How Vampire Bats Find Veins

How Vampire Bats Find Veins

  12:25:00 AM    Science Lover

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Heat-sensing protein channels in vampire bats allow the flying mammals to find the best place to sink their teeth into their prey.

The common vampire bat (Desmodus rotundus)

Researchers have discovered an infrared-sensing protein channel that allows vampire bats to identify the hottest part of the animal—veins close to the skin’s surface that carry 38 degree-Celsius (100° F) blood, and presumably the best spot for feeding.

The channel is a variant of TRPV1, a heat-sensing protein channel that is triggered by high temperatures that could potentially cause injury, according to the study published today (August 3) in Nature, and is distinct from the heat sensor used by snakes—the only other non-insect animals that are known to detect heat by sensing infrared radiation.

“Infrared [detection] allows these guys, in pitch black, to hunt down warm-blooded prey,” said zoologist Bill Schutt, assistant professor at Long Island University, who was not involved in the research. Here, the researchers identified a modification in a common heat-sensing protein channel that lowered its temperature threshold so that it is more attuned to an animal’s body heat, he added.

The common vampire bat was appropriately named after the myth of Dracula—it feeds at night and lives solely on a diet of blood, every day or two consuming up to half its weight in the vital substance from large mammals, especially sleeping livestock. The bats first use echolocation to detect their prey, but once they are within 20 centimeters of their target, they use infrared sensors in specialized pits around their noses to zero in on the best place to feed.

In a previous study, physiologist David Julius at the University of California, San Francisco, and colleagues found that infrared detection by snakes—which, like bats, use nerves located in facial pits to detect their prey—is mediated by a cell-surface protein channel called transient receptor potential cation channel A1 (TRPA1). The channel is actually insensitive to heat in most organisms, but had evolved the capability in snakes, leading the group to suspect that a similar transformation may have given vampire bats their ability to sense infrared.




To see if this was the case, Julius and his collaborators at the University of California, San Francisco, the Venezuelan Institute of Scientific Investigation (IVIC), and the Carnegie Institution in Baltimore, Maryland, compared gene expression in vampire bats’ heat-sensing nerves, called trigeminal ganglia, with expression in a nerve cluster near the spine, called dorsal root ganglia (DRG). They also compared these expression patterns to those of the ganglia in four bat species that do not have infrared sensory abilities.

To their surprise, they did not observe any differences in transcription of the TRPA1-coding gene, nor of any other genes. Instead, they discovered that the protein TRPV1—a heat-sensing protein channel normally triggered by temperatures over 43° C (110° F)—existed in two different isoforms—an approximately 850-amino-acid version and one that was 62 amino acids shorter. The short form, which resulted from alternative splicing of the transcribed mRNA, made up as much as half of the TRPV1 found in the trigeminal ganglia of vampire bats, whereas it comprised only a small percentage of the TRPV1 in the DRG. It was similarly low in both types of nerve clusters in the other bat species, suggesting that the short form may play a role in infrared detection.

To test this hypothesis, the researchers expressed one of the two TRPV1 isoforms in human kidney cells and in frog oocytes grown in vitro, and measured their temperature sensitivity using calcium imaging and electrophysiological assays, respectively. As expected, cells producing the long isoform were activated at 40 degrees Celsius (104° F). Cells producing the short isoform, on the other hand, were activated at just 30 degrees (86° F)—a drop that allows the protein to respond to the warmth of the vampire bats’ prey.

“This is a big jump in understanding how these animals locate their prey,” said Brock Fenton, a biology professor at the University of Western Ontario and author of an accompanying Nature News and Views article. While the longer isoform maintains its normal function of detecting potentially harmful high temperatures, the shorter isoform in the trigeminal nerves of the common vampire bat allows the animals to detect lower temperatures, such as the body heat of their mammalian prey.

“Basically, evolution tweaked a system in vampires bats that was already being used to sense temperatures,” said Schutt, author of the 2008 book Dark Banquet: Blood and the Curious Lives of Blood-Feeding Creatures, turning it into a useful hunting tool.

This is in contrast to the pit viper, whose infrared-sensing ability evolved from a different type of channel not involved in heat detection, but in the detection of noxious smells, added Fenton. The different evolutionary strategies employed by these two lineages “is an example of how plastic our sensory systems can be,” he said.

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New Invisibility Cloak Hides Objects from Human View

New Invisibility Cloak Hides Objects from Human View

  2:26:00 PM    Science Lover

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For the first time, scientists have devised an invisibility cloak material that hides objects from detection using light that is visible to humans. The new device is a leap forward in cloaking materials, according to a report in the ACS journal Nano Letters.

A real-life invisibility cloak, shown in this cross- sectional 
illustration, can hide objects from human view. (Credit: ACS)

Xiang Zhang and colleagues note that invisibility cloaks, which route electromagnetic waves around an object to make it undetectable, "are still in their infancy." Most cloaks are made of materials that can only hide things using microwave or infrared waves, which are just below the threshold of human vision. To remedy this, the researchers built a reflective "carpet cloak" out of layers of silicon oxide and silicon nitride etched in a special pattern. The carpet cloak works by concealing an object under the layers, and bending light waves away from the bump that the object makes, so that the cloak appears flat and smooth like a normal mirror.

Although the study cloaked a microscopic object roughly the diameter of a red blood cell, the device demonstrates that it may be "capable of cloaking any object underneath a reflective carpet layer. In contrast to the previous demonstrations that were limited to infrared light, this work makes actual invisibility for the light seen by the human eye possible," the scientists write.



The authors acknowledge funding from the U.S. Army Research Office, the Natural Sciences and Engineering Research Council of Canada, and the NSF Graduate Research Fellowship Program.

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Solar Cells that See Red

Solar Cells that See Red

  10:25:00 AM    Science Lover

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Metamaterials that convert lower-energy photons to usable wavelengths could offer solar cells an efficiency boost.

Light switch: In a process that could make
solar cells more efficient, green laser light
is "upconverted" to blue light by a
solution of dyes and metal nanoparticles.
Credit: Jennifer Dionne

Researchers at Stanford University have demonstrated a set of materials that could enable solar cells to use a band of the solar spectrum that otherwise goes to waste. The materials layered on the back of solar cells would convert red and near-infrared light—unusable by today's solar cells—into shorter-wavelength light that the cells can turn into energy. The university researchers will collaborate with the Bosch Research and Technology Center in Palo Alto, California, to demonstrate a system in working solar cells in the next four years.

Even the best of today's silicon solar cells can't use about 30 percent of the light from the sun: that's because the active materials in solar cells can't interact with photons whose energy is too low. But though each of these individual photons is low energy, as a whole they represent a large amount of untapped solar energy that could make solar cells more cost-competitive.

The process, called "upconversion," relies on pairs of dyes that absorb photons of a given wavelength and re-emit them as fewer, shorter-wavelength photons. In this case, the Bosch and Stanford researchers will work on systems that convert near-infrared wavelengths (most of which are unusable by today's solar cells). The leader of the Stanford group, assistant professor Jennifer Dionne, believes the group can improve the sunlight-to-electricity conversion efficiency of amorphous-silicon solar cells from 11 percent to 15 percent.



The concept of upconversion isn't new, but it's never been demonstrated in a working solar cell, says Inna Kozinsky, a senior engineer at Bosch. Upconversion typically requires two types of molecules to absorb relatively high-wavelength photons, combine their energy, and re-emit it as higher-energy, lower-wavelength photons. However, the chances of the molecules encountering each other at the right time when they're in the right energetic states are low. Dionne is developing nanoparticles to add to these systems in order to increase those chances. To make better upconversion systems, Dionne is designing metal nanoparticles that act like tiny optical antennas, directing light in these dye systems in such a way that the dyes are exposed to more light at the right time, which creates more upconverted light, and then directing more of that upconverted light out of the system in the end.

The ultimate vision, says Dionne, is to create a solid. Sheets of such a material could be laid down on the bottom of the cell, separated from the cell itself by an electrically insulating layer. Low-wavelength photons that pass through the active layer would be absorbed by the upconverter layer, then re-emitted back into the active layer as usable, higher-wavelength light.

Kozinsky says Bosch's goal is to demonstrate upconversion of red light in working solar cells in three years, and upconversion of infrared light in four years. Factoring in the time needed to scale up to manufacturing, she says, the technology could be in Bosch's commercial solar cells in seven to 10 years.

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Extreme Darkness: Carbon Nanotube Forest Covers Ultra-Dark Detector

Extreme Darkness: Carbon Nanotube Forest Covers Ultra-Dark Detector

  10:46:00 AM    Science Lover

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Harnessing darkness for practical use, researchers at the National Institute of Standards and Technology (NIST) have developed a laser power detector coated with the world's darkest material -- a forest of carbon nanotubes that reflects almost no light across the visible and part of the infrared spectrum.

This is a colorized micrograph of the world's darkest 
material -- a sparse "forest" of fine carbon nanotubes -- 
coating a NIST laser power detector. Image shows a 
region approximately 25 micrometers across. 
(Credit: Aric Sanders, NIST)

NIST will use the new ultra-dark detector, described in a new paper in Nano Letters, to make precision laser power measurements for advanced technologies such as optical communications, laser-based manufacturing, solar energy conversion, and industrial and satellite-borne sensors.

Inspired by a 2008 paper by Rensselaer Polytechnic Institute (RPI) on "the darkest man-made material ever," the NIST team used a sparse array of fine nanotubes as a coating for a thermal detector, a device used to measure laser power. A co-author at Stony Brook University in New York grew the nanotube coating. The coating absorbs laser light and converts it to heat, which is registered in pyroelectric material (lithium tantalate in this case). The rise in temperature generates a current, which is measured to determine the power of the laser. The blacker the coating, the more efficiently it absorbs light instead of reflecting it, and the more accurate the measurements.

The new NIST detector uniformly reflects less than 0.1 percent of light at wavelengths from deep violet at 400 nanometers (nm) to near infrared at 4 micrometers (μm) and less than 1 percent of light in the infrared spectrum from 4 to 14 μm. The results are similar to those reported for the RPI material and in a 2009 paper by a Japanese group. The NIST work is unique in that the nanotubes were grown on pyroelectric material, whereas the other groups grew them on silicon. NIST researchers plan to extend the calibrated operating range of their device to 50 or even 100 micrometer wavelengths, to perhaps provide a standard for terahertz radiation power.

NIST previously made detector coatings from a variety of materials, including flat nanotube mats. The new coating is a vertical forest of multiwalled nanotubes, each less than 10 nanometers in diameter and about 160 micrometers long. The deep hollows may help trap light, and the random pattern diffuses any reflected light in various directions. Measuring how much light was reflected across a broad spectrum was technically demanding; the NIST team spent hundreds of hours using five different methods to measure the vanishingly low reflectance with adequate precision. Three of the five methods involved comparisons of the nanotube-coated detector to a calibrated standard.

Carbon nanotubes offer ideal properties for thermal detector coatings, in part because they are efficient heat conductors. Nickel phosphorous, for example, reflects less light at some wavelengths, but does not conduct heat as well. The new carbon nanotube materials also are darker than NIST's various Standard Reference Materials for black color developed years ago to calibrate instruments.

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Multifunctional Nanoparticle Enables New Type of Biological Imaging

Multifunctional Nanoparticle Enables New Type of Biological Imaging

  12:30:00 PM    Science Lover

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Spotting a single cancerous cell that has broken free from a tumor and is traveling through the bloodstream to colonize a new organ might seem like finding a needle in a haystack. But a new imaging technique from the University of Washington is a first step toward making this possible.

On top are photoacoustic images taken for gold nanorods (left), the new UW particle that has a magnetic core and surrounding gold shell (center), and a simple magnetic nanoparticle (right). Below is the same image after processing to remove pixels not vibrating with the magnetic field. The center blob is retained because of the particles' magnetic core and is bright because of the particles' gold shell. (Credit: Xiaohu Gao, University of Washington)

UW researchers have developed a multifunctional nanoparticle that eliminates the background noise, enabling a more precise form of medical imaging -- essentially erasing the haystack, so the needle shines through. A successful demonstration with photoacoustic imaging was reported n the journal Nature Communications.

Nanoparticles are promising contrast agents for ultrasensitive medical imaging. But in all techniques that do not use radioactive tracers, the surrounding tissues tend to overwhelm weak signals, preventing researchers from detecting just one or a few cells.

"Although the tissues are not nearly as effective at generating a signal as the contrast agent, the quantity of the tissue is much greater than the quantity of the contrast agent and so the background signal is very high," said lead author Xiaohu Gao, a UW assistant professor of bioengineering.

The newly presented nanoparticle solves this problem by for the first time combining two properties to create an image that is different from what any existing technique could have produced.

The new particle combines magnetic properties and photoacoustic imaging to erase the background noise. Researchers used a pulsing magnetic field to shake the nanoparticles by their magnetic cores. Then they took a photoacoustic image and used image processing techniques to remove everything except the vibrating pixels.

Gao compares the new technique to "Tourist Remover" photo editing software that allows a photographer to delete other people by combining several photos of the same scene and keeping only the parts of the image that aren't moving. "We are using a very similar strategy," Gao said. "Instead of keeping the stationary parts, we only keep the moving part.

"We use an external magnetic field to shake the particles," he explained. "Then there's only one type of particle that will shake at the frequency of our magnetic field, which is our own particle."

Experiments with synthetic tissue showed the technique can almost completely suppress a strong background signal. Future work will try to duplicate the results in lab animals, Gao said.

The 30-nanometer particle consists of an iron-oxide magnetic core with a thin gold shell that surrounds but does not touch the center. The gold shell is used to absorb infrared light, and could also be used for optical imaging, delivering heat therapy, or attaching a biomolecule that would grab on to specific cells.

Earlier work by Gao's group combined functions in a single nanoparticle, something that is difficult because of the small size.

"In nanoparticles, one plus one is often less than two," Gao said. "Our previous work showed that one plus one can be equal to two. This paper shows that one plus one is, finally, greater than two."

The first biological imaging, in the 1950s, was used to identify anatomy inside the body, detecting tumors or fetuses. The second generation has been used to monitor function -- fMRI, or functional magnetic resonance imaging, for example, detects oxygen use in the brain to produce a picture of brain activity. The next generation of imaging will be molecular imaging, said co-author Matthew O'Donnell, a UW professor of bioengineering and engineering dean.

This will mean that medical assays and cell counts can be done inside the body. In other words, instead of taking a biopsy and inspecting tissue under a microscope, imaging could detect specific proteins or abnormal activity at the source.

But making this happen means improving the confidence limits of the imaging.

"Today, we can use biomarkers to see where there's a large collection of diseased cells," O'Donnell said. "This new technique could get you down to a very precise level, potentially of a single cell."

Researchers tested the method for photoacoustic imaging, a low-cost method now being developed that is sensitive to slight variations in tissues' properties and can penetrate several centimeters in soft tissue. It works by using a pulse of laser light to heat a cell very slightly. This heat causes the cell to vibrate and produce ultrasound waves that travel through the tissue to the body's surface. The new technique should also apply to other types of imaging, the authors said.

Co-authors are UW postdoctoral researchers Yongdong Jin and Sheng-Wen Huang and University of Michigan doctoral student Congxian Jia.

Research was funded by the National Institutes of Health, the National Science Foundation and the UW Department of Bioengineering.

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