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What's New in Nanotechnology?

July 13, 2016
Rice University scientists have created light-driven, single-molecule submersibles. A new version of the molecule strengthens its fluorescent response for better tracking. Atoms in red make up the light-activated motor. (Credit: Tour Group/Rice University)

The next generation of nanosubmarines being developed at Rice University has been upgraded with tags that fluoresce longer, which enables the submersibles to be tracked for greater periods while being driven through a solution. The single-molecule vehicles introduced by the Rice lab of chemist James Tour last year may someday be used to deliver drugs or other cargo. The new version was built and tested with collaborators at Tel Aviv University in Israel. The first nanosub, USN-1, could be monitored but not imaged by a technique that would irradiate it with light for very short times. But that did not offer information about the submersible’s trajectory, according to lead author Víctor García-Lopéz, a former Rice graduate student. The latest model, the 334-atom USN-2, can be viewed by single-molecule microscopy for at least 1.5 seconds, long enough for 30 frames of video. “This makes it possible for us to track the trajectory of a single nanosubmersible,” Tour said. “It should lead to a better understanding of how our vehicles move.”

The lab attached cyclooctatetraene (COT) to the molecule’s body and motor to keep them from bleaching, which quenches fluorescence. The light-driven motor developed by scientists in the Netherlands is a tail-like ligand that spins about a million times per second. The new subs, like the originals, are capable of moving 15 meters per second over nanoscale distances, based on the thrust provided by each turn of the rotating motor. Between the frequent collisions that stop their forward motion, Tour said, they are “the fastest-moving molecules ever seen in solution.” The nanosubmarines still can’t be steered in the traditional sense, Tour said. The team is satisfied for the moment with achieving “enhanced diffusion” that lets them figure out how to move a one-molecule vehicle in a solution of similarly sized molecules. “The next step is to track these nanosubmarines in solution and see if we can use them to deliver cargo or interact with cells,” Tour said.

Categories : University News
June 15, 2016
Researchers at Washington University in St. Louis hope that nanoparticle technology can help reduce the need for fertilizer, creating a more sustainable way to grow crops such as mung beans.

Scientists are working diligently to prepare for the expected increase in global population — and therefore an increased need for food production— in the coming decades. A team of engineers at Washington University in St. Louis has found a sustainable way to boost the growth of a protein-rich bean by improving the way it absorbs much-needed nutrients.Ramesh Raliya, a research scientist, and Pratim Biswas, the Lucy & Stanley Lopata Professor and chair of the Department of Energy, Environmental & Chemical Engineering, both in the School of Engineering & Applied Science, discovered a way to reduce the use of fertilizer made from rock phosphorus and still see improvements in the growth of food crops by using zinc oxide nanoparticles. Raliya said this is the first study to show how to mobilize native phosphorus in the soil using zinc oxide nanoparticles over the life cycle of the plant, from seed to harvest. Food crops need phosphorus to grow, and farmers are using more and more phosphorus-based fertilizer as they increase crops to feed a growing world population. However, the plants can only use about 42 percent of the phosphorus applied to the soil, so the rest runs off into the water streams, where it grows algae that pollutes our water sources. In addition, nearly 82 percent of the world’s phosphorus is used as fertilizer, but it is a limited supply, Raliya says. Raliya and his collaborators, including Jagadish Chandra Tarafdar at the Central Arid Zone Research Institute in Jodhpur, India, created zinc oxide nanoparticles from a fungus around the plant’s root that helps the plant mobilize and take up the nutrients in the soil. Zinc also is an essential nutrient for plants because it interacts with three enzymes that mobilize the complex form of phosphorus in the soil into a form that plants can absorb. When Raliya and the team applied the zinc nanoparticles to the leaves of the mung bean plant, it increased the uptake of the phosphorus by nearly 11 percent and the activity of the three enzymes by 84 percent to 108 percent. That leads to a lesser need to add phosphorus on the soil, Raliya said.

June 07, 2016
Molecules that alight on a surface used to test nanocars look more like obstacles, according to researchers at Rice University and North Carolina State University testing the mobility of single-molecule cars in open air. (Image Credit: Rice/North Carolina State)

Rice University researchers who developed the first nanocars and colleagues at North Carolina State University found in recent tests that driving their vehicles in ambient conditions – exposed to open air, rather than a vacuum – got dicey after a time because the hydrophobic single-molecule cars stuck to the “road” and created what amounted to large speed bumps. The work by Rice chemist James Tour, NC State analytical chemist Gufeng Wang and their colleagues came as Rice prepares to take part in the first NanoCar Race in Toulouse, France, in October. Rice researchers are members of one of five international teams that plan to enter the competition. Just like in the macro world, driving conditions are important for moving nanocars. Though the race will be run in an ultra-cold vacuum, the Rice researchers thought it wise to study how their latest model of nanocars would fare in a more natural setting. “Our long-term goal is to make nanomachines that operate in ambient environments,” Tour said. “That’s when they will show potential to become useful tools for medicine and bottom-up manufacturing.” The newest generation of Rice nanocars features adamantane wheels that are slightly hydrophobic (water-repellent). Tour said some hydrophobicity is important to help keep the nanocars attached to a surface, but if the tires are too hydrophobic, the cars could become permanently immobilized. That is because hydrophobic things tend to stick together to minimize the amount of surface area that is in contact with water. Things that are hydrophilic, or water-liking, are more amenable to floating freely in water, Tour said. In the latest Rice tests with the new tires, the nanocars were placed on surfaces that were either clean glass or glass coated with the polymer polyethylene glycol (PEG). Glass is the most frequently used substrate in nanocar research. Tour said the PEG-coated glass slides were used for their anti-fouling – nonsticky – properties, while the clean glass slides were treated with hydrogen peroxide so the hydrophobic wheels wouldn’t stick. He said the cars weren’t so much being driven as undergoing “directed diffusion” in the tests. The point, he said, was to establish the kinetics of nanocar movement and understand the potential energy surface interaction between the car and surface over time.

Categories : University News
May 31, 2016
Stanford engineers studying the structures of phase-changing nanoparticles have found that shape matters. Materials composed of cubes and pyramids, for instance, may yield more efficient batteries than those made of icosahedra. (Image credit: Stanford University, Dionne Group)

A team of Stanford University engineers has obtained a first look inside phase-changing nanoparticles, elucidating how their shape and crystallinity – the arrangement of atoms within the crystal – can have dramatic effects on their performance. The work has immediate applications in the design of energy storage materials, but could eventually find its way into data storage, electronic switches and any device in which the phase transformation of a material regulates its performance. For instance, in a lithium ion battery, the ability of the battery to store and release energy repeatedly relies on the electrode’s ability to sustain large deformations over several charge and discharge cycles without degrading. Recently, scientists have improved the efficiency of this process by nanosizing the electrodes. The nanoparticles allow for faster charging, increased energy storage and an extended lifetime, but it is unknown which nanoparticle shapes, sizes and crystallinities produce the best performance. Jennifer Dionne, an assistant professor of materials science and engineering, and her group have been studying the behavior of individual particles to establish a stronger link between structure and function that can direct the design of next-generation energy storage materials. Dionne’s group examined how varying the shapes and crystallinity of palladium nanoparticles affected their ability to absorb and release hydrogen atoms – an analog to a lithium-ion battery discharging and charging. They prepared cubic, pyramidal and icosahedral nanoparticles and developed novel imaging techniques to look inside nanoparticles at various hydrogen pressures, determining where the hydrogen was located. The researchers found that nanoparticle structure significantly influences performance. The icosahedral structures, for instance, show reduced energy storage capacity and more gradual hydrogen absorption than the single crystalline cubes and pyramids. High-resolution maps of the particles demonstrate that hydrogen is excluded from the center of the particle, thus lowering the overall capacity to incorporate hydrogen. Structural characterization shows that the gradual absorption of hydrogen occurs because different regions of the particle absorb hydrogen at different pressures, unlike what is observed in single crystals.

Categories : University News
May 03, 2016
Flexible electrocaloric fabric of nanowire array can cool. (Image Credit: Qing Wang/Penn State)

Firefighters entering burning buildings, athletes competing in the broiling sun and workers in foundries may eventually be able to carry their own, lightweight cooling units with them, thanks to a nanowire array that cools, according to Penn State materials researchers. "Most electrocaloric ceramic materials contain lead," said Qing Wang, professor of materials science and engineering. "We try not to use lead. Conventional cooling systems use coolants that can be environmentally problematic as well. Our nanowire array can cool without these problems." Electrocaloric materials are nanostructured materials that show a reversible temperature change under an applied electric field. Previously available electrocaloric materials were single crystals, bulk ceramics or ceramic thin films that could cool, but are limited because they are rigid, fragile and have poor processability. Ferroelectric polymers also can cool, but the electric field needed to induce cooling is above the safety limit for humans. Wang and his team looked at creating a nanowire material that was flexible, easily manufactured and environmentally friendly and could cool with an electric field safe for human use. Such a material might one day be incorporated into firefighting gear, athletic uniforms or other wearables.

Categories : University News
April 14, 2016
Rice University researchers have discovered a simple method to make films of highly aligned carbon nanotubes. The films can be separated from their backgrounds and show potential for use in electronic and photonic applications. (Credit: Jeff Fitlow/Rice University)

A simple filtration process helped Rice University researchers create flexible, wafer-scale films of highly aligned and closely packed carbon nanotubes. Scientists at Rice, with support from Los Alamos National Laboratory, have made inch-wide films of densely packed, chirality-enriched single-walled carbon nanotubes. In the right solution of nanotubes and under the right conditions, the tubes assemble themselves by the millions into long rows that are aligned better than once thought possible, the researchers reported. The thin films offer possibilities for making flexible electronic and photonic (light-manipulating) devices, said Rice physicist Junichiro Kono, whose lab led the study. Think of a bendable computer chip, rather than a brittle silicon one, and the potential becomes clear, he said. The Rice lab is closing in, Kono said, but the films reported in the current paper are “chirality-enriched” rather than single-chirality. A carbon nanotube is a cylinder of graphene, with its atoms arranged in hexagons. How the hexagons are turned sets the tube’s chirality, and that determines its electronic properties. Some are semiconducting like silicon, and others are metallic conductors. A film of perfectly aligned, single-chirality nanotubes would have specific electronic properties. Controlling the chirality would allow for tunable films, Kono said, but nanotubes grow in batches of random types.

March 17, 2016
A common over-the-counter drug, chopped down into nanoparticle size, stopped growth in a cancer tumor. Image Credit: Washington University in St. Louis

Engineers at Washington University in St. Louis found a way to keep a cancerous tumor from growing by using nanoparticles of the main ingredient in common antacid tablets. The research team, led by Avik Som, an MD/PhD student, and Samuel Achilefu, PhD, professor of radiology and of biochemistry & molecular biophysics in the School of Medicine and of biomedical engineering in the School of Engineering & Applied Science, in collaboration with two labs in the School of Engineering & Applied Science, used two novel methods to create nanoparticles from calcium carbonate that were injected intravenously into a mouse model to treat solid tumors. The compound changed the pH of the tumor environment, from acidic to more alkaline, and kept the cancer from growing. With this work, researchers showed for the first time that they can modulate pH in solid tumors using intentionally designed nanoparticles. “Cancer kills because of metastasis,” said Som, who is working on a doctorate in biomedical engineering in addition to a medical degree. “The pH of a tumor has been heavily correlated with metastasis. For a cancer cell to get out of the extracellular matrix, or the cells around it, one of the methods it uses is a decreased pH.”

Categories : University News
March 10, 2016
Image Credit: McGill University, Thomas Edwardson

Gold nanoparticles have unusual optical, electronic and chemical properties, which scientists are seeking to put to use in a range of new technologies, from nanoelectronics to cancer treatments. Some of the most interesting properties of nanoparticles emerge when they are brought close together – either in clusters of just a few particles or in crystals made up of millions of them.  Yet particles that are just millionths of an inch in size are too small to be manipulated by conventional lab tools, so a major challenge has been finding ways to assemble these bits of gold while controlling the three-dimensional shape of their arrangement. One approach that researchers have developed has been to use tiny structures made from synthetic strands of DNA to help organize nanoparticles. Researchers from McGill University’s Department of Chemistry are working on a procedure for making a DNA structure with a specific pattern of strands coming out of it; at the end of each strand is a chemical “sticky patch.”  When a gold nanoparticle is brought into contact to the DNA nanostructure, it sticks to the patches. The scientists then dissolve the assembly in distilled water, separating the DNA nanostructure into its component strands and leaving behind the DNA imprint on the gold nanoparticle. 

Categories : University News
March 02, 2016
An illustration shows a nanocar design by scientists at Rice University. The first nanocars, invented at Rice, consisted of a chassis, two axles and four wheels, all part of a single molecule. (Credit: Tour Group/Rice University)

Rice University will send an entry to the first international NanoCar Race, which will be held next October at Pico-Lab CEMES-CNRS in Toulouse, France. No one will see this miniature grand prix, at least not directly. But cars from five teams, including a collaborative effort by the Rice lab of chemist James Tour and scientists at the University of Graz, Austria, will be viewable through sophisticated microscopes developed for the event. Time trials will determine which nanocar is the fastest, though there may be head-to-head races with up to four cars on the track at once, according to organizers. A nanocar is a single-molecule vehicle of 100 or so atoms that incorporates a chassis, axles and freely rotating wheels. Each of the entries will be propelled across a custom-built gold surface by an electric current supplied by the tip of a scanning electron microscope. The track will be cold at 5 kelvins (minus 450 degrees Fahrenheit) and in a vacuum. Rice’s entry will be a new model and the latest in a line that began when Tour and his team built the world’s first nanocar more than 10 years ago. The race was first proposed in a 2013 ACS Nano paper by Christian Joachim, a senior researcher at CNRS, and Gwénaël Rapenne, a professor at Paul Sabatier University. Joining Rice are teams from Ohio University; Dresden University of Technology; the National Institute for Materials Science, Tsukuba, Japan; and Paul Sabatier. 

February 26, 2016

Common coaxial cables could be made 50 percent lighter with a new nanotube-based outer conductor developed by Rice University scientists. The Rice lab of Professor Matteo Pasquali has developed a coating that could replace the tin-coated copper braid that transmits the signal and shields the cable from electromagnetic interference. The metal braid is the heaviest component in modern coaxial data cables. Replacing the outer conductor with Rice’s flexible, high-performance coating would benefit airplanes and spacecraft, in which the weight and strength of data-carrying cables are significant factors in performance.Rice research scientist Francesca Mirri made three versions of the new cable by varying the carbon-nanotube thickness of the coating. She found that the thickest, about 90 microns – approximately the width of the average human hair – met military-grade standards for shielding and was also the most robust; it handled 10,000 bending cycles with no detrimental effect on the cable performance. “Current coaxial cables have to use a thick metal braid to meet the mechanical requirements and appropriate conductance,” Mirri said. “Our cable meets military standards, but we’re able to supply the strength and flexibility without the bulk.”

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