The SLAC research program centers on experimental and theoretical research in elementary particle physics using electron beams and a broad program of research in atomic and solid-state physics, chemistry, biology, and medicine using synchrotron radiation.
SLAC National Accelerator Laboratory research articles from Innovation Toronto
- Printing nanomaterials with plasma onto a 3-D object or flexible surface, such as paper or cloth – March 23, 2016
- Microscopic Rake Doubles Efficiency of Low-cost Solar Cells – August 13, 2015
- Pouring Fire on Fuels at the Nanoscale – August 8, 2015
- SLAC Builds One of the World’s Fastest ‘Electron Cameras’ – August 6, 2015
- Rattled Atoms Mimic High-temperature Superconductivity – December 7, 2014
- Warmer superconductors could make virtually everything that runs on electricity much more efficient – November 16, 2014
- Will 2-D Tin be the Next Super Material?
- Scientists invent self-healing battery electrode
- Researchers Demonstrate ‘Accelerator on a Chip’
- Designer Glue Improves Lithium-ion Battery Life
- The World’s Fastest Electrical Switch
- Printing innovations provide 10-fold improvement in organic electronics
- Stanford scientists create novel silicon electrodes that improve lithium-ion battery performance
- New Battery Design Could Help Solar and Wind Energy Power the Grid
- New Solar-Energy Device is 100 Times More Efficient Than Previous Design
- Widely used nanoparticles enter soybean plants from farm soil
- Nanoparticle Leads to World Record for Battery Storage
- Superfast laser delivers record-breaking peak power of one petawatt
- World’s Most Powerful X-Ray Laser Creates 2-Million-Degree Matter
- SLAC invention measures stroke damage in the brain
Researchers Use World’s Smallest Diamonds to Make Wires Three Atoms Wide
Scientists at Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory have discovered a way to use diamondoids – the smallest possible bits of diamond – to assemble atoms into the thinnest possible electrical wires, just three atoms wide.
By grabbing various types of atoms and putting them together LEGO-style, the new technique could potentially be used to build tiny wires for a wide range of applications, including fabrics that generate electricity, optoelectronic devices that employ both electricity and light, and superconducting materials that conduct electricity without any loss. The scientists reported their results today in Nature Materials.
“What we have shown here is that we can make tiny, conductive wires of the smallest possible size that essentially assemble themselves,” said Hao Yan, a Stanford postdoctoral researcher and lead author of the paper. “The process is a simple, one-pot synthesis. You dump the ingredients together and you can get results in half an hour. It’s almost as if the diamondoids know where they want to go.”
The Smaller the Better
Although there are other ways to get materials to self-assemble, this is the first one shown to make a nanowire with a solid, crystalline core that has good electronic properties, said study co-author Nicholas Melosh, an associate professor at SLAC and Stanford and investigator with SIMES, the Stanford Institute for Materials and Energy Sciences at SLAC.
The needle-like wires have a semiconducting core – a combination of copper and sulfur known as a chalcogenide – surrounded by the attached diamondoids, which form an insulating shell.
Their minuscule size is important, Melosh said, because a material that exists in just one or two dimensions – as atomic-scale dots, wires or sheets – can have very different, extraordinary properties compared to the same material made in bulk. The new method allows researchers to assemble those materials with atom-by-atom precision and control.
The diamondoids they used as assembly tools are tiny, interlocking cages of carbon and hydrogen. Found naturally in petroleum fluids, they are extracted and separated by size and geometry in a SLAC laboratory. Over the past decade, a SIMES research program led by Melosh and SLAC/Stanford Professor Zhi-Xun Shen has found a number of potential uses for the little diamonds, including improving electron microscope images and making tiny electronic gadgets.
For this study, the research team took advantage of the fact that diamondoids are strongly attracted to each other, through what are known as van der Waals forces. (This attraction is what makes the microscopic diamondoids clump together into sugar-like crystals, which is the only reason you can see them with the naked eye.)
They started with the smallest possible diamondoids – single cages that contain just 10 carbon atoms – and attached a sulfur atom to each. Floating in a solution, each sulfur atom bonded with a single copper ion. This created the basic nanowire building block.
The building blocks then drifted toward each other, drawn by the van der Waals attraction between the diamondoids, and attached to the growing tip of the nanowire.
“Much like LEGO blocks, they only fit together in certain ways that are determined by their size and shape,” said Stanford graduate student Fei Hua Li, who played a critical role in synthesizing the tiny wires and figuring out how they grew. “The copper and sulfur atoms of each building block wound up in the middle, forming the conductive core of the wire, and the bulkier diamondoids wound up on the outside, forming the insulating shell.”
A Versatile Toolkit for Creating Novel Materials
The team has already used diamondoids to make one-dimensional nanowires based on cadmium, zinc, iron and silver, including some that grew long enough to see without a microscope, and they have experimented with carrying out the reactions in different solvents and with other types of rigid, cage-like molecules, such as carboranes.
The cadmium-based wires are similar to materials used in optoelectronics, such as light-emitting diodes (LEDs), and the zinc-based ones are like those used in solar applications and in piezoelectric energy generators, which convert motion into electricity.
“You can imagine weaving those into fabrics to generate energy,” Melosh said. “This method gives us a versatile toolkit where we can tinker with a number of ingredients and experimental conditions to create new materials with finely tuned electronic properties and interesting physics.”
Discovery Could Make Water-splitting Reaction Cheaper, More Efficient
Researchers at Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory have developed a tough new catalyst that carries out a solar-powered reaction 100 times faster than ever before, works better as time goes on and stands up to acid.
And because it requires less of the rare and costly metal iridium, it could bring down the cost of a process that mimics photosynthesis by using sunlight to split water molecules – a key step in a renewable, sustainable pathway to produce hydrogen or carbon-based fuels that can power a broad range of energy technologies.
The team published their results today in the journal Science.
A Multi-pronged Search
The discovery of the catalyst – a very thin film of iridium oxide layered on top of strontium iridium oxide – was the result of an extensive search by three groups of experts for a more efficient way to accelerate the oxygen evolution reaction, or OER, which is half of a two-step process for splitting water with sunlight.
“The OER has been a real bottleneck, particularly in acidic conditions,” said Thomas Jaramillo, an associate professor at SLAC and Stanford and deputy director of the SUNCAT Center for Interface Science and Catalysis. “The only reasonably active catalysts we know that can survive those harsh conditions are based on iridium, which is one of the rarest metals on Earth. If we want to bring down the cost of such a pathway for making fuels from renewable sources and carry it out on a much larger scale, we need to develop catalyst materials that are more active and that use little or no iridium.”
The search started with SUNCAT theorists, who used computers to explore a database of materials and find the ones with the most potential to do exactly what was needed. Catalysts accelerate chemical reactions without being used up in the process, and databases like this one have become an important tool for designing catalysts to order, rather than testing thousands of materials in a time-consuming, trial-and-error approach.
Based on the results, a team led by SLAC Staff Scientist Yasuyuki Hikita and SLAC/Stanford Professor Harold Hwang, both investigators with the Stanford Institute for Materials and Energy Sciences (SIMES), synthesized one of the catalyst candidates, strontium iridium oxide. Linsey Seitz, a PhD student in Jaramillo’s group and first author of the report, investigated the material’s properties.
A Surprising Improvement
To the team’s surprise, this catalyst worked even better than expected, and kept improving over the first two hours of operation. Experiments probing the surface of the material indicated that a corrosion process released strontium atoms into the surrounding fluid during this initial period. This left a film of iridium oxide just a few atomic layers thick that was much more active than the original material, and 100 times more efficient at promoting the OER than any other acid-stable catalyst known to date.
“A lot of materials do this type of thing – surfaces can be very dynamic, changing during the course of a reaction – but in this case the catalyst changes in a way that gives you excellent performance in acid,” Jaramillo said. “This is unusual, because under these conditions most materials are either poor catalysts or they completely fall apart, or both.”
The researchers still don’t know exactly why this surface layer is so active, although the theorists, including SUNCAT graduate students Colin Dickens and Charlotte Kirk, have provided some ideas. Jaramillo’s group will be taking a closer look at the catalyst with X-ray beams at SLAC’s Stanford Synchrotron Radiation Lightsource, a DOE Office of Science User Facility, to determine exactly how the atoms on the surface rearrange themselves and why this boosts the catalyst’s performance.
“To make a commercially viable catalyst we will need to reduce the amount of iridium in the material even more,” said Jens Nørskov, director of SUNCAT and a professor at SLAC and Stanford. “But there are many possibilities, and this gives us some very good leads.”
Researchers have engineered a low-cost plastic material that could become the basis for clothing that cools the wearer, reducing the need for energy-consuming air conditioning.
Stanford engineers have developed a low-cost, plastic-based textile that, if woven into clothing, could cool your body far more efficiently than is possible with the natural or synthetic fabrics in clothes we wear today.
Describing their work in Science, the researchers suggest that this new family of fabrics could become the basis for garments that keep people cool in hot climates without air conditioning.
“If you can cool the person rather than the building where they work or live, that will save energy,” said Yi Cui, an associate professor of materials science and engineering at Stanford and of photon science at SLAC National Accelerator Laboratory.
This new material works by allowing the body to discharge heat in two ways that would make the wearer feel nearly 4 degrees Fahrenheit cooler than if they wore cotton clothing.
The material cools by letting perspiration evaporate through the material, something ordinary fabrics already do. But the Stanford material provides a second, revolutionary cooling mechanism: allowing heat that the body emits as infrared radiation to pass through the plastic textile.
All objects, including our bodies, throw off heat in the form of infrared radiation, an invisible and benign wavelength of light. Blankets warm us by trapping infrared heat emissions close to the body. This thermal radiation escaping from our bodies is what makes us visible in the dark through night-vision goggles.
“Forty to 60 percent of our body heat is dissipated as infrared radiation when we are sitting in an office,” said Shanhui Fan, a professor of electrical engineering who specializes in photonics, which is the study of visible and invisible light. “But until now there has been little or no research on designing the thermal radiation characteristics of textiles.”
Super-powered kitchen wrap
To develop their cooling textile, the Stanford researchers blended nanotechnology, photonics and chemistry to give polyethylene – the clear, clingy plastic we use as kitchen wrap – a number of characteristics desirable in clothing material: It allows thermal radiation, air and water vapor to pass right through, and it is opaque to visible light.
The easiest attribute was allowing infrared radiation to pass through the material, because this is a characteristic of ordinary polyethylene food wrap. Of course, kitchen plastic is impervious to water and is see-through as well, rendering it useless as clothing.
The Stanford researchers tackled these deficiencies one at a time.
First, they found a variant of polyethylene commonly used in battery making that has a specific nanostructure that is opaque to visible light yet is transparent to infrared radiation, which could let body heat escape. This provided a base material that was opaque to visible light for the sake of modesty but thermally transparent for purposes of energy efficiency.
They then modified the industrial polyethylene by treating it with benign chemicals to enable water vapor molecules to evaporate through nanopores in the plastic, said postdoctoral scholar and team member Po-Chun Hsu, allowing the plastic to breathe like a natural fiber.
That success gave the researchers a single-sheet material that met their three basic criteria for a cooling fabric. To make this thin material more fabric-like, they created a three-ply version: two sheets of treated polyethylene separated by a cotton mesh for strength and thickness.
To test the cooling potential of their three-ply construct versus a cotton fabric of comparable thickness, they placed a small swatch of each material on a surface that was as warm as bare skin and measured how much heat each material trapped.
“Wearing anything traps some heat and makes the skin warmer,” Fan said. “If dissipating thermal radiation were our only concern, then it would be best to wear nothing.”
The comparison showed that the cotton fabric made the skin surface 3.6 F warmer than their cooling textile. The researchers said this difference means that a person dressed in their new material might feel less inclined to turn on a fan or air conditioner.
The researchers are continuing their work on several fronts, including adding more colors, textures and cloth-like characteristics to their material. Adapting a material already mass produced for the battery industry could make it easier to create products.
“If you want to make a textile, you have to be able to make huge volumes inexpensively,” Cui said.
Fan believes that this research opens up new avenues of inquiry to cool or heat things, passively, without the use of outside energy, by tuning materials to dissipate or trap infrared radiation.
“In hindsight, some of what we’ve done looks very simple, but it’s because few have really been looking at engineering the radiation characteristics of textiles,” he said.
SLAC, Stanford Gadget Grabs More Solar Energy to Disinfect Water Faster
In many parts of the world, the only way to make germy water safe is by boiling, which consumes precious fuel, or by putting it out in the sun in a plastic bottle so ultraviolet rays will kill the microbes. But because UV rays carry only 4 percent of the sun’s total energy, the UV method takes six to 48 hours, limiting the amount of water people can disinfect this way.
Now researchers at the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University have created a nanostructured device, about half the size of a postage stamp, that disinfects water much faster than the UV method by also making use of the visible part of the solar spectrum, which contains 50 percent of the sun’s energy.
In experiments reported today in Nature Nanotechnology, sunlight falling on the little device triggered the formation of hydrogen peroxide and other disinfecting chemicals that killed more than 99.999 percent of bacteria in just 20 minutes. When their work was done the killer chemicals quickly dissipated, leaving pure water behind.
“Our device looks like a little rectangle of black glass. We just dropped it into the water and put everything under the sun, and the sun did all the work,” said Chong Liu, lead author of the report. She is a postdoctoral researcher in the laboratory of Yi Cui, a SLAC/Stanford associate professor and investigator with SIMES, the Stanford Institute for Materials and Energy Sciences at SLAC.
Nanoflake Walls and Eager Electrons
Under an electron microscope the surface of the device looks like a fingerprint, with many closely spaced lines. Those lines are very thin films – the researchers call them “nanoflakes” – of molybdenum disulfide that are stacked on edge, like the walls of a labyrinth, atop a rectangle of glass.
In ordinary life, molybdenum disulfide is an industrial lubricant. But like many materials, it takes on entirely different properties when made in layers just a few atoms thick. In this case it becomes a photocatalyst: When hit by incoming light, many of its electrons leave their usual places, and both the electrons and the “holes” they leave behind are eager to take part in chemical reactions.
By making their molybdenum disulfide walls in just the right thickness, the scientists got them to absorb the full range of visible sunlight. And by topping each tiny wall with a thin layer of copper, which also acts as a catalyst, they were able to use that sunlight to trigger exactly the reactions they wanted – reactions that produce “reactive oxygen species” like hydrogen peroxide, a commonly used disinfectant, which kill bacteria in the surrounding water.
Molybdenum disulfide is cheap and easy to make – an important consideration when making devices for widespread use in developing countries, Cui said. It also absorbs a much broader range of solar wavelengths than traditional photocatalysts.
Solving Pollution Problems
The method is not a cure-all; for instance, it doesn’t remove chemical pollutants from water. So far it’s been tested on only three strains of bacteria, although there’s no reason to think it would not kill other bacterial strains and other types of microbes, such as viruses. And it’s only been tested on specific concentrations of bacteria mixed with less than an ounce of water in the lab, not on the complex stews of contaminants found in the real world.
Still, “It’s very exciting to see that by just designing a material you can achieve a good performance. It really works,” said Liu, who has gone on to work on a project in Cui’s lab that is developing air filters for combating smog. “Our intention is to solve environmental pollution problems so people can live better.”
A Stanford University research lab has developed new technologies to tackle two of the world’s biggest energy challenges – clean fuel for transportation and grid-scale energy storage.
The researchers described their findings in two studies published this month in the journals Science Advancesand Nature Communications.
Hydrogen fuel has long been touted as a clean alternative to gasoline. Automakers began offering hydrogen-powered cars to American consumers last year, but only a handful have sold, mainly because hydrogen refueling stations are few and far between.
“Millions of cars could be powered by clean hydrogen fuel if it were cheap and widely available,” said Yi Cui, an associate professor of materials science and engineering at Stanford.
Unlike gasoline-powered vehicles, which emit carbon dioxide (CO2,), hydrogen cars themselves are emissions free. Making hydrogen fuel, however, is not emission free: today, making most hydrogen fuel involves natural gas in a process that releases CO2 into the atmosphere.
To address the problem, Cui and his colleagues have focused on photovoltaic water splitting. This emerging technology consists of a solar-powered electrode immersed in water. When sunlight hits the electrode, it generates an electric current that splits the water into its constituent parts, hydrogen and oxygen.
Laser light exposes the properties of materials used in batteries and electronics
Creating the batteries or electronics of the future requires understanding materials that are just a few atoms thick and that change their fundamental physical properties in fractions of a second. Cutting-edge facilities at SLAC National Accelerator Laboratory and Stanford University have allowed researchers like Aaron Lindenberg to visualize properties of these nanoscale materials at ultrafast time scales.
In one experiment, a team led by Lindenberg showed atoms shifting in trillionths of a second to produce a wrinkle in a 3-atom-thick sample of a material that might someday be used in flexible electronics. Another study observed semiconductor crystals — called “quantum dots” because they defy classical physics at the nanoscale — expand and shrink in response to ultrafast pulses of laser light.
Revealing such intriguing properties at the nanoscale gives clues about the fundamental nature of materials and how they perform in applications we rely on for energy or information.
“Even though some of these materials are completely embedded in everyday technologies, not a lot is understood about how they work,” says Lindenberg, who is an associate professor of materials science and engineering and of photon science. He is also a principal investigator for two SLAC/Stanford joint institutes — Stanford Institute for Materials and Energy Sciences and Stanford PULSE Institute.
“Part of the reason some phenomena are not well understood is because they happen so fast – in billionths, trillionths or even quadrillionths of a second. For the first time, we have tools that allow us to see these things,” he says.
Working at the intersection of materials science and engineering, Lindenberg and his team have a particular focus on finding promising materials for next-generation electronics, light-based data storage technologies and energy applications.
Results Suggest a More Efficient Way to Convert Solar and Wind Power to Renewable Fuels
With a combination of theory and clever, meticulous gel-making, scientists from the Department of Energy’s SLAC National Accelerator Laboratory and the University of Toronto have developed a new type of catalyst that’s three times better than the previous record-holder at splitting water into hydrogen and oxygen – the vital first step in making fuels from renewable solar and wind power.
The research, published today in the journal Science, outlines a potential way to make a future generation of water-splitting catalysts from three abundant metals – iron, cobalt and tungsten – rather than the rare, costly metals that many of today’s catalysts rely on.
“The good things about this catalyst are that it’s easy to make, its production can be very easily scaled up without any super-advanced tools, it’s consistent, and it’s very robust,” said Aleksandra Vojvodic, a SLAC staff scientist with the SUNCAT Center for Interface Science and Catalysis who led the theoretical side of the work.
New method can deposit nanomaterials onto flexible surfaces and 3-D objects
Printing has come a long way since the days of Johannes Gutenberg. Now, researchers have developed a new method that uses plasma to print nanomaterials onto a 3-D object or flexible surface, such as paper or cloth. The technique could make it easier and cheaper to build devices like wearable chemical and biological sensors, flexible memory devices and batteries, and integrated circuits.
One of the most common methods to deposit nanomaterials–such as a layer of nanoparticles or nanotubes–onto a surface is with an inkjet printer similar to an ordinary printer found in an office. Although they use well-established technology and are relatively cheap, inkjet printers have limitations. They can’t print on textiles or other flexible materials, let alone 3-D objects. They also must print liquid ink, and not all materials are easily made into a liquid.
Some nanomaterials can be printed using aerosol printing techniques. But the material must be heated several hundreds of degrees to consolidate into a thin and smooth film. The extra step is impossible for printing on cloth or other materials that can burn, and means higher cost for the materials that can take the heat.
The plasma method skips this heating step and works at temperatures not much warmer than 40 degrees Celsius. “You can use it to deposit things on paper, plastic, cotton, or any kind of textile,” said Meyya Meyyappan of NASA Ames Research Center. “It’s ideal for soft substrates.” It also doesn’t require the printing material to be liquid.
The researchers, from NASA Ames and SLAC National Accelerator Laboratory, describe their work in Applied Physics Letters, from AIP Publishing>.
They demonstrated their technique by printing a layer of carbon nanotubes on paper. They mixed the nanotubes into a plasma of helium ions, which they then blasted through a nozzle and onto paper. The plasma focuses the nanoparticles onto the paper surface, forming a consolidated layer without any need for additional heating.
The team printed two simple chemical and biological sensors. The presence of certain molecules can change the electrical resistance of the carbon nanotubes. By measuring this change, the device can identify and determine the concentration of the molecule. The researchers made a chemical sensor that detects ammonia gas and a biological sensor that detects dopamine, a molecule linked to disorders like Parkinson’s disease and epilepsy.
But these were just simple proofs-of-principle, Meyyappan said. “There’s a wide range of biosensing applications.” For example, you can make sensors that monitor health biomarkers like cholesterol, or food-borne pathogens like E. coli and Salmonella.
Because the method uses a simple nozzle, it’s versatile and can be easily scaled up. For example, a system could have many nozzles like a showerhead, allowing it to print on large areas. Or, the nozzle could act like a hose, free to spray nanomaterials on the surfaces of 3-D objects.
“It can do things inkjet printing cannot do,” Meyyappan said. “But anything inkjet printing can do, it can be pretty competitive.”
The method is ready for commercialization, Meyyappan said, and should be relatively inexpensive and straightforward to develop. Right now, the researchers are designing the technique to print other kinds of materials such as copper. They can then print materials used for batteries onto thin sheets of metal such as aluminum. The sheet can then be rolled into tiny batteries for cellphones or other devices.
Learn more: Printing nanomaterials with plasma
Research that could lead to new medical imaging methods and better treatments for stroke and other brain conditions
A technique Stanford Linear Accelerator Center (SLAC) scientists invented for scanning ancient manuscripts is now being used to probe the human brain, in research that could lead to new medical imaging methods and better treatments for stroke and other brain conditions.
The studies, taking place at SLAC’s Stanford Synchrotron Radiation Lightsource, are led by cell biologist Helen Nichol, of the University of Saskatchewan, with $2.5 million in funding from the Canadian government and the Heart and Stroke Foundation of Canada.
Her team, which includes a Stanford neurosurgeon and stem cell expert, other medical doctors and experts in stroke research and medical imaging, reflects the broad ambitions of this research: to give doctors a better understanding of what they’re seeing in MRI scans of stroke patients; to improve diagnosis and guide treatments; and maybe even to develop new ways to peer inside the living brain. What all these goals have in common is that they depend on the ability to track movements and deposits of tiny traces of metal in human tissue. That’s a job the SSRL technique, known as rapid-scanning XRF, is exquisitely suited to do.
At a synchrotron equipped with this technology, “you can see a large sample of brain, and you have the high resolution the technique offers to actually zoom in on your single cells,” said Dr. Raphael Guzman, a pediatric neurosurgeon and stem cell expert at Stanford University Medical Center who is leading part of the study.
Regular XRF, or X-ray fluorescence imaging, uses the SSRL’s powerful X-ray beam to knock electrons out of the inner shells of atoms in a sample. As more electrons fall in to fill the gaps, they give off light—fluoresce—and the color of that light reveals which chemical elements are present.
In the mid-2000s, SLAC scientists had a chance to use this technique to examine a priceless manuscript—the Archimedes palimpsest, a 10th century parchment containing copies of works by the ancient Greek mathematician that had been erased by monks and recycled as a prayer book. But they soon realized that to examine something this big in a reasonable amount of time, they would have to make the scanning go much faster.
Led by physicist Uwe Bergmann, they developed a way to move the beam continually over the sample, rather than imaging one spot at a time. This allowed them to proceed 300 times faster—a scan that used to take 12 days could now be done in an hour—and opened up the possibility of examining much bigger samples, from art objects and cultural artifacts to fossils of early birds. In 2006, Bergmann and an international team of researchers used rapid-scanning XRF to reveal the words of Archimedes, including passages that had been lost for centuries, beneath the prayer writings on the old parchment.
When she read about this research, Nichol said, “It just grabbed me. I thought, if he could map something as big as a sheet of paper, we could map a brain.”
She and her colleagues began using rapid-scanning XRF at the SSRL to look at metals in the preserved brains of people who had died with Alzheimer’s disease, Parkinson’s disease or multiple sclerosis. The healthy brain needs metals like iron, zinc, manganese and copper to work properly, and some studies had indicated that in people with neurodegenerative diseases, the normal distribution of these metals was out of whack. But did these changes cause the disease, or were they a result of it? And were they consistent enough to offer a tool for diagnosis?
To the team’s disappointment, scans of brain slices from eight people with Parkinson’s disease found no clear pattern—nothing that could help doctors diagnose their brain conditions or understand how they came about. “What we found is that the changes you see in Parkinson’s and Alzheimer’s are sort of variations on normal,” Nichol said.
She decided that beam time on the SSRL was better spent studying a disorder that caused clear, obvious damage in the brain. Stroke fit the bill.
When a stroke blocks the flow of blood to the brain, it produces striking lesions, almost like bruises, caused by bleeding and tissue death. Blood contains iron, which is part of the hemoglobin that carries oxygen in red blood cells. When bleeding occurs, the iron leaks out in a form that can damage surrounding cells, so the body quickly tucks the iron away in various chemical compounds for safe storage.
Standard MRI scans can image and identify those iron compounds and show doctors where bleeding has taken place. But they may not catch the very smallest bleeds, Nichol said, or identify other elements that may be disrupted during a stroke.
That’s where RS-XRF comes in. As the first practical tool for imaging a number of different metals in all of their chemical forms at the same time—and over a large section of the brain—it “opens up a lot of doors to things you can’t see with medical imaging,” Nichol said. It also can tell one form of iron from another; the spectrum of iron in hemoglobin will look different than free-floating iron or the iron compounds produced by bleeding, for instance.
The idea behind the study is that iron in its varied forms can be used as a marker to reveal changes in molecules and cells that follow a stroke, evaluate stroke damage and follow the migration of stem cells that are injected into patients in experimental stroke treatments. The scientists will also look at sulfur compounds that are thought to play a role in protecting the brain from damage, and evaluate the effects of the few stroke treatments available, such as chilling the brain, on the distribution of iron and sulfur.
Members of the team come to the SSRL about three weeks per year to scan brain tissue from rats, including some that have been bred to make them unusually susceptible to stroke, as well as human brain tissue from the National Institutes of Health brain bank. Additional experiments are being done at the Canadian Light Source at the University of Saskatchewan.
While they are not putting live patients in a synchrotron, the scientists hope their findings will someday result in the ability to scan live patients with methods that are much more sensitive to damage from tiny strokes that now go unnoticed.