23 Apr 2015
Real or counterfeit? Northwestern Univ. scientists have invented sophisticated fluorescent inks that one day could be used as multicolored barcodes for consumers to authenticate products that are often counterfeited. Snap a photo with your smartphone, and it will tell you if the item is real and worth your money.
Counterfeiting is very big business worldwide, with $650 billion per year lost globally, according to the International Chamber of Commerce. The new fluorescent inks give manufacturers and consumers an authentication tool that would be very difficult for counterfeiters to mimic.
These inks, which can be printed using an inkjet printer, are invisible under normal light but visible under ultraviolet light. The inks could be stamped as barcodes or QR codes on anything from banknotes and bottles of whisky to luxury handbags and expensive cosmetics, providing proof of authenticity.
A key advantage is the control one has over the color of the ink; the inks can be made in single colors or as multicolor gradients. An ink’s color depends on the amounts and interaction of three different “ingredient” molecules, providing a built-in “molecular encryption” tool. (One of the ingredients is a sugar.) Even a tiny tweak to the ink’s composition results in a significant color change.
“We have introduced a level of complexity not seen before in tools to combat counterfeiters,” said Sir Fraser Stoddart, the senior author of the study. “Our inks are similar to the proprietary formulations of soft drinks. One could approximate their flavor using other ingredients, but it would be impossible to match the flavor exactly without a precise knowledge of the recipe.”
Sir Fraser is the Board of Trustees Professor of Chemistry in the Weinberg College of Arts and Sciences.
“The rather unusual relationship between the composition of the inks and their color makes them ideal for security applications where it’s desirable to keep certain information encrypted or to have brand items with unique labels that can be authenticated easily,” Stoddart said.
With a manufacturer controlling the ink’s “recipe,” or chemical composition, counterfeiters would find it virtually impossible to reverse engineer the color information encoded in the printed barcodes, QR codes or trademarks. Even the inks’ inventors would not be able to reverse engineer the process without a detailed knowledge of the encryption settings.
Details of the fluorescent inks, which are prepared from simple and inexpensive commodity chemicals, are published in Nature Communications.
Stoddart’s research team, led by Xisen Hou and Chenfeng Ke, stumbled across the water-based ink composite serendipitously. A series of rigorous follow-up investigations unraveled the mechanism of the unique behavior of the inks and led the scientists to propose an encryption theory for security printing.
Hou, a third-year graduate student, and Ke, a postdoctoral fellow, are co-first authors of the paper.
The researchers developed an encryption and authentication security system combined with inkjet-printing technology. In the study, they demonstrated both a monochromic barcode and QR code printed on paper from an inkjet printer. The information, invisible under natural light, can be read on a smartphone under UV light.
As another demonstration of the technology, the research team loaded the three chemical components into an inkjet cartridge and printed Vincent Van Gogh’s “Sunflowers” painting with good color resolution. Like the barcodes and QR codes, the printed image is only visible under UV light.
The inks are formulated by mixing a simple sugar (cyclodextrin) and a competitive binding agent together with an active ingredient (a molecule known as heterorotaxane) whose fluorescent color changes along a spectrum of red to yellow to green, depending upon the way the components come together. An infinite number of combinations can be defined easily.
Although the sugar itself is colorless, it interacts with the other components of the ink, encapsulating some parts selectively, thus preventing the molecules from sticking to one another and causing a change in color that is difficult to predict. This characteristic presents a formidable challenge to counterfeiters.
Hou and Ke were trying to prevent fluorophore aggregation by encircling a fluorescent molecule with other ring-shaped molecules, one being cyclodextrin. Unexpectedly, they isolated the compound that is the active ingredient of the inks. They found that the compound’s unusual arrangement of three rings trapped around the fluorescent component affords the unique aggregation behavior that is behind the color-changing inks.
“You never know what Mother Nature will give you,” Hou said. “It was a real surprise when we first isolated the main component of the inks as an unexpected byproduct. The compound shows a beautiful dark-red fluorescence under UV light, yet when we dissolve it in large amounts of water, the fluorescent color turns green. At that moment, we realized we had discovered something that is quite unique.”
The fluorescent colors can be tuned easily by adding the sugar dissolved in water. As more cyclodextrin is added, the fluorescent color changes from red to yellow and then green, giving a wide range of beautiful colors. The fluorescent color can be reversed, by adding another compound that mops up the cyclodextrin.
The researchers also discovered that the fluorescent ink is sensitive to the surface to which it is applied. For example, an ink blend that appears as orange on standard copy paper appears as green on newsprint. This observation means that this type of fluorescent ink can be used to identify different papers.
“This is a smart technology that allows people to create their own security code by manually setting all the critical parameters,” Hou said. “One can imagine that it would be virtually impossible for someone to reproduce the information unless they knew exactly all the parameters.”
The researchers also have developed an authentication mechanism to verify the protected information produced by the fluorescent security inks. Simply by wiping some wet authentication wipes on top of the fluorescent image causes its colors to change under UV light.
“Since the color changing process is dynamic, even if counterfeiters can mimic the initial fluorescent color, they will find it impossible to reproduce the color-changing process,” Ke emphasized.
Source: Northwestern Univ.
23 Apr 2015
Imagine an electronic screen that looks and feels like paper that could connect to your smartphone. You can shift your longer readings and video viewing to this bendable screen, then roll it up and throw it in your bag when you arrive at your subway stop. This may sound like sci-fi, but Israeli researchers have actually found a way to develop such thin, flexible screens you can use on the go.
A new Tel Aviv University study suggests that a novel DNA nanotechnology could produce a structure that can be used to produce ultra-thin, flexible screens. The research team’s building blocks are three molecules they’ve synthesized, which later self-assembled into ordered structures. Essentially, the team has built the molecular backbone of a super-slim, bendable digital display. In the field of bio-nanotechnology, scientists utilize these molecular building blocks to develop cutting-edge technologies with properties not available for inorganic materials such as plastic and metal.
This could provide a solution to roughly 2 billion smartphone users who may not want the content they view to be confined to a pocket-sized screen. That’s because currently the size of smartphone screens makes it particularly hard to read more than a few hundred words at a time or watch videos without feeling like you’re on the tilt-a-whirl at Six Flags.
The number of people using mobile devices to view media is on the rise. According to Pew Research Center, 68 percent of smartphone owners use their phone occasionally to follow breaking news stories, and 33 percent do it frequently. Moreover, YouTube reports that 50 percent of its 4 billion video views per month are watched on a mobile device.
SEE ALSO: CES 2015: The Best Of Israeli Tech
The structures formed by the researchers were found to emit light in every color, as opposed to other fluorescent materials that shine only in one specific color. Moreover, light emission was observed in response to electric voltage — which makes this technology a perfect candidate for display screens.
The TAU researchers, who recently published their findings in the scientific journal Nature Nanotechnology, are currently building a prototype of the screen and are in talks with major consumer electronics companies regarding the technology, which they’ve patented. “Our material is light, organic and environmentally friendly,” TAU’s Prof. Ehud Gazit said in a statement. “It is flexible, and its single layer emits the same range of light that requires several layers today.” Moreover, fewer layers are better for consumers, he says: “By using only one layer, you can minimize production costs dramatically, which will lead to lower prices.”
Back to the good old newspaper display?
It’s important to mention that this technology is still in its early stages and a price tag for these screens remains unknown. What is clear, however, is that the desire to consume content on portable, large screens isn’t going away and consumer preferences are trending more and more toward bigger screens.
Ironically, people seem to be drawn back to the old newspaper display – thin, flexible, and capable of being rolled up; now, all of these features are turning digital.
Regardless of flexibility, the tendency to enlarge mobile screens was already evident last year. It is widely believed that sales of Apple and Samsung (500 million smartphone in 2014) were buoyed by their newest smartphone iterations which boast larger screens than past versions. Apple especially took note of this trend, releasing the iPhone 6 (4.7 inch screen) and iPhone 6 Plus (5.5 inches) simultaneously.
18 Apr 2015
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Research into organic semiconductors could lead to more efficient LED TVs and flexible solar cells that are cheaper to make and take less energy to produce according to researchers at the University of Bath.
Semiconductors are used in devices such as LED TVs to convert electric current to light; and in photovoltaic cells, which absorb light energy and convert it into electricity. Traditionally ‘inorganic semiconductors’, often based on silicon, are used in such devices. However these are relatively difficult to make and take a lot of energy to produce.
It is estimated that solar cells made from silicon can take a year to pay back the total energy consumed in their manufacture.
Despite efforts over the last three decades to develop organic semiconductors on a mass scale, scientists have been challenged by the fact that this type of semiconductor is less efficient at conducting electricity.
Now, a team from the University of Bath, collaborating with scientists in Germany and The Netherlands, has identified how the electronics industry could overcome some of the existing problems associated with using organic semiconductors.
Semiconductors are used in devices such as LED TVs to convert electric current to light; and in photovoltaic cells, commonly known as solar panels, which absorb light energy and convert it into electricity.
Dr Daniele Di Nuzzo, Research Officer in Physics at the University and first author on the paper, explained: “Conventional semiconductor devices are tricky to make because they first require the production of crystalline materials. Because of this, they also use up a lot of energy to be produced.
“In contrast, organic semiconductors can be processed via printing techniques. For example, organic semiconducting polymers can be dissolved in a solvent to make an electronic ink to be printed onto a surface.
“However they have a disordered structure and conduct electrical charges less well than silicon.”
One way of improving the electrical properties of organic semiconductors is to mix them with ‘doping’ molecules, which work by adding electrical charges to the polymer.
Dr Di Nuzzo added: “It’s difficult currently to implement the doping technique in an effective way to produce organic semiconductor devices that work with high performances. Our research shows why this is the case and suggests how we can improve the performance of these materials.”
The study, published in the journal Nature Communications, found that the size and geometrical position of the doping molecule used had an effect on the efficiency of the semiconductor material.
Dr Enrico Da Como from the University’s Department of Physics, led the study. He explained: “The organic polymer consists of a chain of units which is mixed with the doping molecule before it is printed onto a surface. We found that the doping molecule can bind to the polymer in several different orientations, some of which make a more effective semiconductor than others.
“Our work suggests that if you use a larger doping molecule, you limit the number of ways it can bind to the polymer, making the efficiency of the semiconductor more consistent.”
Explore further: Researchers discover N-type polymer for fast organic battery
More information: Daniele Di Nuzzo, et al “How intermolecular geometrical disorder affects the molecular doping of donor–acceptor copolymers” is published in Nature Communications 6, Article number: 6460 DOI: 10.1038/ncomms7460
Faculty Highlight: Vladimir Bulović
MIT’s associate dean for innovation is inventing at the nanoscale.
Imagine hearing aids powered by see-through solar cells coating your eyeglasses, tiny switches operated efficiently by squeezable molecules, and television displays as colorful as nature operating at a fraction of today’s energy consumption. These are just some of the visions being brought to life in the laboratory of MIT Professor Vladimir Bulović. “Basic science discoveries lead us to devices that can exceed the state-of-the-art performances,” says Bulović, the Fariborz Maseeh Chair in Emerging Technology at MIT’s School of Engineering.
An entrepreneur with multiple startups, holder of more than 75 patents, and award-winning educator, Bulović is at heart an applied scientist. His Organic and Nanostructured Electronics Lab (ONE Lab) has 18 students and postdoctoral associates but is used collaboratively by over 70 individuals. “Every student participates as a team member in the operation of the lab,” he says.
One key motivation for Bulović’s work is increasing energy efficiency. “Today, more than 2 percent of the world’s electricity is used on TVs and display monitors. We think we can reduce that by a factor of two, which would be a significant energy impact. Even more, today, 20 percent of electricity is used on powering light bulbs. We think we can reduce that number by a factor of two, as well. Increasing energy efficiency is one key driver of our research,” Bulović explains.
Principles and applications
“All of the pursuits start with the understanding of the basic physical principles which are then applied to the operation of practical devices,” says Bulović. The group combines expertise in electricity and magnetism and knowledge of quantum mechanics together with uses of nanomaterials to make devices as diverse as solar cells, LEDs, lasers, chemosensors, and mechanical actuators. “We use our devices as test beds of physics, and try to ascertain what physical mechanisms dominate the nanoscale proceses within them. If the devices do not perform as well as we expected, they serve as a platform through which we learn physical behavior that we have missed previously, and then from that we apply the new refined physical principle to design a better structure,” he says.
Development of renewable energy technologies that could be manufactured at scale is another driver of the group’s research. In May of last year, Bulović and collaborators set a new record, 8.55 percent efficiency, for quantum-dot solar cells. This collaboration with MIT chemistry Professor Moungi Bawendi and graduate students Chia-Hao Chuang and Patrick Brown demonstrated a fabrication process that does not require an inert atmosphere or high temperatures for its active layers, with the exception of electrodes. In these solar structures, quantum dots, fine-tuned for their optical response and charge transport, absorb the incident light, which promotes an electron from its ground to its excited state, and from there charges can move through the quantum dot film yielding an electric current.
In another recent development, Bulović and Richard Lunt, who was a postdoc at the time and is now a professor at Michigan State University, demonstrated a new solar technology that uses molecular films, which do not absorb visible light, enabling these solar cells to appear uniquely optically transparent, practically invisible. These transparent solar cells can power devices such as an electronic book reader or provide electricity to future office buildings by coating their windows. Bulović also envisions coatings for eyeglasses that power Bluetooth radios or hearing aids from available light. “These invisible coatings absorb infrared light, which we can not see, to generate electricity, and could be as simple to place on your glasses as it is to paint a surface,” he says.
Working in ONE Lab, MIT graduate student Farnaz Niroui and colleagues demonstrated electromechanical switches that use nanoscale deformations of thin films of molecules to control current passage through such switches. Niroui’s latest work builds on her earlier work showing a design for a squeezable switch — or “squitch” — which fills the narrow gap between metal contacts with an organic molecular film that can be compressed tightly enough to allow current to tunnel, or flow, from one electrode to another without any physical contact between the electrodes (the “on” position). When compressing pressure is released, the molecules spring back to open the gap between the electrodes wide enough that current cannot flow (the “off” position). The goal is to develop a fast-acting, low-power switch that can complement or replace switches in transistor-based systems.
“We are just as excited to discover a new physical operation within our structures as we are to make an operating device that exceeds the state of the art,” Bulović explains. “And it’s that interplay between the basic physical principles, demonstration of them in a device, sometimes not meeting the full potential in a device, and hence going back to the demonstration of why the physics has not quite worked the way you expected it. That refinement of ideas, the feedback, is what leads us to the next and next and next advancement.”
“What today’s researchers are exploring is just the beginning of a vast opportunity in the nano sciences and technology,” he adds. For example, Polina Anikeeva and Will Tisdale, former members of the Bulović lab and now both MIT faculty members in their own right, have followed opportunities in biological and optical measurement applications of nanotechnology. “They exemplify the breadth of opportunity that is ahead of us,” Bulović says. The planned MIT.nano facility, whose construction Bulović is supervising, will help move forward the new era of nanotechnology, he says.
“The hardest decision for our group is to decide what not to work on because there are so many exciting research areas one could engage in. I am often delighted to see a field that we might have been among the first to be in, grow and blossom, allowing us to step out of it and allowing us to think about the next challenge we should engage,” Bulović says.
Breakthrough technologies like transparent solar cells come from looking at old problems in a new way. “When our group talks about the next solar cell, we are not considering conventional ones. We are looking at ways of changing the paradigm of what matters for solar technology adoption,” Bulović explains. “Often, solar cell efficiencies are cited as the one metric that you need to push forward to advance the technology, and that is true, as efficiency is a very important metric. However, it is also important to notice that there are other solar technology properties one can advance to deliver impact.”
“In the example of optically transparent devices,” Bulović adds, “their nearly invisible format enables integration of solar technology on any surface, hence advancing a new paradigm for solar deployment. As another example, in our lab we consider how much does the solar cell weigh? If one can provide a lightweight cell, it would be easier to install it, reducing one of the dominant costs of solar deployment. A lightweight solar cell will also be easier to deliver to a remote village, which might have no access to grid electricity and possibly no paved roads. When carrying a solar cell on one’s back to bring it to a remote village, the question of ‘What is the solar cell efficiency?’ is less important than knowing how many trips you will have to make, which is the same as asking how much power can you generate per kilogram of the solar cell. In this case it could be desirable to have a less efficient cell if it is significantly lighter. By changing the weight, we can change modality of use.”
So a solar cell can change its form from a panel that you install on your roof, to a flexible device that you can have on any surface, including clothes, bags, sheets, or whatever else one can imagine. Indeed, a 2011 collaboration between Professor Karen Gleason’s and Bulović’s groups generated extremely light solar cells grown on a sheet of paper. In December 2014, Joel Jean and Annie Wang from the Bulović group further reduced the solar cell substrate thickness to only a few microns, making these solar devices light enough to float on a soap bubble.
Translation of technologies from Bulović’s lab to marketplace is often done by startup ventures initiated by graduating students. Such was the case with the transparent solar cell technology, which was licensed by Ubiquitous Energy, an MIT startup that opened its research facility just a few months ago, with the aim of changing the paradigm of what solar technology can be. Prior to that, in 2005 Bulović co-founded with MIT students QD Vision, which uses quantum dots for display technology that can presently be found in over 2 million televisions. In addition, QD Vision’s quantum dot lighting technology was shown to enhance the color quality of the most efficient lightbulbs, reproducing the glow spectrum of a typical incandescent light bulb, but consuming only one-sixth the power. In 2008, Professor Martin Schmidt and Bulović, with their students, spun out Kateeva, which is commercializing printing technology for large-scale electronics, including the toolsets enabling reliable fabrication of organic light emitting diodes (OLEDs) over 2-meter wide substrates.
Bulović also heads MIT.nano, a $350 million construction project to build a state-of-the-art nanotechnology research facility in the heart of the MIT campus. “The goal of MIT.nano is to provide a transformational 21st-century workshop. In our building designs we are imagining what kind of toolbox will the campus need for the next three decades, ’til 2050. We need to build a flexible research space and a community-oriented space so that people feel empowered to go to it, use it, and then redefine it as the years progress, adapting it to the needs of the next generation of researchers,” he says.
Bulović also is co-chair of the MIT Innovation Initiative, which aims to combine education, research, outreach, and the study of innovation science and policy to positively affect the world by accelerating the impact of multitudes of ideas generated on campus.
A preliminary report in December 2014 made specific recommendations for improving innovation impact, including the creation of a Laboratory for Innovation Science and Policy. The new lab is envisioned to study the social and market context of taking ideas from lab demonstration to practical, large-scale application in the world. It would conduct research on venture formation, scale-up, and understanding the marketplace, as well as social need and response to it.
Also envisioned as part of the Innovation Initiative are new programs in entrepreneurship for postdocs, graduate students, and a minor for undergraduates with a certificate in innovation and entrepreneurship.
Third-, fourth-, and fifth-grade math
Despite his intensive workload, Bulović finds time to teach math to elementary-school students — third-graders this year and fourth- and fifth-graders in years past. “Inspired by the curiosity of our four children, my wife and I have been developing and delivering materials for a number of years that aim to expose early learners to the wonders of math applied to the real world,” he says. “Once a week we have the privilege to join a group of students who engage with us in discovery of how a lever works, help us determine the height of a tree from its shadow, estimate the number of books in a library, practice sorting algorithms, determine angles between hands of a clock. … With cartoons of smiling penguins, mischievous cows, or other unexpected characters on our math worksheets, the math problems are presented as stories of quests and adventures. It has been a remarkably enjoyable experience for all of us, now in its eighth year.”
This transmission electron microscope image shows a graphene quantum dot with zigzag edges. The quantum dots can be created in bulk from carbon fiber through a chemical process discovered at Rice University.
A Rice University laboratory has found a way to turn common carbon fiber into graphene quantum dots, tiny specks of matter with properties expected to prove useful in electronic, optical and biomedical applications.
The Rice lab of materials scientist Pulickel Ajayan, in collaboration with colleagues in China, India, Japan and the Texas Medical Center, discovered a one-step chemical process that is markedly simpler than established techniques for making graphene quantum dots. The results were published online this month in the American Chemical Society’s journal Nano Letters.
“There have been several attempts to make graphene-based quantum dots with specific electronic and luminescent properties using chemical breakdown or e-beam lithography of graphene layers,” said Ajayan, Rice’s Benjamin M. and Mary Greenwood Anderson Professor of Mechanical Engineering and Materials Science and of chemistry. “We thought that as these nanodomains of graphitized carbons already exist in carbon fibers, which are cheap and plenty, why not use them as the precursor?”
Quantum dots, discovered in the 1980s, are semiconductors that contain a size- and shape-dependent band gap. These have been promising structures for applications that range from computers, LEDs, solar cells and lasers to medical imaging devices. The sub-5 nanometer carbon-based quantum dots produced in bulk through the wet chemical process discovered at Rice are highly soluble, and their size can be controlled via the temperature at which they’re created.
The Rice researchers were attempting another experiment when they came across the technique. “We tried to selectively oxidize carbon fiber, and we found that was really hard,” said Wei Gao, a Rice graduate student who worked on the project with lead author Juan Peng, a visiting student from
Green-fluorescing graphene quantum dots created at Rice University surround a blue-stained nucleus in a human breast cancer cell. Cells were placed in a solution with the quantum dots for four hours. The dots, each smaller than 5 nanometers, easily passed through the cell membranes, showing their potential value for bio-imaging.
Nanjing University who studied in Ajayan’s lab last year. “We ended up with a solution and decided to look at a few drops with a transmission electron microscope.”
The specks they saw were bits of graphene or, more precisely, oxidized nanodomains of graphene extracted via chemical treatment of carbon fiber. “That was a complete surprise,” Gao said. “We call them quantum dots, but they’re two-dimensional, so what we really have here are graphene quantum discs.”
Gao said other techniques are expensive and take weeks to make small batches of graphene quantum dots. “Our starting material is cheap, commercially available carbon fiber. In a one-step treatment, we get a large amount of quantum dots. I think that’s the biggest advantage of our work,” she said.Further experimentation revealed interesting bits of information: The size of the dots, and thus their photoluminescent properties, could be controlled through processing at relatively low temperatures, from 80 to 120 degrees Celsius. “At 120, 100 and 80 degrees, we got blue, green and yellow luminescing dots,” she said.
They also found the dots’ edges tended to prefer the form known as zigzag. The edge of a sheet of graphene — the single-atom-thick form of carbon — determines its electrical characteristics, and zigzags are semiconducting.
Their luminescent properties give graphene quantum dots potential for imaging, protein analysis, cell tracking and other biomedical applications, Gao said. Tests at Houston’s MD Anderson Cancer Center and Baylor College of Medicine on two human breast cancer lines showed the dots easily found their way into the cytoplasm and did not interfere with the cells’ proliferation.
“The green quantum dots yielded a very good image,” said co-author Rebeca Romero Aburto, a graduate student in the Ajayan lab who also studies at MD Anderson. “The advantage of graphene dots over fluorophores is that their fluorescence is more stable and they don’t photobleach. They don’t lose their fluorescence as easily. They have a depth limit, so they may be good for in vitro and in vivo (small animal) studies, but perhaps not optimal for deep tissues in humans.
Dark spots on a transmission electron microscope grid are graphene quantum dots made through a wet chemical process at Rice University. The inset is a close-up of one dot. Graphene quantum dots may find use in electronic, optical and biomedical applications.
“But everything has to start in the lab, and these could be an interesting approach to further explore for bioimaging,” Romero Alburto said. “In the future, these graphene quantum dots could have high impact because they can be conjugated with other entities for sensing applications, too.”
Co-authors include Angel Martí, a professor of chemistry and bioengineering, postdoctoral research associates Zheng Liu and Liehui Ge, senior research scientist Lawrence Alemany and graduate student Xiaobo Zhan, all of Rice; Rice alumnus Li Song of Shinshu University, Japan; Bipin Kumar Gupta of the National Physical Laboratory, New Delhi, who worked at the Ajayan lab on an Indo-US Science and Technology Forum fellowship; Guanhui Gao of the Ocean University of China; Sajna Antony Vithayathil, a research technician, and Benny Abraham Kaipparettu, a postdoctoral researcher, both at Baylor College of Medicine; Takuya Hayashi, an associate professor of engineering at Shinshu University, Japan; and Jun-Jie Zhu, a professor of chemistry at Nanjing University.
The research was supported by Nanoholdings, the Office of Naval Research MURI program on graphene, the Natural Science Foundation of China, the National Basic Research Program of China, the Indo-US Science and Technology Forum and the Welch Foundation.
See Also from Rice University:
Quantum Dots from Coal + Graphene Could Dramatically Cut the Cost of Energy from Fuel Cells
Rice University’s cheap hybrid outperforms rare metal as fuel-cell catalyst
Graphene quantum dots created at Rice University grab onto graphene platelets like barnacles attach themselves to the hull of a boat. But these dots enhance the properties of the mothership, making them better than platinum catalysts for certain reactions within fuel cells.
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