Long-Sought Pattern of Ancient Light Detected

The journey of light from the very early universe to modern telescopes is long and winding. The ancient light traveled billions of years to reach us, and along the way, its path was distorted by the pull of matter, leading to a twisted light pattern.

This twisted pattern of light, called B-modes, has at last been detected. The discovery, which will lead to better maps of matter across our universe, was made using the National Science Foundation's South Pole Telescope, with help from the Herschel space observatory.

Scientists have long predicted two types of B-modes: the ones that were recently found were generated a few billion years into our universe's existence (it is presently 13.8 billion years old). The others, called primordial, are theorized to have been produced when the universe was a newborn baby, fractions of a second after its birth in the Big Bang.

"This latest discovery is a good checkpoint on our way to the measurement of primordial B-modes," said Duncan Hanson of McGill University in Montreal, Canada, lead author of the new report published Sept. 30 in the online edition of Physical Review Letters.

The elusive primordial B-modes may be imprinted with clues about how our universe was born. Scientists are currently combing through data from the Planck mission in search of them. Both Herschel and Planck are European Space Agency missions, with important NASA contributions.

The oldest light we see around us today, called the cosmic microwave background, harkens back to a time just hundreds of millions of years after the universe was created. Planck recently produced the best-ever full-sky map of this light, revealing new details about of our cosmos' age, contents and origins. A fraction of this ancient light is polarized, a process that causes light waves to vibrate in the same plane. The same phenomenon occurs when sunlight reflects off lakes, or particles in our atmosphere. On Earth, special sunglasses can isolate this polarized light, reducing glare.

The B-modes are a twisted pattern of polarized light. In the new study, the scientists were on a hunt for the kind of polarized light spawned by matter in a process called gravitational lensing, where the gravitational pull from knots of matter distorts the path of light.

The signals are extremely faint, so Hanson and colleagues used Herschel's infrared map of matter to get a better idea of where to look. The researchers then spotted the signals with the South Pole Telescope, making the first-ever detection of B-modes. This is an important step for better mapping how matter, both normal and dark, is distributed throughout our universe. Clumps of matter in the early universe are the seeds of galaxies like our Milky Way.

Astronomers are eager to detect primordial B-modes next. These polarization signals, from billions of years ago, would be much brighter on larger scales, which an all-sky mission like Planck is better able to see.

"These beautiful measurements from the South Pole Telescope and Herschel strengthen our confidence in our current model of the universe," said Olivier Doré, a member of the U.S. Planck science team at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "However, this model does not tell us how big the primordial signal itself should be. We are thus really exploring with excitement a new territory here, and a potentially very, very old one."

Read more at Science Daily

Baby Dinosaur Unearthed by High-Schooler

A dinosaur skeleton discovered by an eagle-eyed high-school student turns out to be the smallest, youngest and most complete duck-billed dinosaur of its kind ever found.

This Cretaceous-era herbivore, Parasaurolophus, walked the Earth some 75 million years ago. The dinosaurs in this genus are best known for their impressive tube-shaped head crests, which may have been used for display or perhaps to amplify the animals' calls. The little specimen, dubbed "Joe," was so young that its crest was a mere bump on its head.

"We now understand a lot more about how Parasaurolophus grew its crest," said Andrew Farke, a paleontologist and curator at Raymond M. Alf Museum of Paleontology in Claremont, Calif.

The museum is affiliated with The Webb Schools, a private high-school campus outside of Los Angeles. The students at the schools participate in paleontology fieldwork as part of their coursework, which is how student Kevin Terris came to discover "Joe" in 2009.

Farke and a group of students were prospecting for fossils in Utah's Grand Staircase-Escalante National Monument, surveying ground Farke had already covered. Terris spotted a little sliver of bone sticking out from under a boulder and alerted Farke, who thought it looked like a piece of dinosaur rib — nice, but not really worth the trouble of excavating.

"We were going to try to see if we could get something better," Farke told LiveScience.

He walked around the other side of the boulder and picked up what looked like a large cobblestone, turning it over in his hands. A dinosaur skull stared back at him.

In light of the skull, Farke thought it wise to go re-check Terris' discovery. A closer look revealed it to be a string of toe bones.

"We have the skull on one side of this boulder and the toes on the other side. That means the whole dinosaur skeleton has to be in between," Farke said. "So we got pretty excited."

The team had to line up permits to excavate on the public land; they returned in 2010 to dig the bones from the ground. Surrounded by an 800-pound (363 kilograms) armor of rock, the bones had to be airlifted out of the rugged backcountry by helicopter.

After 1,300 painstaking hours of cleaning, chiseling and picking, technicians revealed the fossil buried in all that stone. The completeness of the skeleton turned out to be "pretty spectacular," Farke said.

The paleontologists realized they had an amazing example of a baby Parasaurolophus on their hands. Even better, they were able to sample the baby's leg bone. As dinosaur bones grow, they develop ring patterns, much like trees.

"It didn't have any rings at all," Farke said of "Joe." "So what that shows is that this animal was under a year old when it died."

The infant dinosaur was already 6 feet (1.8 meters) long, however, an impressive feat when you consider that duck-billed dinos hatched at about the same size as a human infant. The fact that "Joe" was already sprouting a crest bump so young suggests that Parasaurolophus started growing its crest earlier than other duck-billed dinosaurs.

"It finally lets us understand how Parasaurolophus evolved that big crest, just by shifting around events in its development," Farke said.

Read more at Discovery News

Gold Particles Found in Tree Tissue

Trees may turn golden for reasons that have nothing to do with the onset of autumn: Eucalyptus trees can hold grains of gold, potentially helping reveal buried treasure, scientists now find.

Many plants root deep into the Earth, drawing up nutrients and minerals they need for life. Researchers hope this fact could one day help miners unearth gold, especially since discoveries of new deposits of the precious metal have dropped 45 percent over the last 10 years.

Scientists in Australia focused on eucalyptus trees, since traces of gold are sometimes found in soils surrounding these plants. However, researchers were not certain until now whether trees could actually absorb the precious metal from underground deposits or if the wind simply blew gold dust there from other sites.

Now one group has discovered the first evidence in nature of gold particles located within living tissue from trees.

Researchers investigated leaves, twigs and bark of eucalyptus trees up to 35 feet (10 meters) tall from two locations in Australia — one in the west, another in the south. Past exploratory drilling revealed these sites had gold buried underground, but the areas were undisturbed by further mining activity that might have contaminated the trees with gold dust.

X-ray analysis revealed gold particles up to about 8 microns wide in cells from the trees, or about 10 times thinner than the average human hair. Field samples and greenhouse experiments suggest these gold particles — which exist at concentrations not harmful to the trees — are absorbed by the roots and transported to its extremities, such as leaves, where the highest concentrations were observed.

These findings, detailed online Oct. 22 in the journal Nature Communications,suggest the trees could tap into gold deposits up to 115 feet (35 meters) below them while searching for water under drought conditions.

"We were astounded at the capability of the eucalyptus trees to bring up gold from the equivalent of a 10-story building,"study lead author Melvyn Lintern, a geochemist at the Commonwealth Scientific and Industrial Research Organization in Australia, told LiveScience's OurAmazingPlanet.

Read more at Discovery News

Exoplanet Count Blasts Through the 1,000 Barrier

Hunting for signs of extrasolar planets — or exoplanets — is hard, but counting them can also prove tricky. Today, however, our historic era of exoplanetary discovery has turned into a red letter day; the first 1,000 exoplanets to be confirmed have been added to the Europe-based Extrasolar Planets Encyclopaedia.

For the last few weeks, astronomers (and the science media) have been waiting with bated breath as the confirmed exoplanet count tallied closer and closer to the 1,000 mark. Then, with the help of the Super Wide Angle Search for Planets (SuperWASP) collaboration, the number jumped from 999 to 1,010 overnight.

The 11 new additions may be noteworthy as breaking the 1,000 barrier, but they’re certainly not noteworthy as being anything remotely habitable. All 11 scoot around their parent stars with periods of between 8 and less than 2 days — making all of these new confirmed worlds “hot-Jupiters.”

Keeping a tally of exoplanets isn’t as easy as it seems. Although the Extrasolar Planets Encyclopaedia has been updated, it may be some time until other exoplanetary lists are updated. For example, NASA’s Jet Propulsion Laboratory keeps its own record called the Exoplanet Archive which currently lists the tally at 919. Why the discrepancy? One reason, according to New Scientist, is that the Extrasolar Planets Encyclopaedia lists exoplanets as soon as their confirmation is announced at conferences. The NASA list, however, only lists them once they’ve been published in a scientific journal. The NASA list will therefore always lag its European counterpart.

Also, some of the 1,000 exoplanets in the list are subject to intense scrutiny as there are some very massive worlds with stellar characteristics. After further study, some may be characterized as brown dwarfs, or “failed stars,” bumping them from being true planetary bodies.

1,000 exoplanets may seem like a big number, but the now defunct NASA Kepler Space Telescope suggests that there are thousands of candidate exoplanetary signals in its transit data awaiting confirmation by other surveys. But even if we end up confirming thousands more over the coming years, that number will pale into insignificance considering there are an estimated 100 billion alien worlds orbiting other stars in our galaxy. Our quest to find habitable exoplanets has only just begun.

Read more at Discovery News

West African Bats No Safe Haven for Malaria Parasites

In Europe, bats are normally discussed in the context of endangered species threatened by loss of their habitats. However, in recent years, bats have caught the eye of infection biologists. The animals are namely hosts to a surprising number of pathogens, many of which could be dangerous to humans. Scientists at the Max Planck Institute for Infection Biology, the Museum für Naturkunde in Berlin and the American Museum of Natural History have been able to identify in West African bats four genera of parasites that are closely related to the malaria pathogen. One of them is the genus Plasmodium, which also includes the species that cause malaria in humans. The Plasmodium species in bats are very similar to that found in rodents and could advance the study of malaria pathogens' defence strategies against immune system responses.

Bats can transmit various diseases to human beings. Indeed, they serve as reservoir hosts for a long list of pathogens, including the "who's who" of dreaded killer viruses: Ebola, Marburg, Nipah, Hendra and Lyssa. The SARS outbreak in 2002 in Asia and the transmission of a previously unidentified virus (MERS) to humans in the Middle East in 2013 can both be traced back to viruses that have switched hosts from bats to humans. Bats have an exceptional immune system that can hold all these viruses in check. However, some infections in humans often have a deadly outcome.

Recently, the researchers have also found an astonishing variety of blood parasites in West African bats. They examined 31 bat species from the West African forest in Guinea, Liberia and the Ivory Coast with regard to parasites that attack red blood cells. 40 per cent of the approximately 270 examined animals carried parasites of the genera Plasmodium, Polychromophilus, Nycteria and Hepatocystis. According to the study, at least two species of Plasmodium can be found in bats. These bat pathogens are very similar to those found in rodents. "There are different arboreal rodents in the tropics that live in close vicinity to bats and in result might attract the same mosquitoes that transmit parasites from one group of animals to another," says Juliane Schaer from the Max Planck Institute in Berlin.

Plasmodium parasites cause malaria, the most important vector-borne infectious disease on the planet. These protozoan parasites reproduce in different host cells and undergo a complex life cycle in two alternating hosts. Their sexual reproduction takes place in insects; usually Anopheles mosquitoes. Following a mosquito bite, they reproduce asexually in different vertebrates. By comparing DNA, the scientists were able to establish a phlyogenetic tree for haemosporidians in bats. This showed that bats were the first mammal hosts to the pathogens. "In a later evolutionary stage, they switched to rodents and primates," Susan Perkins from the American Museum of Natural History in New York says.

It is not yet clear why bats are hosts to such a multitude of microorganisms. "One reason is probably that, in evolutionary terms, this is a very old group of animals, which moreover comprises a large number of different species. The bats' ability to fly and their tendency to form big colonies are other factors that help the parasites spread," explains Schaer.

As a consequence of the pathogen threat, bats have developed a sophisticated immune system. This might explain the finding that certain bat species show infection rates of over 60 per cent by haemosporidians and still manage to keep the parasites at bay without becoming ill. "Also, the fast asexual reproduction of the genera Polychromophilus, Nycteria and Hepatocystis in bats takes place in hepatocytes, and not in erythrocytes as in humans. Such a liver stage cannot be clinically detected in humans. "It may be that the effective immune system ousted the pathogens from the blood cells, so that they were limited to multiply in the liver," says Kai Matuschewski, Leader of the Parasitology Research Group at the Max Planck Institute for Infection Biology.

Read more at Science Daily

Grab-and-Go Beetle Hoards Poo and Gallops

Given the choice between flying and hoarding dried feces, most of us would take to the air, but a certain beetle in Africa prefers to spend its time on the ground collecting poop.

The dung beetle, which lives in the Western Cape, now gallops across the sand — like an insect Lone Ranger — while grasping coveted bits of dried feces.

“This species of Pachysoma grabs bits of poo and gallops forward with it,” Marcus Byrne of the University of Witwatersrand, was quoted as saying in a press release. “That is really odd. Most insects walk with a tripod gait. They plant three legs in a triangle, while swinging the other three legs forward. It’s an incredibly stable way of walking because you’ve always got three legs on the ground.”

“For an insect to abandon the tripod gait and use its legs together in pairs like a galloping horse is really radical. The big question is: why are they doing it?” asked Byrne, who along with his colleagues, studied the unusual insect.

Most dung beetles gather “fresh” poop and pack it into one wet ball that they roll along the ground before their big escape. Pachysoma, on the other hand, collects bits of dry dung and hoards it in a nest. The beetle goes on repeated foraging trips instead of one major journey.

Byrne and his colleagues from Lund University in Sweden think the species might have changed its mode of navigation because it needs to be able to find its way back and forth from its nest.

“For most dung beetles, it’s always a one way trip — grab the poo, run away and never go back,” he explained. “The very marked pacing of Pachysoma’s gallop might be giving it a better signal in terms of estimating the return distance from the food to its nest. When it gallops, it slips less in the soft sand.”

Prior research has found that ants count their steps as a way to navigate back and forth from home, and bees use the optical flow of scenery across their retinas to measure how far they’ve travelled to forage from the hive. Pachysoma dung beetles seem to be using a version of both techniques.

“Bees use optic flow as a measure of how fast and how far they’ve flown,” Byrne said. “Dung beetles have two eyes on each side of their head, one on top and one on the bottom, looking at the sand and we think Pachysoma might be registering optic flow with its bottom eye over the sand.”

But Pachysoma has not only changed the way it moves across land, it has also lost its ability to fly.

“There are 800 species of dung beetle in South Africa and most of them fly,” Byrne said. “To fly makes sense because poo is a very ephemeral resource. It’s only useful for a few days and it’s very patchy — you don’t know where you’re going to find the next dropping. That’s why Pachysoma is so weird. Why would anyone give up flying?”

Read more at Discovery News

Oops! Etruscan Warrior Prince Really a Princess

Last month, archaeologists announced a stunning find: a completely sealed tomb cut into the rock in Tuscany, Italy.

The untouched tomb held what looked like the body of an Etruscan prince holding a spear, along with the ashes of his wife. Several news outlets reported on the discovery of the 2,600-year-old warrior prince.

But the grave held one more surprise.

A bone analysis has revealed the warrior prince was actually a princess, as Judith Weingarten, an alumna of the British School at Athens noted on her blog, Zenobia: Empress of the East.

Etruscan tomb

Historians know relatively little about the Etruscan culture that flourished in what is now Italy until its absorption into the Roman civilization around 400 B.C. Unlike their better-known counterparts, the ancient Greeks and the Romans, the Etruscans left no historical documents, so their graves provide a unique insight into their culture.

The new tomb, unsealed by archaeologists in Tuscany, was found in the Etruscan necropolis of Tarquinia, a UNESCO World Heritage site where more than 6,000 graves have been cut into the rock.

"The underground chamber dates back to the beginning of the sixth century B.C. Inside, there are two funerary beds carved into the rock," Alessandro Mandolesi, the University of Turin archaeologist who excavated the site, wrote in an email.

When the team removed the sealed slab blocking the tomb, they saw two large platforms. On one platform lay a skeleton bearing a lance. On another lay a partially incinerated skeleton. The team also found several pieces of jewelry and a bronze-plated box, which may have belonged to a woman, according to the researchers.

"On the inner wall, still hanging from a nail, was an aryballos [a type of flask] oil-painted in the Greek-Corinthian style," Mandolesi said.

Initially, the lance suggested the skeleton on the biggest platform was a male warrior, possibly an Etruscan prince. The jewelry likely belonged to the second body, the warrior prince’s wife.

But bone analysis revealed the prince holding the lance was actually a 35- to 40-year-old woman, whereas the second skeleton belonged to a man.

Given that, what do archaeologists make of the spear?

"The spear, most likely, was placed as a symbol of union between the two deceased," Mandolesi told Viterbo News 24 on Sept. 26.

Weingarten doesn't believe the symbol of unity explanation. Instead, she thinks the spear shows the woman's high status.

Their explanation is "highly unlikely," Weingarten told LiveScience. "She was buried with it next to her, not him."

Gendered assumptions

The mix-up highlights just how easily both modern and old biases can color the interpretation of ancient graves.

In this instance, the lifestyles of the ancient Greeks and Romans may have skewed the view of the tomb. Whereas Greek women were cloistered away, Etruscan women, according to Greek historian Theopompus, were more carefree, working out, lounging nude, drinking freely, consorting with many men and raising children who did not know their fathers' identities.

Instead of using objects found in a grave to interpret the sites, archaeologists should first rely on bone analysis or other sophisticated techniques before rushing to conclusions, Weingarten said.

Read more at Discovery News

Life After Death? New Methods Halt Dying Process

The line between life and death is not as clear as once thought, now that developments in the science of resuscitation have made it possible to revive people even hours after their heart has stopped beating and they are declared dead, medical experts say.

"Historically, when a person's heart stopped and they stopped breathing, for all intents and purposes, they were dead," said Dr. Sam Parnia, an assistant professor of critical care medicine at State University of New York at Stony Brook. "There was nothing you could do to change that," Parnia told an audience at the New York Academy of Sciences last week.

However, in the process of unraveling mysteries of death at the cellular level, scientists have learned that death does not occur in a single moment, but instead is a process. It is actually after a person has died -- by our current definition of death -- that the cells of the body start their own process of dying.

This process "could take hours of time, and we could potentially reverse that," Parnia said.

It was once thought that after the heart stops pumping blood throughout the body, a person has only few minutes before suffering permanent brain damage caused by lack of oxygen and nutrients getting to the brain cells. This notion, scientists now say, is outdated.

When the heart stops beating, the process of death is only beginning, said Dr. Stephan Mayer, a professor of neurology at Columbia University and a panelist at the discussion.

Brain damage from lack of oxygen to the brain comes in stages. Within seconds, brain activity is affected, but it isn't until several minutes later that sugar-deprived cells start going through the steps of programmed cell death.

"When somebody's been without oxygen, we know there’s a whole bunch of signals that are now starting to tell cells that it's time to die. So we have an opportunity to modify that programing just a little bit, to say 'wait put the brakes on,'" said panelist Dr. Lance Becker, a professor of emergency medicine at the University of Pennsylvania.

Some insights for how to halt the dying process come from case reports of people who were brought back to life with little or no brain damage after hours of a silenced brain and heart.

The key to these successful cases, in addition to good critical care, is hypothermia, experts say. Hypothermia is a state in which the body's core temperature is brought a few degrees lower than its normal temperature of 98.6 degrees Fahrenheit (37 degrees Celsius).

Studies have found that hypothermia seems to protect the brain by decreasing its need for oxygen and aborting activated cell death pathways. Still, there are limits -- although body-cooling techniques have improved recovery in many patients after cardiac arrest, there will be a moment when the damage is too much and it's too late to come back, the experts said.

Moreover, scientists have learned that successful recovery depends on how the patient is treated after the heart is restarted and how the body is warmed after hypothermia.

"What we are learning is counterintuitive, because what we were all taught, if somebody's oxygen is low, I should give them oxygen, if their blood pressure is down, I should crank their blood pressure up," Becker said.

In reality, however, if a patient responds to initial care and his heart is restarted, a sudden rush of blood and too much oxygen to the brain could actually worsen the neurological damage. Instead, moderating the amount of oxygen delivered to the brain may be crucial in resuscitation.

The idea of cooling the body after cardiac arrest has been around for a few decades, but scientists were not certain if it truly was beneficial to patients.

In recent years, however, studies have provided evidence that hypothermia improves patient's survival and recovery, and professional societies such as the American Heart Association recommend considering hypothermia after patient's blood circulation is restored.

Nevertheless, not all hospitals have implemented hypothermia as part of their critical care protocol.

"What is sad is that this knowledge out there, the system is available but is not implemented," Parnia said. Less than 10 percent of people in the United States who might benefit from cooling therapy actually receive it, he said.

In an ideal world, resuscitation protocols would use machines instead of people to deliver chest compressions as long as needed, and to ensure right amounts of oxygen and blood are getting to the brain, Parnia said. Cooling and reducing oxygen after the heart is restarted are among factors that should increase people chances of coming back without brain damage, he said.

Read more at Discovery News

'Random' Cell Movement Is Directed from Within

Cell biologists at The Johns Hopkins University have teased apart two integral components of the machinery that causes cells to move. Their discovery shows that cellular projections, which act as hands to help a cell "crawl," are apparently always initiated by a network of message-relaying proteins inside the cell. It was already known that in directional movement, the network is activated by sensor proteins on the cell's surface in response to external cues. They now know that in random movement, the messenger network is also causative: It can self-activate spontaneously.

Because cellular movement is necessary for everything from embryo development to wound healing to cancer metastasis, the work is expected to have wide-ranging implications for understanding and manipulating these biological processes, the researchers say. In fact, they note that defects in the messenger protein network have been linked to many types of cancer. The findings are summarized in a paper published online Oct. 20 in the journal Nature Cell Biology.

"It was previously thought that messenger proteins were only involved in directional movement: that without them, cells could only move randomly, through the spontaneous formation of these hand-like projections," says Peter Devreotes, Ph.D., professor and director of the Department of Cell Biology at the Johns Hopkins University School of Medicine. "Now we know that even random movement requires the activation of the messenger protein network."

According to Devreotes, a key component of a cell's machinery is a crisscrossing network of protein chains that wrap around the inside edge of the cell, giving it shape and structure and inspiring the name "cytoskeleton." To allow movement, this network must build itself up in a given area of the cell, pushing the cell's membrane outward and creating a hand-like projection that can "grip" the external environment and pull the cell forward.

The cytoskeleton, Devreotes says, takes orders from the messenger protein network, which is connected to sensor proteins on the outside of the cell. The sensors detect directional signals coming from other parts of the body and pass them on to the messenger proteins, which in turn call on the cytoskeletal proteins to create a projection in the right direction.

In their experiments, the Devreotes team sought to understand the relationship between each of these components. They began, he says, by bathing their cells in a drug that paralyzes the cytoskeleton. Not surprisingly, the cells wouldn't move, but the spontaneous responses of the messenger network still occurred.

Devreotes explains, "You can think of the cell as a row boat with several crewmen and a coxswain, sitting in the rear, steering the rudder and shouting at the crew to keep their movements in sync. If the oars are taken away (i.e., a paralyzed cytoskeleton), the coxswain can yell at the crew as much as he wants but the boat won't move."

Using a combination of genetic and imaging techniques, the team then incapacitated the other components of the system one by one and watched what happened. Inhibiting the messenger proteins (the coxswain) showed that the cytoskeleton has an intrinsic rhythm that "ruffles" the cell membrane every 10 seconds, but there were no projections created, so the cells didn't move. "It's as if the crew can still row without the coxswain but each person is rowing in a different direction so the boat just stays where it is," says Chuan-Hsiang Huang, a co-author of the study.

The team expected that when they removed the sensor proteins they would see no movement, based on the old idea that both random and directional cell movement required signaling from these proteins. However, they found instead that the messenger network is "excitable." That is, without the sensor proteins or external cues, the messenger proteins can still work on their own, telling the cytoskeleton to create projections here or there, moving the cells about randomly. "This situation could be compared to a boat without a rudder. The coxswain is there to coordinate the rowing of the crew so the boat does move, but not in any specific direction," explained co-author Ming Tang.

Read more at Science Daily

Mixing Nanoparticles to Make Multifunctional Materials

Scientists at the U.S. Department of Energy's Brookhaven National Laboratory have developed a general approach for combining different types of nanoparticles to produce large-scale composite materials. The technique, described in a paper published online by Nature Nanotechnology on October 20, 2013, opens many opportunities for mixing and matching particles with different magnetic, optical, or chemical properties to form new, multifunctional materials or materials with enhanced performance for a wide range of potential applications.

The approach takes advantage of the attractive pairing of complementary strands of synthetic DNA-based on the molecule that carries the genetic code in its sequence of matched bases known by the letters A, T, G, and C. After coating the nanoparticles with a chemically standardized "construction platform" and adding extender molecules to which DNA can easily bind, the scientists attach complementary lab-designed DNA strands to the two different kinds of nanoparticles they want to link up. The natural pairing of the matching strands then "self-assembles" the particles into a three-dimensional array consisting of billions of particles. Varying the length of the DNA linkers, their surface density on particles, and other factors gives scientists the ability to control and optimize different types of newly formed materials and their properties.

"Our study demonstrates that DNA-driven assembly methods enable the by-design creation of large-scale 'superlattice' nanocomposites from a broad range of nanocomponents now available-including magnetic, catalytic, and fluorescent nanoparticles," said Brookhaven physicist Oleg Gang, who led the research at the Lab's Center for Functional Nanomaterials (CFN). "This advance builds on our previous work with simpler systems, where we demonstrated that pairing nanoparticles with different functions can affect the individual particles' performance, and it offers routes for the fabrication of new materials with combined, enhanced, or even brand new functions."

Future applications could include quantum dots whose glowing fluorescence can be controlled by an external magnetic field for new kinds of switches or sensors; gold nanoparticles that synergistically enhance the brightness of quantum dots' fluorescent glow; or catalytic nanomaterials that absorb the "poisons" that normally degrade their performance, Gang said.

"Modern nano-synthesis methods provide scientists with diverse types of nanoparticles from a wide range of atomic elements," said Yugang Zhang, first author of the paper. "With our approach, scientists can explore pairings of these particles in a rational way."

Pairing up dissimilar particles presents many challenges the scientists investigated in the work leading to this paper. To understand the fundamental aspects of various newly formed materials they used a wide range of techniques, including x-ray scattering studies at Brookhaven's National Synchrotron Light Source (NSLS) and spectroscopy and electron microcopy at the CFN.

For example, the scientists explored the effect of particle shape. "In principle, differently shaped particles don't want to coexist in one lattice," said Gang. "They either tend to separate into different phases like oil and water refusing to mix or form disordered structures." The scientists discovered that DNA not only helps the particles mix, but it can also improve order for such systems when a thicker DNA shell around the particles is used.

They also investigated how the DNA-pairing mechanism and other intrinsic physical forces, such as magnetic attraction among particles, might compete during the assembly process. For example, magnetic particles tend to clump to form aggregates that can hinder the binding of DNA from another type of particle. "We show that shorter DNA strands are more effective at competing against magnetic attraction," Gang said.

For the particular composite of gold and magnetic nanoparticles they created, the scientists discovered that applying an external magnetic field could "switch" the material's phase and affect the ordering of the particles. "This was just a demonstration that it can be done, but it could have an application-perhaps magnetic switches, or materials that might be able to change shape on demand," said Zhang.

The third fundamental factor the scientists explored was how the particles were ordered in the superlattice arrays: Does one type of particle always occupy the same position relative to the other type-like boys and girls sitting in alternating seats in a movie theater-or are they interspersed more randomly? "This is what we call a compositional order, which is important for example for quantum dots because their optical properties-e.g., their ability to glow-depend on how many gold nanoparticles are in the surrounding environment," said Gang. "If you have compositional disorder, the optical properties would be different." In the experiments, increasing the thickness of the soft DNA shells around the particles increased compositional disorder.

These fundamental principles give scientists a framework for designing new materials. The specific conditions required for a particular application will be dependent on the particles being used, Zhang emphasized, but the general assembly approach would be the same.

Read more at Science Daily