Tag Archives: Duke University

An electronics-free, soft robotic dragonfly

From the description on YouTube,

With the ability to sense changes in pH, temperature and oil, this completely soft, electronics-free robot dubbed “DraBot” could be the prototype for future environmental sentinels. …

Music: Joneve by Mello C from the Free Music Archive

A favourite motif in the Art Nouveau movement (more about that later in the post), dragonflies or a facsimile thereof feature in March 25, 2021 Duke University news release (also on EurekAlert) by Ken Kingery,

Engineers at Duke University have developed an electronics-free, entirely soft robot shaped like a dragonfly that can skim across water and react to environmental conditions such as pH, temperature or the presence of oil. The proof-of-principle demonstration could be the precursor to more advanced, autonomous, long-range environmental sentinels for monitoring a wide range of potential telltale signs of problems.

The soft robot is described online March 25 [2021] in the journal Advanced Intelligent Systems.

Soft robots are a growing trend in the industry due to their versatility. Soft parts can handle delicate objects such as biological tissues that metal or ceramic components would damage. Soft bodies can help robots float or squeeze into tight spaces where rigid frames would get stuck.

The expanding field was on the mind of Shyni Varghese, professor of biomedical engineering, mechanical engineering and materials science, and orthopaedic surgery at Duke, when inspiration struck.

“I got an email from Shyni from the airport saying she had an idea for a soft robot that uses a self-healing hydrogel that her group has invented in the past to react and move autonomously,” said Vardhman Kumar, a PhD student in Varghese’s laboratory and first author of the paper. “But that was the extent of the email, and I didn’t hear from her again for days. So the idea sort of sat in limbo for a little while until I had enough free time to pursue it, and Shyni said to go for it.”

In 2012, Varghese and her laboratory created a self-healing hydrogel that reacts to changes in pH in a matter of seconds. Whether it be a crack in the hydrogel or two adjoining pieces “painted” with it, a change in acidity causes the hydrogel to form new bonds, which are completely reversible when the pH returns to its original levels.

Varghese’s hastily written idea was to find a way to use this hydrogel on a soft robot that could travel across water and indicate places where the pH changes. Along with a few other innovations to signal changes in its surroundings, she figured her lab could design such a robot as a sort of autonomous environmental sensor.

With the help of Ung Hyun Ko, a postdoctoral fellow also in Varghese’s laboratory, Kumar began designing a soft robot based on a fly. After several iterations, the pair settled on the shape of a dragonfly engineered with a network of interior microchannels that allow it to be controlled with air pressure.

They created the body–about 2.25 inches long with a 1.4-inch wingspan–by pouring silicon into an aluminum mold and baking it. The team used soft lithography to create interior channels and connected with flexible silicon tubing.

DraBot was born.

“Getting DraBot to respond to air pressure controls over long distances using only self-actuators without any electronics was difficult,” said Ko. “That was definitely the most challenging part.”

DraBot works by controlling the air pressure coming into its wings. Microchannels carry the air into the front wings, where it escapes through a series of holes pointed directly into the back wings. If both back wings are down, the airflow is blocked, and DraBot goes nowhere. But if both wings are up, DraBot goes forward.

To add an element of control, the team also designed balloon actuators under each of the back wings close to DraBot’s body. When inflated, the balloons cause the wings to curl upward. By changing which wings are up or down, the researchers tell DraBot where to go.

“We were happy when we were able to control DraBot, but it’s based on living things,” said Kumar. “And living things don’t just move around on their own, they react to their environment.”

That’s where self-healing hydrogel comes in. By painting one set of wings with the hydrogel, the researchers were able to make DraBot responsive to changes in the surrounding water’s pH. If the water becomes acidic, one side’s front wing fuses with the back wing. Instead of traveling in a straight line as instructed, the imbalance causes the robot to spin in a circle. Once the pH returns to a normal level, the hydrogel “un-heals,” the fused wings separate, and DraBot once again becomes fully responsive to commands.

To beef up its environmental awareness, the researchers also leveraged the sponges under the wings and doped the wings with temperature-responsive materials. When DraBot skims over water with oil floating on the surface, the sponges will soak it up and change color to the corresponding color of oil. And when the water becomes overly warm, DraBot’s wings change from red to yellow.

The researchers believe these types of measurements could play an important part in an environmental robotic sensor in the future. Responsiveness to pH can detect freshwater acidification, which is a serious environmental problem affecting several geologically-sensitive regions. The ability to soak up oils makes such long-distance skimming robots an ideal candidate for early detection of oil spills. Changing colors due to temperatures could help spot signs of red tide and the bleaching of coral reefs, which leads to decline in the population of aquatic life.

The team also sees many ways that they could improve on their proof-of-concept. Wireless cameras or solid-state sensors could enhance the capabilities of DraBot. And creating a form of onboard propellant would help similar bots break free of their tubing.

“Instead of using air pressure to control the wings, I could envision using some sort of synthetic biology that generates energy,” said Varghese. “That’s a totally different field than I work in, so we’ll have to have a conversation with some potential collaborators to see what’s possible. But that’s part of the fun of working on an interdisciplinary project like this.”

Here’s a link to and a citation for the paper,

Microengineered Materials with Self‐Healing Features for Soft Robotics by Vardhman Kumar, Ung Hyun Ko, Yilong Zhou, Jiaul Hoque, Gaurav Arya, Shyni Varghese. Advanced Intelligent Systems DOI: https://doi.org/10.1002/aisy.202100005 First published: 25 March 2021

This paper is open access.

The earlier reference to Art Nouveau gives me an excuse to introduce this March 7, 2020 (?) essay by Bex Simon (artist blacksmith) on her eponymous website.

Dragonflies, in particular, are a very poplar subject matter in the Art Nouveau movement. Art Nouveau, with its wonderful flowing lines and hidden fantasies, is full of symbolism.  The movement was a response to the profound social changes and industrialization of every day life and the style of the moment was, in part, inspired by Japanese art.

Simon features examples of Art Nouveau dragonfly art along with examples of her own take on the subject. She also has this,

[downloaded from https://www.bexsimon.com/dragonflies-and-butterflies-in-art-nouveau/]

This is a closeup of a real dragonfly as seen on Simon’s website. If you have an interest, reading her March 7, 2020 (?) essay and gazing at the images won’t take much time.

Point-of-care diagnostics made easier to read with silver nanocubes

Researchers have shown that plasmonics can enhance the fluorescent markers used to signal positive samples in certain types of tests for diseases. A polymer brush coating keeps unwanted biomolecules away while a capture antibody (red) catches biomarkers of disease (clear). A detection antibody (blue) then latches on to the biomarker and emits light from an attached fluorophore (sphere). All of this is sandwiched by a thin layer of gold and a silver nanocube that is attached by a third antibody (green), creating conditions for the fluorophore to emit brighter light. Courtesy: Duke University

A May 12, 2020 news item on Nanowerk announces new work from scientists at Duke University on making point-of-care diagnostics easier to use by making the readouts brighter,

Engineers at Duke University [North Carolina, US] have shown that nanosized silver cubes can make diagnostic tests that rely on fluorescence easier to read by making them more than 150 times brighter. Combined with an emerging point-of-care diagnostic platform already shown capable of detecting small traces of viruses and other biomarkers, the approach could allow such tests to become much cheaper and more widespread.

A May 12, 2020 Duke University news release (also on EurekAlert), which originated the news item, provides more detail about the work,

Plasmonics is a scientific field that traps energy in a feedback loop called a plasmon onto the surface of silver nanocubes. When fluorescent molecules are sandwiched between one of these nanocubes and a metal surface, the interaction between their electromagnetic fields causes the molecules to emit light much more vigorously. Maiken Mikkelsen, the James N. and Elizabeth H. Barton Associate Professor of Electrical and Computer Engineering at Duke, has been working with her laboratory at Duke to create new types of hyperspectral cameras and superfast optical signals using plasmonics for nearly a decade.

At the same time, researchers in the laboratory of Ashutosh Chilkoti, the Alan L. Kaganov Distinguished Professor of Biomedical Engineering, have been working on a self-contained, point-of-care diagnostic test that can pick out trace amounts of specific biomarkers from biomedical fluids such as blood. But because the tests rely on fluorescent markers to indicate the presence of the biomarkers, seeing the faint light of a barely positive test requires expensive and bulky equipment.

“Our research has already shown that plasmonics can enhance the brightness of fluorescent molecules tens of thousands of times over,” said Mikkelsen. “Using it to enhance diagnostic assays that are limited by their fluorescence was clearly a very exciting idea.”

“There are not a lot of examples of people using plasmon-enhanced fluorescence for point-of-care diagnostics, and the few that exist have not been yet implemented into clinical practice,” added Daria Semeniak, a graduate student in Chilkoti’s laboratory. “It’s taken us a couple of years, but we think we’ve developed a system that can work.”

In the new paper, researchers from the Chilkoti lab build their super-sensitive diagnostic platform called the D4 Assay onto a thin film of gold, the preferred yin to the plasmonic silver nanocube’s yang. The platform starts with a thin layer of polymer brush coating, which stops anything from sticking to the gold surface that the researchers don’t want to stick there. The researchers then use an ink-jet printer to attach two groups of molecules tailored to latch on to the biomarker that the test is trying to detect. One set is attached permanently to the gold surface and catches one part of the biomarker. The other is washed off of the surface once the test begins, attaches itself to another piece of the biomarker, and flashes light to indicate it’s found its target.

After several minutes pass to allow the reactions to occur, the rest of the sample is washed away, leaving behind only the molecules that have managed to find their biomarker matches, floating like fluorescent beacons tethered to a golden floor.

“The real significance of the assay is the polymer brush coating,” said Chilkoti. “The polymer brush allows us to store all of the tools we need on the chip while maintaining a simple design.”

While the D4 Assay is very good at grabbing small traces of specific biomarkers, if there are only trace amounts, the fluorescent beacons can be difficult to see. The challenge for Mikkelsen and her colleagues was to place their plasmonic silver nanocubes above the beacons in such a way that they supercharged the beacons’ fluorescence.

But as is usually the case, this was easier said than done.

“The distance between the silver nanocubes and the gold film dictates how much brighter the fluorescent molecule becomes,” said Daniela Cruz, a graduate student working in Mikkelsen’s laboratory. “Our challenge was to make the polymer brush coating thick enough to capture the biomarkers–and only the biomarkers of interest–but thin enough to still enhance the diagnostic lights.”

The researchers attempted two approaches to solve this Goldilocks riddle. They first added an electrostatic layer that binds to the detector molecules that carry the fluorescent proteins, creating a sort of “second floor” that the silver nanocubes could sit on top of. They also tried functionalizing the silver nanocubes so that they would stick directly to individual detector molecules on a one-on-one basis.

While both approaches succeeded in boosting the amount of light coming from the beacons, the former showed the best improvement, increasing its fluorescence by more than 150 times. However, this method also requires an extra step of creating a “second floor,” which adds another hurdle to engineering a way to make this work on a commercial point-of-care diagnostic rather than only in a laboratory. And while the fluorescence didn’t improve as much in the second approach, the test’s accuracy did.

“Building microfluidic lab-on-a-chip devices through either approach would take time and resources, but they’re both doable in theory,” said Cassio Fontes, a graduate student in the Chilkoti laboratory. “That’s what the D4 Assay is moving toward.”

And the project is moving forward. Earlier in the year, the researchers used preliminary results from this research to secure a five-year, $3.4 million R01 research award from the National Heart, Lung, and Blood Institute. The collaborators will be working to optimize these fluorescence enhancements while integrating wells, microfluidic channels and other low-cost solutions into a single-step diagnostic device that can run through all of these steps automatically and be read by a common smartphone camera in a low-cost device.

“One of the big challenges in point-of-care tests is the ability to read out results, which usually requires very expensive detectors,” said Mikkelsen. “That’s a major roadblock to having disposable tests to allow patients to monitor chronic diseases at home or for use in low-resource settings. We see this technology not only as a way to get around that bottleneck, but also as a way to enhance the accuracy and threshold of these diagnostic devices.”

Here’s a link to and a citation for the paper,

Ultrabright Fluorescence Readout of an Ink-Jet Printed Immunoassay Using Plasmonic Nanogap Cavities by Daniela F. Cruz, Cassio M. Fontes, Daria Semeniak, Jiani Huang, Angus Hucknall, Ashutosh Chilkoti, Maiken H. Mikkelsen. Nano Lett. 2020, XXXX, XXX, XXX-XXX DOI: https://doi.org/10.1021/acs.nanolett.0c01051 Publication Date:May 6, 2020 Copyright © 2020 American Chemical Society

This paper is behind a paywall.

Gold nanoparticles not always always biologically stable

It’s usually silver nanoparticles (with a nod to titanium dioxide as another problem nanoparticle) which star in scenarios regarding environmental concerns, especially with water. According to an Aug. 28, 2018 news item on Nanowerk, gold nanoparticles under certain conditions could also pose problems,

It turns out gold isn’t always the shining example of a biologically stable material that it’s assumed to be, according to environmental engineers at Duke’s Center for the Environmental Implications of NanoTechnology (CEINT).

In a nanoparticle form, the normally very stable, inert, noble metal actually gets dismantled by a microbe found on a Brazilian aquatic weed.

While the findings don’t provide dire warnings about any unknown toxic effects of gold, they do provide a warning to researchers on how it is used in certain experiments.

Here’s an image of one of the researchers standing in the test bed where they made their discovery (the caption will help to make sense of the reference to mesocosms in the news release, which follows,,

Mark Wiesner stands with rows of mesocosms—small, manmade structures containing different plants and microorganisms meant to represent a natural environment with experimental controls. Courtesy: Duke University

An August 28, 2018 Duke University news release (also on EurekAlert) by Ken Kingery, which originated the news item, provides more detail about gold nanoparticle instability,

CEINT researchers from Duke, Carnegie Mellon and the University of Kentucky were running an experiment to investigate how nanoparticles used as a commercial pesticide affect wetland environments in the presence of added nutrients. Although real-world habitats often receive doses of both pesticides and fertilizers, most studies on the environmental effects of such compounds only look at a single contaminant at a time.

For nine months, the researchers released low doses of nitrogen, phosphorus and copper hydroxide nanoparticles into wetland mesocosms [emphasis mine]– small, manmade structures containing different plants and microorganisms meant to represent a natural environment with experimental controls. The goal was to see where the nanoparticle pesticides ended up and how they affected the plant and animal life within the mesocosm.

The researchers also released low doses of gold nanoparticles as tracers, assuming the biologically inert nanoparticles would remain stable while migrating through the ecosystem. This would help the researchers interpret data on the pesticide particles that partly dissolve by showing them how a solid metal particle acts within the system.

But when the researchers went to analyze their results, they found that many of the gold nanoparticles had been oxidized and dissolved.

“We were taken completely by surprise,” said Mark Wiesner, the James B. Duke Professor and chair of civil and environmental engineering at Duke. “The nanoparticles that were supposed to be the most stable turned out to be the least stable of all.”

After further inspection, the researchers found the culprit — the microbiome growing on a common Brazilian waterweed called Egeria densa. Many bacteria secrete chemicals to essentially mine metallic nutrients from their surroundings. With their metabolism spiked by the experiment’s added nutrients, the bacteria living on the E. densa were catalyzing the reaction to dissolve the gold nanoparticles.

This process wouldn’t pose any threat [emphasis mine] to humans or other animal species in the wild. But when researchers design experiments with the assumption that their gold nanoparticles will remain intact, the process can confound the interpretation of their results.

“The assumption that gold is inert did not hold in these experiments,” said Wiesner. “This is a good lesson that underscores how real, complex environments, that include for example the bacteria growing on leaves, can give very different results from experiments run in a laboratory setting that do not include these complexities.”

Here’s a link to and a citation for the paper,

Gold nanoparticle biodissolution by a freshwater macrophyte and its associated microbiome by Astrid Avellan, Marie Simonin, Eric McGivney, Nathan Bossa, Eleanor Spielman-Sun, Jennifer D. Rocca, Emily S. Bernhardt, Nicholas K. Geitner, Jason M. Unrine, Mark R. Wiesner, & Gregory V. Lowry. Nature Nanotechnology (2018) DOI: https://doi.org/10.1038/s41565-018-0231-y Published

This paper is behind a paywall.

Algae outbreaks (dead zones) in wetlands and waterways

It’s been over seven years since I first started writing about Duke University’s  Center for the Environmental Implications of Nanotechnology and mesocosms (miniature ecosystems) and the impact that nanoparticles may have on plants and water (see August 11, 2011 posting). Since then, their focus has shifted from silver nanoparticles and their impact on plants, fish, bacteria, etc. to a more general examination of metallic nanoparticles and water. A June 25, 2018 news item on ScienceDaily announces some of their latest work,

The last 10 years have seen a surge in the use of tiny substances called nanomaterials in agrochemicals like pesticides and fungicides. The idea is to provide more disease protection and better yields for crops, while decreasing the amount of toxins sprayed on agricultural fields.

But when combined with nutrient runoff from fertilized cropland and manure-filled pastures, these “nanopesticides” could also mean more toxic algae outbreaks for nearby streams, lakes and wetlands, a new study finds.

A June 25, 2018 Duke University news release (also on EurekAlert) by Robin A. Smith, which originated the news item, provides more detail,

Too small to see with all but the most powerful microscopes, engineered nanomaterials are substances manufactured to be less than 100 nanometers in diameter, many times smaller than a hair’s breadth.

Their nano-scale gives them different chemical and physical properties from their bulk counterparts, including more surface area for reactions and interactions.

Those interactions could intensify harmful algal blooms in wetlands, according to experiments led by Marie Simonin, a postdoctoral associate with biology professor Emily Bernhardt at Duke University.

Carbon nanotubes and teeny tiny particles of silver, titanium dioxide and other metals are already added to hundreds of commercial products to make everything from faster, lighter electronics, self-cleaning fabrics, and smarter food packaging that can monitor food for spoilage. They are also used on farms for slow- or controlled-release plant fertilizers and pesticides and more targeted delivery, and because they are effective at lower doses than conventional products.

These and other applications have generated tremendous interest and investment in nanomaterials. However the potential risks to human health or the environment aren’t fully understood, Simonin said.

Most of the 260,000 to 309,000 metric tons of nanomaterials produced worldwide each year are eventually disposed in landfills, according to a previous study. But of the remainder, up to 80,400 metric tons per year are released into soils, and up to 29,200 metric tons end up in natural bodies of water.

“And these emerging contaminants don’t end up in water bodies alone,” Simonin said. “They probably co-occur with nutrient runoff. There are likely multiple stressors interacting.”

Algae outbreaks already plague polluted waters worldwide, said Steven Anderson, a research analyst in the Bernhardt Lab at Duke and one of the authors of the research.

Nitrogen and phosphorous pollution makes its way into wetlands and waterways in the form of agricultural runoff and untreated wastewater. The excessive nutrients cause algae to grow out of control, creating a thick mat of green scum or slime on the surface of the water that blocks sunlight from reaching other plants.

These nutrient-fueled “blooms” eventually reduce oxygen levels to the point where fish and other organisms can’t survive, creating dead zones in the water. Some algal blooms also release toxins that can make pets and people who swallow them sick.

To find out how the combined effects of nutrient runoff and nanoparticle contamination would affect this process, called eutrophication, the researchers set up 18 separate 250-liter tanks with sandy sloped bottoms to mimic small wetlands.

Each open-air tank was filled with water, soil and a variety of wetland plants and animals such as waterweed and mosquitofish.

Over the course of the nine-month experiment, some tanks got a weekly dose of algae-promoting nitrates and phosphates like those found in fertilizers, some tanks got nanoparticles — either copper or gold — and some tanks got both.

Along the way the researchers monitored water chemistry, plant and algae growth and metabolism, and nanoparticle accumulation in plant tissues.

“The results were surprising,” Simonin said. The nanoparticles had tiny effects individually, but when added together with nutrients, even low concentrations of gold and copper nanoparticles used in fungicides and other products turned the once-clear water a murky pea soup color, its surface covered with bright green smelly mats of floating algae.

Over the course of the experiment, big algal blooms were more than three times more frequent and more persistent in tanks where nanoparticles and nutrients were added together than where nutrients were added alone. The algae overgrowths also reduced dissolved oxygen in the water.

It’s not clear yet how nanoparticle exposure shifts the delicate balance between plants and algae as they compete for nutrients and other resources. But the results suggest that nanoparticles and other “metal-based synthetic chemicals may be playing an under-appreciated role in the global trends of increasing eutrophication,” the researchers said.

Here’s a link to and a citation for the paper,

Engineered nanoparticles interact with nutrients to intensify eutrophication in a wetland ecosystem experiment by Marie Simonin, Benjamin P. Colman, Steven M. Anderson, Ryan S. King, Matthew T. Ruis, Astrid Avellan, Christina M. Bergemann, Brittany G. Perrotta, Nicholas K. Geitner, Mengchi Ho, Belen de la Barrera, Jason M. Unrine, Gregory V. Lowry, Curtis J. Richardson, Mark R. Wiesner, Emily S. Bernhardt. Ecological Applications, 2018; DOI: 10.1002/eap.1742 First published: 25 June 2018

This paper is behind a paywall.

Burning coal produces harmful titanium dioxide nanoparticles

It turns out that Canada has the fifth largest reserve of coal in the world, according to the Coal in Canada Wikipedia entry (Note: Links have been removed),

Coal reserves in Canada rank fifth largest in the world (following the former Soviet Union, the United States, the People’s Republic of China and Australia) at approximately 10 billion tons, 10% of the world total.[1] This represents more energy than all of the oil and gas in the country combined. The coal industry generates CDN$5 billion annually.[2] Most of Canada’s coal mining occurs in the West of the country.[3] British Columbia operates 10 coal mines, Alberta 9, Saskatchewan 3 and New Brunswick one. Nova Scotia operates several small-scale mines, Westray having closed following the 1992 disaster there.[4]

So, this news from Virginia holds more than the usual interest for me (I’m in British Columbia). From an Aug. 8, 2017 Virginia Tech news release (also on EurekAlert),

Environmental scientists led by the Virginia Tech College of Science have discovered that the burning of coal produces incredibly small particles of a highly unusual form of titanium oxide.

When inhaled, these nanoparticles can enter the lungs and potentially the bloodstream.

The particulates — known as titanium suboxide nanoparticles — are unintentionally produced as coal is burned, creating these tiniest of particles, as small as 100 millionths of a meter [emphasis mine], said the Virginia Tech-led team. When the particles are introduced into the air — unless captured by high-tech particle traps — they can float away from power plant stacks and travel on air currents locally, regionally, and even globally.

As an example of this, these nanoparticles were found on city streets, sidewalks, and in standing water in Shanghai, China.

The findings are published in the latest issue of Nature Communications under team leader Michael F. Hochella Jr., University Distinguished Professor of Geosciences with the College of Science, and Yi Yang, a professor at East China Normal University in Shanghai. Other study participants include Duke University, the University of Kentucky, and Laurentian University in Canada.

“The problem with these nanoparticles is that there is no easy or practical way to prevent their formation during coal burning,” Hochella said, adding that in nations with strong environmental regulations, such as the United States, most of the nanoparticles would be caught by particle traps. Not so in Africa [a continent not a nation], China, or India, where regulations are lax or nonexistent, with coal ash and smoke entering the open air.

“Due to advanced technology used at U.S.-based coal burning power plants, mandated by the Clean Air Act and the Environmental Protection Agency, most of these nanoparticles and other tiny particles are removed before the final emission of the plant’s exhaust gases,” Hochella said. “But in countries where the particles from the coal burning are not nearly so efficiently removed, or removed at all, these titanium suboxide nanoparticles and many other particle types are emitted into the atmosphere, in part resulting in hazy skies that plague many countries, especially in China and India.”

Hochella and his team found these previously unknown nanoparticles not only in coal ash from around the world and in the gaseous waste emissions of coal plants, but on city streets, in soils and storm water ponds, and at wastewater treatment plants.

“I could not believe what I have found at the beginning, because they had been reported so extremely rarely in the natural environment,” said Yang, who once worked as a visiting professor in Virginia Tech’s Department of Geosciences with Hochella. “It took me several months to confirm their occurrence in coal ash samples.”

The newly found titanium suboxide — called Magnéli phases — was once thought rare, found only sparingly on Earth in some meteorites, from a small area of rock formations in western Greenland, and occasionally in moon rocks. The findings by Hochella and his team indicate that these nanoparticles are in fact widespread globally. They are only now being studied for the first time in natural environments using powerful electron microscopes.

Why did the discovery occur now? According to the report, nearly all coal contains traces of the minerals rutile and/or anatase, both “normal,” naturally occurring, and relatively inert titanium oxides, especially in the absence of light. When those minerals are burned in the presence of coal, research found they easily and quickly converted to these unusual titanium suboxide nanoparticles. The nanoparticles then become entrained in the gases that leave the power plant.

When inhaled, the nanoparticles enter deep into the lungs, potentially all the way into the air sacs that move oxygen into our bloodstream during the normal breathing process. While human lung toxicity of these particles is not yet known, a preliminary biotoxicity test by Hochella and Richard Di Giulio, professor of environmental toxicology, and Jessica Brandt, a doctoral candidate, both at Duke University, indicates that the particles do indeed have toxicity potential.

According to the team, further study is clearly needed, especially biotoxicity testing directly relevant to the human lung. Partnering with coal-power plants either in the United States or China would be ideal, said Yang.

More troubling, the study shows that titanium suboxide nanoparticles are biologically active in the dark, making the particles highly suspect. Exact human health effects are yet unknown.

“Future studies will need to very carefully investigate and access the toxicity of titanium suboxide nanoparticles in the human lung, and this could take years, a sobering thought considering its potential danger,” Hochella said.

As the titanium suboxide nanoparticle itself is produced incidentally, Hochella and his team came across the nanoparticle by accident while studying a 2014 coal ash spill in the Dan River, North Carolina. During the study of the downstream movement of toxic metals in the ash in the Dan River, the team discovered and recognized the presence of small amounts of the highly unusual titanium suboxide.

The group later produced the titanium suboxide nanoparticles when burning coal in a lab simulation.

This new potential air pollution health hazard builds on already established findings from the World Health Organization. It estimates that 3.3 million premature deaths occur worldwide per year due to polluted air, Hochella said. In China, 1.6 million premature deaths are estimated annually due to cardiovascular and respiratory injury from air pollution. Most Chinese megacities top 100 severely hazy days each year with particle concentrations two to four times higher than WHO guidelines, Yang said.

Direct health effects on humans is only one factor. Findings of thousands of scientists have determined that the biggest driver of warming of the planet and the resulting climate change is industrial-scale coal burning. The impact of titanium suboxide nanoparticles found in the atmosphere, in addition to greenhouse gases, on animals, water, and plants is not yet known.

They’ve used an unusual unit of measurement, “100 millionths of a meter,” nanoparticles are usually described in nanometers.

Here’s a link to and a citation for the paper,

Discovery and ramifications of incidental Magnéli phase generation and release from industrial coal-burning by Yi Yang, Bo Chen, James Hower, Michael Schindler, Christopher Winkler, Jessica Brandt, Richard Di Giulio, Jianping Ge, Min Liu, Yuhao Fu, Lijun Zhang, Yuru Chen, Shashank Priya, & Michael F. Hochella Jr. Nature Communications 8, Article number: 194 (2017) doi:10.1038/s41467-017-00276-2 Published online: 08 August 2017

This paper is behind a paywall.

This put me in mind of the famous London smog, which one doesn’t hear about much anymore. For anyone not familiar with that phenomenon, here’s more from the Great Smog of London Wikipedia entry (Note: Links have been removed),

The Great Smog of London, or Great Smog of 1952 sometimes called the Big Smoke,[1] was a severe air-pollution event [emphasis mine] that affected the British capital of London in December 1952. A period of cold weather, combined with an anticyclone and windless conditions, collected airborne pollutants – mostly arising from the use of coal [emphasis mine]– to form a thick layer of smog over the city. It lasted from Friday, 5 December to Tuesday, 9 December 1952 and then dispersed quickly when the weather changed.

It caused major disruption by reducing visibility and even penetrating indoor areas, far more severe than previous smog events experienced in the past, called “pea-soupers”. Government medical reports in the following weeks, however, estimated that up until 8 December, 4,000 people had died as a direct result of the smog and 100,000 more were made ill by the smog’s effects on the human respiratory tract. More recent research suggests that the total number of fatalities was considerably greater, about 12,000.[2]

London had suffered since the 1200s from poor air quality,[3] which worsened in the 1600s,[4][5] but the Great Smog is known to be the worst air-pollution event in the history of the United Kingdom,[6] and the most significant in terms of its effect on environmental research, government regulation, and public awareness of the relationship between air quality and health.[2][4] It led to several changes in practices and regulations, including the Clean Air Act 1956. …

Investigating nanoparticles and their environmental impact for industry?

It seems the Center for the Environmental Implications of Nanotechnology (CEINT) at Duke University (North Carolina, US) is making an adjustment to its focus and opening the door to industry, as well as, government research. It has for some years (my first post about the CEINT at Duke University is an Aug. 15, 2011 post about its mesocosms) been focused on examining the impact of nanoparticles (also called nanomaterials) on plant life and aquatic systems. This Jan. 9, 2017 US National Science Foundation (NSF) news release (h/t Jan. 9, 2017 Nanotechnology Now news item) provides a general description of the work,

We can’t see them, but nanomaterials, both natural and manmade, are literally everywhere, from our personal care products to our building materials–we’re even eating and drinking them.

At the NSF-funded Center for Environmental Implications of Nanotechnology (CEINT), headquartered at Duke University, scientists and engineers are researching how some of these nanoscale materials affect living things. One of CEINT’s main goals is to develop tools that can help assess possible risks to human health and the environment. A key aspect of this research happens in mesocosms, which are outdoor experiments that simulate the natural environment – in this case, wetlands. These simulated wetlands in Duke Forest serve as a testbed for exploring how nanomaterials move through an ecosystem and impact living things.

CEINT is a collaborative effort bringing together researchers from Duke, Carnegie Mellon University, Howard University, Virginia Tech, University of Kentucky, Stanford University, and Baylor University. CEINT academic collaborations include on-going activities coordinated with faculty at Clemson, North Carolina State and North Carolina Central universities, with researchers at the National Institute of Standards and Technology and the Environmental Protection Agency labs, and with key international partners.

The research in this episode was supported by NSF award #1266252, Center for the Environmental Implications of NanoTechnology.

The mention of industry is in this video by O’Brien and Kellan, which describes CEINT’s latest work ,

Somewhat similar in approach although without a direction reference to industry, Canada’s Experimental Lakes Area (ELA) is being used as a test site for silver nanoparticles. Here’s more from the Distilling Science at the Experimental Lakes Area: Nanosilver project page,

Water researchers are interested in nanotechnology, and one of its most commonplace applications: nanosilver. Today these tiny particles with anti-microbial properties are being used in a wide range of consumer products. The problem with nanoparticles is that we don’t fully understand what happens when they are released into the environment.

The research at the IISD-ELA [International Institute for Sustainable Development Experimental Lakes Area] will look at the impacts of nanosilver on ecosystems. What happens when it gets into the food chain? And how does it affect plants and animals?

Here’s a video describing the Nanosilver project at the ELA,

You may have noticed a certain tone to the video and it is due to some political shenanigans, which are described in this Aug. 8, 2016 article by Bartley Kives for the Canadian Broadcasting Corporation’s (CBC) online news.

‘Brewing up’ conductive inks for printable electronics

Scientists from Duke University aren’t exactly ‘brewing’ or ‘cooking up’ the inks but they do come close according to a Jan. 3, 2017 news item on ScienceDaily,

By suspending tiny metal nanoparticles in liquids, Duke University scientists are brewing up conductive ink-jet printer “inks” to print inexpensive, customizable circuit patterns on just about any surface.

A Jan. 3, 2017 Duke University news release (also on EurekAlert), which originated the news item, explains why this technique could lead to more accessible printed electronics,

Printed electronics, which are already being used on a wide scale in devices such as the anti-theft radio frequency identification (RFID) tags you might find on the back of new DVDs, currently have one major drawback: for the circuits to work, they first have to be heated to melt all the nanoparticles together into a single conductive wire, making it impossible to print circuits on inexpensive plastics or paper.

A new study by Duke researchers shows that tweaking the shape of the nanoparticles in the ink might just eliminate the need for heat.

By comparing the conductivity of films made from different shapes of silver nanostructures, the researchers found that electrons zip through films made of silver nanowires much easier than films made from other shapes, like nanospheres or microflakes. In fact, electrons flowed so easily through the nanowire films that they could function in printed circuits without the need to melt them all together.

“The nanowires had a 4,000 times higher conductivity than the more commonly used silver nanoparticles that you would find in printed antennas for RFID tags,” said Benjamin Wiley, assistant professor of chemistry at Duke. “So if you use nanowires, then you don’t have to heat the printed circuits up to such high temperature and you can use cheaper plastics or paper.”

“There is really nothing else I can think of besides these silver nanowires that you can just print and it’s simply conductive, without any post-processing,” Wiley added.

These types of printed electronics could have applications far beyond smart packaging; researchers envision using the technology to make solar cells, printed displays, LEDS, touchscreens, amplifiers, batteries and even some implantable bio-electronic devices. The results appeared online Dec. 16 [2016] in ACS Applied Materials and Interfaces.

Silver has become a go-to material for making printed electronics, Wiley said, and a number of studies have recently appeared measuring the conductivity of films with different shapes of silver nanostructures. However, experimental variations make direct comparisons between the shapes difficult, and few reports have linked the conductivity of the films to the total mass of silver used, an important factor when working with a costly material.

“We wanted to eliminate any extra materials from the inks and simply hone in on the amount of silver in the films and the contacts between the nanostructures as the only source of variability,” said Ian Stewart, a recent graduate student in Wiley’s lab and first author on the ACS paper.

Stewart used known recipes to cook up silver nanostructures with different shapes, including nanoparticles, microflakes, and short and long nanowires, and mixed these nanostructures with distilled water to make simple “inks.” He then invented a quick and easy way to make thin films using equipment available in just about any lab — glass slides and double-sided tape.

“We used a hole punch to cut out wells from double-sided tape and stuck these to glass slides,” Stewart said. By adding a precise volume of ink into each tape “well” and then heating the wells — either to relatively low temperature to simply evaporate the water or to higher temperatures to begin melting the structures together — he created a variety of films to test.

The team say they weren’t surprised that the long nanowire films had the highest conductivity. Electrons usually flow easily through individual nanostructures but get stuck when they have to jump from one structure to the next, Wiley explained, and long nanowires greatly reduce the number of times the electrons have to make this “jump”.

But they were surprised at just how drastic the change was. “The resistivity of the long silver nanowire films is several orders of magnitude lower than silver nanoparticles and only 10 times greater than pure silver,” Stewart said.

The team is now experimenting with using aerosol jets to print silver nanowire inks in usable circuits. Wiley says they also want to explore whether silver-coated copper nanowires, which are significantly cheaper to produce than pure silver nanowires, will give the same effect.

Here’s a link to and a citation for the paper,

Effect of Morphology on the Electrical Resistivity of Silver Nanostructure Films by Ian E. Stewart, Myung Jun Kim, and Benjamin J. Wiley. ACS Appl. Mater. Interfaces, Article ASAP
DOI: 10.1021/acsami.6b12289 Publication Date (Web): December 16, 2016

Copyright © 2016 American Chemical Society

This paper is behind a paywall but there is an image of the silver nanowires, which is not exactly compensation but is interesting,

Caption: Duke University chemists have found that silver nanowire films like these conduct electricity well enough to form functioning circuits without applying high temperatures, enabling printable electronics on heat-sensitive materials like paper or plastic.
Credit: Ian Stewart and Benjamin Wiley

Bringing multispectral imaging into daily use

Caption: Researchers tested a new technique for printing and imaging in both color and infrared with this image of a parrot. The inlay shows how a simple RGB color scheme was created by building rectangles of varying lengths for each of the colors, as well as individual nanocubes on top of a gold film that create the plasmonic element. Credit: imageBROKER / Alamy Stock Photo

That caption makes a lot more sense after reading the news item and the news release announcing the work. First, there’s the Dec. 15, 2016 news item on ScienceDaily,

Duke University researchers believe they have overcome a longstanding hurdle to producing cheaper, more robust ways to print and image across a range of colors extending into the infrared.

As any mantis shrimp will tell you, there are a wide range of “colors” along the electromagnetic spectrum that humans cannot see but which provide a wealth of information. Sensors that extend into the infrared can, for example, identify thousands of plants and minerals, diagnose cancerous melanomas and predict weather patterns, simply by the spectrum of light they reflect.

Current imaging technologies that can detect infrared wavelengths are expensive and bulky, requiring numerous filters or complex assemblies in front of an infrared photodetector. The need for mechanical movement in such devices reduces their expected lifetime and can be a liability in harsh conditions, such as those experienced by satellites.

A closeup of the colorful parrot picture printed on a thin gold wafer using the new nanocube-based technology. The colors appear off because of the underlying gold, as well as the difficulties that typical cameras have of imaging the new technology. Credit: Maiken Mikkelsen, Duke University

A Dec. 14, 2016 Duke University news release, which originated the news item, provides more detail (Note: A link has been removed),

In a new paper, a team of Duke engineers reveals a manufacturing technique that promises to bring a simplified form of multispectral imaging into daily use. Because the process uses existing materials and fabrication techniques that are inexpensive and easily scalable, it could revolutionize any industry where multispectral imaging or printing is used.

The results appear online December 14 [2016] in the journal Advanced Materials.

“It’s challenging to create sensors that can detect both the visible spectrum and the infrared,” said Maiken Mikkelsen, the Nortel Networks Assistant Professor of Electrical and Computer Engineering and Physics at Duke.

“Traditionally you need different materials that absorb different wavelengths, and that gets very expensive,” Mikkelsen said. “But with our technology, the detectors’ responses are based on structural properties that we design rather than a material’s natural properties. What’s really exciting is that we can pair this with a photodetector scheme to combine imaging in both the visible spectrum and the infrared on a single chip.”

The new technology relies on plasmonics — the use of nanoscale physical phenomena to trap certain frequencies of light.

Engineers fashion silver cubes just 100 nanometers wide and place them only a few nanometers above a thin gold foil. When incoming light strikes the surface of a nanocube, it excites the silver’s electrons, trapping the light’s energy — but only at a certain frequency.

The size of the silver nanocubes and their distance from the base layer of gold determines that frequency, while controlling the spacing between the nanoparticles allows tuning the strength of the absorption. By precisely tailoring these spacings, researchers can make the system respond to any specific color they want, all the way from visible wavelengths out to the infrared.

The challenge facing the engineers is how to build a useful device that could be scalable and inexpensive enough to use in the real world. For that, Mikkelsen turned to her research team, including graduate student Jon Stewart.

“Similar types of materials have been demonstrated before, but they’ve all used expensive techniques that have kept the technology from transitioning to the market,” said Stewart. “We’ve come up with a fabrication scheme that is scalable, doesn’t need a clean room and avoids using million-dollar machines, all while achieving higher frequency sensitivities. It has allowed us to do things in the field that haven’t been done before.”

To build a detector, Mikkelsen and Stewart used a process of light etching and adhesives to pattern the nanocubes into pixels containing different sizes of silver nanocubes, and thus each sensitive to a specific wavelength of light. When incoming light strikes the array, each area responds differently depending on the wavelength of light it is sensitive to. By teasing out how each part of the array responds, a computer can reconstruct what color the original light was.

The technique can be used for printing as well, the team showed. Instead of creating pixels with six sections tuned to respond to specific colors, they created pixels with three bars that reflect three colors: blue, green and red. By controlling the relative lengths of each bar, they can dictate what combination of colors the pixel reflects. It’s a novel take on the classic RGB scheme first used in photography in 1861.

But unlike most other applications, the plasmonic color scheme promises to never fade over time and can be reliably reproduced with tight accuracy time and again. It also allows its adopters to create color schemes in the infrared.

“Again, the exciting part is being able to print in both visible and infrared on the same substrate,” said Mikkelsen. “You could imagine printing an image with a hidden portion in the infrared, or even covering an entire object to tailor its spectral response.”

Here’s a link to and a citation for the paper,

Toward Multispectral Imaging with Colloidal Metasurface Pixels by Jon W. Stewart, Gleb M. Akselrod, David R. Smith, and Maiken H. Mikkelsen. DOI: 10.1002/adma.201602971 Version of Record online: 14 DEC 2016

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall. (There is a free preview but it is page 1 only of the paper.)

 

Are living bacteria providing camouflage for crustaceans?

When you have no place to hide, you can develop some unique methods to avoid detection according to an Oct. 27, 2016 news item on ScienceDaily,

Crustaceans that thrive in the vastness of the open ocean have no place to hide from their predators. Consequently, many creatures that live at depths where sunlight fades to darkness have developed transparent bodies to be less visible when spotted against the twilight by upward-looking predators. But they also face predators with bioluminescent searchlights that should cause the clear animals to flash brightly, just like shining a flashlight across a window pane.

Well, it turns out the midwater crustaceans have camouflage for that too.

An Oct. 27, 2016 Duke University news release on EurekAlert, which originated the news item, expands on the theme,

A new study from Duke University and the Smithsonian Institution has found that these midwater hyperiid amphipods are covered with anti-reflective coatings on their legs and bodies that can dampen the reflection of light by 250-fold in some cases and prevent it from bouncing back to a hungry lantern fish’s eye.

Weirder still, these coatings appear to be made of living bacteria.

When viewed under an electron microscope, the optical coating appears as a sheet of fairly uniform beads, smaller than the wavelength of light. “This coating of little spheres reduces reflections the same way putting a shag carpet on the walls of a recording studio would soften echoes,” said study leader Laura Bagge, a Ph.D. candidate at Duke working with biologist Sönke Johnsen.

The spheres range from 50 to 300 nanometers in diameter on different species of amphipod, but a sphere of 110 nm would be optimal, resulting in up to a 250-fold reduction in reflectance, Bagge calculated. “But every size of these bumps helps.”

Adding to the impression that the spheres might be bacteria, they are sometimes connected with a net of filaments like a biofilm. Each of the seven amphipod species Bagge looked at appears to have its own species of symbiotic optical bacteria. But that’s not a sure thing yet.

“They have all the features of bacteria, but to be 100 percent sure, we’re going to have to perform an in-depth sequencing project,” Bagge said. That project is already underway.

If the spheres are bacteria, they’re very small ones. But it’s not hard to imagine the natural selection — having your host spotted and eaten — that would drive the microbes to an optimal size, said research zoologist Karen Osborn of the Smithsonian National Museum of Natural History, who provided some of the species for this study.

If the optical coating is alive, the researchers will have to figure out how this symbiotic relationship got started in the first place.

Crustaceans molt to grow, shedding the old shell and perhaps its attendant anti-reflective bacteria. But Osborn thinks it would be pretty easy to re-seed the animal’s new shell. “In that whole process, they’re touching the old carapace.” There’s also a species of hyperiid, Phronima, that raises its young in a little floating nest hollowed out of the body of a salp. In that case, the kids could adopt mom’s anti-reflective bacteria pretty easily, Osborn said.

Another amphipod species, Cystisoma, also extrudes brush-like structures on the exoskeleton of its legs which are just the right size and shape to serve the same purpose as the antireflective spheres. At up to six inches in length, Cystisoma has a serious need for stealth.

“They’re remarkably transparent,” Osborn said. “Mostly you see them because you don’t see them. When you pull up a trawl bucket packed full of plankton, you see an empty spot – why is nothing there? You reach in and pull out a Cystisoma. It’s a firm cellophane bag, essentially.”

“We care about this for the basic biology,” Bagge said. But the discovery of living anti-reflective coatings may have technological applications as well. Reflection-reducing “nipple arrays” are being used in the design of glass windows and have also been found in the eyes of moths, apparently to help them see better at night.

Here’s a link to and a citation for the paper,

Nanostructures and Monolayers of Spheres Reduce Surface Reflections in Hyperiid Amphipods by Laura E. Bagge, Karen J. Osborn, Sönke Johnsen. Current Biology DOI: http://dx.doi.org/10.1016/j.cub.2016.09.033 Publication stage: In Press Corrected Proof

This paper is behind a paywall.

Doing math in a test tube using analog DNA

Basically, scientists at Duke University (US) have created an analog computer at the nanoscale, which can perform basic arithmetic. From an Aug. 23, 2016 news item on ScienceDaily,

Often described as the blueprint of life, DNA contains the instructions for making every living thing from a human to a house fly.

But in recent decades, some researchers have been putting the letters of the genetic code to a different use: making tiny nanoscale computers.

In a new study, a Duke University team led by professor John Reif created strands of synthetic DNA that, when mixed together in a test tube in the right concentrations, form an analog circuit that can add, subtract and multiply as they form and break bonds.

Rather than voltage, DNA circuits use the concentrations of specific DNA strands as signals.

An Aug. 23, 2016 Duke University news release (also on EurekAlert), which originated the news item, describes how most DNA-based circuits operate and what makes the one from Duke different,

Other teams have designed DNA-based circuits that can solve problems ranging from calculating square roots to playing tic-tac-toe. But most DNA circuits are digital, where information is encoded as a sequence of zeroes and ones.

Instead, the new Duke device performs calculations in an analog fashion by measuring the varying concentrations of specific DNA molecules directly, without requiring special circuitry to convert them to zeroes and ones first.

Unlike the silicon-based circuits used in most modern day electronics, commercial applications of DNA circuits are still a long way off, Reif said.

For one, the test tube calculations are slow. It can take hours to get an answer.

“We can do some limited computing, but we can’t even begin to think of competing with modern-day PCs or other conventional computing devices,” Reif said.

But DNA circuits can be far tinier than those made of silicon. And unlike electronic circuits, DNA circuits work in wet environments, which might make them useful for computing inside the bloodstream or the soupy, cramped quarters of the cell.

The technology takes advantage of DNA’s natural ability to zip and unzip to perform computations. Just like Velcro and magnets have complementary hooks or poles, the nucleotide bases of DNA pair up and bind in a predictable way.

The researchers first create short pieces of synthetic DNA, some single-stranded and some double-stranded with single-stranded ends, and mix them in a test tube.

When a single strand encounters a perfect match at the end of one of the partially double-stranded ones, it latches on and binds, displacing the previously bound strand and causing it to detach, like someone cutting in on a dancing couple.

The newly released strand can in turn pair up with other complementary DNA molecules downstream in the circuit, creating a domino effect.

The researchers solve math problems by measuring the concentrations of specific outgoing strands as the reaction reaches equilibrium.

To see how their circuit would perform over time as the reactions proceeded, Reif and Duke graduate student Tianqi Song used computer software to simulate the reactions over a range of input concentrations. They have also been testing the circuit experimentally in the lab.

Besides addition, subtraction and multiplication, the researchers are also designing more sophisticated analog DNA circuits that can do a wider range of calculations, such as logarithms and exponentials.

Conventional computers went digital decades ago. But for DNA computing, the analog approach has its advantages, the researchers say. For one, analog DNA circuits require fewer strands of DNA than digital ones, Song said.

Analog circuits are also better suited for sensing signals that don’t lend themselves to simple on-off, all-or-none values, such as vital signs and other physiological measurements involved in diagnosing and treating disease.

The hope is that, in the distant future, such devices could be programmed to sense whether particular blood chemicals lie inside or outside the range of values considered normal, and release a specific DNA or RNA — DNA’s chemical cousin — that has a drug-like effect.

Reif’s lab is also beginning to work on DNA-based devices that could detect molecular signatures of particular types of cancer cells, and release substances that spur the immune system to fight back.

“Even very simple DNA computing could still have huge impacts in medicine or science,” Reif said.

Here’s a link to and a citation for the paper,

Analog Computation by DNA Strand Displacement Circuits by Tianqi Song, Sudhanshu Garg, Reem Mokhtar, Hieu Bui, and John Reif. ACS Synth. Biol., 2016, 5 (8), pp 898–912 DOI: 10.1021/acssynbio.6b00144 Publication Date (Web): July 01, 2016

Copyright © 2016 American Chemical Society

This paper is behind a paywall.