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An illustration shows the basic nanowire building block.

Self-Assembly Process Strikes Perfect Balance for Making Atoms-Wide Nanowires

A team of researchers from Stanford University and the US Department of Energy’s SLAC National Accelerator Laboratory have developed a self-assembly process that uses diamondoids to create nanowires with a solid, 3-atom wide copper-sulfur crystalline core—the smallest possible.

The resulting nanowires possess superior electrical properties due to the lack of defects present in the solid crystalline core. Perhaps more impotantly, the self-assembly process for making the nanowires could lead to new kinds of optoelectronic devices and superconducting materials.

“Achieving a 'solid core' of a three atom cross section is ideal,” says Nicholas Melosh, an associate professor at SLAC and Stanford, in an e-mail interview with IEEE Spectrum. “It’s small enough to exhibit unique functionality, yet it can tolerate single defects or strains since there is still a pathway for the electrons to flow.”

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CNT-enabled carbon fiber composites offers a new age of unheard of functionalities

Carbon Nanotubes Make Aerospace Composites Conductive

We have all been witness to the proliferation of carbon fiber adding lightweight strength to sporting goods like bicycles and tennis racquets. That application of carbon fiber reinforced polymers (CFRPs) has been no more popular than in the aerospace industry, where every gram counts. 

What many of us may not have understood about CFRPs is something called “polymer sizing.” This is a coating that is applied to the surface of the carbon fibers to make them easier to handle and to improve the adhesion between the fibers and the polymer matrix in which they’re embedded.

Now researchers at the University of Surrey’s Advanced Technology Institute (ATI), the University of Bristol’s Advanced Composite Centre for Innovation and Science (ACCIS), and aerospace company Bombardier have collaborated on the development of a carbon nanotube–enabled material set to replace the polymer sizing.  The reinforced polymers produced with this new material have enhanced electrical and thermal conductivity, opening up new functional possibilities. It will be possible, say the British researchers, to embed gadgets such as sensors and energy harvesters directly into the material.

In research described in the journal Scientific Reports, the researchers were able to grow the carbon nanotubes (CNTs) on the carbon fibers in a chemical vapor deposition (CVD) process.

Professor Ravi Silva, Director of ATI and head of the University of Surrey’s Nanoelectronics Centre (NEC), told IEEE Spectrum: 

We addressed a current challenge with chemical vapor deposition–grown carbon nanotubes on carbon fiber, by utilizing a metallic interlayer, which we have shown in previous work by our group to minimize degradation to the underlying substrate...The low temperature photo-thermal CVD (PT-CVD) growth process we have adopted is highly suited for large area, high quality carbon nanotube growth on temperature sensitive substrates. This means that the substrates do not degrade in the growth of CNT.

While this work does not represent the first time carbon nanotubes have been incorporated into polymer composites, this work does stake claim to being the first to replace polymer sizing.

Silva notes that, even without a polymer sizing layer, the nanotubes improved the mechanical integrity of the carbon fiber fabric. This was remarkable, he says, because carbon fibers without sizing are inherently difficult to manipulate and make process of incorporating them into a composite difficult.

Silva also pointed out that the incorporation of nanotubes within the carbon fiber polymers did not result in high void fractions, and therefore maintained the sheets’ mechanical integrity.

What’s more, the carbon nanotube–modified fiber composites could have electronic gadgets baked right into their structures or be endowed  with self-healing capabilities.

The collaborators in this research, who have jointly protected the intellectual property, say the next challenge for them is to scale the technology for production using a roll-to-roll system.

Silva added: “We have in mind the optimization of growth of CNTs for composite applications, the scale up of the technology and the optimization for the various applications. We are looking to progress the technology in a number of different fields and will be happy to work with partners in agreed fields of research.”

The chip is tested in the lab. The electrodes detect electrical changes that occur when the cancer cells are captured.

Carbon Nanotubes Make New Approach to Microfluidics More Effective

Circulating tumor cells (CTC) are key early indicators of metastasis, which is the process by which cancer cells move from one organ group in the body to another. Once cancer spreads, the prognosis is generally not good. So, early identification of CTCs can help prevent them from creating new colonies of malignant cells.

Researchers at Worcester Polytechnic Institute (WPI) in Massachusetts have developed a new approach to microfluidics to detect CTCs in blood. The WPI researchers believe that their technique could form the basis of a simple lab test for quick detection of early signs of metastasis and help physicians select treatments targeted at the specific cancer cells identified.

Current microfluidic techniques used in tumor cell isolation have been dependent on flow rate and require off-chip post-processing. The WPI researchers’ technique employs static isolation of tumor cells from the blood by fractionation of the blood into small droplets.

In research described in the journal Nanotechnology, the WPI researchers were able to create a chip design in which antibodies are attached to an array of carbon nanotubes at the bottom of a tiny well in the chip. The chips have an array of these tiny wells, each about three millimeters across.

When the blood droplets are put into the well, the heavier cancer cells drop to the bottom where they become attached to the antibodies.  Each of the wells holds a specific antibody that will bind to one type of cancer cell. The chip’s electrodes detect electrical changes that occur when the cancer cells are captured by the antibodies.

Using an array of antibodies makes it possible to identify several different types of cancer cells within a single blood sample. To put that in perspective, the researchers could fill 170 wells with just 0.85 millileter of blood. The chips were able to capture between one and a thousand cells per device, equating to an efficiency of between 62 and 100 percent.

You can see a video that offers a demonstration of how the chip works below.

The advantages of this technique over traditional microfluidic methods are numerous and significant. But let’s just focus on the advantages derived from the use of carbon nanotubes.

First, the nanotube-based microarrays include both detection and capture technology, unlike traditional microfluidics, which only capture. Second, the nanotube microarray allows for a wide variety of antibodies so that it can attract and identify different types of cells that may need to be fought in different ways.

Another one of the advantages of this approach over other microfluidics is that it can capture exosomes, which are produced by cancer cells and carry the same markers.

“These highly elusive 3-nanometer structures are too small to be captured with other types of liquid biopsy devices, such as microfluidics, due to shear forces that can potentially destroy them,” said Balaji Panchapakesan, associate professor of mechanical engineering at WPI and director of the Small Systems Laboratory, in a press release. “Our chip is currently the only device that can potentially capture circulating tumor cells and exosomes directly on the chip, which should increase its ability to detect metastasis.”  Panchapakesan adds that this is important because research is showing that tiny proteins excreted with exosomes can actually suppress cancer drug delivery and hinder treatment.

Panchapakesan believes the technology is ready for commercialization, but his team just needs more data on patients (delineated by stage of cancer) to move the technology along further in its development.

In an e-mail interview with IEEE Spectrum, Panchapakesan added: “If there is any equipment that needs to be developed more, [it’ll probably be] the automation and robotic handling of the entire system from drop deposition to microscopy. But really we just need patients, patients, patients.”

ultrafast black phosphorous switch

Black Phosphorus Enables Plasmonic Logic

Much research has been dedicated to exploiting the waves and oscillations of electrons that are produced on the surface of a metallic structure when photons of light strike it. These waves of electrons are called either surface plasmons when referring to the oscillations in charge alone, or surface plasmon polaritons when referring to both the charge oscillations and the electromagnetic wave. The field developed around exploiting this phenomenon has become known as plasmonics.

Plasmonics has made all sorts of interesting things possible, such as confining wavelengths of light to design smaller photonic devices. However, there has been no good way to turn the waves “on” and “off” rapidly.

Now researchers at the University of Regensburg in Germany, in collaboration with colleagues from Istituto Nanoscienze–CNR and Scuola Normale Superiore in Pisa, Italy, have demonstrated the ability to selectively choose between an “on” state, where surface polaritons can be excited and propagate across the sample, and an “off” state, where no polaritons are present.

So what is the trick to achieving these “on/off” states? Don’t use a metal at all. Instead, employ the two-dimensional material du jour: black phosphorus.

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Graphene and silly putty make for a strain sensor

Graphene and Silly Putty Creates a Super-Sensitive Strain Sensor

For all the talk and research that has gone into exploiting graphene’s pliant properties for use in wearable and flexible electronics, most of the polymer composites it has been mixed with to date have been on the hard and inflexible side.

It took a team of researchers in Ireland to combine graphene with the children’s toy Silly Putty to set the nanomaterial community ablaze with excitement. The combination makes a new composite that promises to make a super-sensitive strain sensor with potential medical diagnostic applications.

In research described in the journal Science, scientists at AMBER, the Science Foundation Ireland-funded materials science research center based at Trinity College Dublin, discovered that if you added nanosheets into a low-viscosity material like silly putty, its electromechanical properties dramatically changed. You suddenly have an extremely sensitive strain sensor.

When you apply a voltage to the graphene-infused silly putty, the slightest touch results in a very large change in the current. Voila a strain sensor. 

“If you take the silly putty and stretch it just by one percent, then the current would change by a factor of five: that’s a very small mechanical change with a very big electrical change,” says Jonathan Coleman, the professor at Trinity College Dublin, who led the research.

In tests with the graphene-enabled putty, the researchers placed the composite onto the people’s chests and necks to measure breathing, pulse, and blood pressure. The results demonstrated an unprecedented sensitivity for a strain and pressure sensor, hundreds of times more sensitive than other sensors.

“What we found is that when you put graphene in extremely soft polymers like this, they act as strain sensors that are light years ahead of anything that had been created before,” says Coleman. “And this is intimately linked with the fact that these polymers are so soft.”

What is surprising about this line of research is that there has been so few investigations previously looking at combining graphene with a low-viscosity polymer. Graphene has been put in many different polymers to make composites,  but the vast majority of those polymers are at the harder end of the spectrum. This practice is typically driven by the aim of adding graphene to a strong, hard polymer to make it even stronger and harder.

While there has been some work in putting graphene into soft polymers, no one has put graphene into polymers anywhere near as soft as silly putty. The softest polymer that people had put graphene in previously would be something like rubber, according to Coleman.

Just as there has been a lot of work into adding graphene to polymers, the use of graphene to make a polymer a strain sensor has some history as well. But no one was quite expecting that these softer materials would enhance the effect so profoundly.

“We knew that there had been very little work done in this area,” said Coleman.  “But I have to be completely honest, we didn’t know that the material would have the interesting properties that we saw in the end result.”

While Coleman believes that there is a wide range of medical sensing applications for the material, by far the most clear-cut and important example would be the continuous measurement of pulse and blood pressure.

“We can measure pulse in a relatively straightforward way,” he says. “There are a number of ways to do it. But we can measure blood pressure simply, cheaply and continuously.”

You can see a demonstration of this blood pressure monitoring in the video below:

Coleman is pretty confident that the path to commercialization for this technology is pretty clear with no major obstacles in sight.

“First of all you would have to have a commercial supply of the material; I don’t see that as challenging,” said Coleman. “There are many commercial suppliers of graphene that can produce graphene in large quantities. And, of course, silly putty is commercially available. The procedure of mixing the two components together is fairly straightforward and that could certainly be industrialized. So making the material is not a problem.”

Engineering the sensing device would be a bit more of a challenge. Coleman explains that you would have to make some kind of housing that could be worn on the wrist and would have the sensing material inside of it. Then you would need the electronics to generate the current and measure the changes in it. You would also need some kind of communication system that would send the signal to a mobile phone where you would need an app to collect and analyze the data.

“To be completely honest, all of that stuff is not that far from being off-the-shelf,” he says. “I don’t think there is a great engineering challenge in this work. So really we are actually quite close to the ability to commercialize this material.”

While the strain sensor that Coleman and his colleagues have developed is sensitive, he believes that this research opens up an entirely new way of making composites that will lead to far more sensitive sensing technologies in the future.

“What we really want to do is to go on to the next generation of sensing,” he says. “We have extremely sensitive materials here, but we see an opportunity to make composites in a different way using different polymers that are up to a factor of ten more sensitive than the ones we have created here.”

he researchers’ machine uses a “nanoporous” stamp through which a solution of nanoparticles, or “ink,” can flow uniformly through the stamp and onto whatever surface is to be printed.

Forest of Carbon Nanotubes Stamps Electronic Ink Onto a Surface

About a dozen years ago, I wrote a report on the future of nanomaterials in printing and packaging.  I think copies of it may exist today only on my bookshelf, but it has served over that time to inform my opinion on how nanomaterials can be applied to these areas—most recently contributing to piece on these pages a few years back.  The basic question: How do you get a nanomaterial onto some packaging cheaply enough that it makes sense for what is essentially a throwaway item?

It has not been easy. But MIT researchers believe they have hit upon a low-cost, robust stamping method that manages to get carbon nanotubes onto a flexible surface so that they can serve as a transistor for controlling individual pixels in high-resolution displays.

In research described in the journal Science Advances, the technique developed for getting the carbon nanotubes onto the surface eschews the use of inkjet printing techniques, which have been thought to be way forward in this application space. Instead they turned to a rather old printing technique: the stamp.

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Image of Mona Lisa that appears and disappears

Novel Nanomaterial Enables Rewritable Optical Circuits

Researchers at the University of Texas at Austin have developed a hybrid nanomaterial that enables the writing, erasing and rewriting of optical components. The researchers believe that this nanomaterial and the techniques used in exploiting it could create a new generation of optical chips and circuits.

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Droplets of ‘photonic water’ can change color by using chemical or magnetic forces to adjust the alignment of internal stacks of reflective nanosheet crystals

'Photonic Water' Could Be Boon for Optoelectronic Applications

A two-dimensional metal oxide material called titanate nanosheets has remained pretty much off the radar of flatland materials expected to transform the worlds of electronics and optoelectronics. Its biggest claim to fame has been that it is pretty effective at cleaning up contaminants.

However, it would seem that titanate nanosheets history of being overlooked  in the catalogue of 2D materials may have come to an end thanks to a serendipitous discovery by researchers in Japan.

Researchers at the RIKEN Center for Emergent Matter Science in Japan were experimenting with the material to see if they could get the nanosheets to break into more uniform pieces rather than the varied sizes they typically take. Unfortunately, they weren’t able to solve this problem. But they did discover that when the material was centrifuged in water, it changed from being transparent to taking on a deep purple color.

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TEM image of sulphur-filled PPy-MnO2 coaxial nanotubes.

Novel Electrode Structure Provides New Promise for Lithium-Sulfur Batteries

Lithium-sulfur batteries (Li-S) can hold as much as five times the energy per unit mass that lithium-ion (Li-ion) batteries can. However, Li-S batteries suffer from the propensity for polysulfides to pass through the cathode, foul the electrolyte, then pass through to the other electrode, depleting it of sulfur after just a few charge-discharge cycles. This phenomenon is known as the “shuttle effect.”

Now researchers at the University of Texas at Austin have developed an electrode structure for a Li-S battery that makes use of coaxial polypyrrole-manganese dioxide (PPy-MnO2) nanotubes. This novel electrode combats the shuttle effect by essentially encapsulating the electrodes with the nanotubes.

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Graphene-based NFC antenna is flexible

Graphene-based Antenna Still Looking for Path to Commercialization

Graphene is a pure conductor, just like a metal, which has led researchers to examine applications like antennas to see if graphene could serve as a replacement.

Along this line of inquiry, researchers at the National Research Council Institute for Organic Synthesis and Photoreactivity (CNR-ISOF) in Italy, which is part of Europe’s Graphene Flagship,  have developed a graphene-based near-field communication (NFC) antenna. Unlike today’s NFC antennas their devices are flexibile and have greater durability.

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IEEE Spectrum’s nanotechnology blog, featuring news and analysis about the development, applications, and future of science and technology at the nanoscale.

Dexter Johnson
Madrid, Spain
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