Graphene-based memory resistors show promise for brain-based computing

Graphene memristors open doors for biomimetic computing.

UNIVERSITY PARK, Pa. — As progress in traditional computing slows, new forms of computing are coming to the forefront. At Penn State, a team of engineers is attempting to pioneer a type of computing that mimics the efficiency of the brain’s neural networks while exploiting the brain’s analog nature.

Modern computing is digital, made up of two states, on-off or one and zero. An analog computer, like the brain, has many possible states. It is the difference between flipping a light switch on or off and turning a dimmer switch to varying amounts of lighting.

Neuromorphic or brain-inspired computing has been studied for more than 40 years, according to Saptarshi Das, the team leader and Penn State assistant professor of engineering science and mechanics.

What’s new is that as the limits of digital computing have been reached, the need for high-speed image processing, for instance for self-driving cars, has grown. The rise of big data, which requires types of pattern recognition for which the brain architecture is particularly well suited, is another driver in the pursuit of neuromorphic computing.

“We have powerful computers, no doubt about that, the problem is you have to store the memory in one place and do the computing somewhere else,” Das said.

The shuttling of this data from memory to logic and back again takes a lot of energy and slows the speed of computing. In addition, this computer architecture requires a lot of space. If the computation and memory storage could be located in the same space, this bottleneck could be eliminated.

“We are creating artificial neural networks, which seek to emulate the energy and area efficiencies of the brain,” explained Thomas Shranghamer, a doctoral student in the Das group and first author on a paper recently published in Nature Communications. “The brain is so compact it can fit on top of your shoulders, whereas a modern supercomputer takes up a space the size of two or three tennis courts.”

Like synapses connecting the neurons in the brain that can be reconfigured, the artificial neural networks the team is building can be reconfigured by applying a brief electric field to a sheet of graphene, the one-atomic-thick layer of carbon atoms. In this work they show at least 16 possible memory states, as opposed to the two in most oxide-based memristors, or memory resistors.

“What we have shown is that we can control a large number of memory states with precision using simple graphene field effect transistors,” Das said.

The team thinks that ramping up this technology to a commercial scale is feasible. With many of the largest semiconductor companies actively pursuing neuromorphic computing, Das believes they will find this work of interest.

In addition to Das and Shranghamer, the additional author on the paper, titled “Graphene Memristive Synapses for High Precision Neuromorphic Computing,” is Aaryan Oberoi, doctoral student in engineering science and mechanics.

The Army Research Office supported this work. The team has filed for a patent on this invention.

Penn State: Fingerprints provide crucial clue to New Nanofiber Fabrication Technique – Applications for Advanced Filtration, Wound care, Drug Delivery, and other Medical Applications

Tortellini-like PECA film obtained by initiation with sodium hydroxide.

Fingerprints are usually used to identify people but, this time, they gave Penn State chemical engineers the crucial clue needed to discover an easy, versatile new method for making nanofibers that have potential uses in advanced filtration as well as wound care, drug delivery, bioassays and other medical applications.

The new technique is based on the way forensic scientists develop fingerprints from a crime scene and is easier and more versatile than either of the current methods, templates or electrospinning, used commercially to make nanofibers. The first nanofibers generated by the technique are made from the basic ingredient of Super Glue , cyanoacrylate, which is a biologically-compatible material already used in liquid sutures, spheres for drug delivery and in experimental cancer treatment. However, the researchers say that other materials, like cyanoacrylate, that form solid polymers when nudged by a catalyst could potentially also be used in the process.

Dr. Henry C. Foley, professor of chemical engineering who directed the project, says, “The new technique is so versatile that it allows us not only to make nano-scale fibers but also nano-sized flat sheets, spheres and even wrinkled sheets that look tortellini-like.”

The researchers can also generate patterned surfaces and say that the process could conceivably be used in an ink jet printer.

The research is detailed in a paper, “Facile Catalytic Growth of Cyanoacrylate Nanofibers,” published online today (Jan. 26) in the British journal, The Royal Society of Chemistry, Chemical Communications. The authors are Pratik J. Mankidy, doctoral candidate in chemical engineering; Ramakrishnan Rajagopalan, research associate at Penn State’s Materials Research Laboratory, and Foley, who is also associate vice president for research at the University. The journal is available at: xlink.rsc.org/?DOI=B514600C

Foley explains that forensic scientists develop latent fingerprints via a process known as cyanoacrylate fuming. Fingerprints left on a surface are exposed to fumes of cyanoacrylate, which form a white polymer residue that makes the ridges of the fingerprint visible.

One of the researchers, Pratik Mankidy, had accidentally left his fingerprints on a piece of research equipment that had been secured with Super Glue and nanofibers appeared. Putting two and two together, the researchers set out to discover what constituents of fingerprints trigger the cyanoacrylate polymerization on the ridges of fingerprints. They made synthetic fingerprints from a mixture of a known polymer initiator, common table salt in water, and a non-initiator, linoleic acid, found on fingers.

Then they exposed the fake prints to cyanoacrylate fuming. Sure enough, they got nanofibers similar to the ones Mankidy’s fingerprints had generated accidentally. They also fumed cyanoacrylate on single initiators and found that sodium hydroxide, potassium hydroxide and potassium acetate produced tortellini-like films of the polymer. When ammonium hydroxide was fumed with cyanoacrylate, it produced nano-sized spheres.

The researchers note that the role played by the presence of the non-initiating components in the fingerprint mixture is not completely understood. They are continuing their experiments to understand the process more completely. A majority of the fibers produced by the new process have diameters in the 200-250-nanometer range and are hundreds of microns long. Typically, nanofibers that are currently commercially available are in this same range. Foley notes, “Our findings open up a whole new world of opportunity for control of nanoscale structures through chemistry via catalysis.”

Source: Penn State

Self-heating, fast-charging batteries could speed up EV adoption

Image above] Researchers at Penn State have developed a fast-charging battery for all outside temperatures that rapidly heats up internally prior to charging battery materials. Credit: Chao-Yang Wang, Penn State University

A barrier to universal adoption of electric vehicles (EVs) has to do with charging the battery. It can take anywhere from a half hour up to 12 hours, depending on the charging point used and the EV’s battery capacity.

And of course, there needs to be a massive charging infrastructure in place so that drivers will feel confident driving long distances on a single charge.

One factor that significantly impacts EV driving range is the outside temperature. According to the Office of Energy Efficiency & Renewable Energy, cold weather can affect the driving range of plug-in EVs by more than 25%. In a project at Idaho National Laboratory, researchers found that plug-in hybrid electric Chevy Volts driven in winter in Chicago had 29% less range than those driven in spring in Chicago.

It’s common knowledge that batteries, in general, don’t do well in freezing temperatures. But if we’re ever to move beyond gas-powered vehicles, we need a battery that can charge quickly, hold its charge in cold weather, and not cost an arm and a leg.

Researchers at Pennsylvania State University have been thinking about this for a while. A little over two years ago, William E. Diefenderfer Chair of mechanical engineering, professor of chemical engineering, and professor of materials science and engineering and director of the Electrochemical Engine Center,  Chao-Yang Wang and his team developed a self-heating lithium battery that uses thin nickel foil with one end attached to the negative terminal and the other end extending outside the battery, creating a third terminal.

The foil serves as a heater of sorts. A temperature sensor sets off electron flow through the foil—heating it up and warming the battery. The sensor switches off after the battery reaches 32oF, allowing electric current to continue flowing normally.

Now, Wang and his team have taken their technology a step further by enabling the battery to charge itself in 15 minutes at temperatures as low as –45oF.

When the battery’s internal temperature reaches room temperature and above, the switch opens to allow electric current to flow in and quickly charge the battery.

“One unique feature of our cell is that it will do the heating and then switch to charging automatically,” Wang explains in a Penn State news release.

He says their battery would not affect the current charging infrastructure. “Also, the stations already out there do not have to be changed,” he adds. “Control of heating and charging is within the battery, not the chargers.”

According to the researchers, charging a lithium-ion battery quickly at temperatures under 50 degrees contributes to its degradation and lithium plating—which can make a battery unsafe. Long, slow charging at 50oF, they say, can avoid lithium plating.

And Wang says their technology can work for other batteries as well.

“The self-heating battery structure is also essential for all solid-state ceramic batteries because it thermally stimulates uniform lithium deposition at the lithium metal anode and compensates for insufficient ionic conductivity of ceramic or glass electrolytes,” he explains in an email. “Plus, solid-state batteries are inherently safe and more efficient to operate at high temperatures. Indeed, a solid state battery would be much inferior without the self-heating battery structure.”

He also says their technology is “pretty mature and readily commercialized by auto OEMs and battery manufacturers.”

That’s good news for those of us who have been hesitant to trade in our gas-powered vehicles for electric ones.

The paper, published in Proceedings of the National Academy of Sciences of the United States of America, is “Fast charging of lithium-ion batteries at all temperatures” (DOI: 10.1073/pnas.1807115115).

 

Penn State: Camouflaged nanoparticles deliver killer ‘knock-out’ protein to cancer

Extracellular vesicle-like metal-organic framework nanoparticles are developed for the intracellular delivery of biofunctional proteins. The biomimetic nanoplatform can protect the protein cargo and overcome various biological barriers to achieve systemic delivery and autonomous release. Credit: Zheng Lab/Penn State

 

A biomimetic nanosystem can deliver therapeutic proteins to selectively target cancerous tumors, according to a team of Penn State researchers.

A biomimetic nanosystem can deliver therapeutic proteins to selectively target cancerous tumors, according to a team of Penn State researchers. Using a protein toxin called gelonin from a plant found in the Himalayan mountains, the researchers caged the proteins in self-assembled metal-organic framework (MOF) nanoparticles to protect them from the body’s immune system. To enhance the longevity of the drug in the bloodstream and to selectively target the tumor, the team cloaked the MOF in a coating made from cells from the tumor itself.

Blood is a hostile environment for drug delivery. The body’s immune system attacks alien molecules or else flushes them out of the body through the spleen or liver. But cells, including cancer cells, release small particles called extracellular vesicles that communicate with other cells in the body and send a “don’t eat me” signal to the immune system.

“We designed a strategy to take advantage of the extracellular vesicles derived from tumor cells,” said Siyang Zheng, associate professor of biomedical and electrical engineering at Penn State. “We remove 99 percent of the contents of these extracellular vesicles and then use the membrane to wrap our metal-organic framework nanoparticles. If we can get our extracellular vesicles from the patient, through biopsy or surgery, then the nanoparticles will seek out the tumor through a process called homotypic targeting.”

Gong Cheng, lead author on a new paper describing the team’s work and a former post-doctoral scholar in Zheng’s group now at Harvard, said, “MOF is a class of crystalline materials assembled by metal nodes and organic linkers. In our design, self-assembly of MOF nanoparticles and encapsulation of proteins are achieved simultaneously through a one-pot approach in aqueous environment. The enriched metal affinity sites on MOF surfaces act like the buttonhook, so the extracellular vesicle membrane can be easily buckled on the MOF nanoparticles. Our biomimetic strategy makes the synthetic nanoparticles look like extracellular vesicles, but they have the desired cargo inside.”

The nanoparticle system circulates in the bloodstream until it finds the tumor and locks on to the cell membrane. The cancer cell ingests the nanoparticle in a process called endocytosis. Once inside the cell, the higher acidity of the cancer cell’s intracellular transport vesicles causes the metal-organic framework nanoparticles to break apart and release the toxic protein into cytosol and kill the cell.

“Our metal-organic framework has very high loading capacity, so we don’t need to use a lot of the particles and that keeps the general toxicity low,” Zheng said.

The researchers studied the effectiveness of the nanosystem and its toxicity in a small animal model and reported their findings in a cover article in the Journal of the American Chemical Society.

The researchers believe their nanosystem provides a tool for the targeted delivery of other proteins that require cloaking from the immune system. Penn State has applied for patent protection for the technology.

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Materials provided by Penn State. Original written by Walt Mills. Note: Content may be edited for style and length.

 

New Targeting strategy developed by Penn State may open door to better cancer drug delivery

In the transition from benign to malignant, cancer cells transition from stiff to soft. Mechanotargeting harnesses mechanics to improve targeting efficiency of nanparticle-based therapeutic agents. Credit: Zhang lab/vecteezy.com

Bioengineers may be able to use the unique mechanical properties of diseased cells, such as metastatic cancer cells, to help improve delivery of drug treatments to the targeted cells, according to a team of researchers at Penn State.

Many labs around the world are developing nanoparticle-based, drug delivery systems to selectively target tumors. They rely on a key-and-lock system in which protein keys on the surface of the nanoparticle click into the locks of a highly expressed protein on the surface of the cancer cell. The cell membrane then wraps around the nanoparticle and ingests it. If enough of the nanoparticles and their drug cargo is ingested, the cancer cell will die.

The adhesive force of the lock and key is what drives the nanoparticle into the cell, said Sulin Zhang, professor of engineering science and mechanics.

“It is almost universal that whenever there is a driving force for a process, there always is a resistive force,” Zhang said. “Here, the driving force is biochemical—the protein-protein interaction.”

The resistive force is the mechanical energy cost required for the membrane to wrap around the nanoparticle. Until now, bioengineers only considered the driving force and designed nanoparticles to optimize the chemical interactions, a targeting strategy called “chemotargeting.” Zhang believes they should also take into account the mechanics of the cells to design nanoparticles to achieve enhanced targeting, which forms a new targeting strategy called “mechanotargeting.”

“These two targeting strategies are complementary; you can combine chemotargeting and mechanotargeting to achieve the full potential of nanoparticle-based diagnostic and therapeutic agents,” Zhang said. “The fact is that targeting efficiency requires a delicate balance between driving and resistive forces. For instance, if there are too many keys on the nanoparticle surface, even though these keys only weakly interact with the nonmatching locks on normal cells, these weak, off-target interactions may still provide enough adhesion energy for the nanoparticles to penetrate the cell membrane and kill the healthy cells.”

On the other hand, if the adhesion energy is not high enough, the nanoparticle won’t get into the cell.

In “Mechanotargeting: Mechanics-dependent Cellular Uptake of Nanoparticles,” published online ahead of print in the journal Advanced Materials, Zhang and the team report the results of experiments on cancer cells grown on hydrogels of variable stiffness. On soft hydrogels the cells remained cohesive and benign and experienced a nearly constant stress that limited the uptake of the nanoparticles. But on stiff hydrogels the cells became metastatic and adopted a three-dimensional shape, offering more surface area for nanoparticles to adhere, and became less stressed. Under this condition, the cells took up five times the number of nanoparticles as the benign cells.

“The nanoparticles are fluorescent, so we count the number of nanoparticles that get into the cell by the fluorescence intensity. We found that in the malignant cells the intensity is five times higher,” Zhang said. “That proves that mechanotargeting works.”

 Explore further: Nanoparticle aggregates for destruction of cancer cells

More information: Qiong Wei et al, Mechanotargeting: Mechanics-Dependent Cellular Uptake of Nanoparticles, Advanced Materials (2018). DOI: 10.1002/adma.201707464

Journal reference: Advanced Materials  

Provided by: Pennsylvania State University

 

Drug combination delivered by nanoparticles may help in melanoma treatment

Gavin Robertson, professor of pharmacology, pathology, dermatology, and surgery; director of the Penn State Melanoma and Skin Cancer Center and member of Penn State Cancer Institute, works with associates in the Melanoma Center.

Credit: Penn State College of Medicine

Summary: The first of a new class of medication that delivers a combination of drugs by nanoparticle may keep melanoma from becoming resistant to treatment, according to Penn State College of Medicine researchers.

CelePlum-777 combines a special ratio of the drugs Celecoxib, an anti-inflammatory, and Plumbagin, a toxin. By combining the drugs, the cells have difficulty overcoming the effect of having more than one active ingredient.

Celecoxib and Plumbagin work together to kill melanoma cells when used in a specific ratio. Researchers used microscopic particles called nanoparticles to deliver the drugs directly to the cancer cells. These particles are several hundred times smaller than the width of a hair and can be loaded with medications.

“Loading multiple drugs into nanoparticles is one innovative approach to deliver multiple cancer drugs to a particular site where they need to act and have them released at that optimal cancer cell killing ratio,” said Raghavendra Gowda, assistant professor of pharmacology, who is the lead author on the study. “Another advantage is that by combining the drugs, lower concentrations of each that are more effective and less toxic can be used.”

Celecoxib and Plumbagin cannot be taken by mouth because the drugs do not enter the body well this way and cannot be used together in the ratio needed because of toxicity.

CelePlum-777 can be injected intravenously without toxicity. Because of its small size, it also accumulates inside the tumors where it then releases the drugs to kill the cancer cells. Researchers report their results in the journals Molecular Cancer Therapeutics and Cancer Letters.

“This drug is the first of a new class, loaded with multiple agents to more effectively kill melanoma cells, that has potential to reduce the possibility of resistance development,” said senior author Gavin Robertson, professor of pharmacology, pathology, dermatology, and surgery; director of the Penn State Melanoma and Skin Cancer Center and member of Penn State Cancer Institute. “There is no drug like it in the clinic today and it is likely that the next breakthrough in melanoma treatment will come from a drug like this one.”

The researchers showed the results of CelePlum-777 on killing cancer cells growing in culture dishes and in tumors growing in mice following intravenous injection. The drug prevented tumor development in mice with no detectable side effects and also prevented proteins from enabling uncontrolled cancer cell growth.

More research is required by the Food and Drug Administration before CelePlum-777 can be tested in humans through clinical trials. Penn State has patented this discovery and licensed it to Cipher Pharmaceuticals, which will perform the next series of FDA-required tests.

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New, carbon-nanotube tool for ultra-sensitive-early virus detection and identification (HIV/Aids – Ebola – Zika)

Scanning electron microscope image (scale bar, 200 nm) of the H5N2 avian influenza virus (purple) trapped inside the aligned carbon nanotube. Credit: Penn State University

A new tool that uses a forest-like array of vertically-aligned carbon nanotubes that can be finely tuned to selectively trap viruses by their size can increase the detection threshold for viruses and speed the process of identifying newly-emerging viruses. The research, by an interdisciplinary team of scientists at Penn State, is published in the October 7, 2016 edition of the journal Science Advances.

Detecting viruses early in an infection before symptoms appear, or from field samples, is difficult because the concentration of the viruses could be very low—often below the threshold of current detection methods,” said Mauricio Terrones, professor of physics, chemistry, and materials science and engineering at Penn State, and one of the corresponding authors of the research. 

“Early detection is important because a virus can begin to spread before we have the ability to detect it. 

The device we have developed allows us to selectively trap and concentrate viruses by their size—smaller than human cells and bacteria, but larger than most proteins and other macromolecules—in incredibly dilute samples. It further increases our ability to detect small amounts of a virus by more than a hundred times.”

The research team developed and tested a small, portable device that increases the sensitivity of virus detection by trapping and concentrating viruses in an array of carbon nanotubes.

 Dilute samples collected from patients or the environment are passed through a filter to remove large particles such as bacteria and human cells, then through the array of carbon nanotubes in the device. Viruses get trapped and build up to usable concentrations within the forest of nanotubes, while other smaller particles pass through and are eliminated. 

The concentrated virus captured in the device can then be put through a panel of tests to identify it, including molecular diagnosis by polymerase chain reaction (PCR), immunological methods, virus isolation, and genome sequencing.

Illustration of size-based virus enrichment by the aligned carbon nanotube array. Credit: Penn State University

“Because our device isolates and concentrates viruses purely by size, we can capture viruses that we don’t know anything about biologically—we don’t need any antibody or other molecular label,” said Terrones. “Once we capture and concentrate the virus, we can then use other techniques such as whole-genome sequencing to characterize it.”

“Most lethal viral outbreaks in the past two decades were caused by newly emerging viruses. This size-based virus-enrichment technology can be particularly powerful in identification of emerging viruses and discovery of new viruses that do not have antibodies and sequence information available,” said Si-Yang Zheng, associate professor of biomedical engineering at Penn State, the other corresponding author on the paper. 

“Not only does our new technology enrich viruses by at least one hundred times, but it also removes host and environmental contaminants, and enables direct virus identification by next-generation sequencing from field-collected samples without virus culture.”
 

Viruses—such as influenza, HIV/AIDS, Ebola, and Zika—can cause sudden, unpredictable outbreaks that lead to severe public-health crises. Currently available techniques for isolating and identifying the viruses that cause these outbreaks are slow, expensive, and use equipment and reagents that can be expensive, bulky, and require specialized storage. 

Additionally, many recent outbreaks have been caused by newly emerging viruses for which there are no established ways to selectively isolate them for identification and characterization.

 

Tunable inter-tubular distance of carbon nanotubes for matching virus dimensions — Scale bars, top 100 nm middle 10 μm bottom 200 nm. Credit: Penn State University

“We developed the technology to grow a forest of nanotubes and we can control the distance between the trunks,” said Zheng. “The intertube distance can range from about 17 nanometers to over 300 nanometers to selectively capture viruses. 

The unique properties of the carbon-nanotube forest allow us to integrate it into a robust, scalable, and portable microdevice that can be adapted for use in the field without the need for bulky instruments and specialized storage of reagents.”

The researchers validated the ability of their newly developed device to capture viruses from dilute samples using known concentrations of previously identified viruses as well as field samples of emerging and unknown viruses. “We developed a portable platform to enrich and isolate viruses based on their physical sizes,” said Yin-Ting Yeh, a postdoctoral researcher at Penn State and first author of the paper. “This tunable size-based approach provides rapid virus enrichment directly from field samples without the use of antibodies. 

The device enables early detection of emerging diseases and potentially allows for vaccine development much sooner in the process of an outbreak.”

 Explore further: Sensing viruses by exploring their electrical properties

More information: “Tunable and label-free virus enrichment for ultrasensitive virus detection using carbon nanotube arrays,” Science Advances, advances.sciencemag.org/content/2/10/e1601026 

Journal reference: Science Advances  

Provided by: Pennsylvania State University  

Genesis Nanotechnology – “Great Things from Small Things”

Penn State: New clues could help scientists harness the power of photosynthesis

This illustration is a model of Chl f synthase, potentially a ChlF dimer, based on the known X-ray structure of the core of the Photosystem II reaction center. Photosystem II is the light-driven enzyme that oxidizes water to produce oxygen …more

Identification of a gene needed to expand light harvesting in photosynthesis into the far-red-light spectrum provides clues to the development of oxygen-producing photosynthesis, an evolutionary advance that changed the history of life on Earth. “Knowledge of how photosynthesis evolved could empower scientists to design better ways to use light energy for the benefit of mankind,” said Donald A. Bryant, the Ernest C. Pollard Professor of Biotechnology and professor of biochemistry and molecular biology at Penn State University and the leader of the research team that made the discovery.

This discovery, which could enable scientists to engineer crop plants that more efficiently harness the energy of the Sun, will be published online by the journal Science on Thursday July 7, 2016.

“Photosynthesis usually ranks about third after the origin of life and the invention of DNA in lists of the greatest inventions of evolution,” said Bryant. “Photosynthesis was such a powerful invention that it changed the Earth’s atmosphere by producing oxygen, allowing diverse and complex life forms—algae, plants, and animals—to evolve.”

The researchers identified the gene that converts chlorophyll a—the most abundant light-absorbing pigment used by plants and other organisms that harness energy through photosynthesis—into chlorophyll f—a type of chlorophyll that absorbs light in the far-red range of the light spectrum. There are several different types of chlorophyll, each tuned to absorb light in different wavelengths. Most organisms that get their energy from photosynthesis use light in the visible range, wavelengths of about 400 to 700 nanometers. Bryant’s lab previously had shown that chlorophyll f allows certain cyanobacteria—bacteria that use photosynthesis and that are sometimes called blue-green algae—to grow efficiently in light just outside of the usual human visual range—far-red light (700 to 800 nanometers). The ability to use light wavelengths other than those absorbed by plants, algae, and other cyanobacteria confers a powerful advantage to those organisms that produce chlorophyll f—they can survive and grow when the visible light they normally use is blocked.

This illustration shows the newly discovered evolutionary scheme for the type-1 and type-2 reaction centers of photosynthesis. Reaction centers are protein machines that convert light energy into stable reductants that can be used by cells …more

 

“There is nearly as much energy in the far-red and near-infrared light that reaches the Earth from the Sun as there is in visible light,” said Bryant. “Therefore, the ability to extend light harvesting in plants into this range would allow the plants to more efficiently use the energy from the Sun and could increase plant productivity.”

The gene the researchers identified encodes an enzyme that is distantly related to one of the main components of the protein machinery used in oxygen-producing photosynthesis. The researchers showed that the conversion of chlorophyll a to chlorophyll f requires only this one enzyme in a simple system that could represent an early intermediate stage in the evolution of photosynthesis. Understanding the mechanism by which the enzyme functions could provide clues that enable scientists to design better ways to use light energy.

“There is intense interest in creating artificial photosynthesis as an alternative energy source,” said Bryant. “Understanding the evolutionary trajectory that nature used to create oxygen production in photosynthesis is one component that will help scientists design an efficient and effective system. The difficulty is that photosynthesis is an incredibly complex process with hundreds of components and, until now, there were few known intermediate stages in its evolution. The simple system that we describe in this paper provides a model that can be further manipulated experimentally for studying those early stages in the evolution of photosynthesis.”

By disabling the gene that encodes the enzyme in two cyanobacteria that normally produce chlorophyll f, the researchers demonstrated that the enzyme is required for the production of chlorophyll f. The experiment showed that, without this enzyme, these cyanobacteria could no longer synthesize chlorophyll f. By artificially adding the gene that encodes the enzyme, the researchers also showed that this one enzyme is all that is necessary to convert cyanobacteria that normally do not produce chlorophyll f into ones that can produce it.

Another clue that the newly identified enzyme could represent an early stage in the evolution of photosynthesis is that the enzyme requires light to catalyze its reaction and may not require oxygen, as scientists had previously suspected. “Because the enzyme that synthesizes chlorophyll f requires light but may not require oxygen for its activity, it is possible that it evolved before Photosystem II, the photosynthetic complex that produces oxygen and to which the enzyme is related. If the enzyme is an evolutionary predecessor of Photosystem II, then evolution borrowed an enzyme that was originally used for chlorophyll synthesis and used it to evolve an enzyme that could produce oxygen, which ultimately led to changes in Earth’s atmosphere,” said Bryant.

Explore further: Hot-spring bacteria reveal ability to use far-red light for photosynthesis

More information: “Light-dependent chlorophyll f synthase is a highly divergent paralog of PsbA of photosystem II,” Science, science.sciencemag.org/cgi/doi/10.1126/science.aaf9178

Journal reference: Science

Provided by: Pennsylvania State University

 

Penn State: Biomimetic Membranes that Self-Assemble for Water Filtration

A synthetic membrane that self assembles and is easily produced may lead to better gas separation, water purification, drug delivery and DNA recognition, according to an international team of researchers. This biomimetic membrane is composed of lipids — fat molecules — and protein-appended molecules that form water channels that transfer water at the rate of natural membranes, and self-assembles into 2-dimensional structures with parallel channels.

“Nature does things very efficiently and transport proteins are amazing machines present in biological membranes,” said Manish Kumar, assistant professor of chemical engineering, Penn State. “They have functions that are hard to replicate in synthetic systems.”

The researchers developed a second-generation synthetic water channel that improves on earlier attempts to mimic aquaporins – natural water channel proteins — by being more stable and easier to manufacture. The peptide-appended pillar[5]arenes (PAP) are also more easily produced and aligned than carbon nanotubes, another material under investigation for membrane separation. Kumar and co-authors report their development in a recent issue of the Proceedings of the National Academy of Science (“Highly permeable artificial water channels that can self-assemble into two-dimensional arrays”). An artificial analogue of the water channel protein, aquaporin, was shown to have permeabilities approaching that of aquaporins and carbon nanotubes. They also arrange in tight two dimensional arrays. (Image: Karl Decker / University of Illinois at Urbana-Champaign, and Yuexiao Shen / Penn State)

“We were surprised to see transport rates approaching the ‘holy grail’ number of a billion water molecules per channel per second,” said Kumar. “We also found that these artificial channels like to associate with each other in a membrane to make 2-dimentional arrays with a very high pore density.”

The researchers consider that the PAP membranes are an order of magnitude better than the first-generation artificial water channels reported to date. The propensity for these channels to automatically form densely packed arrays leads to a variety of engineering applications.

“The most obvious use of these channels is perhaps to make highly efficient water purification membranes,” said Kumar.

Source: Penn State

Scientists use ‘smallest possible diamonds’ to form ultra-thin nanothreads: Video: Will A Space Elevator Be Possible?

For the first time, scientists have discovered how to produce ultra-thin “diamond nanothreads” that promise extraordinary properties, including strength and stiffness greater than that of today’s strongest nanotubes and polymers. A paper describing this discovery by a research team led by John V. Badding, a professor of chemistry at Penn State, was published in the Sept. 21 issue of the journal Nature Materials.

“From a fundamental-science point of view, our discovery is intriguing because the threads we formed have a structure that has never been seen before,” Badding said. The core of the nanothreads that Badding’s team made is a long, thin strand of carbon atoms arranged just like the fundamental unit of a diamond’s structure—zig-zag “cyclohexane” rings of six carbon atoms bound together, in which each carbon is surrounded by others in the strong triangular-pyramid shape of a tetrahedron. “It is as if an incredible jeweler has strung together the smallest possible diamonds into a long miniature necklace,” Badding said. “Because this thread is diamond at heart, we expect that it will prove to be extraordinarily stiff, extraordinarily strong, and extraordinarily useful.”

The team’s discovery comes after nearly a century of failed attempts by other labs to compress separate carbon-containing molecules like liquid benzene into an ordered, diamond-like nanomaterial. “We used the large high-pressure Paris-Edinburgh device at Oak Ridge National Laboratory to compress a 6-millimeter-wide amount of benzene—a gigantic amount compared with previous experiments,” said Malcolm Guthrie of the Carnegie Institution for Science, a co-author of the research paper. “We discovered that slowly releasing the pressure after sufficient compression at normal room temperature gave the carbon atoms the time they needed to react with each other and to link up in a highly ordered chain of single-file carbon tetrahedrons, forming these diamond-core nanothreads.”

John Badding, professor of chemistry at Penn State, leads a research team that has discovered how to produce super-strong, super-thin “diamond nanothreads” that promise extraordinary properties such as strength and stiffness higher than that of carbon nanotubes or conventional high-strength polymers.

Badding’s team is the first to coax molecules containing carbon atoms to form the strong tetrahedron shape, then link each tetrahedron end to end to form a long, thin nanothread. He describes the thread’s width as phenomenally small, only a few atoms across, hundreds of thousands of times smaller than an optical fiber, enormously thinner that an average human hair. “Theory by our co-author Vin Crespi suggests that this is potentially the strongest, stiffest material possible, while also being light in weight,” he said.

The molecule they compressed is benzene—a flat ring containing six carbon atoms and six hydrogen atoms. The resulting diamond-core nanothread is surrounded by a halo of hydrogen atoms. During the compression process, the scientists report, the flat benzene molecules stack together, bend and break apart. Then, as the researchers slowly release the pressure, the atoms reconnect in an entirely different yet very orderly way. The result is a structure that has carbon in the tetrahedral configuration of diamond with hydrogens hanging out to the side and each tetrahedron bonded with another to form a long, thin, nanothread.

“It really is surprising that this kind of organization happens,” Badding said. “That the atoms of the benzene molecules link themselves together at room temperature to make a thread is shocking to chemists and physicists. Considering earlier experiments, we think that, when the benzene molecule breaks under very high pressure, its atoms want to grab onto something else but they can’t move around because the pressure removes all the space between them. This benzene then becomes highly reactive so that, when we release the pressure very slowly, an orderly polymerization reaction happens that forms the diamond-core nanothread.”

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The scientists confirmed the structure of their diamond nanothreads with a number of techniques at Penn State, Oak Ridge, Arizona State University and the Carnegie Institution for Science, including X-ray diffraction, neutron diffraction, Raman spectroscopy, first-principle calculations, transmission electron microscopy and solid-state nuclear magnetic resonance (NMR). Parts of these first diamond nanothreads appear to be somewhat less than perfect, so improving their structure is a continuing goal of Badding’s research program. He also wants to discover how to make more of them. “The high pressures that we used to make the first diamond nanothread material limit our production capacity to only a couple of cubic millimeters at a time, so we are not yet making enough of it to be useful on an industrial scale,” Badding said. “One of our science goals is to remove that limitation by figuring out the chemistry necessary to make these diamond nanothreads under more practical conditions.”

The nanothread also may be the first member of a new class of diamond-like nanomaterials based on a strong tetrahedral core. “Our discovery that we can use the natural alignment of the benzene molecules to guide the formation of this new diamond nanothread material is really interesting because it opens the possibility of making many other kinds of molecules based on carbon and hydrogen,” Badding said. “You can attach all kinds of other atoms around a core of carbon and hydrogen. The dream is to be able to add other atoms that would be incorporated into the resulting nanothread. By pressurizing whatever liquid we design, we may be able to make an enormous number of different materials.”

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                                          Credit: Enshi Xu, Vincent H Crespi lab, Penn State

Potential applications that most interest Badding are those that would be vastly improved by having exceedingly strong, stiff and light materials—especially those that could help to protect the atmosphere, including lighter, more fuel-efficient and therefore less-polluting vehicles. “One of our wildest dreams for the nanomaterials we are developing is that they could be used to make the super-strong, lightweight cables that would make possible the construction of a “space elevator”, which so far has existed only as a science-fiction idea,” Badding said.

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