Lab has made new discoveries at the cellular, molecular levels about how the eye processes light

 

The image shows a Drosophila compound eye stained with antibodies that recognize TRP (magenta) and anti-XPORT-B (green). Credit: Image courtesy of University of California - Santa Barbara An animal's ability to perceive light incorporates many complex processes. Now, researchers in Craig Montell's lab at UC Santa Barbara have used fruit flies and mice to make novel discoveries about sensory physiology at both cellular and molecular levels that are important for light processing. Their most recent findings, which improve the scientific understanding of the signaling cascade necessary for phototransduction -- the process by which light is converted into electrical signals in the photoreceptor cells in the retina of the eye -- appear today in the journal Cell Reports. More than 25 years ago, Montell discovered TRP channels, which allow animals to detect light, chemicals in food, mechanical force and changes in temperature. These proteins act at the cell surface, but very little was known about the mechanism by which they are transported to the cell surface. Until now, scientists knew of only one protein, XPORT, that was a "helper protein" involved in getting TRP proteins to the outer surface of cells. However, using the fruit fly (Drosophila melanogaster), postdoctoral fellow Zijing Chen found that the XPORT gene in fact encodes two unrelated molecular chaperone proteins -- XPORT-A and XPORT-B -- and both are critical for moving TRP channels out of their synthesis site inside the cells. "This discovery is important because if TRP proteins don't get to the cell surface, they are not going to be able to function, and the animals will not see properly," said Montell, a professor in UCSB's Department of Molecular, Cellular, and Developmental Biology. "The light that activates the photoreceptor cells is not directly activating TRP but rather a light sensor called rhodopsin," Montell explained. This primary pigment found in photoreceptor cells is extremely sensitive to light. "What's interesting is that both XPORT-A and XPORT-B are required for getting rhodopsin and TRP to the cell surface," he added. According to Montell, mutations in TRP have been linked to neurodegenerative disorders, pain syndromes, neuropathies and bone deformations. Understanding the intricacies of TRP function is the first step toward identifying drugs that could affect their activity and one day be used as therapeutic targets. TRP channels also function in light sensation in mammals, including humans. However, they do not have central roles in rods or cones, which allow mammals to see images. Rather, TRPs in mammals function in a third class of photoreceptor cell, intrinsically photosensitive retinal ganglion cells (ipRGCs). The ipRGCs are necessary for setting circadian rhythms by light as well as pupillary constriction in response to light. The ipRGCs are activated by bright light and also stimulated through pathways initiated in rods and cones. However, the pathways and molecules that allow rods and cones to stimulate ipRGCs indirectly by light have been poorly understood. In another paper, published in the journal Molecular Biology of the Cell, Marquis Walker, a postdoctoral fellow working with Montell, used mice to explore the indirect pathway for activating ipRGCs. They found that a protein called retinal degeneration B2 (RDGB2) was critical in connector neurons called amacrine cells located in the inner retina, between the rods and cones and ipRGCs. "This study reveals the first molecular player that is important in sending signals from the rods into the ipRGCs," Montell said. "This indirect communication allows the ipRGCs to respond to dim light that activates rod photoreceptor cells." The first RDGB protein was identified in the eye of the fruit fly and Montell and Walker wanted to determine its role in the mammalian retina. They found that RDGB2 in mice is required for normal circadian activity and pupil constriction -- but only in dim light. "Understanding all the cells, pathways and molecules is necessary if you want to develop therapies for jet lag or problems related to circadian rhythm," Montell said. "We need to understand the whole cellular and molecular mechanism in order to ultimately come up with new approaches and drugs to deal with these issues." Story Source: The above post is reprinted from materials provided by University of California - Santa Barbara. The original item was written by Julie Cohen. Note: Materials may be edited for content and length. Journal Reference: zijing Chen, Hsiang-Chin Chen, Craig Montell. TRP and Rhodopsin Transport Depends on Dual XPORT ER Chaperones Encoded by an Operon. Cell Reports, October 2015 DOI: 10.1016/j.celrep.2015.09.018 http://www.sciencedaily.com/releases/2015/10/151008152822.htm

Light-based memory chip is the first ever to store data permanently

 

A schematic of the device, showing its structure and the propagation of light through it. Credit: Image courtesy of University of Oxford The world's first entirely light-based memory chip to store data permanently has been developed by material scientists at Oxford University in collaboration with scientists at Karlsruhe, Munster and Exeter. The device, which makes use of materials used in CDs and DVDs, could help dramatically improve the speed of modern computing. Today's computers are held back by the relatively slow transmission of electronic data between the processor and the memory. 'There's no point using faster processors if the limiting factor is the shuttling of information to-and-from the memory -- the so-called von-Neumann bottleneck,' explains Professor Harish Bhaskaran, who led the research. 'But we think using light can significantly speed this up.' Simply bridging the processor-memory gap with photons isn't efficient, though, because of the need to convert them back into electronic signals at each end. Instead, memory and processing capabilities would need be light-based too. Researchers have tried to create this kind of photonic memory before, but the results have always been volatile, requiring power in order to store data. For many applications -- such as computer disk drives -- it's essential to be able to store data indefinitely, with or without power. Now, an international team of researchers including researchers from Oxford University's Department of Materials has produced the world's first all-photonic nonvolatile memory chip. The new device uses the phase-change material Ge2Sb2Te5 (GST) -- the same as that used in rewritable CDs and DVDs -- to store data. This material can be made to assume an amorphous state, like glass, or a crystalline state, like a metal, by using either electrical or optical pulses. In a paper published in Nature Photonics, the researchers describe the device they've created, which uses a small section of GST on top of a silicon nitride ridge, known as a waveguide, to carry light. The team has shown that intense pulses of light sent through the waveguide can carefully change the state of the GST. An intense pulse causes it to momentarily melt and quickly cool, causing it to assume an amorphous structure; a slightly less-intense pulse can put it into an crystalline state. Later, when light with much lower intensity is sent through the waveguide, the difference in the state of the GST affects how much light is transmitted. The team can measure that difference to identify its state -- and in turn read off the presence of information in the device as a 1 or 0. 'This is the first ever truly non-volatile integrated optical memory device to be created,' explains Clarendon Scholar and DPhil student Carlos Ríos, one of the two lead authors of the paper. 'And we've achieved it using established materials that are known for their long-term data retention -- GST remains in the state that it's placed in for decades.' By sending different wavelengths of light through the waveguide at the same time -- a technique referred to as wavelength multiplexing -- the team also showed that they could use a single pulse to write and read to the memory at the same time. 'In theory, that means we could read and write to thousands of bits at once, providing virtually unlimited bandwidth,' explains Professor Wolfram Pernice of the University of Munster. The researchers have also found that different intensities of strong pulses can accurately and repeatedly create different mixtures of amorphous and crystalline structure within the GST. When lower intensity pulses were sent through the waveguide to read the contents of the device, they were also able to detect the subtle differences in transmitted light, allowing them to reliably write and read off eight different levels of state composition -- from entirely crystalline to completely amorphous. This multi-state capability could provide memory units with more than the usual binary information of 0 and 1, allowing a single bits of memory to store several states or even perform calculations themselves instead of at the processor. 'This is a completely new kind of functionality using proven existing materials,' explains Professor Bhaskaran. 'These optical bits can be written with frequencies of up to one gigahertz and could provide huge bandwidths. This is the kind of ultra-fast data storage that modern computing needs.' Now, the team is working on a number of projects that aim to make use of the new technology. They're particularly interested in developing a new kind of electro-optical interconnect, which will allow the memory chips to directly interface with other components using light, rather than electrical signals. Story Source: The above post is reprinted from materials provided by University of Oxford.Note: Materials may be edited for content and length. Journal Reference: Carlos Ríos, Matthias Stegmaier, Peiman Hosseini, Di Wang, Torsten Scherer, C. David Wright, Harish Bhaskaran, Wolfram H. P. Pernice. Integrated all-photonic non-volatile multi-level memory. Nature Photonics, 2015; DOI:10.1038/nphoton.2015.182 http://www.sciencedaily.com/releases/2015/10/151004112856.htm

Single-crystal phosphors suitable for ultra-bright, high-power white light sources

 

YAG single-crystal phosphor ingot. Credit: Image copyright NIMS Researchers in Japan successfully developed single-crystal phosphors that use a blue LD (laser diode) as an excitation light source, are suitable for ultra-bright, high-power white lighting, and have outstanding temperature characteristics. The Optical Single Crystals Group at National Institute for Materials Science (NIMS) led by Group Leader Kiyoshi Shimamura and Senior Researcher E. Garcia Villora, in collaboration with Tamura Corporation (President, Naoki Tamura) and Koha Co., Ltd. (President, Yasuhiro Nakashima), successfully developed single-crystal phosphors (based on (Y1-xLux)3Al5O12 oxide-garnets) that use a blue LD (laser diode) as an excitation light source, are suitable for ultra-bright, high-power white lighting, and have outstanding temperature characteristics. In line with environmentally conscious efforts to promote power-saving and mercury-free products, white lighting that uses blue LEDs as an excitation light source has grown rapid in popularity in recent years. At the same time, products that use blue LDs as an excitation light source have also been commercialized to meet the needs of certain light-p rojectors and car headlights. These require a high-brightness that is difficult to attain with LED light sources. Due to its optical properties, LD light can be easily collected with a lens or mirror, and it is feasible to focus 100-watt-equivalent LD light on an area as small as several millimeters in diameter. However, as the power density of the LD excitation light increases, the heat generated by the lighting device also increases proportionally. The use of conventional phosphors, with low thermal conductivities and a decreasing internal quantum efficiency with the temperature, requires complex cooling techniques and critically limits the applicable LD power. Further, non-oxide based powder phosphors degrade irreversibly with the temperature. In this study, the developed single-crystal phosphors, grown from the melt by the Czochralski technique, exhibit superior temperature characteristics, overcoming mentioned difficulties. On the one hand, due to the higher thermal conductivity (over two orders of magnitude) they can be cooled much more efficiently, avoiding overheating and enabling downsizing and cost reduction of lighting products. On the other hand, their quantum efficiency does not drop with the temperature, exhibiting an efficiency over 0.9 till 300 °C in either plate or powder form. These two features, high thermal conductivity and quantum efficiency, are so remarkable that when the emission of conventional phosphors is already quenched by the temperature rise, under the same nominal conditions the temperature of single-crystal phosphors barely increases. Thus, in contrast with conventional powder phosphors, single-crystal phosphors will allow the fabrication of brighter and more powerful lighting products. Based on this study, we have already acquired two patents in Japan, and have applied for five additional patents in Japan and abroad. We are aiming at stablishing the growth methods for the efficient mass production of single-crystal phosphors for laser lighting products such as laser projectors and laser headlights by the end of FY2015 in collaboration with Tamura Corporation. Story Source: The above post is reprinted from materials provided by National Institute for Materials Science. Note: Materials may be edited for content and length. National Institute for Materials Science. "Single-crystal phosphors suitable for ultra-bright, high-power white light sources." ScienceDaily. ScienceDaily, 25 August 2015. www.sciencedaily.com/releases/2015/08/150825115150.htm.

Changing the Color of Light

 

The UD research team aims to develop new nanostructures that act like a ratchet to combine the energy of two red photons of light into a single blue photon, which has higher energy. Such an advance could improve solar cell efficiency to chemotherapy treatments. Credit: Image courtesy of University of Delaware Researchers at the University of Delaware have received a $1 million grant from the W.M. Keck Foundation to explore a new idea that could improve solar cells, medical imaging and even cancer treatments. Simply put, they want to change the color of light. They won't be tinkering with what you see out your window: no purple days or chartreuse nights, no edits to rainbows and blazing sunsets. Their goal is to turn low-energy colors of light, such as red, into higher-energy colors, like blue or green. Changing the color of light would give solar technology a considerable boost. A traditional solar cell can only absorb light with energy above a certain threshold. Infrared light passes right through, its energy untapped. However, if that low-energy light could be transformed into higher-energy light, a solar cell could absorb much more of the sun's clean, free, abundant energy. The team predicts that their novel approach could increase the efficiency of commercial solar cells by 25 to 30 percent. The research team, based in UD's College of Engineering, is led by Matthew Doty, associate professor of materials science and engineering and associate director of UD's Nanofabrication Facility. Doty's co-investigators include Joshua Zide, Diane Sellers and Chris Kloxin, all in the Department of Materials Science and Engineering; and Emily Day and John Slater, both in the Department of Biomedical Engineering. "This prestigious $1 million grant from the Keck Foundation underscores the excellence and innovation of our University of Delaware faculty," says Nancy Targett, acting president of the University. "Clearly, the University of Delaware is pursuing big ideas in renewable energy and biomedicine with the potential to benefit the world." "The University's Delaware Will Shine strategic plan challenges us to think boldly as we seek solutions to problems facing society," Domenico Grasso, UD's provost, adds. "We congratulate the research team in the College of Engineering for this major award, and we look forward to their findings." Changing the color of light "A ray of light contains millions and millions of individual units of light called photons," says project leader Matthew Doty. "The energy of each photon is directly related to the color of the light -- a photon of red light has less energy than a photon of blue light. You can't simply turn a red photon into a blue one, but you can combine the energy from two or more red photons to make one blue photon." This process, called "photon upconversion," isn't new, Doty says. However, the UD team's approach to it is. They want to design a new kind of semiconductor nanostructure that will act like a ratchet. It will absorb two red photons, one after the other, to push an electron into an excited state when it can emit a single high-energy (blue) photon. These nanostructures will be so teeny they can only be viewed when magnified a million times under a high-powered electron microscope. "Think of the electrons in this structure as if they were at a water park," Doty says. "The first red photon has only enough energy to push an electron half-way up the ladder of the water slide. The second red photon pushes it the rest of the way up. Then the electron goes down the slide, releasing all of that energy in a single process, with the emission of the blue photon. The trick is to make sure the electron doesn't slip down the ladder before the second photon arrives. The semiconductor ratchet structure is how we trap the electron in the middle of the ladder until the second photon arrives to push it the rest of the way up." The UD team will develop new semiconductor structures containing multiple layers of different materials, such as aluminum arsenide and gallium bismuth arsenide, each only a few nanometers thick. This "tailored landscape" will control the flow of electrons into states with varying potential energy, turning once-wasted photons into useful energy. The UD team has shown theoretically that their semiconductors could reach an upconversion efficiency of 86 percent, which would be a vast improvement over the 36 percent efficiency demonstrated by today's best materials. What's more, Doty says, the amount of light absorbed and energy emitted by the structures could be customized for a variety of applications, from lightbulbs to laser-guided surgery. How do you even begin to make structures so tiny they can only be seen with an electron microscope? In one technique the UD team will use, called molecular beam epitaxy, nanostructures will be built by depositing layers of atoms one at a time. Each structure will be tested to see how well it absorbs and emits light, and the results will be used to tailor the structure to improve performance. The researchers also will develop a milk-like solution filled with millions of identical individual nanoparticles, each one containing multiple layers of different materials. The multiple layers of this structure, like multiple candy shells in an M&M, will implement the photon ratchet idea. Through such work, the team envisions a future upconversion "paint" that could be easily applied to solar cells, windows and other commercial products. Improving medical tests and treatments While the initial focus of the three-year project will be on improving solar energy harvesting, the team also will explore biomedical applications. A number of diagnostic tests and medical treatments, ranging from CT and PET scans to chemotherapy, rely on the release of fluorescent dyes and pharmaceutical drugs. Ideally, such payloads are delivered both at specific disease sites and at specific times, but this is hard to control in practice. The UD team aims to develop an upconversion nanoparticle that can be triggered by light to release its payload. The goal is to achieve the controlled release of drug therapies even deep within diseased human tissue while reducing the peripheral damage to normal tissue by minimizing the laser power required. "This is high-risk, high-reward research," Doty says. "High-risk because we don't yet have proof-of-concept data. High-reward because it has such a huge potential impact in renewable energy to medicine. It's amazing to think that this same technology could be used to harvest more solar energy and to treat cancer. We're excited to get started!" Story Source: The above post is reprinted from materials provided by University of Delaware. Note: Materials may be edited for content and length.

With light echoes, the invisible becomes visible

 

June 17, 2014

Scientists have developed a novel camera system which can see around the corner without using a mirror. Using diffusely reflected light, it reconstructs the shape of objects outside of the field of view. A laser shines on the wall; a camera watches the scene. Nothing more than white ingrain wallpaper with a bright spot of light can be seen through the lens. A computer records these initially unremarkable images and as the data is processed further, little by little, the outlines of an object appear on a screen.

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Prof. Dr.-Ing. Matthias Hullin from the Institute of Computer Science II at the University of Bonn.

Scientists at the University of Bonn and the University of British Columbia (Vancouver, Canada) have developed a novel camera system which can see around the corner without using a mirror. Using diffusely reflected light, it reconstructs the shape of objects outside of the field of view.

The researchers will be reporting their results at the international Conference for Computer Vision and Pattern Recognition (CVPR) from June 24-27 in Columbus (Ohio, USA).

A laser shines on the wall; a camera watches the scene. Nothing more than white ingrain wallpaper with a bright spot of light can be seen through the lens. A computer records these initially unremarkable images and as the data is processed further, little by little, the outlines of an object appear on a screen. Yet, this object is behind a partition and the camera cannot possibly have seen it -- we have apparently looked around the corner. A magic trick? "No," says Prof. Dr.-Ing. Matthias B. Hullin from the Institute of Computer Science II at the University of Bonn. "This is an actual reconstruction from diffusely scattered light. Our camera, combined with a mathematical procedure, enables us to virtually transform this wall into a mirror."

Scattered light is used as a source of information

The laser dot on the wall is by itself a source of scattered light, which serves as the crucial source of information. Some of this light, in a roundabout way, falls back onto the wall and finally into the camera. "We are recording a kind of light echo, that is, time-resolved data, from which we can reconstruct the object," explains the Bonn computer scientist. "Part of the light has also come into contact with the unknown object and it thus brings valuable information with it about its shape and appearance." To be able to measure such echoes, a special camera system is required which Prof. Hullin has developed together with his colleagues at the University of British Columbia (Vancouver, Canada) and further refined after his return to Bonn. In contrast to conventional cameras, it records not just the direction from which the light is coming but also how long it took the light to get from the source to the camera.

The technical complexity for this is comparatively low -- suitable image sensors came onto the mass market long ago. They are mainly found in depth image cameras as they are used, for instance, as video game controllers or for range measurements in the automotive field. The actual challenge is to elicit the desired information from such time-of-flight measurements. Hullin compares the situation to a room which reverberates so greatly that one can no longer have a conversation with one's partner. "In principle, we are measuring nothing other than the sum of numerous light reflections which reached the camera through many different paths and which are superimposed on each other on the image sensor."

This problem, known as multipath interference, has been giving engineers headaches for a long time. Traditionally, one would attempt to remove the undesired multipath scatter and only use the direct portion of the signal. Based on an advanced mathematical model, Hullin and his colleagues, however, developed a method which can obtain the desired information exclusively from what would usually be considered noise rather than signal. Since multipath light also originates from objects which are not at all in the field of view, the researchers can thus make visible what is virtually invisible.

Minimal technical complexity and intelligent programming

"The accuracy of our method has its limits, of course," says Prof. Hullin -- the results are still limited to rough outlines. However, the researchers assume that based on the rapid development of technical components and mathematical models, an even higher resolution can be achieved soon. Together with his colleagues, he will present the method at the international Conference for Computer Vision and Pattern Recognition (CVPR) from June 24 to 27 in Columbus (Ohio, USA). The new technology is received with great interest -- Hullin hopes that similar approaches can be used, for example, in telecommunications, remote sensing and medical imaging.