U sing carbon nanotubes, MIT chemical engineers have devised a new method for detecting proteins, including fibrinogen, one of the coagulation factors critical to the blood-clotting cascade. This approach, if developed into an implantable sensor, could be useful for monitoring patients who are taking blood thinners, allowing doctors to make sure the drugs aren’t interfering too much with blood clotting. The new method is the first to create synthetic recognition sites (similar to natural antibodies) for proteins and to couple them directly to a powerful nanosensor such as a carbon nanotube. The researchers have also made significant progress on a similar recognition site for insulin, which could enable better monitoring of patients with diabetes. It may also be possible to use this approach to detect proteins associated with cancer or heart disease, says Michael Strano, the Carbon P. Dubbs Professor in Chemical Engineering at MIT. Strano is the senior author of a paper describing the method in Nature Communications. Gili Bisker, a postdoc in Strano’s lab, is the paper’s lead author. The new sensor is the latest example of a method developed in Strano’s lab, known as Corona Phase Molecular Recognition (CoPhMoRe). This technique takes advantage of the interactions between a given polymer and a nanoparticle surface such as that of a fluorescent single-walled carbon nanotube, when the polymer is wrapped around the nanotube. Certain regions of the polymers latch onto the nanoparticle surface like anchors, while other regions extend outwards into their environment. This outward-facing region, also known as the adsorbed phase or corona, has a 3-D structure that depends on the composition of the polymer. CoPhMoRe works when a specific polymer adsorbs to the nanoparticle surface and creates a corona that recognizes the target molecule. These interactions are very specific, just like the binding between an antibody and its target. Binding of the target alters the carbon nanotubes’ natural fluorescence, allowing the researchers to measure how much of the target molecule is present. Strano’s lab has previously used this approach to find recognition sites and develop nansensors for estradiol and riboflavin, among other molecules. The new paper represents their first attempt to identify corona phases that can detect proteins, which are larger, more complex, and more fragile than the molecules identified by their previous sensors. For this study, Bisker began by screening carbon nanotubes wrapped in 20 different polymers including DNA, RNA, and polyethylene glycol (PEG), a polymer often added to drugs to increase their longevity in the bloodstream. On their own, none of the polymers had any affinity for the 14 proteins tested, all taken from human blood. However, when the researchers tested polymer-wrapped nanotubes against the same proteins, they turned up a match between one of the modified nanotubes and fibrinogen. “A chemist or a biologist would not be able to predict ahead of time that there should be any kind of affinity between fibrinogen and this corona phase,” Strano says. “It really is a new kind of molecular recognition.” Fibrinogen, one of the most abundant proteins in human blood, is part of the blood-clotting cascade. When a blood vessel is damaged, an enzyme called thrombin converts fibrinogen into fibrin, a stringy protein that forms clots to seal the wound. A sensor for fibrinogen could help doctors determine if patients who are taking blood thinners still have enough clotting capability to protect them from injury, and could allow doctors to calculate more finely tuned dosages. It could also be used to test patients’ blood clotting before they go into surgery, or to monitor wound healing, Bisker says. The researchers believe their synthetic molecular recognition agents are an improvement over existing natural systems based on antibodies or DNA sequences known as aptamers, which are more fragile and tend to degrade over time. “One of the advantages of this is that it’s a completely synthetic system that can have a much longer lifetime within the body,” Bisker says. In 2013, researchers in Strano’s lab demonstrated that carbon nanotube sensors can remain active in mice for more than a year after being embedded in a polymer gel and surgically implanted under the skin. In addition to insulin, the researchers are also interested in detecting troponin, a protein that is released by dying heart cells, or detecting proteins associated with cancer, which would be useful for monitoring the success of chemotherapy. These and other protein sensors could become critical components of devices that deliver drugs in response to a sign of illness. “By measuring therapeutic markers in the human body in real time, we can enable drug delivery systems that are much smarter, and release drugs in precise quantities,” Strano says. “However, measurement of those biomarkers is the first step.”
« Nifco develops thermoplastic oil pan for Jaguar Land Rover ALIVE6 project | Main | Audi to increase participation in Formula E; full factory-backed motorsport program for 2017/2018 » Researchers at MIT have carried out the most detailed analysis yet of lithium dendrite formation from lithium anodes in batteries and have found that there are two entirely different mechanisms at work. While both forms of deposits are composed of lithium filaments, the way they grow depends on the applied current. Clustered, “mossy” deposits, which form at low rates, turn out to grow from their roots and can be relatively easy to control. More sparse and rapidly advancing “dendritic” projections grow only at their tips. The dendritic type, the researchers say, are harder to deal with and are responsible for most of the problems dendrites cause: degraded performance and short-circuits that damage or disable the battery. Their findings are reported in an open-access paper in the RSC journal Energy and Environmental Science. To develop batteries with higher energy density, such as Li–O , Li–S, and other Li metal batteries using intercalation cathodes, lithium is believed to be the ideal anode material for its extremely high theoretical specific capacity (3860 mA h g-1), low density (0.59 g cm-3) and the lowest negative electrochemical potential ( 3.04 V vs. the standard hydrogen electrode). Unfortunately, lithium growth is unstable during battery recharging and leads to rough, mossy deposits, whose fresh surfaces consume the electrolyte to form solid–electrolyte interphase layers, resulting in high internal resistance, low Coulombic efficiency and short cycle life. Finger-like lithium dendrites can also short-circuit the cell by penetrating the porous separator, leading to catastrophic accidents. Controlling such hazardous instabilities requires accurately determining their mechanisms, which are more complex than the well-studied diffusion-limited growth of copper or zinc from aqueous solutions. Such fundamental understanding is critical for the success of the lithium metal anode and could provide guidance for the optimal design and operation of rechargeable lithium metal batteries. The new study is the first to show the two different types of dendritic growth: mossy, which grows slowly from the base, and dendritic, which extends rapidly from the growing tips. While previous research has always lumped the two types of growth together under the blanket term “dendrites”, the new work demonstrates the precise conditions for each distinct growth mode to occur, and how the mossy type can be relatively easily controlled. The root-growing mossy growth, the team found, can be blocked by adding a separator layer made of a nanoporous ceramic material (a sponge-like material with tiny pores at the nanometer scale, or billionths of a meter across). The tip-growing dendritic growth, by contrast, cannot be easily blocked, but fortunately should not occur in practical batteries. The normal working currents of these batteries are much lower than the characteristic current associated with the tip-growing deposits, so these deposits will not form unless significant degradation of the electrolyte has occurred. The research shows that dendritic growths can be effectively controlled at lower current levels, for a given cell capacity, and demonstrates what the upper limits on battery performance would need to be in order to prevent the truly damaging dendritic filaments. Ceramic separators with pores smaller than mossy lithium whiskers could replace conventional polyolefin separators with flexible large pores to enhance safety and cycle life, and the effect could be further reinforced with lithium salts and solvents that favor thicker columnar deposits. To the broader field of electrodeposition, our results clarify the physical connections between lithium and copper/zinc dendrites formed in liquid electrolytes. Mechanisms and mathematical models of copper/zinc dendrite growths cannot be and should not be applied to explain either the development or the suppression of lithium whiskers.Future theoretical investigations should take into account the dynamics of SEI formation during both the root-growth and tip-growth processes of lithium electrodeposition. The separators that could block the mossy growth are made of anodic aluminum oxide, or AAO, which is 60 micrometers thick and has well-aligned, straight nanopores across its thickness. The research suggests that flexible composite ceramic separators, such as those made by coating ceramic particles onto conventional polyolefin separators, should be used in lithium metal batteries to help block the root-growing mossy lithium. Martin Z. Bazant, the E. G. Roos (1944) Professor of Chemical Engineering and a professor of mathematics explained that most previous research on the use of lithium metal anodes has been carried out at low current levels or low battery capacities, and because of that the second type of growth mechanism had not been reliably observed. The MIT team carried out tests at higher current levels that clearly revealed the two distinct types of growth. He said that the findings were made possible by his team’s development of an innovative laboratory setup, a glass capillary cell. Previous research had mostly relied on electrical measurements to infer what was taking place physically inside the battery, but seeing it in action made the differences very clear. The new findings will now provide battery researchers with a better understanding of the underlying scientific principles, and show the limitations on rates and capacity that are achievable. The work was supported by Robert Bosch LLC through the MIT Energy Initiative.
Home > Press > New research shows how nanowires can be formed Abstract: In an article published in Nature today, researchers at Lund University in Sweden show how different arrangements of atoms can be combined into nanowires as they grow. Researchers learning to control the properties of materials this way can lead the way to more efficient electronic devices. Nanowires are believed to be important elements in several different areas, such as in future generations of transistors, energy efficient light emitting diodes (LEDs) and solar cells. The fact that it is possible to affect how nanowires are formed and grow has been known for a long time. What researchers have now been able to show is what needs to be done to give the nanowires a particular structure. The gound-breaking discovery includes showing how nanowires grow, and affect the formation of different atomic layers, by using a powerful microscope and theoretical analysis. "We now have on tape the events that take place, and what is required to be able to control the nanowire growth", says Daniel Jacobsson, former doctoral student at the Lund University Faculty of Engineering, and currently a research engineer at the Lund University Centre for Chemistry and Chemical Engineering. The team wanted to understand how nanowires grow, and chose to film them though an electron microscope. The article in Nature is about these films, which show nanowires made from gallium arsenide and composed of different crystal structures. "The nanowires grow through a self-assembly process which is spontaneous and hard to control. But if we can understand how the nanowires grow, we can control the structures that are formed in a more precise way, and thereby create new types of structures for new fields of application", says Daniel Jacobsson. At the Centre for Chemistry and Chemical Engineering in Lund, a world-leading "super microscope" is under construction, which will be able to show, in high resolution, how atoms are joined together when nanostructures are formed. "In our Nature article, we show how dynamic the growth of nanowires really is. Once the new microscope is in place, we hope to be able to provide even more details and expand the scope of materials studied. Both the current results, and hopefully those to come, are important for an even more exact formation of nanowires for various applications", says Professor Kimberly Dick Thelander. Facts/Study about nanowires Nanotechnology could be seen as engineering of functional systems at the atomic scale, which illustrates the growth of nanowires, where different atomic layers are stacked on top of each other. In the study Interface Dynamics and Crystal Phase Switching in GaAs Nanowires, the researchers were able to monitor in real time where each new atomic layer is placed in a growing nanowire, and explain why they place themselves where they do. The study shows that it is possible to control the position of each new atomic layer, and was conducted in collaboration with researchers at the IBM T. J. Watson Research Center, USA, and Cambridge University, UK. Facts / Nanowires A nanowire is an extremely thin wire with a diameter equal to one thousandth of a human hair. They are made out of many different materials, for example metals such as silver and nickel, semiconductor materials such as silicon and gallium arsenide, and insulating material such as silicon oxide. Nanowires are useful because they enable the formation of complex structures with many chemical compounds, and sometimes different atomic arrangements. Nanowires are usually made out of single crystals, and the specific atomic arrangement is what determines the structure of the crystal. Every new type of complicated structure - whether it be a combination of different materials or a new way of joining atoms together - involve new properties and thereby different applications in areas such as electronics and lighting. For more information, please click Contacts: Cecilia Schubert 46-073-062-3858 Daniel Jacobsson Research engineer Centre for Analysis and Synthesis Phone: +46 736167304, +46 46 222 82 29 Sebastian Lehmann Researcher Solid State Physics Phone: +46 46 2224369 Kimberly Dick Thelander Professor Solid State Physics/ Centre for Analysis and Synthesis Phone: +46 706 111735 If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.
Girgis B.S.,National Research Center of Egypt |
Soliman A.M.,Chemical Engineering |
Fathy N.A.,National Research Center of Egypt
Microporous and Mesoporous Materials | Year: 2011
Seed hulls (or coats) of peanut, soybean, cottonseed, lupine, broad beans, and sunflower seeds, were subjected to various treatments in order to get adsorbing carbons. Characterization of porosity was determined by N 2/77 K adsorption isotherms. Simple pyrolysis at 500 °C yields low adsorbing carbons of meso-/macroporous character, whereas steam activation of these chars at 850 °C enhances porosity, in micropores, to a limited extent. Chemical activation with H3PO4 at 500 °C exerts the best recommending influence in producing high adsorbing carbons with evenly distributed porosity within micro-mesopore ranges. It was found that phosphoric acid activation of the studied precursors enhanced the yield, surface area and pore volume; 32-46%, 437-1022 m2/g and 0.444-0.809, respectively, as compared to other treatments. The capacity to remove methylene blue, in single bottle experiments, complements the state of porosity deduced from the gas phase adsorption of N2. Peanut shells proved the best feasible raw material under all treatment processes, whereas lupine seeds and sunflower seed hulls show relatively the least affected. Dye removal capacity was enhanced by carbon mesoporosity, whereas adversely affected by its increased surface pH and ash content was observed. Low-cost by-products of oil producing industry seem, thus, to be promising precursors for the production of highly valuable adsorbing carbons. © 2010 Elsevier Inc. All rights reserved.
What do engineers see when they look at their nanocrystal, microneedle, and quantum-dot experiments? Results, of course. In a June workshop administered by the Department of Chemical Engineering, a group of graduate students worked with Felice Frankel, a research scientist at the Center for Materials Science and Engineering and an award-winning photographer, to improve both their technical skills and their aesthetic sensibilities and to create engaging and appealing photos of their work. Drawing from the fields of chemistry, materials science, and chemical engineering, the graduate-level researchers created powerful visuals that are intimately linked to the work that motivates and compels them. Here are a few examples of their images. "This is a fully outfitted bioreactor designed for the production of protein-based therapeutics. This reactor enables the rapid manufacturing of multiple high-quality biologics. As a graduate student, I’m interested in the modeling, simulation, optimization, and control of such systems, and this object is one of the more beautiful pieces of process equipment in the unit. I learned a great deal about the use of light. In this case, diffuse light and the use of a white background gave the subject an even cast. I also enjoyed the discussion of ethical considerations of digital manipulation in photography, particularly with research photographs." "These are semiconductor nanocrystals — also called quantum dots — suspended as a colloid in a solvent. Our group studies how these nanocrystals assemble when the solvent evaporates and how energy is transferred between them. In this image, we excited the nanocrystals with an ultraviolet lamp. They absorb the high-energy ultraviolet light then emit light of their own, the color of which is a reflection of the nanocrystal size. I learned how to photograph remissive samples like this, how to properly frame the image and background, and how to better accentuate the vial caps by using a directed white light to provide additional illumination from above." —Aaron Goodman, graduate student in chemistry, and Mark Weidman, graduate student in chemical engineering "This is a stretchable fluidic device imprinted in a tough hydrogel and closed on top with a thin elastomer layer. Similar devices can be used as platforms for biological and tissue engineering experiments by changing the designs patterned on the hydrogel. The angle and framing make this image better than any I’ve done before. I learned about the different options for composing my image, and that changing the background and lighting can make drastic differences in the final look of the device. By making the right choices, a photo of a standard research device can become a cover page." "These are microneedles, which are mostly used for the delivery of drugs and vaccines across the skin, and the silicone mold used to make them. Microneedles provide greater insight into the monitoring of immunity and can aid in the design of new vaccines. I am using them in my research to monitor the immune system and for other disease-related diagnostics. I experimented with different lighting conditions, backgrounds, and angles to get an engaging and crisp image of my scientific endeavors." "These are microscope slides coated with hundreds of polymer patches containing catalase, an antioxidant enzyme, soaking in a solution of hydrogen peroxide. The bubbles form when catalase converts the hydrogen peroxide into water and oxygen. These polymer patches can be attached to the surface of living cells and carried throughout the body as 'cell backpacks.' Our goal is to explore the use of these backpacks for cell-mediated and targeted drug delivery. They enable the non-invasive delivery of drugs to sites of inflammation, even across the blood-brain barrier, which is a significant obstacle to traditional drug treatment. I learned how to create a composition and use visuals to illustrate scientific concepts — and, in turn, share my research work with a much larger audience." "This flow device represents a crucial step in the scale-up of the electrochemical separation processes developed by the Hatton group. The electrochemical cell contains a sandwich redox-electrode configuration, and serves to validate our water purification and remediation technology under flow conditions. We hope to address challenges such as the removal of emerging contaminants in pesticides, pharmaceuticals, and heavy-metal micropollutants. By experimenting with visuals, I learned how to better communicate my work. By optimizing camera settings, lighting conditions, and composition, I can now produce an appealing final product to a wider audience."