Quantum plasmons demonstrated in atomic-scale nanoparticles

 Addressing a half-decade-old debate, engineers at Stanford have positively identified the presence of plasmons, the collective oscillations of electrons, in individual metal particles as small as one nanometer in diameter. The discovery could impact nanotechnology.

The physical phenomenon of plasmon resonances in small metal particles has been apparent for centuries. They are visible in the vibrant hues of the great stained-glass windows of the world. More recently, plasmon resonances have been used by engineers to develop new, light-activated cancer treatments and to enhance light absorption in photovoltaics and photocatalysis.

"The stained-glass windows of Notre Dame Cathedral and Stanford Chapel derive their color from metal nanoparticles embedded in the glass. When the windows are illuminated, the nanoparticles scatter specific colors depending on the particle's size and geometry " said Jennifer Dionne, an assistant professor of materials science and engineering at Stanford and the senior author of a new paper on plasmon resonances to be published in the journal Nature.

In the study, the team of engineers report the direct observation of plasmon resonances in individual metal particles measuring down to one nanometer in diameter, just a few atoms across.

"Plasmon resonances at these scales are poorly understood," said Jonathan Scholl, a doctoral candidate in Dionne's lab and first author of the paper. "So, this class of quantum-sized metal nanoparticles has gone largely under-utilized. Exploring their size-dependent nature could open up some interesting applications at the nanoscale."

The research could lead to novel electronic or photonic devices based on excitation and detection of plasmons in these extremely small particles, the engineers said.

"Alternatively, there could be opportunities in catalysis, quantum optics, and bio-imaging and therapeutics," added Dionne.

Longstanding debate

The science of tiny metal particles has perplexed physicists and engineers for decades. As metallic particles near about 10 nanometers in diameter, classical physics breaks down. The particles begin to demonstrate unique physical and chemical properties that bulk counterparts of the very same materials do not. A nanoparticle of silver measuring a few atoms across, for instance, will respond to photons and electrons in ways profoundly different from a larger particle or slab of silver.

By clearly illustrating the details of this classical-to-quantum transition, Scholl and Dionne have pushed the field of plasmonics into a new realm that could have lasting consequences for catalytic processes such as artificial photosynthesis, for cancer research and treatment, and even quantum computing.

"Particles at this scale are more sensitive and more reactive than bulk materials," said Dionne. "But we haven't been able to take full advantage of their optical and electronic properties without a complete picture of the science. This paper provides the foundation for new avenues of nanotechnology entering the 100-to-10,000 atom regime."

Noble metals

In recent years, engineers have paid particular attention to nanoparticles of the noble metals: silver, gold, palladium, platinum and so forth. These metals are well known to support localized surface plasmon resonances in larger particles. Plasmons are the collective oscillation of electrons at the metal surface in response to light or an electric field.

Additionally, other important physical properties can be driven when plasmons are constrained in extremely small spaces, like the nanoparticles Dionne and Scholl studied, a phenomenon known as quantum confinement.

Depending on the shape and size of the particle, therefore, quantum confinement can dominate a particle's electronic and optical response. This research allows scientists, for the first time, to directly correlate a quantum-sized plasmonic particle's geometry -- its shape and size -- with its plasmon resonances.

Standing to benefit

Nanotechnology stands to benefit from this new understanding. Medical science, for instance, has devised a way to use nanoparticles excited by light to burn away cancer cells, a process known as photothermal ablation. Metal nanoparticles are affixed with molecular appendages called ligands that attach exclusively to chemical receptors on cancerous cells. When irradiated with infrared light, the plasmons begin to resonate and the metal nanoparticles heat up, burning away the cancerous cells while leaving the surrounding healthy tissue unaffected. The use of smaller nanoparticles in these therapies might improve their accuracy and the effectiveness, particularly since they can be more easily integrated into cells.

There is great promise for such small nanoparticles in catalysis, as well. The greater surface-area-to-volume ratios offered by atomic-scale nanoparticles could could significantly improve catalyic rates and efficiencies and provide advances in water-splitting and artificial photosynthesis, yielding clean and renewable energy sources from artificial fuels.

Aiding and abetting

The researchers' ability to observe plasmons in particles of such small size was abetted by the powerful, multi-million dollar environmental scanning transmission electron microscope (E-STEM) installed recently at Stanford's Center for Nanoscale Science and Engineering, one of just a handful of such microscopes in the world.

E-STEM imaging was used in conjunction with electron energy-loss spectroscopy (EELS) -- a research technique that measures the change in an electron's energy as it passes through a material -- to determine the shape and behavior of individual nanoparticles. Combined, STEM and EELS allowed the team to address many of the ambiguities of previous investigations.

"With this new microscope, we can resolve individual atoms within the nanoparticle," said Dionne, "and we can directly observe these particles' quantum plasmon resonances."

Ai Leen Koh, a research scientist at the Stanford Nanocharacterization Laboratory, and co-author of the paper, noted: "Even though plasmons can be probed using both light and electrons, electron excitation is advantageous in that it allows us to image the nanoparticle down to the atomic level and study its plasmon resonances at the same time."

Scholl added, "Someday, we might use this microscope to watch reactions in progress to better understand and optimize them."

Elegant and versatile

The researchers concluded by explaining the physics of their discovery through an elegant and versatile analytical model based on well-known quantum mechanical principles.

"Technically speaking, we've created a relatively simple, computationally light model that describes plasmonic systems where classical theories have failed," said Scholl.

"This paper represents fundamental research. We have clarified what was an ambiguous scientific understanding and, for the first time, directly correlated a particle's geometry with its plasmonic resonance for quantum-sized particles," summarized Dionne. "And this could have some very interesting, and very promising, implications and applications."

Story Source:

The above story is reprinted from materials provided by Stanford School of Engineering. The original article was written by Andrew Myers.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Jonathan A. Scholl, Ai Leen Koh, Jennifer A. Dionne. Quantum plasmon resonances of individual metallic nanoparticles. Nature, 2012; 483 (7390): 421 DOI: 10.1038/nature10904

New measuring techniques can improve efficiency, safety of nanoparticles

Using high-precision microscopy and X-ray scattering techniques, University of Oregon researchers have gained eye-opening insights into the process of applying green chemistry to nanotechnology that results in high yields, improves efficiency and dramatically reduces waste and potential negative exposure to human health or the environment.

University of Oregon chemist James E. Hutchison described his lab's recent efforts to monitor the dynamics of nanoparticles in an invited talk Feb. 28 at the American Physical Society's March Meeting (Feb. 27-March 2) in Boston, Mass. It turns out, Hutchison said, that simply reducing the amount of gold -- the material used in his research -- in the initial stages of the process used to grow nanoparticles allows for better maintenance of the particle size.

That accomplishment, he said, has important implications. The use of lower concentrations of the precursor that forms the nanoparticles virtually eliminates the ability of nanoparticles to aggregate together and thus prevents variations of sizes of the desired end product.

"What we saw while observing the production process with small-angle X-ray scattering (SAXS) was amazing," Hutchison, said in an interview before his lecture. "We realized that it is possible to reduce the concentration of gold and allow the particles to still grow, but shutdown the coalescent, or aggregation, pathway."

He also summarized his lab's use of chemically modified grids (Smart Grids) in transmission electron microscopy to study how nanoparticles are shed from common objects such as silverware and copper jewelry -- findings that were detailed in the journal ACS Nano in October. They studied the transformation of silver nanoparticles coated on Smart Grids as well as the common objects and found that all forms produce smaller silver nanoparticles that could disperse into the environment, especially in humid air, water and light -- and likely have been doing that throughout time without any known health ramifications.

"There may be many beneficial applications to nanotechnology, but they are only beneficial if the net benefits outweigh the deleterious implications for human health and the environment," said Hutchison, who holds the Lokey-Harrington Chair in Chemistry at the University of Oregon.

These new monitoring and measuring techniques, he said, are vital to help understand what modifications are possible in the processes that grow nanoparticles for a desired product. Using green chemistry, he added, can help assure both efficiency and stability of a product, which, in turn, will lower the risk of unwanted environmental or harmful human-health consequences.

"Advancing the safe implementation of nanotechnology is vital to many fields, from electronics to medicine and materials science, in general," said Kimberly Andrews Espy, vice president for research and innovation at the UO. "Professor Hutchison has been a leader in the University of Oregon's efforts to promote green chemistry in this effort, and his work continues to set examples on how best to use it."

Hutchison is co-author of "Green Nanotechnology Challenges and Opportunities," a white paper published by the American Chemical Society's Green Chemistry Institute, and the National Research Council report, "A Research Strategy for Environmental, Health, and Safety Aspects of Engineered Nanomaterials." He also was the founding director of the Safer Nanomaterials and Nanomanufacturing Initiative (SSNI) of the Oregon Nanoscience and Microtechnologies Institute (ONAMI), a state signature research center.

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The above story is reprinted from materials provided by University of Oregon.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Nanoparticles refined for more accurate delivery of cancer drugs

A new class of nanoparticles, synthesized by a UC Davis research team to prevent premature drug release, holds promise for greater accuracy and effectiveness in delivering cancer drugs to tumors. The work is published in the current issue of Angewandte Chemie, a leading international chemistry journal.

In their paper, featured on the inside back cover of the journal, Kit Lam, professor and chair of the Department of Biochemistry and Molecular Medicine, and his team report on the synthesis of a novel class of micelles called dual-responsive boronate cross-linked micelles (BCMs) , which produce physicochemical changes in response to specific triggers.

A micelle is an aggregate of surfactant molecules dispersed in water-based liquid such as saline. Micelles are nano-sized, measuring about 25-50 nanometers (one nanometer is one billionth of a meter), and can function as nanocarriers for drug delivery.

BCMs are a unique type of micelle, which releases the payload quickly when triggered by the acidic micro-environment of the tumor or when exposed to an intravenously administered chemical compound such as mannitol, an FDA-approved sugar compound often used as a diuretic agent, which interferes with the cross-linked micelles.

"This use of reversibly cross-linked targeting micellar nanocarriers to deliver anti-cancer drugs helps prevent premature drug release during circulation and ensures delivery of high concentrations of drugs to the tumor site," said first author Yuanpei Li, a postdoctoral fellow in Lam's laboratory who created the novel nanoparticle with Lam. "It holds great promise for a significant improvement in cancer therapy."

Stimuli-responsive nanoparticles are gaining considerable attention in the field of drug delivery due to their ability to transform in response to specific triggers. Among these nanoparticles, stimuli-responsive cross-linked micelles (SCMs) represent a versatile nanocarrier system for tumor-targeting drug delivery.

Too often, nanoparticles release drugs prematurely and miss their target. SCMs can better retain the encapsulated drug and minimize its premature release while circulating in the blood pool. The introduction of environmentally sensitive cross-linkers makes these micelles responsive to the local environment of the tumor. In these instances, the payload drug is released primarily in the cancerous tissue.

The dual-responsive boronate cross-linked micelles that Lam's team has developed represent an even smarter second generation of SCMs able to respond to multiple stimuli as tools for accomplishing the multi-stage delivery of drugs to the complex in vivo tumor micro-environment. These BCMs deliver drugs based on the self-assembly of boronic acid-containing polymers and catechol-containing polymers, both of which make these micelles unusually sensitive to changes in the pH of the environment. The team has optimized the stability of the resulting boronate cross-linked micelles as well as their stimuli-response to acidic pH and mannitol.

This novel nano-carrier platform shows great promise for drug delivery that minimizes premature drug release and can release the drug on demand within the acidic tumor micro-environment or in the acidic cellular compartments when taken in by the target tumor cells. It also can be induced to release the drug through the intravenous administration of mannitol.

The study was funded by grants from the National Institutes of Health and a Department of Defense Breast Cancer Research Program Postdoctoral Award. Other authors are Wenwu Xiao, Kai Xiao, Lorenzo Berti, Harry P. Tseng, and Gabriel Fung of UC Davis; and Juntao Luo of SUNY Upstate Medical University, Syracuse, New York.

Story Source:

The above story is reprinted from materials provided by University of California - Davis Health System.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Yuanpei Li, Wenwu Xiao, Kai Xiao, Lorenzo Berti, Juntao Luo, Harry P. Tseng, Gabriel Fung, Kit S. Lam. Well-Defined, Reversible Boronate Crosslinked Nanocarriers for Targeted Drug Delivery in Response to Acidic pH Values and cis-Diols. Angewandte Chemie International Edition, 2012; DOI: 10.1002/anie.201107144

NMR used to determine whether gold nanoparticles exhibit 'handedness'

 Carnegie Mellon University's Roberto R. Gil and Rongchao Jin have successfully used NMR to analyze the structure of infinitesimal gold nanoparticles, which could advance the development and use of the tiny particles in drug development.

Their approach offers a significant advantage over routine methods for analyzing gold nanoparticles because it can determine whether the nanoparticles exist in a both right-handed and left-handed configuration, a phenomenon called chirality. Determining a nanoparticle's chirality is an important step toward developing them as chiral catalysts -- tools that are highly sought-after by the pharmaceutical industry. Their results are published online at ACS Nano.

Many drugs on the market today contain at least one molecule that is chiral. Often only one of the configurations, or isomers, is effective in the body. In some cases, the other isomer may even be harmful. A striking example is the drug thalidomide, which consisted of two isomers: one of which helped pregnant women control nausea while the other caused damage to the developing fetus. In an effort to create safer, more effective drugs, drug manufacturers are looking for ways to produce purer substances that contain only the left- or right-handed isomer.

Huifeng Qian, a fourth-year graduate student working with Jin, created a gold nanoparticle that has the potential to catalyze chemical reactions that will produce one isomer rather than the other. The nanoparticle is composed of precisely 38 gold atoms and measures a mere 1.4 nanometers. Qian worked diligently for nearly a year to grow the nanoparticles into high-quality crystals so that he could study their structure using x-ray crystallography.

"Growing a pure crystal from nanoparticles is very challenging, and you may not even be able to get a crystal at all," said Jin, an assistant professor of chemistry in CMU's Mellon College of Science. "In the nanoparticle community, the crystal structures of only three nanoparticles have been reported."

In Jin's case, x-ray crystallography revealed that the gold nanoparticle is chiral. Chemists typically probe the internal chiral structure of gold nanoparticles using a technique called circular dichoism spectroscopy. When pure chiral molecules are exposed to circularly polarized light, each isomer absorbs the light differently, resulting in a unique -- and of opposite sign -- spectrum for each isomer. The process of creating the gold nanoparticles, however, often results in a 50/50 mix of each isomer, known as racemates.

"Because the spectrum is of opposite sign for each isomer, they cancel each other out and the net optical response is zero. This makes circular dichoism (CD) spectroscopy useless when it comes to determining the chirality of gold nanoparticles in 50/50 mixtures," said Gil, associate research professor of chemistry and director of the Department of Chemistry's NMR Facility.

Since Jin couldn't use circular dichoism spectroscopy, Gil was able to use NMR to help Jin distinguish between his gold nanoparticles' left- and right-handed isomers.

NMR spectroscopy takes advantage of the physical phenomenon wherein some nuclei wobble and spin like tops, emitting and absorbing a radio frequency signal in a magnetic field. By observing the behavior of these spinning nuclei, scientists can piece together the chemical structure of the compound.

In 1957, scientists observed that the hydrogen atoms of a freely rotating methylene (CH2) group produced two different frequencies if they were close to a chiral center. Jin's gold nanoparticles, which have a chiral core, are cushioned by several chemical groups, including freely rotating methylene groups. Gil reasoned that the nanoparticles' chiral core should induce the methylene group's two hydrogen atoms to give off different frequencies, a phenomenon known as diastereotopicity.

Gil and Jin compared the NMR signal from the hydrogen atoms in a non-chiral gold nanoparticle with the NMR signal from the hydrogen atoms in chiral gold nanoparticle. The non-chiral nanoparticle's NMR spectrum did not reveal any differences, but the chiral nanoparticle's NMR spectrum revealed two different hydrogen signals, providing a simple and efficient way of telling whether the particle is chiral or not, even for a 50/50 mixture of isomers.

"NMR is an alternative -- and very efficient -- method for providing useful information about how the atoms in nanoparticles form the molecular structure. Because NMR can determine chirality in some cases, it can readily be used to determine the purity of a nanoparticle mixture," Jin said.

In current work, Jin and Qian are striving to turn their 50/50 mixture of right- and left-handed isomers into a pure solution of one or the other.

Story Source:

The above story is reprinted from materials provided by Carnegie Mellon University. The original article was written by Jocelyn Duffy.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Huifeng Qian, Manzhou Zhu, Chakicherla Gayathri, Roberto R. Gil, Rongchao Jin. Chirality in Gold Nanoclusters Probed by NMR Spectroscopy. ACS Nano, 2011; 5 (11): 8935 DOI: 10.1021/nn203113j

Technique to control light from nanoparticles

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.

The above story is reprinted (with editorial adaptations) 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

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

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.

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.

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.

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.'

Provided by Delft University of Technology (news : web)

New technique maps twin faces of smallest Janus nanoparticles

 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.

Story Source:

The above story is reprinted (with editorial adaptations ) 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

Branch offices: New family of gold-based nanoparticles could serve as biomedical 'testbed'

 Gold nanoparticles are becoming the … well … gold standard for medical-use nanoparticles. A new paper by researchers from the National Institute of Standards and Technology (NIST) and the National Cancer Institute's Nanotechnology Characterization Laboratory (NCL) proposes not only a sort of gold nanoparticle "testbed" to explore how the tiny particles behave in biological systems, but also a paradigm for how to characterize nanoparticle formulations to determine just what you're working with.

Prospective uses of gold nanoparticles, says NIST chemist Vince Hackley, include high-precision drug-delivery systems and diagnostic image enhancers. Gold is nontoxic and can be fashioned into particles in a range of sizes and shapes. By itself, gold doesn't do much biologically, but it can be "functionalized" by attaching, for instance, protein-based drugs along with targeting molecules that cluster preferentially around cancer cells. The nanoparticles are generally coated as well, to prevent them from clumping together and to avoid rapid clearance by the body's immune system.

NCL's Anil Patri notes that the coating composition, density and stability have a profound impact on the nanomaterial safety, biocompatibility (how well the nanoparticles distribute in the body), and efficacy of the delivery system. "Understanding these parameters through thorough characterization would enable the research community to design and develop better nanomaterials," he says.

To facilitate such studies, the NIST/NCL team set out to create a nanoparticle testbed -- a uniform, controllable core-shell nanoparticle that could be made-to-order with precise shape and size, and to which could be attached nearly any potentially useful functionality. Researchers then could study how controlled variations fared in a biological system.

Their trial system is based on regularly shaped branching molecules called dendrons, a term derived from the Greek word for "tree." Dendron chemistry is fairly new, dating from the 1980s. They're excellent for this use, says NIST researcher Tae Joon Cho, because the individual dendrons are always the same size, unlike polymers, and can readily be modified to carry "payload" molecules. At the same time, the tip of the structure -- the "tree's" trunk -- is designed to bond easily to the surface of a gold nanoparticle.

The team made an exhaustive set of measurements so they could thoroughly describe their custom-made dendron-coated nanoparticles. "There aren't a lot of protocols around for characterizing these materials -- their physical and chemical properties, stability, et cetera," Hackley says, "so, one of the things that came out of the project is a basic series of measurement protocols that we can apply to any kind of gold-based nanoparticle."

Any single measurement technique, he says, is probably inadequate to describe a batch of nanoparticles, because it likely will be insensitive to some size ranges or confused by other factors -- particularly if the particles are in a biological fluid.

The new NIST/NCL paper provides the beginnings of a catalog of analysis techniques for getting a detailed lowdown on nanoparticles. These techniques include nuclear magnetic resonance spectroscopy, matrix-assisted laser desorption/ionization mass spectrometry, dynamic light scattering, ultra-violet/visible spectroscopy and X-ray photoelectron spectroscopy. The dendron-coated nanoparticles also were tested for stability under "biologically relevant" conditions of temperature, acidity and some recognized forms of chemical attack that would take place in the bloodstream. In vitro biological tests are pending.

The work was funded in part by the National Cancer Institute, National Institutes of Health.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by National Institute of Standards and Technology (NIST).

Journal Reference:

Tae Joon Cho, Rebecca A. Zangmeister, Robert I. MacCuspie, Anil K. Patri, Vincent A. Hackley. Newkome-Type Dendron-Stabilized Gold Nanoparticles: Synthesis, Reactivity, and Stability. Chemistry of Materials, 2011; 23 (10): 2665 DOI: 10.1021/cm200591h

Gold nanoparticles help earlier diagnosis of liver cancer

 Hepatocellular carcinoma is the most common cancer to strike the liver. More than 500,000 people worldwide, concentrated in sub-Saharan Africa and Southeast Asia, are diagnosed with it yearly. Most of those afflicted die within six months.

A big obstacle to treatment of liver cancer is the lack of early diagnosis. Current techniques, including ultrasound, CT and MRI scans, spot tumors only when they have grown to about 5 centimeters in diameter. By that time, the cancer is especially aggressive, resisting chemotherapy and difficult to remove surgically.

Now a research team led by Brown University reports some promising results for earlier diagnosis. In lab tests, the team used gold nanoparticles ringed by a charged polymer coating and an X-ray scatter imaging technique to spot tumor-like masses as small as 5 millimeters. The approach, detailed in the American Chemical Society journal Nano Letters, marks the first time that metal nanoparticles have been used as agents to enhance X-ray scattering signals to image tumor-like masses.

"What we're doing is not a screening method," said Christoph Rose-Petruck, professor of chemistry at Brown University and corresponding author on the paper. "But in a routine exam, with people who have risk factors, such as certain types of hepatitis, we can use this technique to see a tumor that is just a few millimeters in diameter, which, in terms of size, is a factor of 10 smaller."

The team took gold nanoparticles of 10 and 50 nanometers in diameter and ringed them with a pair of 1-nanometer polyelectrolyte coatings. The coating gave the nanoparticles a charge, which increased the chances that they would be engulfed by the cancerous cells. Once engulfed, the team used X-ray scatter imaging to detect the gold nanoparticles within the malignant cells. In lab tests, the nontoxic gold nanoparticles made up just 0.0006 percent of the cell's volume, yet the nanoparticles had enough critical mass to be detected by the X-ray scatter imaging device.

"We have shown that even with these small numbers, we can distinguish these [tumor] cells," Rose-Petruck said.

The next step for the researchers is on the clinical side. Beginning this summer, the group will attach a cancer-targeting antibody to the nanoparticle vehicle to search for liver tumors in mice. The antibody that will be used was developed by Jack Wands, director of the Liver Research Center at Rhode Island Hospital and professor of medical science at the Warren Alpert Medical School of Brown University.

"We have developed a monoclonal antibody that targets a cell surface protein highly expressed on liver cancer cells," Wands said. "We plan to couple the antibody to the gold nanoparticles in an attempt to detect the growth of early tumors in the liver by X-ray imaging."

The researchers say the X-ray scatter imaging method could be used to detect nanoparticle assemblies in other organs. "The idea should be that if you can figure out to get that [nanoparticle] to specific sites in the body, you can figure out how to image it," said Danielle Rand, a second-year graduate student in chemistry and the first author on the paper.

Contributing authors include Yanan Liu from Brown, Wands, Zoltan Derdak and Vivian Ortiz from the Liver Research Center, and Milan Taticek at the Czech Technical University in Prague.

The National Institutes of Health and the U.S. Department of Energy funded the research.

Story Source:

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

Journal Reference:

Danielle Rand, Vivian Ortiz, Yanan Liu, Zoltan Derdak, Jack R. Wands, Milan Tati´cˇek, Christoph Rose-Petruck. Nanomaterials for X-ray Imaging: Gold Nanoparticle Enhancement of X-ray Scatter Imaging of Hepatocellular Carcinoma. Nano Letters, 2011; : 110606111628071 DOI: 10.1021/nl200858y

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.

Research creates nanoparticles perfectly formed to tackle cancer

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) 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

Scientists uncover chemical transformations in cobalt nanoparticles

 The evolution schematics of transition from cobalt to cobalt phosphide nanocrystals.

Understanding the intricacies of how nanoparticles undergo chemical transformations could lead to better ways to tailor their composition, which can lead to advanced material properties.

Using the Cornell High Energy Synchrotron Source, scientists led by Richard Robinson, assistant professor of materials science and engineering, uncovered exactly what happens when cobalt nanoparticles transform into two phases of cobalt phosphides.

Their work, published in the Journal of Materials Chemistry, was featured by the journal as a "Hot Article" earlier this month.

The effect Robinson's team observed in the cobalt phosphide transitions was a nanoparticle hollowing due to asymmetric diffusivities of cations and anions. In other words, the cations move out from the core faster than anions can diffuse in, leading to a hollow particle.

Other groups have reported on this "Kirkendall" effect, but the Robinson team was the first to show that this hollowing is more complex than previously thought and can be studied as a two-step process. Their work could be used to control this process and produce complex particles with properties tailored for use in energy applications. Metal phosphides have a wide range of properties -- ferromagnetism, superconductivity, catalytic activity and magnetoresistance among them.

The work was done in collaboration with scientists led by Richard Hennig, assistant professor of materials science and engineering. It was supported by King Abdullah University of Science and Technology, the Cornell Center for Materials Research and the Energy Materials Center at Cornell.

Provided by Cornell University (news : web)

Nanoparticles help scientists harvest light with solar fuels

 The humble alga, hated by boaters and pool owners, may someday help provide us with the raw machinery to power our appliances.

Utschig and Tiede are part of Argonne's Photosynthesis Group, which has worked for fifty years to understand photosynthesis—one of the most mysterious and wonderful chemical processes in the world. Photosynthesis built a green Earth out of the bare, meteor-blistered planet which had sat empty for a billion years; it tipped the composition of the atmosphere towards oxygen, allowing all kinds of life to blossom, including us.

The chemistry group is part of a larger effort to develop efficient ways to produce what are termed solar fuels. Most people think of solar panels when they think of solar energy, but the energy that solar panels generate has to be used right away—they directly create electricity, which can't be stored easily.

The alternative is solar fuels, which pull energy from the sun to create fuel that can be stored for later, such as hydrogen. Hydrogen, a promising fuel in the effort to reduce carbon dioxide emissions, is appealingly clean: when it's burned as fuel, water is the byproduct. But we have yet to discover a low-cost way to manufacture large amounts of hydrogen.

"Basically, we've been reverse-engineering photosynthesis," said Argonne chemist David Tiede, who co-authored the paper. "If we understand how Nature does it, we can tweak the process to produce hydrogen."

Most solar fuel efforts focus on a type of protein complex called Photosystem I, or PSI, which is the first half of the photosynthetic duo found in all green plants.

When light strikes the PSI complex, it momentarily knocks an electron into an "excited" state. The goal is to separate this electron from its home atom—leaving behind a "hole" of positive charge—and channel it to an artificial catalyst to make hydrogen. But the electron only remains excited for the tiniest fraction of a second; the catalyst needs to grab it during this tiny window.

With co-author Nada Dimitrijevic, the team designed platinum nanoparticle catalysts. These catalysts have a size and surface chemistry that allows them to stick to PSI molecules at the point where the light-generated electrons accumulate. When the modified platinum nanoparticles and PSI are mixed in water, the two link together.

"The platinum nanoparticles have the same size and surface charge as the molecule that PSI would bind to naturally," Tiede said.

Because the study design used platinum as a catalyst, which is too expensive to be cost-effective, the research serves as proof-of-concept. Further studies hope to improve the method's efficiency, reliability and economics.

"The next step we'll take is experimenting with non-platinum catalysts," Utschig said. "Hopefully we can find a catalyst that can be made with a cheaper metal, which would make the process much more attractive on a large scale."

The paper, "Photocatalytic Hydrogen Production from Noncovalent Biohybrid Photosystem I/Pt Nanoparticle Complexes," was published in the Journal of Physical Chemistry Letters and is available online.

Provided by Argonne National Laboratory (news : web)

Carbon black nanoparticles can cause cell death, inflammation in lungs, researchers find

 Researchers from the University of Iowa Roy J. and Lucille A. Carver College of Medicine have found that inhaled carbon black nanoparticles create a double source of inflammation in the lungs.

Their findings were published online in the April 27 edition of the Journal of Biological Chemistry. Martha Monick, Ph.D., UI professor of internal medicine, was lead author of the paper which outlined the results.

Monick said researchers expected to find one level of inflammation when cells were exposed to carbon black nanoparticles. They were surprised, however, to find that nanoparticles activated a special inflammatory process and killed cells in a way that further increased inflammation. She said the research showed that the intake of carbon black nanoparticles from sources such as diesel fuel or printer ink caused an initial inflammatory response in lung cells. The surprising results came when the team discovered that these nanoparticles killed macrophages -- immune cells in the lungs responsible for cleaning up and attacking infections -- in a way that also increases inflammation.

"Apoptosis is one way cells die in which all the contents stay in the cell, the cell just keeps shrinking onto itself and the surrounding tissue is protected," Monick said. "We thought that was what was happening with the carbon nanoparticles; we were wrong. A different process called pyroptosis was occurring, causing the cells to burst and spill their contents."

That, she said, can cause a secondary inflammatory response.

Monick cautioned that the doses of carbon black nanoparticles used in the study were much more concentrated than the amounts to which a person might typically be exposed.

"This doesn't mean that walking through a cloud of diesel exhaust will hurt your lungs," she said. "It does show that we may have an environmental exposure that could contribute to inflammation in the lung."

The study was a collaborative project involving researchers in the Department of Internal Medicine in the UI Carver College of Medicine and the Department of Chemistry in the College of Liberal Arts and Sciences. In addition to Monick, a key contributor to the research was Vicki Grassian, Ph.D., UI professor of chemistry who holds the F. Wendell Miller Professorship.

The research team also included Anna C. Reisetter, Linda Powers, and Amit Gupta from internal medicine and Larissa V. Stebounova, and Jonas Baltrusaitis in chemistry.

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

Story Source:

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

Journal Reference:

A. C. Reisetter, L. V. Stebounova, J. Baltrusaitis, L. Powers, A. Gupta, V. H. Grassian, M. M. Monick. Induction of inflammasome dependent pyroptosis by carbon black nanoparticles. Journal of Biological Chemistry, 2011; DOI: 10.1074/jbc.M111.238519

Drug delivery with nanoparticles

 Researchers are able to produce medicine encapsulated in nanoparticles the size of viruses, but new research has shown another great challenge in nanomedicine -- the immune system -- and the importance of the coating polymers on the nanoparticle surface.

Researchers have over time been able to show that medicine designed at nanoscale offers unprecedented opportunities for targeted treatment of serious diseases such as cancer. However, now research also shows that the body's immune system plays a significant part in the drug delivery process.

"Researchers today are able encapsulate medicine in nanoparticles the size of viruses. The nanoparticles are effective for drug delivery -- the delivery of the medicine to the body -- because they can very precisely find diseased cells and carry the medicine to them. This means that you can suffice with less dosage and thereby fewer side effects," explains Professor Moein Moghimi from the Faculty of Pharmaceutical Sciences at the University of Copenhagen.

Professor Moghimi has along with colleagues at the University of Brighton and the Technical University of Denmark recently published a landmark paper in ACS Nano regarding the immune system's attack on nanoparticles.

A water disguise

The new research has shown that the coating of the nanoparticle surface has great influence on the activation of the immune system -- the particle's polymer coating can be designed in various ways, and the form can drastically change the body's immune response.

"Drug delivery with nanoparticles camouflaged as water soluble polymers has proven very effective. One way of delivering drugs safely to diseased sites in the body is to encapsulate them in small polymeric particles in similar size to viruses. However, when injected into the blood these particles are intercepted by the body's defence system. This can be overcome by camouflaging the surface of these nanocarriers with water soluble polymers. This makes the surface 'water-like' and less visible to the immune system," says Professor Moghimi.

Significance of changing the coating polymers

Professor Moghimi works at the Department of Pharmaceutics and Analytical Chemistry where he heads the Centre for Pharmaceutical Nanotechnology and Nanotoxicology, which is supported by the Danish Agency for Science, Technology and Innovation. This work was done as part of ongoing research at the Centre.

Professor Moghimi's main focus is nanotoxicology -- and the possible consequences of drug delivery with nanoparticles.

"Our newest research indicates that we should be very cautious when designing the surface of the nanoparticles. Remarkably, changing the conformation of the coating polymers on nanoparticle surface from a 'mushroom-type' to a 'brush-type' appearance can switch complement activation from one pathway to another," explains Professor Moghimi.

The research demonstrates difficulty in design and surface engineering of polymeric nanoparticles such that it is hydrophilic enough to be compatible with biological fluids and yet prevent complement activation. This is also very important from clinical perspectives since complement activation may induce adverse reactions in some patients.

The importance of this work was also highlighted in an all exclusive "News and Views" by the journal Nature Nanotechnology.

Story Source:

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

Journal Reference:

Robert B. Sim, Russell Wallis. Surface properties: Immune attack on nanoparticles. Nature Nanotechnology, 2011; 6 (2): 80 DOI: 10.1038/nnano.2011.4