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Understanding electron transport in graphene nanoribbons

Posted By Graphene Council, Tuesday, September 15, 2020
Graphene is a modern wonder material possessing unique properties of strength, flexibility and conductivity whilst being abundant and remarkably cheap to produce, lending it to a multitude of useful applications -- especially true when these 2D atom-thick sheets of carbon are split into narrow strips known as Graphene Nanoribbons (GNRs).

New research published in EPJ Plus, authored by Kristians Cernevics, Michele Pizzochero, and Oleg V. Yazyev, Ecole Polytechnique Federale de Lausanne (EPFL), Lausanne, Switzerland, aims to better understand the electron transport properties of GNRs and how they are affected by bonding with aromatics. This is a key step in designing technology such chemosensors.

"Graphene nanoribbons -- strips of graphene just few nanometres wide -- are a new and exciting class of nanostructures that have emerged as potential building blocks for a wide variety of technological applications," Cernevics says.

The team performed their investigation with the two forms of GNR, armchair and zigzag, which are categorised by the shape of the edges of the material. These properties are predominantly created by the process used to synthesise them. In addition to this, the EPFL team experimented p-polyphenyl and polyacene groups of increasing length.

"We have employed advanced computer simulations to find out how electrical conductivity of graphene nanoribbons is affected by chemical functionalisation with guest organic molecules that consist of chains composed of an increasing number of aromatic rings," says Cernevics.

The team discovered that the conductance at energies matching the energy levels of the corresponding isolated molecule was reduced by one quantum, or left unaffected based on whether the number of aromatic rings possessed by the bound molecule was odd or even. The study shows this 'even-odd effect' originates from a subtle interplay between the electronic states of the guest molecule spatially localised on the binding sites and those of the host nanoribbon.

"Our findings demonstrate that the interaction of the guest organic molecules with the host graphene nanoribbon can be exploited to detect the 'fingerprint' of the guest aromatic molecule, and additionally offer a firm theoretical ground to understand this effect," Cernevics concludes: "Overall, our work promotes the validity of graphene nanoribbons as promising candidates for next-generation chemosensing devices."

These potentially wearable or implantable sensors will rely heavily on GRBs due to their electrical properties and could spearhead a personalised health revolution by tracking specific biomarkers in patients.

Tags:  Biosensor  EPFL  Graphene  Graphene Nanoribbons  Healthcare  Kristians Cernevics  Michele Pizzochero  Oleg V. Yazyev  Sensors 

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A tiny instrument to measure the faintest magnetic fields

Posted By Graphene Council, Wednesday, September 9, 2020

Physicists at the University of Basel have developed a minuscule instrument able to detect extremely faint magnetic fields. At the heart of the superconducting quantum interference device are two atomically thin layers of graphene, which the researchers combined with boron nitride. Instruments like this one have applications in areas such as medicine, besides being used to research new materials.

To measure very small magnetic fields, researchers often use superconducting quantum interference devices, or SQUIDs. In medicine, their uses include monitoring brain or heart activity, for example, while in the earth sciences researchers use SQUIDs to characterize the composition of rocks or detect groundwater flows. The devices also have a broad range of uses in other applied fields and basic research.

The team led by Professor Christian Schönenberger of the University of Basel's Department of Physics and the Swiss Nanoscience Institute has now succeeded in creating one of the smallest SQUIDs ever built. The researchers described their achievement in the scientific journal Nano Letters.

A superconducting ring with weak links

A typical SQUID consists of a superconducting ring interrupted at two points by an extremely thin film with normal conducting or insulating properties. These points, known as weak links, must be so thin that the electron pairs responsible for superconductivity are able to tunnel through them. Researchers recently also began using nanomaterials such as nanotubes, nanowires or graphene to fashion the weak links connecting the two superconductors.

As a result of their configuration, SQUIDs have a critical current threshold above which the resistance-free superconductor becomes a conductor with ordinary resistance. This critical threshold is determined by the magnetic flux passing through the ring. By measuring this critical current precisely, the researchers can draw conclusions about the strength of the magnetic field.

SQUIDs with six layers

"Our novel SQUID consists of a complex, six-layer stack of individual two-dimensional materials," explains lead author David Indolese. Inside it are two graphene monolayers separated by a very thin layer of insulating boron nitride. "If two superconducting contacts are connected to this sandwich, it behaves like a SQUID - meaning it can be used to detect extremely weak magnetic fields."

In this setup, the graphene layers are the weak links, although in contrast to a regular SQUID they are not positioned next to each other, but one on top of the other, aligned horizontally. "As a result, our SQUID has a very small surface area, limited only by the constraints of nanofabrication technology," explains Dr. Paritosh Karnatak from Schönenberger's team.

The tiny device for measuring magnetic fields is only around 10 nanometers high - roughly a thousandth of the thickness of a human hair. The instrument can trigger supercurrents that flow in minuscule spaces. Moreover, its sensitivity can be adjusted by changing the distance between the graphene layers. With the help of electrical fields, the researchers are also able to increase the signal strength, further enhancing the measurement accuracy.

Analyzing topological insulators

The Basel research team's primary goal in developing the novel SQUIDs was to analyze the edge currents of topological insulators. Topological insulators are currently a focus of countless research groups all over the world. On the inside, they behave like insulators, while on the outside - or along the edges - they conduct current almost losslessly, making them possible candidates for a broad range of applications in the field of electronics.

"With the new SQUID, we can determine whether these lossless supercurrents are due to a material's topological properties, and thereby tell them apart from non-topological materials. This is very important for the study of topological insulators," remarked Schönenberger of the project. In future, SQUIDs could also be used as low-noise amplifiers for high-frequency electrical signals, or for instance to detect local brainwaves (magnetoencephalography), as their compact design means a large number of the devices can be connected in series.

Tags:  Christian Schönenberger  David Indolese  Graphene  Healthcare  nanomaterials  Paritosh Karnatak  University of Basel 

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Fixing 'food miles': how graphene-enhanced farming can cut costs and emissions

Posted By Graphene Council, Wednesday, September 2, 2020
A start-up company based at The University of Manchester has begun trials of a graphene-enhanced growth material that could revolutionise food production in the UK and overseas, reducing transportation and contributing to sustainability in farming worldwide.

AEH Innovative Hydrogel Ltd secured £1m of Government funding through Innovate UK in July and begins work on the project in the University’s Graphene Engineering Innovation Centre on 1 September 2020. The two-year project will develop a unique, virtually maintenance-free ‘vertical farming’ system (‘GelPonic’).

GelPonic relies on a growth substrate for indoor fruit-and-veg that improves performance in numerous ways. The hydrogel growth medium conserves water and filters out pathogens to protect plants from disease, while a graphene sensor allows remote monitoring, reducing labour costs. Moreover, the production of the growth medium outputs significantly less CO2 compared to traditional solutions and can also be used in areas with drought conditions and infertile soil.

Help for farming through technology

AEH - led by Dr Beenish Siddique (pictured) - has been supported by the European Research Development Fund (ERDF) Bridging the Gap programme and was a 2019 prize-winner in the prestigious Eli Harari competition, run by the University. The extra funding announced by the Government on 17 July is part of a broader £24 million spend to assist UK farming through pioneering technology.

Beenish said: “One of the biggest hurdles in controlled environment agriculture is operational cost, which makes it a low-profit-margin business. The fact this system is almost maintenance-free could make a big difference to whether farms can be successful or not.”

“We believe there is an opportunity here to change the future of farming not just here in the UK but around the world," she added. "Globally, around 70% of the fresh water available to humans is used for agriculture and 60% of that is wasted; agriculture also contributes around 20% of global greenhouse-gas emissions. Our system helps control that waste and those emissions, shortens germination times and could enable an increase of 25% in crop yields.”

Post-COVID sustainability

One of Beenish’s colleagues at the GEIC is Commercialisation Director Ray Gibbs, whose role is to help to bring innovative ideas to fruition through launching start-up and early-stage companies such as AEH. He believes the current pandemic, in tandem with net-zero targets, has sharpened the Government’s focus on investment in innovation.

Ray said: “The COVID-19 pandemic has demonstrated the fragility of the UK supply chains, none more so than food supply. Indoor farming allows us to grow food in the UK that would normally come from another part of the world. That contributes to self-sustainability, reduces food miles and means we’re not so reliant on international markets for our food.”

AEH is developing its system alongside project partners and subcontractors including Crop Health & Protection (CHAP), Labman Automation, Grobotic Systems and Stockbridge Technology Centre (STC).

CHAP’s Innovation Network Lead Dr Harry Langford said: “There is a significant market demand for more sustainable hydroponic substrates. This project is an exciting opportunity to optimise and scale-up a novel hydrogel product and demonstrate this product directly to the end-user, within a highly innovative automated production system”.

Tags:  AEH Innovative Hydrogel Ltd  Beenish Siddique  Covid-19  European Research Development Fund  Graphene  Harry Langford  Healthcare  Innovate UK  Ray Gibbs  University of Manchester 

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Graphene additives show a new way to control the structure of organic crystals

Posted By Graphene Council, Wednesday, September 2, 2020
A team of researchers at The University of Manchester has demonstrated that the surface properties of graphene can be used to control the structure of organic crystals obtained from solution.

Organic crystal structures can be found in a large number of products, such as food, explosives, colour pigments and pharmaceuticals. However, organic crystals can come in different structures, called polymorphs: each of these forms has very different physical and chemical properties, despite having the same chemical composition.

To make a comparison, diamond and graphite are polymorphs because they are composed both by carbon atoms, but they have very different properties because the atoms are bonded to form different structures. The same concept can be extended to organic molecules, when interacting between each other to form crystals.

Understanding and reacting to how materials work on a molecular level is key because the wrong polymorph can cause a food to have a bad taste, or a drug to be less effective. There are several examples of drugs removed from the market because of polymorphism-related problems. As such, production of a specific polymorph is currently a fundamental problem for both research and industry and it does involve substantial scientific and economic challenges.

New research from The University of Manchester has now demonstrated that adding graphene to an evaporating solution containing organic molecules can substantially improve the selectivity towards a certain crystalline form. This opens up new applications of graphene in the field of crystal engineering, which have been completely unexplored so far.

Professor Cinzia Casiraghi, who led the team, said: “Ultimately, we have shown that advanced materials, such as graphene and the tools of nanotechnology enable us to study crystallisation of organic molecules from a solution in a radically new way. We are now excited to move towards molecules that are commonly used for pharmaceuticals and food to further investigate the potential of graphene in the field of crystal engineering."

In the report, published in ACS Nano, the team has shown that by tuning the surface properties of graphene, it is possible to change the type of polymorphs produced. Glycine, the simplest amino acid, has been used as reference molecule, while different types of graphene have been used either as additive or as templates.

Matthew Boyes, and Adriana Alieva, PhD students at The University of Manchester, both contributed to this work: “This is a pioneering work on the use of graphene as an additive in crystallisation experiments. We have used different types of graphene with varying oxygen content and looked at their effects on the crystal outcome of glycine. We have observed that by carefully tuning the oxygen content of graphene, it is possible to induce preferential crystallisation.” said Adriana.

Computer modelling, performed by Professor Melle Franco at the University of Aveiro, Portugal, supports the experimental results and attributes the polymorph selectivity to the presence of hydroxyl groups allowing for hydrogen bonding interactions with the glycine molecules, thereby favouring one polymorph over the other, once additional layers of the polymorph are added during crystal growth.

This work has been financially supported by the European Commission in the framework of the European Research Council (ERC Consolidator), which supports the most innovative research ideas in Europe, by placing emphasis on the quality of the idea rather than the research area, and it is a joint collaboration between the Department of Chemistry and the Department of Chemical Engineering, with Dr Thomas Vetter.

Tags:  ACS Nano  Adriana Alieva  Cinzia Casiraghi  European Research Council  Graphene  graphite  Healthcare  Matthew Boyes  Melle Franco  Thomas Vetter  University of Aveiro  University of Manchester 

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An improved wearable, stretchable gas sensor using nanocomposites

Posted By Graphene Council, Friday, August 28, 2020
A stretchable, wearable gas sensor for environmental sensing has been developed and tested by researchers at Penn State, Northeastern University and five universities in China.

The sensor combines a newly developed laser-induced graphene foam material with a unique form of molybdenum disulfide and reduced-graphene oxide nanocomposites. The researchers were interested in seeing how different morphologies, or shapes, of the gas-sensitive nanocomposites affect the sensitivity of the material to detecting nitrogen dioxide molecules at very low concentration. To change the morphology, they packed a container with very finely ground salt crystals.

Nitrogen dioxide is a noxious gas emitted by vehicles that can irritate the lungs at low concentrations and lead to disease and death at high concentrations.

When the researchers added molybdenum disulfide and reduced graphene oxide precursors to the canister, the nanocomposites formed structures in the small spaces between the salt crystals. They tried this with a variety of different salt sizes and tested the sensitivity on conventional interdigitated electrodes, as well as the newly developed laser-induced graphene platform. When the salt was removed by dissolving in water, the researchers determined that the smallest salt crystals enabled the most sensitive sensor.

“We have done the testing to 1 part per million and lower concentrations, which could be 10 times better than conventional design,” says Huanyu Larry Cheng, assistant professor of engineering science and mechanics and materials science and engineering. “This is a rather modest complexity compared to the best conventional technology which requires high-resolution lithography in a cleanroom.”

Ning Yi and Han Li, doctoral students at Penn State and co-authors on the paper in Materials Today Physics, added, “The paper investigated the sensing performance of the reduced graphene oxide/moly disulfide composite. More importantly, we find a way to enhance the sensitivity and signal-to-noise ratio of the gas sensor by controlling the morphology of the composite material and the configuration of the sensor-testing platform. We think the stretchable nitrogen dioxide gas sensor may find applications in real-time environmental monitoring or the healthcare industry.”

Other Penn State authors on the paper, titled “Stretchable, Ultrasensitive, and Low-Temperature NO2 Sensors Based on MoS2@rGO Nanocomposites,” are Li Yang, Jia Zhu, Xiaoqi Zheng and Zhendong Liu.

Tags:  composite  Graphene  graphene oxide  Healthcare  Huanyu Larry Cheng  nanocomposites  Northeastern University  Penn State  Sensors 

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Epitaxial Graphene-Based Biosensor Provides Rapid Detection of COVID-19

Posted By Graphene Council, Thursday, August 27, 2020
Assistant Professor Kevin Daniels (ECE/IREAP) and his colleagues, have developed an epitaxial graphene based biosensor that provides rapid detection of COVID-19. 

The biosensor, created by Daniels, Dr. Soaram Kim of the Institute for Research in Electronics and Applied Physics (IREAP), Dr. Heeju Ryu of the Fred Hutchinson Cancer Research Center, Dr. Seo Hyun Kim of the University of Georgia, and Dr. Rachael Myers-Ward of the U.S. Naval Research Laboratory, tested COVID spike protein ranging from one attogram to one microgram, and can detect COVID spike protein in a few seconds, reuse sensors by simply rinsing in sodium chloride (NaCl), and attain results without sending it off to a lab, unlike the current real-time reverse transcription-polymerase chain reaction (RT-PCR) test. Although It is the fastest, most reliable and universally used method for diagnosis, RT-PCR requires a ribonucleic acid (RNA) preparation step, causing a decrease in accuracy as well as sensitivity. In addition, it takes over three hours to complete the current diagnosis for COVID-19. 

The researchers use epitaxial graphene, a single to a few layers of carbon atoms with incredibly high surface area, high electronic conductivity and carrier mobility resulting in ultimate sensitivity for biological sensors. SARS-CoV-2 spike protein antibody & antigen allows high selectivity and an experimental environment that is not dangerous. Therefore the antibody/graphene heterostructure can synergistically improve sensitivity and provide ultra-fast detection.

“These graphene-based sensors are not only much faster than PCR and Rapid test for detecting COVID, but are orders of magnitude more sensitive with the possibility of detecting the virus sooner post-exposure," says Daniels. "The ability to rapidly detect the virus in individuals, even those who were exposed too recently to be detected by other means, is the goal.”

Tags:  Biosensor  COVID-19  Fred Hutchinson Cancer Research Center  Graphene  Healthcare  Heeju Ryu  Institute for Research in Electronics and Applied   Kevin Daniels  Rachael Myers-Ward  Seo Hyun Kim  Soaram Kim  U.S. Naval Research Laboratory  University of Georgia 

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THE FUTURE OF CARBON: AN UPDATE ON GRAPHENE’S DERMAL, INHALATION, AND GENE TOXICITY

Posted By Graphene Council, Tuesday, August 25, 2020

Recent studies on gene, inhalation and dermal toxicity of few-layer graphene have revealed much lower health risk than expected. This could pave the way for graphene as a young member of the nanocarbons family to become the “heir presumptive” to the long-reigning carbon black. Read the entire article

 

Tags:  Graphene  Healthcare  nanocarbons  NanoXplore  Nima Moghimian  Soroush Nazarpour 

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Versarien PLC - Launch of Graphene Enhanced Protective Face Mask

Posted By Graphene Council, Tuesday, August 4, 2020
Versarien plc is pleased to announce the launch of its first Graphene Enhanced Protective Face Mask, which utilises PolygreneTM, Versarien's graphene enhanced polymer.

The launch of the new protective face mask coincides with the first two orders Versarien has received following recent prelaunch sales activity, which resulted in 100,000 masks being delivered to a leading British university and 20,000 ordered by a UK electrical and mechanical servicing and repairs business.

Designed and manufactured with a Chinese partner, Versarien's graphene enhanced mask is a filtering facepiece (FFP2 rated version), which is designed to help provide enhanced protection against airborne bacteria and to minimise the spread of viral infection.

It meets the important BS EN 149:2001+A1:2009 standard (Respiratory protective devices), its antibacterial performance is certified according to GB/T 20944.2.2007 and its anti-viral performance is certified according to ISO 18184:2014 (E).  Consequently, it meets the guidelines issued by the World Health Organisation.

The new mask is enhanced with a coated layer utilising Polygrene, an advanced graphene-based material featuring Nanene - the world's only independently Verified Graphene Product certified by The Graphene Council. The addition of graphene to polymers provides many benefits including allowing innovative products to be developed utilising existing production processes. The Polygrene is blended with a sustainably sourced cellulose (viscose) material mix. 

Neill Ricketts, CEO of Versarien, commented: "Our new graphene enhanced mask is just one example of Polygrene's versatility and the high-quality design specifications that can be met using the material. We have taken great encouragement from the initial level of interest and are already in discussions with a number of other potential customers. Importantly, through our partner, we also have the capacity to fulfil much larger numbers of product orders going forward."

Tags:  Graphene  Healthcare  Neill Ricketts  polymers  Versarien 

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Certainty in just 15 minutes – researchers develop a graphene oxide-based rapid test to detect infections

Posted By Graphene Council, Tuesday, August 4, 2020
The current situation with the COVID-19 pandemic underscores the importance of detecting infections quickly and accurately to prevent further spread. Today, symptoms provide the clues that help diagnose viral or bacterial infections. However, many infections have similar symptoms, so these signs can easily be misread and the disease misdiagnosed. Blood tests provide certainty, but laboratories only carry these out when prescribed by the family physician. By the time the results arrive from the lab, doctors have often prescribed an antibiotic that may well be unnecessary.

Just one drop of blood for a diagnosis
Researchers at the Fraunhofer IZM in Berlin have been working on the project Graph-POC since April 2018 on a graphene oxide-based sensor platform to rise to precisely these challenges in diagnosing infections. A single drop of blood or saliva is all it takes to perform an accurate analysis. Just a few minutes after the drop is applied to the sensor’s surface, electrical signals convey the test result to the family doctor’s office. This rapid test provides certainty within just 15 minutes to replace the protracted blood work in the lab. It takes the error and guesswork out of diagnosis so the physician can prescribe the appropriate treatment or suitable antibiotics.

The test may also be set up to detect antibodies that are present after a patient has recovered from an infection. Fraunhofer IZM researchers are now focusing on this application to detect earlier infections with the COVID-19 virus, which can help with efforts to trace how the infection has spread. The human body forms molecules or proteins called biomarkers in response to an infection. Capture molecules placed on the surface of the graphene-based sensor to detect these biomarkers. Differential measurements of biomarkers’ concentration determine if an infection is present.

3D structure to enlarge the measuring surface
This sensor platform’s most remarkable feature is its base material: Electrically conductive and biocompatible, graphene oxide is also a very reliable means of detection. To date, it has only been used in microelectronics in its original form, a 2D monolayer. Fraunhofer IZM researchers are now applying it in a 3D structure in form of flakes. This 3D form increases the measuring surface and the accuracy of measurements.

Manuel Bäuscher, scientist at Fraunhofer IZM and sub-project manager at Graph-POC, sees great prospects ahead for these graphene oxide sensors: “We can pivot from the current medical field to also develop in the direction of the point of need; that is, towards environmental technology and the detection of environmental impacts. But of course the corona application is our first priority.” The graphene oxide flakes’  3D array and heightened sensitivity also open the door to further applications. For example, it could detect harmful gases such as carbon monoxide or acetone even at room temperature. As it stands, these gases have to first be heated to trigger a surface reaction that today’s sensors can detect. The graphene oxide sensor reacts at lower temperatures when metal oxides bond with its sensitive surface.

Fraunhofer IZM researchers are taking on another challenge to scale the production process up for mass manufacturing: They are looking to apply the graphene oxide coating at the wafer level so that hundreds of chips can be processed at once.

Antibodies detectable after coronavirus infections in about one year
The graphene oxide-based sensors have to be integrated into a plastic carrier and the reliability of the system have to be tested before the rapid tests can be deployed. Although the original project to detect infections is slated to run until spring 2021, the researchers do not expect to be able to verify the sensor for the coronavirus for another year yet. The partners in this project are the Charité, Aptarion Biotech AG, Technische Universität Berlin, MicroDiscovery GmbH and alpha-board GmbH. It is funded by the German Federal Ministry of Education and Research (BMBF).

Tags:  Biosensor  Fraunhofer IZM  Graphene  Healthcare  Manuel Bäuscher 

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ZEN Begins Commercial Collaborations

Posted By Graphene Council, Thursday, July 30, 2020

ZEN Graphene Solutions is pleased to announce it has commenced collaborations with research teams at a number of personal protective equipment (PPE) manufacturers to incorporate ZEN’s virucidal graphene ink into commercial products, including masks, gloves, gowns and other clothing following Zen’s promising results for an antiviral, graphene-based ink formulation from The University of Western Ontario’s ImPaKT Facility, biosafety Level 3 lab.

The company continues to optimize its proprietary formulation for dosage and delivery mechanism for highest antiviral impact. The next phase of testing is currently underway at the ImPaKT Facility and includes a preferred mask fabric, from one of our collaborators, coated in ZEN’s virucidal ink exposed to and tested against the COVID-19 virus.

Dr. Francis Dubé CEO commented, “Based on results so far and our discussions with the team at Western, we are quickly moving to integrate our material into commercial products with partners who wish to increase the level of COVID-19 protection their products currently offer.”

ZEN continues to be interested in collaborating with any PPE manufacturer that is looking to incorporate an antiviral compound into their products with the goal of bringing them to market and help the fight against COVID-19.

Tags:  Francis Dubé  Graphene  Healthcare  The University of Western Ontario  ZEN Graphene Solutions 

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