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  • richardmitnick 9:04 am on February 19, 2015 Permalink | Reply
    Tags: , , , Nanotechnology   

    From MIT: “New nanogel for drug delivery” 


    MIT News

    February 19, 2015
    Anne Trafton | MIT News Office

    1

    Self-healing gel can be injected into the body and act as a long-term drug depot.

    Scientists are interested in using gels to deliver drugs because they can be molded into specific shapes and designed to release their payload over a specified time period. However, current versions aren’t always practical because must be implanted surgically.

    To help overcome that obstacle, MIT chemical engineers have designed a new type of self-healing hydrogel that could be injected through a syringe. Such gels, which can carry one or two drugs at a time, could be useful for treating cancer, macular degeneration, or heart disease, among other diseases, the researchers say.

    The new gel consists of a mesh network made of two components: nanoparticles made of polymers entwined within strands of another polymer, such as cellulose.

    “Now you have a gel that can change shape when you apply stress to it, and then, importantly, it can re-heal when you relax those forces. That allows you to squeeze it through a syringe or a needle and get it into the body without surgery,” says Mark Tibbitt, a postdoc at MIT’s Koch Institute for Integrative Cancer Research and one of the lead authors of a paper describing the gel in Nature Communications on Feb. 19.

    Koch Institute postdoc Eric Appel is also a lead author of the paper, and the paper’s senior author is Robert Langer, the David H. Koch Institute Professor at MIT. Other authors are postdoc Matthew Webber, undergraduate Bradley Mattix, and postdoc Omid Veiseh.

    Heal thyself

    Scientists have previously constructed hydrogels for biomedical uses by forming irreversible chemical linkages between polymers. These gels, used to make soft contact lenses, among other applications, are tough and sturdy, but once they are formed their shape cannot easily be altered.

    The MIT team set out to create a gel that could survive strong mechanical forces, known as shear forces, and then reform itself. Other researchers have created such gels by engineering proteins that self-assemble into hydrogels, but this approach requires complex biochemical processes. The MIT team wanted to design something simpler.

    “We’re working with really simple materials,” Tibbitt says. “They don’t require any advanced chemical functionalization.”

    The MIT approach relies on a combination of two readily available components. One is a type of nanoparticle formed of PEG-PLA copolymers, first developed in Langer’s lab decades ago and now commonly used to package and deliver drugs. To form a hydrogel, the researchers mixed these particles with a polymer — in this case, cellulose.

    Each polymer chain forms weak bonds with many nanoparticles, producing a loosely woven lattice of polymers and nanoparticles. Because each attachment point is fairly weak, the bonds break apart under mechanical stress, such as when injected through a syringe. When the shear forces are over, the polymers and nanoparticles form new attachments with different partners, healing the gel.

    Using two components to form the gel also gives the researchers the opportunity to deliver two different drugs at the same time. PEG-PLA nanoparticles have an inner core that is ideally suited to carry hydrophobic small-molecule drugs, which include many chemotherapy drugs. Meanwhile, the polymers, which exist in a watery solution, can carry hydrophilic molecules such as proteins, including antibodies and growth factors.

    Long-term drug delivery

    In this study, the researchers showed that the gels survived injection under the skin of mice and successfully released two drugs, one hydrophobic and one hydrophilic, over several days.

    This type of gel offers an important advantage over injecting a liquid solution of drug-delivery nanoparticles: While a solution will immediately disperse throughout the body, the gel stays in place after injection, allowing the drug to be targeted to a specific tissue. Furthermore, the properties of each gel component can be tuned so the drugs they carry are released at different rates, allowing them to be tailored for different uses.

    The researchers are now looking into using the gel to deliver anti-angiogenesis drugs to treat macular degeneration. Currently, patients receive these drugs, which cut off the growth of blood vessels that interfere with sight, as an injection into the eye once a month. The MIT team envisions that the new gel could be programmed to deliver these drugs over several months, reducing the frequency of injections.

    Another potential application for the gels is delivering drugs, such as growth factors, that could help repair damaged heart tissue after a heart attack. The researchers are also pursuing the possibility of using this gel to deliver cancer drugs to kill tumor cells that get left behind after surgery. In that case, the gel would be loaded with a chemical that lures cancer cells toward the gel, as well as a chemotherapy drug that would kill them. This could help eliminate the residual cancer cells that often form new tumors following surgery.

    “Removing the tumor leaves behind a cavity that you could fill with our material, which would provide some therapeutic benefit over the long term in recruiting and killing those cells,” Appel says. “We can tailor the materials to provide us with the drug-release profile that makes it the most effective at actually recruiting the cells.”

    The research was funded by the Wellcome Trust, the Misrock Foundation, the Department of Defense, and the National Institutes of Health.

    See the full article here.

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  • richardmitnick 2:38 am on February 14, 2015 Permalink | Reply
    Tags: , Nanotechnology,   

    From phys.org: “Getting two for one: ‘Bonus’ electrons in germanium nanocrystals can lead to better solar cells” 

    physdotorg
    phys.org

    February 14, 2015
    Ans Hekkenberg

    1
    The material is illuminated with photons. In some of the germanium nanocrystals, the photons cause electrons to be excited, and thus form an electron-hole (e-h) pair. There are two possibilities. (1) The incoming photon has an energy in the range between once and twice the bandgap energy. One e-h pair is formed. (2) The incoming photon has an energy of more than two times the bandgap energy. The excess energy of the electron – the ‘kinetic’ energy of the electron which is excited high up in the conduction band – is sufficient to create a second e-h pair in the same nanocrystal. In that way, carrier multiplication is achieved. Credit: Fundamental Research on Matter (FOM)

    Researchers from FOM, the University of Amsterdam, the Delft University of Technology and the University of the Algarve have discovered that when light hits germanium nanocrystals, the crystals produce ‘bonus electrons’. These additional electrons could increase the yield of solar cells and improve the sensitivity of photodetectors. The researchers will publish their work in Light: Science & Applications today.

    In nanocrystals, the absorption of a single photon can lead to the excitation of multiple electrons: two for one! This phenomenon, known as carrier multiplication, was already well known in silicon nanocrystals. Silicon is the most commonly used material in solar cells. However, the researchers found that carrier multiplication also occurs in germanium nanocrystals, which are more suitable for optimizing the efficiency than silicon nanocrystals. Their discovery could lead to better solar cells.

    Semiconductor physics

    Germanium and silicon are examples of semiconductors: materials that have an energy bandgap. When these materials absorb light, electrons from the band below this energy gap (valence band) leap to the band above the gap (conduction band). These excited ‘hot’ electrons and the holes they leave behind can be harvested to form an electrical current. They form the basic fuel for a solar cell.

    Nanocrystals and carrier multiplication

    If an absorbed photon contains more energy than an electron requires to leap over the bandgap, the excess energy can be used to excite a second electron. Earlier research has shown that a bandgap energy from 0.6 to 1.0 electronvolts is ideal to achieve this carrier multiplication.

    Nanocrystals are extremely small, about a thousand times smaller than the width of a human hair. Due to their size, the energy structure of the crystals is dramatically different from that of bulk material. In fact, the bandgap energy depends on the nanocrystal size. Bulk germanium has an energy bandgap of 0.67 electronvolts. By tuning the germanium nanocrystals’ size, the researchers can change the bandgap energy to values between 0.6 and 1.4 electronvolts. This is within the ideal range for optimizing carrier multiplication, or the amount of ‘bonus electrons’.

    Performing the experiment

    To investigate carrier multiplication in nanocrystals, the researchers used an optical technique called pump-probe spectroscopy. An initial laser pulse, called the pump, emits photons that excite the nanocrystal by creating one free electron in the conduction band. A second pulse of photons, called the probe, can then be absorbed by this electron.

    The researchers found that if the energy of the pump photon is twice the bandgap energy of the germanium nanocrystals, the probe light is absorbed by two electrons instead of one. This effect is the well-known fingerprint of carrier multiplication. In other words, if the pump photon carries sufficient energy, the hot electron contains enough excess energy to excite a second electron in the same nanocrystal. Using this carrier multiplication, germanium nanocrystals can help achieve the maximum efficiency of solar cells.

    See the full article here.

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    About Phys.org in 100 Words

    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

     
  • richardmitnick 5:34 am on February 13, 2015 Permalink | Reply
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    From phys.org: “Gold nanotubes launch a three-pronged attack on cancer cells” 

    physdotorg
    phys.org

    Feb 13, 2015

    1
    Pulsed near infrared light (shown in red) is shone onto a tumour (shown in white) that is encased in blood vessels. The tumour is imaged by multispectral optoacoustic tomography via the ultrasound emission (shown in blue) from the gold nanotubes. Credit: Jing Claussen (Ithera Medical, Germany)

    Scientists have shown that gold nanotubes have many applications in fighting cancer: internal nanoprobes for high-resolution imaging; drug delivery vehicles; and agents for destroying cancer cells.

    The study, published today in the journal Advanced Functional Materials, details the first successful demonstration of the biomedical use of gold nanotubes in a mouse model of human cancer.

    Study lead author Dr Sunjie Ye, who is based in both the School of Physics and Astronomy and the Leeds Institute for Biomedical and Clinical Sciences at the University of Leeds, said: “High recurrence rates of tumours after surgical removal remain a formidable challenge in cancer therapy. Chemo- or radiotherapy is often given following surgery to prevent this, but these treatments cause serious side effects.

    Gold nanotubes – that is, gold nanoparticles with tubular structures that resemble tiny drinking straws – have the potential to enhance the efficacy of these conventional treatments by integrating diagnosis and therapy in one single system.”

    The researchers say that a new technique to control the length of nanotubes underpins the research. By controlling the length, the researchers were able to produce gold nanotubes with the right dimensions to absorb a type of light called ‘near infrared’.

    The study’s corresponding author Professor Steve Evans, from the School of Physics and Astronomy at the University of Leeds, said: “Human tissue is transparent for certain frequencies of light – in the red/infrared region. This is why parts of your hand appear red when a torch is shone through it.

    “When the gold nanotubes travel through the body, if light of the right frequency is shone on them they absorb the light. This light energy is converted to heat, rather like the warmth generated by the Sun on skin. Using a pulsed laser beam, we were able to rapidly raise the temperature in the vicinity of the nanotubes so that it was high enough to destroy cancer cells.”

    In cell-based studies, by adjusting the brightness of the laser pulse, the researchers say they were able to control whether the gold nanotubes were in cancer-destruction mode, or ready to image tumours.

    In order to see the gold nanotubes in the body, the researchers used a new type of imaging technique called ‘multispectral optoacoustic tomography’ (MSOT) to detect the gold nanotubes in mice, in which gold nanotubes had been injected intravenously. It is the first biomedical application of gold nanotubes within a living organism. It was also shown that gold nanotubes were excreted from the body and therefore are unlikely to cause problems in terms of toxicity, an important consideration when developing nanoparticles for clinical use.

    Study co-author Dr James McLaughlan, from the School of Electronic & Electrical Engineering at the University of Leeds, said: “This is the first demonstration of the production, and use for imaging and cancer therapy, of gold nanotubes that strongly absorb light within the ‘optical window’ of biological tissue.

    “The nanotubes can be tumour-targeted and have a central ‘hollow’ core that can be loaded with a therapeutic payload. This combination of targeting and localised release of a therapeutic agent could, in this age of personalised medicine, be used to identify and treat cancer with minimal toxicity to patients.”

    The use of gold nanotubes in imaging and other biomedical applications is currently progressing through trial stages towards early clinical studies.

    See the full article here.

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    About Phys.org in 100 Words

    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

     
  • richardmitnick 7:26 pm on February 9, 2015 Permalink | Reply
    Tags: , , , Nanotechnology,   

    From Rice: “Nano-antioxidants prove their potential” 

    Rice U bloc

    Rice University

    February 9, 2015
    Mike Williams

    Rice-led study shows how particles quench damaging superoxides

    Injectable nanoparticles that could protect an injured person from further damage due to oxidative stress have proven to be astoundingly effective in tests to study their mechanism.

    Scientists at Rice University, Baylor College of Medicine and the University of Texas Health Science Center at Houston (UTHealth) Medical School designed methods to validate their 2012 discovery that combined polyethylene glycol-hydrophilic carbon clusters — known as PEG-HCCs — could quickly stem the process of overoxidation that can cause damage in the minutes and hours after an injury.

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    A polyethylene glycol-hydrophilic carbon cluster developed at Rice University has the potential to quench the overexpression of damaging superoxides through the catalytic turnover of reactive oxygen species that can harm biological functions. Illustration by Errol Samuel

    The tests revealed a single nanoparticle can quickly catalyze the neutralization of thousands of damaging reactive oxygen species molecules that are overexpressed by the body’s cells in response to an injury and turn the molecules into oxygen. These reactive species can damage cells and cause mutations, but PEG-HCCs appear to have an enormous capacity to turn them into less-reactive substances.

    The researchers hope an injection of PEG-HCCs as soon as possible after an injury, such as traumatic brain injury or stroke, can mitigate further brain damage by restoring normal oxygen levels to the brain’s sensitive circulatory system.

    The results were reported today in the Proceedings of the National Academy of Sciences.

    “Effectively, they bring the level of reactive oxygen species back to normal almost instantly,” said Rice chemist James Tour. “This could be a useful tool for emergency responders who need to quickly stabilize an accident or heart attack victim or to treat soldiers in the field of battle.” Tour led the new study with neurologist Thomas Kent of Baylor College of Medicine and biochemist Ah-Lim Tsai of UTHealth.

    PEG-HCCs are about 3 nanometers wide and 30 to 40 nanometers long and contain from 2,000 to 5,000 carbon atoms. In tests, an individual PEG-HCC nanoparticle can catalyze the conversion of 20,000 to a million reactive oxygen species molecules per second into molecular oxygen, which damaged tissues need, and hydrogen peroxide while quenching reactive intermediates.

    Tour and Kent led the earlier research that determined an infusion of nontoxic PEG-HCCs may quickly stabilize blood flow in the brain and protect against reactive oxygen species molecules overexpressed by cells during a medical trauma, especially when accompanied by massive blood loss.

    Their research targeted traumatic brain injuries, after which cells release an excessive amount of the reactive oxygen species known as a superoxide into the blood. These toxic free radicals are molecules with one unpaired electron that the immune system uses to kill invading microorganisms. In small concentrations, they contribute to a cell’s normal energy regulation. Generally, they are kept in check by superoxide dismutase, an enzyme that neutralizes superoxides.

    But even mild traumas can release enough superoxides to overwhelm the brain’s natural defenses. In turn, superoxides can form such other reactive oxygen species as peroxynitrite that cause further damage.

    “The current research shows PEG-HCCs work catalytically, extremely rapidly and with an enormous capacity to neutralize thousands upon thousands of the deleterious molecules, particularly superoxide and hydroxyl radicals that destroy normal tissue when left unregulated,” Tour said.

    “This will be important not only in traumatic brain injury and stroke treatment, but for many acute injuries of any organ or tissue and in medical procedures such as organ transplantation,” he said. “Anytime tissue is stressed and thereby oxygen-starved, superoxide can form to further attack the surrounding good tissue.”

    The researchers used an electron paramagnetic resonance spectroscopy technique that gets direct structure and rate information for superoxide radicals by counting unpaired electrons in the presence or absence of PEG-HCC antioxidants. Another test with an oxygen-sensing electrode, peroxidase and a red dye confirmed the particles’ ability to catalyze superoxide conversion.

    “In sharp contrast to the well-known superoxide dismutase, PEG-HCC is not a protein and does not have metal to serve the catalytic role,” Tsai said. “The efficient catalytic turnover could be due to its more ‘planar,’ highly conjugated carbon core.”

    The tests showed the number of superoxides consumed far surpassed the number of possible PEG-HCC bonding sites. The researchers found the particles have no effect on important nitric oxides that keep blood vessels dilated and aid neurotransmission and cell protection, nor was the efficiency sensitive to pH changes.

    “PEG-HCCs have enormous capacity to convert superoxide to oxygen and the ability to quench reactive intermediates while not affecting nitric oxide molecules that are beneficial in normal amounts,” Kent said. “So they hold a unique place in our potential armamentarium against a range of diseases that involve loss of oxygen and damaging levels of free radicals.”

    The study also determined PEG-HCCs remain stable, as batches up to 3 months old performed as good as new.

    Graduate student Errol Samuel and alumna Daniela Marcano, both of Rice, and Vladimir Berka, a senior research scientist at UTHealth, are lead authors of the study. Co-authors are Rice alumnus Austin Potter; alumnus Brittany Bitner and associate professor Robia Pautler of Baylor College of Medicine; instructor Gang Wu of UTHealth and Roderic Fabian of Baylor College of Medicine and the Michael E. DeBakey Veterans Affairs Medical Center.

    Kent is a professor of neurology and director of stroke research and education at Baylor College of Medicine and chief of neurology and a member of the Center for Translational Research on Inflammatory Diseases at the DeBakey Center. Tour is the T.T. and W.F. Chao Chair in Chemistry as well as a professor of materials science and nanoengineering and of computer science and a member of Rice’s Richard E. Smalley Institute for Nanoscale Science and Technology. Tsai is a professor of hematology at UTHealth and adjunct professor of biochemistry and cell biology at Rice.

    The Mission Connect Mild Traumatic Brain Injury Consortium from the Department of Defense and the National Institutes of Health, the Alliance for NanoHealth and UTHealth supported the research.

    See the full article here.

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    Rice U campus

    In his 1912 inaugural address, Rice University president Edgar Odell Lovett set forth an ambitious vision for a great research university in Houston, Texas; one dedicated to excellence across the range of human endeavor. With this bold beginning in mind, and with Rice’s centennial approaching, it is time to ask again what we aspire to in a dynamic and shrinking world in which education and the production of knowledge will play an even greater role. What shall our vision be for Rice as we prepare for its second century, and how ought we to advance over the next decade?

    This was the fundamental question posed in the Call to Conversation, a document released to the Rice community in summer 2005. The Call to Conversation asked us to reexamine many aspects of our enterprise, from our fundamental mission and aspirations to the manner in which we define and achieve excellence. It identified the pressures of a constantly changing and increasingly competitive landscape; it asked us to assess honestly Rice’s comparative strengths and weaknesses; and it called on us to define strategic priorities for the future, an effort that will be a focus of the next phase of this process.

     
  • richardmitnick 5:28 pm on February 9, 2015 Permalink | Reply
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    From LBL: “New Design Tool for Metamaterials” 

    Berkeley Logo

    Berkeley Lab

    February 9, 2015
    Lynn Yarris (510) 486-5375

    1
    Confocal microscopy confirmed that the nonlinear optical properties of metamaterials can be predicted using a
    theory about light passing through nanostructures.

    Metamaterials – artificial nanostructures engineered with electromagnetic properties not found in nature – offer tantalizing future prospects such as high resolution optical microscopes and superfast optical computers. To realize the vast potential of metamaterials, however, scientists will need to hone their understanding of the fundamental physics behind them. This will require accurately predicting nonlinear optical properties – meaning that interaction with light changes a material’s properties, for example, light emerges from the material with a different frequency than when it entered. Help has arrived.

    Scientists with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley have shown, using a recent theory for nonlinear light scattering when light passes through nanostructures, that it is possible to predict the nonlinear optical properties of metamaterials.

    “The key question has been whether one can determine the nonlinear behavior of metamaterials from their exotic linear behavior,” says Xiang Zhang, director of Berkeley Lab’s Materials Sciences Division and an international authority on metamaterial engineering who led this study. “We’ve shown that the relative nonlinear susceptibility of large classes of metamaterials can be predicted using a comprehensive nonlinear scattering theory. This will allow us to efficiently design metamaterials with strong nonlinearity for important applications such as coherent Raman sensing, entangled photon generation and frequency conversion.”

    2
    Xiang Zhang, Haim Suchowski and Kevin O’Brien were part of the team that discovered a way to predict thenon-linear optical properties of metamaterials. (Photo by Roy Kaltschmidt)

    Zhang, who holds the Ernest S. Kuh Endowed Chair at UC Berkeley and is a member of the Kavli Energy NanoSciences Institute at Berkeley (Kavli ENSI), is the corresponding author of a paper describing this research in the journal Nature Materials. The paper is titled Predicting nonlinear properties of metamaterials from the linear response. The other authors are Kevin O’Brien, Haim Suchowski, Junsuk Rho, Alessandro Salandrino, Boubacar Kante and Xiaobo Yin.

    The unique electromagnetic properties of metamaterials stem from their physical structure rather than their chemical composition. This structure, for example, provides certain metamaterials with a negative refractive index, an optical property in which the phase front of light moving through a material propagates backward towards the source. The phase front light moving through natural materials always propagates forward, away from its source.

    Zhang and his group have already exploited the linear optical properties of metamaterials to create the world’s first optical invisibility cloak and mimic black holes. Most recently they used a nonlinear metamaterial with a refractive index of zero to generate “phase mismatch–free nonlinear light,” meaning light waves moved through the material gaining strength in all directions. However, engineering nonlinear metamaterials remains in its infancy, with no general conclusion on the relationship between linear and nonlinear properties.

    3
    Metamaterial arrays whose geometry varied gradually from a symmetric bar to an asymmetric U-shape were used to compare the predictive abilities of Miller’s rule and a non-linear light scattering theory.

    For the past several decades, scientists have estimated the nonlinear optical properties in natural crystals using a formulation known as “Miller’s rule,” for the physicist Robert Miller who authored it. In this new study, Zhang and his group found that Miller’s rule doesn’t work for a number of metamaterials. That’s the bad news. The good news is that a nonlinear light scattering theory, developed for nanostructures by Dutch scientist Sylvie Roke, does.

    “From the linear properties, one calculates the nonlinear polarization and the mode of the nanostructure at the second harmonic,” says Kevin O’Brien, co-lead author of the Nature Materials paper and a member of Zhang’s research group. “We found the nonlinear emission is proportional to the overlap integral between these, not simply determined by their linear response.”

    Zhang, O’Brien, Suchowski, and the other contributors to this study evaluated Miller’s rule and the nonlinear light scattering theory by comparing their predictions to experimental results obtained using a nonlinear stage-scanning confocal microscope.

    “Nonlinear stage-scanning confocal microscopy is critical because it allows us to rapidly measure the nonlinear emission from thousands of different nanostructures while minimizing the potential systematic errors, such as intensity or beam pointing variations, often associated with tuning the wavelength of an ultrafast laser,” O’Brien says.

    The researchers used confocal microscopy to observe the second harmonic generation from metamaterial arrays whose geometry was gradually shifted from a symmetric bar-shape to an asymmetric U-shape. Second harmonic light is a nonlinear optical property in which photons with the same frequency interact with a nonlinear material to produce new photons at twice the energy and half the wavelength of the originals. It was the discovery of optical second harmonic generation in 1961 that started modern nonlinear optics.

    “Our results show that nonlinear scattering theory can be a valuable tool in the design of nonlinear metamaterials not only for second-order but also higher order nonlinear optical responses over a broad range of wavelengths,” O’Brien says. “We’re now using these experimental and theoretical techniques to explore other nonlinear processes in metamaterials, such as parametric amplification and entangled photon generation.”

    This research was supported by the DOE Office of Science.

    See the full article here.

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  • richardmitnick 3:17 pm on January 23, 2015 Permalink | Reply
    Tags: , BNL, , , , Nanotechnology   

    From BNL: “Self-Assembled Nanotextures Create Antireflective Surface on Silicon Solar Cells” 

    Brookhaven Lab

    January 21, 2015
    Karen McNulty Walsh, (631) 344-8350 or Peter Genzer, (631) 344-3174

    Nanostructured surface textures—with shapes inspired by the structure of moths’ eyes—prevent the reflection of light off silicon, improving conversion of sunlight to electricity

    1
    Chuck Black of the Center for Functional Nanomaterials displays a nanotextured square of silicon on top of an ordinary silicon wafer. The nanotextured surface is completely antireflective and could boost the production of solar energy from silicon solar cells.

    Reducing the amount of sunlight that bounces off the surface of solar cells helps maximize the conversion of the sun’s rays to electricity, so manufacturers use coatings to cut down on reflections. Now scientists at the U.S. Department of Energy’s Brookhaven National Laboratory show that etching a nanoscale texture onto the silicon material itself creates an antireflective surface that works as well as state-of-the-art thin-film multilayer coatings.

    The surface nanotexture … drastically cut down on reflection of many wavelengths of light simultaneously.

    Their method, described in the journal Nature Communications and submitted for patent protection, has potential for streamlining silicon solar cell production and reducing manufacturing costs. The approach may find additional applications in reducing glare from windows, providing radar camouflage for military equipment, and increasing the brightness of light-emitting diodes.

    “For antireflection applications, the idea is to prevent light or radio waves from bouncing at interfaces between materials,” said physicist Charles Black, who led the research at Brookhaven Lab’s Center for Functional Nanomaterials (CFN), a DOE Office of Science User Facility.

    Preventing reflections requires controlling an abrupt change in “refractive index,” a property that affects how waves such as light propagate through a material. This occurs at the interface where two materials with very different refractive indices meet, for example at the interface between air and silicon. Adding a coating with an intermediate refractive index at the interface eases the transition between materials and reduces the reflection, Black explained.

    “The issue with using such coatings for solar cells,” he said, “is that we’d prefer to fully capture every color of the light spectrum within the device, and we’d like to capture the light irrespective of the direction it comes from. But each color of light couples best with a different antireflection coating, and each coating is optimized for light coming from a particular direction. So you deal with these issues by using multiple antireflection layers. We were interested in looking for a better way.”

    For inspiration, the scientists turned to a well-known example of an antireflective surface in nature, the eyes of common moths. The surfaces of their compound eyes have textured patterns made of many tiny “posts,” each smaller than the wavelengths of light. This textured surface improves moths’ nighttime vision, and also prevents the “deer in the headlights” reflecting glow that might allow predators to detect them.

    “We set out to recreate moth eye patterns in silicon at even smaller sizes using methods of nanotechnology,” said Atikur Rahman, a postdoctoral fellow working with Black at the CFN and first author of the study.

    2
    A closeup shows how the nanotextured square of silicon completely blocks reflection compared with the surrounding silicon wafer.

    The scientists started by coating the top surface of a silicon solar cell with a polymer material called a “block copolymer,” which can be made to self-organize into an ordered surface pattern with dimensions measuring only tens of nanometers. The self-assembled pattern served as a template for forming posts in the solar cell like those in the moth eye using a plasma of reactive gases—a technique commonly used in the manufacture of semiconductor electronic circuits.

    The resulting surface nanotexture served to gradually change the refractive index to drastically cut down on reflection of many wavelengths of light simultaneously, regardless of the direction of light impinging on the solar cell.

    “Adding these nanotextures turned the normally shiny silicon surface absolutely black,” Rahman said.

    Solar cells textured in this way outperform those coated with a single antireflective film by about 20 percent, and bring light into the device as well as the best multi-layer-coatings used in the industry.

    “We are working to understand whether there are economic advantages to assembling silicon solar cells using our method, compared to other, established processes in the industry,” Black said.

    Hidden layer explains better-than-expected performance

    One intriguing aspect of the study was that the scientists achieved the antireflective performance by creating nanoposts only half as tall as the required height predicted by a mathematical model describing the effect. So they called upon the expertise of colleagues at the CFN and other Brookhaven scientists to help sort out the mystery.

    3
    Details of the nanotextured antireflective surface as revealed by a scanning electron microscope at the Center for Functional Nanomaterials. The tiny posts, each smaller than the wavelengths of light, are reminiscent of the structure of moths’ eyes, an example of an antireflective surface found in nature.

    “This is a powerful advantage of doing research at the CFN—both for us and for academic and industrial researchers coming to use our facilities,” Black said. “We have all these experts around who can help you solve your problems.”

    Using a combination of computational modeling, electron microscopy, and surface science, the team deduced that a thin layer of silicon oxide similar to what typically forms when silicon is exposed to air seemed to be having an outsized effect.

    “On a flat surface, this layer is so thin that its effect is minimal,” explained Matt Eisaman of Brookhaven’s Sustainable Energy Technologies Department and a professor at Stony Brook University. “But on the nanopatterned surface, with the thin oxide layer surrounding all sides of the nanotexture, the oxide can have a larger effect because it makes up a significant portion of the nanotextured material.”

    Said Black, “This ‘hidden’ layer was the key to the extra boost in performance.”

    The scientists are now interested in developing their self-assembly based method of nanotexture patterning for other materials, including glass and plastic, for antiglare windows and coatings for solar panels.

    This research was supported by the DOE Office of Science.

    See the full article here.

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    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
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  • richardmitnick 10:32 am on January 22, 2015 Permalink | Reply
    Tags: AIP, , Nanotechnology   

    From AIP: “Zinc Oxide Materials Tapped for Tiny Energy Harvesting Devices” 

    AIP Publishing Bloc

    American Institute of Physics

    January 13, 2015
    AIP News Staff
    Jason Socrates Bardi
    +1 240-535-4954
    jbardi@aip.org
    @jasonbardi

    Today, we’re surrounded by a variety of electronic devices that are moving increasingly closer to us – we can attach and wear them, or even implant electronics inside our bodies.

    Many types of smart devices are readily available and convenient to use. The goal now is to make wearable electronics that are flexible, sustainable and powered by ambient renewable energy.

    This last goal inspired a group of Korea Advanced Institute of Science and Technology (KAIST) researchers to explore how the attractive physical features of zinc oxide (ZnO) materials could be more effectively used to tap into abundant mechanical energy sources to power micro devices. They discovered that inserting aluminum nitride insulating layers into ZnO-based energy harvesting devices led to a significant improvement of the devices’ performance. The researchers report their findings in the journal Applied Physics Letters, from AIP Publishing.

    “Mechanical energy exists everywhere, all the time, and in a variety of forms – including movement, sound and vibration. The conversion from mechanical energy to electrical energy is a reliable approach to obtain electricity for powering the sustainable, wireless and flexible devices – free of environmental limitations,” explained Giwan Yoon, a professor in the Department of Electrical Engineering at KAIST.

    Piezoelectric materials such as ZnO, as well as several others, have the ability to convert mechanical energy to electrical energy, and vice versa. “ZnO nanostructures are particularly suitable as nanogenerator functional elements, thanks to their numerous virtues including transparency, lead-free biocompatibility, nanostructural formability, chemical stability, and coupled piezoelectric and semiconductor properties,” noted Yoon.

    The key concept behind the group’s work? Flexible ZnO-based micro energy harvesting devices, aka “nanogenerators,” can essentially be comprised of piezoelectric ZnO nanorod or nanowire arrays sandwiched between two electrodes formed on the flexible substrates. In brief, the working mechanisms involved can be explained as a transient flow of electrons driven by the piezoelectric potential.

    “When flexible devices can be easily mechanically deformed by various external excitations, strained ZnO nanorods or nanowires tend to generate polarized charges, which, in turn, generate piezoelectronic fields,” said Yoon. “This allows charges to accumulate on electrodes and it generates an external current flow, which leads to electronic signals. Either we can use the electrical output signals directly or store them in energy storage devices.”

    Other researchers have reported that the use of insulating materials can help provide an extremely large potential barrier. “This makes it critically important that insulating materials are carefully selected and designed – taking both the material properties and the device operation mechanism into consideration,” said Eunju Lee, a postdoctoral researcher in Yoon’s group.

    To date, however, there have been few efforts made to develop new insulating materials and assess their applicability to nanogenerator devices or determine their effects on the device output performance.

    The KAIST researchers proposed, for the first time, new piezoelectric ZnO/aluminum nitride (AlN) stacked layers for use in nanogenerators.

    2
    This illustration shows stacked flexible nanogenerators (left), and a cross-sectional transmission electron microscopy image of the ZnO/AlN-stacked structure. The scale bar on the right represents 200 nm.
    CREDIT: Giwan Yoon/Korea Advanced Institute of Science and Technology

    “We discovered that inserting AlN insulating layers into ZnO-based harvesting devices led to a significant improvement of their performance – regardless of the layer thickness and/or layer position in the devices,” said Lee. “Also, the output voltage performance and polarity seem to depend on the relative position and thickness of the stacked ZnO and AlN layers, but this needs to be explored further.”

    The group’s findings are expected to provide an effective approach for realizing highly energy-efficient ZnO-based micro energy harvesting devices. “This is particularly useful for self-powered electronic systems that require both ubiquity and sustainability – portable communication devices, healthcare monitoring devices, environmental monitoring devices and implantable medical devices,” pointed out Yoon. And there are potentially many other applications.

    Next up, Yoon and colleagues plan to pursue a more in-depth study to gain a much more precise and comprehensive understanding of device operation mechanisms. “We’ll also explore the optimum device configurations and dimensions based on the operation mechanism analysis work,” he added.

    Article title:
    Characteristics of piezoelectric ZnO/AlN—stacked flexible nanogenerators for energy harvesting applications
    Authors:
    Eunju Lee, Jaedon Park, Munhyuk Yim, Yeongseon Kim and Giwan Yoon
    Author affiliations:
    Korea Advanced Institute of Science and Technology

    See the full article here.

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    AIP Building

    AIP serves a federation of physical science societies in a common mission to promote physics and allied fields.

     
  • richardmitnick 4:15 pm on January 21, 2015 Permalink | Reply
    Tags: , , Nanotechnology   

    From Caltech: “Size Matters: The Importance of Building Small Things” 

    Caltech Logo
    Caltech

    01/21/2015
    Watson Lecture Preview

    Strong materials, such as concrete, are usually heavy, and lightweight materials, such as rubber (for latex gloves) and paper, are usually weak and susceptible to tearing and damage. Julia R. Greer, professor of materials science and mechanics in Caltech’s Division of Engineering and Applied Science, is helping to break that linkage.

    Q: What do you do?

    A: I’m a materials scientist, and I work with materials whose dimensions are at the nanoscale. A nanometer is one-billionth of a meter, or about one-hundred-thousandth the diameter of a hair. At those dimensions, ordinary materials such as metals, ceramics, and glasses take on properties quite unlike their bulk-scale counterparts. Many materials become 10 or more times stronger. Some become damage-tolerant. Glass shatters very easily in our world, for example, but at the nanoscale, some glasses become deformable and less breakable. We’re trying to harness these so-called size effects to create “meta-materials” that display these properties at scales we can see.

    We can fabricate essentially any structure we like with the help of a special instrument that is like a tabletop microprinter, but uses laser pulses to “write” a three-dimensional structure into a tiny droplet of a polymer. The laser “sets” the polymer into our three-dimensional design, creating a minuscule plastic scaffold. We rinse away the unset polymer and put our scaffold in another machine that essentially wraps it in a very thin, nanometers-thick ribbon of the stuff we’re actually interested in—a metal, a semiconductor, or a biocompatible material. Then we get rid of the plastic, leaving just the interwoven hollow tubular structure. The final structure is hollow, and it weighs nothing. It’s 99.9 percent air.

    We can even make structures nested within other structures. We recently started making hierarchical nanotrusses—trusses built from smaller trusses, like a fractal.

    1
    A fractal nanotruss made in Greer’s lab.
    Credit: Lucas Meza, Greer lab/Caltech

    Q: How big can you make these things, and where might that lead us?

    A: Right now, most of them are about 100 by 100 by 100 microns cubed. A micron is a millionth of a meter, so that is very small. And the unit cells, the individual building blocks, are very, very small—a few microns each. I recently asked my graduate students to create a demo big enough to be visible, so I could show it at seminars. They wrote me an object about 6 millimeters by 6 millimeters by about 100 microns tall. It took them about a week just to write the polymer, never mind the ribbon deposition and all the other steps.

    The demo piece looks like a little white square from the top, until you hold it up to the light. Then a rainbow of colors play across its surface, and it looks like a fine opal. That’s because the nanolattices and the opals are both photonic crystals, which means that their unit cells are the right size to interact with light. Synthetic three-dimensional photonic crystals are relatively hard to make, but they could be extremely useful as high-speed switches for fiber-optic networks.

    Our goal is to figure out a way to mass produce nanostructures that are big enough to see. The possibilities are endless. You could make a soft contact lens that can’t be torn, for example. Or a very lightweight, very safe biocompatible material that could go into someone’s body as a scaffold on which to grow cells. Or you could use semiconductors to build 3-D logic circuits. We’re working with Assistant Professor of Applied Physics and Materials Science Andrei Faraon [BS ’04] to try to figure out how to simultaneously write a whole bunch of things that are all 1 centimeter by 1 centimeter.

    Q: How did you get into this line of work? What got you started?

    A: When I first got to Caltech, I was working on metallic nanopillars. That was my bread and butter. Nanopillars are about 50 nanometers to 1 micron in diameter, and about three times taller than their width. They were what we used to demonstrate, for example, that smaller becomes stronger—the pillars were stronger than the bulk metal by an order of magnitude, which is nothing to laugh at.

    Nanopillars are awesome, but you can’t build anything out of them. And so I always wondered if I could use something like them as nano-LEGOs and construct larger objects, like a nano-Eiffel Tower. The question I asked myself was if each individual component had that very, very high strength, would the whole structure be incredibly strong? That was always in the back of my mind. Then I met some people at DARPA (Defense Advanced at HRL (formerly Hughes Research Laboratories) who were interested in some similar questions, specifically about using architecture in material design. My HRL colleagues were making microscale structures called micro-trusses, so we started a very successful DARPA-funded collaboration to make even smaller trusses with unit cells in the micron range. These structures were still far too big for my purposes, but they brought this work closer to reality.

    See the full article here.

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    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
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  • richardmitnick 2:14 pm on January 19, 2015 Permalink | Reply
    Tags: , , Nanotechnology   

    From ICL: “Scientists use “pen and ink” to control how materials interact with light” 

    Imperial College London
    Imperial College London

    19 January 2015
    Sam Wong

    1

    Threatened with extinction by biros and computers, the nib pen could be set to make an unexpected comeback in the field of nanotechnology.

    Scientists at Imperial College London have developed a way to manipulate the optical properties of polymers on a tiny scale by drawing patterns with a solvent “ink”, allowing much more precise control over how these materials interact with light.

    The technique marks a new approach to creating “metamaterials” – materials with complex internal structures on scales smaller than the wavelength of the light they interact with, resulting in unusual effects.

    It could have applications in all kinds of devices that emit, detect and control light, such as LEDs and lasers, photodiodes, and routers and couplers.

    The research, which was funded by the Engineering and Physical Sciences Research Council, is published in Nature Communications.

    Polymers – the main constituent of plastics – are made of many small molecular repeat units linked together to form chains. Some polymers, referred to as conjugated polymers or polymer semiconductors, are functional optoelectronic materials, meaning for example that they can absorb and emit light.

    The researchers used a tiny pen to draw patterns on a thin film of polymer semiconductor with a solvent. The solvent changes the shape of a selection of chain segments from a disordered state, like cooked spaghetti, to ordered rigid strands, like uncooked spaghetti. Similar naturally occurring changes in certain biological polymers – specifically proteins – can lead to undesirable disease states but here the changes are deliberately induced and beneficial.

    This change in the polymer physical structure alters the way the material interacts with light, changing its refractive index – the amount that light is bent upon entering the material – as well as the colour of light it emits.

    The new nib pen (or more commonly termed dip-pen) approach allows scientists to alter these properties on a much smaller scale than they could before, over distances shorter than the wavelength of light. The researchers expect this will make it possible to build a variety of novel structures leading to new and more efficient devices.

    One example might be to make tiny LEDs that emit light in one direction only, rather than across a broad range of angles, thereby offering the prospect of compact light source arrays for medical diagnostic applications.

    Professor Donal Bradley, Director of the Centre for Plastic Electronics at Imperial College London, who led the research, said: “Usually we use lenses or mirrors to change the direction of light. This method lets us manipulate a light source itself to tightly control the direction of light that it emits. The material adopts the desired structure naturally – it just requires a little encouragement to do so.”

    Aleksandr Perevedentsev, a PhD student who worked on the study, said: “Among other things, this technique essentially allows us to write optical fibers into a thin polymer film, and thus make components that are easy to integrate into devices. It’s very new at the moment, but opens up a lot of possibilities for useful applications. In the process of developing this technique we’ve also began to unravel fundamental questions, such as: can we, in principle, modify the physical structure of a single polymer chain or is an ensemble of chains required for stable structuring? The answer affects the resolution limit of our dip-pen patterning approach and pushes our understanding of these materials beyond the current limits.”

    Dr Paul Stavrinou, who led the underpinning theoretical and modeling activity, added: “The ability to pattern at sub-wavelength scales now allows us to manipulate, within the material, the spatial distribution of electromagnetic energy at this length scale. That we achieve this with help from the material itself is the key to achieving more complex photonic patterns.”

    The picture shows a 6 x 6 µm confocal photoluminescence microscopy image of a conjugated polymer thin film, showing a stripe drawn with a solvent ink that modifies the shape of the polymer chains. This change in structure modifies the optical properties relative to the rest of the film, notably the wavelength of light it emits and the refractive index.

    See the full article here.

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    Imperial College London

    Imperial College London is a science-based university with an international reputation for excellence in teaching and research. Consistently rated amongst the world’s best universities, Imperial is committed to developing the next generation of researchers, scientists and academics through collaboration across disciplines. Located in the heart of London, Imperial is a multidisciplinary space for education, research, translation and commercialisation, harnessing science and innovation to tackle global challenges.

     
  • richardmitnick 5:33 am on January 16, 2015 Permalink | Reply
    Tags: , , , Nanotechnology   

    From MIT: “MIT team enlarges brain samples, making them easier to image” 


    MIT News

    January 15, 2015
    Anne Trafton | MIT News Office

    New technique enables nanoscale-resolution microscopy of large biological specimens.

    temp

    Beginning with the invention of the first microscope in the late 1500s, scientists have been trying to peer into preserved cells and tissues with ever-greater magnification. The latest generation of so-called “super-resolution” microscopes can see inside cells with resolution better than 250 nanometers.

    A team of researchers from MIT has now taken a novel approach to gaining such high-resolution images: Instead of making their microscopes more powerful, they have discovered a method that enlarges tissue samples by embedding them in a polymer that swells when water is added. This allows specimens to be physically magnified, and then imaged at a much higher resolution.

    This technique, which uses inexpensive, commercially available chemicals and microscopes commonly found in research labs, should give many more scientists access to super-resolution imaging, the researchers say.

    “Instead of acquiring a new microscope to take images with nanoscale resolution, you can take the images on a regular microscope. You physically make the sample bigger, rather than trying to magnify the rays of light that are emitted by the sample,” says Ed Boyden, an associate professor of biological engineering and brain and cognitive sciences at MIT.

    Boyden is the senior author of a paper describing the new method in the Jan. 15 online edition of Science. Lead authors of the paper are graduate students Fei Chen and Paul Tillberg.

    Physical magnification

    Most microscopes work by using lenses to focus light emitted from a sample into a magnified image. However, this approach has a fundamental limit known as the diffraction limit, which means that it can’t be used to visualize objects much smaller than the wavelength of the light being used. For example, if you are using blue-green light with a wavelength of 500 nanometers, you can’t see anything smaller than 250 nanometers.

    “Unfortunately, in biology that’s right where things get interesting,” says Boyden, who is a member of MIT’s Media Lab and McGovern Institute for Brain Research. Protein complexes, molecules that transport payloads in and out of cells, and other cellular activities are all organized at the nanoscale.

    Scientists have come up with some “really clever tricks” to overcome this limitation, Boyden says. However, these super-resolution techniques work best with small, thin samples, and take a long time to image large samples. “If you want to map the brain, or understand how cancer cells are organized in a metastasizing tumor, or how immune cells are configured in an autoimmune attack, you have to look at a large piece of tissue with nanoscale precision,” he says.

    To achieve this, the MIT team focused its attention on the sample rather than the microscope. Their idea was to make specimens easier to image at high resolution by embedding them in an expandable polymer gel made of polyacrylate, a very absorbent material commonly found in diapers.

    Before enlarging the tissue, the researchers first label the cell components or proteins that they want to examine, using an antibody that binds to the chosen targets. This antibody is linked to a fluorescent dye, as well as a chemical anchor that can attach the dye to the polyacrylate chain.

    Once the tissue is labeled, the researchers add the precursor to the polyacrylate gel and heat it to form the gel. They then digest the proteins that hold the specimen together, allowing it to expand uniformly. The specimen is then washed in salt-free water to induce a 100-fold expansion in volume. Even though the proteins have been broken apart, the original location of each fluorescent label stays the same relative to the overall structure of the tissue because it is anchored to the polyacrylate gel.

    “What you’re left with is a three-dimensional, fluorescent cast of the original material. And the cast itself is swollen, unimpeded by the original biological structure,” Tillberg says.

    The MIT team imaged this “cast” with commercially available confocal microscopes, commonly used for fluorescent imaging but usually limited to a resolution of hundreds of nanometers. With their enlarged samples, the researchers achieved resolution down to 70 nanometers. “The expansion microscopy process … should be compatible with many existing microscope designs and systems already in laboratories,” Chen adds.

    Large tissue samples

    Using this technique, the MIT team was able to image a section of brain tissue 500 by 200 by 100 microns with a standard confocal microscope. Imaging such large samples would not be feasible with other super-resolution techniques, which require minutes to image a tissue slice only 1 micron thick and are limited in their ability to image large samples by optical scattering and other aberrations.

    “The exciting part is that this approach can acquire data at the same high speed per pixel as conventional microscopy, contrary to most other methods that beat the diffraction limit for microscopy, which can be 1,000 times slower per pixel,” says George Church, a professor of genetics at Harvard Medical School who was not part of the research team.

    “The other methods currently have better resolution, but are harder to use, or slower,” Tillberg says. “The benefits of our method are the ease of use and, more importantly, compatibility with large volumes, which is challenging with existing technologies.”

    The researchers envision that this technology could be very useful to scientists trying to image brain cells and map how they connect to each other across large regions.

    “There are lots of biological questions where you have to understand a large structure,” Boyden says. “Especially for the brain, you have to be able to image a large volume of tissue, but also to see where all the nanoscale components are.”

    While Boyden’s team is focused on the brain, other possible applications for this technique include studying tumor metastasis and angiogenesis (growth of blood vessels to nourish a tumor), or visualizing how immune cells attack specific organs during autoimmune disease.

    The research was funded by the National Institutes of Health, the New York Stem Cell Foundation, Jeremy and Joyce Wertheimer, the National Science Foundation, and the Fannie and John Hertz Foundation.

    See the full article here.

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