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New Study Indicates Nanoparticles Do Not Pass Through Skin

For at least the last several years, NGO’s like Friends of the Earth (FoE) have been leveraging preliminary studies that indicated that nanoparticles might pass right through our skin to call for a complete moratorium on the use of any nanomaterials in sunscreens and cosmetics.

Even if you’re a world-renowned expert on assessing the risk of nanomaterials, you had better not challenge the orthodoxy of that line of thinking.  Or if you’re an NGO that investigated the issue of nanoparticles in sunscreens and found no risk, you should be prepared to be so marginalized by other NGOs that you will hardly warrant a mention.

On the contrary, the prevailing argument was that if you’re a company using nanoparticles in your sunscreen you had to prove your product was safe, even if there was no conclusive evidence that your product was risky and a fair amount of evidence that it was safe. So frightening and compelling was this scare screed that in a poll of Australians they said they would prefer to risk getting skin cancer rather than use a sunscreen that might contain nanoparticles. Fear almost always wins out over reason.

Unfortunately for the fear mongers, the evidence is mounting that nanoparticles cannot penetrate the skin. Researchers at the University of Bath in the UK found that even the smallest nanoparticles are not capable of passing through the skin barrier.

The research, which was published in the Journal of Controlled Release (“Objective assessment of nanoparticle disposition in mammalian skin after topical exposure”),  employed laser scanning confocal microscopy to see whether fluorescently tagged polystyrene beads on the scale of 20 to 200 nanometers were absorbed into the skin.

“Previous studies have reached conflicting conclusions over whether nanoparticles can penetrate the skin or not,” says Professor Richard Guy from the University’s Department of Pharmacy & Pharmacology, in the press release. “Using confocal microscopy has allowed us to unambiguously visualize and objectively assess what happens to nanoparticles on an uneven skin surface. Whereas earlier work has suggested that nanoparticles appear to penetrate the skin, our results indicate that they may in fact have simply been deposited into a deep crease within the skin sample.”

This latest UK research certainly won’t put this issue to rest. These experiments will need to be repeated and the results duplicated. That’s how science works. We should not be jumping to any conclusions that this research proves nanoparticles are absolutely safe any more than we should be jumping to the conclusion that they are a risk. Science cuts both ways.

 

Graphene Replaces Traditional Silicon Substrates in Future Devices

Researchers at the Norwegian University of Science and Technology (NTNU) have patented and are commercializing a method by which gallium arsenide (GaAs) nanowires are grown on graphene.

The method, which was described and published in the journal Nano Letters (“Vertically Aligned GaAs Nanowires on Graphite and Few-Layer Graphene: Generic Model and Epitaxial Growth”), employs Molecular Beam Epitaxy (MBE) to grow the GaAs nanowires layer by layer. A video describing the process can be seen below.

"We do not see this as a new product," says Professor Helge Weman, a professor at NTNU's Department of Electronics and Telecommunications in the press release. "This is a template for a new production method for semiconductor devices. We expect solar cells and light emitting diodes to be first in line when future applications are planned."

Whether it is a method or a product, Weman and his colleagues have launched a new company called Crayonano that will be commercializing the hybrid material that the researchers developed.

The researchers contend that replacing traditional semiconductor materials as a substrate will reduce material costs. The silicon materials are fairly expensive and are usually over 500µm thick for 100mm wafers. As the video explains, using graphene reduces the substrate thickness to the width of one atom. Obviously reduction in material is really only a side benefit to the use of graphene. The real advantage is that the electrode is transparent and flexible, thus its targeting for solar cells and LEDs.

Interestingly Weman sees his team's work as a compliment to the work of companies like IBM that have used graphene “to make integrated circuits on 200-mm wafers coated with a continuous layer of the atom-thick material.”

Weman notes: "Companies like IBM and Samsung are driving this development in the search for a replacement for silicon in electronics as well as for new applications, such as flexible touch screens for mobile phones. Well, they need not wait any more. Our invention fits perfectly with the production machinery they already have. We make it easy for them to upgrade consumer electronics to a level where design has no limits."

As magnanimous as Weman’s invitation sounds, one can’t help but think it comes from concern. The prospect of a five-year-development period before a product gets to market might be somewhat worrying for a group of scientists who just launched a new startup. A nice licensing agreement from one of the big electronics companies must look appealing right about now.

Graphene Proves To Be One Hundred Times Better at Rustproofing Metals

While the wonder material graphene continues to come under pressure from other two-dimensional materials in electronics applications, it has continued to build up applications far afield from electronics.

One of the applications that has opened up over the last year is rustproofing. In May of this year, researchers from the University of Buffalo demonstrated that they could use graphene in rustproofing steel.

Now researchers at Monash University in Australia and Rice University in the USA have used graphene to rustproof copper.

The research, which was published in the journal Carbon (“Protecting copper from electrochemical degradation by graphene coating”), claims that the graphene-based coating renders copper nearly 100 times more resistant to corrosion than if left unprotected.

“We have obtained one of the best improvements that has been reported so far,” says study co-author Dr Mainak Majumder in the university press release. “At this point we are almost 100 times better than untreated copper. Other people are maybe five or six times better, so it’s a pretty big jump.”

To achieve the atomic-scale rustproof coating, the researchers simply heated the graphehe to temperatures between 800 and 900 degrees celcisus and then applied the graphene to the copper through chemical vapor deposition. Seeing whether they can apply the graphene coating at a lower temperature will be a focus for future research.

The University of Buffalo researchers explained that their research into rustproofing steel was in part motivated by a desire to find a more environmentally friendly method than the chrome electroplating that is typically used. But the Monash and Rice team see their graphene film replacing polymer coatings used in metals, so the environmental aspect is less acute in this case.

Nonetheless, the Australian-U.S. research team believes that this use of graphene could change the rustproofing methods for products as varied as ocean-going vessels and electronics.

Carbon Nanotubes Form Smallest Pixels for 3D Holographic Imaging

The holograms we have seen for the past 50 years have at once fascinated and disappointed us. If we had been hoping to see something along the lines of the projected image of Princess Leia from Star Wars, or the holodeck from Star Trek Next Generation, disappointment would likely have overwhelmed our sense of fascination.

Two years ago researchers at the University of Arizona for the first time “demonstrated an optical material that can display "holographic video," as opposed to static holograms found in credit cards and product packages.” Since then it seemed our hopes for holograms have been getting brighter.

Now researchers at the University of Cambridge’s Centre of Molecular Materials for Photonics and Electronics (CMMPE) have used carbon nanotubes to create 3D hologram images with an extremely wide field of view and the highest possible resolution.

The research, which was published in the journal Advanced Materials (“Carbon Nanotube Based High Resolution Holograms”), essentially used the carbon nanotubes as diffractive elements that turn the carbon nanotubes into optical projectors. The small size of the carbon nanotubes created smaller pixels thus boosting the resolution of the image.

“Smaller pixels allow the diffraction of light at larger angles – increasing the field of view. Essentially, the smaller the pixel, the higher the resolution of the hologram,” says Dr. Haider Butt from CMMPE in a press release.

The demonstration of their new carbon nanotube-based pixels involved spelling out the name “Cambridge” using various colors of laser light that had been scattered through the carbon nanotube pixels. While initially a fairly modest display and dependent on the prohibitively expensive carbon nanotubes, Butt believes that some kind of nanomaterials will form the basis of a new approach to holographic images.

Butt adds in the release: “A new class of highly sensitive holographic sensors can be developed that could sense distance, motion, tilt, temperature and density of biological materials. What’s certain is that these results pave the way towards utilizing nanostructures to producing 3D holograms with wide field of view and the very highest resolution.”

To replace the carbon nanotubes, the researchers are looking at the prospect of using zinc oxide nanowires, which Zhong Lin Wang at Georgia Tech has been using over the years for its of piezoelectric qualities.

The other big issue that the researchers still we need to address is investigating “holographic video” because currently the carbon nanotube pixels can only project static holograms. Looks like there’s still some work to be done before Princess Leia holograms are projected, at least with a nanomaterial as the pixel.

Wearable Health Monitoring Project Turns to Nanotechnology for Power Sources

Sometimes significant innovations result just from aggregating a number of different innovations into one product. So it is with a multi-institution research effort to exploit recent developments in wireless health monitoring systems and couple them with thermoelectric and piezoelectric nanomaterials to power them.

The research is being led by the Nanosystems Engineering Research Center for Advanced Self-Powered Systems of Integrated Sensors and Technologies (ASSIST) headquartered at North Carolina State University in collaboration with partner institutions Florida International University, Pennsylvania State University and the University of Virginia.

“Currently there are many devices out there that monitor health in different ways,” says Dr. Veena Misra, the center’s director and professor of electrical and computer engineering at NC State in the university press release covering the research. “What’s unique about our technologies is the fact that they are powered by the human body, so they don’t require battery charging.”

While Misra may be correct in her assertion that this combination is unique within health monitoring systems, both thermoelectric and piezoelectric nanomaterials for powering devices is an area being vigorously pursued.

In the area of thermoelectric nanomaterials, we have seen significant developments this year. One coming from Wake Forest University involved using multi-walled carbon nanotubes to fabricate a thin film that the researchers claim can convert differences in temperature into electrical energy. In that case, the researchers were targeting the powering of cell phones.

A month after the Wake Forest research was announced, an international team of researchers from the California Institute of Technology, the Chinese Academy of Science's Shanghai Institute of Ceramics, Brookhaven National Laboratory and the University of Michigan developed a liquid-like material in which selenium atoms make a crystal lattice and copper atoms flow through the crystal structure like a liquid. This unusual behavior of the copper ions around the selenium lattice resulted in very low thermal conductivity (bad at conducting heat) in what is otherwise a fairly simple semiconductor (good at conducting electricity), making it an excellent candidate as a thermoelectric material.

Piezoelectric nanomaterials have been dominated until late by the use of nanowires, and specifically the research of Professor Zhong Lin Wang, Director of the Center for Nanostructure Characterization at Georgia Tech, who has almost singlehandedly kept the somewhat obscure topic of piezoelectric qualities of zinc oxide nanowires in the news. But recently graphene has entered into the area of piezoelectric materials with research coming out of Stanford University. While the Stanford research was only conducted in modeling and simulation software, it did promise to open up the fairly new conceptual field of “straintronics”.

It is not clear from either the NC State press materials or even the video that they have produced (see below), what nanomaterials they intend to use to bring on either the thermoelectric or piezoelectric effects. It will be interesting to see which direction they go with their materials.

Directed Self-Assembly Accomplished with Magnets

As chips shrink ever smaller, traditional lithography techniques have begun to lose their ability to remain accurate and the hopes of maintaining Moore's Law have dimmed as a result. But directed self-assembly, a way to build integrated circuits from the bottom up, has been held out as a possible way to keep shrinking chip feature sizes and and sustain Moore’s Law.

Basically, directed self-assembly is a way of exploiting the ability of molecules to arrange themselves into ordered structures—with a little direction from our end. Previously, H.-S. Philip Wong used lithography to carve indentations that served as a template for the molecules to self-assemble themselves. This combination of traditional lithography with self-assembly techniques has been a line of research that has seemed to be the most promising in the field. 

A less traditional line of research for directed self-assembly has been the work of Angela Belcher, in which DNA serves as the template and viruses actually build up the integrated circuit

A new addition to the field comes from the University of Delaware. Eric M. Furst and his colleagues have demonstrated how paramagnetic colloids can be directed to self-assemble in the presence of a magnetic field. 

The research, which was published in the Proceedings of the National Academies of Science (PNAS) online edition (“Multi-scale kinetics of a field-directed colloidal phase transition”),  was able to observe how the particles transitioned from a solid-like material into an organized crystalline structure. Furst claims that this represents the first time that anyone has observed this guided “phase separation” of particles.

“This development is exciting because it provides insight into how researchers can build organized structures, crystals of particles, using directing fields and it may prompt new discoveries into how we can get materials to organize themselves,” Furst says in the university press release covering the research.

An interesting twist to the research was the enlistment of NASA to see how the particles would react in a weightless environment. To realize this some of the experiments were conducted in the International Space Station. The weightless environment allowed for some fresh observations on the self-assembly process. The particles first developed into its solid-like form and then coarsened to the point of breaking apart. After separating—not unlike the way water and oil separate when combined—the particles formed themselves into the crystalline lattice structure.

Furst further notes in the article: “This is the first time we've presented the relationship between an initially disordered structure and a highly organized one and at least one of the paths between the two. We’re excited because we believe the concept of directed self-assembly will enable a scalable form of nanotechnology.”

Nanotechnology Takes Aim at Improving Beer

The motivations for certain applications of nanotechnology can run the gamut from ending our dependence on fossil fuels to providing clean drinking water in poor, remote regions of the world.  But these high-minded aspirations are not always the goal for nanotechnology applications; sometimes we just want to have a better beer drinking experience.

Australian researchers created a better way to keep beer cool two-and-a-half years ago. But  it seems that scientists in Ireland were not entirely satisfied and are developing a new material for extending the shelf life of beer

Until quite recently, it was unheard of to use plastic for beer containers because oxygen and carbon monoxide would escape through the relatively porous plastic and take away the taste of the beer.  But for some years now Nanocor Inc., which is wholly owned subsidiary of AMCOL International Corporation, has been selling its nanoclay materials to create gas-proof plastic composites for beer packaging.

Researchers at CRANN--the Science Foundation Ireland-funded nanoscience institute based at Trinity College Dublin--have decided on a different approach. Instead of using a nanoclay, the researchers will exfoliate nanosheets of boron nitride and mix them into a polymer.

The CRANN team have partnered with the brewing company SABMiller, which has agreed to invest in the research over the next two years, so we're pretty sure to have a commercial product at the end.

So, if we combine the Australian and Irish research we should be able to enjoy a plastic bottle of beer that remains cold over a much longer period of time. The joys of science.

Individual Molecular Bonds Imaged for First Time

IBM has been pushing the boundaries of Atomic Force Microscopy (AFM) all this year. In February we learned that IBM Zurich had imaged the charge distribution within a molecule for the first time.  Then the same team in May not only imaged individual hydrogen atoms but also manipulated them with the use of AFM. 

After having established new boundaries for AFM, IBM scientist Leo Gross and his colleagues next set out to apply these tools. What they've developed is a method, using AFM, for distinguishing individual molecular bonds.The researchers believe that being able to image these individual bonds could prove critical in studying graphene devices, with potential applications in high-bandwidth wireless communication and electronic displays.

“We found two different contrast mechanisms to distinguish bonds. The first one is based on small differences in the force measured above the bonds. We expected this kind of contrast but it was a challenge to resolve,” says Gross in the IBM press release covering the research. “The second contrast mechanism really came as a surprise: Bonds appeared with different lengths in AFM measurements. With the help of ab initio calculations we found that the tilting of the carbon monoxide molecule at the tip apex is the cause of this contrast.”

The researchers, who published their findings in the 14 September edition of Sciencewere able to image the bond order and length of individual carbon-carbon bonds in C60 (or buckyballs). 

While the concept of bond order had predicted that the individual bonds between carbon atoms in molecules like the buckyball differed in their length and strength, this research is the first to actually visualize these differences.

The IBM researchers expect their work to lead to greater understanding of individual molecules, which in turn could improve research into novel electronic devices, organic solar cells, and organic light-emitting diodes (OLEDs).

Ever since IBM Zurich opened up its new $90-million nanotechnology research facility last year (aptly named the “Binnig and Rohrer Nanotechnology Center”, after the joint discoverers of the AFM), it seems the researchers there have been on a tear to push AFM into the forefront of nanotechnology research. 

Nanoparticle Sensor Detects Mercury at Levels a Million Times Below Current Technology

An international team of researchers has developed a nanoparticle that is the most sensitive sensor yet for detecting the known toxin mercury in our water—an interesting and ironic use of nanotechnology, given that a number of other researchers are hard at work determining whether other nanoparticles might be hazardous to our health or the environment.

Researchers at Northwestern University in collaboration with colleagues at Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland have developed a sensor system based around a nanoparticle that can detect minute levels of mercury and other heavy metals in water and fish. 

The research ("Ultrasensitive detection of toxic cations through changes in the tunnelling current across films of striped nanoparticles"), which was published in the journal Nature Materials, has produced a sensor capable of detecting heavy metals in much smaller concentrations than today's state-of-the-art methods.

“The system currently being used to test for mercury and its very toxic derivative, methyl mercury, is a time-intensive process that costs millions of dollars and can only detect quantities at already toxic levels,” says Bartosz Grzybowski, lead author of the study, in the university press release covering the research. “Ours can detect very small amounts, over [a] million times smaller than the state-of-the-art current methods. This is important because if you drink polluted water with low levels of mercury every day, it could add up and possibly lead to diseases later on. With this system consumers would one day have the ability to test their home tap water for toxic metals.”

The device the researchers have developed is basically a commercial strip of glass covered with a nanoparticle that gives the glass a kind of coat of hair—“a kind of nano-velcro”—that can then be dipped into water for testing purposes. If a metal cation—a positively charged ion—from something like methyl mercury comes in contact with the hairs, the hairs close up around the pollutant, trapping it.

The film then becomes electrically conductive and alerts the tester to the presence of the cation. A measurement of the voltage along the nanostructure film indicates the level of contamination. The researchers also found if they shortened the length of the nano-hairs they could detect cadmium.

What sounds particularly attractive about the method is that the nanofilm can be produced at a cost of somewhere between $1 to $10 to make, according to Grzybowski.

The researchers carried out studies on water in Lake Michigan near Chicago and on a mosquito fish from the Florida Everglades. The tests of the Lake Michigan water came within the range of the measurements found by the FDA and the fish testing was nearly identical to that of the US Geological Survey.

When you see a technology that is capable of improving on the current state-of –the-art by one million times and does so in a field designed for our health and safety, you have to wonder why it seems others are so keen to find replacements for it before it’s even been determined a risk.

All-Optical Nanowire Switch Promises “Consumer Photonics” in the Future

 

While nanophotonic devices have been used for optical processing for some time, the aim of late has been to use light to actually throw switches to control electronic circuits. Hong X. Tang of Yale University wrote on the pages of Spectrum three years ago about his success in using the pressure of light to operate nanomechanical devices

Now researchers at the University of Pennsylvania have developed what they claim is the first all-optical nanowire switch. The research, which was published in the journal Nature Nanotechnology (“All-optical active switching in individual semiconductor nanowires”), not only succeeded in fashioning a switch from cadmium sulfide nanowires, but also managed to combine the photonic switches into a logic gate.

The idea that cadmium sulfide nanowires could be used to make optical switches derived from the researchers previous research that demonstrated that these nanowires possessed extraordinary strong light-matter coupling

With that previous work as inspiration, the researchers set off on their current research and started by cutting a gap into a nanowire. They then ran energy through one of the nanowire pieces until it started to emit laser light from one end of it and started to bridge the gap to the other piece of nanowire.

“Once we have the light in the second segment, we shine another light through the structure and turn off what is being transported through that wire,” says associate professor Ritesh Agarwal in the university press release covering the research. “That's what makes it a switch.”

Agarwal and his colleague in the research, graduate student Brian Piccione, opted to combine their new switches together to assemble a logic gate. “We used these optical switches to construct a NAND gate, which is a fundamental building block of modern computer processing,” says Piccione in the press release.

While Agarwal makes a fair assessment that this work at least indicates that the future could become “consumer photonics” as opposed to “consumer electronics”, I think it also fair to say that we may still be a long way off from that eventual future. Definitely a step in the right direction though.

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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
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