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A Single Nanoparticle Enables Two Medical Imaging Techniques

Researchers at the Massachusetts Institute of Technology (MIT) have developed a nanoparticle that enables both magnetic resonance imaging (MRI) as well as fluorescent imaging in living animals.  The researchers believe that a single nanoparticle capable of performing these two functions should be able to help track specific molecules through the body, monitor a tumor’s environment, and determine whether drugs have reached their intended target.

In research published in the journal Nature Communications, the MIT team combined an MRI contrasting agent called nitroxide and a fluorescent molecule called Cy5.5 to produce a nanostructure called a branched bottlebrush polymer. The ratio of the two materials in the nanoparticle is 99 percent nitroxide and 1 percent Cy5.5.

This combination enables both MRIs and fluorescent imaging because of the interesting way these materials interact with each other. The nitroxides are reactive molecules in which a nitrogen atom is bound to an oxygen atom with one unpaired electron. Typically, the nitroxides suppress the Cy5.5’s fluorescence, except when the nitroxides are in the presence of molecule from which they can grab an electron, which, in the case of this study, was a vitamin C molecule. Once the free electrons in the nitroxides bind with the free electrons from another molecule, the MRI signal switches off and the Cy5.5 fluoresces.

In the study, which used mice as subjects, the researchers found that the nanoparticles headed towards the liver, where nanoparticles typically end up. It was there that the nanoparticles came in contact with vitamin C (which is produced by the mouse's liver), the MRI signals were turned off, and the Cy5.5 began to fluoresce. Vitamin C ultimately finds its way to a mouse’s brain, and so the researchers were able to detect fluorescence there. Meanwhile, in areas where the concentration of vitamin C was low, the MRI contrast proved to be strong.

The researchers continue to work on enhancing the signal differences that occur when the nanoparticles encounter a target molecule, such as vitamin C. They have also experimented with adding up to three different drugs to the nanostructure. The aim of having these drugs hitch a ride on the nanostructure is to give diagnosticians the ability to track whether they reach their intended target. A fair amount of research is currently being done in this area, wherein nanoparticles behave as both diagnostic tools and therapeutic devices—a capability that has led to the nanoparticles being dubbed “theranostic” nanoparticles.

“That’s the advantage of our platform—we can mix and match and add almost anything we want,” said Jeremiah Johnson, an assistant professor of chemistry at MIT and senior author of the study, in a press release.

The researchers also believe that this platform should allow detection of oxygen radicals inside a patient’s tumor—a biomarker that can indicate how aggressive the tumor is.

“We think we may be able to reveal information about the tumor environment with these kinds of probes, if we can get them there,” said Johnson. “Someday you might be able to inject this in a patient and obtain real-time biochemical information about disease sites and also healthy tissues, which is not always straightforward.”

Topological Insulators Move Closer to Practical Applications

Nearly a decade ago, theorists predicted the upside-down world of topological insulators, which were supposed to possess the peculiar property of being insulators on the inside but conductors on the outside.  While the theories were experimentally confirmed just a couple of years later, making practical devices out of the material has remained a largely unsolved challenge.

Now researchers at Purdue University claim they have found evidence that is the “smoking gun” proving that topological insulators are indeed a path towards realizing practical quantum computers as well as “spintronic” devices that are far more powerful than today’s number crunchers.

The “smoking gun” in this case comes in the form of something called a half-integer quantum Hall effect on the surface of a topological insulator. This is an effect that is seen in graphene in which there is a no resistance plateau at a zero magnetic field.

“This is unambiguous smoking-gun evidence to confirm theoretical predictions for the conduction of electrons in these materials,” said Purdue doctoral student Yang Xu, lead author of the paper detailing the discovery, in a press release.

The research, which appears in the journal Nature Physics, demonstrated for the first time that a three-dimensional material’s electrical resistance did not have to be dependent on the thickness of the material.

The researchers discovered further evidence that the conduction of electrons were topologically protected in these materials, which means their surfaces are guaranteed to be robust conductors. In the experiments, the researchers would slice off thin layers from the surface of the material and after each thinning of the material, the surface maintained its conductance without the slightest change.

“For the thinnest samples, such topological conduction properties were even observed at room temperature, paving the way for practical applications,” Xu said in the release.

This conduction on the surface of topological insulators is important for spintronic devices. The unique applicability of topological insulators to spintronic devices comes from the fact that the conducting electrons on the surface have no mass and are automatically “spin polarized,” leading to the unique half-integer quantum Hall effect that was observed in this research.

This past summer, researchers at Penn State and Cornell University provided one of the first promising indications that it might actually be possible to derive practical applications such as spintronic devices from these topological insulator materials.

In addition to spintronics, researchers believe that topological insulators, when combined with superconductors, could lead to a practical quantum computer

“One of the main problems with prototype quantum computers developed so far is that they are prone to errors,” said Yong P. Chen, a Purdue associate professor, in the press release. “But if topologically protected, there is a mechanism to fundamentally suppress those errors, leading to a robust way to do quantum computing.”

Chen added: "This experimental system provides an excellent platform to pursue a plethora of exotic physics and novel device applications predicted for topological insulators.”

A Drop of Water and a Push Transfers 2-D Material Between Substrates

The production of molybdenum disulfide (MoS2) films has been getting better of late. Recently researchers at Rice University found a way to orient the two-dimensional (2-D) material on its side so that the maximum amount of edge is exposed—a good thing for fuel cell catalysts and the supercapcitor electrodes.

Now researchers at North Carolina State University (NCSU) have developed a method for transferring these MoS2 films onto any substrate without causing any damage to the 2-D material  in the process. The researchers believe that this comparitively easy process could lead to the material’s use in flexible electronics for computing, photonic systems, and more.

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Nanofilm Serves as Artificial Retina

Israel-based Nano Retina made some noise a few years back with its development of so-called “nanoelectrodes” that “interface with the eye’s bipolar neurons” and restart neural stimulation, allowing for messages to go to the brain. The nanoelectrodes served as a kind of artificial retina.

Since then it doesn’t appear that Nano Retina has had much more to report on the development of its implantable device, at least from what its website reveals. But it other Israeli researchers do, in a paper published in the journal Nano Letters. The team from Tel Aviv University, the Hebrew University of Jerusalem Centers for Nanoscience and Nanotechnology and Newcastle University combined semiconductor nanorods and carbon nanotubes to create a wireless, light-sensitive, flexible film that could potentially act in the place of a damaged retina.

The researchers used a plasma polymerized acrylic acid midlayer to make covalent bonds with the semiconductor nanorods directly onto neuro-adhesive, three-dimensional carbon nanotube surfaces.

The researchers have tested the device in a chick’s retina that in normal conditions would not have responded to light. These tests demonstrated that the flexible film absorbed light, which then triggered neuronal activity in the chick.

The researchers claim that this film is more durable, flexible and efficient, as well as better able to stimulate neurons, compared to other competitive devices. While there have been a number of approaches to creating artificial retinas to address diseases of the retina, such as macular degeneration, the stumbling block has largely been getting the device to fit inside the eye itself.

This is why solutions such as Nano Retina’s nanoelectrodes have been so attractive. It would seem, based Nano Retina’s reticence since its initial announcement, that the engineering issues are significant even with a nanoscale solution. Whether this latest research can find a way around them remains to be seen.

Each Nanopore in a Material Serves as a Battery

We have seen batteries get so small that their anodes consist of a single nanowire. In that instance, the research was not really aimed at creating a new battery design but instead at demonstrating that the researchers could use a liquid electrolyte in the vacuum of a transmission electron microscope (TEM).

In contrast, researchers at the University of Maryland have their focus on building a new type of battery that is based on tiny nanopores in a ceramic material. The researchers have developed a method for introducing an electrolyte into the nanopores so that each cavity acts as an individual battery cell and all of them are joined in parallel.

Commenting on their research, published in the journal Nature Nanotechnology, the Maryland researchers note that: “a single nanopore structure that embeds all components of an electrochemical storage device could bring about the ultimate miniaturization in energy storage.”

In the video below, one of the authors of the paper, Chanyuan Liu, explains that the battery they developed in the lab can undergo one thousands charge/discharge cycles. It can be fully charged in 12 minutes, she adds in the press release.

Eleanor Gillette, another member of the group, says in the video that the aim is to develop the manufacturing technology to make larger nanopore  structures possible. Liu says that they have already identified ways to increase the power of the batteries by ten times.

The entire design of the battery involves each of its nanobattery components being composed of an anode, a cathode, and a liquid electrolyte confined within the nanopores of anodic aluminium oxide, which is an advanced ceramic material. Each nanoelectrode includes an outer ruthenium nanotube current collector and an inner nanotube of vanadium pentoxide storage material. These together form a symmetric full nanopore storage cell with anode and cathode separated by an electrolyte region. The vanadium pentoxide is treated with lithium at one end to serve as the anode, with pristine vanadium pentoxide at the other end serving as the cathode.

The researchers believe that the key to the success of the design is the uniformity in shape and size of the nanopores, which allows for a dense packing of the nanopores into the ceramic material.

Graphene-based Supercapacitors Take Another Crack at All-electric Vehicles

Researchers at the Queensland University of Technology (QUT) in Australia have developed a supercapacitor featuring graphene carbon nanotube films. They’re confident that their creation could dramatically boost the power and range of all-electric vehicles that now rely on lithium-ion (Li-ion) batteries for propulsion.

In research that was published in both the Journal of Power Sources and Nanotechnology, the Australian researchers used graphene films as the electrodes and carbon nanotube films as current collectors. The result was devices demonstrating energy densities ranging from  8 to 14 watt-hours per kilogram, and power densities between 250 and 450 kilowatts per kilogram.

The hope has been that someone could make graphene electrodes for supercapacitors that would boost their energy density into the range of chemical-based batteries. The supercapacitors currently on the market have on average an energy density around 28 Wh/kg, whereas a Li-ion battery holds about 200Wh/kg. That’s a big gap to fill.

The research in the field thus far has indicated that graphene’s achievable surface area in real devices—the factor that determines how many ions a supercapacitor electrode can store, and therefore its energy density—is not any better than traditional activated carbon. In fact, it may not be much better than a used cigarette butt.

Though graphene may not help increase supercapacitors’ energy density, its usefulness in this application may lie in the fact that its natural high conductivity will allow superconductors to operate at higher frequencies than those that are currently on the market. Another likely benefit that graphene will yield comes from the fact that it can be structured and scaled down, unlike other supercapacitor materials.

It is this ability to be molded into various shapes that the Australian researchers hope to exploit; they suggest that the supercapacitor films they have developed could be used to line parts of a car’s chassis to offer a quick energy boost to all-electric vehicles using Li-ion batteries.

"Vehicles need an extra energy spurt for acceleration, and this is where supercapacitors come in. They hold a limited amount of charge, but they are able to deliver it very quickly, making them the perfect complement to mass-storage batteries," said Marco Notarianni, a QUT researcher, in a press release.

Notarianni added: "Supercapacitors offer a high power output in a short time, meaning a faster acceleration rate of the car and a charging time of just a few minutes, compared to several hours for a standard electric car battery."

Graphene-based supercapacitors have been a bit of a disappointment to those who envisioned them completely replacing lithium-ion (Li-ion) batteries for powering all-electric vehicles.  This latest complementary role suggested by the Australian researchers may be a way to see them put to some use.

However, it’s not clear that the energy density numbers achieved during this latest round of research have given us any reason to think that a graphene-based supercapacitor will be the route leading to an all-electric vehicle that operates solely on supercapacitors.

Nanodiamond Production Technique Opens Up Electronic Applications

With news just last week that nanodiamonds could aid in the development of new methods for drug delivery and cancer therapeutics, the prospects for successful cancer treatment got a shot in the arm.

While medical applications for nanodiamonds got a boost, it left the fortunes of nanodiamonds in electronics-related applications a bit out in the cold. The wait was not long, however, with research out of Purdue University that demonstrated a pulsed laser could be used to create synthetic nanodiamond films and patterns on the surface of graphite. This development should have an impact on potential applications for nanodiamonds including biosensors, quantum computing, fuel cells and next-generation computer chips.

"The biggest advantage is that you can selectively deposit nanodiamond on rigid surfaces without the high temperatures and pressures normally needed to produce synthetic diamond," said Gary Cheng, an associate professor of industrial engineering at Purdue University, in a press release. "We do this at room temperature and without a high temperature and pressure chamber, so this process could significantly lower the cost of making diamond. In addition, we realize a direct writing technique that could selectively write nanodiamond in designed patterns."

In research published in the Nature journal Scientific Reports, the Purdue team started with a multilayered film containing a layer of graphite and covered with a glass sheet. They then exposed this layered structure to an ultra-fast pulsing laser that instantaneously transformed the graphite into an ionized plasma that generates a downward pressure. The graphite plasma is prevented from escaping by the glass cover of the multilayered film where, trapped, it quickly solidifies into diamond.

"These are super-small diamonds and the coating is super-strong, so it could be used for high-temperature sensors," Cheng said in the release.

Strength was always the aim of the research. In fact, the technique was originally developed to find a way to strengthen metals. It was only serendipitously that they discovered that it produced this nanodiamond film.

With this development, the researchers believe nanodiamonds could begin to have an impact in electronics. For instance, nanodiamonds have been suggested as a way to get quantum computers to operate at room temperature as opposed to near absolute zero. This would be accomplished by replacing the ions used in some quantum computers with nitrogen-vacancy centers in diamonds.

Nanodiamonds could also lead to next-generation computer chips based on optical transitors in which photons replace electrons. In this scenario, nanodiamonds would replace the special dye molecules that are used in today’s optical transistors. The use of these dyes requires special cooling, which eliminates them from practical use. However, researchers at the Institute of Photonics Sciences (ICFO) in Barcelona demonstrated last year showed that nanodiamond operating at room temperature could be used in an ultrafast optical switch, replacing the dye molecules.

New Method for Producing Molybdenum Disulfide Provides Two Potential Applications

Molybdenum disulfide (MoS2) started out as the next big thing after graphene in electronic applications. But that excitement started to wane somewhat when it was revealed that MoS2 contained traps—impurities or dislocations that can trap an electron or hole and hold it until a pair is completed—that limit its electronic properties.

While researchers continue to work on removing those traps in order to improve its electronic properties, others have been looking at uses for MoS2 outside of digital electronics in applications including photovoltaics and wearable electronics.

In this ever-expanding application universe, researchers at Rice University have found a method for manipulating MoS2 so that it could serve both as an improved catalyst for fuel cells and as the electrodes of supercapacitors.

In research published in the journal Advanced Materials, the Rice team, led by James Tour, developed a simple method for producing flexible films made from MoS2 that orients the material on its sides. In other words, they made the material in such a way that the maxiumum amount of its edges are exposed.

The researchers showed that when oriented in this manner, the MoS2 can serve as an effective catalyst in the hydrogen evolution reaction (HER), a process used in fuel cells to pull hydrogen from water.

“So much of chemistry occurs at the edges of materials,” said Tour in a press release. “A two-dimensional material is like a sheet of paper: a large plane with very little edge. But our material is highly porous. What we see in the images are short, 5- to 6-nanometer planes and a lot of edge, as though the material had bore holes drilled all the way through.”

Tour added: “Its performance as a HER generator is as good as any molybdenum disulfide structure that has ever been seen, and it’s really easy to make.”

Other research has attempted to take advantage of MoS2 as a catalyst for fuel cells by standing them up on their sides. The Rice team took a different approach. First, they grew a porous molybdenum oxide film onto a molybdenum substrate through room-temperature anodization, an electrochemical process for thickening metal parts by adding a natural oxide layer.

The researchers then exposed the film to sulfur vapor at 300 °C (572 °F) for one hour. The result was molybdenum disulfide that had a flexible, nano-porous sponge-like structure.

Since the key to catalysts and to the electrodes in supercapacitors is surface area, the researchers immediately realized that the material would fit the bill for both applications. The Rice team developed a supercapacitor using the material and found the device retained 90 percent of its capacity after 10,000 charge-discharge cycles and 83 percent after 20,000 cycles.

Tour believes that this method of exploiting anodization could serve as a platform for a range of applications and devices.

“We see anodization as a route to materials for multiple platforms in the next generation of alternative energy devices,” Tour said. “These could be fuel cells, supercapacitors and batteries. And we’ve demonstrated two of those three are possible with this new material.”

Nanomaterial Promises to Reduce Shutdowns of Concentrating Solar Power Plants

Researchers at the University of California at San Diego have developed a composite nanomaterial that can convert 90 percent of the sunlight it captures into heat, making it an ideal candidate for solar absorption at concentrating solar power (CSP) plants.

"We wanted to create a material that absorbs sunlight [and] doesn't let any of it escape. We want the black hole of sunlight," said Sungho Jin, a professor at UC San Diego, in a press release.

The hybrid material, which is described in the journal Nano Energy,  combines copper oxide nanowires with cobalt oxide nanoparticles to create a multi-scale surface for the material with dimensions ranging from 10 nanometers to micrometers. This multi-scale surface gives the material its extraordinary efficiency at trapping and absorbing light.

Previous research has proposed the use of nanowires for concentrating the sun’s rays into a very small area of solar cells. And copper sulfide nanoparticles in combination with single-walled carbon nanotubes have proven effective in converting both light and thermal radiation into electricity.

In contrast to these other nanomaterials, which were intended for use in photovoltaics that convert light directly into electricity, the hybrid material developed by the UCSD team is being targeted for solar absorption to create heat. The heat is then used to boil water, which in turn creates steam that runs turbines to produce electricity.

The materials that are currently used for solar absorption lack the resistance to high temperatures that the job requires. As a result, they have to be replaced every year. This new hybrid material is unique in that it can withstand temperatures above 700 degrees Celsius.

This should make a significant difference for CSP plants that, as it stands now, have to shut down once a year to remove the degraded sunlight-absorbing material and apply a new coating. Because this means that there is no power generation occurring during this reapplication, the U.S. Department of Energy’s SunShot program was keen to support this most recent research to find a material that would have a significantly longer life span.

With CSP plants already producing approximately 3.5 gigawatts of power globally, the prospect of eliminating an annual shutdown and extending the maintenance interval to several years would make a big difference to the amount of electricity they produce and the confidence people have in this source of electricity.

Nanodiamonds Could Become Mankind's Best Friend

Researchers at Cardiff University in Wales have developed a new method for taking readings of processes going on inside living cells. The technique, which relies on nanodiamonds, could eventually aid in developing new modes of drug delivery and cancer therapeutics.

The traditional method for imaging cellular processes has depended on fluorophores, which are a fluorescent chemical compound that can re-emit light upon light excitation. But they degrade under the light used to illuminate them. This renders them ineffective as visualization targets after a short period of time. Furthermore, fluorophores have been shown to become toxic over time, sometimes killing nearby cells.

Nanodiamonds have been proposed as a one-to-one replacement for fluorophores for sometime now. But getting them to fluoresce required designing small defects into them. Manufacturing these defects into the diamonds proved to be costly and time consuming.

In research published in the journal Nature Nanotechnology, the Cardiff researchers developed a new method wherein the nanodiamonds are used differently, thus eliminating the need for this difficult trick of producing them with specific defects.

Instead, the Cardiff team demonstrated that nanodiamonds without defects can be imaged optically through the interaction between the illuminating light and the vibration of the chemical bonds inside the diamond lattice structure. These vibrations cause the light to scatter in such a way that they produce a different color.

To get this effect, the researchers used two laser beams pulsing at a specific frequency so that laser light triggers the chemical bonds inside the nanodiamonds to vibrate in sync. The researchers then focus one of two lasers at these vibrations, which produces a light known as, coherent anti-Stokes Raman scattering (CARS).

The researchers were then able to use a microscope to measure the intensity of the CARS light on a series of nanodiamonds of varying sizes. After using electron microscopy and other optical contrast methods developed by the researchers, the team was able to accurately measure the sizes of the diamonds. This then made it possible to quantify the relationship between the size of the nanodiamonds and the intensity of light that they produce.

The end result was a method that allowed the researchers to measure the size and number of nanodiamonds that had been delivered into the living cells.

“This new imaging modality opens the exciting prospect of following complex cellular trafficking pathways quantitatively with important applications in drug delivery,” said Paola Borri from the School of Biosciences, who led the study, in a press release. “The next step for us will be to push the technique to detect nanodiamonds of even smaller sizes than what we have shown so far and to demonstrate a specific application in drug delivery.”

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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
 
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Rachel Courtland
Associate Editor, IEEE Spectrum
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