Tag Archives: gold nanoparticles

Pretty in violet, a new antimicrobial surface that works in the dark

 Samples of silicone with the various dyes infused. Courtesy: University College of London

Samples of silicone with the various dyes infused. Courtesy: University College of London

A March 25, 2014 news item on Azonano profiles a new antimicrobial surface which works in the dark, as well as, in the light,

Researchers at UCL [University College of London] have developed a new antibacterial material which has potential for cutting hospital acquired infections. The combination of two simple dyes with nanoscopic particles of gold is deadly to bacteria when activated by light – even under modest indoor lighting. And in a first for this type of substance, it also shows impressive antibacterial properties in total darkness.

The UCL March 24, 2014 news release, which originated the news item, describes the current situation with infections in hospitals and the team’s approach to mitigating the problem,

Hospital-acquired infections are a major issue for modern medicine, with pathogens like methicillin-resistant Staphylococcus aureus (MRSA) and Clostridium difficile (C. diff) getting extensive publicity. Although medical establishments have stringent cleaning policies, insist on frequent hand-washing by staff, and have powerful drugs at their disposal, it is difficult to eliminate these infections unless you can make the hospital environment more hostile to microbes. Surfaces, such as door handles, medical equipment, keyboards, pens and so on are an easy route for germs to spread, even onto freshly-cleaned hands.

One possible solution to this is to develop alternative strategies such as antibacterial coatings that make surfaces less accommodating to germs. These surfaces are not like antibacterial fluids that just wash away – the goal is to make a surface which is intrinsically deadly to harmful bacteria.

“There are certain dyes that are known to be harmful to bacteria when subjected to bright light,” explains the study’s corresponding author Ivan Parkin (Head of UCL Chemistry). “The light excites electrons in them, promoting the dye molecules to an excited triplet state and ultimately produces highly reactive oxygen radicals that damage bacteria cell walls. Our project tested new combinations of these dyes along with gold nanoparticles, and simplified ways of treating surfaces which could make the technology easier and cheaper to roll out.”

The UCL news release then goes on to describe the research in some detail,

The team, tested several different combinations of the dyes crystal violet (already used to treat staph infections), methylene blue and nanogold, deposited on the surface of silicone. This flexible rubbery substance is widely used as a sealant, a coating and to build medical apparatus such as tubes, catheters and gaskets, and can also be used as protective casings for things like keyboards and telephones.

While work to create antimicrobial surfaces in the past has often concentrated on complex ways of bonding dyes to the surface, this study took a simpler approach. The researchers used an organic solvent to swell the silicone, allowing the methylene blue and gold nanoparticles to diffuse through the polymer. They then dipped the silicone into a crystal violet solution to form a thin dye layer at the polymer surface.

In their tests, in which infected surfaces were subjected to light levels similar to those measured in hospital buildings, surfaces treated with a combination of crystal violet, methylene blue and nanogold showed the most potent bactericidal effect ever observed in such a surface. Moreover, the treatment did not significantly change the properties of the silicone (for instance, how water repellent it is), and the coating was not affected by rubbing with alcohol wipes, meaning it can stand up to the repeated cleaning that goes on in hospitals, without being worn off.

“Despite contaminating the surface with far more bacteria than you would ever see in a hospital setting, placed under a normal fluorescent light bulb, the entire sample was dead in three to six hours, depending on the type of bacteria,” says the paper’s lead author, Sacha Noimark. “That was an excellent result, but the bigger surprise was the sample which we left in the dark. That sample too showed significant reductions in bacterial load, albeit over longer timescales of about three to eighteen hours. The precise mechanism by which this dark-kill works is not yet clear, though.”

This is the first time a light-activated antimicrobial surface has had any kind of effect in the dark. This, along with its unprecedented performance under hospital lighting conditions, and relatively simple and cost-effective manufacture, means that the technology is extremely promising for future applications.

The team have been granted a patent on the formulation. The work was sponsored through the UCL M3S engineering doctorate centre and co-funded by Ondine Biopharma.

Here’s a link to and a citation for the paper,

Light-activated antimicrobial surfaces with enhanced efficacy induced by a dark-activated mechanism by Sacha Noimark, Elaine Allan, and Ivan P. Parkin. Chem. Sci., 2014, Advance Article DOI: 10.1039/C3SC53186D First published online 05 Mar 2014

This article is behind a paywall. One final note, I believe the difference in publication dates, March 24, 2014 in the news release as opposed to March 5, 2014 as listed on the publication’s website, is due to the probability that the print version was published later.

Getting new information on trafficking viruses with gold nanoparticles

Finnish researchers have developed a new technique for studying viruses according to a Jan. 15, 2014 news release on EurekAlert,

Researchers at the Nanoscience Center (NSC) of University of Jyväskylä in Finland have developed a novel method to study enterovirus structures and their functions. The method will help to obtain new information on trafficking of viruses in cells and tissues as well as on the mechanisms of virus opening inside cells.

The news release explains enteroviruses and describes the technique in more detail,

Enteroviruses are pathogenic viruses infecting humans. This group consists of polioviruses, coxsackieviruses, echoviruses and rhinoviruses. Enteroviruses are the most common causes of flu, but they also cause serious symptoms such as heart muscle infections and paralysis. Recently, enteroviruses have been linked with chronic diseases such as diabetes (2).

The infection mechanisms and infectious pathways of enteroviruses are still rather poorly known. Previous studies in the group of Dr. Varpu Marjomäki at the NSC have focused on the cellular factors that are important for the infection caused by selected enteroviruses (3). The mechanistic understanding of virus opening and the release of the viral genome in cellular structures for starting new virus production is still largely lacking. Furthermore, the knowledge of infectious processes in tissues is hampered by the lack of reliable tools for detecting virus infection.

The newly developed method involves a chemical modification of a known thiol-stabilized gold nanoparticle, the so-called Au102 cluster that was first synthesized and structurally solved by the group of Roger D Kornberg in 2007 (4) and later characterized at NSC by the groups of prof. Hannu Häkkinen and prof. Mika Pettersson in collaboration with Kornberg. (5) The organic thiol surface of the Au102 particles is modified by attaching linker molecules that make a chemical bond to sulfur-containing cysteine residues that are part of the surface structure of the virus. Several tens of gold particles can bind to a single virus, and the binding pattern shows up as dark tags reflecting the overall shape and structure of the virus (see the figure). The gold particles allow for studies on the structural changes of the viruses during their lifespan.

The study showed also that the infectivity of the viruses is not compromised by the attached gold particles which indicates that the labeling method does not interfere with the normal biological functions of viruses inside cells. This facilitates new investigations on the virus structures from samples taken from inside cells during the various phases of the virus infection, and gives possibilities to obtain new information on the mechanisms of virus uncoating (opening and release of the genome). The new method allows also for tracking studies of virus pathways in tissues. This is important for further understanding of acute and chronic symptoms caused by viruses. Finally, the method is expected to be useful for developing of new antiviral vaccines that are based on virus-like particles.

The method was developed at the NSC as a wide cross-disciplinary collaboration between chemists, physicists and biologists.

Here’s an image provided by the researchers, which illustrates their work,

Left: transmission electron microscopy (TEM) image of a single CVB3 virus showing tens of gold nanoparticles attached to its surface. The particles form a distinct "tagging pattern" that reflects the shape and the structure of the virus. The TEM image can be correlated to the model of the virus (right), where the yellow spheres mark the possible binding sites of the gold particles. The diameter of the virus is about 35 nanometers (nanometer = one billionth of a millimeter). The figure is taken from the publication. Courtesy: University of Jyväskylä

Left: transmission electron microscopy (TEM) image of a single CVB3 virus showing tens of gold nanoparticles attached to its surface. The particles form a distinct “tagging pattern” that reflects the shape and the structure of the virus. The TEM image can be correlated to the model of the virus (right), where the yellow spheres mark the possible binding sites of the gold particles. The diameter of the virus is about 35 nanometers (nanometer = one billionth of a millimeter). The figure is taken from the publication. Courtesy: University of Jyväskylä

Unfortunately, the researchers have published in the Proceedings f the National Academy of Sciences (PNAS). I noted in a previous posting that this publisher has developed a time-consuming process for getting access to a paper and payment options for reading it. I can provide a link to and a citation to the abstract for this paper but I’m not willing to spend several minutes trying to bypass the block they’ve placed on accessing papers and their payment options,

Site-specific targeting of enterovirus capsid by functionalized monodisperse gold nanoclusters by Varpu Marjomäki, Tanja Lahtinen, Mari Martikainen, Jaakko Koivisto, Sami Malola, Kirsi Salorinne, Mika Pettersson, and Hannu Häkkinenb. Proc. Natl. Acad. Sci. USA (2014), www.pnas.org/cgi/doi/10.1073/pnas.1310973111.

The University of Jyväskylä Jan. ??, 2014 news release about this work provides references (scroll down) to previous papers published on this work.

A planet-satellite model for nanoparticles

For anyone who visualizes atoms as planets (many of us were taught to think of atoms and their electrons in that way) then, the planet-satellite model for nanoparticles proposed by scientists at the Nanosystems Initiative Munich (NIM) will have a comforting familiarity, Here’s the model as per a Dec. 13, 2013 news item from Nanowerk,

Nanosystems Initiative Munich (NIM) physicists have developed a “planet-satellite model” to precisely connect and arrange nanoparticles in three-dimensional structures. Like photosystems of plants and algae, the model might in future serve to collect and convert energy.

If the scientists‘ nanoparticles were one million times larger, the laboratory would look like an arts and crafts room at Christmas time: gold, silver and colorful shiny spheres in different sizes and filaments in various lengths. For at the center of the nanoscale “planet-satellite model” there is a gold particle which is orbited by other nanoparticles made of silver, cadmium selenide or organic dyes.

A Dec. 2, 2013 NIM press release, which originated the news item, describes the proposed model in detail,

As if by magic, cleverly designed DNA strands connect the satellites with the central planet in a very precise manner. The technique behind this, called “DNA origami”, is a specialty of physics professor Tim Liedl (LMU Munich) and his team. The expertise on the optical characterization of the individual nanosystems is contributed by Professor Jochen Feldmann, Chair of Photonics and Optoelectronics at LMU and Coordinator of the Nanosystems Initiative Munich (NIM).

Large or small, near or far

A distinctive feature of the new model is the modular assembly system which allows the scientists to modify all aspects of the structure very easily and in a controlled manner: the size of the central nanoparticle, the types and sizes of the “satellites” and the distance between planet and satellite particle. It also enables the physicists to adapt and optimize their system for other purposes.

Artificial photosystem

Metals, semiconductors or fluorescent organic molecules serve as satellites. Thus, like the antenna molecules in natural photosystems, such satellite elements might in future be organized to collect light energy and transfer it to a catalytic reaction center where it is converted into another form of energy. For the time being, however, the model allows the scientists to investigate basic physical effects such as the so-called quenching process, which refers to the changing fluorescence intensity of a dye molecule as a function of the distance to the central gold nanoparticle.

“The modular assembly principle and the high yield we obtained in the production of the planet-satellite systems were the crucial factors for reliably investigating this well-known effect with the new methods,” explains Robert Schreiber, lead author of the study.

A whole new cosmos

In addition, the scientists succeeded in joining individual planet-satellite units together into larger structures, combining them as desired. This way, it might be possible to develop complex and functional three-dimensional nanosystems in future, which could be used as directed energy funnels, in Raman spectroscopy or as nanoporous materials for catalytic applications.

The physicists have supplied an image illustrating their model,

 

[downloaded from http://www.nano-initiative-munich.de/index.php?eID=tx_cms_showpic&file=uploads%2Fpics%2FBasiccover_6_Zeilen_02.jpg&md5=aec790fc11262dc94b41a440fa6788baeacfac97&parameters[0]=YTo0OntzOjU6IndpZHRoIjtzOjQ6IjUwMG0iO3M6NjoiaGVpZ2h0IjtzOjM6IjUw&parameters[1]=MCI7czo3OiJib2R5VGFnIjtzOjI0OiI8Ym9keSBiZ0NvbG9yPSIjZmZmZmZmIj4i&parameters[2]=O3M6NDoid3JhcCI7czozNzoiPGEgaHJlZj0iamF2YXNjcmlwdDpjbG9zZSgpOyI%2B&parameters[3]=IHwgPC9hPiI7fQ%3D%3D] Courtesy NIM

[downloaded from http://www.nano-initiative-munich.de/index.php?eID=tx_cms_showpic&file=uploads%2Fpics%2FBasiccover_6_Zeilen_02.jpg&md5=aec790fc11262dc94b41a440fa6788baeacfac97&parameters[0]=YTo0OntzOjU6IndpZHRoIjtzOjQ6IjUwMG0iO3M6NjoiaGVpZ2h0IjtzOjM6IjUw&parameters[1]=MCI7czo3OiJib2R5VGFnIjtzOjI0OiI8Ym9keSBiZ0NvbG9yPSIjZmZmZmZmIj4i&parameters[2]=O3M6NDoid3JhcCI7czozNzoiPGEgaHJlZj0iamF2YXNjcmlwdDpjbG9zZSgpOyI%2B&parameters[3]=IHwgPC9hPiI7fQ%3D%3D] Courtesy NIM

 

Here’s a link to and a citation for the researchers’ paper,

Hierarchical assembly of metal nanoparticles, quantum dots and organic dyes using DNA origami scaffolds by Robert Schreiber, Jaekwon Do, Eva-Maria Roller, Tao Zhang, Verena J. Schüller, Philipp C. Nickels, Jochen Feldmann, & Tim Liedl. Nature Nanotechnology (2013) doi:10.1038/nnano.2013.253 Published online 01 December 2013

It is behind a paywall but you can preview it for free via ReadCube Access.

Stabilizing or destabilitizing gold nanoparticles

Every once in a while I stumble across a ‘nanotechnology’ news release from Oregon (either Oregon State University or the University of Oregon) and as I recall it’s always environment-focused. The latest in an almost complete change-of-pace is, a Dec. 9, 2013 University of Oregon news release (also on EurekAlert) profiling some work on gold nanoparticles and nanoelectronics,

University of Oregon chemists studying the structure of ligand-stabilized gold nanoparticles have captured fundamental new insights about their stability. The information, they say, could help to maintain a desired, integral property in nanoparticles used in electronic devices, where stability is important, or to design them so they readily condense into thin films for such things as inks or catalysts in electronic or solar devices.

The news release goes on to detail the work,

They focused on nanoparticles less than two nanometers in diameter — the smallest studied to date — to better understand structural stability of these tiny particles being engineered for use in electronics, medicine and other materials. Whether a nanoparticle needs to remain stable or condense depends on how they are being used. Those used as catalysts in industrial chemical processing or quantum dots for lighting need to remain intact; if they are precursors for coatings in solar devices or for printing ink, nanoparticles need to be unstable so they sinter and condense into a thin mass.

For their experiments, Smith and Hutchison produced gold nanoparticles in four well-controlled sizes, ranging from 0.9 nanometers to 1.5 nanometers, and analyzed ligand loss and sintering with thermogravimetric analysis and differential scanning calorimetry, and examined the resulting films by scanning electron microscopy and X-ray photoelectron spectroscopy. As the nanoparticles were heated at 5 degrees Celsius per minute, from room temperature to 600 degrees Celsius, the nanoparticles began to transform near 150 degrees Celsius.

The researchers found that smaller nanoparticles have better structural integrity than larger-sized particles that have been tested. In other words, Hutchison said, they are less likely to lose their ligands and bind together. “If you have unstable particles, then the property you want is fleeting,” he said. “Either the light emission degrades over time and you’re done, or the metal becomes inactive and you’re done. In that case, you want to preserve the function and keep the particles from aggregating.”The opposite is desired for Hutchison and others working in the National Science Foundation-funded Center for Sustainable Materials Chemistry, a multi-universities collaboration led by the UO and Oregon State University. Researchers there are synthesizing nanoparticles as precursors for thin films.

“We want solution precursors that can lead to inorganic thin films for use in electronics and solar industries,” said Hutchison, who also is a member of the UO Materials Science Institute.

“In this case, we want to know how to keep our nanoparticles or other precursors stable enough in solution so that we can work with them, using just a tiny amount of additional energy to make them unstable so that they condense into a film — where the property that you want comes from the extended solid that is generated, not from the nanoparticles themselves.”

The research, Hutchison said, identified weak sites on nanoparticles where ligands might pop off. If only a small amount do so, he said, separate nanoparticles are more likely to come together and begin the sintering process to create thin films.

“That’s a really stabilizing effect that, in turn, kicks out all these ligands on the outside,” he said. “The surface area decreases quickly and the particles get bigger, but now all the extra ligands gets excluded into the film and then, over time, the ligands vaporize and go away.”

The coming apart, however, is a “catastrophic failure” if protecting against sintering is the goal. It may be possible to use the findings, he said, to explore ways to strengthen nanoparticles, such as developing ligands that bind in at least two sites or avoiding volatile ligands.

The process, as studied, produced porous gold films. “A next step might be to study how to manipulate the process to get a more dense film if that is desired,” Hutchison said. Understanding how nanoparticles respond to certain conditions, such as changing temperatures, he added, may help researchers reduce waste in the manufacturing process.

As I hinted earlier, this work retains an ‘environment focus’,

“Researchers at the University of Oregon are re-engineering the science, manufacturing and business processes behind critical products,” said Kimberly Andrews Espy, vice president for research and innovation and dean of the UO Graduate School. “This research analyzing the structural stability of nanoparticles by Dr. Hutchison and his team has the potential to improve the engineering of electronics, medicine and other materials, helping to foster a sustainable future for our planet and its people.” [emphasis mine]

Here’s a link to and a citation for the paper,

Transformations during Sintering of Small (Dcore < 2 nm) Ligand-Stabilized Gold Nanoparticles: Influence of Ligand Functionality and Core Size by Beverly L. Smith and James E. Hutchison. J. Phys. Chem. C, 2013, 117 (47), pp 25127–25137 DOI: 10.1021/jp408111v Publication Date (Web): October 24, 2013
Copyright © 2013 American Chemical Society

This paper is behind a paywall.

Bejweled and bedazzled but not bewitched, bothered, or bewildered at Northwestern University

When discussing DNA (deoxyribonucleic acid) one doesn’t usually expect to encounter gems as one does in a Nov. 28, 2013 news item on Azonano,

Nature builds flawless diamonds, sapphires and other gems. Now a Northwestern University [located in Chicago, Illinois, US] research team is the first to build near-perfect single crystals out of nanoparticles and DNA, using the same structure favored by nature.

The Nov. 27, 2013 Northwestern University news release by Megan Fellman (also on EurekAlert), which originated the news item,, explains why single crystals are of such interest,

“Single crystals are the backbone of many things we rely on — diamonds for beauty as well as industrial applications, sapphires for lasers and silicon for electronics,” said nanoscientist Chad A. Mirkin. “The precise placement of atoms within a well-defined lattice defines these high-quality crystals.

“Now we can do the same with nanomaterials and DNA, the blueprint of life,” Mirkin said. “Our method could lead to novel technologies and even enable new industries, much as the ability to grow silicon in perfect crystalline arrangements made possible the multibillion-dollar semiconductor industry.”

His research group developed the “recipe” for using nanomaterials as atoms, DNA as bonds and a little heat to form tiny crystals. This single-crystal recipe builds on superlattice techniques Mirkin’s lab has been developing for nearly two decades.

(I wrote about Mirkin’s nanoparticle DNA work in the context of his proposed periodic table of modified nucleic acid nanoparticles in a July 5, 2013 posting.) The news release goes on to describe Mirkin’s most recent work,

In this recent work, Mirkin, an experimentalist, teamed up with Monica Olvera de la Cruz, a theoretician, to evaluate the new technique and develop an understanding of it. Given a set of nanoparticles and a specific type of DNA, Olvera de la Cruz showed they can accurately predict the 3-D structure, or crystal shape, into which the disordered components will self-assemble.

The general set of instructions gives researchers unprecedented control over the type and shape of crystals they can build. The Northwestern team worked with gold nanoparticles, but the recipe can be applied to a variety of materials, with potential applications in the fields of materials science, photonics, electronics and catalysis.

A single crystal has order: its crystal lattice is continuous and unbroken throughout. The absence of defects in the material can give these crystals unique mechanical, optical and electrical properties, making them very desirable.

In the Northwestern study, strands of complementary DNA act as bonds between disordered gold nanoparticles, transforming them into an orderly crystal. The researchers determined that the ratio of the DNA linker’s length to the size of the nanoparticle is critical.

“If you get the right ratio it makes a perfect crystal — isn’t that fun?” said Olvera de la Cruz, who also is a professor of chemistry in the Weinberg College of Arts and Sciences. “That’s the fascinating thing, that you have to have the right ratio. We are learning so many rules for calculating things that other people cannot compute in atoms, in atomic crystals.”

The ratio affects the energy of the faces of the crystals, which determines the final crystal shape. Ratios that don’t follow the recipe lead to large fluctuations in energy and result in a sphere, not a faceted crystal, she explained. With the correct ratio, the energies fluctuate less and result in a crystal every time.

“Imagine having a million balls of two colors, some red, some blue, in a container, and you try shaking them until you get alternating red and blue balls,” Mirkin explained. “It will never happen.

“But if you attach DNA that is complementary to nanoparticles — the red has one kind of DNA, say, the blue its complement — and now you shake, or in our case, just stir in water, all the particles will find one another and link together,” he said. “They beautifully assemble into a three-dimensional crystal that we predicted computationally and realized experimentally.”

To achieve a self-assembling single crystal in the lab, the research team reports taking two sets of gold nanoparticles outfitted with complementary DNA linker strands. Working with approximately 1 million nanoparticles in water, they heated the solution to a temperature just above the DNA linkers’ melting point and then slowly cooled the solution to room temperature, which took two or three days.

The very slow cooling process encouraged the single-stranded DNA to find its complement, resulting in a high-quality single crystal approximately three microns wide. “The process gives the system enough time and energy for all the particles to arrange themselves and find the spots they should be in,” Mirkin said.

The researchers determined that the length of DNA connected to each gold nanoparticle can’t be much longer than the size of the nanoparticle. In the study, the gold nanoparticles varied from five to 20 nanometers in diameter; for each, the DNA length that led to crystal formation was about 18 base pairs and six single-base “sticky ends.”

“There’s no reason we can’t grow extraordinarily large single crystals in the future using modifications of our technique,” said Mirkin, who also is a professor of medicine, chemical and biological engineering, biomedical engineering and materials science and engineering and director of Northwestern’s International Institute for Nanotechnology.

Here’s a link to and a citation for the published paper,

DNA-mediated nanoparticle crystallization into Wulff polyhedra by Evelyn Auyeung, Ting I. N. G. Li, Andrew J. Senesi, Abrin L. Schmucker, Bridget C. Pals, Monica Olvera de la Cruz, & Chad A. Mirkin. Nature (2013) doi:10.1038/nature12739 Published online 27 November 2013

This article is behind a paywall.

Points to anyone who recognized the song title (Bewitched, Bothered and Bewildered) embedded in the head for this posting.

Recycling carbon dioxide with gold nanoparticles

Researchers at Brown University (in Providence, Rhode Island) have developed a technique using gold nanoparticles to capture carbon dioxide and turn it into carbon monoxide (from the Oct. 24, 2013 Brown University news release [also on EurekAlert]),

It’s a 21st-century alchemist’s dream: turning Earth’s superabundance of carbon dioxide — a greenhouse gas — into fuel or useful industrial chemicals. Researchers from Brown have shown that finely tuned gold nanoparticles can do the job. The key is maximizing the particles’ long edges, which are the active sites for the reaction.[This paragraph is present only on the Brown website news release]

By tuning gold nanoparticles to just the right size, researchers from Brown University have developed a catalyst that selectively converts carbon dioxide (CO2) to carbon monoxide (CO), an active carbon molecule that can be used to make alternative fuels and commodity chemicals.

“Our study shows potential of carefully designed gold nanoparticles to recycle CO2 into useful forms of carbon,” said Shouheng Sun, professor of chemistry and one of the study’s senior authors. “The work we’ve done here is preliminary, but we think there’s great potential for this technology to be scaled up for commercial applications.”

The scientists were trying to solve a major problem with recycling carbon dioxide when using gold (from the news release),

Converting CO2 to CO isn’t easy. Prior research has shown that catalysts made of gold foil are active for this conversion, but they don’t do the job efficiently. The gold tends to react both with the CO2 and with the water in which the CO2 is dissolved, creating hydrogen byproduct rather than the desired CO.

The Brown research team decided to try gold nanoparticles and had a surprising result (from the news release),

The Brown experimental group, led by Sun and Wenlei Zhu, a graduate student in Sun’s group, wanted to see if shrinking the gold down to nanoparticles might make it more selective for CO2. They found that the nanoparticles were indeed more selective, but that the exact size of those particles was important. Eight nanometer particles had the best selectivity, achieving a 90-percent rate of conversion from CO2 to CO. Other sizes the team tested — four, six, and 10 nanometers — didn’t perform nearly as well.

“At first, that result was confusing,” said Andrew Peterson, professor of engineering and also a senior author on the paper. “As we made the particles smaller we got more activity, but when we went smaller than eight nanometers, we got less activity.”

The researchers investigated further and found a relationship between size and shape which affects the gold nanoparticles’ performance (from the news release),

To understand what was happening, Peterson and postdoctoral researcher Ronald Michalsky used a modeling method called density functional theory. They were able to show that the shapes of the particles at different sizes influenced their catalytic properties.

“When you take a sphere and you reduce it to smaller and smaller sizes, you tend to get many more irregular features — flat surfaces, edges and corners,” Peterson said. “What we were able to figure out is that the most active sites for converting CO2 to CO are the edge sites, while the corner sites predominantly give the by-product, which is hydrogen. So as you shrink these particles down, you’ll hit a point where you start to optimize the activity because you have a high number of these edge sites but still a low number of these corner sites. But if you go too small, the edges start to shrink and you’re left with just corners.”

Now that they understand exactly what part of the catalyst is active, the researchers are working to further optimize the particles. “There’s still a lot of room for improvement,” Peterson said. “We’re working on new particles that maximize these active sites.”

The researchers believe these findings could be an important new avenue for recycling CO2 on a commercial scale.

“Because we’re using nanoparticles, we’re using a lot less gold than in a bulk metal catalyst,” Sun said. “That lowers the cost for making such a catalyst and gives the potential to scale up.”

Here’s a link to and a citation for the research paper,

Monodisperse Au Nanoparticles for Selective Electrocatalytic Reduction of CO2 to CO by Wenlei Zhu, Ronald Michalsky, Önder Metin, Haifeng Lv, Shaojun Guo, Christopher J. Wright, Xiaolian Sun, Andrew A. Peterson, and Shouheng Sun. J. Am. Chem. Soc., DOI: 10.1021/ja409445p Publication Date (Web): October 24, 2013
Copyright © 2013 American Chemical Society

This article is behind a paywall.

So, why do gold nanoparticles facilitate cell penetration without damage to cell walls?

Researchers at the Massachusetts Institute of Technology (MIT) and l’École Polytechnique Fédérale de Lausanne (EPFL) in Switerzerland have found an answer to the question about why gold nanoparticles facilitate cell penetration without damage to the cell walls. Apparently it has nothing to with the gold; it’s all in the coating according to an Aug. 23, 2013 MIT news release by David L. Chandler (also on EurekAlert),

Cells are very good at protecting their precious contents — and as a result, it’s very difficult to penetrate their membrane walls to deliver drugs, nutrients or biosensors without damaging or destroying the cell. One effective way of doing so, discovered in 2008, is to use nanoparticles of pure gold, coated with a thin layer of a special polymer. But nobody knew exactly why this combination worked so well, or how it made it through the cell wall.

Now, researchers at MIT and the Ecole Polytechnique de Lausanne in Switzerland have figured out how the process works, and the limits on the sizes of particles that can be used. …

Until now, says Van Lehn, the paper’s lead author [Reid Van Lehn], “the mechanism was unknown. … In this work, we wanted to simplify the process and understand the forces” that allow gold nanoparticles to penetrate cell walls without permanently damaging the membranes or rupturing the cells. The researchers did so through a combination of lab experiments and computer simulations.

The news release goes on to provide details about the research,

The team demonstrated that the crucial first step in the process is for coated gold nanoparticles to fuse with the lipids — a category of natural fats, waxes and vitamins — that form the cell wall. The scientists also demonstrated an upper limit on the size of such particles that can penetrate the cell wall — a limit that depends on the composition of the particle’s coating. [emphases mine]

The coating applied to the gold particles consists of a mix of hydrophobic and hydrophilic components that form a monolayer — a layer just one molecule thick — on the particle’s surface. Any of several different compounds can be used, the researchers explain. [emphases mine]

“Cells tend to engulf things on the surface,” says Alexander-Katz, an associate professor of materials science and engineering at MIT, but it’s “very unusual” for materials to cross that membrane into the cell’s interior without causing major damage. Irvine and Stellacci demonstrated in 2008 that monolayer-coated gold nanoparticles could do so; they have since been working to better understand why and how that works.

Since the nanoparticles themselves are completely coated, the fact that they are made of gold doesn’t have any direct effect, except that gold nanoparticles are an easily prepared model system, the researchers say. However, there is some evidence that the gold particles have therapeutic properties, which could be a side benefit.

Gold particles are also very good at capturing X-rays — so if they could be made to penetrate cancer cells, and were then heated by a beam of X-rays, they could destroy those cells from within. “So the fact that it’s gold may be useful,” says Irvine, a professor of materials science and engineering and biological engineering and member of the Koch Institute for Integrative Cancer Research.

Significantly, the mechanism that allows the nanoparticles to pass through the membrane seems also to seal the opening as soon as the particle has passed. “They would go through without allowing even small molecules to leak through behind them,” Van Lehn says.

Irvine says that his lab is also interested in harnessing this cell-penetrating mechanism as a way of delivering drugs to the cell’s interior, by binding them to the surface coating material. One important step in making that a useful process, he says, is finding ways to allow the nanoparticle coatings to be selective about what types of cells they attach to. “If it’s all cells, that’s not very useful,” he says, but if the coatings can be targeted to a particular cell type that is the target of a drug, that could be a significant benefit.

Another potential application of this work could be in attaching or inserting biosensing molecules on or into certain cells, Van Lehn says. In this way, scientists could detect or monitor specific biochemical markers, such as proteins that indicate the onset or decline of a disease or a metabolic process.

The research paper can be found here,

Effect of Particle Diameter and Surface Composition on the Spontaneous Fusion of Monolayer-Protected Gold Nanoparticles with Lipid Bilayers by Reid C. Van Lehn, Prabhani U. Atukorale, Randy P. Carney, Yu-Sang Yang, Francesco Stellacci, Darrell J. Irvine, and Alfredo Alexander-Katz. Nano Lett., Article ASAP DOI: 10.1021/nl401365n Publication Date (Web): August 5, 2013
Copyright © 2013 American Chemical Society

It is behind a paywall.

Eucalyptus leaves and gold nanoparticles

An Aug. 1, 2013 news item on Nanowerk highlights some ‘green’ chemistry in Australia,

Murdoch University (Australia) researchers have developed a ‘green’ method to create antibacterial gold nanoparticles for potential use in the medical field with the help of common eucalyptus leaves (“Green biosynthesis of gold nanometre scale plates using the leaf extracts from an indigenous Australian plant Eucalyptus macrocarpa”)

The Aug. 1, 2013 Murdoch University news release, which originated the news item, provides more information from the lead researcher about the use of gold nanoparticles in the medical field and about the ‘eucalyptus leaf’ technique,

“Gold nanoparticles have proven to be very versatile across a range of treatments, including in the delivery of double-stranded DNA in the emerging gene therapy area,” Dr Poinern said.

“They can also be passively accumulated in tumours for thermal treatment therapies, where they are heated to damage and kill cancer cells.

“And studies have shown that cancer drugs bonded to the surface of gold nanoparticles can effectively target tumours, improving delivery and minimising treatment durations and the side effects of anticancer drugs.”

Dr Poinern [Dr Gérrard Eddy Poinern, Director of the Murdoch Applied Nanotechnology Research Group (MANRG)] said, however, that up until recently, the particles’ production had involved expensive chemical and physical processes that often used toxic materials with potential hazards such as environmental toxicity, cytotoxicity and carcinogenicity.

“Thanks to the Eucalyptus macrocarpa, we’re changing that. Our method is water-based, performed at room temperature and without the need for complex equipment and is clean and non-toxic,” he said.

The ‘green’ production of gold nanometre scale particles involves dissolving high purity gold wire into a mixture of nitric and hydrochloric acid to produce gold chloride.

The gold chloride is then mixed with a water-based solution of leaf extracts from the common Eucalyptus macrocarpa and allowed to synthesize at room temperature.

“Not only does this result in the creation of nanometre scale gold prisms, but the wax of the eucalypt leaf extract provides an additional antibacterial and antifungal quality,” Dr Poinern said.

“Since bacterial and fungal species have the ability to develop immunity against commonly used antibiotics over time, our gold nanometre scale particles also stand to be a new tool against antibiotic resistant forms of microorganisms.”

Dr Poinern said the nanometre scale gold particles were tested as antibacterial agents against both E. coli and B. subtilis, producing zone inhibition of 19mm and 16mm respectively.

Murdoch University has provided an image of eucalyptus leaves,

Eucalyptus macrocarpa is giving nano-medicine a boost

Eucalyptus macrocarpa is giving nano-medicine a boost

Here’s a link to and a citation for the published paper,

Green biosynthesis of gold nanometre scale plates using the leaf extracts from an indigenous Australian plant Eucalyptus macrocarpa by Gérrard Eddy Jai Poinern, Peter Chapman, Xuan Le, and Derek Fawcett. Gold Bulletin DOI: 10.1007/s13404-013-0096-7 Online ISSN 2190-7579

The paper is open access.

One final note, I trust the koala population is willing to share one of the mainstays of their diet.

Unique ‘printing’ process boosts supercapacitor performance

In addition to creating energy, we also need to store some of it for future use as a July 29, 2013 news release from the University of Central Florida notes,

Researchers at the University of Central Florida have developed a technique to increase the energy storage capabilities of supercapacitors, essential devices for powering high-speed trains, electric cars, and the emergency doors of the Airbus A380.

The finding, which offers a solution to a problem that has plagued the growing multi-billion dollar industry, utilizes a unique three-step process to “print” large – area nanostructured electrodes, structures necessary to improve electrical conductivity and boost performance of the supercapacitor.

Jayan Thomas, an assistant professor in UCF’s NanoScience Technology Center, led the project which is featured in the June edition of Advanced Materials, one of the leading peer-reviewed scientific journals covering materials science in the world. Thomas’ research appears on the journal’s highly-coveted frontispiece, the illustration page of the journal that precedes the title page.

The news release goes on to describe the supercapacitor issue the researchers were addressing,

Supercapacitors have been around since the 1960’s. Similar to batteries, they store energy. The difference is that supercapacitors can provide higher amounts of power for shorter periods of time, making them very useful for heavy machinery and other applications that require large amounts of energy to start.  However, due to their innate low energy density; supercapacitors are limited in the amount of energy that they can store.

“We had been looking at techniques to print nanostructures,” said Thomas. “Using a simple spin-on nanoprinting (SNAP) technique, we can print highly-ordered nanopillars without the need for complicated development processes. By eliminating these processes, it allows multiple imprints to be made on the same substrate in close proximity.“

This simplified fabrication method devised by Thomas and his team is very attractive for the next-generation of energy storage systems. “What we’ve found is by adding the printed ordered nanostructures to supercapacitor electrodes, we can increase their surface area many times,” added Thomas. “We discovered that supercapacitors made using the SNAP technique can store much more energy than ones made without.”

Here’s a link to and a citation for the research paper abut this new technique for supercapacitors,

Energy Storage: Highly Ordered MnO2 Nanopillars for Enhanced Supercapacitor Performance (Adv. Mater. 24/2013) by Zenan Yu, Binh Duong, Danielle Abbitt, and Jayan Thomas. Article first published online: 20 JUN 2013 DOI: 10.1002/adma.201370160 Advanced Materials Volume 25, Issue 24, page 3301, June 25, 2013.

Lead researcher Thomas was recently featured in a video for his work on creating plasmonic nanocrystals from gold nanoparticles (from the news release),

Thomas, who is also affiliated with the College of Optics and Photonics (CREOL), and the College of Engineering, was recently featured on American Institute of Physics’ Inside Science TV for his collaborative research to develop a new material using nanotechnology that could potentially help keep pilots safe by diffusing harmful laser light.

Here’s the video,

You can find videos, news, and blogs featuring other research at Inside Science and you can find out more about Dr. Jayan Thomas here.

The gold beneath your skin (artificial skin, that is)

Artificial skin that can sense as if it were real skin isn’t here yet but scientists at Technion-Israel Institute of Technology have created a flexible sensor that could fulfill that promise. From a July 9, 2013 news item on Azonano,

Using tiny gold particles and a kind of resin, a team of scientists at the Technion-Israel Institute of Technology has discovered how to make a new kind of flexible sensor that one day could be integrated into electronic skin, or e-skin.

If scientists learn how to attach e-skin to prosthetic limbs, people with amputations might once again be able to feel changes in their environments. The findings appear in the June issue of ACS Applied Materials & Interfaces.

The July 8, 2013 American Technion Society news release by Kevin Hattori, which originated the news item, describes the problems with developing flexible sensors that can mimic natural skin,

Researchers have long been interested in flexible sensors, but have had trouble adapting them for real-world use. To make its way into mainstream society, a flexible sensor would have to run on low voltage (so it would be compatible with the batteries in today’s portable devices), measure a wide range of pressures, and make more than one measurement at a time, including humidity, temperature, pressure, and the presence of chemicals. In addition, these sensors would also have to be able to be made quickly, easily, and cheaply.

Here are more details about the sensor and about how the researchers created it,

The Technion team’s sensor has all of these qualities. The secret is the use of monolayer-capped nanoparticles that are only 5-8 nanometers in diameter. They are made of gold and surrounded by connector molecules called ligands. In fact, “monolayer-capped nanoparticles can be thought of as flowers, where the center of the flower is the gold or metal nanoparticle and the petals are the monolayer of organic ligands that generally protect it,” says Haick.

The team discovered that when these nanoparticles are laid on top of a substrate – in this case, made of PET (flexible polyethylene terephthalate), the same plastic found in soda bottles – the resulting compound conducted electricity differently depending on how the substrate was bent. (The bending motion brings some particles closer to others, increasing how quickly electrons can pass between them.) This electrical property means that the sensor can detect a large range of pressures, from tens of milligrams to tens of grams. “The sensor is very stable and can be attached to any surface shape while keeping the function stable,” says Dr. Nir Peled, Head of the Thoracic Cancer Research and Detection Center at Israel’s Sheba Medical Center, who was not involved in the research.

And by varying how thick the substrate is, as well as what it is made of, scientists can modify how sensitive the sensor is. Because these sensors can be customized, they could in the future perform a variety of other tasks, including monitoring strain on bridges and detecting cracks in engines.

According to research team leader Professor Hossam Haick the new sensor is more sensitive (x 10 or more) in touch than existing touch-based e-skin.

Here’s a link to and a citation for the published paper,

Tunable Touch Sensor and Combined Sensing Platform: Toward Nanoparticle-based Electronic Skin by Meital Segev-Bar , Avigail Landman, Maayan Nir-Shapira, Gregory Shuster, and Hossam Haick. ACS Appl. Mater. Interfaces, 2013, 5 (12), pp 5531–5541 DOI: 10.1021/am400757q Publication Date (Web): June 4, 2013

Copyright © 2013 American Chemical Society

The paper is behind a paywall.