Tuesday, March 22, 2011

Quantum cryptography? Physicists move closer to efficient single-photon sources

A team of physicists in the United Kingdom has taken a giant step toward realizing efficient single-photon sources, which are expected to enable much-coveted completely secure optical communications, also known as "quantum cryptography."

The team presents its findings in Applied Physics Letters, a journal published by the American Institute of Physics.

Fluorescent "defect centers" in diamond act like atomic-scale light sources and are trapped in a transparent material that's large enough to be picked up manually. They don't need to be kept at super cold cryogenic temperatures or trapped in large electromagnetic fields to be stable -- unlike quantum dots or trapped atoms.

This makes them strong contenders for use as sources of single photons (the quantum light particle) in provably secure quantum cryptography schemes, explains J. P. Hadden, a Ph.D. candidate in the Centre for Quantum Photonics, Department of Electrical and Electronic Engineering & H. H. Wills Physics Laboratory at the University of Bristol.

"Defect centers could also be used as building blocks for 'solid-state quantum computers,' which would use quantum effects to solve problems that are not efficiently solvable with current computer technology," Hadden says.

To fulfill the potential of diamond defect centers, it's essential that the light be collected efficiently from the diamond material. But this collection efficiency is dramatically reduced by reflection and refraction of light passing through the diamond-air interface.

"We managed to show an improvement in the brightness of these defect centers of up to ten times by etching hemispherical 'solid immersion lenses' into the diamond," notes Hadden. "This is an important result, showing how nanofabrication techniques can complement and enhance quantum technologies, and opens the door to diamond-defect-center-based implementations of quantum cryptography and quantum computation."

More recently, Hadden and colleagues developed a technique that allows them to reliably etch these structures over previously characterized defect centers to a precision of about 100 nanometers -- another significant step toward a practical and repeatable combination of nanotechnology and quantum optics.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by American Institute of Physics, via EurekAlert!, a service of AAAS.

Journal Reference:

J. P. Hadden, J. P. Harrison, A. C. Stanley-Clarke, L. Marseglia, Y.-L. D. Ho, B. R. Patton, J. L. O’Brien, J. G. Rarity. Strongly enhanced photon collection from diamond defect centers under microfabricated integrated solid immersion lenses. Applied Physics Letters, 2010; 97 (24): 241901 DOI: 10.1063/1.3519847

Scientists use light to move molecules within living cells

Using a light-triggered chemical tool, Johns Hopkins scientists report that they have refined a means of moving individual molecules around inside living cells and sending them to exact locations at precise times.

This new tool, they say, gives scientists greater command than ever in manipulating single molecules, allowing them to see how molecules in certain cell locations can influence cell behavior and to determine whether cells will grow, die, move or divide. A report on the work was published online December 13 in the Journal of the American Chemical Society.

Studying how just one signaling molecule communicates in various parts of a living cell has posed a challenge for scientists investigating how different interactions influence cell behavior, such as the decision to move, change shape or divide.

"By using one magical chemical set off by light, we modified our previous technique for moving molecules around and gained much more control," says Takanari Inoue, Ph.D., assistant professor of cell biology and member of the Center for Cell Dynamics in the Institute for Basic Biomedical Sciences. "The advantage of using light is that it is very controllable, and by confining the light, we can manipulate communication of molecules in only a tiny region of the cell," he says.

Specifically, the Hopkins team designed a way to initiate and spatially restrict the molecular interactions to a small portion of the cell by attaching a light-triggered chemical to a bulky molecule, the bond between which would break when researchers shined a defined beam of ultraviolet light on it. This enabled the chemical to enter the cell and force two different and specific proteins in that cell to mingle when they otherwise wouldn't. Normally, these proteins would have nothing to do with each other without the presence of the light-triggered chemical, but researchers decided to take advantage of this mingling to explore how certain proteins in a cell behave when transported to precise locations.

Next, researchers modified the two mingling proteins by attaching special molecules to them -- one sent one of the proteins to the edge of the cell and another caused ripples to form on the edge of the cell -- so that if ripples form on the edge of the cell, they would know that the proteins were interacting there.

The researchers put both modified proteins inside human skin cells and bathed the cells in the light-triggered chemical tool. Then, they shone a tiny UV beam directed on approximately ten percent of the edge of a skin cell. Ripples appeared only on the region of the cell near where the light was beamed, demonstrating that the tool could limit cell activity to a precise location in the cell.

The tool can be used in larger cells, Inoue says, to monitor as little as one percent of a specific molecule if the beam intensity is varied. That in turn could reveal in even more detail the secret affairs of proteins in cellular cubbyholes.

"With this technique, we can get a finer understanding of cell function on the molecular level," says Inoue. "Our technique allows us to monitor whatever molecule we choose in whichever tiny space we choose so that we can understand how a molecule functions in a specific part of a live cell."

This study was funded by the National Institutes of Health and fellowships from the Japan Society for the Promotion of Science.

Other authors on this manuscript are Nobuhiro Umeda, Tasuku Ueno and Christopher Pohlmeyer, and Tetsuo Nagano of The University of Tokyo.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by Johns Hopkins Medical Institutions.

Journal Reference:

Nobuhiro Umeda, Tasuku Ueno, Christopher Pohlmeyer, Tetsuo Nagano, Takanari Inoue. A Photocleavable Rapamycin Conjugate for Spatiotemporal Control of Small GTPase Activity. Journal of the American Chemical Society, 2011; 133 (1): 12 DOI: 10.1021/ja108258d

Construction of a record-breaking laser gets off the ground

In the Laser Centre of the Institute of Physical Chemistry of the Polish Academy of Sciences and the Faculty of Physics of the Warsaw University work has started on the construction of an innovative laser. The compact device will make use of a unique light amplification technology to allow single laser pulses to reach the power of tens of terawatts with world record-breaking amplification parameters.

Most lasers amplify light by making use of classical technology with titanium ions doped sapphire crystals. An external laser is used to pump energy into the crystal where a part of the energy is subsequently taken over by a laser beam being amplified. Laser crystals have, however, numerous disadvantages, e.g., they warm up strongly and distort the cross section of the laser beam. An alternative is provided by parametric amplifiers that exploit non-linear optical effects. A laser with such an amplifier is being developed in the Laser Centre at the Institute of Physical Chemistry of the Polish Academy of Sciences (IPC PAS) and the Faculty of Physics of the Warsaw University (FPWU). „Our goal is simple. We want to construct the most efficient and compact parametric amplifier in the world" -- says Dr Yuriy Stepanenko from IPC PAS.

The multi-pass optical parametric amplifier technology NOPCPA (Noncollinear Optical Parametric Chirped Pulse Amplifier) has been for several years developed in the Laser Centre in a group headed by Prof. Czesław Radzewicz (IPC PAS, FPWU). The method consists in an efficient energy transfer directly from the pumping laser beam to the beam being amplified. Combined with numerical modelling, theoretical tools developed by Polish researchers allow to optimize precisely the parameters of both beams and of the amplifier. These issues are non-trivial as field intensity distributions are inhomogeneous in time and space, and in addition the pulse being amplified has a time-dependent frequency (which the physicists call a chirp).

As no energy is being accumulated in a parametric amplifier, there are no damaging thermal effects, and the amplified pulses have excellent parameters. A NOPCPA amplifier has also compact dimensions: a length of several centimetres is enough to reach an amplification of hundreds of millions of times. Theoretical efficiency of such an amplifier is approximately 60% but it is difficult to get, and so far the best laser amplifier of this type reach below 30%. „Our minimum plan is to reach an efficiency of 40%, we will try, however, to overcome a barrier of 50%" -- says Dr Paweł Wnuk (IPC PAS).

The researchers expect to get the first 10 terawatt pulses with duration of dozen femtoseconds emitted by their laser next year. But this is only the beginning of the way. „We hope that already the present version of the parametric amplifier will allow us to generate over 100 TW pulses" -- stresses Prof. Radzewicz. The calculations indicate that 500 TW laser pulses could be used to accelerate protons to energies enabling them to be applied in medical therapies including anti-cancer treatment. The lasers with so high power can be found today only in a few research centres worldwide. „We have all the grounds to assume that our method of light amplification can in future help us to build relatively cheap lasers for proton acceleration, in addition with so compact size that they essentially would be considered portable devices" -- says Dr Stepanenko.

Under the research project being completed the new laser will be used to construct two demonstration setups. The first one, being developed in collaboration with the Military Academy of Technology (MAT) in Warsaw and the Institute of Physics of the PAS, will be used to construct x-ray sources with micrometric dimensions. Such sources are used in, e.g., x-ray microscopy, and in particular in non-destructive testing of structural materials. The second demonstrator will be a lidar for measurements of atmospheric pollution and will be developed with participation of the researchers from the Military Academy of Technology.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by Institute of Physical Chemistry of the Polish Academy of Sciences, via AlphaGalileo.

Graphene cloak protects bacteria, leading to better images

It's a cloak that surpasses all others: a microscopic carbon cloak made of graphene that could change the way bacteria and other cells are imaged.

Vikas Berry, assistant professor of chemical engineering at Kansas State University, and his research team are wrapping bacteria with graphene to address current challenges with imaging bacteria under electron microscopes. Berry's method creates a carbon cloak that protects the bacteria, allowing them to be imaged at their natural size and increasing the image's resolution.

Graphene is a form of carbon that is only one atom thick, giving it several important properties: it's impermeable, it's the strongest nanomaterial, it's optically transparent and it has high thermal conductance.

"Graphene is the next-generation material," Berry said. "Although only an atom thick, graphene does not allow even the smallest of molecules to pass through. Furthermore, it's strong and highly flexible so it can conform to any shape."

Berry's team has been researching graphene for three years, and Berry recently saw a connection between graphene and cell imaging research. Because graphene is impermeable, he decided to use the material to preserve the size of bacterial cells imaged under high-vacuum electron microscopes.

The research results appear in the paper "Impermeable Graphenic Encasement of Bacteria," which was published in a recent issue of Nano Letters, a monthly scientific journal published by the American Chemical Society. The team's preliminary research appeared in Nature News in 2010.

The current challenge with cell imaging occurs when scientists use electron microscopes to image bacterial cells. Because these microscopes require a high vacuum, they remove water from the cells. Biological cells contain 70 to 80 percent water, and the result is a severely shrunk cell. As a result, it is challenging to obtain an accurate image of the cells and their components in their natural state.

But Berry and his team created a solution to the imaging challenge by applying graphene. The graphene acts as an impermeable cloak around the bacteria so that the cells retain water and don't shrink under the high vacuum of electron microscopes. This provides a microscopic image of the cell at its natural size.

The carbon cloaks can be wrapped around the bacteria using two methods. The first method involves putting a sheet of graphene on top of the bacteria, much like covering up with a bed sheet. The other method involves wrapping the bacteria with a graphene solution, where the graphene sheets swaddle the bacteria. In both cases the graphene sheets were functionalized with a protein to enhance binding with the bacterial cell wall.

Under the high vacuum of an electron microscope, the wrapped bacteria did not change in size for 30 minutes, giving scientists enough time to observe them. This is a direct result of the high strength and impermeability of the graphene cloak, Berry said.

Graphene's other extraordinary properties enhance the imaging resolution in microscopy. Its electron-transparency enables a clean imaging of the cells. Since graphene is a good conductor of heat and electricity, the local electronic-charging and heating is conducted off the graphene cloak, giving a clear view of the bacterial cell well. Unwrapped bacterial cells appear dark with an indistinguishable cell wall.

"Uniquely, graphene has all the properties needed to image bacteria at high resolutions," Berry said. "The project provides a very simple route to image samples in their native wet state."

The process has potential to influence future research. Scientists have always had trouble observing liquid samples under electron microscopes, but using carbon cloaks could allow them to image wet samples in a vacuum. Graphene's strong and impermeable characteristics ensure that wrapped cells can be easily imaged without degrading them. Berry said it might be possible in the future to use graphene to keep bacterium alive in a vacuum while observing its biochemistry under a microscope.

The research also paves the way for enhanced protein microscopy. Proteins act differently when they are dry and when they are in an aqueous solution. So far most protein studies have been conducted in dry phases, but Berry's research may allow proteins to be observed more in aqueous environments.

"This research could be the point of evolution for processing of sensitive samples with graphene to achieve enhanced imaging," Berry said.

Other researchers involved in the project include Daniel Boyle, research assistant professor in biology; Nihar Mohanty, doctoral student in chemical engineering, India; Ashvin Nagaraja, former master's student in electrical engineering; and Monica Fahrenholtz, a May 2010 chemical engineering graduate from Clearwater.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by Kansas State University.

Journal Reference:

Nihar Mohanty, Monica Fahrenholtz, Ashvin Nagaraja, Daniel Boyle, Vikas Berry. Impermeable Graphenic Encasement of Bacteria. Nano Letters, 2011; 11 (3): 1270 DOI: 10.1021/nl104292k

New way to test cancer drugs

A Purdue University scientist's nanopolymer would make it easier and cheaper for drug developers to test the effectiveness of a widely used class of cancer inhibitors.

W. Andy Tao, an associate professor of biochemistry analytical chemistry and a member of the Purdue Center for Cancer Research team, created the Purdue-patented pIMAGO nanopolymer that can be used to determine whether cancer drugs have been effective against biochemical processes that can lead to cancer cell formation. The nanopolymers would attach themselves to target proteins that would later be detected by a relatively simple laboratory procedure called chemiluminescence.

Tymora Analytical, a company Tao started in the Purdue Research Park, will manufacture the pIMAGO nanopolymers. The 'p' stands for phosphor, and the IMAGO comes from the Greek word for image.

Tao's pIMAGO nanopolymers are coated in titanium ions and would attract and bond with phosphorylated proteins, ones in which a phosphate group has been added to a protein activating an enzyme called kinase. Kinase, when overactive, is known to cause cancer cell formation, and many cancer drugs are aimed at inhibiting kinase activity.

"It is universal. You can detect any kind of phosphorylation in a protein," said Tao, whose findings were reported in the early online version of the journal Analytical Chemistry. "It is also cheaper and would be more widely available."

The nanopolymers would be added to a solution of proteins, a chemical agent to start phosphorylation and a drug to inhibit kinase activity. Phosphorylated proteins would only be present if the drug is ineffective.

Avidin-HRP -- the protein Avidin bound with the enzyme horseradish peroxidase -- would be added. Avidin would bind with a vitamin B acid called biotin that is also on the nanopolymers' surfaces. A chemical called a substrate, added later, would cause a reaction with HRP, causing the solution to change color.

A lightly colored solution would mean there had been little kinase activity and few phosphorylated proteins and that the drug was effective. A darker solution would signal more kinase activity and a less effective drug.

"This could have a lot of applications in pharmaceuticals for drug discovery," Tao said.

Screening kinase inhibitors using antibodies can be cost-prohibitive for many laboratories because antibodies are in short supply and aren't available for many types of cells. Radioisotope tests are highly regulated and possibly dangerous because of radiation involved.

"We want to develop this as a commercial application to replace radioisotopes and antibodies as a universal method for screening kinase inhibitors," Tao said.

The National Science Foundation and the National Institutes of Health funded the research.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by Purdue University. The original article was written by Brian Wallheimer.

Journal Reference:

Anton Iliuk, Juan S. Martinez, Mark C. Hall, W. Andy Tao. Phosphorylation Assay Based on Multifunctionalized Soluble Nanopolymer. Analytical Chemistry, 2011; : 110311102308028 DOI: 10.1021/ac2000708

Good vibrations lead to molecular revelation

 A little luck and the wisdom to recognize what they were seeing helped Rice University researchers solve a molecular conundrum in a way that could be a boon to chemists.

Rice chemist Junrong Zheng and his colleagues in Houston and China have improved upon a long-standing theory for electrolytes through the discovery that vibrational can be used to probe how ions cluster in such aqueous solutions.

The discovery opens a path for Zheng, an assistant professor of chemistry at Rice, to measure short-range intermolecular distances without fluorescent or other labeling devices that could skew results. The tool that makes it possible is an ultrafast, time-resolved infrared spectroscope he had custom-built to understand dynamic processes at the subnanoscale.

Zheng is planting a flag in a new field of research with the paper that appeared this week in the Proceedings of the National Academy of Science. The paper specifically shows how the vibrational energy common to all molecules can reveal the mechanics of ion clusters in a solution.

Very dilute solutions of electrolytes are well understood through Debye-Hueckel theory, which was developed in 1923, but as these solutions become slightly more concentrated the theory breaks down, as its authors predicted. A better understanding of electrolyte solutions is essential to scientists who study electochemistry, and biological systems. Zheng's work provides a new way to enlarge this understanding.

The Rice discovery is important for several reasons. First, the strength of an -- think of the liquid in a car battery -- depends strongly on how well ions from salts or acids dissolve in the solution. More ions in a solution make it less ideal because of more opposite-charge attraction, according to Debye-Hueckel.

Zheng and his team found unexpected but clear evidence that a significant portion of ions of the same charge form clusters even in less-saturated solutions, in direct opposition to the equation.

Second, the Rice team's technique provides a window for scientists who want to view, for instance, concentrations of sodium and potassium ions in living cells, the ion-dependent movement of proteins or the properties of ion channels in cell membranes.

"Junrong's remarkable accomplishment is to devise a completely new way to learn much more about the structures present in concentrated ionic solutions," said Nobel laureate Robert Curl, Rice's University Professor Emeritus and the Kenneth S. Pitzer-Schlumberger Professor Emeritus of Natural Sciences, who advised Zheng on the paper. "This is exciting and it is important and should be expandable to other important situations."

"Our understanding of concentrated salt solutions is poor, yet these are highly relevant to practical applications, such as solar cells and batteries,” said Gerald Meyer, the Bernard N. Baker Professor of Chemistry at Johns Hopkins University. “Junrong's approach is clever and provides some valuable insights from which new models can be developed. The use of isotopes for the demonstration of energy transfer within the clusters was particularly novel."

The path revealed itself to Zheng and Rice postdoctoral researcher Hongtao Bian last October. "This particular work was not intentionally designed," Zheng said. "It came from a small observation by Bian when I asked him to measure the rotation time constant of an anion in a concentrated solution.

"When he told me the rotation time was only 2.5 picoseconds, I knew something was wrong. I remembered the rotational time constant of this anion in a very dilute solution was around 3.7 picoseconds. We've measured this.

"In a dilute solution, the viscosity is very small," Zheng explained. "People move fast in an easy environment, but when it's crowded you cannot go so fast -- and the same applies here. When a solution is diluted, the molecules should move faster.

"But here in this very viscous solution, the molecules were moving too fast," he said. "Something was up. That's when I realized we weren't actually seeing the molecules rotate at all."

What the probe saw as a too-fast rotation was the vibrational energy as it transferred from one molecule to another with a different orientation. "I had thought that this, at some point, should happen, but I really couldn't experiment to demonstrate it," Zheng said. "The tools didn't exist. Then, just by this small accident, we're developing a whole methodology."

Zheng said his calculations may not apply to all electrolytes, but should cover a wide range of those of interest to researchers. "Only certain types of ions with active infrared modes and the vibrational lifetimes of the modes are comparable to the energy transfer time scales -- but that includes many important ions in biology or electrochemistry. Certainly this method is not limited to . It is, in principle, applicable to any molecules with active vibrational modes," he said.

Zheng, a native of China who came to Rice three years ago after completing his doctorate at Stanford, relied on the steady hands of Rice colleagues Anatoly Kolomeisky, an associate professor of chemistry, and Curl, who in fact carried his calculations one step beyond.

"It took us months to figure out a mathematical model to explain the data, and when Bob read it, he said, 'You know, I don't believe you're right,'" Zheng recalled. He said Curl objected to the fact that calculations were based on the average distribution of clusters in a given solution. "It was statistically right," Zheng said, "but it wasn't rigorous.

"Bob took our physical picture and counted the signal size from each cluster. He came up with a very rigorous model that accounts for the distribution of clusters. So his model is perfectly right. No assumptions."

Zheng said both his and Curl's models were in close agreement, since the averaged sample was so large. "But he really helped me to question every detail of the math, to make sure that this is really right.

"I had spent a month with a student who has a bachelor's degree in physics -- in math -- creating our model. It's hard to imagine that Bob could have figured all this out, by himself, in a week."

The paper's co-authors include graduate students Xiewen Wen, Jiebo Li and Hailong Chen, all of Rice; Suzee Han, a student at Clements High School in Sugar Land, Texas, who volunteered in Zheng's lab; and Xiuquan Sun, Jian Song and Wei Zhuang of the Chinese Academy of Sciences, Dalian, China.

More information: http://www.pnas.or … 108.abstract

Provided by Rice University (news : web)

Advanced carbon aerogels for energy applications

 Because of their unique structure, carbon aerogels may be used for hydrogen and electrical energy storage in the future.

Carbon aerogels (CAs) are a unique class of high-surface area materials derived by sol-gel chemistry in which the liquid component of a polymer gel has been replaced with a gas.

Their high and , environmental compatibility and chemical inertness make them very promising materials for many energy related applications.

Recent research has shown that the structure of CAs can be manipulated for a variety of uses in the energy field from hydrogen and electrical storage to desalination and catalysis.

Laboratory research in the aerogel field was recently featured on the back cover of Energy and Environmental Science authored by Juergen Biener, Monika Biener, Michael Stadermann, Marcus Worsley, Theodore Baumann, Matthew Suss and Klint Rose.

Although the first aerogels based on silica gels were discovered in 1931, it was another 60 years until LLNL developed polymer-based carbon aerogels in the late '80s.

Because of their unusual chemical and textural characteristics, carbon aerogels are promising materials for use as in supercapacitors and , advanced catalyst supports, adsorbents and thermal insulation.

According to the LLNL team, the sol-gel reaction chemistry allows researchers to manipulate the structure and properties of CAs.

"Carbon aerogels are attractive materials for applications that require both high surface areas and fast mass transport," because the structure, surface area and pore size distribution can be controlled systematically, Juergen Biener said.

For example, the hydrogen and electrical energy storage capacity of CAs depends on the presence of micropores to provide surface area, but the dynamics of loading and unloading depends on the presence of macropores to facilitate mass transport.

The storage capacity for hydrogen and electricity could be improved by manipulating the structure of the carbon aerogels, Baumann said.

The team currently develops new CAs that improve the of electrical double-layer capacitors. In these devices charge is stored in the form of ions accumulated on the surface of the material, creating an intermediate between batteries and electrostatic capacitors. These capacitors are an ideal complement to batteries in devices with peak power demands above the base level, where they extend the life of the battery.

Carbon aerogels also have an important role in capacitive deionization (CDI), a desalination method in which ions are removed from electrolytes (seawater or brackish water flowing between electrode pairs) to create a clean water source. The first CDI system that used aerogel electrodes was developed in the 1990s at LLNL.

"Tuning the pore size distribution in hierarchically structured CAs can improve the energy efficiency of a CDI system by reducing ionic transport losses while maintain a high capacitance," Stadermann said.

Another promising energy application for carbon aerogels is their use as electrode materials and catalyst support in proton-exchange membrane fuel cells.

"The advantage of aerogels over other more traditional supports is that its surface area, pore size and pore volume can be tailored independently of each other," Biener said.

Provided by Lawrence Livermore National Laboratory (news : web)