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166
A chip developed by mechanical engineers at Worcester Polytechnic Institute (WPI) can trap and identify metastatic cancer cells in a small amount of blood drawn from a cancer patient. The breakthrough technology uses a simple mechanical method that has been shown to be more effective in trapping cancer cells than the microfluidic approach employed in many existing devices.

The WPI device uses antibodies attached to an array of carbon nanotubes at the bottom of a tiny well. Cancer cells settle to the bottom of the well, where they selectively bind to the antibodies based on their surface markers (unlike other devices, the chip can also trap tiny structures called exosomes produced by cancers cells). This "liquid biopsy," described in a recent issue of the journal Nanotechnology, could become the basis of a simple lab test that could quickly detect early signs of metastasis and help physicians select treatments targeted at the specific cancer cells identified.

Metastasis is the process by which a cancer can spread from one organ to other parts of the body, typically by entering the bloodstream. Different types of tumors show a preference for specific organs and tissues; circulating breast cancer cells, for example, are likely to take root in bones, lungs, and the brain. The prognosis for metastatic cancer (also called stage IV cancer) is generally poor, so a technique that could detect these circulating tumor cells before they have a chance to form new colonies of tumors at distant sites could greatly increase a patient's survival odds.

"The focus on capturing circulating tumor cells is quite new," said Balaji Panchapakesan, associate professor of mechanical engineering at WPI and director of the Small Systems Laboratory. "It is a very difficult challenge, not unlike looking for a needle in a haystack. There are billions of red blood cells, tens of thousands of white blood cells, and, perhaps, only a small number of tumor cells floating among them. We've shown how those cells can be captured with high precision."

The device developed by Panchapakesan's team includes an array of tiny elements, each about a tenth of an inch (3 millimeters) across. Each element has a well, at the bottom of which are antibodies attached to carbon nanotubes. Each well holds a specific antibody that will bind selectively to one type of cancer cell type, based on genetic markers on its surface. By seeding elements with an assortment of antibodies, the device could be set up to capture several different cancer cells types using a single blood sample. In the lab, the researchers were able to fill a total of 170 wells using just under 0.3 fluid ounces (0.85 milliliter) of blood. Even with that small sample, they captured between one and a thousand cells per device, with a capture efficiency of between 62 and 100 percent.

The carbon nanotubes used in the device act as semiconductors. When a cancer cell binds to one of the attached antibodies, it creates an electrical signature that can be detected. These signals can be used to identify which of the elements in the array have captured cancer cells. Those individual arrays can then be removed and taken to a lab, where the captured cells can be stained and identified under a microscope. In the lab, the binding and electrical signature generation process took just a few minutes, suggesting the possibility of getting same-day results from a blood test using the chip, Panchapakesan says.

In a paper published in the journal Nanotechnology ["Static micro-array isolation, dynamic time series classification, capture and enumeration of spiked breast cancer cells in blood: the nanotube-CTC chip"], Panchapakesan's team, which includes graduate students Farhad Khosravi, the paper's lead author, and researchers at the University of Louisville and Thomas Jefferson University, describe a study in which antibodies specific for two markers of metastatic breast cancer, EpCam and Her2, were attached to the carbon nanotubes in the chip. When a blood sample that had been "spiked" with cells expressing those markers was placed on the chip, the device was shown to reliably capture only the marked cells.

In addition to capturing tumor cells, Panchapakesan says the chip will also latch on to tiny structures called exosomes, which are produced by cancers cells and carry the same markers. "These highly elusive 3-nanometer structures are too small to be captured with other types of liquid biopsy devices, such as microfluidics, due to shear forces that can potentially destroy them," he noted. "Our chip is currently the only device that can potentially capture circulating tumor cells and exosomes directly on the chip, which should increase its ability to detect metastasis. This can be important because emerging evidence suggests that tiny proteins excreted with exosomes can drive reactions that may become major barriers to effective cancer drug delivery and treatment."

Panchapakesan said the chip developed by his team has additional advantages over other liquid biopsy devices, most of which use microfluidics to capture cancer cells. In addition to being able to capture circulating tumor cells far more efficiently than microfluidic chips (in which cells must latch onto anchored antibodies as they pass by in a stream of moving liquid), the WPI device is also highly effective in separating cancer cells from the other cells and material in the blood through differential settling.

"White blood cells, in particular, are a problem, because they are quite numerous in blood and they can be mistaken for cancer cells," he said. "Our device uses what is called a passive leukocyte depletion strategy. Because of density differences, the cancer cells tend to settle to the bottom of the wells (and this only happens in a narrow window), where they encounter the antibodies. The remainder of the blood contents stays at the top of the wells and can simply be washed away."

While the initial tests with the chip have focused on breast cancer, Panchapakesan says the device could be set up to detect a wide range of tumor types, and plans are already in the works for development of an advanced device as well as testing for other cancer types, including lung and pancreas cancer. He says he envisions a day when a device like his could be employed not only for regular follow ups for patients who have had cancer, but in routine cancer screening.

"Imagine going to the doctor for your yearly physical," he said. "You have blood drawn and that one blood sample can be tested for a comprehensive array of cancer cell markers. Cancers would be caught at their earliest stage and other stages of development, and doctors would have the necessary protein or genetic information from these captured cells to customize your treatment based on the specific markers for your cancer. This would really be a way to put your health in your own hands."

167
Scientists at the National Institute of Standards and Technology (NIST) have developed a new device that measures the motion of super-tiny particles traversing distances almost unimaginably small -- shorter than the diameter of a hydrogen atom, or less than one-millionth the width of a human hair. Not only can the handheld device sense the atomic-scale motion of its tiny parts with unprecedented precision, but the researchers have devised a method to mass produce the highly sensitive measuring tool.

It's relatively easy to measure small movements of large objects but much more difficult when the moving parts are on the scale of nanometers, or billionths of a meter. The ability to accurately measure tiny displacements of microscopic bodies has applications in sensing trace amounts of hazardous biological or chemical agents, perfecting the movement of miniature robots, accurately deploying airbags and detecting extremely weak sound waves traveling through thin films.

NIST physicists Brian Roxworthy and Vladimir Aksyuk describe their work (link is external) in the Dec. 6, 2016, Nature Communications.

The researchers measured subatomic-scale motion in a gold nanoparticle. They did this by engineering a small air gap, about 15 nanometers in width, between the gold nanoparticle and a gold sheet. This gap is so small that laser light cannot penetrate it.

However, the light energized surface plasmons -- the collective, wave-like motion of groups of electrons confined to travel along the boundary between the gold surface and the air.

The researchers exploited the light's wavelength, the distance between successive peaks of the light wave. With the right choice of wavelength, or equivalently, its frequency, the laser light causes plasmons of a particular frequency to oscillate back and forth, or resonate, along the gap, like the reverberations of a plucked guitar string.

Meanwhile, as the nanoparticle moves, it changes the width of the gap and, like tuning a guitar string, changes the frequency at which the plasmons resonate.

The interaction between the laser light and the plasmons is critical for sensing tiny displacements from nanoscale particles, notes Aksyuk. Light can't easily detect the location or motion of an object smaller than the wavelength of the laser, but converting the light to plasmons overcomes this limitation. Because the plasmons are confined to the tiny gap, they are more sensitive than light is for sensing the motion of small objects like the gold nanoparticle.

The amount of laser light reflected back from the plasmon device reveals the width of the gap and the motion of the nanoparticle. Suppose, for example, that the gap changes -- due to the motion of the nanoparticle -- in such a way that the natural frequency, or resonance, of the plasmons more closely matches the frequency of the laser light. In that case, the plasmons are able to absorb more energy from the laser light, and less light is reflected.

To use this motion-sensing technique in a practical device, Aksyuk and Roxworthy embedded the gold nanoparticle in a microscopic-scale mechanical structure -- a vibrating cantilever, sort of a miniature diving board -- that was a few micrometers long, made of silicon nitride. Even when they're not set in motion, such devices never sit perfectly still, but vibrate at high frequency, jostled by the random motion of their molecules at room temperature. Even though the amplitude of the vibration was tiny -- moving subatomic distances -- it was easy to detect with the new plasmonic technique. Similar, though typically larger, mechanical structures are commonly used for both scientific measurements and practical sensors; for example, detecting motion and orientation in cars and smartphones. The NIST scientists hope their new way of measuring motion at the nanoscale will help to further miniaturize and improve performance of many such micromechanical systems.

"This architecture paves the way for advances in nanomechanical sensing," the researchers write. "We can detect tiny motion more locally and precisely with these plasmonic resonators than any other way of doing it," said Aksyuk.

The team's fabrication approach allows production of some 25,000 of the devices on a computer chip, with each device tailored to detect motion according to the needs of the manufacturer.

168
New technology that could enhance both the electrical and thermal conductivity of conventional composite materials has been developed thanks to a collaboration between the University of Surrey, University of Bristol and the aerospace company Bombardier.

Carbon fibre composites, composed of reinforcing carbon fibres within a plastic, have revolutionised industries that demand strong, yet light materials. However, their application has been hindered by inherently poor electrical and thermal conductivities.

New research, published in the journal Scientific Reports, demonstrates that by growing nanomaterials, specifically carbon nanotubes, on the surface of the carbon fibres it is possible to impart these necessary properties.

The research, conducted at the University of Surrey's Advanced Technology Institute (ATI) and the University of Bristol's Advanced Composite Centre for Innovation and Science (ACCIS), shows off the potential of a carbon fibre reinforced plastic to be made multifunctional, while still maintaining its structural integrity. Novel functionality including sensors, energy harvesting lighting and communication antennae can now be integrated into the structure of the composite to usher in a new era in composite technology.

Professor Ravi Silva, Director of the ATI and Head of the Nanoelectronics Centre (NEC) at the University of Surrey said: "In the future, carbon nanotube modified carbon fibre composites could lead to exciting possibilities such as energy harvesting and storage structures with self-healing capabilities. We are currently working on such prototypes and have many ideas including the incorporation of current aerospace/satellite technology in automotive design."

Dr Thomas Pozegic, Research Associate in ACCIS and formerly a PhD student at the University of Surrey, explained: "The aerospace industry still relies on metallic structures, in the form of a copper mesh, to provide lightning strike protection and prevent static charge accumulation on the upper surface of carbon fibre composites because of the poor electrical conductivity. This adds weight and makes fabrication with carbon fibre composites difficult. The material that we have developed utilises high-quality carbon nanotubes grown at a high density to allow electrical transport throughout the composite material."

Dr Ian Hamerton, Reader in Polymers and Composite Materials in ACCIS, commented: "The research has shown that carbon nanotubes can significantly enhance the thermal conductivity of carbon fibre composites. This will have wide-reaching benefits in the aerospace industry, from enhancing de-icing solutions to minimising the formation of fuel vapours at cruising altitudes."

169
Science and Information / Into the Light
« on: January 14, 2017, 08:57:18 PM »
Modeling the fluorescence enhancing capabilities of materials paves the way for more sensitive biological and chemical tracking technologies.

The capacity of various noble metals and dielectrics to enhance fluorescence has been compared by Singapore's Agency for Science, Technology and Research (A*STAR) researchers, with a view for more sensitive technologies to create new applications in biology and medicine.

Fluorescence occurs when an electron, after excitation from a fluorophore molecule, drops back from the excited state back to its ground state and emits a photon of light. Utilizing this phenomena, fluorescent labeling, a highly sensitive and non-destructive technique, allows for binding to a specific region or functional group on a target molecule, such as a protein or enzyme.

Fluorescent labeling is commonly used for tracking biological or chemical compounds in mineralogy, forensics, and medicine. Its application in DNA sequencing, molecular and cell biology, and the food safety industry is also attracting considerable interest, but relies upon light emitted by a single fluorophore, which is generally weak, thwarting its sensitivity.

This is pushing the search for technologies that amplify the fluorescence, spurring Bai Ping and colleagues from the Electronics and Photonics Department at the A*STAR Singapore Institute of High Performance Computing to compare the fluorescence enhancing capabilities of dielectric nanoparticles and silver and gold plasmonic metal nanoparticles.

"Previously, metals have been used because they are able to confine the light into a small area, producing a stronger signal," explains Bai. "But, when the metal is placed close to the fluorophore, some of the light is re-absorbed by the metal -- called quenching -- reducing its fluorescence enhancing capabilities."

As dielectric materials do not undergo quenching, particularly in the visible light range, they have also been used; but have poorer confinement capabilities compared to metals.

"A hybrid that combines the advantages of both materials is needed," Bai says. "Our work compares the performance of both materials by taking their structures and operating environments into account, providing for an objective comparison."

Because of the tiny distances between the materials and the fluorophores, an experimental comparison is very challenging. The researchers used a simulation based on a simple sphere nanoparticle model, and observed the fluorescence enhancement in an air and water environment. This allowed them to observe the different physical confinement characteristics for each material.

"Our results show that in air the dielectric is better, but in water the metals perform better," says Bai. "This provided us with knowledge to explore new materials and structures that could combine the advantages of both materials, with the potential for more sensitive technologies."

The A*STAR-affiliated researchers contributing to this research are from the Institute of High Performance Computing. For more information about the team's research, please visit the Photonics & Plasmonics Group webpage.

170
Scientists from Queen Mary University of London (QMUL) have discovered the secret behind the toughness of deer antlers and how they can resist breaking during fights.

The team looked at the antler structure at the 'nano-level', which is incredibly small, almost one thousandth of the thickness of a hair strand, and were able to identify the mechanisms at work, using state-of-the-art computer modelling and x-ray techniques.

First author Paolino De Falco from QMUL's School of Engineering and Materials Science said: "The fibrils that make up the antler are staggered rather than in line with each other. This allows them to absorb the energy from the impact of a clash during a fight."

The research, published today in the journal ACS Biomaterials Science & Engineering, provides new insights and fills a previous gap in the area of structural modelling of bone. It also opens up possibilities for the creation of a new generation of materials that can resist damage.

Co-author Dr Ettore Barbieri, also from QMUL's School of Engineering and Materials Science, said: "Our next step is to create a 3D printed model with fibres arranged in staggered configuration and linked by an elastic interface.

The aim is to prove that additive manufacturing -- where a prototype can be created a layer at a time -- can be used to create damage resistant composite material."

171
Science and Information / Fuel cells with PFIA-membranes
« on: January 14, 2017, 08:55:50 PM »
Fuel cells convert chemical energy of fuels such as hydrogen into electricity. The technology is highly efficient and quite clean -- with water as its only exhaust. But for wider application either in electric cars or mobile devices, low cost and highly efficient and stable materials are needed. A core component of fuel cells is the proton exchange membrane, which allows protons to selectively diffuse towards the cathode while blocking the oxygen and hydrogen gas. Most commonly used NAFIONTM membrane is only performing well at high humidity conditions and temperatures below 90 °C, thus limiting its efficiency and operational area and increasing the fuel cell cost.

Recently, a different low cost proton exchange membrane material was developed by 3M Company's Fuel Cell Components Group: Perfluoroimide acid or PFIA is already widely applied, but much less understood than NAFIONTM. Whereas PFIA has the same mechanically stable hydrophobic backbone, its hydrophilic side chains contain one more acidic site per each chain than in NAFIONTM. These additional acidic sites on each hydrophilic side chain provide additional protons for the proton transport and allow for the formation of larger water channels. Especially the water management in the PFIA membrane is of interest, since it is crucial for the performance of the fuel cell: in order to function it needs to be humid but never wet.

Now a science team at HZB analyzed PFIA membrane samples, provided by 3M. They combined infrared spectroscopy methods at BESSY II and examined the samples in situ under different temperatures and humidity conditions. By means of statistical analysis and advanced mathematical evaluation of the data, they could deduce the sequence of molecular events connected to the loss of water and reconstruct how water is retained in the PFIA molecules. "We wanted to better understand the behavior of water inside the nano-sized water channels of the proton exchange membranes, particularly during the transition to dryer conditions," Dr. Ljiljana Puskar, first author of the publication, explains.

The experimental data reveal a huge difference in the water management between NAFIONTM and PFIA in low humidity conditions: "We can clearly see that PFIA is better at both water retention and water uptake," Puskar says. They could even deduce how water is retained in the PFIA membrane at dryer conditions: The multiple side chains of PFIA are ideally suited to host water molecules and give rise to the building of a hydrogen bonded network. "These experiments have provided a much better understanding of the water retention capability of PFIA membranes.

This is very helpful for further optimization of such membranes to extend their operational area to higher temperatures and low humidity," Puskar states. She is looking forward to further cooperation projects with 3M. "This is a significant step forward in addressing the water management in an alternative proton exchange membrane type in collaboration with 3M company using the infrared facilities of BESSY II synchrotron. We are further expanding the capability of this excellent facility to allow for operando IR spectroscopy and microscopy and address a wide range of applications related to energy materials in operation, " states Prof. Emad Aziz, who is directing the HZB Institute of Methods for Materials development.

172
Science and Information / An invisible electrode
« on: January 14, 2017, 08:55:19 PM »
Transparent conductors are one of the key elements of today's electronic and optoelectronic devices such as displays, light emitting diodes, photovoltaic cells, smart phones, etc. Most of the current technology is based on the use of the semiconductor Indium Tin Oxide (ITO) as a transparent conducting material. However, even though ITO presents several exceptional properties, such as a large transmission and low resistance, it still lacks mechanical flexibility, needs to be processed under high temperatures and is expensive to produce.

An intensive effort has been devoted to the search of alternative TC materials that could definitively replace ITO, especially in the search for device flexibility. While the scientific community has investigated materials such as Al-doped ZnO (AZO), carbon nanotubes, metal nanowires, ultrathin metals, conducting polymers and most recently graphene, none of these have been able to present optimal properties that would make them the candidate to replace ITO.

Today ultrathin metal films (UTMFs) have been shown to present very low resistance although their transmission is also low unless antireflection (AR) undercoat and overcoat layers are added to the structure. ICFO researchers Rinu Abraham Maniyara, Vahagn K. Mkhitaryan, Tong Lai Chen, and Dhriti Sundar Ghosh, led by ICREA Prof at ICFO Valerio Pruneri, have developed a room temperature processed multilayer transparent conductor optimizing the antireflection properties to obtain high optical transmissions and low losses, with large mechanical flexibility properties. They have published their results in a recent paper published in Nature Communications.

In their study, ICFO researchers applied an Al doped ZnO overcoat and a TiO2 undercoat layer with precise thicknesses to a highly conductive Ag ultrathin film. By using destructive interference, the researchers showed that the proposed multilayer structure could lead to an optical loss of approximately 1.6% and an optical transmission greater than 98% in the visible. As Prof. Valerio Pruneri states, "we have used a simple design to achieve a transparent conductor with the highest performance to date and at the same time other outstanding attributes required for relevant applications in industry." This result represents a record fourfold improvement in figure of merit over ITO and also presents superior mechanical flexibility in comparison to this material.

The results of this study show the potential that this multilayer structure could have in future technologies that aim at more efficient and flexible electronic and optoelectronic devices.

173
Science and Information / First use of graphene to detect cancer cells
« on: January 14, 2017, 08:54:49 PM »
What can't graphene do? You can scratch "detect cancer" off of that list.

By interfacing brain cells onto graphene, researchers at the University of Illinois at Chicago have shown they can differentiate a single hyperactive cancerous cell from a normal cell, pointing the way to developing a simple, noninvasive tool for early cancer diagnosis.

"This graphene system is able to detect the level of activity of an interfaced cell," says Vikas Berry, associate professor and head of chemical engineering at UIC, who led the research along with Ankit Mehta, assistant professor of clinical neurosurgery in the UIC College of Medicine.

"Graphene is the thinnest known material and is very sensitive to whatever happens on its surface," Berry said. The nanomaterial is composed of a single layer of carbon atoms linked in a hexagonal chicken-wire pattern, and all the atoms share a cloud of electrons moving freely about the surface.

"The cell's interface with graphene rearranges the charge distribution in graphene, which modifies the energy of atomic vibration as detected by Raman spectroscopy," Berry said, referring to a powerful workhorse technique that is routinely used to study graphene.

The atomic vibration energy in graphene's crystal lattice differs depending on whether it's in contact with a cancer cell or a normal cell, Berry said, because the cancer cell's hyperactivity leads to a higher negative charge on its surface and the release of more protons.

"The electric field around the cell pushes away electrons in graphene's electron cloud," he said, which changes the vibration energy of the carbon atoms. The change in vibration energy can be pinpointed by Raman mapping with a resolution of 300 nanometers, he said, allowing characterization of the activity of a single cell.

The study, reported in the journal ACS Applied Materials & Interfaces, looked at cultured human brain cells, comparing normal astrocytes to their cancerous counterpart, the highly malignant brain tumor glioblastoma multiforme. The technique is now being studied in a mouse model of cancer, with results that are "very promising," Berry said. Experiments with patient biopsies would be further down the road.

"Once a patient has brain tumor surgery, we could use this technique to see if the tumor relapses," Berry said. "For this, we would need a cell sample we could interface with graphene and look to see if cancer cells are still present."

The same technique may also work to differentiate between other types of cells or the activity of cells.

"We may be able to use it with bacteria to quickly see if the strain is Gram-positive or Gram-negative," Berry said. "We may be able to use it to detect sickle cells."

Earlier this year, Berry and other coworkers introduced nanoscale ripples in graphene, causing it to conduct differently in perpendicular directions, useful for electronics. They wrinkled the graphene by draping it over a string of rod-shaped bacteria, then vacuum-shrinking the germs.

"We took the earlier work and sort of flipped it over," Berry said. "Instead of laying graphene on cells, we laid cells on graphene and studied graphene's atomic vibrations."

174
Scientists at Brigham and Women's Hospital have developed a novel method for delivering therapeutic molecules into cells. The method harnesses gold nanoparticles that are electrically activated, causing them to oscillate and bore holes in cells' outer membranes and allowing key molecules -- such as DNA, RNA, and proteins -- to gain entry. Unlike other approaches, the nanoparticles are not tethered to their biological cargo, a refinement that can boost therapeutic potency and effectiveness.

The research team, led by Hadi Shafiee, PhD, assistant professor at Brigham and Women's Hospital, together with first author Mohamed Shehata Draz, PhD, evaluated the technique's ability to deliver a DNA vaccine -- specifically, one against the hepatitis C virus (HCV) -- into mice. They found that it induced a strong immune response, reflected by high levels of anti-HCV antibodies and immune cells that secrete specific inflammatory hormones. Importantly, Shafiee and his colleagues detected no signs of toxicity in the mice throughout the study period, which lasted nearly 3 months.

"Our concept is unique," says Draz. "Both the electric field parameters and the nanoparticle properties can be augmented to perform other important functions, such as precisely removing cells or blood clots."

There is growing interest in DNA vaccines. First, they offer a potential alternative to conventional vaccines, which are sometimes constructed using weakened microbes -- either whole or specific parts. These foreign substances can pose risks to patients, which could potentially be minimized if DNA -- now readily synthesized in the laboratory -- is used instead. DNA vaccines also show promise as a tool for taming cancer growth.

Although Draz, Shafiee, and their colleagues began by applying their novel nanoparticle method to DNA vaccines, they underscore its wide-ranging applications.

"One of the really exciting aspects of this new method is that it enables drug delivery into tissues or cells in a universal way," says Shafiee. "We are eager to explore its use for other important biological molecules, including RNA."

175
Hydrogen gas is a promising alternative energy source to overcome our reliance on carbon-based fuels, and has the benefit of producing only water when it is reacted with oxygen. However, hydrogen is highly reactive and flammable, so it requires careful handling and storage. Typical hydrogen storage materials are limited by factors like water sensitivity, risk of explosion, difficulty of control of hydrogen-generation. Hydrogen gas can be produced efficiently from organosilanes, some of which are suitably air-stable, non-toxic, and cheap. Catalysts that can efficiently produce hydrogen from organosilanes are therefore desired with the ultimate goal of realizing safe, inexpensive hydrogen production in high yield. Ideally, the catalyst should also operate at room temperature under aerobic conditions without the need for additional energy input.

A research team led by Kiyotomi Kaneda and Takato Mitsudome at Osaka University have now developed a catalyst that realizes efficient environmentally friendly hydrogen production from organosilanes. The catalyst is composed of gold nanoparticles with a diameter of around 2 nm supported on hydroxyapatite. The catalyst was synthesized from chloroauric acid using glutathione as a capping agent to prevent nanoparticle aggregation, resulting the formation of small size of gold nanoparticles. Glutathione-capped gold nanoparticles were then adsorbed on hydroxyapatite and glutathione was removed by subsequent calcination.

The team then added the nanoparticle catalyst to solutions of different organosilanes to measure its ability to induce hydrogen production. The nanoparticle catalyst displayed the highest turnover frequency and number attained to date for hydrogen production catalysts from organosilanes. For example, the nanoparticle catalyst converted 99% of dimethylphenylsilane to the corresponding silanol in just 9 min at room temperature, releasing an equimolar amount of hydrogen gas at the same time. Importantly, the catalyst was recyclable without loss of activity. On/off switching of hydrogen production was achieved using the nanoparticle catalyst because it could be easily separated from its organosilane substrate by filtration. The activity of the catalyst increased as the nanoparticle size decreased.

A prototype portable hydrogen fuel cell containing the nanoparticle catalyst and an organosilane substrate was fabricated. The fuel cell generated power in air at room temperature and could be switched on and off as desired. Images of the catalyst after use in the fuel cell resembled those of the unused catalyst, indicating that the hydroxyapatite-supported nanoparticle catalyst readily resisted aggregation.

Generation of hydrogen from inexpensive organosilane substrates under ambient conditions without additional energy input represents an exciting advance towards the goal of using hydrogen as a green energy source.

176
Scientists have witnessed the birth of atmospheric ice clouds, creating ice cloud crystals in the laboratory and then taking images of the process through a microscope, essentially documenting the very first steps of cloud formation.

The team witnessed a process known as ice nucleation in unprecedented detail, taking time-lapse movies of the first few seconds when a particle attracts water vapor, forming ice crystals that become the core of icy cirrus clouds -- the high, wispy clouds that act much like a blanket for our planet.

How clouds form and what they do has a major influence on our climate and is a focus of scientists studying our planet. Clouds can reflect the sun's light, keeping the planet cool, or absorb Earth's radiation, heating the planet. The latter is the case for ice clouds created under the conditions in this study. The complex chemistry of airborne particles that serve as the birthplace of the ice crystals adds additional challenges.

"This is one of the most critical but least understood parts of the process of how cold clouds form," said first author Bingbing Wang, a scientist formerly with EMSL, the Environmental Molecular Sciences Laboratory at the Department of Energy's Pacific Northwest National Laboratory.

"The fundamental process of how ice grows is relatively well understood, but ice nucleation -- that moment when the first group of molecules comes together -- remains a big challenge," said Wang, who is now a professor at Xiamen University in China.

To take a close-up look at the initial steps, Alexander Laskin, a leader of the EMSL group, brought together scientists from Stony Brook University, Lawrence Berkeley National Laboratory, and PNNL, as well as the resources of two DOE Office of Science User Facilities: EMSL and the Advanced Light Source, which is at the Berkeley Lab. The team, with Daniel Knopf leading the Stony Brook group and Mary Gilles leading the Berkeley group, describes the work in the Nov. 21 issue of Physical Chemistry Chemical Physics.

Cloud in a lab

The first step for creating a microscopic cold cloud is replicating conditions found high above Earth's surface.

To do that, the team created a highly confined climate-controlled chamber about the size of a poppy seed where scientists regulate conditions like temperature, pressure and relative humidity precisely. The sample can then be placed inside the environmental scanning electron microscope at EMSL.

Then the team set out to re-create ice nucleation events. Almost anyone who lives in a colder climate has seen the phenomenon. It happens when water vapor from the air freezes and becomes ice quickly, for instance, when frosty streaks form on your windows during cold mornings.

The process of ice nucleation is also at play when aircraft ice up or when frozen foods are made and packaged. Aberrant ice nucleation would give your ice cream the texture of frozen ice cubes, for example.

In the atmosphere, airborne particles including those containing mineral dust, volcanic ash, carbon-based material, soot, aircraft emissions or even microbes are at the core of cloud-formation events. In this experiment scientists used particles of kaolinite, a mineral that scientists often use to study the phenomenon.

When temperatures are very low -- as they are above 20,000 feet, where cold cirrus clouds form -- and relative humidity is high, the particles attract surrounding water vapor which freezes and deposits as ice. Cirrus clouds are mostly made of ice crystals that grow by taking up the surrounding water vapor.

Particle flicks

The particle's size, shape, texture and other features all play a role in how the ice crystal forms. The particles in the experiment were just two or three microns in size -- less than one-tenth the width of a human hair. While many labs study ice nucleation, few start with observations about individual particles, to replicate the earliest stages of ice formation.

During the nucleation events, Laskin's team photographed the particle every three seconds, then combined the photos in several time-lapse movies. The environmental high-resolution scanning electron microscope was able to record regions on the particle only 50 nanometers wide, about one-thousandth the width of a human hair. To the untrained eye, the exercise is similar to staring out into space searching for small dots that are actually stars and planets. In the ice nucleation movies, small ice crystals barely visible at first grow as water vapor freezes onto them.

The team also used the system to watch ice nucleation happen on particles collected in the atmosphere May 19, 2010, in the CalNex 2010 field campaign. The particles, made mostly of carbon, nitrogen and oxygen, were put under observation at EMSL.

In both sets of experiments, nucleation took place at temperatures as low as 205 degrees Kelvin (around minus 90 degrees Fahrenheit) and relative humidity from about 70 to 80 percent.

"We were able to monitor moment by moment the formation of an ice crystal, at nanoscale resolution and under atmospherically relevant conditions," said co-author Daniel Knopf, an EMSL user from Stony Brook University. "Doing so and knowing that this process is replicated a million times, resulting in a cloud visible to the naked eye, is tremendously exciting and a huge step forward for our predictive understanding of cloud formation with important ramifications for climate."

177
Science and Information / Coffee-ring phenomenon explained in new theory
« on: January 14, 2017, 08:52:20 PM »
The formation of a simple coffee stain has been the subject of complex study for decades, though it turns out that there remain some stones still to be turned. Researchers at the University of Nevada, Reno have modeled how a colloidal droplet evaporates and found a previously overlooked mechanism that more accurately determines the dynamics of particle deposition in evaporating sessile droplets, which has ramifications in many fields of today's technological world.

"Understanding and manipulating the dynamics of particle deposition during evaporation of colloidal drops can be used in DNA sequencing, painting, ink jet printing and fabricating ordered micro/nano-structures," Hassan Masoud, assistant professor in the Department of Mechanical Engineering, said. "And now we understand it better than ever before. Our discovery builds on a large body of work; we took an extra step though, modeling the interaction of suspended particles with the free surface of the drop. We believe our findings are going to fundamentally change the common perception on the mechanism responsible for the so-called 'coffee-ring' phenomenon."

When a droplet dries on a surface, the particles suspended in it usually deposit in a ring-like pattern, leaving a stain or residue, called the coffee-ring effect. Until now, the stain was thought to form as a result of the fluid flow inside the drop. Masoud and his team found that the free surface of the droplet, the top layer where it is in contact with the air, plays a critical role in the deposition of the particles.

"When the drop evaporates, the free surface collapses and traps the suspended particles," Masoud said. "Our theory shows that eventually all the particles are captured by the free surface and stay there for the rest of their trip towards the edge of the drop."

Masoud and his team used a less familiar modeling system, known as the Toroidal Coordinate System, that allowed them to reduce the three-dimensional governing equations into a one-dimensional form. Despite a decent amount of server space and speed, the team opted to write out their many equations long-hand, on dozens of very large pieces of news print paper.

"Our innovative approach -- and using some ugly-long equations -- distinguishes our work from previous research," he said. "No one else has used this coordinate system for this problem, and this allows us to track the motion of particles in the drop in a natural way."

The discovery allows scientists to manipulate the motion of solute particles by altering the surface tension of the liquid-gas interface rather than controlling the bulk flow inside the drop.

"We can use surfactants to tweak the surface tension," Masoud said. "In a simple example, if you are cleaning solar panels, which can lose up to 90 percent of their efficiency when dirty, the preferred method of cleaning is water, but that leaves behind a stain that is hard to wipe out. Changing the flow dynamics during evaporation with a specialized cleaning agent can leave the panels cleaner and more efficient."

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Science and Information / Bright future for energy devices
« on: January 14, 2017, 08:51:51 PM »
A little sodium goes a long way. At least that's the case in carbon-based energy technology. Specifically, embedding sodium in carbon materials can tremendously improve electrodes.

A research team led by Yun Hang Hu, the Charles and Carroll McArthur Professor of materials science and engineering at Michigan Tech, created a brand-new way to synthesize sodium-embedded carbon nanowalls. Previously, the material was only theoretical and the journal Nano Letters recently published this invention.

High electrical conductivity and large accessible surface area, which are required for ideal electrode materials in energy devices, are opposed to each other in current materials. Amorphous carbon has low conductivity but large surface area. Graphite, on the other hand, has high conductivity but low surface area. Three-dimensional graphene has the best of both properties -- and the sodium-embedded carbon invented by Hu at Michigan Tech is even better.

"Sodium-embedded carbon's conductivity is two orders of magnitude larger than three-dimensional graphene," Hu says. "The nanowall structure, with all its channels and pores, also has a large accessible surface area comparable to graphene."

This is different from metal-doped carbon where metals are simply on the surface of carbon and are easily oxidized; embedding a metal in the actual carbon structure helps protect it. To make such a dream material, Hu and his team had to create a new process. They used a temperature-controlled reaction between sodium metal and carbon monoxide to create a black carbon powder that trapped sodium atoms. Furthermore, in collaboration with researchers at University of Michigan and University of Texas at Austin, they demonstrated that the sodium was embedded inside the carbon instead of adhered on the surface of the carbon. The team then tested the material in several energy devices.

In the dye-sensitized solar cell world, every tenth of a percent counts in making devices more efficient and commercially viable. In the study, the platinum-based solar cell reached a power conversion efficiency of 7.89 percent, which is considered standard. In comparison, the solar cell using Hu's sodium-embedded carbon reached efficiencies of 11.03 percent.

Supercapacitors can accept and deliver charges much faster than rechargeable batteries and are ideal for cars, trains, elevators and other heavy-duty equipment. The power of their electrical punch is measured in farads (F); the material's density, in grams (g), also matters.

Activated carbon is commonly used for supercapacitors; it packs a 71 F g-1 punch. Three-dimensional graphene has more power with a 112 F g-1 measurement. Sodium-embedded carbon knocks them both out of the ring with a 145 F g-1 measurement. Plus, after 5,000 charge/discharge cycles, the material retains a 96.4 percent capacity, which indicates electrode stability.

Hu says innovation in energy devices is in great demand. He sees a bright future for sodium-embedded carbon and the improvements it offers in solar tech, batteries, fuel cells, and supercapacitors.

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Molecules 10,000 times narrower than the width of a human hair could hold the key to making possible wooden skyscrapers and more energy-efficient paper production, according to research published in the journal Nature Communications. The study, led by a father and son team at the Universities of Warwick and Cambridge, solves a long-standing mystery of how key sugars in cells bind to form strong, indigestible materials.

The two most common large molecules -- or 'polymers' -- found on Earth are cellulose and xylan, both of which are found in the cell walls of materials such as wood and straw. They play a key role in determining the strength of materials and how easily they can be digested.

For some time, scientists have known that these two polymers must somehow stick together to allow the formation of strong plant walls, but how this occurs has, until now, remained a mystery: xylan is a long, winding polymer with so-called 'decorations' of other sugars and molecules attached, so how could this adhere to the thick, rod-like cellulose molecules?

"We knew the answer must be elegant and simple," explains Professor Paul Dupree from the Department of Biochemistry at the University of Cambridge, who led the research. "And in fact, it was. What we found was that cellulose induces xylan to untwist itself and straighten out, allowing it to attach itself to the cellulose molecule. It then acts as a kind of 'glue' that can protect cellulose or bind the molecules together, making very strong structures."

The finding was made possible due to an unexpected discovery several years ago in Arabidopsis, a small flowering plant related to cabbage and mustard. Professor Dupree and colleagues showed that the decorations on xylan can only occur on alternate sugar molecules within the polymer -- in effect meaning that the decorations only appear on one side of xylan. This led the team of researchers to survey other plants in the Cambridge University Botanic Garden and discover that the phenomenon appears to occur in all plants, meaning it must have evolved in ancient times, and must be important.

To explore this in more detail, they turned to an imaging technique known as solid state nuclear magnetic resonance (ssNMR), which is based on the same physics as hospital MRI scanners, but can reveal structure at the nanoscale. However, while ssNMR can image carbon, it requires a particular heavy isotope of carbon, carbon-13. This meant that the team had to grow their plants in an atmosphere enriched with a special form of carbon dioxide -- carbon-13 dioxide.

Professor Ray Dupree -- Paul Dupree's father, and a co-author on the paper -- supervised the work at the University of Warwick's ssNMR laboratory. "By studying these molecules, which are over 10,000 times narrower than the width of a human hair, we could see for the first time how cellulose and xylan slot together and why this makes for such strong cell walls."

Understanding how cellulose and xylan fit together could have a dramatic effect on industries as diverse as biofuels, paper production and agriculture, according to Paul Dupree.

"One of the biggest barriers to 'digesting' plants -- whether that's for use as biofuels or as animal feed, for example -- has been breaking down the tough cellular walls," he says. "Take paper production -- enormous amounts of energy are required for this process. A better understanding of the relationship between cellulose and xylan could help us vastly reduce the amount of energy required for such processes."

But just as this could improve how easily materials can be broken down, the discovery may also help them create stronger materials, he says. There are already plans to build houses in the UK more sustainably using wood, and Paul Dupree is involved in the Centre for Natural Material Innovation at the University of Cambridge, which is looking at whether buildings as tall as skyscrapers could be built using modified wood.

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Before modern medical lab techniques became available, doctors diagnosed some diseases by smelling a patient's breath. Scientists have been working for years to develop analytical instruments that can mimic this sniff-and-diagnose ability. Now, researchers report in the journal ACS Nano that they have identified a unique "breathprint" for each disease. Using this information, they have designed a device that screens breath samples to classify and diagnose several types of diseases.

Exhaled breath contains nitrogen, carbon dioxide and oxygen, as well as a small amount of more than 100 other volatile chemical components. The relative amounts of these substances vary depending on the state of a person's health. As far back as around 400 B.C., Hippocrates told his students to "smell your patients' breath" to search for clues of diseases such as diabetes (which creates a sweet smell). In more recent times, several teams of scientists have developed experimental breath analyzers, but most of these instruments focus on a single type of disease, such as cancer. In their own work, Hossam Haick and a team of collaborators in 14 clinical departments worldwide wanted to create a breathalyzer that could distinguish among multiple diseases.

The researchers developed an array of nanoscale sensors to detect the individual components in thousands of breath samples from patients who were either healthy or had one of 17 different diseases, such as kidney cancer or Parkinson's disease. By analyzing the results with artificial intelligence techniques, the team could use the array to classify and diagnose the conditions. The team used mass spectrometry to identify the breath components associated with the diseases. They found that each disease produces a unique volatile chemical breathprint, based on differing amounts of 13 components. They also showed that the presence of one disease would not prevent the detection of others -- a prerequisite for developing a practical device to screen and diagnose various diseases in a noninvasive, inexpensive and portable manner.

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