Tag Archives: CNT

The yin and the yang of carbon nanotubes and toxicity


Illustration courtesy of the University College of London (UCL). Downloaded from http://www.ucl.ac.uk/news/news-articles/0113/130115-chemistry-resolves-toxic-concerns-about-carbon-nanotubes

Illustration courtesy of the University College of London (UCL). Downloaded from http://www.ucl.ac.uk/news/news-articles/0113/130115-chemistry-resolves-toxic-concerns-about-carbon-nanotubes

Researchers at the University College of London (UCL), France’s Centre national de la recherche scientifique (CNRS), and Italy’s University of Trieste have determined that carbon nanotube toxicity issues can be addressed be reducing their length and treating them chemically. From the Jan. 15,2013 news item on ScienceDaily,

In a new study, published January 15 [2013] in the journal Angewandte Chemie, evidence is provided that the asbestos-like reactivity and pathogenicity reported for long, pristine nanotubes can be completely alleviated if their surface is modified and their effective length is reduced as a result of chemical treatment.

First atomically described in the 1990s, carbon nanotubes are sheets of carbon atoms rolled up into hollow tubes just a few nanometres in diameter. Engineered carbon nanotubes can be chemically modified, with the addition of chemotherapeutic drugs, fluorescent tags or nucleic acids — opening up applications in cancer and gene therapy.

Furthermore, these chemically modified carbon nanotubes can pierce the cell membrane, acting as a kind of ‘nano-needle’, allowing the possibility of efficient transport of therapeutic and diagnostic agents directly into the cytoplasm of cells.

Among their downsides however, have been concerns about their safety profile. One of the most serious concerns, highlighted in 2008, involves the carcinogenic risk from the exposure and persistence of such fibres in the body. Some studies indicate that when long untreated carbon nanotubes are injected to the abdominal cavity of mice they can induce unwanted responses resembling those associated with exposure to certain asbestos fibres.

In this paper, the authors describe two different reactions which ask if any chemical modification can render the nanotubes non-toxic. They conclude that not all chemical treatments alleviate the toxicity risks associated with the material. Only those reactions that are able to render carbon nanotubes short and stably suspended in biological fluids without aggregation are able to result in safe, risk-free material.

Here’s a citation and link for this latest  research, from the ScienceDaily news item where you can also read the lead researcher’s comments about carbon nanotubes, safety, and unreasonable proposals to halt production,

Hanene Ali-Boucetta, Antonio Nunes, Raquel Sainz, M. Antonia Herrero, Bowen Tian, Maurizio Prato, Alberto Bianco, Kostas Kostarelos. Asbestos-like Pathogenicity of Long Carbon Nanotubes Alleviated by Chemical Functionalization. Angewandte Chemie International Edition, 2013; DOI: 10.1002/anie.201207664

The article is behind a paywall. I have mentioned long carbon nanotubes and their resemblance to asbestos fibres in several posts. The  Oct. 26, 2009 posting [scroll down about 1/3 of the way] highlights research which took place after the study where mice had carbon nanotubes injected into their bellies; in this second piece of research they inhaled the nanotubes.

ETA Jan. 21, 2013: Dexter Johnson gives context and commentary about this latest research into long multiwalled nanotubes (MWNTs) which he sums up as the answer to this question “What if you kept the MWNTs short?”  in a Jan. 18, 2013 posting on his Nanoclast blog (on the IEEE [Institute of Electrical and Electronics Engineers] website)

Using carbon nanotubes to treat neural injuries?

It’s more usual to hear about toxicology when discussing carbon nanotubes (CNTs) and health but recent work from Duke University Medical Center suggests that CNTs could be used in therapeutic treatments for neural injuries. From the Dec. 10,2012 news item on ScienceDaily,

A nanomaterial engineered by researchers at Duke can help regulate chloride levels in nerve cells that contribute to chronic pain, epilepsy, and traumatic brain injury.

The findings, published online Dec. 10, 2012, in the journal Small, were demonstrated in individual nerve cells as well as in the brains of mice and rats, and may have future applications in intracranial or spinal devices to help treat neural injuries.

The Dec. 10, 2012 news release from Duke Medicine News and Communications discusses carbon nanotubes and the applications they are usually associated with,

Carbon nanotubes are a nanomaterial with unique features, including mechanical strength and electrical conductivity. These characteristics, along with their tiny size, make them appealing to researchers in technology and medicine alike.

In a world of shrinking computers and smartphones, carbon nanotubes have been tapped as a solution for improving microchips. They outpace silicon microchips in size and performance, meeting a demand for smaller, faster devices. For people with nerve injury and certain neurological disorders, devices coated with or entirely made of carbon nanotubes could offer a new avenue for improving treatment options.

“Carbon nanotubes hold great promise for an array of applications, and we are only beginning to see their enormous potential,” said lead author Wolfgang Liedtke, M.D., PhD, associate professor of medicine and neurobiology at Duke. “Their exceptional mechanical and electrical properties make them ideal for developing devices that interface with nervous tissues. However, the precise mechanisms behind carbon nanotubes and their effect on neurons remain elusive.”

One of the Duke researchers actually developed a new kind of carbon nanotube for this research (from the Duke news release),

Not all carbon nanotubes are the same. Jie Liu, PhD, George Barth Geller Professor of Chemistry at Duke University and senior author of the study, developed specific carbon nanotubes that are extraordinarily pure. Termed few-walled carbon nanotubes, they have superior properties to their commercially-available counterparts.

Duke researchers initially set out to gauge if carbon nanotubes had toxic or adverse effects on living tissue. Studying neurons cultured from rodents, representing a “cerebral cortex in a dish,” they found the opposite. Exposing the cells to carbon nanotubes appeared to have a nourishing effect on the neurons, making them bigger and stronger.

“Previous studies have looked at the behavior of carbon nanotubes on neurons. However, the impurity in the nanotubes significantly affected the results. After we developed pure few-walled carbon nanotubes in our lab, we discovered that nanotubes actually accelerated the growth of the neuronal cells significantly,” said Liu.

Here’s what happens in some cases of neural injury and the impact that few-walled carbon nanotubes might have on future therapeutics (from the Duke news release),

Neural circuits can be corrupted by elevated chloride within neurons. A number of diseases involve such neural circuit damage, including chronic pain, epilepsy, and traumatic brain injury.

Low levels of chloride within neurons are maintained by a chloride transporter protein called KCC2, which functions by churning chloride ions out of the cell. In mature neurons, there is no back-up for this function.

The immature neurons cultured in Liedtke’s laboratory had high levels of chloride, but as the cells matured, their chloride levels dropped as KCC2 increased. When the neurons were exposed to carbon nanotubes, the cells matured much faster, and the chloride levels dropped more quickly. Researchers learned that younger cells exposed to carbon nanotubes produced more KCC2 protein.

“Carbon nanotubes enhanced the regulation of chloride in neurons to normal levels. These changes are of enormous significance to the cell,” Liedtke said.

The increase in KCC2 protein was also connected to a rise in calcium in the neurons. The increased calcium levels activated a protein found in the brain called CaMKII which signals a neuron to make more KCC2.

Similar results were observed in the brains of mice, as the carbon nanotubes prompted an increase in activity of the KCC2 gene, suggesting that the few-walled carbon nanotubes influence gene regulation of KCC2.

These findings may lead to the development of a new generation of neural engineering devices using carbon nanotubes. Existing devices that modulate the function of nerve cells use electrical systems that date back several decades.

“We hope that carbon nanotubes will work as well in injured nerves as they did in our study of developing neurons,” Liedtke continued. “The use of carbon nanotubes is just in its infancy, and we are excited to be part of a developing field with so much potential.”

Naturally (sarcasm alert), the researchers have done this (from the Duke news release),

Liedtke and Liu have filed a preliminary patent application for the few-walled carbon nanotubes used in this research. [emphasis mine]

How how many new therapies will be developed (or even researched) if the materials needed for the research are patented?

For anyone who’s interested in the paper, here’s a citation and link (from the ScienceDaily news item),

Wolfgang Liedtke, Michele Yeo, Hongbo Zhang, Yiding Wang, Michelle Gignac, Sara Miller, Ken Berglund and Jie Liu. Highly Conductive Carbon Nanotube Matrix Accelerates Developmental Chloride Extrusion in Central Nervous System Neurons by Increased Expression of Chloride Transporter KCC2. Small, 10 DEC 2012 DOI: 10.1002/smll.201201994

This paper is behind a paywall.

It should be mentioned that ScienceDaily offers a choice of citation formats, APA or MLA. This citation is in APA format.

Using microwaves to test for carbon nanotube toxicity in soil

It’s been a while since I’ve mentioned soil or environmental testing for this this Oct. 19, 2012 news item by Karen Slyker on physorg.com, which highlights some research on environmental testing of carbon nanotubes, lets me redress the situation,

Industrial uses are growing, as are concerns that these novel nanomaterials may have negative or unintended effects on organisms and the environment. With this in mind, environmental toxicologists at Texas Tech are exploring the fate of CNTs in biological environments and their ability to accumulate in soil, plants or other organisms.

One recurring question has slowed these studies: How can anyone be certain the tiny CNTs are present in the given sample?

“It’s like a needle in a haystack,” Green said [Micah Green, assistant professor of chemical engineering]. “How can you prove the effects of the needle, if you’re not sure that it’s really in there?”

The impetus for the work initially began with a conversation between Green and Jaclyn Cañas, associate professor of environmental toxicology at The Institute for Environmental and Human Health at Texas Tech. Cañas described the problem of detecting CNTs in crop samples. Green suggested that exposing samples to microwaves could reveal the presence of even trace quantities of nanotubes.

The Texas Technical University Oct. 19, 2012 news release (which originated the news item) provides more detail about the approach,

CNTs have the unusual property of evolving extreme amounts of heat upon exposure to microwaves, much more so than typical materials. In fact, nanotube powder will quickly and spontaneously ignite if placed in a conventional kitchen microwave. Green’s idea was to expose the sample to low-power microwaves and measure the resulting increase in temperature.

Mohammad Saed, an associate professor in electrical and computer engineering, joined the team to contribute his expertise in the area of microwave physics.

Together, the three research groups successfully built a testing apparatus and proved the concepts that microwave-based heating can quantify CNT loading inside a plant sample.

The team has refined its testing protocols and extended the scope from soil testing only to including earthworms,

Continued development of the device led to a double-blind test, where a student was given samples of a specified CNT loading but was not told what the concentration was. Graduate student Fahmida Irin was principally responsible for applying the method. The double-blind test successfully duplicated the true values, and was then applied to studying the uptake of nanotubes into alfalfa plant roots grown in soil spiked with nanotubes.

“Since we started the method, we have started collaborating with other groups as well to look at the presence of nanotubes in organisms like earthworms,” Green said.

The method was recently published in a paper entitled “Detection of carbon nanotubes in biological samples through microwave-induced heating” by Irin et al. in the journal Carbon.

I’m not quite sure how to take this research. They do mention that nanotube powder will ignite in a kitchen microwave. Here’s hoping the researchers have designed an apparatus that cannot accidentally ignite carbon nanotubes in soil, plants, or earthworms.

From Germany’s Fraunhofer Center Nanoelectronic Technologies, with (love) and bubbles

Fraunhofer Center Nanoelectronic Technologies is establishing a partnership with Leipzig-based, bubbles and beyond according to the March 9, 2012 news item on Nanowerk,

bubbles & beyond, a technology company focusing on customized intelligent fluids®, and Fraunhofer Center Nanoelectronic Technologies (CNT), Dresden, today announced their collaboration to jointly develop novel cleaning solutions for the microelectronics industry.

During the two-year collaboration, bubbles & beyond and Fraunhofer Center Nanoelectronic Technologies will create novel decoating products for semiconductor applications with the goal to provide a more efficient, more cost-effective and eco-friendly alternative to currently available surface treatments, which are primarily composed of aggressive chemicals. The novel cleaning approach is based on bubbles & beyond’s proprietary phase fluid technology (intelligent fluids®), which is already used successfully for other microelectronic applications. Fraunhofer CNT brings the necessary semiconductor expertise, the respective research know-how and comprehensive, highly precise measurement analysis to the project.

I find the name ‘bubbles and beyond’ quite delightful but after looking at their website, I have the disturbing impression they’re going to change it to something more ‘high tech’, more staid—Intelligent Fluids—if you go here, http://www.bubbles-beyond.com, that’s where you will be redirected. I’m tired of intelligence, please don’t take the bubbles away!

In honour of bubbles, here’s a video of the Mills Brothers and the Count Basie Band performing both ‘Tiny Bubbles’ (and the song, Release Me),

Happy weekend and may all your bubbles be tiny and in wine!

University of Texas at Dallas lab demos cloaking device visible to naked eye

Invisibility cloaks have been everywhere lately and I’ve been getting a little blasé about them but then I saw this Oct. 4, 2011 news item on physorg.com,

Scientists have created a working cloaking device that not only takes advantage of one of nature’s most bizarre phenomenon, but also boasts unique features; it has an ‘on and off’ switch and is best used underwater.

For the first time, I was able to see an invisibility cloak in action, here’s the video,

For the curious here’s how it works (from the Oct. 4, 2011 news release on the Institute of Physics website),

This novel design, presented today, Tuesday 4 September [Tuesday 4 October?], in IOP [Institute of Physics] Publishing’s journal Nanotechnology, makes use of sheets of carbon nanotubes (CNT) – one-molecule-thick sheets of carbon wrapped up into cylindrical tubes.

CNTs have such unique properties, such as having the density of air but the strength of steel, that they have been extensively studied and put forward for numerous applications; however it is their exceptional ability to conduct heat and transfer it to surrounding areas that makes them an ideal material to exploit the so-called “mirage effect”.

The most common example of a mirage is when an observer appears to see pools of water on the ground. This occurs because the air near the ground is a lot warmer than the air higher up, causing lights rays to bend upward towards the viewer’s eye rather than bounce off the surface.

This results in an image of the sky appearing on the ground which the viewer perceives as water actually reflecting the sky; the brain sees this as a more likely occurrence.

Through electrical stimulation, the transparent sheet of highly aligned CNTs can be easily heated to high temperatures. They then have the ability to transfer that heat to its surrounding areas, causing a steep temperature gradient. Just like a mirage, this steep temperature gradient causes the light rays to bend away from the object concealed behind the device, making it appear invisible.

With this method, it is more practical to demonstrate cloaking underwater as all of the apparatus can be contained in a petri dish. It is the ease with which the CNTs can be heated that gives the device its unique ‘on and off’ feature.

Congratulations to Dr. Ali Aliev (lead author) and the rest of the University of Texas at Dallas team!

ETA Oct. 5, 2011: I added the preposition ‘of’ to the title and I’m adding a comment about invisibility cloaks.

Comment: Most of the invisibility cloaks I’ve read about are at the nanoscale which means none of us outside a laboratory could possibly observe the cloak in action. Seeing this video demonstrating an invisibility cloak in the range of visible light and at a macroscale was a dream come true, so to speak.