Tag Archives: carbon nanotubes

Carbon nanotubes as sensors in the body

Rachel Ehrenberg has written an Aug. 21, 2015 news item about the latest and greatest carbon nanotube-based biomedical sensors for the journal Nature,

The future of medical sensors may be going down the tubes. Chemists are developing tiny devices made from carbon nanotubes wrapped with polymers to detect biologically important compounds such as insulin, nitric oxide and the blood-clotting protein fibrinogen. The hope is that these sensors could simplify and automate diagnostic tests.

Preliminary experiments in mice, reported by scientists at a meeting of the American Chemical Society in Boston, Massachusetts, this week [Aug. 16 – 20, 2015], suggest that the devices are safe to introduce into the bloodstream or implant under the skin. Researchers also presented data showing that the nanotube–polymer complexes could measure levels of large molecules, a feat that has been difficult for existing technologies.

Ehrenberg focuses on one laboratory in particular (Note: Links have been removed),

“Anything the body makes, it is meant to degrade,” says chemical engineer Michael Strano, whose lab at the Massachusetts Institute of Technology (MIT) in Cambridge is behind much of the latest work1. “Our vision is to make a sensing platform that can monitor a whole range of molecules, and do it in the long term.”

To design one sensor, MIT  researchers coated nanotubes with a mix of polymers and nucleotides and screened for configurations that would bind to the protein fibrinogen. This large molecule is important for building blood clots; its concentration can indicate bleeding disorders, liver disease or impending cardiovascular trouble. The team recently hit on a material that worked — a first for such a large molecule, according to MIT nanotechnology specialist Gili Bisker. Bisker said at the chemistry meeting that the fibrinogen-detecting nanotubes could be used to measure levels of the protein in blood samples, or implanted in body tissue to detect changing fibrinogen levels that might indicate a clot.

The MIT team has also developed2 a sensor that can be inserted beneath the skin to monitor glucose or insulin levels in real time, Bisker reported. The team imagines putting a small patch that contains a wireless device on the skin just above the embedded sensor. The patch would shine light on the sensor and measure its fluorescence, then transmit that data to a mobile phone for real-time monitoring.

Another version of the sensor, developed3 at MIT by biomedical engineer Nicole Iverson and colleagues, detects nitric oxide. This signalling molecule typically indicates inflammation and is associated with many cancer cells. When embedded in a hydrogel matrix, the sensor kept working in mice for more than 400 days and caused no local inflammation, MIT chemical engineer Michael Lee reported. The nitric oxide sensors also performed well when injected into the bloodstreams of mice, successfully passing through small capillaries in the lungs, which are an area of concern for nanotube toxicity. …

There’s at least one corporate laboratory (Google X), working on biosensors although their focus is a little different. From a Jan. 9, 2015 article by Brian Womack and Anna Edney for BloombergBusiness,

Google Inc. sent employees with ties to its secretive X research group to meet with U.S. regulators who oversee medical devices, raising the possibility of a new product that may involve biosensors from the unit that developed computerized glasses.

The meeting included at least four Google workers, some of whom have connections with Google X — and have done research on sensors, including contact lenses that help wearers monitor their biological data. Google staff met with those at the Food and Drug Administration who regulate eye devices and diagnostics for heart conditions, according to the agency’s public calendar. [emphasis mine]

This approach from Google is considered noninvasive,

“There is actually one interface on the surface of the body that can literally provide us with a window of what happens inside, and that’s the surface of the eye,” Parviz [Babak Parviz, … was involved in the Google Glass project and has talked about putting displays on contact lenses, including lenses that monitor wearer’s health]  said in a video posted on YouTube. “It’s a very interesting chemical interface.”

Of course, the assumption is that all this monitoring is going to result in  healthier people but I can’t help thinking about an old saying ‘a little knowledge can be a dangerous thing’. For example, we lived in a world where bacteria roamed free and then we learned how to make them visible, determined they were disease-causing, and began campaigns for killing them off. Now, it turns out that at least some bacteria are good for us and, moreover, we’ve created other, more dangerous bacteria that are drug-resistant. Based on the bacteria example, is it possible that with these biosensors we will observe new phenomena and make similar mistakes?

Wearable technologies, electric vehicles and conundrums at Wollongong University (Australia)

A July 25, 2015 news item on Nanowerk announces research at the University of Wollongong designed to address a conundrum (Note: A link has been removed),

UOW’s Institute for Superconducting and Electronic Materials (ISEM) has successfully pioneered a way to construct a flexible, foldable and lightweight energy storage device that provides the building blocks for next-generation batteries needed to power wearable electronics and implantable medical devices (ACS Central Science, “Self-Assembled Multifunctional Hybrids: Toward Developing High-Performance Graphene-Based Architectures for Energy Storage Devices”).

The conundrum researchers have faced in developing miniature energy storage devices, such as batteries and supercapacitors, has been figuring out how to increase the surface area of the device, to store more charge, without making it larger.

A July 27, 2015 University of Wollongong news release by Grant Reynolds, which originated the news item, describes the research in more detail,

To solve this problem, a team of PhD students, led by Dr Konstantin Konstantinov under the patronage of ISEM Director Professor Shi Xue Dou and with the support of Professor Hua Kun Liu, the head of ISEM Energy Storage Division, have developed a three-dimensional structure using a flat-pack self-assembly of three components: graphene, a conductive polymer and carbon nanotubes, which are atom-thick lattice-like networks of carbon formed into cylinders.

Graphene, made from single atom-thick layers of graphite, was a suitable candidate due its electronic performance and mechanical strength.

“We knew in theory that if you can make a sort of carbon skeleton you have a greater surface area and greater surface area means more charge,” Dr Konstantinov said. “If we could efficiently separate the layers of carbon we could then use both surfaces of each layer for charge accumulation. The problem we faced was that fabricating these 3D shapes in practice, not just theory, is a challenging, if not impossible task.”

The solution was to flat-pack the components by building the 3D shape layer-by-layer, much like a miniature exercise in cake decoration. The graphene in liquid form was mixed with the conductive polymer and reduced to solid and the carbon nanotubes carefully inserted between the graphene layers to form a self-assembled flat-packed, wafer-thin supercapacitor material.

“The real challenge was how to assemble these three components into a single structure with the best use of the space available,” PhD student Monirul Islam said. “Getting the proportions or ratios of the components appropriately in order to obtain a composite material with maximum energy storage performance was another challenge.”

Wrong proportions of either ingredient result in a lumpy mess, or a 3D shape that isn’t strong enough to retain the needed flexibility as well as the charge storage ability. There’s also elegance in the simplicity of the team’s design: the researchers dispersed the components in liquid crystalline, which enabled natural chemical interactions to prevent the graphene layers clumping together.

The result was a 3D shape with, thanks to the carbon nanotubes, a massive surface area, excellent charge capacity that is also foldable. It can also be cheaply and easily fabricated without the need for expensive vacuum chambers or sophisticated equipment.

“Our graphene-based flexible composite is highly conductive, lightweight, is able to fold like a roll or stack like a paper in electronic devices to store a huge amount of charge,” Monirul said. “This material can store charge in a second and deliver the charge in superfast speed and will be more lightweight than traditional batteries used in present day’s electronics.”

The ISEM study has been financially supported by the Automotive Australia 2020 CRC as part of its research into electric vehicles. ISEM is the program leader for electrification and plays crucial role for design of next generation electric vehicles A key to unlocking the electric vehicle’s capability is a lightweight and powerful battery pack.

“Our simple fabrication method of eco-friendly materials with increased performance has great potential to be scaled up for use supercapacitor and battery technology. Our next step is to use this material to fabricate flexible wearable supercapacitors with high power density and energy density as well as large scale supercapacitors for electric vehicles.”

Here’s a link to and a citation for the paper,

Self-Assembled Multifunctional Hybrids: Toward Developing High-Performance Graphene-Based Architectures for Energy Storage Devices by Md. Monirul Islam, Seyed Hamed Aboutalebi, Dean Cardillo, Hua Kun Liu, Konstantin Konstantinov, and Shi Xue Dou. ACS Cent. Sci., 2015, 1 (4), pp 206–216 DOI: 10.1021/acscentsci.5b00189 Publication Date (Web): July 2, 2015

Copyright © 2015 American Chemical Society

This appears to be an open access paper.

Replacing metal with nanocellulose paper

The quest to find uses for nanocellulose materials has taken a step forward with some work coming from the University of Maryland (US). From a July 24, 2015 news item on Nanowerk,

Researchers at the University of Maryland recently discovered that paper made of cellulose fibers is tougher and stronger the smaller the fibers get … . For a long time, engineers have sought a material that is both strong (resistant to non-recoverable deformation) and tough (tolerant of damage).

“Strength and toughness are often exclusive to each other,” said Teng Li, associate professor of mechanical engineering at UMD. “For example, a stronger material tends to be brittle, like cast iron or diamond.”

A July 23, 2015 University of Maryland news release, which originated the news item, provides details about the thinking which buttresses this research along with some details about the research itself,

The UMD team pursued the development of a strong and tough material by exploring the mechanical properties of cellulose, the most abundant renewable bio-resource on Earth. Researchers made papers with several sizes of cellulose fibers – all too small for the eye to see – ranging in size from about 30 micrometers to 10 nanometers. The paper made of 10-nanometer-thick fibers was 40 times tougher and 130 times stronger than regular notebook paper, which is made of cellulose fibers a thousand times larger.

“These findings could lead to a new class of high performance engineering materials that are both strong and tough, a Holy Grail in materials design,” said Li.

High performance yet lightweight cellulose-based materials might one day replace conventional structural materials (i.e. metals) in applications where weight is important. This could lead, for example, to more energy efficient and “green” vehicles. In addition, team members say, transparent cellulose nanopaper may become feasible as a functional substrate in flexible electronics, resulting in paper electronics, printable solar cells and flexible displays that could radically change many aspects of daily life.

Cellulose fibers can easily form many hydrogen bonds. Once broken, the hydrogen bonds can reform on their own—giving the material a ‘self-healing’ quality. The UMD discovered that the smaller the cellulose fibers, the more hydrogen bonds per square area. This means paper made of very small fibers can both hold together better and re-form more quickly, which is the key for cellulose nanopaper to be both strong and tough.

“It is helpful to know why cellulose nanopaper is both strong and tough, especially when the underlying reason is also applicable to many other materials,” said Liangbing Hu, assistant professor of materials science at UMD.

To confirm, the researchers tried a similar experiment using carbon nanotubes that were similar in size to the cellulose fibers. The carbon nanotubes had much weaker bonds holding them together, so under tension they did not hold together as well. Paper made of carbon nanotubes is weak, though individually nanotubes are arguably the strongest material ever made.

One possible future direction for the research is the improvement of the mechanical performance of carbon nanotube paper.

“Paper made of a network of carbon nanotubes is much weaker than expected,” said Li. “Indeed, it has been a grand challenge to translate the superb properties of carbon nanotubes at nanoscale to macroscale. Our research findings shed light on a viable approach to addressing this challenge and achieving carbon nanotube paper that is both strong and tough.”

Here’s a link to and a citation for the paper,

Anomalous scaling law of strength and toughness of cellulose nanopaper by Hongli Zhu, Shuze Zhu, Zheng Jia, Sepideh Parvinian, Yuanyuan Li, Oeyvind Vaaland, Liangbing Hu, and Teng Li. PNAS (Proceedings of the National Academy of Sciences) July 21, 2015 vol. 112 no. 29 doi: 10.1073/pnas.1502870112

This paper is behind a paywall.

There is a lot of research on applications for nanocellulose, everywhere it seems, except Canada, which at one time was a leader in the business of producing cellulose nanocrystals (CNC).

Here’s a sampling of some of my most recent posts on nanocellulose,

Nanocellulose as a biosensor (July 28, 2015)

Microscopy, Paper and Fibre Research Institute (Norway), and nanocellulose (July 8, 2015)

Nanocellulose markets report released (June 5, 2015; US market research)

New US platform for nanocellulose and occupational health and safety research (June 1, 2015; Note: As you find new applications, you need to concern yourself with occupational health and safety.)

‘Green’, flexible electronics with nanocellulose materials (May 26, 2015; research from China)

Treating municipal wastewater and dirty industry byproducts with nanocellulose-based filters (Dec. 23, 2014; research from Sweden)

Nanocellulose and an intensity of structural colour (June 16, 2014; research about replacing toxic pigments with structural colour from the UK)

I ask again, where are the Canadians? If anybody has an answer, please let me know.

Crowd computing for improved nanotechnology-enabled water filtration

This research is the product of a China/Israel/Switzerland collaboration on water filtration with involvement from the UK and Australia. Here’s some general information about the importance of water and about the collaboration in a July 5, 2015 news item on Nanowerk (Note: A link has been removed),

Nearly 800 million people worldwide don’t have access to safe drinking water, and some 2.5 billion people live in precariously unsanitary conditions, according to the Centers for Disease Control and Prevention. Together, unsafe drinking water and the inadequate supply of water for hygiene purposes contribute to almost 90% of all deaths from diarrheal diseases — and effective water sanitation interventions are still challenging scientists and engineers.

A new study published in Nature Nanotechnology (“Water transport inside carbon nanotubes mediated by phonon-induced oscillating friction”) proposes a novel nanotechnology-based strategy to improve water filtration. The research project involves the minute vibrations of carbon nanotubes called “phonons,” which greatly enhance the diffusion of water through sanitation filters. The project was the joint effort of a Tsinghua University-Tel Aviv University research team and was led by Prof. Quanshui Zheng of the Tsinghua Center for Nano and Micro Mechanics and Prof. Michael Urbakh of the TAU School of Chemistry, both of the TAU-Tsinghua XIN Center, in collaboration with Prof. Francois Grey of the University of Geneva.

A July 5, 2015 American Friends of Tel Aviv University news release (also on EurekAlert), which originated the news item, provides more details about the work,

“We’ve discovered that very small vibrations help materials, whether wet or dry, slide more smoothly past each other,” said Prof. Urbakh. “Through phonon oscillations — vibrations of water-carrying nanotubes — water transport can be enhanced, and sanitation and desalination improved. Water filtration systems require a lot of energy due to friction at the nano-level. With these oscillations, however, we witnessed three times the efficiency of water transport, and, of course, a great deal of energy saved.”

The research team managed to demonstrate how, under the right conditions, such vibrations produce a 300% improvement in the rate of water diffusion by using computers to simulate the flow of water molecules flowing through nanotubes. The results have important implications for desalination processes and energy conservation, e.g. improving the energy efficiency for desalination using reverse osmosis membranes with pores at the nanoscale level, or energy conservation, e.g. membranes with boron nitride nanotubes.

Crowdsourcing the solution

The project, initiated by IBM’s World Community Grid, was an experiment in crowdsourced computing — carried out by over 150,000 volunteers who contributed their own computing power to the research.

“Our project won the privilege of using IBM’s world community grid, an open platform of users from all around the world, to run our program and obtain precise results,” said Prof. Urbakh. “This was the first project of this kind in Israel, and we could never have managed with just four students in the lab. We would have required the equivalent of nearly 40,000 years of processing power on a single computer. Instead we had the benefit of some 150,000 computing volunteers from all around the world, who downloaded and ran the project on their laptops and desktop computers.

“Crowdsourced computing is playing an increasingly major role in scientific breakthroughs,” Prof. Urbakh continued. “As our research shows, the range of questions that can benefit from public participation is growing all the time.”

The computer simulations were designed by Ming Ma, who graduated from Tsinghua University and is doing his postdoctoral research in Prof. Urbakh’s group at TAU. Ming catalyzed the international collaboration. “The students from Tsinghua are remarkable. The project represents the very positive cooperation between the two universities, which is taking place at XIN and because of XIN,” said Prof. Urbakh.

Other partners in this international project include researchers at the London Centre for Nanotechnology of University College London; the University of Geneva; the University of Sydney and Monash University in Australia; and the Xi’an Jiaotong University in China. The researchers are currently in discussions with companies interested in harnessing the oscillation knowhow for various commercial projects.

 

Here’s a link to and a citation for the paper,

Water transport inside carbon nanotubes mediated by phonon-induced oscillating friction by Ming Ma, François Grey, Luming Shen, Michael Urbakh, Shuai Wu,    Jefferson Zhe Liu, Yilun Liu, & Quanshui Zheng. Nature Nanotechnology (2015) doi:10.1038/nnano.2015.134 Published online 06 July 2015

This paper is behind a paywall.

Final comment, I find it surprising that they used labour and computing power from 150,000 volunteers and didn’t offer open access to the paper. Perhaps the volunteers got their own copy? I certainly hope so.

Tiny, electrically conductive 3D-printed chair made from cellulose

Sweden’s Chalmers University of Technology researchers have just announced that they’ve printed a very small 3D chair with electrical properties using cellulose nanomaterials. From a June 17, 2015 news item on Nanowerk,

A group of researchers at Chalmers University of Technology have managed to print and dry three-dimensional objects made entirely by cellulose for the first time with the help of a 3D-bioprinter. They also added carbon nanotubes to create electrically conductive material. The effect is that cellulose and other raw material based on wood will be able to compete with fossil-based plastics and metals in the on-going additive manufacturing revolution, which started with the introduction of the 3D-printer.

Here’s the 3D-printed chair,

The tiny chair made of cellulose is a demonstrational object, printed using the 3D bioprinter at Chalmers University of Technology. Photo: Peter Widing

The tiny chair made of cellulose is a demonstrational object, printed using the 3D bioprinter at Chalmers University of Technology. Photo: Peter Widing

A June 17, 2015 Chalmers University of Technology press release (also on EurekAlert*), which originated the news item, describes the problem with printing from cellulose nanomaterials and how it was solved,

The difficulty using cellulose in additive manufacturing is that cellulose does not melt when heated. Therefore, the 3D printers and processes designed for printing plastics and metals cannot be used for materials like cellulose. The Chalmers researchers solved this problem by mixing cellulose nanofibrils in a hydrogel consisting of 95-99 percent water. The gel could then in turn be dispensed with high fidelity into the researchers’ 3D bioprinter, which was earlier used to produce scaffolds for growing cells, where the end application is patient-specific implants.

The next challenge was to dry the printed gel-like objects without them losing their three-dimensional shape.

“The drying process is critical,” Paul Gatenholm explains. “We have developed a process in which we freeze the objects and remove the water by different means as to control the shape of the dry objects. It is also possible to let the structure collapse in one direction, creating thin films.”

Furthermore, the cellulose gel was mixed with carbon nanotubes to create electrically conductive ink after drying. Carbon nanotubes conduct electricity, and another project at Wallenberg Wood Science Center aims at developing carbon nanotubes using wood.

Using the two gels together, one conductive and one non-conductive, and controlling the drying process, the researchers produced three-dimensional circuits, where the resolution increased significantly upon drying.

The two gels together provide a basis for the possible development of a wide range of products made by cellulose with in-built electric currents.

“Potential applications range from sensors integrated with packaging, to textiles that convert body heat to electricity, and wound dressings that can communicate with healthcare workers,” says Paul Gatenholm. “Our research group now moves on with the next challenge, to use all wood biopolymers, besides cellulose.”

The research findings are presented this week at the conference New Materials From Trees that takes place in Stockholm, Sweden, June 15-17 [2015].

The research team members are Ida Henriksson, Cristina de la Pena, Karl Håkansson, Volodymyr Kuzmenko and Paul Gatenholm at Chalmers University of Technology.

This research reminds me of another effort, a computer chip fashioned of cellulose nanofibrils (CNF) from the University of Wisconsin-Madison (mentioned in my May 27, 2015 post).

* EurekAlert link added June 18, 2015.

Improving battery electrodes and air filters with a ‘transistorized’ carbon nanotube for more precise measurements

Researchers at the University of Washington (state) have been able to use carbon nanotubes to make the most precise measurements yet of the interactions between gas and carbon atoms. From a May 28, 2015 news item on Nanotechnology Now,

Physicists at the University of Washington have conducted the most precise and controlled measurements yet of the interaction between the atoms and molecules that comprise air and the type of carbon surface used in battery electrodes and air filters — key information for improving those technologies.

A May 28, 2015 University of Washington news release (also on EurekAlert), which originated the news item, describes the work in more detail,

A team led by David Cobden, UW professor of physics, used a carbon nanotube — a seamless, hollow graphite structure a million times thinner than a drinking straw — acting as a transistor to study what happens when gas atoms come into contact with the nanotube’s surface. …

Cobden said he and co-authors found that when an atom or molecule sticks to the nanotube a tiny fraction of the charge of one electron is transferred to its surface, resulting in a measurable change in electrical resistance.

“This aspect of atoms interacting with surfaces has never been detected unambiguously before,” Cobden said. “When many atoms are stuck to the miniscule tube at the same time, the measurements reveal their collective dances, including big fluctuations that occur on warming analogous to the boiling of water.”

Lithium batteries involve lithium atoms sticking and transferring charges to carbon electrodes, and in activated charcoal filters, molecules stick to the carbon surface to be removed, Cobden explained.

“Various forms of carbon, including nanotubes, are considered for hydrogen or other fuel storage because they have a huge internal surface area for the fuel molecules to stick to. However, these technological situations are extremely complex and difficult to do precise, clear-cut measurements on.”

This work, he said, resulted in the most precise and controlled measurements of these interactions ever made, “and will allow scientists to learn new things about the interplay of atoms and molecules with a carbon surface,” important for improving technologies including batteries, electrodes and air filters.

Here’s an illustration of gas atoms adhering to a carbon nanotube provided by the researchers,

An illustration of atoms sticking to a carbon nanotube, affecting the electrons in its surface.David Cobden and students Courtesy: University of Washington (state)

An illustration of atoms sticking to a carbon nanotube, affecting the electrons in its surface.David Cobden and students Courtesy: University of Washington (state)

Here’s a link to and a citation for the paper,

Surface electron perturbations and the collective behaviour of atoms adsorbed on a cylinder by Boris Dzyubenko, Hao-Chun Lee, Oscar E. Vilches, & David H. Cobden. Nature Physics 11, 398–402 (2015) doi:10.1038/nphys3302 Published online 20 April 2015

This paper is behind a paywall but a free preview is available via ReadCube Access.

An efficient method for signal transmission from nanocomponents

A May 23, 2015 news item on Nanotechnology Now describes research into perfecting the use of nanocomponents in electronic circuits,

Physicists have developed an innovative method that could enable the efficient use of nanocomponents in electronic circuits. To achieve this, they have developed a layout in which a nanocomponent is connected to two electrical conductors, which uncouple the electrical signal in a highly efficient manner. The scientists at the Department of Physics and the Swiss Nanoscience Institute at the University of Basel have published their results in the scientific journal Nature Communications together with their colleagues from ETH Zurich.

A May 22, 2015 University of Basel press release (also on EurkeAlert) describes why there is interest in smaller components and some of the challenges once electrodes can be measured in atoms,

Electronic components are becoming smaller and smaller. Components measuring just a few nanometers – the size of around ten atoms – are already being produced in research laboratories. Thanks to miniaturization, numerous electronic components can be placed in restricted spaces, which will boost the performance of electronics even further in the future.

Teams of scientists around the world are investigating how to produce such nanocomponents with the aid of carbon nanotubes. These tubes have unique properties – they offer excellent heat conduction, can withstand strong currents, and are suitable for use as conductors or semiconductors. However, signal transmission between a carbon nanotube and a significantly larger electrical conductor remains problematic as large portions of the electrical signal are lost due to the reflection of part of the signal.

Antireflex increases efficiency

A similar problem occurs with light sources inside a glass object. A large amount of light is reflected by the walls, which means that only a small proportion reaches the outside. This can be countered by using an antireflex coating on the walls.

The press release goes on to describe new technique for addressing the issue,

Led by Professor Christian Schönenberger, scientists in Basel are now taking a similar approach to nanoelectronics. They have developed an antireflex device for electrical signals to reduce the reflection that occurs during transmission from nanocomponents to larger circuits. To do so, they created a special formation of electrical conductors of a certain length, which are coupled with a carbon nanotube. The researchers were therefore able to efficiently uncouple a high-frequency signal from the nanocomponent.

Differences in impedance cause the problem

Coupling nanostructures with significantly larger conductors proved difficult because they have very different impedances. The greater the difference in impedance between two conducting structures, the greater the loss during transmission. The difference between nanocomponents and macroscopic conductors is so great that no signal will be transmitted unless countermeasures are taken. The antireflex device minimizes this effect and adjusts the impedances, leading to efficient coupling. This brings the scientists significantly closer to their goal of using nanocomponents to transmit signals in electronic parts.

Here’s a link to and a citation for the paper,

Clean carbon nanotubes coupled to superconducting impedance-matching circuits by V. Ranjan, G. Puebla-Hellmann, M. Jung, T. Hasler, A. Nunnenkamp, M. Muoth, C. Hierold, A. Wallraff, & C. Schönenberger. Nature Communications 6, Article number: 7165 doi:10.1038/ncomms8165 Published 15 May 2015

This paper is behind a paywall.

Carbon nanotubes sense spoiled food

CNT_FoodSpolage

Courtesy: MIT (Massachusetts Institute of Technology)

I love this .gif; it says a lot without a word. However for details, you need words and here’s what an April 15, 2015 news item on Nanowerk has to say about the research illustrated by the .gif,

MIT [Massachusetts Institute of Technology] chemists have devised an inexpensive, portable sensor that can detect gases emitted by rotting meat, allowing consumers to determine whether the meat in their grocery store or refrigerator is safe to eat.

The sensor, which consists of chemically modified carbon nanotubes, could be deployed in “smart packaging” that would offer much more accurate safety information than the expiration date on the package, says Timothy Swager, the John D. MacArthur Professor of Chemistry at MIT.

An April 14, 2015 MIT news release (also on EurekAlert), which originated the news item, offers more from Dr. Swager,

It could also cut down on food waste, he adds. “People are constantly throwing things out that probably aren’t bad,” says Swager, who is the senior author of a paper describing the new sensor this week in the journal Angewandte Chemie.

This latest study is builds on previous work at Swager’s lab (Note: Links have been removed),

The sensor is similar to other carbon nanotube devices that Swager’s lab has developed in recent years, including one that detects the ripeness of fruit. All of these devices work on the same principle: Carbon nanotubes can be chemically modified so that their ability to carry an electric current changes in the presence of a particular gas.

In this case, the researchers modified the carbon nanotubes with metal-containing compounds called metalloporphyrins, which contain a central metal atom bound to several nitrogen-containing rings. Hemoglobin, which carries oxygen in the blood, is a metalloporphyrin with iron as the central atom.

For this sensor, the researchers used a metalloporphyrin with cobalt at its center. Metalloporphyrins are very good at binding to nitrogen-containing compounds called amines. Of particular interest to the researchers were the so-called biogenic amines, such as putrescine and cadaverine, which are produced by decaying meat.

When the cobalt-containing porphyrin binds to any of these amines, it increases the electrical resistance of the carbon nanotube, which can be easily measured.

“We use these porphyrins to fabricate a very simple device where we apply a potential across the device and then monitor the current. When the device encounters amines, which are markers of decaying meat, the current of the device will become lower,” Liu says.

In this study, the researchers tested the sensor on four types of meat: pork, chicken, cod, and salmon. They found that when refrigerated, all four types stayed fresh over four days. Left unrefrigerated, the samples all decayed, but at varying rates.

There are other sensors that can detect the signs of decaying meat, but they are usually large and expensive instruments that require expertise to operate. “The advantage we have is these are the cheapest, smallest, easiest-to-manufacture sensors,” Swager says.

“There are several potential advantages in having an inexpensive sensor for measuring, in real time, the freshness of meat and fish products, including preventing foodborne illness, increasing overall customer satisfaction, and reducing food waste at grocery stores and in consumers’ homes,” says Roberto Forloni, a senior science fellow at Sealed Air, a major supplier of food packaging, who was not part of the research team.

The new device also requires very little power and could be incorporated into a wireless platform Swager’s lab recently developed that allows a regular smartphone to read output from carbon nanotube sensors such as this one.

The funding sources are interesting, as I am appreciating with increasing frequency these days (from the news release),

The researchers have filed for a patent on the technology and hope to license it for commercial development. The research was funded by the National Science Foundation and the Army Research Office through MIT’s Institute for Soldier Nanotechnologies.

Here’s a link to and a citation for the paper,

Single-Walled Carbon Nanotube/Metalloporphyrin Composites for the Chemiresistive Detection of Amines and Meat Spoilage by Sophie F. Liu, Alexander R. Petty, Dr. Graham T. Sazama, and Timothy M. Swager. Angewandte Chemie International Edition DOI: 10.1002/anie.201501434 Article first published online: 13 APR 2015

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This article is behind a paywall.

There are other posts here about the quest to create food sensors including this Sept. 26, 2013 piece which features a critique (by another blogger) about trying to create food sensors that may be more expensive than the item they are protecting, a problem Swager claims to have overcome in an April 17, 2015 article by Ben Schiller for Fast Company (Note: Links have been removed),

Swager has set up a company to commercialize the technology and he expects to do the first demonstrations to interested clients this summer. The first applications are likely to be for food workers working with meat and fish, but there’s no reason why consumers shouldn’t get their own devices in due time.

There are efforts to create visual clues for food status. But Swager says his method is better because it doesn’t rely on perception: it produces hard data that can be logged and tracked. And it also has potential to be very cheap.

“The resistance method is a game-changer because it’s two to three orders of magnitude cheaper than other technology. It’s hard to imagine doing this cheaper,” he says.

Taking the baking out of aircraft manufacture

It seems that ovens are an essential piece of equipment when manufacturing aircraft parts but that may change if research from MIT (Massachusetts Institute of Technology) proves successful. An April 14, 2015 news item on ScienceDaily describes the current process and the MIT research,

Composite materials used in aircraft wings and fuselages are typically manufactured in large, industrial-sized ovens: Multiple polymer layers are blasted with temperatures up to 750 degrees Fahrenheit, and solidified to form a solid, resilient material. Using this approach, considerable energy is required first to heat the oven, then the gas around it, and finally the actual composite.

Aerospace engineers at MIT have now developed a carbon nanotube (CNT) film that can heat and solidify a composite without the need for massive ovens. When connected to an electrical power source, and wrapped over a multilayer polymer composite, the heated film stimulates the polymer to solidify.

The group tested the film on a common carbon-fiber material used in aircraft components, and found that the film created a composite as strong as that manufactured in conventional ovens — while using only 1 percent of the energy.

The new “out-of-oven” approach may offer a more direct, energy-saving method for manufacturing virtually any industrial composite, says Brian L. Wardle, an associate professor of aeronautics and astronautics at MIT.

“Typically, if you’re going to cook a fuselage for an Airbus A350 or Boeing 787, you’ve got about a four-story oven that’s tens of millions of dollars in infrastructure that you don’t need,” Wardle says. “Our technique puts the heat where it is needed, in direct contact with the part being assembled. Think of it as a self-heating pizza. … Instead of an oven, you just plug the pizza into the wall and it cooks itself.”

Wardle says the carbon nanotube film is also incredibly lightweight: After it has fused the underlying polymer layers, the film itself — a fraction of a human hair’s diameter — meshes with the composite, adding negligible weight.

An April 14, 2015 MIT news release, which originated the news item, describes the origins of the team’s latest research, the findings, and the implications,

Carbon nanotube deicers

Wardle and his colleagues have experimented with CNT films in recent years, mainly for deicing airplane wings. The team recognized that in addition to their negligible weight, carbon nanotubes heat efficiently when exposed to an electric current.

The group first developed a technique to create a film of aligned carbon nanotubes composed of tiny tubes of crystalline carbon, standing upright like trees in a forest. The researchers used a rod to roll the “forest” flat, creating a dense film of aligned carbon nanotubes.

In experiments, Wardle and his team integrated the film into airplane wings via conventional, oven-based curing methods, showing that when voltage was applied, the film generated heat, preventing ice from forming.

The deicing tests inspired a question: If the CNT film could generate heat, why not use it to make the composite itself?

How hot can you go?

In initial experiments, the researchers investigated the film’s potential to fuse two types of aerospace-grade composite typically used in aircraft wings and fuselages. Normally the material, composed of about 16 layers, is solidified, or cross-linked, in a high-temperature industrial oven.

The researchers manufactured a CNT film about the size of a Post-It note, and placed the film over a square of Cycom 5320-1. They connected electrodes to the film, then applied a current to heat both the film and the underlying polymer in the Cycom composite layers.

The team measured the energy required to solidify, or cross-link, the polymer and carbon fiber layers, finding that the CNT film used one-hundredth the electricity required for traditional oven-based methods to cure the composite. Both methods generated composites with similar properties, such as cross-linking density.

Wardle says the results pushed the group to test the CNT film further: As different composites require different temperatures in order to fuse, the researchers looked to see whether the CNT film could, quite literally, take the heat.

“At some point, heaters fry out,” Wardle says. “They oxidize, or have different ways in which they fail. What we wanted to see was how hot could this material go.”

To do this, the group tested the film’s ability to generate higher and higher temperatures, and found it topped out at over 1,000 F. In comparison, some of the highest-temperature aerospace polymers require temperatures up to 750 F in order to solidify.

“We can process at those temperatures, which means there’s no composite we can’t process,” Wardle says. “This really opens up all polymeric materials to this technology.”

The team is working with industrial partners to find ways to scale up the technology to manufacture composites large enough to make airplane fuselages and wings.

“There needs to be some thought given to electroding, and how you’re going to actually make the electrical contact efficiently over very large areas,” Wardle says. “You’d need much less power than you are currently putting into your oven. I don’t think it’s a challenge, but it has to be done.”

Gregory Odegard, a professor of computational mechanics at Michigan Technological University, says the group’s carbon nanotube film may go toward improving the quality and efficiency of fabrication processes for large composites, such as wings on commercial aircraft. The new technique may also open the door to smaller firms that lack access to large industrial ovens.

“Smaller companies that want to fabricate composite parts may be able to do so without investing in large ovens or outsourcing,” says Odegard, who was not involved in the research. “This could lead to more innovation in the composites sector, and perhaps improvements in the performance and usage of composite materials.”

It can be interesting to find out who funds the research (from the news release),

This research was funded in part by Airbus Group, Boeing, Embraer, Lockheed Martin, Saab AB, TohoTenax, ANSYS Inc., the Air Force Research Laboratory at Wright-Patterson Air Force Base, and the U.S. Army Research Office.

Here’s a link to and citation for the research paper,

Impact of carbon nanotube length on electron transport in aligned carbon nanotube networks by Jeonyoon Lee, Itai Y. Stein, Mackenzie E. Devoe, Diana J. Lewis, Noa Lachman, Seth S. Kessler, Samuel T. Buschhorn, and Brian L. Wardle. Appl. Phys. Lett. 106, 053110 (2015); http://dx.doi.org/10.1063/1.4907608

This paper is behind a paywall.

Nanobionic plant materials

This is a bioinspired story with a bit of a twist. From a March 30, 2015 news item on Nanowerk (Note: A link has been removed),

Humans have been inspired by nature since the beginning of time. We mimic nature to develop new technologies, with examples ranging from machinery to pharmaceuticals to new materials. Planes are modelled on birds and many drugs have their origins in plants. Researchers at the Department of Mechanical and Process Engineering [ETH Zurich; Swiss Federal Institute of Technology] have taken it a step further: in order to develop an extremely sensitive temperature sensor they took a close look at temperature-sensitive plants. However, they did not mimic the properties of the plants; instead, they developed a hybrid material that contains, in addition to synthetic components, the plant cells themselves (“Plant nanobionic materials with a giant temperature response mediated by pectin-Ca2+”). [emphasis mine] “We let nature do the job for us,” explains Chiara Daraio, Professor of Mechanics and Materials.

The scientists were able to develop by far the most sensitive temperature sensor: an electronic module that changes its conductivity as a function of temperature. “No other sensor can respond to such small temperature fluctuations with such large changes in conductivity. Our sensor reacts with a responsivity at least 100 times higher compared to the best existing sensors,” says Raffaele Di Giacomo, a post-doc in Daraio’s group.

The scientists have provided an illustration of their concept using a tobacco leaf as the backdrop,

ETH scientists used cells form the tobacco plant to build the by far most sensitive temperature sensor. (Illustration: Daniele Flo / ETH Zurich)

ETH scientists used cells form the tobacco plant to build the by far most sensitive temperature sensor. (Illustration: Daniele Flo / ETH Zurich)

A March 31, 2015 ETH Zurich press release, which despite the release date originated the news item, describes the concept in more detail,

It has been known for decades that plants have the extraordinary ability to register extremely fine temperature differences and respond to them through changes in the conductivity of their cells. In doing so, plants are better than any man-made sensor so far.

Di Giacomo experimented with tobacco cells in a cell culture. “We asked ourselves how we might transfer these cells into a lifeless, dry material in such a way that their temperature-sensitive properties are preserved,” he recounts. The scientists achieved their objective by growing the cells in a medium containing tiny tubes of carbon. These electrically conductive carbon nanotubes formed a network between the tobacco cells and were also able to penetrate the cell walls. When Di Giacomo dried the nanotube-cultivated cells, he discovered a woody, firm material that he calls ‘cyberwood’. In contrast to wood, this material is electrically conductive thanks to the nanotubes, and interestingly the conductivity is temperature-dependent and extremely sensitive, just like in living tobacco cells.

The scientists considered  the new material’s (cyberwood) properties and possible future applications (from the news release),

As demonstrated by experiments, the cyberwood sensor can identify warm bodies even at distance; for example, a hand approaching the sensor from a distance of a few dozen centimetres. The sensor’s conductivity depends directly on the hand’s distance from the sensor.

According to the scientists, cyberwood could be used in a wide range of applications; for instance, in the development of a ‘touchless touchscreen’ that reacts to gestures, with the gestures recorded by multiple sensors. Equally conceivable might be heat-sensitive cameras or night-vision devices.

The Swiss researchers along with a collaborator at the University of Salerno (Italy) did further research into the origins of the material’s behaviour (from the news release),

The ETH scientists, together with a collaborator at the University of Salerno, Italy, not only subjected their new material’s properties to a detailed examination, they also analysed the origins of their extraordinary behaviour. They discovered that pectins and charged atoms (ions) play a key role in the temperature sensitivity of both living plant cells and the dry cyberwood. Pectins are sugar molecules found in plant cell walls that can be cross-linked, depending on temperature, to form a gel. Calcium and magnesium ions are both present in this gel. “As the temperature rises, the links of the pectin break apart, the gel becomes softer, and the ions can move about more freely,” explains Di Giacomo. As a result, the material conducts electricity better when temperature increases.

The news release goes on to mention a patent and future plans,

The scientists submitted a patent application for their sensor. In ongoing work, they are now further developing it such that it functions without plant cells, essentially with only pectin and ions. Their goal is to create a flexible, transparent and even biocompatible sensor with the same ultrahigh temperature sensitivity. Such a sensor could be moulded into arbitrary shapes and produced at extremely low cost. This will open the door to new applications for thermal sensors in biomedical devices, consumer products and low cost thermal cameras.

Here’s a link to and a citation for the paper,

Plant nanobionic materials with a giant temperature response mediated by pectin-Ca2+ by Raffaele Di Giacomo, Chiara Daraio, and Bruno Maresca. Published online before print March 30, 2015, doi: 10.1073/pnas.1421020112 PNAS March 30, 2015

This paper is behind a paywall.