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Farnesol is released from the nanoparticle carriers into the cavity-causing dental plaque. (Graphic by Michael Osadciw/University of Rochester)

Therapeutic agents intended to reduce dental plaque and prevent tooth decay are often removed by saliva and the act of swallowing before they can take effect. But a team of researchers has developed a way to keep the drugs from being washed away. Dental plaque is made up of bacteria enmeshed in a sticky matrix of polymers—a polymeric matrix—that is firmly attached to teeth. The researchers, led by Danielle Benoit at the University of Rochester and Hyun Koo at the University of Pennsylvania’s School of Dental Medicine, found a new way to deliver an antibacterial agent within the plaque, despite the presence of saliva. To deliver the agent—known as farnesol—to the targeted sites, the researchers created a spherical mass of particles, referred to as a nanoparticle carrier. They constructed the outer layer out of cationic—or positively charged—segments of the polymers. For inside the carrier, they secured the drug with hydrophobic and pH-responsive polymers.

The positively-charged outer layer of the carrier is able to stay in place at the surface of the teeth because the enamel is made up, in part, of HA (hydroxyapatite), which is negatively charged. Just as oppositely charged magnets are attracted to each other, the same is true of the nanoparticles and HA. Because teeth are coated with saliva, the researchers weren’t certain the nanoparticles would adhere. But not only did the particles stay in place, they were also able to bind with the polymeric matrix and stick to dental plaque. Since the nanoparticles could bind both to saliva-coated teeth and within plaque, Benoit and colleagues used them to carry an anti-bacterial agent to the targeted sites.

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This transmission electron microscope image shows cellulose nanocrystals, tiny structures derived from renewable sources that might be used to create a new class of biomaterials with many potential applications. The structures have been shown to increase the strength of concrete. (Purdue Life Sciences Microscopy Center)

Cellulose nanocrystals derived from industrial byproducts have been shown to increase the strength of concrete, representing a potential renewable additive to improve the ubiquitous construction material. The cellulose nanocrystals (CNCs) could be refined from byproducts generated in the paper, bioenergy, agriculture and pulp industries. They are extracted from structures called cellulose microfibrils, which help to give plants and trees their high strength, lightweight and resilience. Now, researchers at Purdue University have demonstrated that the cellulose nanocrystals can increase the tensile strength of concrete by 30 percent.

"This is an abundant, renewable material that can be harvested from low-quality cellulose feedstocks already being produced in various industrial processes," said Pablo Zavattieri, an associate professor in the Lyles School of Civil Engineering. The cellulose nanocrystals might be used to create a new class of biomaterials with wide-ranging applications, such as strengthening construction materials and automotive components. One factor limiting the strength and durability of today's concrete is that not all of the cement particles are hydrated after being mixed, leaving pores and defects that hamper strength and durability. "So, in essence, we are not using 100 percent of the cement," Zavattieri said. However, the researchers have discovered that the cellulose nanocrystals increase the hydration of the concrete mixture, allowing more of it to cure and potentially altering the structure of concrete and strengthening it.  As a result, less concrete needs to be used.

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Stanford engineering graduate student Ashwin Atre uses an electron microscope to investigate the optical properties of nanoscale materials in three dimensions. (Linda A. Cicero / Stanford News Service)

To design the next generation of optical devices, ranging from efficient solar panels to LEDs to optical transistors, engineers will need a 3-dimensional image depicting how light interacts with these objects on the nanoscale. Unfortunately, the physics of light has thrown up a roadblock in traditional imaging techniques: the smaller the object, the lower the image's resolution in 3-D. Now, engineers at Stanford and the FOM Institute AMOLF, a research laboratory in the Netherlands, have developed a technique that makes it possible to visualize the optical properties of objects that are several thousandths the size of a grain of sand, in 3-D and with nanometer-scale resolution. The technique involves a unique combination of two technologies, cathodoluminescence and tomography, enabling the generation of 3-D maps of the optical landscape of objects, said study lead author Ashwin Atre, a graduate student in the lab group of Jennifer Dionne, an assistant professor of materials science and engineering.

For decades, techniques to image light-matter interactions with sub-diffraction-limited resolution have been limited to 2D. The technique can be used to probe many systems in which light is emitted upon electron excitation. "It has applications for testing various types of engineered and natural materials," Atre said. "For instance, it could be used in manufacturing LEDs to optimize the way light is emitted, or in solar panels to improve the absorption of light by the active materials." The technique could even be modified for imaging biological systems without the need for fluorescent labels.

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On the left, a scanning electron micrograph of a carbon nanotube forest. The figure on the right is a numerically simulated CNT forest. Credit: University of Missouri, Matt Maschmann

Carbon nanotubes (CNTs) are microscopic tubular structures that engineers “grow” through a process conducted in a high-temperature furnace. The forces that create the CNT structures known as “forests” often are unpredictable and are mostly left to chance. Now, a University of Missouri researcher has developed a way to predict how these complicated structures are formed. By understanding how CNT arrays are created, designers and engineers can better incorporate the highly adaptable material into devices and products such as baseball bats, aerospace wiring, combat body armor, computer logic components and micro sensors used in biomedical applications.

CNTs are much smaller than the width of a human hair and naturally form “forests” when they are created in large numbers. These forests, held together by a nanoscale adhesive force known as the van der Waals force, are categorized based on their rigidity or how they are aligned. Currently, most models that examine CNT forests analyze what happens when you compress them or test their thermal or conductivity properties after they’ve formed. However, these models do not take into account the process by which that particular forest was created and struggle to capture realistic CNT forest structure. Experiments conducted in Maschmann’s lab will help scientists understand the process and ultimately help control it, allowing engineers to create nanotube forests with desired mechanical, thermal and electrical properties.

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Researchers at Rice University are working to determine the electronic properties of double-walled carbon nanotubes. In this example, the team analyzed a nanotube with two zigzag components. The individual nanotubes have band gaps and are semiconductors, but when combined, the band gaps overlap and make the double-walled a semimetal. (Illustration by Matías Soto/Rice University)

Rice University researchers have determined that two walls are better than one when turning carbon nanotubes into materials like strong, conductive fibers or transistors. Rice materials scientist Enrique Barrera and his colleagues used atomic-level models of double-walled nanotubes to see how they might be tuned for applications that require particular properties. They knew from others’ work that double-walled nanotubes are stronger and stiffer than their single-walled cousins. But they found it may someday be possible to tune double-walled tubes for specific electronic properties by controlling their configuration, chiral angles and the distance between the walls.

The Rice team found there’s even more to carbon nanotubes when they started looking at how the inner and outer walls match up using tubes with zigzag chirality. Because the electrical properties of single-walled tubes depend on their chirality – the angles of their hexagonal arrangement of atoms – the researchers thought it would be interesting to learn more about those properties in double-walled tubes. It turned out that both the distance between the walls — as small as a fraction of a nanometer — and the individual chirality of the tubes impact the double-walls’ electrical properties. In addition, the researchers found the diameter of the tube — especially the inner one, with its more pronounced curvature — has a small but significant impact on the structure’s semiconducting properties.

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The image illustrates how proteins (copper-colored coils) modified with polyhistidine-tags (green diamonds) can be attached to nanoparticles (red circle). Credit: SUNY University at Buffalo, Jonathan Lovell.

Fastening protein-based medical treatments to nanoparticles isn’t easy. With arduous chemistry, scientists can do it. But the fragile binding that holds them together often separates. This problem, which has limited how doctors can use proteins to treat serious disease, may soon change. University at Buffalo researchers have discovered a way to easily and effectively fasten proteins to nanoparticles – essentially an arranged marriage – by simply mixing them together. While in its infancy, the biotechnology model already has shown promise for developing an HIV vaccine and as a way to target cancer cells.

To create the biotechnology, the researchers use nanoparticles made of chlorophyll (a natural pigment), phospholipid (a fat similar to vegetable oil) and cobalt (a metal often used to prepare magnetic, water-resistant and high-strength alloys).  The proteins, meanwhile, are modified with a chain of amino acids called a polyhistidine-tag. Uncommon in medicine, polyhistidine-tags are used extensively in protein research. Next, the researchers mixed the modified proteins and nanoparticles in water. There, one end of the protein embeds into the nanoparticle’s outer layer while the rest of it sticks out like a tentacle. To test the new binding model’s usefulness, the researchers added to it an adjuvant, which is an immunological agent used to enhance the efficacy of vaccines and drug treatments. The results were impressive. The three parts – adjuvant, protein and nanoparticle – worked together to stimulate an immune response against HIV.

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New and improved solar panels could result from the discovery of a new liquid crystal material, making printable organic solar cells better performing. University of Melbourne researchers say their discovery of the highly sought-after ‘nematic liquid crystals’ can now lead to vastly improved organic solar cell performance. Dr David Jones of the University’s School of Chemistry and Bio 21 Institute, said these cells will be easier to manufacture, with the new crystals now able to work in cells that are double in thickness on the previous limit of 200 nanometers. “We have improved the performance of this type of solar cell from around 8 per cent efficient to 9.3 per cent, finally approaching the international benchmark of 10 per cent.”

It means that consumers can look forward to more competitive pricing in the solar energy sector, and according to Dr Jones, the discovery is a shot-in-the-arm for the whole organic materials sector. “The discovery is a step forward for the wider commercialization of printed organic solar cells. But more than this, could aid in the development of new materials with improved performance such as LCD screens.” Uptake of the current generation of organic solar cells has lagged behind more widespread silicon-based models, due to their comparative lack of performance even with a simplified construction via large printers.

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Graphene nanoribbons can be enticed to form favorable “reconstructed” edges by pulling them apart with the right force and at the right temperature, according to researchers at Rice University. The illustration shows the crack at the edge that begins the formation of five- and seven-atom pair under the right conditions. (Credit: ZiAng Zhang/Rice University)

Theoretical physicists at Rice University are living on the edge as they study the astounding properties of graphene. In a new study, they figure out how researchers can fracture graphene nanoribbons to get the edges they need for applications. New research by Rice physicist Boris Yakobson and his colleagues shows it should be possible to control the edge properties of graphene nanoribbons by controlling the conditions under which the nanoribbons are pulled apart. The way atoms line up along the edge of a ribbon of graphene — the atom-thick form of carbon — controls whether it’s metallic or semiconducting. Current passes through metallic graphene unhindered, but semiconductors allow a measure of control over those electrons. Since modern electronics are all about control, semiconducting graphene (and semiconducting two-dimensional materials in general) are of great interest to scientists and industry working to shrink electronics for applications. In the work, the Rice team used sophisticated computer modeling to show it’s possible to rip nanoribbons and get graphene with either pristine zigzag edges or what are called reconstructed zigzags.

Perfect graphene looks like chicken wire, with each six-atom unit forming a hexagon. The edges of pristine zigzags look like this: /\/\/\/\/\/\/\/\. Turning the hexagons 30 degrees makes the edges “armchairs,” with flat tops and bottoms held together by the diagonals. The electronic properties of the edges are known to vary from metallic to semiconducting, depending on the ribbon’s width. “Reconstructed” refers to the process by which atoms in graphene are enticed to shift around to form connected rings of five and seven atoms. The Rice calculations determined reconstructed zigzags are the most stable, a desirable quality for manufacturers. All that is great, but one still has to know how to make them. “Making graphene-based nano devices by mechanical fracture sounds attractive, but it wouldn’t make sense until we know how to get the right types of edges — and now we do,” said ZiAng Zhang, a Rice graduate student.

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Image Credit: University of Twente

Spherical gold particles are able to ‘drill’ a nano-diameter tunnel in ceramic material when heated. This is an easy and attractive way to equip chips with nanopores for DNA analysis, for example. Researcher Lennart de Vreede of the University of Twente applied a large number of microscopic discs of gold on a surface of silicon dioxide. When heated up for several hours, the gold is moving into the material, perpendicular to the surface, like nanometer-sized spheres. Nine hours of heating gives a tunnel of 800 nanometers in length, for example, and a diameter of 25 nanometer: these results can normally only be acieved by using complex processes. The gold can even fully move through the material. All nanotunnels together then form a sieve. Leaving the tunnel closed at one end, leaves open the possibility of creating molds for nano structures. Once heated to close to their melting point, the gold discs – diameter one micron -, don’t spread out over the surface, but they form spheres. They push away the siliciumdioxide, causing a circular ‘ridge’, a tiny dam. While moving into the silicondioxide, the ball gets smaller: it evaporates and there is a continuos movement of silicondioxide.

In DNA-sequencing applications, De Vreede sees applications for this new fabrication technology. In that case, a DNA-string is pulled through one of these nano-channels, after which the building blocks of DNA, the nucleotides, can be analysed subsequently. Furthermore, De Vreede expects the ‘gold method’ to be applicable to other ceramic materials as well. His recent experiments on silicium nitride indicate that. Research has been done in the BIOS Lab-on-a-chip group, part of two research institutes of the University of Twente: the MESA+ Institute for Nanotechnology and the MIRA Institute for Biomedical Technology and Technical Medicine.

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Schematic of an infrared photodetector with graphene as its active element (Image Credit: AMO GmbH)

Infrared photodetectors in communications systems have traditionally been built as discrete devices connected to the optical fibre carrying the signal, and an electronic circuit for processing the received data. An improvement on this arrangement would be to integrate the detector and electronics on a single chip. This would substantially reduce the device footprint and fabrication cost. The maximum data rate achieved with a state-of-the-art germanium detector fabricated using the standard silicon-based CMOS production system for integrated circuits is 40 gigabits per second. However, the performance of such photodetectors is limited by the material properties, and is less than optimal, owing to silicon’s vanishing light absorption at the wavelengths used. This is driving the search for new and better materials, and graphene is considered a promising candidate.

In a paper recently published in the journal ACS Photonics, Daniel Schall and a team based at AMO in Aachen, and Alcatel-Lucent Bell Labs in Stuttgart, demonstrated photodetectors based on wafer-scale graphene. The devices are capable of recording data at up to 50 gigabits per second, and display excellent signal integrity.  Study leader Daniel Schall is a 32-year-old electrical engineer who has been with AMO since 2009, and is currently working toward a PhD at RWTH Aachen University. His work on graphene is supported by the European Commission through the Graphene Flagship.

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