Rice University (NEWT) / China team use phage-enhanced nanoparticles to kill bacteria that foul water treatment systems


Clusters of nanoparticles with phage viruses attached find and kill Escherichia coli bacteria in a lab test at Rice University. 

Abstract:
Magnetic nanoparticle clusters have the power to punch through biofilms to reach bacteria that can foul water treatment systems, according to scientists at Rice University and the University of Science and Technology of China.
Magnetized viruses attack harmful bacteria: Rice, China team uses phage-enhanced nanoparticles to kill bacteria that foul water treatment systems.

Researchers at Rice and the University of Science and Technology of China have developed a combination of antibacterial phages and magnetic nanoparticle clusters that infect and destroy bacteria that are usually protected by biofilms in water treatment systems. (Credit: Alvarez Group/Rice University)

The nanoclusters developed through Rice’s Nanotechnology-Enabled Water Treatment (NEWT) Engineering Research Center carry bacteriophages – viruses that infect and propagate in bacteria – and deliver them to targets that generally resist chemical disinfection.

Without the pull of a magnetic host, these “phages” disperse in solution, largely fail to penetrate biofilms and allow bacteria to grow in solution and even corrode metal, a costly problem for water distribution systems.

The Rice lab of environmental engineer Pedro Alvarez and colleagues in China developed and tested clusters that immobilize the phages. A weak magnetic field draws them into biofilms to their targets.

The research is detailed in the Royal Society of Chemistry’s Environmental Science: Nano.
“This novel approach, which arises from the convergence of nanotechnology and virology, has a great potential to treat difficult-to-eradicate biofilms in an effective manner that does not generate harmful disinfection byproducts,” Alvarez said.

Biofilms can be beneficial in some wastewater treatment or industrial fermentation reactors owing to their enhanced reaction rates and resistance to exogenous stresses, said Rice graduate student and co-lead author Pingfeng Yu. “However, biofilms can be very harmful in water distribution and storage systems since they can shelter pathogenic microorganisms that pose significant public health concerns and may also contribute to corrosion and associated economic losses,” he said.

The lab used phages that are polyvalent – able to attack more than one type of bacteria – to target lab-grown films that contained strains of Escherichia coli associated with infectious diseases and Pseudomonas aeruginosa, which is prone to antibiotic resistance.

The phages were combined with nanoclusters of carbon, sulfur and iron oxide that were further modified with amino groups. The amino coating prompted the phages to bond with the clusters head-first, which left their infectious tails exposed and able to infect bacteria.

The researchers used a relatively weak magnetic field to push the nanoclusters into the film and disrupt it. Images showed they effectively killed E. coli and P. aeruginosa over around 90 percent of the film in a test 96-well plate versus less than 40 percent in a plate with phages alone.

The researchers noted bacteria may still develop resistance to phages, but the ability to quickly disrupt biofilms would make that more difficult. Alvarez said the lab is working on phage “cocktails” that would combine multiple types of phages and/or antibiotics with the particles to inhibit resistance.

Graduate student Ling-Li Li of the University of Science and Technology of China, Hefei, is co-lead author of the paper. Co-authors are graduate student Sheng-Song Yu and Han-Qing Yu, a professor at the University of Science and Technology of China, and graduate student Xifan Wang and temporary research scientist Jacques Mathieu of Rice.


The National Science Foundation and its Rice-based NEWT Engineering Research Center supported the research.

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MIT: Key flow mechanisms, crucial to carbon sequestration, Oil recovery and fuel-cell operation, have been visualized.


MIT-Multiphase-Flow_0 Wetability 082616

Lab experiments carried out by an MIT and Oxford University team provide detailed information about how a liquid moves through spaces in a porous material, revealing the key role of a characteristic called wettability.

Courtesy of the researchers

One of the most promising approaches to curbing the flow of human-made greenhouse gases into the atmosphere is to capture these gases at major sources, such as fossil-fuel-burning power plants, and then inject them into deep, water-saturated rocks where they can remain stably trapped for centuries or millennia.

This is just one example of fluid-fluid displacement in a porous material, which also applies to a wide variety of natural and industrial processes — for example, when rainwater penetrates into soil by displacing air, or when oil recovery is enhanced by displacing the oil with injected water.

Now, a new set of detailed lab experiments has provided fresh insight into the physics of this phenomenon, under an unprecedented range of conditions. These results should help researchers understand what happens when carbon dioxide flows through deep saltwater reservoirs, and could shed light on similar interactions such as those inside fuel cells being used to produce electricity without burning hydrocarbons.

The new findings are being published this week in the journal PNAS, in a paper by Ruben Juanes, MIT’s ARCO Associate Professor in Energy Studies; Benzhong Zhao, an MIT graduate student; and Chris MacMinn, an associate professor at Oxford University.

A crucial aspect of fluid-fluid displacement is the displacement efficiency, which measures how much of the pre-existing fluid can be pushed out of the pore space. High displacement efficiency means that most of the pre-existing fluid is pushed out, which is usually a good thing — with oil recovery, for example, it means that more oil would be captured and less would be left behind. Unfortunately, displacement efficiency has been very difficult to predict.

A key factor in determining displacement efficiency, Juanes says, is a characteristic called wettability. Wettability is a material property that measures a preference by the solid to be in contact with one of the fluids more than the other. The team found that the stronger the preference for the injected fluid, the more effective the displacement of the pre-existing fluid from the pores of the material — up to a point. But if the preference for the injected fluid increases beyond that optimal point, the trend reverses, and the displacement becomes much less efficient. The discovery of the existence of this ideal degree of wettability is one of the significant findings of the new research.

The work was partly motivated by recent advances in scanning techniques that make it possible to “directly characterize the wettability of real reservoir rocks under in-situ conditions,” says Zhao. But just being able to characterize the wettability was not sufficient, he explains. The key question was “Do we understand the physics of fluid-fluid displacement in a porous medium under different wettability conditions?” And now, after their detailed analysis, “We do have a fundamental understanding” of the process, Zhao says. MacMinn adds that “it comes from the design of a novel system that really allowed us to look in detail at what is happening at the pore scale, and in three dimensions.”

This GIF shows the way fluid distribution through pore spaces varies under different injection rates of water. The colors show the degree of saturation of the invading water. At low rates (left), the water advances in rapid bursts followed by quiet periods. At intermediate rates (center), the invading fluid advances by sequentially coating the walls of posts used to simulate pores in the team’s microfluidic cell. At high rates (right), the water advances in thin films along the solid surfaces.

 

 

 

 

 

 

 

In order to clearly define the physics behind these flows, the researchers did a series of lab experiments in which they used different porous materials with a wide range of wetting characteristics, and studied how the flows varied.

In natural environments such as aquifers or oil reservoirs, the wettability of the material is predetermined. But even so, Juanes says, “there are ways you can modify the wettability in the field,” such as by adding specific chemical compounds like surfactants (similar to soap) to the injected fluid.

By making it possible to understand just what degree of wettability is desirable for a particular situation, the new findings “in principle, could be very advantageous” for designing carbon sequestration or enhanced oil recovery schemes for a specific geological setting.

The same principles apply to some polymer electrolyte fuel cells, where water vapor condenses at the fuel cell’s cathode and has to migrate through a porous membrane. Depending on the exact mix of gas and liquid, these flows can be detrimental to the performance of the fuel cell, so controlling and predicting the way these flows work can be important in designing such cells.

In addition, the same process of liquid and gas interacting in pore spaces also applies to the way freshwater aquifers get recharged by rainfall, as the water percolates into the ground and displaces air in the soil. A better understanding of this process could be important for management of ever-scarcer water resources, the team says.

“This is a very interesting study of pore-scale multiphase fluid flow in two-dimensional micromodels,” says David Weitz, a professor of physics and applied physics at Harvard University, who was not involved in this work. “The advantage of this work is that the authors look in more detail at the mechanisms of wetting and displacement of the fluid in the pores,” he says. “This is a very important aspect of fluid flow in porous media.”

This research was supported by the U.S. Department of Energy and the MIT Energy Initiative.

Update: MIT; UC San Diego; Harvard Universities: Energy-carrying particles called ‘topological plexcitons’ could make possible the design of ‘next generation’ solar cells and miniaturized optical circuitry


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Plexcitons travel for 20,000 nanometers, a length which is on the order of the width of human hair. Credit: Joel Yuen-Zhou

Scientists at UC San Diego, MIT and Harvard University have engineered “topological plexcitons,” energy-carrying particles that could help make possible the design of new kinds of solar cells and miniaturized optical circuitry.

The researchers report their advance in an article published in the current issue of Nature Communications.

Within the Lilliputian world of physics, light and matter interact in strange ways, exchanging energy back and forth between them.

plexciton-plasmonexciton-coupling-1 II 060916 -638

“When light and matter interact, they exchange energy,” explained Joel Yuen-Zhou, an assistant professor of chemistry and biochemistry at UC San Diego and the first author of the paper. “Energy can flow back and forth between light in a metal (so called plasmon) and light in a molecule (so called exciton). When this exchange is much faster than their respective decay rates, their individual identities are lost, and it is more accurate to think about them as hybrid particles; excitons and plasmons marry to form plexcitons.” mit_logo

Materials scientists have been looking for ways to enhance a process known as exciton energy transfer, or EET, to create better as well as miniaturized photonic circuits which are dozens of times smaller than their silicon counterparts.

“Understanding the fundamental mechanisms of EET enhancement would alter the way we think about designing solar cells or the ways in which energy can be transported in nanoscale materials,” said Yuen-Zhou.

The drawback with EET, however, is that this form of energy transfer is extremely short-ranged, on the scale of only 10 nanometers, and quickly dissipates as the excitons interact with different molecules.

plexciton-plasmonexciton-coupling-13-638One solution to avoid those shortcomings is to hybridize excitons in a molecular crystal with the collective excitations within metals to produce plexcitons, which travel for 20,000 nanometers, a length which is on the order of the width of human hair.

Plexcitons are expected to become an integral part of the next generation of nanophotonic circuitry, light-harvesting solar energy architectures and chemical catalysis devices. But the main problem with plexcitons, said Yuen-Zhou, is that their movement along all directions, which makes it hard to properly harness in a material or device.

He and a team of physicists and engineers at MIT and Harvard found a solution to that problem by engineering particles called “topological plexcitons,” based on the concepts in which solid state physicists have been able to develop materials called “topological insulators.”

“Topological insulators are materials that are perfect electrical insulators in the bulk but at their edges behave as perfect one-dimensional metallic cables,” Yuen-Zhou said. “The exciting feature of is that even when the material is imperfect and has impurities, there is a large threshold of operation where electrons that start travelling along one direction cannot bounce back, making electron transport robust. In other words, one may think about the electrons being blind to impurities.”

Plexcitons, as opposed to electrons, do not have an electrical charge. Yet, as Yuen-Zhou and his colleagues discovered, they still inherit these robust directional properties. Adding this “topological” feature to plexcitons gives rise to directionality of EET, a feature researchers had not previously conceived. This should eventually enable engineers to create plexcitonic switches to distribute selectively across different components of a new kind of solar cell or light-harvesting device.

Explore further: Topological insulators could exist in six new types not seen before, theorists predict

More information: Nature Communications, DOI: 10.1038/NCOMMS11783

 

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Tiny packages may pack powerful treatment for brain tumors: Nanocarrier provides efficient delivery of chemotherapeutic drug


Brain Tumor 052416 160521071206_1_540x360Dr. Ann-Marie Broome, right, likes collaborating with Dr. Amy Lee Bredlau, left, who brings a clincial perspective to the laboratory.
Credit: Sarah Pack

Medical University of South Carolina: Great discoveries do come in small packages. Few know that better than Ann-Marie Broome, Ph.D., who feels nanotechnology holds the future of medicine with its ability to deliver powerful drugs in tiny, designer packages.

Her latest research finds the perfect application — targeting cancerous brain tumor cells.

Results from her recent paper published online in the international journal Nanomedicine — Future Medicine found that a lipid nanocarrier engineered to be small enough to get past the blood-brain barrier could be targeted to deliver a chemotherapeutic drug more efficiently to tumor cells in the brain. In vivo studies showed specific uptake and increased killing in glial cells, so much so that Broome initially questioned the results.

“I was very surprised by how efficiently and well it worked once we got the nanocarrier to those cells,” she said, explaining that initial results were so promising that she had her team keep repeating the experiments, using different cell lines, dosage amounts and treatment times.Researchers and clinicians are excited because it potentially points the way to a new treatment option for patients with certain conditions, such as glioblastoma multiforme (GBM), the focus of this study.

Glioblastoma multiforme is a devastating disease with no curative options due to several challenges, said Broome, who is the director of Molecular Imaging of the Medical University of South Carolina’s Center for Biomedical Imaging and director of Small Animal Imaging of Hollings Cancer Center. The brain tumor has a significant overall mortality, in part due to its location, difficulty of surgical treatment and the inability to get drugs through the blood-brain barrier, a protective barrier designed to keep a stable environment within and surrounding the brain.

In 40 percent of cases, standard treatments will extend life expectancy 4 to 7 months. “It’s really a dismal outcome. There are better ways to deliver standard of care.”

That’s where Broome and her nanotechnology lab enter in.

Nanotechnology is medicine, engineering, chemistry, and biology all bundled together and conducted at the nanoscale, between the range of 1 to 1,000 nanometers. For comparison, a thin newspaper page is about 100,000 nanometers thick. Broome and her team took what they know about the cancer’s biology and of platelet-derived growth factor (PDGF), one of numerous growth factor proteins that regulates cell growth and division and is also overexpressed on tumor cells in the brain. With that in mind, they engineered a micelle that is a phospholipid nanocarrier, “a bit of fat globule,” to deliver a concentrated dose of the chemotherapy drug temozolomide (TMZ) to the GBM tumor cells.

“Micelles of a certain size will cross the blood-brain barrier carrying a concentrated amount of TMZ,” she explained about how the nanotechnology works. “The PDGF is used much like a postal address. The micelle gets it to the street, and the PDGF gets it to the house.” This targeting ability is important because researchers have learned that it’s likely that the GBM will recur, she said.

“It’s thought that satellite cells left behind after surgical removal are the fastest growing and most dangerous ones. We’re trying to kill those rapidly growing satellite cells that will grow into new tumors in that location or others. These satellite tumors grow more aggressively than others. You have to hit them hard, fast and aggressively.”

Surprisingly, nanotechnology is already a part of everyday life in many ways that people don’t realize. It’s used in everything from makeup as moisturizers or UV sunscreens to ice cream to maintain frozen temperatures and creamy textures.

In medicine, Broome said, researchers construct nanocarriers that are stable and stealthy. “Your immune cells can’t attack them. They remain hidden.”When the package gets to where it’s going, nanotechnologists have various methods to get the micelles to release their payloads- one way is to use the acidic nature of a rapidly growing tumor. In normal circulation, the pH of blood is slightly alkaline and the micelle stays intact. What researchers have discovered is that in many tumor types, the pH drastically changes to an acidic environment.

“While the tumor is growing, it creates waste by-products and metabolites that alter the pH, thus lowering it. As the center becomes more necrotic, it becomes even more acidic.”

The change in pH triggers a release of the drug from our micelles just where clinicians want it to go to reduce toxicity to the rest of the body, she said.

“We take advantage of the tumor’s natural environment as well as the cellular expression. I’m a big proponent of understanding that microenvironment has an impact on how well you can treat tumors. It’s probably why so many therapeutics fail — because you have to take into account the immune system, the local environment, and the cells themselves — all three of these are important considerations.”

That’s why nanotechnology has an edge in shaping future cancer treatments.

“It’s very important that the public recognize that nanotechnology is the future. It impacts so many different fields. It has a clear impact on cancer biology and potentially has an impact on cancers that are inaccessible, untreatable, undruggable — that in normal circumstances are ultimately a death knell.”All too familiar with this is researcher and clinician Amy Lee Bredlau, M.D., director of MUSC Health’s Pediatric Brain Tumor Program, who also was a part of the study. Broome said she relishes having a clinician’s perspective in the lab to focus the group on translational outcomes for the patients.

“That’s why it’s so gratifying working with Amy Lee. She works with many cancers for which there are no options. We’re trying to provide options.”

Bredlau agreed. “This paper is exciting because it demonstrates a novel approach to treating brain tumors, combining nanotechnology targeting to a marker of brain tumors with a specialized delivery system. It will allow us eventually to target aggressive childhood and adult brain tumors.”

Bredlau said she’s taking time out from her clinical practice to be in Broome’s research lab because she knows that’s how she can best accelerate the process.

“I am passionate about improving the lives of my patients, now and in the future. Advancing research now is the best way to improve the lives of my patients to come.”

Bredlau sees nanotechnology as having the power to revolutionize treatment for brain tumors. “When we perfect this strategy, we will be able to deliver potent chemotherapies only to the area that needs them. This will dramatically improve our cure rates while cutting out a huge portion of our side effects from chemotherapy. Imagine a world where a cancer diagnosis not only was not life-threatening, but also did not mean that you would be tired, nauseated or lose your hair.”

Though excited by the study’s results, Broome cautions that there’s much more work to be done before new treatment options are readily available for patients.

“It may or may not be effective for all types of GBMs. There are subtypes as well as therapeutic-resistant GBMs that these nanocarriers may not impact. We need to continue rigorous testing to verify and validate our initial findings.”

They will be exploring an expanding field of targeted biomarkers available for GBM tumor cells. As is common in breast cancer and other cancer types, this cancer has specific cell surface receptors that are overexpressed, she said.

And though the drug TMZ in this protocol works very efficiently, it may not be the best drug for the majority of the people, she said. “Now that we know we can get the drug to its designated location and get it to work efficiently, we have a comparator. We can test more lethal and different combinations of drugs that have never before been used in this scenario.”

This method of drug delivery also opens new windows to immunotherapy treatments garnering recognition internationally. Broome wants to take chemotherapeutics and combine them with new immuno-therapeutic treatments to form unique combination delivery packages.

It’s ambitious.

Broome, whose team jokes that she keeps “a long, running list of impossible tasks,” said the work also translates to so many fields beyond cancer including stroke, transplant and regenerative medicine, where it could be used for example in wound healing in dermatology or organ maintenance in transplantation. It’s one reason she submitted her latest research to an international journal because she wants to accelerate advances in nanotechnology, a field she has no doubt will change how medicine is done.

“They are the primary reason I continue to do what I do,” she said of the patients who face grim diagnoses. “They give me hope. The possibilities for nanotherapeutics are endless and bright.”


Story Source:

The above post is reprinted from materials provided by Medical University of South Carolina. The original item was written by Dawn Brazell. Note: Materials may be edited for content and length.


Journal Reference:

  1. Kayla Miller, Suraj Dixit, Amy-Lee Bredlau, Alfred Moore, Emilie McKinnon, Ann-Marie Broome. Delivery of a drug cache to glioma cells overexpressing platelet-derived growth factor receptor using lipid nanocarriers.Nanomedicine, 2016; 11 (6): 581 DOI: 10.2217/nnm.15.218

Rice University: Microwaved “Nanoribbons” may bolster oil and gas wells


Oil and Gas Nanoribbons 051316 3-microwavedna
Rice University researchers have developed a method to treat composite materials of graphene nanoribbons and thermoset polymers with microwaves in a way that could dramatically reinforce wellbores for oil and gas production. Credit: Nam Dong Kim/Rice University

 

Wellbores drilled to extract oil and gas can be dramatically reinforced with a small amount of modified graphene nanoribbons added to a polymer and microwaved, according to Rice University researchers.

The Rice labs of chemist James Tour and civil and environmental engineer Rouzbeh Shahsavari combined the nanoribbons with an oil-based thermoset intended to make wells more stable and cut production costs. When cured in place with low-power microwaves emanating from the drill assembly, the composite would plug the microscopic fractures that allow drilling fluid to seep through and destabilize the walls.

Results of their study appeared in the American Chemical Society journal ACS Applied Materials and Interfaces.

The researchers said that in the past, drillers have tried to plug fractures with mica, calcium carbonate, gilsonite and asphalt to little avail because the particles are too large and the method is not efficient enough to stabilize the wellbore.

In lab tests, a polymer-nanoribbon mixture was placed on a sandstone block, similar to the rock that is encountered in many wells. The team found that rapidly heating the to more than 200 degrees Celsius with a 30-watt microwave was enough to cause crosslinking in the polymer that had infiltrated the sandstone, Tour said. The needed is just a fraction of that typically used by a kitchen appliance, he said.

“This is a far more practical and cost-effective way to increase the stability of a well over a long period,” Tour said.

In the lab, the nanoribbons were functionalized—or modified—with polypropylene oxide to aid their dispersal in the polymer. Mechanical tests on composite-reinforced sandstone showed the process increased its average strength from 5.8 to 13.3 megapascals, a 130 percent boost in this measurement of internal pressure, Shahsavari said. Similarly, the toughness of the composite increased by a factor of six.

“That indicates the composite can absorb about six times more energy before failure,” he said. “Mechanical testing at smaller scales via nanoindentation exhibited even more local enhancement, mainly due to the strong interaction between nanoribbons and the polymer. This, combined with the filling effect of the nanoribbon-polymer into the pore spaces of the sandstone, led to the observed enhancements.”

The researchers suggested a low-power microwave attachment on the drill head would allow for in-well curing of the nanoribbon-polymer solution.

Explore further: Graphene nanoribbons grow due to domino-like effect

More information: Nam Dong Kim et al, Microwave Heating of Functionalized Graphene Nanoribbons in Thermoset Polymers for Wellbore Reinforcement, ACS Applied Materials & Interfaces (2016). DOI: 10.1021/acsami.6b01756

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Beyond geometry: Shape entropy links nanostructures with emergent macroscopic behavior in natural and engineered systems


Entropy rntropicinteShape has a pervasive but often overlooked impact on how natural systems are ordered. At the same time, entropy (the probabilistic measure of the degree of energy delocalization in a system) – while often misunderstood as the state of a system’s disorder – and emergence (the sometimes controversial observance of macroscopic behaviors not seen in isolated systems of a few constituents) are two areas of research that have long received, and are likely to continue receiving, significant scientific attention. Now, materials science and chemical engineering researchers working with computer simulations of colloidal suspensions of hard nanoparticles at University of Michigan, Ann Arbor have linked entropy and emergence through a little-understood property they refer to as shape entropy – an emergent, entropic effect – unrelated to geometric entropy or topological entropy – that differs from and competes with intrinsic shape properties that arise from both the shape geometry and the material itself and affect surface, chemical and other intrinsic properties.

According to the researchers, shape entropy directly affects system structure through directional entropic forces (DEFs) that align neighboring particles and thereby optimize local packing density. Interestingly, the scientists demonstrate that shape entropy drives the emergence of DEFs in a wide class of soft matter systems as particles adopt local dense packing configurations when crowded and drives the phase behavior of systems of anisotropic shapes into complex crystals, liquid crystals and even ordered but non-periodic structures called quasicrystals through these DEFs. (Anisotropy refers to a difference in a material’s physical or mechanical properties – absorbance, refractive index, conductivity, tensile strength, and so on – when measured along different axes.)

Prof. Sharon C. Glotzer discussed the paper that she, lead author and Research Investigator Dr. Greg van Anders and their co-authors published in Proceedings of the National Academy of Sciences, noting that one of the fundamental issues they faced was the historical problem of linking microscopic mechanisms with macroscopic emergent behavior. “This is a difficult problem that was really, to our knowledge, only brought into sharp contrast for physical systems by Philip Warren Anderson in his 1972 essay More is Different1 – and really, the title says it all,” van Anders tells Phys.org. (Anderson is a physicist and Nobel laureate who in his essay addressed emergent phenomena and the limitations of reductionism.) “We’re interested in the type of systems that are dominated by entropy – meaning that their behavior originates from effects of the system as whole,” Glotzer points out. “In a way, we’re grappling with the problem of how things that operate with basic rules can produce complicated behavior.” For Glotzer and her team, the rules are shapes, and the behavior takes the form of complex crystals. “It’s very important to understand shape effects in nanosystems,” she adds, “because nanoparticles tend to have a natural shape to them because of how they grow.”

In addressing this problem, the scientists – in addition to isolating shape entropy in model systems – had to precisely delineate between and correlate the relative influences of shape entropy and intrinsic shape effects. This can be formidable: While the intrinsic shape of a cell or nanoparticle affects a range of other intrinsic properties, such as its surface and chemical characteristics, shape entropy is an effect that emerges from the geometry of the shape itself in the context of other shapes crowded around it. “Intrinsic shape effects are conceptually straightforward because they’re forces that originate from van der Waals, Coulomb, and other electrostatic and other forces, though in practice they may not be easy to measure experimentally,” Glotzer explains. “However, comparing intrinsic shape effects to shape entropy is a bit like comparing apples and oranges: there are many ways to characterize shapes, but forces aren’t typically one of them.” Moreover, research has historically focused on shape effects in specific systems, so a general solution was elusive, and there were no rules specifying the types of systems where shape effects might be seen.

Entropy 2 pmftinmonodi

In monodisperse systems, we compute the PMFT by considering pairs of particles (A, C, and E). Density dependence of the PMFT along an axis perpendicular to the polyhedral face for a hard tetrahedron fluid (B), a fluid of tetrahedrally faceted …more

Not surprisingly, then, a significant obstacle was quantitatively demonstrating that shape drives the phase behavior of systems of anisotropic particles upon crowding through directional entropic forces. “Our main problem here was trying to understand how there could be a local mechanism for global ordering that acts through entropy – which is a global construct,” Glotzer says. “It took us a while to realize that other investigators had already been asking this question for systems containing mixtures of large particles and very small particles.” (The latter, known as depletants, induce assembly or crystallization of larger particles.) “However,” she continues, “it was more challenging to determine how to pose and interpret this question mathematically when all particles are the same.” Glotzer adds that the technique van Anders and the rest of her team used to understand these systems – the potential of mean force and torque (PMFT), a treatment of isotropic entropic forces first given in 1949 by Jan de Boer2 at the Institute for Theoretical Physics, University of Amsterdam – is in many ways rather basic. Nevertheless, and somewhat remarkably, PMFT provided them with the key by allowing them to quantify directional entropic forces between anisotropic particles at arbitrary density. (PMFT is related to the potential of mean force, or PMF, an earlier approach that – unlike PMFT – has no concept of relative orientation between particles, and regarding shapes would only provide insight into radial, but not angular, dependence.)

The paper also address the relationships between shape entropy, self-assembly and packing behavior. (Self-assembly refers to thermodynamically stable or metastable phases that arise from systems maximizing their generalized entropy through spontaneous self-assembly in the presence of energetic and volumetric constraints, such as temperature and pressure; or through directed self-assembly due to other constraints, such as electromagnetic fields.) “Once we had determined how to measure the directional entropic forces,” van Anders explains, “the entropy/self-assembly connection became evident: On the systems we studied, the forces we were able to measure between particles were exactly in the range they should be to contribute to self-assembly (several kBT), which is on the order of intrinsic interactions between nanoparticles and on the scale of temperature-induced random motion.” (The metric kBT is the product of the Boltzmann constant, k, and the temperature, T, used in physics as a scaling factor for energy values or as a unit of energy in molecular-scale systems.)

That said, the scientists were able to use directional entropic forces to draw a distinction between self-assembly and packing behavior. “This was puzzling: For a long time, global density packing arguments have been used to predict assembly behavior in a range of systems,” Glotzer continues. “However, in the last few years – especially as researchers began looking more seriously at the anisotropic shapes being fabricated in the lab – these packing arguments started failing. Around the same time my group wrote a paper that showed that the assembled behavior can often be predicted by looking at the structure of a dense fluid of particles that hasn’t yet assembled.” The researchers realized that the forces they were seeing in their calculations were coming from local dense packing that happens in the fluid and the assembled systems. This showed that self-assembly and packing behavior were related, but not by global dense packing.

An important implication of understanding how shape entropy drives both self-assembly and packing despite their observable differences, Glotzer points out, is that there is growing interest in making ordered materials for various optical, electronic and other applications. “We’ve shown that, in general, it’s possible to use shape to control the structure of these materials,” she explains. “Now that we understand why particles are doing what they do when they form these materials, it becomes much easier to determine how to design them to generate desired materials rather than just going by trial-and-error.”

Directional entropic forces are emergent in systems of particles and, as such, cannot be imaged directly through microscopy. Here we show the location of potential wells by taking slices of the PMFT (computed from the frequency histogram of …more

Another dramatic realization was that shape entropy drives the phase behavior of systems of anisotropic shapes through directional entropic forces. “We already knew from prior work in my group that you can quite often predict what crystal structure will form by looking at the fluid and the particle shape,” Glotzer tells Phys.org. “The problem for us was identifying what caused particles to arrange into the local structures they did in the fluid, and to show that they had the same sort of structure when they assembled.” Van Anders adds that the scientists were able to find the forces that induced and kept the particles in their preferred structures. “When they turned out to be in the right range we knew that we had it right.”

To date, the researchers have conducted their simulation studies only on idealized model systems. “Still,” says Glotzer, “our simulations capture what we believe to be the most important features of real colloidal systems.” Indeed, a growing number of published experimental studies now report the same structures her team predicted, and no counter-results have yet been observed. “We’re working closely with collaborators to leverage existing experimental techniques that will allow us to measure the strength of these forces and compare them with our predictions.” One such approach is measuring directional entropic forces in the lab by using confocal microscopy to determine the location and orientation of particles in assembling systems.

Moreover, Glotzer’s research group is collaborating with several experimental groups to investigate potential approaches to exploiting shape effects in the laboratory. “Now that we understand how local entropic forces work,” she tells Phys.org, “we can begin to think about designing so that entropy and internal energy balance in just the right way to yield complex target structures.”

Glotzer and van Anders conclude that “Researchers have been thinking about different kinds of entropy-driven systems since the 1930s, and since the 1950s have done a lot of work in systems in so-called depletant mixtures – but to our knowledge most people tend to think of those systems as having little to do with densely crowded, single-particle systems. Our work helps to tie these different lines of research together – and we hope that the decades of work done by the community in trying to understand depletant systems can help us get a deeper understanding of pure, dense systems, so that we can narrow our search for interesting new materials.”

Explore further: Competing forces coax nanocubes into helical structures

Nanoparticles infiltrate, kill cancer cells from within


Cancer 24-nanoparticleConventional treatment seeks to eradicate cancer cells by drugs and therapy delivered from outside the cell, which may also affect (and potentially harm) nearby normal cells.

In contrast to conventional cancer therapy, a University of Cincinnati team has developed several novel designs for iron-oxide based nanoparticles that detect, diagnose and destroy cancer cells using photo-thermal therapy (PTT). PTT uses the nanoparticles to focus light-induced heat energy only within the , harming no adjacent normal cells.

The results of the UC work will be presented at the Materials Research Society Conference in Boston Nov. 30-Dec. 5 by Andrew Dunn, doctoral student in materials science engineering in UC’s College of Engineering and Applied Science. Working with Dunn in this study are Donglu Shi, professor of materials science engineering in UC’s College of Engineering and Applied Science; David Mast, associate professor of physics in UC’s McMicken College of Arts and Sciences; and Giovanni Pauletti, associate professor in the James L. Winkle College of Pharmacy.

Cancer 24-nanoparticle

The UC study used the living cells of mice to successfully test the efficacy of their two-sided nanoparticle designs (one side for cell targeting and the other for treatment delivery) in combination with the PTT. However, the U.S. Food and Drug Administration has now approved the use of iron-oxide nanoparticles in humans. That means the photo-thermal effect of iron-oxide nanoparticles may show, in the next decade, a strong promise in human cancer therapy, likely with localized tumors.

How the nanoparticles work with photothermal therapy

With this technology, a low-power laser beam is directed at the tumor where a small amount of magnetic are present, either by injecting the particles directly into the tumor or injecting them into the blood stream whereby the particles find and bind to the abnormal cancer cells via cell-specific targeting.

Sufficient heat is then generated locally by the laser light, raising the tumor temperature rapidly to above 43 degrees Celsius, and thereby burning the abnormal cancer cells. This particular PTT treatment does not involve any medicine, but only generates local heat within the tumor, therefore posing much less side effects than the traditional chemo or radiation therapies.

“This treatment is much more ideal because it goes straight to the cancer cell,” says Shi. “The nanomaterials enter only the , illuminating those cells and then doing whatever it is you have designed them to do. In this case, it is to heat up hot enough to burn and kill the cancer cells, but not harm the surrounding normal cells.”

Shi added that physicians are often frustrated with the current conventional means for early imaging of cancer cells through Medical Resonance Imaging or Computerized Tomography scans because the tumors are usually stage three or four before they can be detected. He stated, “With nanomaterial technology, we can detect the tumor early and kill it on sight at the same time.”

Cell targeting

Each tumor has a corresponding protein that is cancer specific called a tumor specific ligand or an antibody antigen reaction that only has expression for that specific cancer such as breast or prostate cancer.

Scientists identify this certain bio-marker that is specific to a certain tumor, then conjugates this bio-marker on the surface of the nanocarrier that only has the expression for that specific kind of cancer cell.

It then only targets the abnormal cancer cell, not normal, , and because it is so small it can break the membrane and enter that conjugated cancer cell and release the PTT.

The nanotech carriers go into the body through a vein in the blood stream, seek the abnormal cancer cells, find the bio-marker or cancer cells and attach to those cells and unlock their florescent particles so they can be detected by a photon laser-light.

The laser-light heats the nanoparticles to at least 43 degrees Celsius to kill the , ultimately leaving all the other cells in the body unharmed.

Potential DIY cancer treatment

The procedure can ultimately be carried out by the patient following training to direct a small laser light device to the affected area for a specified amount of time two to three times a day. This method can ultimately improve the success rate, as well as cut costs to the patient. This gives “point and shoot” a whole new meaning.

Future research in nanoparticle PTT will look at toxicity, biodegradability and compatibility issues. Shi said that the team is currently looking for other diverse biodegradable materials to use for the carriers such as plant chlorophylls like those in cabbage that are both edible and photothermal. This material is biocompatible and biodegradable and can potentially stay in the until its job is finished, then dissolve and be passed out through the digestive system.

Explore further: First genetic-based tool to detect circulating cancer cells in blood

Silver Nanowire Ink Printed on Paper to Create Flexible Electronic Sensors


Nano Skin SensorsFlexible electronic sensors based on paper — an inexpensive material — have the potential to some day cut the price of a wide range of medical tools, from helpful robots to diagnostic tests.

Scientists have now developed a fast, low-cost way of making these sensors by directly printing conductive ink on paper. They published their advance in the journal ACS Applied Materials & Interfaces.

Anming Hu and colleagues point out that because paper is available worldwide at low cost, it makes an excellent surface for lightweight, foldable electronics that could be made and used nearly anywhere. Scientists have already fabricated paper-based point-of-care diagnostic tests and portable DNA detectors. But these require complicated and expensive manufacturing techniques. Silver nanowire ink, which is highly conductive and stable, offers a more practical solution. Hu’s team wanted to develop a way to print it directly on paper to make a sensor that could respond to touch or specific molecules, such as glucose.

Rice Sensors nanophotonic

The researchers developed a system for printing a pattern of silver ink on paper within a few minutes and then hardening it with the light of a camera flash. The resulting device responded to touch even when curved, folded and unfolded 15 times, and rolled and unrolled 5,000 times. The team concluded their durable, lightweight sensor could serve as the basis for many useful applications.

Source: http://www.acs.org/

Two sensors in one: Nanoparticles that enable both MRI and fluorescent imaging could monitor cancer, other diseases


12-Sensors 141118125600-largeNovember 18, 2014 Source: Massachusetts Institute of Technology

MIT chemists have developed new nanoparticles that can simultaneously perform magnetic resonance imaging (MRI) and fluorescent imaging in living animals. Such particles could help scientists to track specific molecules produced in the body, monitor a tumor’s environment, or determine whether drugs have successfully reached their targets.

In a paper appearing in the Nov. 18 issue of Nature Communications, the researchers demonstrate the use of the particles, which carry distinct sensors for fluorescence and MRI, to track vitamin C in mice. Wherever there is a high concentration of vitamin C, the particles show a strong fluorescent signal but little MRI contrast. If there is not much vitamin C, a stronger MRI signal is visible but fluorescence is very weak.

Future versions of the particles could be designed to detect reactive oxygen species that often correlate with disease, says Jeremiah Johnson, an assistant professor of chemistry at MIT and senior author of the study. They could also be tailored to detect more than one molecule at a time.

12-Sensors 141118125600-large

MIT chemists have developed new nanoparticles that can simultaneously perform magnetic resonance imaging (MRI) and fluorescent imaging in living animals.
Credit: Illustration by Christine Daniloff/MIT

“You may be able to learn more about how diseases progress if you have imaging probes that can sense specific biomolecules,” Johnson says.

Dual action

Johnson and his colleagues designed the particles so they can be assembled from building blocks made of polymer chains carrying either an organic MRI contrast agent called a nitroxide or a fluorescent molecule called Cy5.5.

When mixed together in a desired ratio, these building blocks join to form a specific nanosized structure the authors call a branched bottlebrush polymer. For this study, they created particles in which 99 percent of the chains carry nitroxides, and 1 percent carry Cy5.5.

Nitroxides are reactive molecules that contain a nitrogen atom bound to an oxygen atom with an unpaired electron. Nitroxides suppress Cy5.5’s fluorescence, but when the nitroxides encounter a molecule such as vitamin C from which they can grab electrons, they become inactive and Cy5.5 fluoresces.

Nitroxides typically have a very short half-life in living systems, but University of Nebraska chemistry professor Andrzej Rajca, who is also an author of the new Nature Communications paper, recently discovered that their half-life can be extended by attaching two bulky structures to them. Furthermore, the authors of the Nature Communications paper show that incorporation of Rajca’s nitroxide in Johnson’s branched bottlebrush polymer architectures leads to even greater improvements in the nitroxide lifetime. With these modifications, nitroxides can circulate for several hours in a mouse’s bloodstream — long enough to obtain useful MRI images.

The researchers found that their imaging particles accumulated in the liver, as nanoparticles usually do. The mouse liver produces vitamin C, so once the particles reached the liver, they grabbed electrons from vitamin C, turning off the MRI signal and boosting fluorescence. They also found no MRI signal but a small amount of fluorescence in the brain, which is a destination for much of the vitamin C produced in the liver. In contrast, in the blood and kidneys, where the concentration of vitamin C is low, the MRI contrast was maximal.

Mixing and matching

The researchers are now working to enhance the signal differences that they get when the sensor encounters a target molecule such as vitamin C. They have also created nanoparticles carrying the fluorescent agent plus up to three different drugs. This allows them to track whether the nanoparticles are delivered to their targeted locations.

“That’s the advantage of our platform — we can mix and match and add almost anything we want,” Johnson says.

These particles could also be used to evaluate the level of oxygen radicals in a patient’s tumor, which can reveal valuable information about how aggressive the tumor is.

“We think we may be able to reveal information about the tumor environment with these kinds of probes, if we can get them there,” Johnson says. “Someday you might be able to inject this in a patient and obtain real-time biochemical information about disease sites and also healthy tissues, which is not always straightforward.”

Steven Bottle, a professor of nanotechnology and molecular science at Queensland University of Technology, says the most impressive element of the study is the combination of two powerful imaging techniques into one nanomaterial.

“I believe this should deliver a very powerful, metabolically linked, multi-combination imaging modality which should provide a highly useful diagnostic tool with real potential to follow disease progression in vivo,” says Bottle, who was not involved in the study.

The research was funded by the National Institutes of Health, the Department of Defense, the National Science Foundation, and the Koch Institute for Integrative Cancer Research.


Story Source:

The above story is based on materials provided by Massachusetts Institute of Technology. The original article was written by Anne Trafton. Note: Materials may be edited for content and length.


Journal Reference:

  1. Molly A. Sowers, Jessica R. McCombs, Ying Wang, Joseph T. Paletta, Stephen W. Morton, Erik C. Dreaden, Michael D. Boska, M. Francesca Ottaviani, Paula T. Hammond, Andrzej Rajca, Jeremiah A. Johnson. Redox-responsive branched-bottlebrush polymers for in vivo MRI and fluorescence imaging. Nature Communications, 2014; 5: 5460 DOI: 10.1038/ncomms6460

Chemists Gain Edge in “Next-Gen Energy: Discover Dual-Purpose Film for Energy Storage & Hydrogen Catalysis


1- Rice ES ricechemistsRice University scientists who want to gain an edge in energy production and storage report they have found it in molybdenum disulfide.

The Rice lab of chemist James Tour has turned disulfide’s two-dimensional form into a nanoporous film that can catalyze the production of hydrogen or be used for energy storage.

The versatile chemical compound classified as a dichalcogenide is inert along its flat sides, but previous studies determined the material’s edges are highly efficient catalysts for hydrogen evolution reaction (HER), a process used in fuel cells to pull hydrogen from water.

Tour and his colleagues have found a cost-effective way to create flexible films of the material that maximize the amount of exposed edge and have potential for a variety of energy-oriented applications.

The Rice research appears in the journal Advanced Materials.

1- Rice ES ricechemists

A new material developed at Rice University based on molybdenum disulfide exposes as much of the edge as possible, making it efficient as both a catalyst for hydrogen production and for energy storage. Credit: Tour Group/Rice University 

Molybdenum disulfide isn’t quite as flat as graphene, the atom-thick form of pure carbon, because it contains both molybdenum and sulfur atoms. When viewed from above, it looks like graphene, with rows of ordered hexagons. But seen from the side, three distinct layers are revealed, with in their own planes above and below the molybdenum.

This crystal structure creates a more robust edge, and the more edge, the better for catalytic reactions or storage, Tour said.

“So much of chemistry occurs at the edges of materials,” he said. “A two-dimensional material is like a sheet of paper: a large plain with very little edge. But our material is highly porous. What we see in the images are short, 5- to 6-nanometer planes and a lot of edge, as though the material had bore holes drilled all the way through.”

A thin, flexible film developed at Rice University shows excellent potential as a hydrogen catalyst or as an energy storage device. The two-dimensional film could be a cost-effective component in such applications as fuel cells. Credit: Tour Group/Rice University

The new film was created by Tour and lead authors Yang Yang, a postdoctoral researcher; Huilong Fei, a graduate student; and their colleagues. It catalyzes the separation of hydrogen from water when exposed to a current. “Its performance as a HER generator is as good as any molybdenum disulfide structure that has ever been seen, and it’s really easy to make,” Tour said.

While other researchers have proposed arrays of molybdenum disulfide sheets standing on edge, the Rice group took a different approach. First, they grew a porous molybdenum oxide film onto a molybdenum substrate through room-temperature anodization, an electrochemical process with many uses but traditionally employed to thicken natural oxide layers on metals.

The film was then exposed to sulfur vapor at 300 degrees Celsius (572 degrees Fahrenheit) for one hour. This converted the material to without damage to its nano-porous sponge-like structure, they reported.

The films can also serve as supercapacitors, which store energy quickly as static charge and release it in a burst. Though they don’t store as much energy as an electrochemical battery, they have long lifespans and are in wide use because they can deliver far more power than a battery. The Rice lab built supercapacitors with the films; in tests, they retained 90 percent of their capacity after 10,000 charge-discharge cycles and 83 percent after 20,000 cycles.

“We see anodization as a route to materials for multiple platforms in the next generation of alternative energy devices,” Tour said. “These could be fuel cells, supercapacitors and batteries. And we’ve demonstrated two of those three are possible with this new material.”

Explore further: Harnessing an unusual ‘valley’ quantum property of electrons