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Toward a coronavirus breathalyzer test

Few people who have undergone nasopharyngeal swabs for coronavirus testing would describe it as a pleasant experience. The procedure involves sticking a long swab up the nose to collect a sample from the back of the nose and throat, which is then analyzed for SARS-CoV-2 RNA by the reverse-transcription polymerase chain reaction (RT-PCR). Now, researchers reporting in ACS Nano have developed a prototype device that non-invasively detected COVID-19 in the exhaled breath of infected patients.

In addition to being uncomfortable, the current gold standard for COVID-19 testing requires RT-PCR, a time-consuming laboratory procedure. Because of backlogs, obtaining a result can take several days. To reduce transmission and mortality rates, healthcare systems need quick, inexpensive and easy-to-use tests. Hossam Haick, Hu Liu, Yueyin Pan and colleagues wanted to develop a nanomaterial-based sensor that could detect COVID-19 in exhaled breath, similar to a breathalyzer test for alcohol intoxication. Previous studies have shown that viruses and the cells they infect emit volatile organic compounds (VOCs) that can be exhaled in the breath.

The researchers made an array of gold nanoparticles linked to molecules that are sensitive to various VOCs. When VOCs interact with the molecules on a nanoparticle, the electrical resistance changes. The researchers trained the sensor to detect COVID-19 by using machine learning to compare the pattern of electrical resistance signals obtained from the breath of 49 confirmed COVID-19 patients with those from 58 healthy controls and 33 non-COVID lung infection patients in Wuhan, China. Each study participant blew into the device for 2-3 seconds from a distance of 1¬-2 cm. Once machine learning identified a potential COVID-19 signature, the team tested the accuracy of the device on a subset of participants. In the test set, the device showed 76% accuracy in distinguishing COVID-19 cases from controls and 95% accuracy in discriminating COVID-19 cases from lung infections. The sensor could also distinguish, with 88% accuracy, between sick and recovered COVID-19 patients. Although the test needs to be validated in more patients, it could be useful for screening large populations to determine which individuals need further testing, the researchers say.

The authors acknowledge funding from the Technion-Israel Institute of Technology.

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Spider silk inspires new class of functional synthetic polymers

Synthetic polymers have changed the world around us, and it would be hard to imagine a world without them. However, they do have their problems. It is for instance hard from a synthetic point of view to precisely control their molecular structure. This makes it harder to finely tune some of their properties, such as the ability to transport ions. To overcome this problem, University of Groningen assistant professor Giuseppe Portale decided to take inspiration from nature. The result was published in Science Advances on July 17: a new class of polymers based on protein-like materials that work as proton conductors and might be useful in future bio-electronic devices.

‘I have been working on proton conducting materials on and off since my PhD’, says Portale. ‘I find it fascinating to know what makes a material transport a proton so I worked a lot on optimizing structures at the nanoscale level to get greater conductivity.’ But it was only a few years ago that he considered the possibility of making them from biological, protein-like structures. He came to this idea together with professor Andreas Hermann, a former colleague at the University of Groningen, now working at the DWI — Leibniz Institute for Interactive Materials in Germany. ‘We could immediately see that proton-conducting bio-polymers could be very useful for applications like bio-electronics or sensors’, Portale says.

More active groups, more conductivity

But first, they had to see if the idea would work. Portale: ‘Our first goal was to prove that we could precisely tune the proton conductivity of the protein-based polymers by tuning the number of ionisable groups per polymer chain’. To do this, the researchers prepared a number of unstructured biopolymers that had different numbers of ionisable groups, in this case, carboxylic acid groups. Their proton conductivity scaled linearly with the number of charged carboxylic acid groups per chain. ‘It was not groundbreaking, everybody knows this concept. But we were thrilled that we were able to make something that worked as expected’, Portale says.

For the next step, Portale relied on his expertise in the field of synthetic polymers: ‘I have learned over the years that the nanostructure of a polymer can greatly influence the conductivity. If you have the right nanostructure, it allows the charges to bundle together and increase the local concentration of these ionic groups, which dramatically boosts proton conductivity.’ Since the first batch of biopolymers was completely amorphous, the researchers had to switch to a different material. They decided to use a known protein that had the shape of a barrel. ‘We engineered this barrel-like protein and added strands containing carbocyclic acid to its surface’, Portale explains. ‘This increased conductivity greatly.’

Novel Spider silk polymer

Unfortunately, the barrel-polymer was not very practical. It had no mechanical strength and it was difficult to process, so Portale and his colleagues had to look for an alternative. They landed on a well-known natural polymer: spider silk. ‘This is one of the most fascinating materials in nature, because it is very strong but can also be used in many different ways’, says Portale. ‘I knew spider silk has a fascinating nanostructure, so we engineered a protein-like polymer that has the main structure of spider silk but was modified to host strands of carbocyclic acid.’

The novel material worked like a charm. ‘We found that it self-assembles at the nanoscale similarly to spider silk while creating dense clusters of charged groups, which are very beneficial for the proton conductivity’, Portale explains. ‘And we were able to turn it into a robust centimetre-sized membrane.’ The measured proton conductivity was higher than any previously known biomaterials, but they are not there yet according to Portale: ‘This was mainly fundamental work. In order to apply this material, we really have to improve it and make it processable.’

Dreams

But even though the work is not yet done, Portale and his co-workers can already dream about applying their polymer: ‘We think this material could be useful as a membrane in fuel cells. Maybe not for the large scale fuel cells that you see in cars and factories, but more on a small scale. There is a growing field of implantable bio-electronic devices, for instance, glucose-powered pacemakers. In the coming years, we hope to find out if our polymer can make a difference there, since it is already bio-compatible.’

For the short term, Portale mainly thinks about sensors. ‘The conductivity we measure in our material is influenced by factors in the environment, like humidity or temperature. So if you want to store something at a certain humidity you can place this polymer between two electrodes and just measure if anything changes.’ However, before all these dreams come true, there are a lot of questions to be answered. ‘I am very proud that we were able to control these new materials on a molecular scale and build them from scratch. But we still have to learn a lot about their capabilities and see if we can improve them even further.’

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Move over, Siri! Researchers develop improv-based Chatbot

What would conversations with Alexa be like if she was a regular at The Second City?

Jonathan May, research lead at the USC Information Sciences Institute (ISI) and research assistant professor of computer science at USC’s Viterbi School of Engineering, is exploring this question with Justin Cho, an ISI programmer analyst and prospective USC Viterbi Ph.D. student, through their Selected Pairs Of Learnable ImprovisatioN (SPOLIN) project. Their research incorporates improv dialogues into chatbots to produce more engaging interactions.

The SPOLIN research collection is made up of over 68,000 English dialogue pairs, or conversational dialogues of a prompt and subsequent response. These pairs model yes-and dialogues, a foundational principle in improvisation that encourages more grounded and relatable conversations. After gathering the data, Cho and May built SpolinBot, an improv agent programmed with the first yes-and research collection large enough to train a chatbot.

The project research paper, “Grounding Conversations with Improvised Dialogues,” was presented on July 6 at the Association of Computational Linguistics conference, held July 5-10.

Finding Common Ground

May was looking for new research ideas in his work. His love for language analysis had led him to work on Natural Language Processing (NLP) projects, and he began searching for more interesting forms of data he could work with.

“I’d done some improv in college and pined for those days,” he said. “Then a friend who was in my college improv troupe suggested that it would be handy to have a ‘yes-and’ bot to practice with, and that gave me the inspiration — it wouldn’t just be fun to make a bot that can improvise, it would be practical!”

The deeper May explored this idea, the more valid he found it to be. Yes-and is a pillar of improvisation that prompts a participant to accept the reality that another participant says (“yes”) and then build on that reality by providing additional information (“and”). This technique is key in establishing a common ground in interaction. As May put it, “Yes-and is the improv community’s way of saying ‘grounding.'”

Yes-ands are important because they help participants build a reality together. In movie scripts, for example, maybe 10-11% of the lines can be considered yes-ands, whereas in improv, at least 25% of the lines are yes-ands. This is because, unlike movies, which have settings and characters that are already established for audiences, improvisers act without scene, props, or any objective reality.

“Because improv scenes are built from almost no established reality, dialogue taking place in improv actively tries to reach mutual assumptions and understanding,” said Cho. “This makes dialogue in improv more interesting than most ordinary dialogue, which usually takes place with many assumptions already in place (from common sense, visual signals, etc.).”

But finding a source to extract improv dialogue from was a challenge. Initially, May and Cho examined typical dialogue sets such as movie scripts and subtitle collections, but those sources didn’t contain enough yes-ands to mine. Moreover, it can be difficult to find recorded, let alone transcribed, improv.

The Friendly Neighborhood Improv Bot

Before visiting USC as an exchange student in Fall 2018, Cho reached out to May, inquiring about NLP research projects that he could participate in. Once Cho came to USC, he learned about the improv project that May had in mind.

“I was interested in how it touched on a niche that I wasn’t familiar with, and I was especially intrigued that there was little to no prior work in this area,” Cho said. “I was hooked when Jon said that our project will be answering a question that hasn’t even been asked yet: the question of how modeling grounding in improv through the yes-and act can contribute to improving dialogue systems.”

Cho investigated multiple approaches to gathering improv data. He finally came across Spontaneanation, an improv podcast hosted by prolific actor and comedian Paul F. Tompkins that ran from 2015 to 2019.

With its open-topic episodes, about a good 30 minutes of continuous improvisation, high quality recordings, and substantial size, Spontaneanation was the perfect source to mine yes-ands from for the project. The duo fed their Spontaneanation data into a program, and SpolinBot was born.

“One of the cool parts of the project is that we figured out a way to just use improv,” May explained. “Spontaneanation was a great resource for us, but is fairly small as data sets go; we only got about 10,000 yes-ands from it. But we used those yes-ands to build a classifier (program) that can look at new lines of dialogue and determine whether they’re yes-ands.”

Working with improv dialogues first helped the researchers find yes-ands from other sources as well, as most of the SPOLIN data comes from movie scripts and subtitles. “Ultimately, the SPOLIN corpus contains more than five times as many yes-ands from non-improv sources than from improv, but we only were able to get those yes-ands by starting with improv,” May said.

SpolinBot has a few controls that can refine its responses, taking them from safe and boring to funny and wacky, and also generates five response options that users can choose from to continue the conversation.

SpolinBot #Goals

The duo has a lot of plans for SpolinBot, along with extending its conversational abilities beyond yes-ands. “We want to explore other factors that make improv interesting, such as character-building, scene-building, ‘if this (usually an interesting anomaly) is true, what else is also true?,’ and call-backs (referring to objects/events mentioned in previous dialogue turns),” Cho said. “We have a long way to go, and that makes me more excited for what I can explore throughout my PhD and beyond.”

May echoed Cho’s sentiments. “Ultimately, we want to build a good conversational partner and a good creative partner,” he said, noting that even in improv, yes-ands only mark the beginning of a conversation. “Today’s bots, SpolinBot included, aren’t great at keeping the thread of the conversation going. There should be a sense that both participants aren’t just establishing a reality, but are also experiencing that reality together.”

That latter point is key, because, as May explained, a good partner should be an equal, not subservient in the way that Alexa and Siri are. “I’d like my partner to be making decisions and brainstorming along with me,” he said. “We should ultimately be able to reap the benefits of teamwork and cooperation that humans have long benefited from by working together. And the virtual partner has the added benefit of being much better and faster at math than me, and not actually needing to eat!”

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Higher concentration of metal in Moon’s craters provides new insights to its origin

Life on Earth would not be possible without the Moon; it keeps our planet’s axis of rotation stable, which controls seasons and regulates our climate. However, there has been considerable debate over how the Moon was formed. The popular hypothesis contends that the Moon was formed by a Mars-sized body colliding with Earth’s upper crust which is poor in metals. But new research suggests the Moon’s subsurface is more metal-rich than previously thought, providing new insights that could challenge our understanding of that process.

Today, a study published in Earth and Planetary Science Letters sheds new light on the composition of the dust found at the bottom of the Moon’s craters. Led by Essam Heggy, research scientist of electrical and computer engineering at the USC Viterbi School of Engineering, and co-investigator of the Mini-RF instrument onboard NASA Lunar Reconnaissance Orbiter (LRO), the team members of the Miniature Radio Frequency (Mini-RF) instrument on the Lunar Reconnaissance Orbiter (LRO) mission used radar to image and characterize this fine dust. The researchers concluded that the Moon’s subsurface may be richer in metals (i.e. Fe and Ti oxides) than scientists had believed.

According to the researchers, the fine dust at the bottom of the Moon’s craters is actually ejected materials forced up from below the Moon’s surface during meteor impacts. When comparing the metal content at the bottom of larger and deeper craters to that of the smaller and shallower ones, the team found higher metal concentrations in the deeper craters.

What does a change in recorded metal presence in the subsurface have to do with our understanding of the Moon? The traditional hypothesis is that approximately 4.5 billion years ago there was a collision between Earth and a Mars-sized proto-planet (named Theia). Most scientists believe that that collision shot a large portion of Earth’s metal-poor upper crust into orbit, eventually forming the Moon.

One puzzling aspect of this theory of the Moon’s formation, has been that the Moon has a higher concentration of iron oxides than the Earth — a fact well-known to scientists. This particular research contributes to the field in that it provides insights about a section of the moon that has not been frequently studied and posits that there may exist an even higher concentration of metal deeper below the surface. It is possible, say the researchers that the discrepancy between the amount of iron on the Earth’s crust and the Moon could be even greater than scientists thought, which pulls into question the current understanding of how the Moon was formed.

The fact that our Moon could be richer in metals than the Earth challenges the notion that it was portions of Earth’s mantle and crust that were shot into orbit. A greater concentration of metal deposits may mean that other hypotheses about the Moon’s formation must be explored. It may be possible that the collision with Theia was more devastating to our early Earth, with much deeper sections being launched into orbit, or that the collision could have occurred when Earth was still young and covered by a magma ocean. Alternatively, more metal could hint at a complicated cool-down of an early molten Moon surface, as suggested by several scientists.

According to Heggy, “By improving our understanding of how much metal the Moon’s subsurface actually has, scientists can constrain the ambiguities about how it has formed, how it is evolving and how it is contributing to maintaining habitability on Earth.” He further added, “Our solar system alone has over 200 moons — understanding the crucial role these moons play in the formation and evolution of the planets they orbit can give us deeper insights into how and where life conditions outside Earth might form and what it might look like.”

Wes Patterson of the Planetary Exploration Group (SRE), Space Exploration Sector (SES) at Johns Hopkins University Applied Physics Laboratory, who is the project’s principal investigator for Mini-RF and a co-author of the study, added, “The LRO mission and its radar imager Mini-RF are continuing to surprise us with new insights into the origins and complexity of our nearest neighbor.”

The team plans to continue carrying out additional radar observations of more crater floors with the Mini-RF experiment to verify the initial findings of the published investigation.

This research project was funded through the University of Southern California under NASA award NNX15AV76G.

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Laser allows solid-state refrigeration of a semiconductor material

To the general public, lasers heat objects. And generally, that would be correct.

But lasers also show promise to do quite the opposite — to cool materials. Lasers that can cool materials could revolutionize fields ranging from bio-imaging to quantum communication.

In 2015, University of Washington researchers announced that they can use a laser to cool water and other liquids below room temperature. Now that same team has used a similar approach to refrigerate something quite different: a solid semiconductor. As the team shows in a paper published June 23 in Nature Communications, they could use an infrared laser to cool the solid semiconductor by at least 20 degrees C, or 36 F, below room temperature.

The device is a cantilever — similar to a diving board. Like a diving board after a swimmer jumps off into the water, the cantilever can vibrate at a specific frequency. But this cantilever doesn’t need a diver to vibrate. It can oscillate in response to thermal energy, or heat energy, at room temperature. Devices like these could make ideal optomechanical sensors, where their vibrations can be detected by a laser. But that laser also heats the cantilever, which dampens its performance.

“Historically, the laser heating of nanoscale devices was a major problem that was swept under the rug,” said senior author Peter Pauzauskie, a UW professor of materials science and engineering and a senior scientist at the Pacific Northwest National Laboratory. “We are using infrared light to cool the resonator, which reduces interference or ‘noise’ in the system. This method of solid-state refrigeration could significantly improve the sensitivity of optomechanical resonators, broaden their applications in consumer electronics, lasers and scientific instruments, and pave the way for new applications, such as photonic circuits.”

The team is the first to demonstrate “solid-state laser refrigeration of nanoscale sensors,” added Pauzauskie, who is also a faculty member at the UW Molecular Engineering & Sciences Institute and the UW Institute for Nano-engineered Systems.

The results have wide potential applications due to both the improved performance of the resonator and the method used to cool it. The vibrations of semiconductor resonators have made them useful as mechanical sensors to detect acceleration, mass, temperature and other properties in a variety of electronics — such as accelerometers to detect the direction a smartphone is facing. Reduced interference could improve performance of these sensors. In addition, using a laser to cool the resonator is a much more targeted approach to improve sensor performance compared to trying to cool an entire sensor.

In their experimental setup, a tiny ribbon, or nanoribbon, of cadmium sulfide extended from a block of silicon — and would naturally undergo thermal oscillation at room temperature.

At the end of this diving board, the team placed a tiny ceramic crystal containing a specific type of impurity, ytterbium ions. When the team focused an infrared laser beam at the crystal, the impurities absorbed a small amount of energy from the crystal, causing it to glow in light that is shorter in wavelength than the laser color that excited it. This “blueshift glow” effect cooled the ceramic crystal and the semiconductor nanoribbon it was attached to.

“These crystals were carefully synthesized with a specific concentration of ytterbium to maximize the cooling efficiency,” said co-author Xiaojing Xia, a UW doctoral student in molecular engineering.

The researchers used two methods to measure how much the laser cooled the semiconductor. First, they observed changes to the oscillation frequency of the nanoribbon.

“The nanoribbon becomes more stiff and brittle after cooling — more resistant to bending and compression. As a result, it oscillates at a higher frequency, which verified that the laser had cooled the resonator,” said Pauzauskie.

The team also observed that the light emitted by the crystal shifted on average to longer wavelengths as they increased laser power, which also indicated cooling.

Using these two methods, the researchers calculated that the resonator’s temperature had dropped by as much as 20 degrees C below room temperature. The refrigeration effect took less than 1 millisecond and lasted as long as the excitation laser was on.

“In the coming years, I will eagerly look to see our laser cooling technology adapted by scientists from various fields to enhance the performance of quantum sensors,” said lead author Anupum Pant, a UW doctoral student in materials science and engineering.

Researchers say the method has other potential applications. It could form the heart of highly precise scientific instruments, using changes in oscillations of the resonator to accurately measure an object’s mass, such as a single virus particle. Lasers that cool solid components could also be used to develop cooling systems that keep key components in electronic systems from overheating.

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Egg-based coating preserves fresh produce

Eggs that would otherwise be wasted can be used as the base of an inexpensive coating to protect fruits and vegetables, according to Rice University researchers.

The Brown School of Engineering lab of materials scientist Pulickel Ajayan and colleagues have developed a micron-thick coating that solves problems both for the produce and its consumers, as well as for the environment.

When the coating was applied to produce by spraying or dipping, it showed a remarkable ability to resist rotting for an extended period comparable to standard coatings like wax but without some of the inherent problems.

The work by Rice undergraduate students Seohui (Sylvia) Jung and Yufei (Nancy) Cui is detailed in Advanced Materials.

The coating relies on eggs that never reach the market. As the United States produces more than 7 billion eggs a year and manufacturers reject 3% of them, the researchers estimate more than 200 million eggs end up in landfills.

Even before the impact of the new coronavirus, the world wasted a third of the food produced around the globe, the researchers wrote.

“Reducing food shortages in ways that don’t involve genetic modification, inedible coatings or chemical additives is important for sustainable living,” Ajayan said. “The work is a remarkable combination of interdisciplinary efforts involving materials engineers, chemists and biotechnologists from multiple universities across the U.S.”

Along with being edible, the multifunctional coating retards dehydration, provides antimicrobial protection and is largely impermeable both to water vapor to retard dehydration and to gas to prevent premature ripening. The coating is all-natural and washes off with water.

“If anyone is sensitive to the coating or has an egg allergy, they can easily eliminate it,” Jung said.

Egg whites (aka albumen) and yolks account for nearly 70 percent of the coating. Most of the rest consists of nanoscale cellulose extracted from wood, which serves as a barrier to water and keeps produce from shriveling, a small amount of curcumin for its antimicrobial powers and a splash of glycerol to add elasticity.

Lab tests on dip-coated strawberries, avocadoes, bananas and other fruit showed they maintained their freshness far longer than uncoated produce. Compression tests showed coated fruit were significantly stiffer and more firm than uncoated and demonstrated the coating’s ability to keep water in the produce, slowing the ripening process.

An analysis of freestanding films of the coating showed it to be extremely flexible and able to resist cracking, allowing better protection of the produce. Tests of the film’s tensile properties showed it to be just as tough as other products, including synthetic films used in produce packaging. Further tests proved the coating to be nontoxic, and solubility tests showed a thicker-than-usual film is washable.

Rinsing in water for a couple of minutes can completely disintegrate it, Ajayan said.

The researchers continue to refine the coating’s composition and are considering other source materials. “We chose egg proteins because there are lots of eggs wasted, but it doesn’t mean we can’t use others,” said co-corresponding author Muhammad Rahman, a research scientist in Ajayan’s Rice lab, who mentored and led the team.

Jung noted the team is testing proteins that could be extracted from plants rather than animal produce to make coatings.

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Media Feeds API for Chrome Would Enable Recommended Video Feeds

Google Chrome is in the early stages of developing a tool that would bring YouTube-like video recommendation feeds to most any website that has the content to support one. The fresh feature has already found its way to Canary builds of Chrome, where it lets people see what videos are queued up next.

A commit titled “Enables Media Feeds” recently added to the Chromium Gerrit. According to the description, it “enables the Media Feeds feature, which allows us to fetch feeds of media items from websites that support the feature.” How does the proposed Media Feed API function? 

Websites that have video content would, in effect, be able to generate a feed of that content and serve it up to visitors to or registrants of the website. The feed would live in the browser, where site users could view and interact with it. 

“To improve the functionality of [media controls], we want to be able to add support for sites to recommend media content to a user that might be completely new or they might be something the user has started watching,” said the description of the API. “This allows us to deliver a much better experience to users.”

As far as what that experience is, think no further than YouTube or Netflix, which has new videos just a quick tap away waiting to be watched. Three distinct tools would live in the API. First, Chrome could recommend related or relevant content, suggest users continue watching a video they already started, or simply play the next piece of content in the queue. 

Google hasn’t revealed much else about the fledgling API, and in fact, much of the documentation has been pulled from public view. Some limitations were, however, spelled out: the API targets video only, so music or other audio content (think podcasts) are not supported.

While the Media Feeds API works its way through Canary builds of Chrome, website developers would do well to test its functionality to see if it can be put to use on their own web pages. After all, it won’t be of much use if there’s no content to support it once it reaches beta or live status. 

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ClimaCell Announces Weather API Improvements Following Dark Sky API’s Demise

Last month’s announcement that Apple had purchased the popular Dark Sky weather app, and would be killing the API, left a significant void in the weather API landscape. It appears that ClimaCell is hoping to fill this void with well-timed advancements to its ClimaCell Weather API.

Andrew Orr, a writer for macobserver.com, made the observation earlier today that ClimaCell’s announcement of UI improvements and API enhancements is likely more than a coincidence. The company’s newly designed user interface is aimed at highlighting the way that weather data affects life more broadly. Specifically, the UI highlights Road Risk, Wildfires, and Air Quality. ClimaCell also notes improved customizability in an effort to ensure the best user experience possible in all applications. The API also sees the addition of a new data layer that will provide access to a proprietary index analyzing pollen seasonality. 

The API has a free tier for developers that are looking to test out the platform. Anyone requiring over 30,000 calls/month will need to above to paid tiers. Make sure to check out the API documentation for more detail. 

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Electronics that mimic the human brain in efficient learning

Only 10 years ago, scientists working on what they hoped would open a new frontier of neuromorphic computing could only dream of a device using miniature tools called memristors that would function/operate like real brain synapses.

But now a team at the University of Massachusetts Amherst has discovered, while on their way to better understanding protein nanowires, how to use these biological, electricity conducting filaments to make a neuromorphic memristor, or “memory transistor,” device. It runs extremely efficiently on very low power, as brains do, to carry signals between neurons. Details are in Nature Communications.

As first author Tianda Fu, a Ph.D. candidate in electrical and computer engineering, explains, one of the biggest hurdles to neuromorphic computing, and one that made it seem unreachable, is that most conventional computers operate at over 1 volt, while the brain sends signals called action potentials between neurons at around 80 millivolts — many times lower. Today, a decade after early experiments, memristor voltage has been achieved in the range similar to conventional computer, but getting below that seemed improbable, he adds.

Fu reports that using protein nanowires developed at UMass Amherst from the bacterium Geobacter by microbiologist and co-author Derek Lovely, he has now conducted experiments where memristors have reached neurological voltages. Those tests were carried out in the lab of electrical and computer engineering researcher and co-author Jun Yao.

Yao says, “This is the first time that a device can function at the same voltage level as the brain. People probably didn’t even dare to hope that we could create a device that is as power-efficient as the biological counterparts in a brain, but now we have realistic evidence of ultra-low power computing capabilities. It’s a concept breakthrough and we think it’s going to cause a lot of exploration in electronics that work in the biological voltage regime.”

Lovely points out that Geobacter’s electrically conductive protein nanowires offer many advantages over expensive silicon nanowires, which require toxic chemicals and high-energy processes to produce. Protein nanowires also are more stable in water or bodily fluids, an important feature for biomedical applications. For this work, the researchers shear nanowires off the bacteria so only the conductive protein is used, he adds.

Fu says that he and Yao had set out to put the purified nanowires through their paces, to see what they are capable of at different voltages, for example. They experimented with a pulsing on-off pattern of positive-negative charge sent through a tiny metal thread in a memristor, which creates an electrical switch.

They used a metal thread because protein nanowires facilitate metal reduction, changing metal ion reactivity and electron transfer properties. Lovely says this microbial ability is not surprising, because wild bacterial nanowires breathe and chemically reduce metals to get their energy the way we breathe oxygen.

As the on-off pulses create changes in the metal filaments, new branching and connections are created in the tiny device, which is 100 times smaller than the diameter of a human hair, Yao explains. It creates an effect similar to learning — new connections — in a real brain. He adds, “You can modulate the conductivity, or the plasticity of the nanowire-memristor synapse so it can emulate biological components for brain-inspired computing. Compared to a conventional computer, this device has a learning capability that is not software-based.”

Fu recalls, “In the first experiments we did, the nanowire performance was not satisfying, but it was enough for us to keep going.” Over two years, he saw improvement until one fateful day when his and Yao’s eyes were riveted by voltage measurements appearing on a computer screen.

“I remember the day we saw this great performance. We watched the computer as current voltage sweep was being measured. It kept doing down and down and we said to each other, ‘Wow, it’s working.’ It was very surprising and very encouraging.”

Fu, Yao, Lovely and colleagues plan to follow up this discovery with more research on mechanisms, and to “fully explore the chemistry, biology and electronics” of protein nanowires in memristors, Fu says, plus possible applications, which might include a device to monitor heart rate, for example. Yao adds, “This offers hope in the feasibility that one day this device can talk to actual neurons in biological systems.”

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Unique physical, chemical properties of cicada wings

Biological structures sometimes have unique features that engineers would like to copy. For example, many types of insect wings shed water, kill microbes, reflect light in unusual ways and are self-cleaning. While researchers have dissected the physical characteristics that likely contribute to such traits, a new study reveals that the chemical compounds that coat cicada wings also contribute to their ability to repel water and kill microbes.

The scientists report their findings in the journal Advanced Materials Interfaces.

The researchers looked at the physical traits and chemical characteristics of the wings of two cicada species, Neotibicen pruinosus and Magicicada casinnii. N. pruinosus is an annual cicada; M. casinnii emerges from the soil once every 17 years. Previous studies have shown that both species have a highly ordered pattern of tiny pillars, called nanopillars, on their wings. The nanopillars contribute to the wings’ hydrophobicity — they shed water better than a raincoat — and likely play a role in killing microbes that try to attach to the wings.

“We knew a lot about the surface structure of cicada wings before this study, but we knew very little about the chemistry of those structures,” said Marianne Alleyne, an entomology professor at the University of Illinois at Urbana-Champaign who led the study with analytical chemist Jessica Román-Kustas, of the Sandia National Laboratories in Albuquerque, New Mexico; Donald Cropek, of the U.S. Army Corps of Engineers’ Construction Engineering Research Laboratory; and Nenad Miljkovic, a professor of mechanical science and engineering at Illinois.

To study nanopillar chemistry, Román-Kustas developed a method to gradually extract the compounds on the surface without damaging the overall structure of the wings. She placed each wing in solvent in an enclosed chamber and slowly microwaved each one.

“We extracted all these different compounds over different time periods, and then we analyzed what came off,” Román-Kustas said. “And we also looked at the corresponding changes in the nanopillar structure.”

The effort revealed that cicada wings are coated in a stew of hydrocarbons, fatty acids and oxygen-containing molecules like sterols, alcohols and esters. The oxygen-containing molecules were most abundant deeper in the nanopillars, while hydrocarbons and fatty acids made up more of the outermost nanopillar layers.

“Finding these particular molecules on the surface is not a surprise,” Alleyne said. “Hydrocarbons and fatty acids on insect cuticle is fairly common.”

The ratio of surface chemicals differed between the two cicada species, as did their nanopillar structures.

The study revealed that altering the surface chemicals also changed the nanopillar structure. In the N. pruinosis cicadas, the nanopillars began to shift in relation to one another as the chemicals were extracted, and later shifted back to a more parallel configuration. This also changed the wings’ wettability and anti-microbial characteristics.

The wings of the M. cassinni cicadas had shorter nanopillars and a higher proportion of hydrophobic compounds on their surface. Their nanopillar configuration orientation did not change as a result of extracting their surface chemicals.

While preliminary, the new findings offer insight into the interplay of structure and chemistry in determining function, Alleyne said. By dissecting these characteristics, the researchers hope to one day design artificial structures with some of the same surface traits. Finding materials that shed water and kill microbes, for example, would be useful in many applications, from agriculture to medicine, she said.

Alleyne is also an affiliate of the Beckman Institute for Advanced Science and Technology at Illinois.

The U.S. Army Corps of Engineers’ Construction Engineering Research Laboratory, National Science Foundation and the Japanese Ministry of Education, Culture, Sports, Science, and Technology supported this research.

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