carbon nanotubes

Spiders sprayed with carbon nanotubes spin superstrong webs

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A team of researchers working in Italy has found that simply spraying a spider with a carbon nanotube solution can cause the spider to spin stronger webs. In their paper they have uploaded to the preprint server arXiv, the team describes their experiments with both graphene and nanotube solutions and what happened when they sprayed it on ordinary spiders.

Spiders sprayed with carbon nanotubes spin superstrong webs

As the researchers note, while using silkworms has been quite successful, doing the same to harvest from has not, (because of their territorial traits, the complex nature of the silk they make and their cannibalistic tendencies) which is frustrating as the silk they make to spin their webs has so many outstanding qualities. Intrigued by prior research efforts that investigated the possibility of enhancing spider silk by spraying the spiders or feeding them different materials (titanium, zinc, aluminum, lead, etc.) to improve the mechanical, electrical, magnetic or even fluorescent properties of the silk, the researchers wondered what would happen if they sprayed the arachnids, with a graphene or carbon nanotube solution.

To find out, they wandered out into the natural environs near their lab and collected a host of cellar spiders and carefully brought them back to their lab. They then proceeded to spray ten of them with a solution and five with a graphene solution (the particles were 200 to 300 nanometers in width). Sadly, four of the spiders died shortly thereafter, and some produced poor quality webs, but a few of them produced webs that were actually stronger than their normal webs. Testing showed that some of the silk with nanotubes in it was 3.5 times as strong as giant riverine orb spider silk, which is considered the strongest natural . Also closer examination using Ramen spectroscopy revealed peaks in the silk where the nanotubes were present.

The researchers do not know how the carbon in either form wound up in the silk, but have excluded the possibility that it became drenched with it as it exited the spider’s body, the uniformity of the silk was too fine—they think that the spiders pull materials in from their immediate environment and use it as an ingredient in their silk making. Their results suggest it should be possible to produce such silk in small quantities, though it is not clear to what use it would be put.

Here, we report the production of silk incorporating graphene and carbon nanotubes directly by spider spinning, after spraying spiders with the corresponding aqueous dispersions. We observe a significant increment of the mechanical properties with respect to the pristine silk, in terms of fracture strength, Young’s and toughness moduli. We measure a fracture strength up to 5.4 GPa, a Young’s modulus up to 47.8 GPa and a toughness modulus up to 2.1 GPa, or 1567 J/g, which, to the best of our knowledge, is the highest reported to date, even when compared to the current toughest knotted fibres. This approach could be extended to other animals and plants and could lead to a new class of bionic materials for ultimate applications.

Stanford scientists use lasers and carbon nanotubes to look inside living brains.

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A team of Stanford scientists has developed an entirely non-invasive technique that provides a view of blood flow in the brain. The tool could provide powerful insights into strokes and possibly Alzheimer’s disease.

This illustration shows how carbon nanotubes, once injected into the subject, can be fluoresced using near-infrared light in order to visualize the brain vasculature and track cerebral blood flow.

Some of the most damaging BRAIN DISEASES can be traced to irregular blood delivery in the brain. Now, Stanford chemists have employed lasers and carbon nanotubes to capture an unprecedented look at blood flowing through a living brain.

The technique was developed for mice but could one day be applied to humans, potentially providing vital information in the study of stroke and migraines, and perhaps even Alzheimer’s and Parkinson’s diseases. The work is described in the journal Nature Photonics.

Current procedures for exploring the brain in living animals face significant tradeoffs. Surgically removing part of the skull offers a clear view of activity at the cellular level. But the trauma can alter the function or activity of the brain or even stimulate an immune response. Meanwhile, non-invasive techniques such as CT scans or MRI visualize function best at the whole-organ level; they cannot visualize individual vessels or groups of neurons.

The first step of the new technique, called near infrared-IIa imaging, or NIR-IIa, calls for injecting water-soluble carbon nanotubes into a live mouse’s bloodstream. The RESEARCHERS then shine a near-infrared laser over the rodent’s skull.

The light causes the specially designed nanotubes to fluoresce at wavelengths of 1,300-1,400 nanometers; this range represents a sweet spot for optimal penetration with very little light scattering. The fluorescing nanotubes can then be detected to visualize the blood vessels’ structure.

Amazingly, the technique allows scientists to view about three millimeters underneath the scalp and is fine enough to visualize blood coursing through single capillaries only a few microns across, said senior authorHongjie Dai, a professor of chemistry at Stanford. Furthermore, it does not appear to have any adverse affect on innate brain functions.

“The NIR-IIa light can pass through intact scalp skin and skull and penetrate millimeters into the brain, allowing us to see vasculature in an almost non-invasive way,” said first author Guosong Hong, who conducted the research as a graduate student in Dai’s lab and is now a postdoctoral fellow at Harvard. “All we have to remove is some hair.”

The technique could eventually be used in human clinical trials, Hong said, but will need to be tweaked. First, the light penetration depth needs to be increased to pass deep into the human brain. Second, injecting carbon nanotubes needs approval for clinical application; the scientists are currently investigating alternative fluorescent agents.

For now, though, the technique provides a new technique for studying human cerebral-vascular diseases, such as stroke and migraines, in animal models. Other research has shown that Alzheimer’s and Parkinson’s diseases might elicit – or be caused in part by – changes in blood flow to certain parts of the brain, Hong said, and NIR-IIa imaging might offer a means of better understanding the role of healthy vasculature in those diseases.

“We could also label different neuron types in the brain with bio-markers and use this to monitor how each neuron performs,” Hong said. “Eventually, we might be able to use NIR-IIa to learn how each neuron functions inside of the brain.”

Your T-shirt’s ringing: Printable tiny flexible cell phones for clothes?

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A new version of “spaser” technology being investigated could mean that mobile phones become so small, efficient, and flexible they could be printed on clothing.
A team of researchers from Monash University’s Department of Electrical and Computer Systems Engineering (ECSE) has modelled the world’s first spaser (surface plasmon amplification by stimulated emission of radiation) to be made completely of carbon.
A spaser is effectively a nanoscale laser or nanolaser. It emits a beam of light through the vibration of free electrons, rather than the space-consuming electromagnetic wave emission process of a traditional laser.
PhD student and lead researcher Chanaka Rupasinghe said the modelled spaser design using carbon would offer many advantages.
“Other spasers designed to date are made of gold or silver nanoparticles and semiconductor quantum dots while our device would be composed of a graphene resonator and a carbon nanotube gain element,” Chanaka said.
“The use of carbon means our spaser would be more robust and flexible, would operate at high temperatures, and be eco-friendly.
“Because of these properties, there is the possibility that in the future an extremely thin mobile phone could be printed on clothing.”
Spaser-based devices can be used as an alternative to current transistor-based devices such as microprocessors, memory, and displays to overcome current miniaturising and bandwidth limitations.
The researchers chose to develop the spaser using graphene and carbon nanotubes. They are more than a hundred times stronger than steel and can conduct heat and electricity much better than copper. They can also withstand high temperatures.
Their research showed for the first time that graphene and carbon nanotubes can interact and transfer energy to each other through light. These optical interactions are very fast and energy-efficient, and so are suitable for applications such as computer chips.
“Graphene and carbon nanotubes can be used in applications where you need strong, lightweight, conducting, and thermally stable materials due to their outstanding mechanical, electrical and optical properties. They have been tested as nanoscale antennas, electric conductors and waveguides,” Chanaka said.


Chanaka said a spaser generated high-intensity electric fields concentrated into a nanoscale space. These are much stronger than those generated by illuminating metal nanoparticles by a laser in applications such as cancer therapy.
“Scientists have already found ways to guide nanoparticles close to cancer cells. We can move graphene and carbon nanotubes following those techniques and use the high concentrate fields generated through the spasing phenomena to destroy individual cancer cells without harming the healthy cells in the body,” Chanaka said

Journal Reference:
Chanaka Rupasinghe, Ivan D. Rukhlenko, Malin Premaratne. Spaser Made of Graphene and Carbon Nanotubes. ACS Nano, 2014; 8 (3): 2431 DOI: 10.1021/nn406015d

Sensing the infrared: Researchers improve infrared detectors using single-walled carbon nanotubes

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Whether used in telescopes or optoelectronic communications, infrared detectors must be continuously cooled to avoid being overwhelmed by stray thermal radiation. Now, a team of researchers from Peking University, the Chinese Academy of Sciences, and Duke University (USA) is harnessing the remarkable properties of single-walled carbon nanotubes (SWNTs) to create highly sensitive, “uncooled” photovoltaic infrared detectors.

This new type of detector, which the team describes in a paper published today in the Optical Society’s (OSA) open-access journal Optical Materials Express, may prove useful for industrial, military, manufacturing, optical communications, and scientific applications.

Carbon nanotubes are known for their outstanding mechanical, electrical, and optical properties. “They also are an ideal nanomaterial for infrared applications,” says Sheng Wang, an associate professor in the Department of Electronics at Peking University in Beijing, China, and an author of the Optical Materials Express paper. “For starters, these nanotubes exhibit strong and broadband infrared light absorption, which can be tuned by selecting nanotubes of different diameters. Also, due to their high electron mobility, nanotubes react very rapidly – on the order of picoseconds – to infrared light.” In comparison to traditional infrared detectors, which are based on semiconductors made of a mercury-cadmium-telluride alloy, the SWNTs are an order of magnitude more efficient, the researchers report.

The team’s photovoltaic infrared detector is formed by aligning SWNT arrays on a silicon substrate. The nanotubes arrays are then placed between asymmetric palladium and scandium contacts. These two metals have properties that collectively create what is known as an Ohmic contact, a region in a semiconductor device that has very low electrical resistance, which helps make the detector operate more efficiently.

“Fabrication of carbon nanotube infrared detectors can be readily implemented on a flexible substrate and large wafer at a low cost,” explains Wang.

The detector demonstrated “acceptable sensitivity” at room temperature and may be significantly improved by increasing the density of the carbon nanotubes, according to the team. The signal-to-noise performance of conventional infrared photodetectors is limited by their natural infrared emission, which is subsequently absorbed by the detector. To avoid having this stray radiation overwhelm the detector, liquid nitrogen or electric cooling is generally used to suppress this thermal effect. However, this makes infrared detectors more complex and expensive to operate. The new design eliminates this need because carbon nanotubes have special thermal properties. At room temperature, they emit comparatively little infrared radiation of their own, especially when the carbon nanotube is on the substrate. In addition, nanotubes are very good at conducting heat, so temperatures do not build up on the detector itself.

One of the biggest surprises for the team was achieving relatively high infrared detectivity (the radiation power required to produce a signal from a photoconductor) using a carbon nanotube thin film only a few nanometers thick, Wang points out. Notably, conventional infrared detectors require much thicker films, on the scale of hundreds of nanometers, to obtain comparable detectivity.

Another huge advantage of the detector is that the fabrication process is completely compatible with carbon nanotube transistors – meaning no big expensive equipment changes are necessary. “Our doping-free chemical approach provides an ideal platform for carbon nanotube electronic and optoelectronic integrated circuits,” says Wang.

The next step for the team is to focus on improving the detectivity of the detector with greater SWNT density, and to also achieve a wide spectrum response with improved diameter control.

More information: The paper, “Carbon Nanotube Arrays Based High-Performance Infrared Photodetector,” by Q. Zeng et al. will appear in a special feature issue on “Nanocarbon for Photonics and Optoelectronics” in Vol. 2, Issue 6 of Optical Materials Express.

Journal reference: Optical Materials Express

Source: Optical Society of America