Nanoparticles and their size may not be big issues

ScienceDaily (Oct. 24, 2011) — If you've ever eaten from silverware or worn copper jewelry, you've been in a perfect storm in which nanoparticles were dropped into the environment, say scientists at the University of Oregon.

Since the emergence of nanotechnology, researchers, regulators and the public have been concerned that the potential toxicity of nano-sized products might threaten human health by way of environmental exposure.

Now, with the help of high-powered transmission electron microscopes, chemists captured never-before-seen views of miniscule metal nanoparticles naturally being created by silver articles such as wire, jewelry and eating utensils in contact with other surfaces. It turns out, researchers say, nanoparticles have been in contact with humans for a long, long time.

The project involved researchers in the UO's Materials Science Institute and the Safer Nanomaterials and Nanomanufacturing Initiative (SNNI), in collaboration with UO technology spinoff Dune Sciences Inc. SNNI is an initiative of the Oregon Nanoscience and Microtechnologies Institute (ONAMI), a state signature research center dedicated to research, job growth and commercialization in the areas of nanoscale science and microtechnologies.

The research -- detailed in a paper placed online in advance of regular publication in the American Chemistry Society's journal ACS Nano -- focused on understanding the dynamic behavior of silver nanoparticles on surfaces when exposed to a variety of environmental conditions.

Using a new approach developed at UO that allows for the direct observation of microscopic changes in nanoparticles over time, researchers found that silver nanoparticles deposited on the surface of their SMART Grids electron microscope slides began to transform in size, shape and particle populations within a few hours, especially when exposed to humid air, water and light. Similar dynamic behavior and new nanoparticle formation was observed when the study was extended to look at macro-sized silver objects such as wire or jewelry.

"Our findings show that nanoparticle 'size' may not be static, especially when particles are on surfaces. For this reason, we believe that environmental health and safety concerns should not be defined -- or regulated -- based upon size," said James E. Hutchison, who holds the Lokey-Harrington Chair in Chemistry. "In addition, the generation of nanoparticles from objects that humans have contacted for millennia suggests that humans have been exposed to these nanoparticles throughout time. Rather than raise concern, I think this suggests that we would have already linked exposure to these materials to health hazards if there were any."

Any potential federal regulatory policies, the research team concluded, should allow for the presence of background levels of nanoparticles and their dynamic behavior in the environment.

Because copper behaved similarly, the researchers theorize that their findings represent a general phenomenon for metals readily oxidized and reduced under certain environmental conditions. "These findings," they wrote, "challenge conventional thinking about nanoparticle reactivity and imply that the production of new nanoparticles is an intrinsic property of the material that is now strongly size dependent."

While not addressed directly, Hutchison said, the naturally occurring and spontaneous activity seen in the research suggests that exposure to toxic metal ions, for example, might not be reduced simply by using larger particles in the presence of living tissue or organisms.

Co-authors with Hutchison on the paper were Richard D. Glover, a doctoral student in Hutchison's laboratory, and John M. Miller, a research associate. Hutchison and Miller were co-founders of Dune Sciences Inc., a Eugene-based company that specializes in products and services geared toward the development and commercialization of nano-enabled products. Miller currently is the company's chief executive officer; Hutchison is chief science officer.

The electron microscopes used in this study are located at the Center for Advanced Materials Characterization in Oregon in the underground Lorry I. Lokey Laboratories at the UO. The U.S. Air Force Research Laboratory and W.M. Keck Foundation supported the research. Glover's participation also was funded by the National Science Foundation's STEM (science, technology, engineering, mathematics) Fellows in K-12 Education Program.

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Journal Reference:

Richard D. Glover, John M. Miller, James E. Hutchison. Generation of Metal Nanoparticles from Silver and Copper Objects: Nanoparticle Dynamics on Surfaces and Potential Sources of Nanoparticles in the Environment. ACS Nano, 2011; 111019095813007 DOI: 10.1021/nn2031319

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New technique maps twin faces of smallest Janus nanoparticles

ScienceDaily (Sep. 28, 2011) — New drug delivery systems, solar cells, industrial catalysts and video displays are among the potential applications of special particles that possess two chemically distinct sides. These particles are named after the two-faced Roman god Janus and their twin chemical faces allow them to form novel structures and new materials.

However, as scientists have reduced the size of Janus particles down to a few nanometers in diameter -- about the size of individual proteins, which has the greatest potential for drug therapy -- their efforts have been hampered because they haven't had a way to accurately map the surfaces of the particles that they produce. This uncertainty has made it difficult to evaluate the effectiveness of these particles for various applications and to improve the methods researchers are using to produce them.

Now, a team of Vanderbilt chemists has overcome this obstacle by developing the first method that can rapidly and accurately map the chemical properties of the smallest of these Janus nanoparticles.

The results, published online this month in the German chemistry journal Angewandte Chemie, address a major obstacle that has slowed the development and application of the smallest Janus nanoparticles.

The fact that Janus particles have two chemically distinct faces makes them potentially more valuable than chemically uniform particles. For example, one face can hold onto drug molecules while the other is coated with linker molecules that bind to the target cells. This advantage is greater when the different surfaces are cleanly separated into hemispheres than when the two types of surfaces are intermixed.

For larger nanoparticles (with sizes above 10 nanometers), researchers can use existing methods, such as scanning electron microscopy, to map their surface composition. This has helped researchers improve their manufacturing methods so they can produce cleanly segregated Janus particles. However, conventional methods do not work at sizes below 10 nanometers.

The Vanderbilt chemists -- Associate Professor David Cliffel, Assistant Professor John McLean, graduate student Kellen Harkness and Lecturer Andrzej Balinski -- took advantage of the capabilities of a state-of-the-art instrument called an ion mobility-mass spectrometer (IM-MS) that can simultaneously identify thousands of individual particles.

The team coated the surfaces of gold nanoparticles ranging in size from two to four nanometers with two different chemical compounds. Then they broke the nanoparticles down into clusters of four gold atoms and ran these fragments through the IM-MS.

Molecules from the two coatings were still attached to the clusters. So, by analyzing the resulting pattern, the chemists showed that they could distinguish between original nanoparticles where the two surface compounds were completely separated, those where they were randomly mixed and those that had an intermediate degree of separation.

"There is no other way to analyze structure at this scale except X-ray crystallography," said Cliffel, "and X-ray crystallography is extremely difficult and can take months to get a single structure."

"IM-MS isn't quite as precise as X-ray crystallography but it is extremely practical," added McLean, who has helped pioneer the new instrument's development. "It can provide structural information in a few seconds. Two years ago a commercial version became available so people who want to use it no longer have to build one for themselves."

The research was funded in part by a grant from the National Institutes of Health.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Vanderbilt University. The original article was written by David Salisbury.

Journal Reference:

Kellen M. Harkness, Andrzej Balinski, John A. McLean, David E. Cliffel. Nanoscale Phase Segregation of Mixed Thiolates on Gold Nanoparticles. Angewandte Chemie International Edition, 2011; DOI: 10.1002/anie.201102882

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

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Cheap and efficient solar cell made possible by linked nanoparticles

ScienceDaily (Sep. 26, 2011) — Researchers of the Chemical Engineering department and the Kavli institute of the TU DElft have demonstrated that electrons can move freely in layers of linked semiconductor nanoparticles under the influence of light. This new knowledge will be very useful for the development of cheap and efficient quantum dot solar cells.

The researchers published their findings on September 25 on the website of the scientific journal Nature Nanotechnology.

Cheap and efficient

The current crystalline silicon solar panels are expensive to produce. Cheaper solar cells are available, but these are inefficient. For example, an organic solar cell has a maximum efficiency of 8%. One way of increasing the efficiency of cheap solar cells is the use of semiconductor nanoparticles, quantum dots. In theory, the efficiency of these cells can be increased to 44%. This is in part due to the avalanche effect, demonstrated by researchers from TU Delft and the FOM Foundation in 2008. In the current solar cells, an absorbed light particle can only excite one electron (creating an electron-hole pair), while in a quantum dot solar cell a light particle can excite several electrons. The more electrons that are excited, the greater the efficiency of the solar cell.

Linked nanoparticles

Up to now, the creation of electron-hole pairs under the influence of light was only demonstrated within the limits of a quantum dot. To be usable in solar cells, it is essential that electrons and holes are able to move. This is what creates an electrical current that can be collected at an electrode. Researchers from the same research group have now demonstrated that the electron-hole pairs can also move as free charges between the nanoparticles. To this end they linked nanoparticles together, using very small molecules, so that they were very densely clustered while still remaining separate from each other. The nanoparticles are so close together that every single light particle that is absorbed by the solar cell actually causes electrons to move.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Delft University of Technology.

Journal Reference:

Elise Talgorn, Yunan Gao, Michiel Aerts, Lucas T. Kunneman, Juleon M. Schins, T. J. Savenije, Marijn A. van Huis, Herre S. J. van der Zant, Arjan J. Houtepen, Laurens D. A. Siebbeles. Unity quantum yield of photogenerated charges and band-like transport in quantum-dot solids. Nature Nanotechnology, 2011; DOI: 10.1038/nnano.2011.159

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Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Cheap and efficient solar cell made possible by linked nanoparticles

ScienceDaily (Sep. 26, 2011) — Researchers of the Chemical Engineering department and the Kavli institute of the TU DElft have demonstrated that electrons can move freely in layers of linked semiconductor nanoparticles under the influence of light. This new knowledge will be very useful for the development of cheap and efficient quantum dot solar cells.

The researchers published their findings on September 25 on the website of the scientific journal Nature Nanotechnology.

Cheap and efficient

The current crystalline silicon solar panels are expensive to produce. Cheaper solar cells are available, but these are inefficient. For example, an organic solar cell has a maximum efficiency of 8%. One way of increasing the efficiency of cheap solar cells is the use of semiconductor nanoparticles, quantum dots. In theory, the efficiency of these cells can be increased to 44%. This is in part due to the avalanche effect, demonstrated by researchers from TU Delft and the FOM Foundation in 2008. In the current solar cells, an absorbed light particle can only excite one electron (creating an electron-hole pair), while in a quantum dot solar cell a light particle can excite several electrons. The more electrons that are excited, the greater the efficiency of the solar cell.

Linked nanoparticles

Up to now, the creation of electron-hole pairs under the influence of light was only demonstrated within the limits of a quantum dot. To be usable in solar cells, it is essential that electrons and holes are able to move. This is what creates an electrical current that can be collected at an electrode. Researchers from the same research group have now demonstrated that the electron-hole pairs can also move as free charges between the nanoparticles. To this end they linked nanoparticles together, using very small molecules, so that they were very densely clustered while still remaining separate from each other. The nanoparticles are so close together that every single light particle that is absorbed by the solar cell actually causes electrons to move.

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Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Delft University of Technology.

Journal Reference:

Elise Talgorn, Yunan Gao, Michiel Aerts, Lucas T. Kunneman, Juleon M. Schins, T. J. Savenije, Marijn A. van Huis, Herre S. J. van der Zant, Arjan J. Houtepen, Laurens D. A. Siebbeles. Unity quantum yield of photogenerated charges and band-like transport in quantum-dot solids. Nature Nanotechnology, 2011; DOI: 10.1038/nnano.2011.159

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Technique to control light from nanoparticles

ScienceDaily (Sep. 30, 2011) — A nanoscale game of "now you see it, now you don't" may contribute to the creation of metamaterials with useful optical properties that can be actively controlled, according to scientists at Rice University.

A Rice laboratory led by chemist Stephan Link has discovered a way to use liquid crystals to control light scattered from gold nanorods. The researchers use voltage to sensitively manipulate the alignment of liquid crystal molecules that alternately block and reveal light from the particles; the gold nanorods collect and retransmit light in a specific direction.

The research was reported in the American Chemical Society journal Nano Letters.

It seems simple, but Link said the technique took two years to refine to the point where light from the nanoparticles could be completely controlled.

"The key to our approach is the in-plane rotation of liquid crystal molecules covering individual gold nanorods that act as optical antennas," said Link, an assistant professor of chemistry and electrical and computer engineering. "Learning how our devices work was exciting and has provided us with many ideas of how to manipulate light at the nanoscale."

Link said the device is actually a super half wave plate, a refined version of a standard device that alters the polarization of light.

With the new device, the team expects to be able to control light from any nanostructure that scatters, absorbs or emits light, even quantum dots or carbon nanotubes. "The light only has to be polarized for this to work," said Link, who studies the plasmonic properties of nanoparticles and recently authored a perspective on his group's recent research in plasmonics for the Journal of Physical Chemistry Letters.

In polarized light, like sunlight reflecting off water, the light's waves are aligned in a particular plane. By changing the direction of their alignment, liquid crystals can tunably block or filter light.

The Rice team used gold nanorods as their polarized light source. The rods act as optical antennas; when illuminated, their surface plasmons re-emit light in a specific direction.

In their experiment, the team placed randomly deposited nanorods in an array of alternating electrodes on a glass slide; they added a liquid crystal bath and a cover slip. A polyimide coating on the top cover slip forced the liquid crystals to orient themselves parallel with the electrodes.

Liquid crystals in this homogenous phase blocked light from nanorods turned one way, while letting light from nanorods pointed another way pass through a polarizer to the detector.

What happened then was remarkable. When the team applied as little as four volts to the electrodes, liquid crystals floating in the vicinity of the nanorods aligned themselves with the electric field between the electrodes while crystals above the electrodes, still under the influence of the cover slip coating, stayed put.

The new configuration of the crystals -- called a twisted nematic phase -- acted like a shutter that switched the nanorods' signals like a traffic light.

"We don't think this effect depends on the gold nanorods," Link said. "We could have other nano objects that react with light in a polarized way, and then we could modulate their intensity. It becomes a tunable polarizer."

Critical to the experiment's success was the gap -- in the neighborhood of 14 microns -- between the top of the electrodes and the bottom of the cover slip. "The thickness of this gap determines the amount of rotation," Link said. "Because we created the twisted nematic in-plane and have a certain thickness, we always get 90-degree rotation. That's what makes it a super half wave plate."

The research was funded by the Robert A. Welch Foundation, the Office of Naval Research, the American Chemical Society Petroleum Research Fund and a 3M Nontenured Faculty Grant.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Rice University, via EurekAlert!, a service of AAAS.

Journal Reference:

Saumyakanti Khatua, Wei-Shun Chang, Pattanawit Swanglap, Jana Olson, Stephan Link. Active Modulation of Nanorod Plasmons. Nano Letters, 2011; 11 (9): 3797 DOI: 10.1021/nl201876r

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Hydrogen released to fuel cell more quickly when stored in metal nanoparticles

ScienceDaily (Oct. 1, 2011) — Researchers from TU Delft and VU University Amsterdam in the Netherlands have demonstrated that the size of a metal alloy nanoparticle influences the speed with which hydrogen gas is released when stored in a metal hydride. The smaller the size of the nanoparticle, the greater the speed at which the hydrogen gas makes its way to the fuel cell.

The researchers publish their findings in the October issue of the scientific journal Advanced Energy Materials.

Hydrogen heaven

On 27 September Dutch Minister of Infrastructure and the Environment, Ms Schultz van Haegen, announced she will earmark 5 million Euros to stimulate hydrogen transport in the Netherlands. According to the Minister the Netherlands and neighbouring countries have all it takes to become a 'hydrogen heaven'. In July 2011, the German car manufacturer Daimler announced its intention to build twenty new hydrogen fuelling stations along Germany's motorways. Hydrogen is back on the agenda. Hydrogen gas is currently stored in a vehicle fuel tank at 700 bar pressure. Fuelling stations thus require high-pressure pumps to fill these tanks and these systems consume a lot of energy.

Hydrogen storage

There are thus good reasons for finding alternative hydrogen storage techniques. Hydrogen can be absorbed in high densities in metals such as magnesium, without the need for high pressure. However, the disadvantage is that releasing the hydrogen again is a very difficult and very slow process. One way of speeding up the release of the hydrogen is to use magnesium nanoparticles that are fixed in a matrix to prevent them from aggregating.

Nanoparticles in a matrix

Professor of Materials for Energy Conversion and Storage, Bernard Dam, and his colleagues at TU Delft and VU University Amsterdam have demonstrated experimentally that the interaction between the nanoparticles and the matrix can cause the hydrogen gas to be released faster. Using models consisting of thin layers of magnesium and titanium, they show how the pressure of the hydrogen being released from the magnesium increases as the layers become thinner. This means that it indeed makes sense to store hydrogen in nanoparticles in a matrix. The choice of matrix determines to what extent the hydrogen desorption pressure increases. The researchers published their findings in the October 2011 edition of the scientific journal Advanced Energy Materials.

Efficient and affordable hydrogen storage techniques can play an important role in the large-scale adoption of hydrogen fuel cells. Bernard Dam foresees the development of hybrid vehicles that use batteries for short distances but switch to hydrogen for long distances: 'Your electric motor will be powered by batteries inside the city, and by hydrogen when you go further afield.'

The research was funded by the ACTS Sustainable Hydrogen Program of the Netherlands Organisation for Scientific Research.

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Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Delft University of Technology.

Journal Reference:

Lennard P.A. Mooij, Andrea Baldi, Christiaan Boelsma, Kun Shen, Marnix Wagemaker, Yevheniy Pivak, Herman Schreuders, Ronald Griessen, Bernard Dam. Interface Energy Controlled Thermodynamics of Nanoscale Metal Hydrides. Advanced Energy Materials, Volume 1, issue 5, pages 754-758, October 2011.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Technique to control light from nanoparticles

ScienceDaily (Sep. 30, 2011) — A nanoscale game of "now you see it, now you don't" may contribute to the creation of metamaterials with useful optical properties that can be actively controlled, according to scientists at Rice University.

A Rice laboratory led by chemist Stephan Link has discovered a way to use liquid crystals to control light scattered from gold nanorods. The researchers use voltage to sensitively manipulate the alignment of liquid crystal molecules that alternately block and reveal light from the particles; the gold nanorods collect and retransmit light in a specific direction.

The research was reported in the American Chemical Society journal Nano Letters.

It seems simple, but Link said the technique took two years to refine to the point where light from the nanoparticles could be completely controlled.

"The key to our approach is the in-plane rotation of liquid crystal molecules covering individual gold nanorods that act as optical antennas," said Link, an assistant professor of chemistry and electrical and computer engineering. "Learning how our devices work was exciting and has provided us with many ideas of how to manipulate light at the nanoscale."

Link said the device is actually a super half wave plate, a refined version of a standard device that alters the polarization of light.

With the new device, the team expects to be able to control light from any nanostructure that scatters, absorbs or emits light, even quantum dots or carbon nanotubes. "The light only has to be polarized for this to work," said Link, who studies the plasmonic properties of nanoparticles and recently authored a perspective on his group's recent research in plasmonics for the Journal of Physical Chemistry Letters.

In polarized light, like sunlight reflecting off water, the light's waves are aligned in a particular plane. By changing the direction of their alignment, liquid crystals can tunably block or filter light.

The Rice team used gold nanorods as their polarized light source. The rods act as optical antennas; when illuminated, their surface plasmons re-emit light in a specific direction.

In their experiment, the team placed randomly deposited nanorods in an array of alternating electrodes on a glass slide; they added a liquid crystal bath and a cover slip. A polyimide coating on the top cover slip forced the liquid crystals to orient themselves parallel with the electrodes.

Liquid crystals in this homogenous phase blocked light from nanorods turned one way, while letting light from nanorods pointed another way pass through a polarizer to the detector.

What happened then was remarkable. When the team applied as little as four volts to the electrodes, liquid crystals floating in the vicinity of the nanorods aligned themselves with the electric field between the electrodes while crystals above the electrodes, still under the influence of the cover slip coating, stayed put.

The new configuration of the crystals -- called a twisted nematic phase -- acted like a shutter that switched the nanorods' signals like a traffic light.

"We don't think this effect depends on the gold nanorods," Link said. "We could have other nano objects that react with light in a polarized way, and then we could modulate their intensity. It becomes a tunable polarizer."

Critical to the experiment's success was the gap -- in the neighborhood of 14 microns -- between the top of the electrodes and the bottom of the cover slip. "The thickness of this gap determines the amount of rotation," Link said. "Because we created the twisted nematic in-plane and have a certain thickness, we always get 90-degree rotation. That's what makes it a super half wave plate."

The research was funded by the Robert A. Welch Foundation, the Office of Naval Research, the American Chemical Society Petroleum Research Fund and a 3M Nontenured Faculty Grant.

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and Google +1:

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Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Rice University, via EurekAlert!, a service of AAAS.

Journal Reference:

Saumyakanti Khatua, Wei-Shun Chang, Pattanawit Swanglap, Jana Olson, Stephan Link. Active Modulation of Nanorod Plasmons. Nano Letters, 2011; 11 (9): 3797 DOI: 10.1021/nl201876r

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Hydrogen released to fuel cell more quickly when stored in metal nanoparticles

ScienceDaily (Oct. 1, 2011) — Researchers from TU Delft and VU University Amsterdam in the Netherlands have demonstrated that the size of a metal alloy nanoparticle influences the speed with which hydrogen gas is released when stored in a metal hydride. The smaller the size of the nanoparticle, the greater the speed at which the hydrogen gas makes its way to the fuel cell.

The researchers publish their findings in the October issue of the scientific journal Advanced Energy Materials.

Hydrogen heaven

On 27 September Dutch Minister of Infrastructure and the Environment, Ms Schultz van Haegen, announced she will earmark 5 million Euros to stimulate hydrogen transport in the Netherlands. According to the Minister the Netherlands and neighbouring countries have all it takes to become a 'hydrogen heaven'. In July 2011, the German car manufacturer Daimler announced its intention to build twenty new hydrogen fuelling stations along Germany's motorways. Hydrogen is back on the agenda. Hydrogen gas is currently stored in a vehicle fuel tank at 700 bar pressure. Fuelling stations thus require high-pressure pumps to fill these tanks and these systems consume a lot of energy.

Hydrogen storage

There are thus good reasons for finding alternative hydrogen storage techniques. Hydrogen can be absorbed in high densities in metals such as magnesium, without the need for high pressure. However, the disadvantage is that releasing the hydrogen again is a very difficult and very slow process. One way of speeding up the release of the hydrogen is to use magnesium nanoparticles that are fixed in a matrix to prevent them from aggregating.

Nanoparticles in a matrix

Professor of Materials for Energy Conversion and Storage, Bernard Dam, and his colleagues at TU Delft and VU University Amsterdam have demonstrated experimentally that the interaction between the nanoparticles and the matrix can cause the hydrogen gas to be released faster. Using models consisting of thin layers of magnesium and titanium, they show how the pressure of the hydrogen being released from the magnesium increases as the layers become thinner. This means that it indeed makes sense to store hydrogen in nanoparticles in a matrix. The choice of matrix determines to what extent the hydrogen desorption pressure increases. The researchers published their findings in the October 2011 edition of the scientific journal Advanced Energy Materials.

Efficient and affordable hydrogen storage techniques can play an important role in the large-scale adoption of hydrogen fuel cells. Bernard Dam foresees the development of hybrid vehicles that use batteries for short distances but switch to hydrogen for long distances: 'Your electric motor will be powered by batteries inside the city, and by hydrogen when you go further afield.'

The research was funded by the ACTS Sustainable Hydrogen Program of the Netherlands Organisation for Scientific Research.

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Delft University of Technology.

Journal Reference:

Lennard P.A. Mooij, Andrea Baldi, Christiaan Boelsma, Kun Shen, Marnix Wagemaker, Yevheniy Pivak, Herman Schreuders, Ronald Griessen, Bernard Dam. Interface Energy Controlled Thermodynamics of Nanoscale Metal Hydrides. Advanced Energy Materials, Volume 1, issue 5, pages 754-758, October 2011.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

New technique maps twin faces of smallest Janus nanoparticles

ScienceDaily (Sep. 28, 2011) — New drug delivery systems, solar cells, industrial catalysts and video displays are among the potential applications of special particles that possess two chemically distinct sides. These particles are named after the two-faced Roman god Janus and their twin chemical faces allow them to form novel structures and new materials.

However, as scientists have reduced the size of Janus particles down to a few nanometers in diameter -- about the size of individual proteins, which has the greatest potential for drug therapy -- their efforts have been hampered because they haven't had a way to accurately map the surfaces of the particles that they produce. This uncertainty has made it difficult to evaluate the effectiveness of these particles for various applications and to improve the methods researchers are using to produce them.

Now, a team of Vanderbilt chemists has overcome this obstacle by developing the first method that can rapidly and accurately map the chemical properties of the smallest of these Janus nanoparticles.

The results, published online this month in the German chemistry journal Angewandte Chemie, address a major obstacle that has slowed the development and application of the smallest Janus nanoparticles.

The fact that Janus particles have two chemically distinct faces makes them potentially more valuable than chemically uniform particles. For example, one face can hold onto drug molecules while the other is coated with linker molecules that bind to the target cells. This advantage is greater when the different surfaces are cleanly separated into hemispheres than when the two types of surfaces are intermixed.

For larger nanoparticles (with sizes above 10 nanometers), researchers can use existing methods, such as scanning electron microscopy, to map their surface composition. This has helped researchers improve their manufacturing methods so they can produce cleanly segregated Janus particles. However, conventional methods do not work at sizes below 10 nanometers.

The Vanderbilt chemists -- Associate Professor David Cliffel, Assistant Professor John McLean, graduate student Kellen Harkness and Lecturer Andrzej Balinski -- took advantage of the capabilities of a state-of-the-art instrument called an ion mobility-mass spectrometer (IM-MS) that can simultaneously identify thousands of individual particles.

The team coated the surfaces of gold nanoparticles ranging in size from two to four nanometers with two different chemical compounds. Then they broke the nanoparticles down into clusters of four gold atoms and ran these fragments through the IM-MS.

Molecules from the two coatings were still attached to the clusters. So, by analyzing the resulting pattern, the chemists showed that they could distinguish between original nanoparticles where the two surface compounds were completely separated, those where they were randomly mixed and those that had an intermediate degree of separation.

"There is no other way to analyze structure at this scale except X-ray crystallography," said Cliffel, "and X-ray crystallography is extremely difficult and can take months to get a single structure."

"IM-MS isn't quite as precise as X-ray crystallography but it is extremely practical," added McLean, who has helped pioneer the new instrument's development. "It can provide structural information in a few seconds. Two years ago a commercial version became available so people who want to use it no longer have to build one for themselves."

The research was funded in part by a grant from the National Institutes of Health.

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Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Vanderbilt University. The original article was written by David Salisbury.

Journal Reference:

Kellen M. Harkness, Andrzej Balinski, John A. McLean, David E. Cliffel. Nanoscale Phase Segregation of Mixed Thiolates on Gold Nanoparticles. Angewandte Chemie International Edition, 2011; DOI: 10.1002/anie.201102882

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Lasers used to form 3-D crystals made of nanoparticles

ScienceDaily (June 3, 2011) — University of Michigan physicists used the electric fields generated by intersecting laser beams to trap and manipulate thousands of microscopic plastic spheres, thereby creating 3-D arrays of optically induced crystals.

The technique could someday be used to analyze the structure of materials of biological interest, including bacteria, viruses and proteins, said U-M physicist Georg Raithel.

Raithel is co-author of a research paper on the topic published online May 31 in the journal Physical Review E. The other author is U-M research fellow Betty Slama-Eliau.

The standard method used to characterize biological molecules like proteins involves crystallizing them, then analyzing their structure by bombarding the crystals with X-rays, a technique called X-ray crystallography. But the method cannot be used on many of the proteins of highest interest -- such as cell-membrane proteins -- because there's no way to crystallize those molecules.

"So we came up with this idea that one could use, instead of a conventional crystal, an optically induced crystal in order to get the crystallization of a sample that could be suitable for structural analysis," said Raithel, professor of physics and associate chair of the department.

To move toward that goal, Raithel and his colleagues are developing the laser technique using microscopically small plastic spheres instead of the molecules. Other researchers have created 3-D optically induced crystals, but Raithel said the crystals his team created are denser than those previously achieved.

The process involves shining laser beams through two opposed microscope lenses, one directly beneath the other. Two infrared laser beams are directed through each lens, and they meet at a common focal point on a microscope slide that holds thousands of plastic nanoparticles suspended in a drop of water.

The intersecting laser beams create electric fields that vary in strength in a regular pattern that forms a 3-D grid called an optical lattice. The nanoparticles get sucked into regions of high electric-field strength, and thousands of them align to form optically induced crystals. The crystals are spherical in shape and about 5 microns in diameter. A micron is one millionth of a meter.

Imagine an egg crate containing hundreds of eggs. The cardboard structure of the crate is the optical lattice, and each of the eggs represents one of the nanoparticles. Stack several crates on top of each other and you get a 3-D crystal structure.

"The crate is the equivalent of the optical lattice that the laser beams make," Raithel said. "The structure of the crystal is determined by the egg carton, not by the eggs."

The optical crystals dissipate as soon as the laser is switched off.

The research was funded by the National Science Foundation.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Michigan.

Journal Reference:

B. Slama-Eliau, G. Raithel. Three-dimensional arrays of submicron particles generated by a four-beam optical lattice. Physical Review E, 2011; 83 (5) DOI: 10.1103/PhysRevE.83.051406

Note: If no author is given, the source is cited instead.

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Lasers used to form 3-D crystals made of nanoparticles

ScienceDaily (June 3, 2011) — University of Michigan physicists used the electric fields generated by intersecting laser beams to trap and manipulate thousands of microscopic plastic spheres, thereby creating 3-D arrays of optically induced crystals.

The technique could someday be used to analyze the structure of materials of biological interest, including bacteria, viruses and proteins, said U-M physicist Georg Raithel.

Raithel is co-author of a research paper on the topic published online May 31 in the journal Physical Review E. The other author is U-M research fellow Betty Slama-Eliau.

The standard method used to characterize biological molecules like proteins involves crystallizing them, then analyzing their structure by bombarding the crystals with X-rays, a technique called X-ray crystallography. But the method cannot be used on many of the proteins of highest interest -- such as cell-membrane proteins -- because there's no way to crystallize those molecules.

"So we came up with this idea that one could use, instead of a conventional crystal, an optically induced crystal in order to get the crystallization of a sample that could be suitable for structural analysis," said Raithel, professor of physics and associate chair of the department.

To move toward that goal, Raithel and his colleagues are developing the laser technique using microscopically small plastic spheres instead of the molecules. Other researchers have created 3-D optically induced crystals, but Raithel said the crystals his team created are denser than those previously achieved.

The process involves shining laser beams through two opposed microscope lenses, one directly beneath the other. Two infrared laser beams are directed through each lens, and they meet at a common focal point on a microscope slide that holds thousands of plastic nanoparticles suspended in a drop of water.

The intersecting laser beams create electric fields that vary in strength in a regular pattern that forms a 3-D grid called an optical lattice. The nanoparticles get sucked into regions of high electric-field strength, and thousands of them align to form optically induced crystals. The crystals are spherical in shape and about 5 microns in diameter. A micron is one millionth of a meter.

Imagine an egg crate containing hundreds of eggs. The cardboard structure of the crate is the optical lattice, and each of the eggs represents one of the nanoparticles. Stack several crates on top of each other and you get a 3-D crystal structure.

"The crate is the equivalent of the optical lattice that the laser beams make," Raithel said. "The structure of the crystal is determined by the egg carton, not by the eggs."

The optical crystals dissipate as soon as the laser is switched off.

The research was funded by the National Science Foundation.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Michigan.

Journal Reference:

B. Slama-Eliau, G. Raithel. Three-dimensional arrays of submicron particles generated by a four-beam optical lattice. Physical Review E, 2011; 83 (5) DOI: 10.1103/PhysRevE.83.051406

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Research creates nanoparticles perfectly formed to tackle cancer

ScienceDaily (June 8, 2011) — Researchers from the University of Hull have discovered a way to load up nanoparticles with large numbers of light-sensitive molecules to create a more effective form of photodynamic therapy (PDT) for treating cancer.

Photodynamic therapy uses molecules which, when irradiated with light, cause irreparable damage to cells by creating toxic forms of oxygen, called reactive oxygen species. Most PDT works with individual light-sensitive molecules -- but the new nanoparticles could each carry hundreds of molecules to a cancer site.

A number of different light-sensitive molecules -- collectively known as photosensitisers -- are used in PDT and each absorbs a very specific part of the light spectrum. The research team -- from the University of Hull's Department of Chemistry -- placed one kind of photosensitiser inside each nanoparticle and another on the outside, which meant that far more reactive oxygen species could be created from the same amount of light. The findings are published in the current issue of Molecular Pharmaceutics.

The nanoparticles have also been designed to be the perfect size and shape to penetrate easily into the tumour, as lead researcher, Dr Ross Boyle, explains.

"Small cancer tumours get nutrients and oxygen by diffusion, but once tumours reach a certain size, they need to create blood vessels to continue growing, " he says. "These new blood vessels, or neovasculature, are 'leaky' because the vessel walls are not as tightly knit as normal blood vessels. Our nanoparticles have been designed so the pressure in the blood vessels will push them through the space between the cells to get into the tumour tissue."

The nanoparticles are made from a material that limits the leaching of its contents while in the bloodstream, but when activated with light, at the tumour, the toxic reactive oxygen species can diffuse freely out of the particles; meaning that damage is confined to the area of the cancer.

The researchers tested the nanoparticles on colon cancer cells, and while they were able to penetrate the cells, they also found that the nanoparticles could still be effective when near -- rather than inside -- the cancer cells.

"Some types of cancer cell are able to expel conventional drugs, so if we can make this kind of therapy work simply by getting the nanoparticles between the cancer cells, rather than inside them, it could be very beneficial," says Dr Boyle.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Hull.

Journal Reference:

Maheshika Kuruppuarachchi, Huguette Savoie, Ann Lowry, Cristina Alonso, and Ross W. Boyle. Polyacrylamide Nanoparticles as a Delivery System in Photodynamic Therapy. Molecular Pharmaceutics, 2011; 110316145246004 DOI: 10.1021/mp200023y

Note: If no author is given, the source is cited instead.

Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of ScienceDaily or its staff.

View the original article here