano gap by scanning cathodoluminescence images. Constructed 3D Gap-Plasmon Antenna Structure. Figure 2: Constructed 3D Gap-Plasmon Antenna Structure. (Image: KAIST) This technology is expected to improve the speed of data transfer and processing up to the level of terahertz (one trillion times per second) and to enlarge the storage volume per unit area on hard disks by 100 times. In addition, high definition images of sub-molecule size can be taken with actual light, instead of using an electron microscope, while it can improve the semiconductor process to a smaller size of few nanometers. Professor Kim said, “A simple yet genuine idea has shifted the research paradigm from 2D gap-plasmon antennas to 3D antennas. This technology sees numerous applications including in the field of information technology, data storage, image medical science, and semiconductor process.”
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