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Graphene-coated fibres as low-power wearable body temperature sensors

Posted By Graphene Council, Friday, July 3, 2020
A team of scientists from the UK and Portugal has produced graphene-coated polypropylene (PP) fibres that can be used in wearable textiles as temperature sensors. Operating in the range of 30 to 45 oC at voltages as low as 1 V, textiles incorporating these fibres could be used to actively measure body temperature of the wearer.

Fibres with integrated sensing functionality overcome some key issues related to the use of monolithic sensors that are attached to either clothes or skin, such as ease of use and wearer comfort. Moreover, many attachable sensors are not robust against washing, and some require external high-power voltage supplies. The new graphene-PP based solution resolves all these issues, as described in the application-driven work published in ACS Applied Materials & Interfaces.

PP is a textile fibre material that is strong and transparent, lightweight, eco-friendly and recyclable. The researchers coat PP, an electrical insulator, with graphene to create fibres that are electrically conductive, their resistance changing with temperature. With an outlook for practical device development, the researchers tested two types of graphene that is suitable for mass production, CVD grown and shear exfoliated. The CVD grown graphene exhibited higher sensitivity to temperature, due to its better uniformity. The resistance changes by several percent across temperatures of interest, which is suitable for practical use.

Figure: Graphene on polypropylene fibre temperature sensor – real life use test. Reprinted with permission from ACS Appl. Mater. Interfaces 2020, 12, 26, 29861–29867. Copyright 2020 American Chemical Society.

In order to simulate real-life usage, the novel fibres were tested against bending for up to 1000 cycles and washing in laundry detergent at different temperatures. The devices exhibited excellent stability under all tested conditions. These sensors have potential applications in continuous measurement of human body temperature through integration in garments, or ambient temperature through integration in upholstery.

Tags:  Chemical Vapour Deposition  Graphene  Sensors 

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DIAMONDS VS. COAL: DISCOVERY COULD HELP FINE-TUNE CARBON MICROSTRUCTURE

Posted By Graphene Council, Thursday, July 2, 2020
Superheroes squeeze a lump of coal and turn it into a sparkling diamond – in comic books, anyway. There is some scientific validity to this fictional feat. Coal and diamonds are both composed of carbon. The two materials differ in their microscopic arrangement of atoms, and that leads to quite a difference in appearance, conductivity, hardness and other properties.

As this shows, the microstructure of carbon-based materials is important. Optimizing carbon microstructure could benefit applications in energy storage, sensors and next generation nuclear material systems.

Now a group of researchers at Idaho National Laboratory (INL) have conducted a study that could lead to improved methods to fine-tune the carbon microstructure. The scientists reported on their work in a June 2020 Materials Today Chemistry paper.

CREATING CRYSTALLINE STRUCTURE
Kunal Mondal, an INL materials science researcher, conducted the group’s experiments, which involved subjecting tiny carbon films and fibers to temperatures as high as 3000o C (5400o F). That heat caused the microstructure in the films and fibers to become less disordered (or amorphous) and more diamondlike (or crystalline).

“When carbon structure gets more crystalline, it makes many things possible. First, conductivity of the carbon increases. That means you can get a lot of good applications out of it,” said Mondal, the paper’s lead author. Some of these applications include batteries and sensors, he added.

A goal of the research was to see how the final microstructure varied depending on the temperature and the starting material.

For the initial material, the researchers spun out miniature carbon fibers and coated substrates with thin carbon films. They heat treated these polymer precursors at temperatures ranging from 1000 to 3000o C. They then examined the results with transmission electron microscopes and other instruments, determining the degree of conversion from a loosely organized polymer to a more structured, crystalline arrangement.

SHORTCUTS IN MICROSTRUCTURE ROADMAP
Heat treatments are used worldwide to create carbon composite materials with the desired microstructure, which varies by application. The precursors that researchers selected are also widely used. Yet commercial production with these precursors and manufacturing methods can be an intricate process that requires a series of precise heat treatments and other actions.

The final recipe for a product may be reached by trial and error, which can sometimes be extensive. The INL research aims, among other things, to provide a road map with shortcuts to speed up this search.

So, in addition to experimental work, the INL group also did simulations that modeled how the fibers and films would evolve during heat treatment. Gorakh Pawar, another co-author of the paper and an INL staff scientist in the Department of Material Science and Engineering, handled these simulations. The computer models predicted outcomes that were similar to the experimental results. The work was funded through INL’s Laboratory Directed Research and Development program.

The INL study provides clues that can be used to help design precursors and processes that will yield preferred nanostructures, Pawar said. For instance, starting with a film resulted in higher electron mobility than what resulted when starting from fibers, which could be a consequence of the many boundaries in a fiber and their impact on the free movement of electrons. So, for a sensor or another application where conductivity is important, starting with a film might lead to a device that is more sensitive, is faster or uses less power.

In exploring all the possible combinations of processing steps, researchers at national labs, in industry and elsewhere need to be cost-effective in their investigations and outcomes. Simulations like those done by the INL group can help minimize the time, effort and expense of zeroing in on the right process and starting material.

“You cannot run an experiment forever. You need some guidance to optimize your experimental protocol,” Pawar said.

CHARGING BATTERIES FASTER

These batteries have an electrode made of graphite, a form of carbon. In operating the battery, the lithium ions are stored between layers in the graphite, which means the amount of void and defects in the material is important. With graphite of the proper structure, that movement of ions can be rapid, a requirement for extreme fast charging. Yet the graphite materials cannot be so porous that it renders the electrode useless.

Such charging might allow electric vehicles to get the equivalent of a full tank of gasoline within minutes instead of hours. That capability would make operating these emission-free cars and trucks similar to what people are used to with current gas-powered vehicles. This means the INL research project could prove beneficial in figuring out how to achieve that type of performance, a capability consumers seek.

“That’s our future goal in energy storage: how we can optimize this graphite structure,” Pawar said.

To help accomplish that, the researchers continue to expand their understanding of carbon microstructures and how they can be produced. In the end, this work may help create an electric vehicle battery that can reach full charge quickly – or, to put it in superhero terms, faster than a speeding bullet.

Tags:  carbon films  carbon nanofibre  Energy Storage  Graphene  Idaho National Laboratory  Kunal Mondal  Sensors 

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Researchers print, tune graphene sensors to monitor food freshness, safety

Posted By Graphene Council, Friday, June 26, 2020
Researchers dipped their new, printed sensors into tuna broth and watched the readings. It turned out the sensors – printed with high-resolution aerosol jet printers on a flexible polymer film and tuned to test for histamine, an allergen and indicator of spoiled fish and meat – can detect histamine down to 3.41 parts per million.

The U.S. Food and Drug Administration has set histamine guidelines of 50 parts per million in fish, making the sensors more than sensitive enough to track food freshness and safety.

Making the sensor technology possible is graphene, a supermaterial that’s a carbon honeycomb just an atom thick and known for its strength, electrical conductivity, flexibility and biocompatibility. Making graphene practical on a disposable food-safety sensor is a low-cost, aerosol-jet-printing technology that’s precise enough to create the high-resolution electrodes necessary for electrochemical sensors to detect small molecules such as histamine.

“This fine resolution is important,” said Jonathan Claussen, an associate professor of mechanical engineering at Iowa State University and one of the leaders of the research project. “The closer we can print these electrode fingers, in general, the higher the sensitivity of these biosensors.”

Claussen and the other project leaders – Carmen Gomes, an associate professor of mechanical engineering at Iowa State; and Mark Hersam, the Walter P. Murphy Professor of Materials Science and Engineering at Northwestern University in Evanston, Illinois – have recently reported their sensor discovery in a paper published online by the journal 2D Materials. (See sidebar for a full listing of co-authors.)

The National Science Foundation, the U.S. Department of Agriculture, the Air Force Research Laboratory and the National Institute of Standards and Technology have supported the project.

The paper describes how graphene electrodes were aerosol jet printed on a flexible polymer and then converted to histamine sensors by chemically binding histamine antibodies to the graphene. The antibodies specifically bind histamine molecules.

The histamine blocks electron transfer and increases electrical resistance, Gomes said. That change in resistance can be measured and recorded by the sensor.

“This histamine sensor is not only for fish,” Gomes said. “Bacteria in food produce histamine. So it can be a good indicator of the shelf life of food.”

The researchers believe the concept will work to detect other kinds of molecules, too.

“Beyond the histamine case study presented here, the (aerosol jet printing) and functionalization process can likely be generalized to a diverse range of sensing applications including environmental toxin detection, foodborne pathogen detection, wearable health monitoring, and health diagnostics,” they wrote in their research paper.

For example, by switching the antibodies bonded to the printed sensors, they could detect salmonella bacteria, or cancers or animal diseases such as avian influenza, the researchers wrote.

Claussen, Hersam and other collaborators (see sidebar) have demonstrated broader application of the technology by modifying the aerosol-jet-printed sensors to detect cytokines, or markers of inflammation. The sensors, as reported in a recent paper published by ACS Applied Materials & Interfaces, can monitor immune system function in cattle and detect deadly and contagious paratuberculosis at early stages.

Claussen, who has been working with printed graphene for years, said the sensors have another characteristic that makes them very useful: They don’t cost a lot of money and can be scaled up for mass production.

“Any food sensor has to be really cheap,” Gomes said. “You have to test a lot of food samples and you can’t add a lot of cost.”

Claussen and Gomes know something about the food industry and how it tests for food safety. Claussen is chief scientific officer and Gomes is chief research officer for NanoSpy Inc., a startup company based in the Iowa State University Research Park that sells biosensors to food processing companies.

They said the company is in the process of licensing this new histamine and cytokine sensor technology.

It, after all, is what they’re looking for in a commercial sensor. “This,” Claussen said, “is a cheap, scalable, biosensor platform.”

Tags:  3D Printing  Biosensor  Carmen Gomes  Graphene  Iowa State University  Jonathan Claussen  Mark Hersam  Northwestern University  Sensors 

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Graphene transistors enable selective ion sensing

Posted By Graphene Council, Friday, June 26, 2020
New research shows that graphene field effect transistors can be used to selectively detect ions in a liquid solution. The work, just published in Nature Communications, paves the way to applications such as genome sequencing, medical diagnostics, environmental monitoring, and industrial process control.

State of the art technology for detecting and resolving ions in solution relies on ion sensitive field effect transistors (ISFETs). Standard ISFETs are made of silicon, due to the ease of technological processing, however silicon ISFETs have some drawbacks that hinder their performance in real-life scenarios.

To achieve selectivity to different ionic species, ISFETs that are selective to specific ions are assembled into arrays and post-processing is used to estimate ion concentration. Since many ISFETs are packed on small areas to implement selectivity, each ISFET has to be made small, which leads to low-frequency noise that is prominent in silicon. Increasing the size of individual ISFETs leads to loss of resolution, which imposes a tradeoff that limits practical use.

The present research, reported by teams in Canada and Spain, overcomes the tradeoff by using graphene instead of silicon as the ISFET channel. Graphene has high carrier mobility even in large-area devices, which enables construction of a single large sensor for multiple ionic species. Post-processing of the transistor signal enables the measuring of concentration of K+, Na+, NH4+, NO3-, SO42-, and Cl- ions down to concentrations lower than 10-5 M in a multianalyte solution. These ions were chosen due to their prominence in agriculture runoff, hence the importance of their detection in water quality monitoring.

Practical graphene ISFET use was demonstrated by monitoring the uptake of ions by duckweed in an aquarium over a period of three weeks. The researchers tracked, with high precision and selectivity, the concentration of seven different ionic species over time after adding plant nutrients to the aquarium. This novel work demonstrates that large-area graphene ISFETs can be fabricated from wafer scale graphene by a facile method, yielding ISFETs with a high signal-to-noise-ratio and high-resolution sensing. Graphene ISFETs hence overcome poor selectivity typically associated with ISFETs made of other materials and can be applied to real-life scenarios in environmental sensing.

Tags:  Electronics  Graphene  Sensors  transistor 

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CERN trials graphene for magnetic measurements

Posted By Graphene Council, Thursday, June 18, 2020
First isolated in 2004 by physicists at the University of Manchester using pieces of sticky tape and a graphite block, the one-atom-thick carbon allotrope graphene has been touted as a wonder material on account of its exceptional electrical, thermal and physical properties. Turning these properties into scalable commercial devices has proved challenging, however, which makes a recently agreed collaboration between CERN and UK firm Paragraf on graphene-based Hall-probe sensors especially novel.

There is probably no other facility in the world to be able to confirm this, so the project has been a big win on both sides, Ellie Galanis

With particle accelerators requiring large numbers of normal and superconducting magnets, high-precision and reliable magnetic measurements are essential. While the workhorse for these measurements is the rotating-coil magnetometer with a resolution limit of the order of 10–8 Vs, the most important tool for local field mapping is the Hall probe, which passes electrical current proportional to the field strength when the sensor is perpendicular to a magnetic field. 

However, measurement uncertainties in the 10–4 range required for determining field multipoles are difficult to obtain, even with the state-of-the-art devices. False signals caused by non-perpendicular field components in the three-dimensional sensing region of existing Hall probes can increase the measurement uncertainty, requiring complex and time-consuming calibration and processing to separate true signals from systematic errors. With an active sensing component made of atomically thin graphene, which is effectively two-dimensional, a graphene-based Hall probe in principle suffers negligible planar Hall effects and therefore could enable higher precision mapping of local magnetic fields.

Inspiration strikes
Stephan Russenschuck, head of the magnetic measurement section at CERN, spotted the potential of graphene-based Hall probes when he heard about a talk given by Paragraf – a recent spin-out from the department of materials science at the University of Cambridge – at a magnetic measurement conference in December 2018. This led to a collaboration, formalised between CERN and Paragraf in April, which has seen several graphene sensors installed and tested at CERN during the past year. 

The firm sought to develop and test the device ahead of a full product launch by the end of this year, and the results so far, based on well-calibrated field measurements in CERN’s reference magnets, have been very promising. “The collaboration has proved that the sensor has no planar effect,” says Paragraf’s Ellie Galanis. “This was a learning step. There is probably no other facility in the world to be able to confirm this, so the project has been a big win on both sides.”

The graphene Hall sensor also operates over a wide temperature range, down to liquid-helium temperatures at which superconducting magnets in the LHC operate. “How these sensors behave at cryogenic temperatures is very interesting,” says Russenschuck. “Usually the operation of Hall sensors at cryogenic temperatures requires careful calibration and in situ cross-calibration with fluxmetric methods. Moreover, we are now exploring the sensors on a rotating shaft, which could be a breakthrough for extracting local, transversal field harmonics. Graphene sensors could get rid of the spurious modes that come from nonlinearities and planar effects.”

CERN and Paragraf, which has patented a scalable process for depositing two-dimensional materials directly onto semiconductor-compatible substrates, plan to release a joint white paper communicating the results so far and detailing the sensor’s performance across a range of magnetic fields.

Tags:  CERN  Ellie Galanis  Graphene  Paragraf  Sensors  Stephan Russenschuck 

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UT Projects Win $23.6M in R&D Funds as Part of Portuguese Government Technology Program

Posted By Graphene Council, Wednesday, June 10, 2020
The UT Austin Portugal program, a 13-year-old innovation partnership between the university and the Portuguese government, received $23.6 million in funding to pursue 11 R&D projects as part of a major technology initiative from Portugal’s Ministry of Science, Technology and Higher Education.

The projects fall under four major categories: nanomaterials, earth-space interactions, medical physics and advanced computing. The teams will spend the next three years developing their projects, which could transform industries like automotive, space, health care and data science.

“Ranging from electromagnetic interference shielding nanomaterials, to in-beam time-of-flight positron emission tomography for proton radiation therapy, all the way to an ocean and climate change monitoring constellation based on radar altimeter data combined with gravity and ocean temperature and salinity measurements, the spread, number, and quality of the UT Austin Portugal joint strategic projects selected for funding within the recent competitive solicitation set forth by the Foundation for Science and Technology and National Innovation Agency are truly outstanding,” said Manuel Heitor, Portugal’s Minister of Science, Technology and Higher Education. “I look forward to witnessing the results of such collaborative research between Portuguese and UT researchers.”

The call for proposals included just three universities: The University of Texas at Austin, Carnegie Mellon University and the Massachusetts Institute of Technology. UT won the majority of the investment dollars, about 40% of the funding, and saw the most projects funded among the three engineering powerhouses.

“We had anticipated four to five projects would be selected for strategic grant awards and were astounded when we learned 11 had been selected by the evaluation panel in Portugal,” said John Ekerdt, Cockrell School associate dean for research and principal investigator for UT Austin Portugal. “This is a testament to the outstanding faculty and quality projects they proposed with collaborators in Portugal and to the close ties that have been forged between UT researchers and faculty and counterparts in Portugal.”

“The performance of the UT Austin Portugal program in the 2019 call for strategic projects has been remarkable,” said Marco Bravo, executive director of the UT Austin Portugal program. “Eleven of 14 project proposals submitted by the UT Austin Portugal research consortia were approved for funding through an independent assessment process. Overall, UT Austin Portugal saw 11 of its groundbreaking, industry-led proposals approved out of a total of 25 projects approved at this solicitation that included proposals from two other international partnerships, corresponding to nearly $24 million over three years. That’s 40% of total funding to UT Austin Portugal projects, the largest share of research dollars available. UT Austin researchers are to be congratulated on this effort.”

The UT Austin Portugal program dates back to 2007, and it is one of several partnerships between the Portuguese government and research institutions. The goal is to elevate science and technology in Portugal while fostering strong partnerships to help universities continue to innovate. The partnership with UT was extended in 2018, continuing the alliance until at least 2030.

“Of the three international partnerships with American universities sponsored by the Portuguese Foundation for Science and Technology in Portugal, the partnership with UT Austin had the best performance in this call, which was designed and launched on the Portuguese side,” said José Manuel Mendonça, national director of the program. “The 11 approved projects represent a proposal success rate of almost 80% for the UT Austin Portugal Program. The approved projects will, undoubtedly, contribute to promoting and strengthening collaborations with UT Austin in high-level R&D matters with immediate transposition to various sectors of economic activity, several of which are critical to Portugal's competitive position at an international level.”

About a third of the funds for UT’s projects come from the university, with the rest coming from a combination of public and private Portuguese entities. Each project team in Portugal is led by a Portuguese company. The UT side includes 21 faculty members and one from the MD Anderson Cancer Center.

Here is a look at the UT projects:

Shielding electronic devices from electromagnetic interference
This project proposes to use the “wonder material” graphene to improve on methods to combat electromagnetic interference, which can disrupt circuits and cause devices to fail. The team plans to create two composites with electromagnetic interference shielding capabilities and fabricate a solution to protect electric wires used in the automotive industry.

UT Austin Faculty: Deji Akinwande, Cockrell School of Engineering, Department of Electrical and Computer Engineering; Brian Korgel, Cockrell School of Engineering, McKetta Department of Chemical Engineering

New lasers for next-generation biomedical imaging
The use of multiphoton microscopy to examine cell behavior in live tissue over time has become an important research tool for learning more about brains and tumors. This project aims to increase the speed and depth of this form of imaging and diagnostics through the development and application of ultrashort laser pulses.

UT Austin Faculty: Andrew Dunn, Cockrell School of Engineering, Department of Biomedical Engineering; Adela Ben-Yakar, Cockrell School of Engineering, Walker Department of Mechanical Engineering

Nano-satellites for gravitational field assessment
Researchers propose to develop a nano-satellite prototype for studying gravitational fields. The project will also develop a platform for future nano-satellite capabilities, including Earth observation, communications and exploration missions.

UT Austin Faculty: Byron Tapley, Cockrell School of Engineering, Department of Aerospace Engineering and Engineering Mechanics, and the Center for Space Research; Brandon Jones, Cockrell School of Engineering, Department of Aerospace Engineering and Engineering Mechanics, and the Texas Spacecraft Laboratory

Software to match big data with high-performance computing
The advancement of technology has generated huge troves of data, which requires stronger computing power to process and analyze all that information. This project aims to create a software bundle to help companies pair their big data operations with high-performance computing, which includes tools for managing challenges such as computing and research storage.

UT Austin Faculty: Vijay Chidambaram, College of Nature Sciences, Department of Computer Science; Todd Evans, Texas Advanced Computing Center

Sensors for monitoring cancer patients
This project will develop a biosensor that can be injected into prostate cancer patients after surgery. The minimally invasive sensor would allow medical personnel to monitor high-risk patients remotely and look for the development of early tumors, with the potential to increase the predictive value of cancer screenings.

UT Austin Faculty: Thomas Milner, Cockrell School of Engineering, Department of Biomedical Engineering; James Tunnell, Cockrell School of Engineering, Department of Biomedical Engineering

Wearable rehabilitation devices
Researchers will develop a series of nano-sensors embedded into clothing that administer electrostimulation to people suffering from a lack of mobility and motor deficiency. The sensors could be monitored remotely by health professionals, creating a mobile rehabilitation option for people who have trouble getting to a doctor’s office consistently or want greater freedom to complete treatment anywhere. The team envisions its project as a tool mostly for elderly people, but it has applications for training high-level athletes as well.

UT Austin Faculty: George Biros, Cockrell School of Engineering, Walker Department of Mechanical Engineering, and the Oden Institute for Computational Engineering and Sciences; Michael Cullinan, Cockrell School of Engineering, Walker Department of Mechanical Engineering

Software for gathering better data on manufacturing
Getting reliable data on manufacturing processes proves challenging due to issues with placing sensors in the right spots and retaining strong connectivity. Thin films loaded with small sensors that can be applied directly to the equipment represent a promising solution; however, installation has proved difficult. This project proposes a new set of software to make it easier to layer these films on top of equipment by providing necessary data to avoid mechanical problems during installation.

UT Austin Faculty: Rui Huang, Cockrell School of Engineering, Department of Aerospace Engineering and Engineering Mechanics, Center for Mechanics of Solids, Structures and Materials; Kenneth M. Liechti, Cockrell School of Engineering, Department of Aerospace Engineering and Engineering Mechanics, Center for Mechanics of Solids, Structures and Materials

A new way to measure next-generation cancer therapy
Proton radiation therapy, the use of protons rather than X-rays to treat cancer patients, is on the rise, but measuring the distance protons travel proves problematic. Typically, it takes a ring of detectors surrounding the patient to get accurate measurements, but that poses geometric challenges. This project proposes to develop a new type of Positron Emission Tomography scan, which shows how tissues and organs are functioning to better understand the range of protons and whether they are traveling to the right spots to attack the cancer.

UT Faculty: Karol Lang, College of Natural Sciences, Department of Physics; Narayan Sahoo, University of Texas MD Anderson Cancer Center, Department of Radiation Physics

Satellite constellations for monitoring climate change
This project aims to develop the next generation of radar altimeter instruments — which measure the distance between an aircraft and the terrain below it — and a series of small satellites that can understand long-term variability in local, regional and global climate created by changes in sea levels due to water temperature. The project also includes a data processing and visualization system using advanced modeling, estimation techniques, statistical and scientific machine learning methods and error analysis.

UT Austin Faculty: Byron Tapley, Cockrell School of Engineering, Department of Aerospace Engineering and Engineering Mechanics Department, and the Center for Space Research; Patrick Heimbach, Jackson School of Geosciences, Department of Geological Sciences, and the Oden Institute for Computational Engineering and Sciences

Improving cutting tools for airline and automotive components
Fabricating parts of cars and planes is hard on cutting tools and tends to ware them down. This project aims to develop coatings that better protect and extend the lifespan of these crucial pieces of equipment. The team also plans to develop simulation programs to improve cutting tools’ performance.

UT Austin Faculty: Gregory J. Rodin, Cockrell School of Engineering, Department of Aerospace Engineering and Engineering Mechanics, and the Oden Institute for Computational Engineering and Sciences; Filippo Mangolini, Cockrell School of Engineering, Walker Department of Mechanical Engineering

An alternative to traditional water treatment options
Traditional water treatment tech struggles to efficiently remove high amounts of pollutants from some types of surface and groundwater. This team is looking to use metallic nanoparticles to clean water by improving a process called catalytic hydrogenation, which involves adding hydrogen via a metallic catalyst.

UT Austin Faculty: Charles J. Werth, Cockrell School of Engineering, Department of Civil, Architectural, and Environmental Engineering; Simon M. Humphrey, College of Natural Sciences, Department of Chemistry

Tags:  Biomedical  Carnegie Mellon University  Electronics  Environment  Graphene  Healthcare  John Ekerdt  Marco Bravo  Massachusetts Institute of Technology  nanomaterials  Sensors  The University of Texas at Austin  Water Purification 

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Aerosol-printed graphene unveiled as low cost, faster food toxin sensor

Posted By Graphene Council, Wednesday, June 10, 2020
Researchers in the USA have developed a graphene-based electrochemical sensor capable of detecting histamines (allergens) and toxins in food much faster than standard laboratory tests.

The team used aerosol-jet printing to create the sensor. The ability to change the pattern geometry on demand through software control allowed rapid prototyping and efficient optimization of the sensor layout.

Commenting on the findings, which are published today in the IOP Publishing journal 2D Materials, senior author Professor Mark Hersam, from Northwestern University, said: "We developed an aerosol-jet printable graphene ink to enable efficient exploration of different device designs, which was critical to optimizing the sensor response."

As an additive manufacturing method that only deposits material where it is needed and therefore minimizes waste, aerosol-jet-printed sensors are low-cost, straightforward to make, and portable. This could potentially enable their use in places where continuous on-site monitoring of food samples is needed to determine and maintain the quality of products, as well as other applications.

Senior author Professor Carmen Gomes, from Iowa State University, said: "Aerosol-jet printing was fundamental to the development of this sensor. Carbon nanomaterials like graphene have unique material properties such as high electrical conductivity, surface area, and biocompatibility that can significantly improve the performance of electrochemical sensors.

"But, since in-field electrochemical sensors are typically disposable, they need materials that are amenable to low-cost, high-throughput, and scalable manufacturing. Aerosol-jet printing gave us this."

The team created high-resolution interdigitated electrodes (IDEs) on flexible substrates, which they converted into histamine sensors by covalently linking monoclonal antibodies to oxygen moieties created on the graphene surface by a CO2 thermal annealing process.

They then tested the sensors in both a buffering solution (PBS) and fish broth, to see how effective they were at detecting histamines.

Co-author Kshama Parate, from Iowa State University, said: "We found the graphene biosensor could detect histamine in PBS and fish broth over toxicologically-relevant ranges of 6.25 to 100 parts per million (ppm) and 6.25 to 200 ppm, respectively, with similar detection limits of 2.52 ppm and 3.41 ppm, respectively. These sensor results are significant, as histamine levels over 50 ppm in fish can cause adverse health effects including severe allergic reactions - for example, scombroid food poisoning.

"Notably, the sensors also showed a quick response time of 33 minutes, without the need for pre-labelling and pre-treatment of the fish sample. This is a good deal faster than the equivalent laboratory tests."

The researchers also found the biosensor's sensitivity was not significantly affected by the non-specific adsorption of large protein molecules commonly found in food samples and used as blocking agents.

Senior author Dr Jonathan Claussen, from Iowa State University, said: "This type of biosensor could be used in food processing facilities, import and export ports, and supermarkets where continuous on-site monitoring of food samples is needed. This on-site testing will eliminate the need to send food samples for laboratory testing, which requires additional handling steps, increases time and cost to histamine analysis, and consequently increases the risk of foodborne illnesses and food wastage.

"It could also likely be used in other biosensing applications where rapid monitoring of target molecules is needed, as the sample pre-treatment is eliminated using the developed immunosensing protocol. Apart from sensing small allergen molecules such as histamine, it could be used to detect various targets such as cells and protein biomarkers. By switching the antibody immobilized on the sensor platform to one that is specific towards the detection of suitable biological target species, the sensor can further cater to specific applications. Examples include food pathogens (Salmonella spp.), fatal human diseases (cancer, HIV) or animal or plant diseases (avian influenza, Citrus tristeza)."

Tags:  Biosensor  Carmen Gomes  Graphene  Iowa State University  Jonathan Claussen  Kshama Parate  Mark Hersam  Northwestern University  Sensors 

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A touch of gold and silver

Posted By Graphene Council, Saturday, June 6, 2020

Metals are usually characterized by good electrical conductivity. This applies in particular to gold and silver. However, researchers from the Max Planck Institute for Solid State Research in Stuttgart, together with partners in Pisa and Lund, have now discovered that some precious metals lose this property if they are thin enough. The extreme of a layer only one atom thick thus behaves like a semiconductor. This once again demonstrates that electrons behave differently in the two-dimensional layer of a material than in three-dimensional structures. The new properties could potentially lead to applications, for example in microelectronics and sensor technology.

One might think that gold leaf, which is only 0.1 µm thick, is actually quite thin. Far from it. It can actually be several hundred times thinner. For example, the research team of Ulrich Starke and his former doctoral student Stiven Forti have successfully created a gold layer only a single atom thick. Two-dimensional gold, so to speak.

Starke is head of the Interface Analysis Facility at the Max Planck Institute for Solid State Research in Stuttgart. His team has long been working on the border between three-dimensional (voluminous) and two-dimensional (planar) materials. Solid state researchers are interested in this transition because it is associated with changes in certain material properties. This has previously been demonstrated in two-dimensional carbon, or graphene. Among other things, its electrons are significantly more mobile and allow the electrical conductivity to increase to 30 times that of the related three-dimensional graphite.

Gold atoms are pushed between graphene and silicon carbide

However, for many metals, producing layers of material just one atom thick is not an easy task. “With classical deposition methods, gold atoms, for example, would immediately agglomerate into three-dimensional clusters”, explains Starke. His team is therefore working with a different method – intercalation – on which they did pioneering work around 10 years ago. Intercalation literally means sliding something in between. And that is precisely how it works. The researchers start with a silicon carbide wafer. Using a process they developed themselves, they first convert its surface into a single-atomic layer of graphene. “If we vaporise sublimated gold on to this silicon carbide-graphene arrangement in a high vacuum, the gold atoms migrate between the carbide and the graphene”, explains Forti. The former Max Planck doctoral candidate is now doing research at the Center for Nanotechnology Innovation in Pisa. It is not yet fully understood how the thick gold atoms get into the interstitial space. But this much is clear: higher temperatures favour the process.

The team had also applied the intercalation technique to other elements, including germanium, copper, and gadolinium. Yet, according to Forti, the main focus was the influence on the properties of graphene. In the case of gold, however, it was found for the first time that the intercalated atoms arranged themselves in a regular, periodically recurring two-dimensional structure – crystalline – along the silicon carbide surface. “If the intercalation is carried out at 600°C, the graphene layer prevents the gold atoms from agglomerating to form drops”, says Forti about the function of the carbon layer in the sandwich structure.

A gold layer consisting of only two atomic layers conducts like a metal
The successful preparation of the gold layer of one atom thickness was only the first step. Subsequently, the extremely thin materials and their possibly special characteristics became interesting for the researchers. They could indeed show that the extremely thin layer of gold develops its own electronic – and semiconductor – properties. To compare: the electrical conductivity of voluminous (i.e. three-dimensional gold) is nearly as good as that of copper. Because theoretical considerations forecast a metallic character for pure 2D gold, the semiconductor finding was somewhat surprising. “Interactions between the gold atoms and either the silicon carbide or the graphene carbon obviously still play a role here. This influences the energy levels of the electrons”, says Starke.

Semiconductors are essential materials in microelectronics and other fields. For example, electronic switching elements such as diodes or transistors are based on it. Starke’s team can envisage some typical semiconductor applications for the new 2D material. A second layer of gold atoms again gives a metallic character – and thus influences the electrical conductivity. “By varying the amount of sublimated gold, we can tightly control whether one or two layers of gold form”, explains Forti.

It would therefore be conceivable to use components with alternating single- or double-atomic gold layers. The new manufacturing method would then have to be suitably combined with common lithographic methods of chip production. For example, diodes significantly smaller than conventional ones could be produced. According to Starke, the different electronic states of single and double-layer gold could also be used in optical sensors.

Electronic effects also in the graphene layer

Another application idea results from effects caused by the intercalated gold in the adjacent graphene layer, which apparently depend on the thickness of the gold. “A gold layer one atom thick causes an n-doping in the graphene. This means we obtain electrons as charge carriers”, says Forti. In spots where the gold is two atomic layers thick, exactly the opposite – p-doping – happens. There, missing electrons or positively charged so-called “holes” act as charge carriers. The gold also enhances the interaction of plasmons (i.e. fluctuations in the density of charge carriers) with electromagnetic radiation. “A structured, alternating arrangement of n- and p-doping in the graphene could thus be used. For example, as a highly sensitive yet high-resolution detector array for terahertz radiation like those used in materials testing, for security checks at airports, or for wireless data transmission”, says Starke.

Starke’s team has already taken the next step in the production of two-dimensional precious metal layers. Also in an intercalation experiment with silver, a strictly crystalline two-dimensional silver layer formed between silicon carbide and graphene. And what’s more: even this metal, which is usually an even better electrical conductor than gold, becomes a semiconductor when reduced to two dimensions. The initial results indicate that the energy required to make the silver layer electrically conductive is probably higher than for 2D gold. “The semiconductor properties of a component made from this material might therefore be thermally more stable than those of gold”, says Starke about possible practical consequences.

Tags:  2D materials  Graphene  Graphite  Max Planck Institute for Solid State Research  Sensors  Stiven Forti  Ulrich Starke 

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Graphene masks: facing up to coronavirus (COVID-19)

Posted By Graphene Council, Wednesday, May 20, 2020
Since the development and isolation of graphene by researchers at Manchester University in 2004, the “2D miracle material” has been put to use in everything from airplanes to anti-corrosive paints, from batteries to body armour (read our earlier blogs Graphene: a new '2D' world and Advanced materials: game-changing graphene). Unsurprisingly, the wonder material is now being put to work in the global fight against COVID-19.

Graphene has been investigated in various biosensor set-ups, including nucleic acid sequencing devices (see the paper Graphene nanodevices for DNA sequencing published in the journal Nature) and diagnostic devices for the monitoring and treatment of HIV (see Graphene-info). Recently, Korean researchers have developed a graphene-based FET biosensor which can detect the SARS-CoV-2 spike protein (the protein on the surface of the COVID-19 virus) from patients’ swabs in less than a minute (see Graphene-info).

However, one key issue in the fight against COVID-19 is maintaining a supply of high quality protective equipment such as masks, gloves and gowns for medical staff.

Among graphene’s myriad of useful properties is its antimicrobial activity attributed, among other reasons, to graphene’s ability to perturb membranes. Several teams have taken advantage of graphene’s antimicrobial, antistatic and electrically conductive properties to develop face masks which can be re-sterilised and, importantly, reused.

For example, IDEATI have developed a cotton fabric facemask with a coating containing both graphene and other carbon nanomaterials. The coating on the mask has been shown to reduce levels of Staphylococcus aureus bacteria by 99.95% within a 24 hour period. The graphene coating also repels dust and is effective against airborne particles of less than 2.5 microns in diameter. The mask can be washed and reused up to 10 times without losing its antibacterial or antistatic properties. The product has currently only been shown to be effective against bacteria. However, IDEATI are currently evaluating the masks antiviral properties (see Graphene-info).

An innovative approach to PPE
Taking a slightly different approach, LIGC Applications have recently launched a graphene-based respirator mask which claims to compete with gold standard N95 respirator masks. N95 respirator masks are used by medical staff as part of their PPE (personal protective gear) and can block 95% of particles over 0.3 microns. However, the COVID-19 virus is approximately 0.2 microns in diameter and can still be transmitted in tiny water droplets of less than 0.3 microns in size (see Graphene-info).

LIGC Applications’ “Guardian G-Volt” mask is allegedly 99% efficient against particles over 0.3 microns, as well as being 80% efficient against anything smaller. The mask has an electrically embedded graphene filtration system formed from laser-induced graphene, a microporous foam which is conductive and can trap pathogens.

The mask, powered by a portable battery pack which is plugged into the mask via a USB port, works by applying a low level electric charge to the surface to sterilise it and repel particles trapped in its graphene filter. The mask also has an LED light which alerts the user when the mask needs to be replaced. N95 masks must be disposed of once they become damp, however, the Guardian G-Volt can be heated and sterilised in a home docking system, which allows the mask to be safely reused.

Of course, wearing a mask alone will not give absolute protection against pathogens, such as the COVID-19 virus. But these advances illustrate that there are a plethora properties of graphene which can be utilised in different ways to achieve a common goal.

Tags:  Batteries  Graphene  Healthcare  nanodevices  Sensors 

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Defective graphene has high electrocatalytic activity

Posted By Graphene Council, Tuesday, May 12, 2020
Scientists from the Moscow Institute of Physics and Technology, Skoltech, and the Russian Academy of Sciences Joint Institute for High Temperatures have conducted a theoretical study of the effects of defects in graphene on electron transfer at the graphene-solution interface. Their calculations show that defects can increase the charge transfer rate by an order of magnitude. Moreover, by varying the type of defect, it is possible to selectively catalyze the electron transfer to a certain class of reagents in solution. This can be very useful for creating efficient electrochemical sensors and electrocatalysts. The findings were published in Electrochimica Acta.

Carbon is widely used in electrochemistry. A new type of carbon-based electrodes, made of graphene, has great potential for biosensors, photovoltaics, and electrochemical cells. For example, chemically modified graphene can be used as a cheap and effective analogue of platinum or iridium catalysts in fuel cells and metal-air batteries.

The electrochemical characteristics of graphene strongly depend on its chemical structure and electronic properties, which have a significant impact on the kinetics of redox processes. The interest in studying the kinetics of heterogeneous electron transfer on the graphene surface has recently been stimulated by new experimental data showing the possibility of accelerating the transfer at structural defects, such as vacancies, graphene edges, impurity heteroatoms, and oxygen-containing functional groups.

A recent paper co-authored by three Russian scientists presents a theoretical study of the kinetics of electron transfer on the surface of graphene with various defects: single and double vacancies, the Stone-Wales defect, nitrogen impurities, epoxy and hydroxyl groups. All these changes significantly affected the transfer rate constant. The most pronounced effect was associated with a single vacancy: The transfer rate was predicted to grow by an order of magnitude relative to defect-free graphene (fig. 1). This increase should only be observed for redox processes with a standard potential of ?0.2 volts to 0.3 volts -- relative to the standard hydrogen electrode. The calculations also showed that due to the low quantum capacitance of the graphene sheet, the electron transfer kinetics can be controlled by changing the capacitance of the bilayer.

"In our calculations, we tried to establish a relation between the kinetics of heterogeneous electron transfer and the changes in the electronic properties of graphene caused by defects. It turned out that introducing defects into a pristine graphene sheet can lead to an increase in the density of electronic states near the Fermi level and catalyze electron transfer," said Associate Professor Sergey Kislenko of the Department for Physics of High-Temperature Processes, MIPT.

"Also, depending on the kind of defect, it affects the density of electronic states across various energy regions in different ways. This suggests a possibility for implementing selective electrochemical catalysis. We believe that these effects can be useful for electrochemical sensor applications, and the theoretical apparatus that we are developing can be used for targeted chemical design of new materials for electrochemical applications," the scientist added.

Tags:  Graphene  Moscow Institute of Physics and Technology  Sensors  Sergey Kislenko 

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