Nano-LEDs emit full visible spectrum of light

Nano-LEDs emit full visible spectrum of light

  2:04:00 AM    Science Lover

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Physicists through Taiwan possess designed along with fabricated nano-sized light-emitting diodes (LEDs) that emit light source spanning your whole visible spectrum. Although all the tiny full-color LEDs aren't meant for commercial lighting fixtures applications, they must be useful within high-resolution microscopy and additionally subwavelength photolithography.

A single nanodisk-nanorod LED viewed with a field-emission
scanning electron microscope. (Right) Some colors of light
emissions from nanodisk-nanorod LEDs - violet, blue, cyan,
green, and yellow - viewed with an optical microscope.
Image credit: Lu, et al. ©2011 American Institute of Physics

A researchers, Yu-Jung Lu, et ing., from National Tsing-Hua University or college in Hsinchu, Taiwan, have published their study to the nano-LEDs in a the latest issue of Applied Physics Letters.

The new nano-LEDs have a very good unique structure that is made of 40-nm-thick nanodisks sandwiched involving two layers of nanorods, creating a nanodisk-in-nanorod geometry. The nanodisks are made from indium gallium nitride (InGaN), a semiconducting material that is definitely widely used in LEDs and solar cells, while the nanorods are made from gallium nitride (GaN). Having said that, InGaN LEDs capable of emitting light belonging to the entire visible spectrum haven’t been achieved until now.



“The InGaN/GaN nanodisk/nanorod structure is just like a well-known quantum well structure, but in a lower dimensionality (reduction during lateral sizes), ” coauthor Shangjr Gwo, your physics professor at National Tsing-Hua University, told PhysOrg. com. “The InGaN nanodisks sandwiched regarding the p- and n-GaN regions be working as the full-color visible-light emitters anytime electrons and holes are injected through the p-n junction at a forward bias voltage. The electroluminescent light hails from the electron-hole recombination during the InGaN nanodisks. ”

As being the researchers explained, the essential to achieving full-color LEDs was first overcoming large lattice traces, which degrade long-wavelength emissions. The InGaN/GaN nanorod method resolves this issue as a consequence of strain relaxation in all the nanostructured geometry.

The researchers hope the full-color nano-LEDs work extremely well in high-resolution imaging techniques which could resolve ultrasmall subwavelength features of objects. To do this approach, these techniques must overcome the diffraction limit, the fundamental limit on imaging resolution as a result of the spreading out – and / or “diffraction” – of surf. Imaging techniques can find their way this limit by employing evanescent waves, which reveal home elevators objects’ subwavelength features, and decay exponentially away through the object. Due to the short range of the evanescent waves, imaging techniques that detect them depend on near-field optics.

One of such techniques is scanning near-field optical microscopy (SNOM), which operates on the all tiny probe to acquire and retrieve evanescent ocean. One of the biggest challenges in SNOM gets a light source that could be small and versatile enough to function on this probe, and that’s where new nano-LEDs come for. While previous research has demonstrated learn about using nano-LEDs on your probes, this is to start with that a nano-LED using a full-color range has already been available.

“For microscopy, we will use the nano-LED as being a localized excitation light source with a chosen wavelength to selectively inspire specific fluorescent molecules, ” Lu reported.

In their study, the researchers experimentally demonstrated making use of the nanodisk-in-nanorod LEDs for subwavelength photolithography, in which light is used to generate a pattern on a light-sensitive materials. They predict that, by way of fabricating the nano-LEDs upon the SNOM probe suggestions, they could achieve far better spatial control for near future subwavelength photolithography.

“For a applications of photolithography, the freedom of utilizing nano-LEDs at any wavelength broadens the options of photoresist and consists of the control of most of the photo-response, ” Lu reported.

More information: Yu-Jung Lu, et ing. “Single InGaN nanodisk lumination emitting diodes as full-color subwavelength lighting sources. ” Applied Physics Albhabets. DOI: 10. 1063/1. 3597211.

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Electron Microscopy: New Type of Genetic Tag Illuminates Life in Never-Before-Seen Detail

Electron Microscopy: New Type of Genetic Tag Illuminates Life in Never-Before-Seen Detail

  11:01:00 PM    Science Lover

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By modifying a protein from a plant that is much favored by science, researchers at the University of California, San Diego School of Medicine and colleagues have created a new type of genetic tag visible under an electron microscope, illuminating life in never-before-seen detail.

Confocal fluorescence images of miniSOG-targeted 
endoplasmic reticulum (A), Rab5a (B), zyxin (C), 
tubulin (D), ²-actin (E), ±-actinin (F), mitochondria
(G), and histone 2B (H) in HeLa cells; scale bars, 
10 µm. (Credit: Xiaokun Shu, Varda Lev-Ram, Thomas 
J. Deerinck, Yingchuan Qi, Ericka B. Ramko, Michael W. 
Davidson, Yishi Jin, Mark H. Ellisman, Roger Y. Tsien.
A Genetically Encoded Tag for Correlated Light and 
Electron Microscopy of Intact Cells, Tissues, and 
Organisms. PLoS Biology, 2011; 9 (4): e1001041 
DOI: 10.1371/journal.pbio.1001041)

Led by Nobel laureate Roger Tsien, PhD, Howard Hughes Medical Institute investigator and UCSD professor of pharmacology, chemistry and biochemistry, a team of scientists radically re-engineered a light-absorbing protein from the flowering cress plant Arabidopsis thaliana. When exposed to blue light, the altered protein produces abundant singlet oxygen, a form of molecular oxygen that can be made visible by electron microscopy (EM).

The findings are published in the online, open access journal PLoS Biology.

Tsien was co-winner of the 2008 Nobel Prize in chemistry for his role in helping develop and expand the use of green fluorescent protein (GFP), a protein from jellyfish that is now widely employed in light microscopy to peer inside living cells or whole animals and observe molecules interacting in real-time. Tsien said the development of the small, highly engineered Arabidopsis protein, dubbed "miniSOG," may elevate the abilities of electron microscopy in the same way that GFP and its relatives have made modern light microscopy in biological research much more powerful and useful.


"The big advantage of EM is that it has much higher spatial resolution than light microscopy. You can get up to a hundred-fold higher useful magnification from EM than from light microscopy," said Tsien. The result has been extraordinarily detailed, three-dimensional images of microscopic objects at resolutions measuring in the tens of nanometers, tiny enough to meticulously render the internal anatomy of individual cells. But current EM technologies do not distinguish or highlight individual proteins in these images. Although individual proteins can be tagged with GFP or other fluorescent proteins to aid localization by light microscopy, there has been no equivalent technology for the higher-resolution images provided by EM.

To create this ability, the scientists began with a protein from Arabidopsis that absorbs incoming blue light. It's normal function is to trigger biochemical signals that inform the plant how much sunlight it is receiving. "We rationally engineered the protein based on its atomic model so that it changes incoming blue light into a little bit of green fluorescence and a lot of singlet oxygen," said the paper's first author, Xiaokun Shu, now an assistant professor at UC San Francisco. Established methods were then used to convert singlet oxygen production into a tissue stain that the electron microscope can "see." The scientists tested the modified protein's utility as an EM marker by first using it to confirm the locations of several well-understood proteins in mammalian cells, nematodes and rodents, and then used miniSOG to successfully tag two neuronal proteins in mice whose locations had not been known.

Tsien is optimistic that miniSOG will grant new powers to electron microscopy, permitting scientists to pursue answers to questions previously impossible to ask. MiniSOG will especially be useful to scientists who investigate cellular and subcellular structures including neuronal circuits at nanometer resolution in multicellular organisms since previous methods have great difficulty in achieving both efficient labeling and good preservation of the structures under study. While EM can provide much higher useful magnification than light microscopy, EM will not replace light microscopy. "When we use miniSOG, we see the tagged proteins plus the landmarks that we are used to navigating by," said Tsien. "On the other hand, EM has the disadvantage that it gives a snapshot of cells before we killed them (to make the image), whereas light microscopy can show the dynamics in live cells. Each technique has different complementary strengths and weaknesses."

Co-authors of the paper include: Varda Lev-Ram, UCSD Department of Pharmacology; Thomas J. Deerinck, National Center for Microscopy and Imaging Research, Center for Research on Biological Systems, UCSD; Yingchuan Qi and Yishi Jin, Howard Hughes Medical Institute, UCSD and UCSD Division of Biological Science; Ericka B. Ramko and Michael W. Davidson, National High Magnetic Field Laboratory and Department of Biological Science, Florida State University; and Mark H. Ellisman, National Center for Microscopy and Imaging Research, Center for Research on Biological Systems, UCSD and UCSD Department of Neurosciences

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A Shot to the Heart: Nanoneedle Delivers Quantum Dots to Cell Nucleus

A Shot to the Heart: Nanoneedle Delivers Quantum Dots to Cell Nucleus

  9:46:00 AM    Science Lover

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Getting an inside look at the center of a cell can be as easy as a needle prick, thanks to University of Illinois researchers who have developed a tiny needle to deliver a shot right to a cell's nucleus.

University of Illinois researchers developed a nanoneedle that releases quantum dots directly into the nucleus of a living cell when a small electrical charge is applied. The quantum dots are tracked to gain information about conditions inside the nucleus. (Credit: Image courtesy Min-Feng Yu)

Understanding the processes inside the nucleus of a cell, which houses DNA and is the site for transcribing genes, could lead to greater comprehension of genetics and the factors that regulate expression. Scientists have used proteins or dyes to track activity in the nucleus, but those can be large and tend to be sensitive to light, making them hard to use with simple microscopy techniques.

Researchers have been exploring a class of nanoparticles called quantum dots, tiny specks of semiconductor material only a few molecules big that can be used to monitor microscopic processes and cellular conditions. Quantum dots offer the advantages of small size, bright fluorescence for easy tracking, and excellent stability in light.

"Lots of people rely on quantum dots to monitor biological processes and gain information about the cellular environment. But getting quantum dots into a cell for advanced applications is a problem," said professor Min-Feng Yu, a professor of mechanical science and engineering.

Getting any type of molecule into the nucleus is even trickier, because it's surrounded by an additional membrane that prevents most molecules in the cell from entering.

Yu worked with fellow mechanical science and engineering professor Ning Wang and postdoctoral researcher Kyungsuk Yum to develop a nanoneedle that also served as an electrode that could deliver quantum dots directly into the nucleus of a cell -- specifically to a pinpointed location within the nucleus. The researchers can then learn a lot about the physical conditions inside the nucleus by monitoring the quantum dots with a standard fluorescent microscope.

"This technique allows us to physically access the internal environment inside a cell," Yu said. "It's almost like a surgical tool that allows us to 'operate' inside the cell."

The group coated a single nanotube, only 50 nanometers wide, with a very thin layer of gold, creating a nanoscale electrode probe. They then loaded the needle with quantum dots. A small electrical charge releases the quantum dots from the needle. This provides a level of control not achievable by other molecular delivery methods, which involve gradual diffusion throughout the cell and into the nucleus.

"Now we can use electrical potential to control the release of the molecules attached on the probe," Yu said. "We can insert the nanoneedle in a specific location and wait for a specific point in a biologic process, and then release the quantum dots. Previous techniques cannot do that."

Because the needle is so small, it can pierce a cell with minimal disruption, while other injection techniques can be very damaging to a cell. Researchers also can use this technique to accurately deliver the quantum dots to a very specific target to study activity in certain regions of the nucleus, or potentially other cellular organelles.

"Location is very important in cellular functions," Wang said. "Using the nanoneedle approach you can get to a very specific location within the nucleus. That's a key advantage of this method." The new technique opens up new avenues for study. The team hopes to continue to refine the nanoneedle, both as an electrode and as a molecular delivery system.

They hope to explore using the needle to deliver other types of molecules as well -- DNA fragments, proteins, enzymes and others -- that could be used to study a myriad of cellular processes.

"It's an all-in-one tool," Wang said. "There are three main types of processes in the cell: chemical, electrical, and mechanical. This has all three: It's a mechanical probe, an electrode, and a chemical delivery system."

The team's findings will appear in the Oct. 4 edition of the journal Small. The National Institutes of Health and the National Science Foundation supported this work.

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Microscope 'Sees' Atoms for First Time

Microscope 'Sees' Atoms for First Time

  9:16:00 PM    Science Lover

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UCLA researchers report in the April 30 edition of the journal Cell that they have imaged a virus structure at a resolution high enough to effectively "see" atoms, the first published instance of imaging biological complexes at such a resolution.

Cover of the journal Cell showing an artistic 
representation of a Cryo-EM 3-D reconstruction 
of an aquareovirus, the colors are added to show 
contrast between various structures in the virus. 
(Credit: Image courtesy of UCLA)

The research team, led by Hong Zhou, UCLA professor of microbiology, immunology and molecular genetics, used cryo-electron microscopy to image the structure at 3.3 angstroms. An angstrom is the smallest recognized division of a chemical element and is about the distance between the two hydrogen atoms in a water molecule.

The study, the researchers say, demonstrates the great potential of cryo-electron microscopy, or Cryo-EM, for producing extremely high-resolution images of biological samples in their native environment.

"This is the first study to determine an atomic resolution structure through Cryo-EM alone," said Xing Zhang, a postdoctoral candidate in Zhou's group and lead author of the Cell paper. "By proving the effectiveness of this microscopy technique, we have opened the door to a wide variety of biological studies."

With traditional light microscopy, a magnified image of a sample is viewed through a lens. Some samples, however, are too small to diffract visible light (in the 500 to 800 nm range, or 5,000 to 8,000 angstroms) and therefore cannot be seen. To image objects at the sub-500 nm scale, scientists must turn to other tools, such as atomic force microscopes, which use an atomically thin tip to generate an image by probing a surface, in much the same way a blind person reads by touching Braille lettering.

With electron microscopy, another sub-500 nm technology, a beam of electrons is fired at a sample, passing through empty areas and bouncing off dense areas. A digital camera reads the path of the electrons passing through the sample to create a two-dimensional projection image of the sample. By repeating this process at hundreds of different angles, a computer can construct a three-dimensional image of the sample at a very high resolution.

Zhou is faculty director of the Electron Imaging Center for Nanomachines (EICN) at UCLA's California NanoSystems Institute, which is using cryo-electron microscopy to create 3-D reconstructions of nano-machineries, nano-devices and biological nano-structures, such as viruses.

Structurally accurate 3-D reconstructions of biological complexes are possible with cryo-electron microscopy because the samples are flash frozen, which allows them to be imaged in their native environment, and the microscope operates in a vacuum, because electrons travel better in that environment. The Cell paper focused on a structural study of the aquareovirus, a non-envelope virus that causes disease in fish and shellfish, in an effort to better understand how non-envelope viruses infect host cells.

"We are extremely excited about the recent breakthrough achieved by Hong Zhou and his team at the EICN lab," said Leonard H. Rome, senior associate dean for research at the David Geffen School of Medicine at UCLA and associate director of the California NanoSystems Institute. "The ability to understand the structure of viruses at an atomic level will open avenues for manipulating them for use in drug delivery and propel numerous innovations in treatments of diseases. UCLA is fortunate to have such specialized instrumentation and the expertise of Professor Zhou and his team to take advantage of these marvelous microscopes."

Viruses can be classed into two types: envelope and non-envelope. Envelope viruses, which include influenza and HIV, are surrounded by an envelope-like membrane which the virus uses to fuse with and infect a host cell. Non-envelope viruses lack this membrane and instead use a protein to fuse with and infect cells. This process was poorly understood until Zhou's study.

"Through better knowledge of virus structures, we hope to engineer medications in three ways," Zhou said. "If we understand how viruses work, first we can identify small molecules or drugs that block their infection; second, we can engineer ultra-stable and non-infectious virus-like particles as optimal vaccines; and third, we can alter their characteristics so that instead of delivering a disease, viruses could deliver medications.

"Indeed, we are working with UCLA physicians and engineers to engineer viruses for gene therapy and drug delivery," he said. "In essence, we hope to take advantage of millions of years of evolution that have made viruses incredibly effective delivery platforms."

From the high-resolution 3-D images produced with the cryo-electron microscopy, Zhou's group was able to determine that the aquareovirus employs a priming stage to accomplish cell infection. In its dormant state, the virus has a protective protein covering, which it sheds during priming. Once the outer shell has been shed, the virus is in a primed state and is ready to use a protein called an "insertion finger" to infect a cell.

The team's study ushers in a new era of structural biology for understanding important biological processes. The group was able to discover this functionality because of the accurate structural model produced through cryo-electron microscopy. In addition to producing a high-resolution 3-D image of samples, the technology allows samples to be imaged in their native environment, so the structural model is faithful to the original sample. From a technical point of view, this work also demonstrates the power of cryo-electron microscopy in obtaining 3-D structures of biological complexes without needing to grow a crystal.

The California NanoSystems Institute at UCLA is an integrated research center operating jointly at UCLA and UC Santa Barbara whose mission is to foster interdisciplinary collaborations for discoveries in nanosystems and nanotechnology; train the next generation of scientists, educators and technology leaders; and facilitate partnerships with industry, fueling economic development and the social well-being of California, the United States and the world. The CNSI was established in 2000 with $100 million from the state of California and an additional $250 million in federal research grants and industry funding. At the institute, scientists in the areas of biology, chemistry, biochemistry, physics, mathematics, computational science and engineering are measuring, modifying and manipulating the building blocks of our world -- atoms and molecules. These scientists benefit from an integrated laboratory culture enabling them to conduct dynamic research at the nanoscale, leading to significant breakthroughs in the areas of health, energy, the environment and information technology.

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Spontaneous Assembly: A New Look At How Proteins Assemble And Organize Themselves Into Complex Patterns

Spontaneous Assembly: A New Look At How Proteins Assemble And Organize Themselves Into Complex Patterns

  9:28:00 PM    Science Lover

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Self-assembling and self-organizing systems are the Holy Grails of nanotechnology, but nature has been producing such systems for millions of years. A team of scientists has taken a unique look at how thousands of bacterial membrane proteins are able to assemble into clusters that direct cell movement to select chemicals in their environment. Their results provide valuable insight into how complex periodic patterns in biological systems can be generated and repaired.

PALM is an an ultrahigh-precision visible light microscopy
technique that enables scientists to photo-actively fluoresce
and image individual proteins. This PALM composite of an
E.coli bacterial cell shows the organization of proteins in
the chemotaxis signaling network.
(Credit: Image courtesy of DOE/Lawrence Berkeley National Laboratory)

Researchers with Berkeley Lab, the University of California (UC) Berkeley, the Howard Hughes Medical Institute, and Princeton University, used an ultrahigh-precision visible light microscopy technique called PALM - for Photo-Activated Localization Microscopy - to show that the chemotaxis network of signaling proteins in E.coli bacteria is able to spontaneously form from clusters of proteins without being actively distributed or attached to specific locations in cells. This simple organizational mechanism - dubbed “stochastic self-assembly” - is related to the self-organizing patterns first described in 1952 by the British computer scientist Alan Turing.

“It is not widely appreciated that complex periodic patterns can spontaneously emerge from simple mechanisms, but that is probably what is happening here,” said Jan Liphardt, the biophysicist who led this research.

Liphardt holds a joint appointment with Berkeley Lab’s Physical Biosciences Division and UC Berkeley’s Physics Department. He is the principal author of a paper now available PLoS Biology. Co-authoring the paper with Liphardt were Derek Greenfield, Ann McEvoy, Hari Shroff, Gavin Crooks, Ned Wingreen and Eric Betzig.

Key to a cell’s survival is the manner in which its critical components - proteins, lipids, nucleic acids, etc. - are arranged. For cells to thrive, the organization of these components must be optimized for their respective activities and also reproducible for succeeding generations of cells. Eukaryotic cells feature distinct subcellular structures, such as membrane-bound organelles and protein transport systems, whose complex organization is readily apparent. However, there is also complex spatial organization to be found within prokaryotic cells, such as rod-shaped bacteria like E. coli.

“It has remained somewhat mysterious how bacteria are able to organize and spatially segregate their interiors and membranes,” said Liphardt. “Two cells which are biochemically identical can have very different behaviors, depending upon their spatial organization. With new technologies such as PALM, we are able to see exactly how cells are organized and relate spatial organization with biological function.”

PALM and the Chemotaxis Network

In the PALM technique, target proteins are labeled with tags that fluoresce when activated by weak ultraviolet light. By keeping the intensity of this light sufficiently low, researchers can photoactivate individual proteins.

“Since individual proteins are imaged one at a time, we can localize and count them, and then computationally assemble the locations of all proteins into a composite, high-precision image,” said Liphardt. “With other technologies, we have to choose between observing large clusters or observing single proteins. With PALM, we can examine a cell and see single proteins, protein dimers, and so forth, all the way up to large clusters containing thousands of proteins. This enables us to see the relative organization of individual proteins within clusters and at the same time see how clusters are arranged with respect to one-another.”

Liphardt and his colleagues applied the PALM technique to the E.coli chemotaxis network of signaling proteins, which direct the movement of the bacteria towards or away from sugars, amino acids, and many other soluble molecules in response to environmental cues. The E.coli chemotaxis network is one of the best-understood of all biological signaling systems and is a model for studying bacterial spatial organization because its components display a nonrandom, periodic distribution in the cell membrane.

“Chemotaxis proteins cluster into large sensory complexes that localize to the poles of the bacterial cell,” Liphardt said. “We wanted to understand how these clusters form, what controls their size and density, and how the cellular location of clusters is robustly maintained in growing and dividing cells.”

Using PALM, Liphardt and his colleagues mapped the cellular locations of three proteins central to the chemotaxis signaling network - Tar, CheY and CheW - with a mean precision of 15 nanometers. They found that cluster sizes were distributed with no one size being “characteristic.” For example, a third of the Tar proteins were part of smaller lateral clusters and not of the large polar clusters. Analysis of the relative cellular locations of more than one million individual proteins from 326 cells determined that they are not actively distributed or attached to specific locations in cells, as had been hypothesized.

“Instead,” said Liphardt, “random lateral protein diffusion and protein-protein interactions are probably sufficient to generate the observed complex, ordered patterns. This simple stochastic self-assembly mechanism, which can create and maintain periodic structures in biological membranes without direct cytoskeletal involvement or active transport, may prove to be widespread in both prokaryotic and eukaryotic cells.”

Liphardt and his research group are now applying PALM to signaling complexes in eukaryotic membranes to see how widespread is stochastic self-assembly in nature. Given that biological systems are nature’s version of nanotechnology, the demonstration that stochastic self-assembly is capable of organizing thousands of proteins into complex and reproducible patterns holds promise for a wide range of applications in nanotechnology, including the fabrication of nanodevices and the development of nanoelectronic circuits.

This work was funded by the U.S. Department of Energy’s Office of Science, Energy Biosciences Program, the Sloan and Searle Foundations, and National Institutes of Health grants.

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World's smallest periscopes

World's smallest periscopes

  2:05:00 AM    Science Lover

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A team of scientists has designed the world's tiniest version of the periscope to peer at cells and other micro-organisms from all the sides at once.

"With an off-the-shelf laboratory microscope you only see cells from one side, the top," said Chris Janetopoulos, assistant professor of biological sciences at the Vanderbilt University (VU) and member of the research team.

"Now not only can we see the tops of cells, we can view their sides as well - something biologists almost never see," he added.

The researchers dubbed their devices "mirrored pyramidal wells". They consist of pyramidal-shaped cavities moulded into silicon whose interior surfaces are coated with a reflective layer of gold or platinum.

They are about the width of a human hair and can be made in a range of sizes to view different-sized objects. When a cell is placed in such a well and viewed with a regular microscope, the researcher can see several sides simultaneously.

"This technology is exciting because these mirrored wells can be made at very low cost, unlike other, more complex methods for 3D microscopy," said VU assistant professor Kevin Seale.

"This could easily become as ubiquitous as the microscope slide and could replace more expensive methods currently used to position individual cells," said Ron Reiserer, lab manager at the Vanderbilt Institute for Integrative Biosystems Research and Education (VIIBRE) who helped design the protocol used to make the micropyramids.

The Vanderbilt group is not the first to make microscopic pyramidal wells, but it is the first to apply them to make 3D images of microorganisms, said a Vanderbilt release.

These findings were published in the Journal of Microscopy.

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