Nanoclast iconNanoclast

Band-Gap Engineering of Nanowires Could Boost Batteries

The reason for replacing graphite in the electrodes of the ubiquitous lithium-ion (Li-ion) battery is clear to anyone who uses a smartphone: The batteries run out of charge in just a few hours under regular use.

One answer has been to replace the graphite with silicon. Unfortunately, the expanding and contracting that occurred as the lithium ions transported in and out of silicon electrodes quickly cracks it.

The next solution was to create “nanostructured silicon” electrodes, sometimes with the help of graphene or good old carbon nanotubes.

Now researchers at the University of California San Diego (UCSD) have brought a new perspective to the issue. They are  taking a page from band-gap engineering, in which heterostructures are used to create energy barriers between electrons and holes, and applied the concept to creating barriers to the ions as they enter into an electrode so they diffuse in a very specific way.

The research, which was published in the journal Nano Letters (“Tailoring Lithiation Behavior by Interface and Bandgap Engineering at the Nanoscale”), describes a method by which the typical surface diffusion of lithium ions into a nanowire electrode is blocked and instead the ions are diffused layer-by-layer along the length of the nanowire.

As the Nano Letters article notes: “These results demonstrate for the first time that interface and band-gap engineering of electrochemical reactions can be utilized to control the nanoscale ionic transport / insertion paths and thus may be a new tool to define the electrochemical reactions in Li-ion batteries.” 

In the video below you can see the different way this impacts the nanowire. Instead of blowing up around its middle, it gradually grows along its axis as the lithium ions transport into the nanowire. The video also demonstrates some new breakthroughs in nanoscale imaging with transmission electron microscopy. It shows lithium-ion reactions in real time at nanoscale precision.

In the press release about his work, Shadi Dayeh, a professor at UCSD, explains that this control of how the ions diffuse could result in “an effective way to tailor volume expansion of lithium ion battery electrodes, which could potentially minimize their cracking, improve their durability, and perhaps influence how one could think about different electrode architectures.”

The new technology starts with germanium nanowires that are then coated with silicon.The research builds on previous work of Dayeh and his colleagues published in the journal Applied Physics Letters and again in Nano Letters in which they demonstrated control over the heterostructuring of germanium-silicon nanowires.

 According to Dayeh, the new electrodes would allow for battery designs in which the expansion of the electrodes would not cause any shorting between the cathode and the anode.

Images: UC San Diego Electrical and Computer Engineering

Previously Unheralded 2-D Material Exhibits High Charge-Storage Capacity

The landscape for two-dimensional materials has been getting a little crowded lately. We, of course, hear stories every day about graphene, but molybdenum disulfide has been getting a lot of interest and perhaps even edging ahead of graphene in transistor applications. Finally hexagonal boron nitride is gaining attention and rounding out this trilogy of 2-D materials that all promise to displace silicon in future electronics.

But another two-dimensional material has been in our midst for years and has largely gone unnoticed.

Researchers at Drexel University developed the 2-D material three years ago to little fanfare. But now they have discovered that the material has extraordinary energy storage capacity and could power flexible devices.

Michel W. Barsoum and Yury Gogotsi, both professors at Drexel’s college of engineering, dubbed the material an “MXene” because of its origin from the process of etching and exfoliating atomically thin layers of aluminum from layered carbides called “MAX phases.” [The M is for transition metal, the A for "A group" metal, and the X for carbon and/or nitrogen.]

Over the last three years, the engineers have been investigating applications for the materials. The research, which was published in the journal Science (“Cation Intercalation and High Volumetric Capacitance of Two-dimensional Titanium Carbide”), shows that MXenes store ions and molecules between layers of the material in a process known as intercalation.

Intercalation is the inclusion of a molecule between two other molecules. The process is sometimes required in order to give two-dimensional materials their unique properties. In the Drexel research, they were able to place lithium ions between MXene sheets, making the materials good candidates for use in lithium-ion batteries.

“Currently, nine MXenes have been reported by our team, but there are likely many more that will be discovered—the MXene-and-ion combinations that have been tested to date are by no means an exhaustive demonstration of the material’s energy storage capabilities,” said Gogotsi, who is also director of the A.J. Drexel Nanotechnology Institute, in a press release. “So even the impressive capacitances that we are seeing here are probably not the highest possible values to be achieved using MXenes. Intercalation of magnesium and aluminum ions that we observed may also pave the way to development of new kinds of metal ion batteries.”

In addition to lithium, the researchers have been looking at intercalating ions of sodium, magnesium, potassium, ammonium, and aluminum in between the MXene sheets. In each case, the resulting material demonstrated a high capacity for energy storage, they said.

“Two-dimensional, titanium carbide MXene electrodes show excellent volumetric super capacitance of up to 350 F/cm3 due to intercalation of cations between its layers,” Barsoum said. “This capacity is significantly higher than what is currently possible with porous carbon electrodes. In other words, we can now store more energy in smaller volumes, an important consideration as mobile devices get smaller and require more energy”

- See more at: http://www.drexel.edu/now/news-media/releases/archive/2013/September/MXenes-Science/#sthash.PS22z2pL.dpuf

“Two-dimensional, titanium carbide MXene electrodes show excellent volumetric super capacitance of up to 350 F/cm3 due to intercalation of cations between its layers,” Barsoum said. “This capacity is significantly higher than what is currently possible with porous carbon electrodes. In other words, we can now store more energy in smaller volumes, an important consideration as mobile devices get smaller and require more energy”

- See more at: http://www.drexel.edu/now/news-media/releases/archive/2013/September/MXenes-Science/#sthash.PS22z2pL.dpuf

“Two-dimensional, titanium carbide MXene electrodes show excellent volumetric super capacitance of up to 350 F/cm3 due to intercalation of cations between its layers,” Barsoum said. “This capacity is significantly higher than what is currently possible with porous carbon electrodes. In other words, we can now store more energy in smaller volumes, an important consideration as mobile devices get smaller and require more energy”

- See more at: http://www.drexel.edu/now/news-media/releases/archive/2013/September/MXenes-Science/#sthash.PS22z2pL.dpuf

“Two-dimensional, titanium carbide MXene electrodes show excellent volumetric super capacitance of up to 350 [farads per cubic centimeter] due to intercalation of cations between its layers,” Barsoum said in a press release. “This capacity is significantly higher than what is currently possible with porous carbon electrodes. In other words, we can now store more energy in smaller volumes, an important consideration as mobile devices get smaller and require more energy.”

Image: Drexel University

Spray-On Technique Could Bring Carbon Nanotubes to Retailers’ Shelves

Carbon nanotubes appear to be getting back some of their glory—after seemingly being eclipsed by graphene—with the news yesterday that an entire computer could be made from the material.  Now researchers at Technische Universität München (TUM) in Germany are continuing the carbon nanotube comeback with a new, inexpensive process that promises to enable their use in a wide range of applications including electronic skin and sensors integrated into food packaging.

The process, which involves simply spraying the carbon nanotubes onto a flexible, plastic substrate, is described in the journal Carbon (“Fabrication of carbon nanotube thin films on flexible substrates by spray deposition and transfer printing”)

"To us it was important to develop an easily scalable technology platform for manufacturing large-area printed and flexible electronics based on organic semiconductors and nanomaterials," said postdoctoral researcher Alaa Abdellah in a press release. "To that end, spray deposition forms the core of our processing technology."

In the food packaging application, the carbon nanotubes would serve as gas sensors. Nanotubes have long proven themselves to be good sensors. They can be made to bind to certain substances, which changes the electrical properties of the nanotubes in a way that can be measured with a high degree of sensitivity.

In practical applications, the carbon-nanotube-enabled plastic would cover a grocery store product like chicken. If the product contained the chemical indicators of, say, salmonella, the packaging would detect them and alert the consumer.

While this sounds great, the obstacle preventing this from becoming a reality has always been cost. Thin-film sensory packaging may make sense for a high-cost item, but for an inexpensive grocery store product, it’s hard to justify an additional cost that may be as much as the product itself. I made this point nearly a decade ago in report I authored titled, "The Future of Nanotechnology in Printing and Packaging".

This doesn’t even take into account the often biased opinion people have about nanotechnology in relation to food.

For these reasons, I recommend that the researchers focus their attention on high-ticket applications such as electronic skin for robotics and bionics. In those applications, they will likely find greater resistance to the fear mongering practiced by the NGOs. And it just might make more economic sense to adopt their technology for those applications.

Image: Uli Benz/TUM

Plastic OLEDs Just Got a Bump from Silver Nanowires

Polymer-based OLEDs (organic light-emitting devices) have been held out as a kind of Holy Grail in lighting and display applications. Part of their unachievable-quest notoriety stems from the fact that they are expensive in part due to the complex processing involved. Nonetheless, they do possess the magical feature of being flexible.

Researchers at the University of California Los Angeles (UCLA) have developed just such an OLED material that can be twisted and folded and even stretched while remaining lit the entire time and could become the template for all future polymer OLEDs.

"Our new material is the building block for fully stretchable electronics for consumer devices," said Qibing Pei, a UCLA professor of materials science and engineering and principal investigator on the research, in a press release. "Along with the development of stretchable thin-film transistors, we believe that fully stretchable interactive OLED displays that are as thin as wallpaper will be achieved in the near future. And this will give creative electronics designers new dimensions to exploit."

The material, which was described in the journal Nature Photonics ("Elastomeric polymer light-emitting devices and displays"),  owes at least part of its remarkable stretching capabilities to new transparent electrodes the researcher made out of silver nanowires that have been inlaid into the polymer.

Silver nanowires are currently being market by companies like Cambrios Technologies and Blue Nano for use as a replacement to indium tin oxide (ITO) as a transparent conductor to control display pixels.

In this latest application, the UCLA researchers found that when a single layer of an electro-luminescent polymer blend is sandwiched between the silver nanowire electrodes it was possible for the OLED to bend and stretch at room temperature.

As you can see from the video below, the researchers are able to bend and stretch the OLED into every conceivable shape and do it while in normal ambient conditions.

"The lack of suitable elastic transparent electrodes is one of the major obstacles to the fabrication of stretchable display," said Jiajie Liang, a postdoctoral scholar, in a press release. "Our new transparent, elastic composite electrode has high visual transparency, good surface electrical conductivity, high stretchability and high surface smoothness — all features essential to the fabrication of the stretchable OLED."

While the video demonstrates an OLED with just a solid block of light, the researchers have shown that they can create an OLED made up of different pixels, which opens up the possibility of stretch displays as well as new kinds of lighting.

The researchers were able to accomplish this pixel capability by arranging the silver nanowire-based electrodes into a cross-hatched pattern made up of one layer of columns and one layer of rows.

"While we perceive a bright future where information and lighting are provided in various thin, stretchable or conformable form factors, or are invisible when not needed, there are still major technical challenges," Pei conceded in the press release "This includes how to seal these materials that are otherwise sensitive to air. Researchers around the world are racing the clock tackling the obstacles. We are confident that we will get there and introduce a number of cool products along the way."

Graphene Investment Advice Needed, Just Not the Stock Market Variety

With research developments coming daily—if not hourly—in graphene, it really was just a matter of time before investment gurus were going to start giving stock tips. This is not altogether bad. It keeps everything focused on the purpose of pursuing graphene developments to create new and improved products that will enable somebody to make some money.

Unfortunately, the field of nanotechnology has a somewhat checkered past with the stock market and with investment gurus. We’ve been subjected to nanotechnology stock indices that thankfully have (for the most part) withered away. And we’ve seen so-called stock market experts proclaim that a huge company with enormous revenues and cash reserves is the same kind of speculative stock investment as a small start-up. It would seem these “experts” not only don’t know nanotechnology, but also don’t understand simple stock analysis metrics like price-to-earnings ratios.

Now it’s graphene’s turn. There has been a recent flurry of investment reports on graphene, motivating some bloggers to comment on the trend. I was finally nudged into a offering my observations now because of a piece that appeared this week in Forbes (“Graphene Stock Investing: What The Pros Think”) . As these articles go, this is a top-notch effort. But I have to quibble about one point—and it’s a big one—graphene at the moment is not a stock market play.

Here is a list of 39 graphene companies, and I don’t believe that there’s one of them on that list that is at this moment publicly traded. So, after the author asks two investment experts what stocks they would suggest for exploiting all the activity in graphene, we get as a response: Enersys, Tesla Motors, and Johnson Controls without giving any explanation of why these companies constitute  good graphene investments. It’s not even clear how they are involved in graphene.

I suppose in the case of Enersys and Tesla it’s a belief that graphene could enable improved batteries for all-electric vehicles. While I have no idea whether these companies are good stock investments or not, I am pretty certain that their fortunes good or bad are not tied to the fate of graphene one way or the other, especially for a hugely diversified company like Johnson Controls.

I support and would even champion articles that could raise awareness of how crucial it is to invest in companies that are trying to develop products based on graphene. We actually need more of them. Unfortunately, we rarely get those kinds of articles and instead get articles like the one in Forbes that are aimed at those interested to know how they can spend their savings on a “graphene stock market investment,” when, in fact, there is no such thing.

While this is unfortunate, it indicates a perhaps more troubling issue. The kind of early, pre-IPO investment that a company trying to develop products based on graphene needs has become increasingly difficult to source outside of governments as large private capital sources still prefer the fast investment turnarounds offered in complex financial instruments. It’s even got graphene’s co-discoverer, Andre Geim, lamenting society’s current attitude of “throw[ing] a little bit of money at something and expect[ing] it to change the world.

By most estimates products enabled by graphene should really start hitting the market in 2020. With that investment horizon, why are we even talking about the stock market when we should really be discussing how we can support innovation at these early stages. Do that and someday we can actually have publicly traded companies that make products based on graphene.

Image: Erik Vrielink

Graphene Leading the Way to Optical Chips

In a joint research project, researchers from the Massachusetts Institute of Technology (MIT), Columbia University, and IBM’s T. J. Watson Research Center have used graphene as a photodetector for enabling an optical chip.

Graphene has tantalized researchers in photodetector applications with its wide spectral range (from the ultraviolet to the infrared), fast optoelectronic response that is the result of high electron mobility, and its lack of a band gap. However, graphene can absorb only a small fraction of incoming light, so its responsivity has been limited.

While this minimal light sensitivity may limit its use in digital camera applications, the MIT, Columbia, and IBM researchers may have engineered a way to use graphene as a photodetector for converting light into electricity for integrated optoelectronic chips.

The research team, which published its work in the journal Nature Photonics (“Chip-integrated ultrafast graphene photodetector with high responsivity”)  developed a method by which they could overcome graphene’s low responsivity to incoming light (measured at between 2 and 3 percent of the light passing through it being converted to electrical current). They turned to creating a bias in the photodetector so that electrons that were disrupted by incoming photons would remain in a higher energy state.

Typically, creating this bias involves maintaining voltage through the photodetector. However, this voltage is a source of noise that compromises the photodetector’s readings. To avoid this noise, the researchers turned to the work of Fengnian Xia and his colleagues at IBM; they produced a bias in a photodetector without the application of a voltage.

This trick is accomplished through an ingenious design in which light is funneled into the photodetector through a channel—or a waveguide—that is capped with a piece of graphene oriented perpendicular to the channel. The graphene has gold electrodes on either side of it, but instead of them being evenly spaced, one of the electrodes is closer to the graphene than the other.

“There’s a mismatch between the energy of electrons in the metal contact and in graphene,” said Dirk Englund, an assistant professor at MIT and the leader of the research team, in a press release. “And this creates an electric field near the electrode.”

So in operation, photons come through the channel and start kicking the electrons up to a higher energy state. These excited electrons are then pulled to the electrodes by the electric field, thereby creating a current—without applying a voltage.

This voltage-free bias boosts the photodetector to the point where it could generate 100 milliamps per watt, a responsivity equal to that of germanium. The researchers believe that with a bit of engineering (i.e., thinner electrodes, and a narrower waveguide), it could be possible to boost these results by a factor of two or perhaps even four.

The impact of chips that use light rather than electricity is clear. They will consume less power and produce less heat. Both of these factors have become ever more critical as chip features get smaller and smaller.

Thomas Mueller, an assistant professor at the Vienna University of Technology’s Photonics Institute, and a co-author of very similar research in the same journal, noted in the press release: “The other thing that I like very much is the integration with a silicon chip, which really shows that, in the end, you’ll be able to integrate graphene into computer chips to realize optical links and things like that.”

Image: MIT/Columbia University/IBM

Top-Down and Bottom-Up Manufacturing Combined in One Technique

An international team of researchers has combined ink-jet printing and self-assembling block copolymers to create a hybrid between top-down and bottom-up manufacturing. This new hybrid approach to building nanostructures promises to overcome the obstacles of fabricating nanostructures out of polymers and other soft materials.

The research, which was published in the journal Nature Nanotechnology ("Hierarchical patterns of three-dimensional block-copolymer films formed by electrohydrodynamic jet printing and self-assembly"),  found that by using self-assembling block copolymers  in combination with ink-jet printing that the resolution for even the best ink jet printers  could be improved from approximately 200 nanometers down to about 15 nm.

Block copolymers are chain like molecules made up of blocks of two types of chemicals. (Imagine a string of Christmas lights having a repeating pattern of 5 green lights and 5 red lights.) Under the right circumstances, such copolymers can fold up to form patterns such as a repeating array of holes.

The ITRS roadmap has long identified block copolymers for use in reducing chip feature sizes. For years block copolymers have demonstrated their usefulness in creating self-assembled photoresists for chip manufacturing.

While the potential for self-assembling block copolymers have long been understood, this work—which is a cooperative effort of researchers from University of Illinois at Urbana-Champaign, the University of Chicago, and Hanyang University in Korea—adds an important twist.

“The most interesting aspect of this work is the ability to combine ‘top-down’ techniques of jet printing with ‘bottom-up’ processes of self-assembly, in a way that opens up new capabilities in lithography—applicable to soft and hard materials alike,” said John Rogers, a materials science professor at Illinois and one of the authors of the paper, in a press release.

In the work described, the international team turned to the Belgium-based nanoelectronics powerhouse Imec to create chemical patterns over large areas of a substrate with high precision. The research team in Illinois then used ink jet printing to deposit block copolymers on top of these patterns. The block copolymers would self-organize following the patterns laid on the underlying template. The result was that it created patterns that had a greater resolution than the template itself.

While previous work had managed to deposit films on these templates, the result was that the patterns only possessed one characteristic feature size and spacing. With the ultra-precise ink-jet printing tool, it became possible to create multiple dimensions in one layer.

“This invention, to use inkjet printing to deposit different block copolymer films with high spatial resolution over the substrate, is highly enabling in terms of device design and manufacturing in that you can realize different dimension structures all in one layer,” said Paul Nealey, a professor at the University of Chicago and co-author of the paper, in the press release. “Moreover, the different dimension patterns may actually be directed to assemble with either the same or different templates in different regions.”

Image: Serdar Onses/University of Illinois-Urbana

"Piranha Etching" Could Push Nanowire Solar Cells Way Past Theoretical Limits

Researchers at the Eindhoven University of Technology, Delft University of Technology and the company Philips in the Netherlands have developed a method for increasing the conversion efficiency of nanowire-based photovoltaic cells: Give them a good cleaning.  While the researchers have demonstrated an increase to 11.1 percent efficiency with their technique, it is the long-term prospects of the method that appear the most promising with estimates for the conversion efficiency ultimately reaching 65 percent.

The potential for nanowire-based photovoltaics to reach extremely high conversion efficiencies was demonstrated earlier this year when researchers at the Nano-Science Center at the Niels Bohr Institut in Denmark and the Ecole Polytechnique Fédérale de Lausanne in Switzerland suggested that nanowire photovoltaic cells could surpass the Shockley-Queisser limit. The Shockley-Queisser limit is a theory established in 1960 that suggested among other things that that only 33.7 percent of all the sun’s energy could be converted into electricity for solar cells with a single p-n junction. To surpass this limit has been a  Holy Grail quest of sorts for photovoltaics.

Now with this latest research  the Shockley-Queisser limit could be surpassed by a huge margin. The technique, which is described in the journal Nano Letters (“Efficiency Enhancement of InP Nanowire Solar Cells by Surface Cleaning”)  involves a surface cleaning of the nanowires.

The cleaning is a chemical reaction that the researchers have dubbed “piranha etching”. The result of the process is that indium phosphide nanowires come out much smoother and have fewer imperfections.

This cleaning of the surface addresses the Achilles Heel of nanowire photovoltaics. While the surface area of nanowires enables photovoltaics to be produced without using as much costly semiconductor material as ordinary photovoltaics do, the nanowires cell's large surface area is prone to have imperfections that result in energy loss.

The 11.1 percent conversion efficiency achieved by the Netherlands-based researchers does not equal the record of 13.8 percent achieved by an international team of researchers earlier this year. However, that may be of little consequence if the promise of this latest research can be realized.

“By varying the thickness of the nanowires and improving the way the crystals inside them are stacked, we think we should soon be able to approach an efficiency of 20 percent”, says Professor Erik Bakkers, one of the lead researchers, in a press release.

Following this basic approach, the researchers believe that theoretically they could reach a conversion efficiency as high as 65 percent. If that’s true, and it can be produced relatively inexpensively, it'll be a game changer.

Image: Eindhoven University of Technology

Article Makes a Hash out of Nanotechnology and its Impact

Over the years, I thought I had become accustomed to mainstream journalists making a hash out of the subject of nanotechnology. I've even had the misfortune of watching videos starring famed TV physicists making bizarre predictions about the problems that will ensue from the changes brought on by nanotechnology. I thought I had steeled myself so I would not be bothered by these sorts of things anymore, but along came the latest mishmash of half-informed scaremongering.

It’s a perfect storm of wrongheadedness. It was penned by Ainissa G. Ramirez, Ph.D., a noted author and “science evangelist,” giving it an air of veracity. But that doesn't keep the piece from going wrong right from the outset. You can find the first misstep in the second sentence: “By miniaturizing matter, science fact will look like science fiction.” Okay, once and for all: Nanotechnology has nothing to do with miniaturizing matter. Nanotechnology is not the real-life version of the 1960s sci-fi film “Fantastic Voyage.” We are not shrinking matter.

Ramirez apparently skimmed the wrong articles to mine that nugget of information. The rest of the article, as far as nanotechnology is concerned, scans about right; it includes all the typical references you would expect from someone who skimmed some articles on nanotechnology: gold is red at the nanoscale, using hair to visualize the nanoscale, et cetera.

This is not to say Ramirez does not fudge some other references to nanotechnology for dramatic effect. For example, there's this gem: “Do we want small particles—which we can't imagine let alone see—swimming in our water supply and covering everything around us?”

Swimming? Covering everything around us? Really? The "scholarly paper" she must have been referencing is Michael Crichton’s novel “Prey.” Outside the world of fiction, man-made nanoparticles are not going to cover everything.

While these egregious misstatements of fact got my blood boiling, it’s the main thesis of the article that is perhaps the biggest problem. Ramirez’s argument boils down to the idea that pursuing technology has unintended consequences that, in balance, are bad for us. This is a popular meme among so-called environmentalists. Ramirez suggests that the automobile, while likely considered a really great idea at the time of its invention, brought on obesity because it eliminated an alternate course of history wherein we would have been walking or cycling. I suppose this line of argument appeals to a certain segment of the population that would like us to return to the bucolic times before all the inventions of our modern age. Sigh. Why can’t these technology-for-dummies summaries ever be informed or reasonable?

To address the crossroads that Ramirez believes we are approaching with nanotechnology (where it could potentially be the next thing to blame for our obesity), she suggests public engagement and dialog about its impact. Really? What a novel idea. Too bad it seems to have escaped Dr. Ramirez’s skimming that there has been so much public engagement for years now that research has been looking at whether it has any usefulness. It also doesn’t help matters that the very people that will accept Ramirez's line of thinking are the ones who have boycotted public engagement efforts.

Worse yet, the article was published in the perfect vehicle for wide dissemination: the Huffington Post, which is as mainstream as it gets. So a lot of people are apt to read the article and be misinformed. The Huffington Post is developing a rather poor reputation for its coverage of nanotechnology. And it's a pity because there are lots of brilliant commentators on the subject of nanotechnology’s potential impact—people who could provide well-reasoned and substantiated arguments on the topic.  Ramirez's article, unfortunately, does neither.

Photo: David Monniaux/Wikipedia

Bismuth-filled Carbon Nanotubes Improve CT Scans

Research has shown in recent years that carbon nanotubes can improve fluorescence imaging, replacing the dyes that are typically used. Now researchers at Rice University have demonstrated that carbon nanotubes combined with bismuth can improve the capabilities of computed tomography (CT) scans.

The Rice team has filled single-walled carbon nanotubes with bismuth compounds to make for a more effective contrast agent than is currently available for CT scans.

The research, which was published in the journal of Materials Chemistry B (“Bismuth@US-tubes as a potential contrast agent for X-ray imaging applications”), builds on previous work that examined the use of bismuth as a contrast agent in CT scans and on the Rice team’s own research into using carbon nanotubes as a contrast agent in magnetic resonance imaging (MRI).

According to Rice chemist Lon Wilson, this is the first time that bismuth has been combined with nanotubes for use as a contrast agent for imaging individual cells.

“At some point, we realized no one has ever tracked stem cells, or any other cells that we can find, by CT,” Wilson said in a press release. “CT is much faster, cheaper and more convenient, and the instrumentation is much more widespread (than MRI). So we thought if we put bismuth inside the nanotubes and the nanotubes inside stem cells, we might be able to track them in vivo in real time.”

The new contrast agent starts off as single-walled carbon nanotubes that have been chemically processed to make them into capsules with dimensions of between 20 and 80 nanometers long and about 1.4 nanometers in diameter. These nanocapsules are then are mixed with bismuth chloride to form what the researchers have dubbed Bi@US-tubes.

Once the Bi@US-tubes are introduced in vivo, they are small enough to diffuse into individual cells where they aggregate into a clump approximately 300 nanometers in diameter. “We think the surfactant used to suspend them in biological media is stripped off when they pass through the cell membrane,” Wilson said in the press release. “The nanotubes are lipophilic, so when they find each other in the cell they stick together.”

“The cells adjust over time to the incorporation of these chunks of carbon and then they go about their business,” Wilson adds in the release.

Bismuth is more effective at diffracting X-rays than the iodine in today's contrast agents, or just about any other material. When it is put in the nanocapsules, the resulting combination can produce high contrasts in very low concentrations.

The surfaces of the nanotubes can also be modified in ways to make them target different kinds of cells and make them more biocompatible.

The next step in the research will be to increase the amount of bismuth in the capsules so as to improve their contrasting capability.

Image: Eladio Rivera/Rice University

Most Commented Posts

Nanoclast

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

 
Editor
Dexter Johnson
Madrid, Spain
 
Contributor
Rachel Courtland
Associate Editor, IEEE Spectrum
New York, NY
Advertisement
Advertisement
Load More