NT/ Researchers use light to control magnetic fields at the nanoscale
Nanotechnology & nanomaterials biweekly vol.33, 7th October — 21st October
TL;DR
- Researchers from the University of Chicago’s Pritzker School of Molecular Engineering (PME) have discovered how to use nanoscale, low-power laser beams to precisely control magnetism within a 2D semiconductor. Their approach, described online in the journal Science Advances, has implications for both studying the emergence of the correlated phase as well as designing new optoelectronic and spintronic devices.
- A team of physicists has created a new way to self-assemble particles — an advance that offers new promise for building complex and innovative materials at the microscopic level.
- Scientists have gotten bacteria to spontaneously take up fluorescent carbon nanotubes for the first time. The breakthrough unlocks new biotechnology applications for prokaryotes, such as near-infrared bacteria tracking and ‘living photovoltaics’ — devices that generate energy using light-harvesting bacteria.
- Research into the synthesis of new materials could lead to more sustainable and environmentally friendly items such as solar panels and light-emitting diodes (LEDs). Scientists have developed a colloidal synthesis method for alkaline earth chalcogenides. This method allows them to control the size of the nanocrystals in the material and study the surface chemistry of the nanocrystals.
- Researchers at LSU, in collaboration with Zuse Institute in Berlin, Germany, have developed an ultraviolet metasurface that discriminates between left- and right-handed amino acids with attomolar sensitivity.
- The world’s whitest paint — seen in this year’s edition of Guinness World Records and “The Late Show With Stephen Colbert” — keeps surfaces so cool that it could reduce the need for air conditioning. Now the Purdue University researchers who created the paint have developed a new formulation that is thinner and lighter — ideal for radiating heat away from cars, trains and airplanes.
- In a new study, scientists explore a basic building block used in the fabrication of many DNA nanoforms. Known as a Holliday junction, this nexus of two segments of double-stranded DNA has been used to form elaborate, self-assembling crystal lattices at the nanometer scale, (or roughly 1/75,000th the width of a human hair).
- A method to draw data in an area smaller than 10 nanometers has been proposed in a recent study published in Physical Review Letters.
- What happens when we breathe in nanoparticles emitted by, for example, a laser printer? Could these nanoparticles damage the respiratory tract or perhaps even other organs? To answer these questions, Fraunhofer researchers are developing the “NanoCube” exposure device. The Nanocube’s integrated multi-organ chip set up in the laboratory of the Technical University of Berlin (TU Berlin) and by its spin-off organization “TissUse” detects interaction between nanoparticles and lung cells, the uptake of nanoparticles into the bloodstream and possible effects on the liver.
- A research team has developed a new type of polymer aerogel materials with vast applicational values for diverse functional devices.
- And more!
Nanotech Market
Nanotechnology deals with the ability to see, understand, measure, predict, produce or control matter at the nanoscale (below 100 nanometers). The realm of nanotechnology lies between 0.1 and 100 nanometers, wherein a nanometer is defined as one-thousandth of a micron. As a versatile technology with widespread applications in a wide range of end-use sectors, nanotechnology is currently facing a mixed bag of challenges and opportunities as the COVID-19 pandemic continues to spread across the globe. With the world fighting its biggest public health crisis in history, nanotechnology healthcare applications are storming into the spotlight led by the focus on nano intervention in terms of designing effective ways to identify, diagnose, treat and eliminate the spread of COVID-19 infections. Their role as nanocarriers has the potential to design risk-free and effective immunization strategies. In the post-COVID-19 period, the use of nanotechnology solutions in the production of a multitude of devices & products will continue to grow.
Amid the COVID-19 crisis, the global market for Nanotechnology estimated at US$42.2 Billion in the year 2020, is projected to reach a revised size of US$70.7 Billion by 2026, growing at a CAGR of 9.2% over the analysis period. Nanocomposites, one of the segments analyzed in the report, is projected to record a 8.7% CAGR and reach US$35.4 Billion by the end of the analysis period. After a thorough analysis of the business implications of the pandemic and its induced economic crisis, growth in the Nanomaterials segment is readjusted to a revised 10.1% CAGR for the next 7-year period.
Global nanotechnology market to reach US $126.8 billion by the year 2027. Amid the COVID-19 crisis, the global market for Nanotechnology is estimated at US $54.2 billion in the year 2020, and is projected to reach a revised size of US $126 billion.
Latest News & Research
Optically controllable magnetism in atomically thin semiconductors
by Kai Hao et al in Science Advances
Researchers from the University of Chicago’s Pritzker School of Molecular Engineering (PME) have discovered how to use nanoscale, low-power laser beams to precisely control magnetism within a 2D semiconductor. Their approach described online in the journal Science Advances has implications for both studying the emergence of the correlated phase as well as designing new optoelectronic and spintronic devices.
In thin, two-dimensional semiconductors, electrons move, spin and synchronize in unusual ways. For researchers, understanding the way these electrons carry out their intricate dances — and learning to manipulate their choreography — not only lets them answer fundamental physical questions, but can yield new types of circuits and devices.
One correlated phase that such electrons can take on is magnetic order, in which they align their spin in the same direction. Traditionally, the ability to manipulate magnetic order within a 2D semiconductor has been limited; scientists have used unwieldy, external magnetic fields, which limit technological integration and potentially conceal interesting phenomena.
“The fact that we can now use light to manipulate electrons in this way means we have unprecedented control over this magnetic order,” said Asst. Prof. Alex High, the senior author of the new work.
High’s lab focused on transition metal dichalcogenides (TMDs), a family of semiconductors that can be exfoliated into single, two-dimensional flakes, measuring just three atoms thick. Scientists had previously hypothesized that electrons within TMDs could assume a correlated phase, with their spin aligned in the same direction to lower the system energy — this ferromagnetic phase is what we colloquially call magnetism. Generating or modeling this transition to the correlated state, however, has been difficult.
High has long been interested in how light can be controlled and, in turn, can alter states of matter. His team wondered whether, instead of external magnetic fields, miniscule beams of light could be used to create a correlated magnetic phase. They aimed a tightly-focused laser beam, less than a micron (one-thousandth of a millimeter) in diameter at a monolayer TMD. They flashed the laser for nanoseconds at a time, while also monitoring the TMD with an optical probe that let them track the activity of its electrons.
The probe revealed that the pulsing laser was impacting the spin-polarization of electrons within a 5 micron by 8 micron area of the TMD, spreading a correlated phase outward from the laser. In other words, the electrons were aligning their spin; the researchers could control the magnetic order of electrons within the tiny area.
“This new technique provides us a handy way to manipulate electron correlation, making the study of the correlated phases much more practical than it has been in the past,” said postdoctoral fellow Kai Hao, co-first author of the paper.
“One of the things that makes this really attractive is the rather straightforward nature of it,” said graduate student Andrew Kindseth, who also contributed to the new work. “In many ways, it’s as simple as just shining a circularly polarized laser on this material.”
The new technique for controlling magnetism in atomically thin semiconductors offers a jumping-off point for a plethora of new studies, the researchers said.
Besides magnetic phases, TMD systems have also been hypothesized to form more exotic correlated electronic phases such as Wigner crystals, charge density waves, Mott states and superconductivity. The capability to locally manipulate the electron spins in TMDs within an ultrashort timescale and with nanoscale precision may provide previously inaccessible information, which will further aid the theoretical study of these exotic phases.
On the application side, there is an urgent need for novel optoelectronic and spintronic devices to meet the explosive growth in the information industry. The demonstration of efficient optical control of spin order has great potential for device applications. Immediate impacts include building on-chip spin sources, tunable optical isolators, and efficient fan-out in spintronic circuits.
“The capability to optically manipulate magnetic memory and generate spin amplification in TMDs — materials widely studied for next-generation technologies — will push optoelectronics and spintronics in new directions,” said graduate student Robert Shreiner, a co-first author of the paper.
Self-assembly of emulsion droplets through programmable folding
by Angus McMullen, Maitane Muñoz Basagoiti, Zorana Zeravcic, Jasna Brujic in Nature
A team of physicists has created a new way to self-assemble particles — an advance that offers new promise for building complex and innovative materials at the microscopic level.
Self-assembly, introduced in the early 2000s, gives scientists a means to “pre-program” particles, allowing for the building of materials without further human intervention — the microscopic equivalent of Ikea furniture that can assemble itself.
The breakthrough, reported in the journal Nature, centers on emulsions — droplets of oil immersed in water — and their use in the self-assembly of foldamers, which are unique shapes that can be theoretically predicted from the sequence of droplet interactions.
The self-assembly process borrows from the field of biology, mimicking the folding of proteins and RNA using colloids. In the Nature work, the researchers created tiny, oil-based droplets in water, possessing an array of DNA sequences that served as assembly “instructions.” These droplets first assemble into flexible chains and then sequentially collapse, or fold, via sticky DNA molecules. This folding yields a dozen types of foldamers, and further specificity could encode more than half of 600 possible geometric shapes.
“Being able to pre-program colloidal architectures gives us the means to create materials with intricate and innovative properties,” explains Jasna Brujic, a professor in New York University’s Department of Physics and one of the researchers. “Our work shows how hundreds of self-assembled geometries can be uniquely created, offering new possibilities for the creation of the next generation of materials.”
The research also included Angus McMullen, a postdoctoral fellow in NYU’s Department of Physics, as well as Maitane Muñoz Basagoiti and Zorana Zeravcic of ESPCI Paris.
The scientists emphasize the counterintuitive, and pioneering, aspect of the method: Rather than requiring a large number of building blocks to encode precise shapes, its folding technique means only a few are necessary because each block can adopt a variety of forms.
“Unlike a jigsaw puzzle, in which every piece is different, our process uses only two types of particles, which greatly reduces the variety of building blocks needed to encode a particular shape,” explains Brujic. “The innovation lies in using folding similar to the way that proteins do, but on a length scale 1,000 times bigger — about one-tenth the width of a strand of hair. These particles first bind together to make a chain, which then folds according to preprogrammed interactions that guide the chain through complex pathways into a unique geometry.”
“The ability to obtain a lexicon of shapes opens the path to further assembly into larger scale materials, just as proteins hierarchically aggregate to build cellular compartments in biology,” she adds.
Carbon nanotube uptake in cyanobacteria for near-infrared imaging and enhanced bioelectricity generation in living photovoltaics
by Alessandra Antonucci, Melania Reggente, Charlotte Roullier, Alice J. Gillen, Nils Schuergers, Vitalijs Zubkovs, Benjamin P. Lambert, Mohammed Mouhib, Elisabetta Carata, Luciana Dini, Ardemis A. Boghossian in Nature Nanotechnology
Scientists at EPFL have gotten bacteria to spontaneously take up fluorescent carbon nanotubes for the first time. The breakthrough unlocks new biotechnology applications for prokaryotes, such as near-infrared bacteria tracking and “living photovoltaics” — devices that generate energy using light-harvesting bacteria.
“We put nanotubes inside of bacteria,” says Professor Ardemis Boghossian at EPFL’s School of Basic Sciences. “That doesn’t sound very exciting on the surface, but it’s actually a big deal. Researchers have been putting nanotubes in mammalian cells that use mechanisms like endocytosis, that are specific to those kinds of cells. Bacteria, on the other hand, don’t have these mechanisms and face additional challenges in getting particles through their tough exterior. Despite these barriers, we’ve managed to do it, and this has very exciting implications in terms of applications.”
Boghossian’s research focuses on interfacing artificial nanomaterials with biological constructs, including living cells. The resulting “nanobionic” technologies combine the advantages of both the living and non-living worlds. For years, her group has worked on the nanomaterial applications of single-walled carbon nanotubes (SWCNTs), tubes of carbon atoms with fascinating mechanical and optical properties.
These properties make SWCNTs ideal for many novel applications in the field of nanobiotechnology. For example, SWCNTs have been placed inside mammalian cells to monitor their metabolisms using near-infrared imaging. The insertion of SWCNTs in mammalian cells has also led to new technologies for delivering therapeutic drugs to their intracellular targets, while in plant cells they have been used for genome editing. SWCNTs have also been implanted in living mice to demonstrate their ability to image biological tissue deep inside the body.
In an article published in Nature Nanotechnology, Boghossian’s group with their international colleagues were able to “convince” bacteria to spontaneously take up SWCNTs by “decorating” them with positively charged proteins that are attracted by the negative charge of the bacteria’s outer membrane. The two types of bacteria explored in the study, Synechocystis and Nostoc, belong to the Cyanobacteria phylum, an enormous group of bacteria that get their energy through photosynthesis — like plants. They are also “Gram-negative,” which means that their cell wall is thin, and they have an additional outer membrane that “Gram-positive” bacteria lack.
The researchers observed that the cyanobacteria internalized SWCNTs through a passive, length-dependent and selective process. This process allowed the SWCNTs to spontaneously penetrate the cell walls of both the unicellular Synechocystis and the long, snake-like, multicellular Nostoc.
Following this success, the team wanted to see if the nanotubes can be used to image cyanobacteria — as is the case with mammalian cells. “We built a first-of-its-kind custom setup that allowed us to image the special near-infrared fluorescence we get from our nanotubes inside the bacteria,” says Boghossian.
Alessandra Antonucci, a former PhD student at Boghossian’s lab adds:
“When the nanotubes are inside the bacteria, you could very clearly see them, even though the bacteria emit their own light. This is because the wavelengths of the nanotubes are far in the red, the near-infrared. You get a very clear and stable signal from the nanotubes that you can’t get from any other nanoparticle sensor. We’re excited because we can now use the nanotubes to see what is going on inside of cells that have been difficult to image using more traditional particles or proteins. The nanotubes give off a light that no natural living material gives off, not at these wavelengths, and that makes the nanotubes really stand out in these cells.”
The scientists were able to track the growth and division of the cells by monitoring the bacteria in real-time. Their findings revealed that the SWCNTs were being shared by the daughter cells of the dividing microbe.
“When the bacteria divide, the daughter cells inherent the nanotubes along with the properties of the nanotubes,” says Boghossian. “We call this ‘inherited nanobionics.’ It’s like having an artificial limb that gives you capabilities beyond what you can achieve naturally. And now imagine that your children can inherit its properties from you when they are born. Not only did we impart the bacteria with this artificial behavior, but this behavior is also inherited by their descendants. It’s our first demonstration of inherited nanobionics.”
“Another interesting aspect is when we put the nanotubes inside the bacteria, the bacteria show a significant enhancement in the electricity it produces when it is illuminated by light,” says Melania Reggente, a postdoc with Boghossian’s group. “And our lab is now working towards the idea of using these nanobionic bacteria in a living photovoltaic.”
“Living” photovoltaics are biological energy-producing devices that use photosynthetic microorganisms. Although still in the early stages of development, these devices represent a real solution to our ongoing energy crisis and efforts against climate change.
“There’s a dirty secret in photovoltaic community,” says Boghossian. “It is green energy, but the carbon footprint is really high; a lot of CO2 is released just to make most standard photovoltaics. But what’s nice about photosynthesis is not only does it harness solar energy, but it also has a negative carbon footprint. Instead of releasing CO2, it absorbs it. So it solves two problems at once: solar energy conversion and CO2 sequestration. And these solar cells are alive. You do not need a factory to build each individual bacterial cell; these bacteria are self-replicating. They automatically take up CO2 to produce more of themselves. This is a material scientist’s dream.”
Boghossian envisions a living photovoltaic device based on cyanobacteria that have automated control over electricity production that does not rely on the addition of foreign particles. “In terms of implementation, the bottleneck now is the cost and environmental effects of putting nanotubes inside of cyanobacteria on a large scale.”
With an eye toward large-scale implementation, Boghossian and her team are looking to synthetic biology for answers:
“Our lab is now working towards bioengineering cyanobacteria that can produce electricity without the need for nanoparticle additives. Advancements in synthetic biology allow us to reprogram these cells to behave in totally artificial ways. We can engineer them so that producing electricity is literally in their DNA.”
Ultrastrong and multifunctional aerogels with hyperconnective network of composite polymeric nanofibers
by Huimin He, Xi Wei, Bin Yang, Hongzhen Liu, Mingze Sun, Yanran Li, Aixin Yan, Chuyang Y. Tang, Yuan Lin, Lizhi Xu in Nature Communications
Aerogels are lightweight materials with extensive microscale pores, which could be used in thermal insulation, energy devices, aerospace structures, as well as emerging technologies of flexible electronics. However, traditional aerogels based on ceramics tend to be brittle, which limits their performance in load-bearing structures. Due to restrictions posed by their building blocks, recently developed classes of polymeric aerogels can only achieve high mechanical strength by sacrificing their structural porosity or lightweight characteristics.
A research team led by Dr Lizhi Xu and Dr Yuan Lin from the Department of Mechanical Engineering of the Faculty of Engineering of the University of Hong Kong (HKU), has developed a new type of polymer aerogel materials with vast applicational values for diverse functional devices.
In this study, a new type of aerogels was successfully created using a self-assembled nanofiber network involving aramids, or Kevlar, a polymer material used in bullet-proof vests and helmets. Instead of using millimetre-scale Kevlar fibres, the research team used a solution-processing method to disperse the aramids into nanoscale fibrils. The interactions between the nanofibers and polyvinyl alcohol, another soft and “gluey” polymer, generated a 3D fibrillar network with high nodal connectivity and strong bonding between the nanofibers.
“It’s like a microscopic 3D truss network, and we managed to weld the trusses firmly together, resulting in a very strong and tough material that can withstand extensive mechanical loads, outperforming other aerogel materials,” said Dr Xu.
The team has also used theoretical simulations to explain the outstanding mechanical performance of the developed aerogels.
“We constructed a variety of 3D network models in computer, which captured the essential characteristics of nanofibrillar aerogels,” said Dr Lin, who led the theoretical simulations of the research. “The nodal mechanics of fibrillar networks are essential to their overall mechanical behaviours. Our simulations revealed that the nodal connectivity and the bonding strength between the fibres influenced the mechanical strength of the network by many orders of magnitudes even with the same solid content,” said Dr Lin.
“The results are very exciting. We not only developed a new type of polymer aerogels with excellent mechanical properties but also provided insights for the design of various nanofibrous materials,” said Dr Xu, adding, “the simple fabrication processes for these aerogels also allow them to be used in various functional devices, such as wearable electronics, thermal stealth, filtration membranes, and other systems.”
Alkaline-Earth Chalcogenide Nanocrystals: Solution-Phase Synthesis, Surface Chemistry, and Stability
by Alison N. Roth, Yunhua Chen, Marquix A. S. Adamson, Eunbyeol Gi, Molly Wagner, Aaron J. Rossini, Javier Vela in ACS Nano
Research into the synthesis of new materials could lead to more sustainable and environmentally friendly items such as solar panels and light emitting diodes (LEDs). Scientists from Ames National Laboratory and Iowa State University developed a colloidal synthesis method for alkaline earth chalcogenides. This method allows them to control the size of the nanocrystals in the material. They were also able to study the surface chemistry of the nanocrystals and assess the purity and optical properties of the materials involved.
Alkaline earth chalcogenides are a type of semiconductor that is of growing interest among scientists. They have a variety of possible applications such as bioimaging, LEDs, and thermal sensors. These compounds may also be used to make optical materials such as perovskites, which convert light into energy.
According to Javier Vela, Ames Lab scientist and the John D. Corbett Professor of Chemistry at Iowa State University, one reason these new materials are of interest is because, “they are comprised of earth-abundant and biocompatible elements, which make them favorable alternatives compared to the more widely used toxic or expensive semiconductors.”
Vela explained that more widely used semiconductors contain lead or cadmium, both elements that are detrimental to human health and the environment. Additionally, the most popular technique scientists use to synthesize these materials involves solid-state reactions.
“These reactions often occur at extremely high temperatures (above 900 °C or 1652 °F) and require reaction times that can last anywhere from days to weeks,” he said.
On the other hand, Vela explained that “solution-phase (colloidal) chemistry can be performed using much lower (below 300 °C or 572 °F) temperatures and shorter reactions times.” So, the colloidal method Vela’s team used requires less energy and time to synthesize the materials.
Vela’s team found that the colloidal synthesis method allowed them to control the size of the nanocrystals. Nanocrystal size is important because it determines the optical properties of some materials. Vela explained that by changing the size of the particles, scientists can influence how well the materials absorb light.
“This means we can potentially synthesize materials that are more suited for specific applications just by changing the nanocrystal size,” he said.
According to Vela, the team’s original goal was to synthesize semiconducting alkaline-earth chalcogenide perovskites, because of their potential use in solar devices. However, to accomplish this goal, they needed a deeper understanding of the fundamental chemistry of alkaline earth chalcogenides. So, they chose to focus on these binary materials instead.
Vela said that their research fills a need to improve scientists’ understanding of photovoltaic, luminescent, and thermoelectric materials that are made of earth-abundant and non-toxic elements.
He said, “We hope that our developments with this project ultimately aid in the synthesis of more complex nanomaterials, such as the alkaline-earth chalcogenide perovskites.”
Multi-organ chip detects dangerous nanoparticles
by Fraunhofer researchers
What happens when we breathe in nanoparticles emitted by, for example, a laser printer? Could these nanoparticles damage the respiratory tract or perhaps even other organs? To answer these questions, Fraunhofer researchers are developing the “NanoCube” exposure device. The Nanocube’s integrated multi-organ chip set up in the laboratory of the Technical University of Berlin (TU Berlin) and by its spin-off organization “TissUse” detects interaction between nanoparticles and lung cells, the uptake of nanoparticles into the bloodstream and possible effects on the liver.
Having a laser printer right next to your workstation is certainly very practical. That being said, there is the risk that these machines, just like 3D printers, could emit aerosols during operation that contain, among other things, nanoparticles — particles that are between one and one hundred nanometers in size. By comparison, one hair is about 60,000 to 80,000 nanometers thick.
Nanoparticles are also produced by passing road vehicles, for example, through the abrasion of tires. As yet, however, little is known about how these particles affect the human body when they are inhaled into the lungs. Until now, the only way to study this would have been by animal testing. What’s more, large sample quantities of the relevant aerosol would have to be collected at great expense.
Researchers from the Fraunhofer Institute for Toxicology and Experimental Medicine ITEM and the Fraunhofer Institute for Algorithms and Scientific Computing SCAI are collaborating with TU Berlin and its spin-off organization TissUse GmbH on the “NanoINHAL” project to investigate the impact of nanoparticles on the human body.
“We are able to analyze the biological impact of the aerosols directly and easily using in vitro methods — and without animal testing,” says Dr. Tanja Hansen, Group Manager at Fraunhofer ITEM.
Combining two existing technologies has made this possible: The multi-organ chip Humimic Chip3 from TU Berlin and its spin-off organization TissUse, and the P.R.I.T. ExpoCube, developed by Fraunhofer ITEM. The Humimic Chip3 is a chip the size of a standard laboratory slide measuring 76 x 26 mm. Tissue cultures miniaturized 100,000-fold can be placed on it, with nutrient solutions supplied to the tissue cultures by micropumps. In this way, for example, tissue samples of the lung and liver and their interaction with nanoparticles can be artificially recreated.
Four of these multi-organ chips fit into the P.R.I.T. ExpoCube. This is an exposure device used to study airborne substances such as aerosols in vitro. Using a sophisticated system of micropumps, heating electronics, aerosol lines and sensors, the ExpoCube is able to expose the cell samples on the multi-organ chip to various aerosols or even nanoparticles at the air-liquid interface — as in the human lung — in a controllable and reproducible manner.
The nanoparticles flow through a microduct, from which several branches lead downward to conduct the air and nanoparticles to the four multi-organ chips.
“If lung cells are to be exposed at the air-liquid interface, numerous parameters come into play, such as temperature, the flow of the culture medium in the chip, and the aerosol flow. This makes experiments of this kind very complicated,” Hansen explains.
The system is currently undergoing further optimization. At the end of the project, the combination of NanoCube and multi-organ chip will facilitate detailed studies of aerosols in vitro. Only then will it be possible to investigate the direct impact of the potentially harmful nanoparticles on the respiratory tract and, at the same time, possible effects on other organs, such as the liver.
But how can aerosols, in particular nanoparticles, be directed towards lung cells in such a way that a specified quantity is deposited on the cell surface? This is where the expertise of Fraunhofer SCAI comes in: The researchers studied this point and similar aspects in a simulation. They had to overcome special challenges in the process: For example, the physical and numerical models required for a detailed simulation of nanoparticles are significantly more complex than for particles with larger diameters. This, in turn, causes a significant increase in computing time.
But the time and effort are worth it, because the computationally intensive simulation helps to optimize the real-life test system. Let’s take an example: As mentioned above, the aerosol has to flow through a line from which several branches extend downward to direct the nanoparticles onto the multi-organ chips, with conditions at the sampling points that are as identical as possible.
The inertial forces of the nanoparticles are low, however, so the particles would be less likely to move out of the diverted flow path and onto the cell surface. Gravity alone is not sufficient in this case. The researchers resolve the issue by exploiting the phenomenon of thermophoresis.
“This relates to a force in a fluid with a temperature gradient that causes the particles to migrate to the cooler side,” explains Dr. Carsten Brodbeck, Project Manager at Fraunhofer SCAI. “By allowing the aerosol to flow through the line in a heated state, while the cells are cultivated naturally at body temperature, the nanoparticles move towards the cells, which the simulation clearly shows.”
The researchers also used simulations to investigate how to achieve the highest possible temperature gradient without damaging the cells and how the corresponding device should be constructed. They also examined how different flow speeds and supply line geometries would affect uptake.
The temperature distribution in the exposure device was optimized by selecting different materials, making adjustments to the geometry and modifying the cooling and heating design.
“Using simulations, we can quickly and easily change the boundary conditions and understand the effects of these changes. We can also see things that would remain hidden in experiments,” explains Brodbeck.
The basic technological problems have been solved. Now, the initial prototype of the NanoCube exposure device, including a multi-organ chip, is expected to be ready in the fall, after which the first experiments with the system will be carried out.
For now, the researchers at Fraunhofer are using reference particles instead of aerosols from printers, for example, nanoparticles from zinc oxide or what is known as “carbon black”, i.e. the black pigment in printing ink. In future practical applications, the measuring system is to be set up wherever the nanoparticles are produced, for example, next to a laser printer.
The NanoINHAL project will see the creation of an innovative test system that can be used to investigate the toxic effects of airborne nanoparticles on cells in the respiratory tract and lungs, as well as on downstream organs such as the liver.
Due to the combination of two organ systems in a microphysiological system, it will also be possible to study the uptake and distribution of nanoparticles in the organism. In the future, the test system will provide data on the long-term effects of inhaled nanoparticles as well as their biokinetics. This will play a major role in assessing the potential health hazard posed by such particles.
Resonant Plasmonic–Biomolecular Chiral Interactions in the Far-Ultraviolet: Enantiomeric Discrimination of sub-10 nm Amino Acid Films
by Tiago Ramos Leite et al in Nano Letters
Researchers at LSU, in collaboration with Zuse Institute in Berlin, Germany, have developed an ultraviolet metasurface that discriminates between left- and right-handed amino acids with attomolar sensitivity.
“Detecting the handedness of dilute concentrations of biomolecules is a key step towards the early detection of many neurodegenerative disorders such as Alzheimer’s, Huntington’s, or Parkinson’s disease,” said LSU Chemical Engineering Associate Professor Kevin McPeak, lead author on the paper. “What is unique about our work is that we developed an aluminum metasurface with chiroptical resonances that overlap with the bio-chiral signal. Developing metasurfaces with ultraviolet chiral response in resonance with biomolecular chirality is critical to maximizing the signal enhancement of weak biomolecular activity.”
Resonant plasmonic-molecular chiral interactions are a promising route to enhanced biosensing, the group writes. However, biomolecular optical activity primarily exists in the far-ultraviolet regime, posing significant challenges for spectral overlap with current metasurfaces. The group developed an optical model of a chiral biomolecular film on a plasmonic metasurface. The model showed that detectable enhancements in the chiroptical signals from the biomolecules were only possible when tight spectral overlap exists between the plasmonic and biomolecular chiral responses.
“Chiral objects are those whose mirror image is not superimposable,” McPeak said. “Your hands are a good example of this. Biomolecules, such as amino acids and proteins, which govern much of the biological processes in our bodies, are chiral as well. Light can also be chiral through polarization. Chiral-chiral interactions can be thought of as handshaking, i.e., shaking two right hands works, whereas shaking right hand to left hand can lead to some awkward moments.
“Thus, chiral biomolecules absorb chiral light in a way that lets us understand the structure of the molecules. The problem is that this is a very weak effect, and therefore, we miss much information. But metasurfaces with chiral resonances in the same wavelength regime as the biomolecular chiral response (e.g., far-ultraviolet) can amplify the weak, chiral biological signals. By tuning the plasmonic chiral response into the far-ultraviolet regime, where biomolecules have their chiral response, we maximize the potential signal enhancement and bring them into resonance.”
Thin layer lightweight and ultrawhite hexagonal boron nitride nanoporous paints for daytime radiative cooling
by Andrea Felicelli et al in Cell Reports Physical Science
The world’s whitest paint — seen in this year’s edition of Guinness World Records and “The Late Show With Stephen Colbert” — keeps surfaces so cool that it could reduce the need for air conditioning. Now the Purdue University researchers who created the paint have developed a new formulation that is thinner and lighter — ideal for radiating heat away from cars, trains and airplanes.
“I’ve been contacted by everyone from spacecraft manufacturers to architects to companies that make clothes and shoes,” said Xiulin Ruan, a Purdue professor of mechanical engineering and developer of the paint. “They mostly had two questions: Where can I buy it, and can you make it thinner?”
The original world’s whitest paint used nanoparticles of barium sulfate to reflect 98.1% of sunlight, cooling outdoor surfaces more than 4.5°C below ambient temperature. Cover your roof in that paint, and you could essentially cool your home with much less air conditioning. But there’s a problem.
“To achieve this level of radiative cooling below the ambient temperature, we had to apply a layer of paint at least 400 microns thick,” Ruan said. “That’s fine if you’re painting a robust stationary structure, like the roof of a building. But in applications that have precise size and weight requirements, the paint needs to be thinner and lighter.”
That’s why Ruan’s team began experimenting with other materials, pushing the limit of materials’ capability to scatter sunlight. Their latest formulation is a nanoporous paint incorporating hexagonal boron nitride as the pigment, a substance mostly used in lubricants. This new paint achieves nearly the same benchmark of solar reflectance (97.9%) with just a single 150-micron layer of paint.
“Hexagonal boron nitride has a high refractive index, which leads to strong scattering of sunlight,” said Andrea Felicelli, a Purdue Ph.D. student in mechanical engineering who worked on the project. “The particles of this material also have a unique morphology, which we call nanoplatelets.”
Ioanna Katsamba, another Ph.D. student in mechanical engineering at Purdue, ran computer simulations to understand if the nanoplatelet morphology offers any benefits. “The models showed us that the nanoplatelets are more effective in bouncing back the solar radiation than spherical nanoparticles used in previous cooling paints,” Katsamba said.
The paint also incorporates voids of air, which make it highly porous on a nanoscale. This lower density, together with the thinness, provides another huge benefit: reduced weight. The newer paint weighs 80% less than barium sulfate paint yet achieves nearly identical solar reflectance.
“This light weight opens the doors to all kinds of applications,” said George Chiu, a Purdue professor of mechanical engineering and an expert in inkjet printing. “Now this paint has the potential to cool the exteriors of airplanes, cars or trains. An airplane sitting on the tarmac on a hot summer day won’t have to run its air conditioning as hard to cool the inside, saving large amounts of energy. Spacecraft also have to be as light as possible, and this paint can be a part of that.”
As to that other big question — where can I buy the paint? — Ruan explains. “We are in discussions right now to commercialize it,” he said. “There are still a few issues that need to be addressed, but progress is being made.”
Either way, these Purdue researchers look forward to what the paint could accomplish.
“Using this paint will help cool surfaces and greatly reduce the need for air conditioning,” Ruan said. “This not only saves money, but it reduces energy usage, which in turn reduces greenhouse gas emissions. And unlike other cooling methods, this paint radiates all the heat into deep space, which also directly cools down our planet. It’s pretty amazing that a paint can do all that.”
The influence of Holliday junction sequence and dynamics on DNA crystal self-assembly
by Chad R. Simmons et al in Nature Communications
In a new study, Hao Yan and his colleagues Nicholas Stephanopoulos and Petr Sulc, explore a basic building block used in the fabrication of many DNA nanoforms. Known as a Holliday junction, this nexus of two segments of double-stranded DNA has been used to form elaborate, self-assembling crystal lattices at the nanometer scale, (or roughly 1/75,000th the width of a human hair).
In the world of biomolecules, none is more iconic, nor more versatile, than DNA. Nature uses the famous double helix to store the blueprints of all living forms, drawing on a four-letter alphabet of nucleotides.
Researchers in the field of DNA nanotechnology have been inspired by the seemingly inexhaustible variety of living forms nature has fashioned from this genetic raw material. The field seeks to emulate nature’s creative enterprise and even extend the possibilities of DNA architecture beyond what nature has created.
The structures take their name from molecular biologist Robin Holliday, who first proposed their existence in 1964. Holliday junctions play an essential role in nature, where they are involved in a process known as homologous recombination, a driving force in generating novel genetic variation in living things.
Since the inception of DNA nanotechnology, the field has made remarkable strides, using DNA components to design tiny structures of intricate beauty as well as nanoscale devices whose applications touch on fields as varied as photonics, computer storage, biosensing and tissue regeneration.
Yan has been at the forefront of the field’s rapid transformations, designing a myriad of useful nanoarchitectural forms, from cartwheeling nanorobots and DNA spiders to cancer-fighting seek-and-destroy devices.
The new study uses crystallography techniques to describe the characteristics of 36 basic variants of the Holliday junction. The results show that the effectiveness of a given Holliday junction for the construction of crystalline nanoarchitectures is sensitively dependent not only on the arrangement of the four nucleotide pairs forming the junction, but also on sequences forming the junction’s four protruding arms. Some DNA sequences act to enhance the crystallization process of these forms, while six of the 36 Holliday junction variants were deemed “fatal” due to their failure to form crystals.
Yan directs the Biodesign Center for Molecular Design and Biomimetics and holds the Milton D. Glick Distinguished Professorship in ASU’s School of Molecular Sciences. Stephanopoulos and Sulc are also faculty members in center and school.
The research findings, which represent the first systematic study of Holliday junctions, recently appeared in the journal Nature Communications.
DNA proves to be an ideal material with which to design and fabricate nanoscale structures. The consistent and predictable nature of base pairing among DNA’s four nucleotides ensures that properly engineered forms will reliably self-assemble into desired structures. To this end, various elaborate nanoforms have been constructed using fundamental DNA building blocks, one of the most popular and useful being the Holliday junction. DNA crystals composed of repeating structural units are key ingredients for nanotechnology applications, allowing for versatile and scalable design features.
Holliday junctions are observed in nature as an intermediary stage during the process of cell meiosis. The result of this transformation is an exchange of genes between maternal and paternal chromosomes. This process, known as homologous recombination, occurs in four stages. (See illustration above.)
First, a pair of double-stranded DNA helices sit alongside each other. An enzyme known as an endonuclease then causes a single-stranded break in each of the two double strands. The next step, known as strand invasion, occurs when the free ends of each single-stranded break join together, causing the originally separate double strands to be intertwined.
This cross-shaped structure, which joins the two separate double strands of DNA together, is the Holliday junction. In biological processes, the junction is then “resolved” when another enzyme cuts the Holliday junction in one of two ways, both resulting in two separate DNA strands, which differ from the original strands because the Holliday junction has introduced new DNA segments into the two DNA double strands.
This form of DNA recombination is a universal biological event of great importance. It simultaneously acts to preserve genome integrity through mechanisms of DNA repair while generating novel variability, without which, organisms would soon reach an evolutionary dead end. The key structure in the shuffling of the DNA deck during cell division is the Holliday junction.
It was later noted that the Holliday junction motif could be used as a powerful building block for a multiplicity of artificial DNA structures. Although the Holliday junctions occurring during cell division can slide along the DNA length, in a process known as branch migration, the junctions used for constructing DNA nanostructures are immobilized because the sequences flanking them are not complementary.
“The first immobile Holliday junction was described in 1982, and this sequence has since been used exclusively in self-assembling DNA crystals,” said Chad Simmons, first author of the paper and the lead scientist applying X-ray crystallography for this study. “Our work sought to change this paradigm by probing the 35 other possible immobile junctions. As a result, we were able to identify several sequences that yielded superior performance compared to their predecessors in terms of their ability to robustly crystallize and diffract to high resolution, and which allowed the ability to control the symmetry of the lattice arrangement.
“This required an exhaustive effort that yielded 134 new crystal structures, and we are very excited to share a comprehensive toolbox of sequence combinations to direct the design and construction of future self-assembling DNA crystal systems.”
The new research demonstrates that most Holliday junction variants produce self-assembling crystals, though six fatal junction arrangements were incompatible with crystal formation. The common feature in these failed junctions was their lack of two critical binding sites for ions, which are essential for crystal formation.
“This study was fascinating because it showed how subtle variations in Holliday junction geometries — which could be understood at the single-nucleotide level — could have dramatic effects on crystal assembly and symmetry. This is truly ‘molecular science,’ allowing us to eventually engineer interactions at the molecular level that will give rise to exciting nanomaterials with unprecedented control,” Stephanopolous said.
“One of the challenges of this research was to determine why some Holliday junctions could produce crystals, but others do not. Empirically, we could study the crystal structures of those junctions that crystallize, but to understand the behavior of the fatal junction arrangements that do not, computational chemistry was needed,” Sulc said.
“To this end, we teamed up with Dr. Miroslav Krepl and Professor Jiri Sponer from the Czech Academy of Sciences, who simulated all Holliday junctions at atomistic resolution, and gained the critical insight that the fatal junctions were not able to bind ions that stabilize conformation. This effort provided an excellent example of where computer modeling and experiments can jointly explain complex phenomena,” he said.
The new research provides valuable clues for the design and development of novel forms to be added to the ever-growing plethora of nanostructures and nanodevices serving a broad range of applications in electronics, imaging, computer science and medicine.
Flexoelectricity-Driven Mechanical Switching of Polarization in Metastable Ferroelectrics
by Ji Hye Lee et al in Physical Review Letters
A method to draw data in an area smaller than 10 nanometers has been proposed in a recent study published in Physical Review Letters. A joint research team led by Professor Daesu Lee (Department of Physics) of POSTECH, Professor Se Young Park (Department of Physics) at Soongsil University, and Dr. Ji Hye Lee (Department of Physics and Astronomy) of Seoul National University has proposed a method for densely storing data by “poking” with a sharp probe. This method utilizes a material in the metastable state, whose properties change easily even with slight stimulation.
A thin film of metastable ferroelectric calcium titanate (CaTiO3) enables the polarization switching of material even with a slight pressure of a probe: A very weak force of 100 nanonewtons (nN) is more than enough. The joint research team succeeded in making the width of the polarization path smaller than 10 nm by using this force and found a way to dramatically increase the capacity of data storage. This is because the smaller the size of the path, the more data the single material can store.
The data storage capacity increased by up to 1 terabit (Tbit)/cm as a result of drawing the data storage area using a probe on the thin film. This result is 10 times greater than that of a previous study (0.11 Tbit/cm²) which suggested a probe-based storage method using another material. Unlike the data storage method that uses electric fields, this probe method only requires a very small force, so the burden on the device is also small.
The results from the study are drawing attention as they have proved that materials achieve higher performance in an unstable metastable state. The findings are anticipated to be applicable in next-generation electronic devices with improved integration and efficiency in the future.
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