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Graphene: A Talented 2D Material Gets a New Gig

Posted By Graphene Council, Monday, March 9, 2020
Ever since graphene’s discovery in 2004, scientists have looked for ways to put this talented, atomically thin 2D material to work. Thinner than a single strand of DNA yet 200 times stronger than steel, graphene is an excellent conductor of electricity and heat, and it can conform to any number of shapes, from an ultrathin 2D sheet, to an electronic circuit.

Last year, a team of researchers led by Feng Wang, a faculty scientist in Berkeley Lab’s Materials Sciences Division and a professor of physics at UC Berkeley, developed a multitasking graphene device that switches from a superconductor that efficiently conducts electricity, to an insulator that resists the flow of electric current, and back again to a superconductor.

Now, as reported in Nature today, the researchers have tapped into their graphene system’s talent for juggling not just two properties, but three: superconducting, insulating, and a type of magnetism called ferromagnetism. The multitasking device could make possible new physics experiments, such as research in the pursuit of an electric circuit for faster, next-generation electronics like quantum computing technologies.

“So far, materials simultaneously showing superconducting, insulating, and magnetic properties have been very rare. And most people believed that it would be difficult to induce magnetism in graphene, because it’s typically not magnetic. Our graphene system is the first to combine all three properties in a single sample,” said Guorui Chen, a postdoctoral researcher in Wang’s Ultrafast Nano-Optics Group at UC Berkeley, and the study’s lead author.

Using electricity to turn on graphene’s hidden potential

Graphene has a lot of potential in the world of electronics. Its atomically thin structure, combined with its robust electronic and thermal conductivity, “could offer a unique advantage in the development of next-generation electronics and memory storage devices,” said Chen, who also worked as a postdoctoral researcher in Berkeley Lab’s Materials Sciences Division at the time of the study.

The problem is that the magnetic materials used in electronics today are made of ferromagnetic metals, such as iron or cobalt alloys. Ferromagnetic materials, like the common bar magnet, have a north and a south pole. When ferromagnetic materials are used to store data on a computer’s hard disk, these poles point either up or down, representing zeros and ones – called bits.

Graphene, however, is not made of a magnetic metal – it’s made of carbon.

So the scientists came up with a creative workaround.

They engineered an ultrathin device, just 1 nanometer in thickness, featuring three layers of atomically thin graphene. When sandwiched between 2D layers of boron nitride, the graphene layers – described as trilayer graphene in the study – form a repeating pattern called a moiré superlattice.

By applying electrical voltages through the graphene device’s gates, the force from the electricity prodded electrons in the device to circle in the same direction, like tiny cars racing around a track. This generated a forceful momentum that transformed the graphene device into a ferromagnetic system.

More measurements revealed an astonishing new set of properties: The graphene system’s interior had not only become magnetic but also insulating; and despite the magnetism, its outer edges morphed into channels of electronic current that move without resistance. Such properties characterize a rare class of insulators known as Chern insulators, the researchers said.

Even more surprising, calculations by co-author Ya-Hui Zhang of the Massachusetts Institute of Technology revealed that the graphene device has not just one, but two conductive edges, making it the first observed “high-order Chern insulator,” a consequence of the strong electron-electron interactions in the trilayer graphene.

Scientists have been in hot pursuit of Chern insulators in a field of research known as topology, which investigates exotic states of matter. Chern insulators offer potential new ways to manipulate information in a quantum computer, where data is stored in quantum bits, or qubits. A qubit can represent a one, a zero, or a state in which it is both a one and a zero at the same time.

“Our discovery demonstrates that graphene is an ideal platform for studying different physics, ranging from single-particle physics, to superconductivity, and now topological physics to study quantum phases of matter in 2D materials,” Chen said. “It’s exciting that we can now explore new physics in a tiny device just 1 millionth of a millimeter thick.”

The researchers hope to conduct more experiments with their graphene device to have a better understanding of how the Chern insulator/magnet emerged, and the mechanics behind its unusual properties.

Researchers from Berkeley Lab; UC Berkeley; Stanford University; SLAC National Accelerator Laboratory; Massachusetts Institute of Technology; China’s Shanghai Jiao Tong University, Collaborative Innovation Center of Advanced Microstructures, and Fudan University; and Japan’s National Institute for Materials Science participated in the work.

This work was supported by the Center for Novel Pathways to Quantum Coherence in Materials, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science.

Tags:  2D materials  Berkeley Lab’s Materials Sciences Division  DNA  Feng Wang  Graphene 

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Cardea Bio Announces New Partnership with Nanosens Innovations

Posted By Graphene Council, Friday, April 5, 2019
Updated: Thursday, April 4, 2019
Cardea Bio, leading manufacturer of commercial-quality graphene digital biosensors, together with Nanosens Innovations, introduces the new CRISPR-Chip which has the potential to detect genetic mutations within minutes. The relationship with Nanosens falls under Cardea's Innovation Partnership Program, which enables Nanosens to build breakthrough science on top of Cardea's IP-protected graphene biosensors.

The co-developed CRISPR-Chip is the first unamplified label-free nucleic acid testing device. Details about its development can be found in the recently published Nature Biomedical Engineering paper, "Detection of Unamplified Target Genes via CRISPR/Cas9 Immobilized on a Graphene Field-Effect Transistor," from the Keck Graduate Institute at Claremont College.

CRISPR-Chip inventor and corresponding author Dr. Kiana Aran explains, "I first considered using CRISPR-Cas9 on a digital biosensor as a DNA search engine while I was at UC Berkeley. At Keck, I attempted to design and develop the biosensors myself, but it was difficult to construct them with the consistency and quality needed for this research. When I understood that a partnership with Cardea was possible, where the company's patented, commercial-grade, high-volume graphene biosensors could be used in place of building my own, it cut months to years out of my research."

CRISPR-Chip is a hand-held device that combines thousands of CRISPR molecules with Cardea's graphene transistor. The device scans though applied DNA to find specific genes or mutations. The transistor is extremely sensitive to electrically charged materials, like DNA. If the specified DNA is found, it binds to the surface, creating an additional charge which is sensed by the device.

"In its current format, CRISPR-Chip can be used to help researchers design better CRISPR complexes for gene editing," continues Dr. Aran. "With CRISPR-Chip, the complexes can be tested faster than ever before."

Tags:  Biosensor  Cardea Bio  DNA  Graphene  Keck Graduate Institute at Claremont College  Kiana Aran  Nanosens Innovations 

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Directed evolution builds nanoparticles

Posted By Graphene Council, Thursday, March 7, 2019
Updated: Friday, March 1, 2019

The 2018 Nobel Prize in Chemistry went to three scientists who developed the method that forever changed protein engineering: directed evolution. Mimicking natural evolution, directed evolution guides the synthesis of proteins with improved or new functions.

First, the original protein is mutated to create a collection of mutant protein variants. The protein variants that show improved or more desirable functions are selected. These selected proteins are then once more mutated to create another collection of protein variants for another round of selection. This cycle is repeated until a final, mutated protein is evolved with optimized performance compared to the original protein.

Now, scientists from the lab of Ardemis Boghossian at EPFL, have been able to use directed evolution to build not proteins, but synthetic nanoparticles (Chemical Communications, "Directed evolution of the optoelectronic properties of synthetic nanomaterials").

These nanoparticles are used as optical biosensors – tiny devices that use light to detect biological molecules in air, water, or blood. Optical biosensors are widely used in biological research, drug development, and medical diagnostics, such as real-time monitoring of insulin and glucose in diabetics.

“The beauty of directed evolution is that we can engineer a protein without even knowing how its structure is related to its function,” says Boghossian. “And we don't even have this information for the vast, vast majority of proteins.”

Her group used directed evolution to modify the optoelectronic properties of DNA-wrapped single-walled carbon nanotubes (or, DNA-SWCNTs, as they are abbreviated), which are nano-sized tubes of carbon atoms that resemble rolled up sheets of graphene covered by DNA. When they detect their target, the DNA-SWCNTs emit an optical signal that can penetrate through complex biological fluids, like blood or urine.

Using a directed evolution approach, Boghossian’s team was able to engineer new DNA-SWCNTs with optical signals that are increased by up to 56% – and they did it over only two evolution cycles.

“The majority of researchers in this field just screen large libraries of different materials in hopes of finding one with the properties they are looking for,” says Boghossian. “In optical nanosensors, we try to improve properties like selectivity, brightness, and sensitivity. By applying directed evolution, we provide researchers with a guided approach to engineering these nanosensors.”

The study shows that what is essentially a bioengineering technique can be used to more rationally tune the optoelectronic properties of certain nanomaterials.

Boghossian explains: “Fields like materials science and physics are mostly preoccupied with defining material structure-function relationships, making materials that lack this information difficult to engineer. But this is a problem that nature solved billions of years ago – and, in recent decades, biologists have tackled it as well. I think our study shows that as materials scientists and physicists, we can still learn a few pragmatic lessons from biologists.”

Tags:  Ardemis Boghossian  biosensors  DNA  EPFL  Graphene  nanomaterials  optoelectronics 

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Graphene Enables Sensitive HIV Sensor

Posted By Terrance Barkan, Tuesday, June 19, 2018

If you manage to get one of the big corporate research institutes to tell you what they’ve looking at  when it comes to graphene, the response is usually: sensors.

 

Now researchers at the University of Pennsylvania have leveraged both graphene and DNA to produce a new sensor that increase the sensitivity of diagnostic devices used to monitor HIV

 

Just as in other uses of graphene for sensors, in this application graphene’s property of being only one-thick and highly conductive makes it extremely sensitive to detecting biological signals. The way the actual device exploits that property is that when DNA or RNA molecules bind to the graphene surface, they dramatically change the materials conductivity. 

 

This is not the first time that this basic design has been used as a biological sensor. However, in this case instead of using a single-stranded DNA that can only bind to the target DNA molecule, they developed what they have dubbed a “DNA hairpin” in which its curled structure opens up when the target molecule binds to it.

 

When it opens, another DNA molecule that has been added to the system kicks the target molecule out, making it possible to bind with many different sites on the graphene.


Tags:  DNA  HIV  Penn State  Sensors 

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