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/

Tough Textile Batteries


With the launch of Google Glass and the Samsung Galaxy Gear wristwatch this year, wearable electronics have moved from abstract concepts to tangible products. To integrate these electronic devices seamlessly into clothing, watchbands, and backpacks, some engineers are developing flexible, powerful textile-based batteries. Now researchers in South Korea have built one of the most durable wearable batteries to date on polyester fabric (Nano Lett. 2013, DOI: 10.1021/nl403860k). The battery, which the researchers sewed into a shirt, can be folded 10,000 times without losing function.

Textile 1 1384358962084

Most attempts to make textile batteries have had limited success, says materials scientist Jang Wook Choi of the Korea Advanced Institute of Science and Technology (KAIST).

 

Fashionable Batteries            

            South Korean researchers fabricated lithium ion batteries on polyester cloth and then sewed them into a hoodie (left) and a watch wristband (right). The bottom cartoons show the shape of the batteries used in the shirt (left) and wristband (right).

The problem has been finding battery materials that can retain high function while being bent repeatedly. For example, batteries with metal foils as electrodes can bend only a few times before breaking. Electrodes made by dipping cloth in nanoparticle inks, such as solutions of carbon nanotubes, are more durable than the foils, but the electrical resistance of these cloth electrodes is relatively high, which limits the size of the batteries and the total amount of energy they can store.

Polyester Electrode            

            In a new textile battery, researchers fabricated electrodes by electroplating nickel onto polyester fabric (top, center). After adding the nickel layer, they completed the electrode by coating the fabric with a lithium electrode composite using a polyurethane binder (top, right). The nickel coated the individual fibers of polyester yarn, allowing the fabric to retain most of its mechanical properties (bottom, right). The electrode composite then coated each strand of yarn in the fabric. (below)

Textile 2 1384358970137To solve these challenges, Choi rethought the entire design of textile batteries, starting with the electrode. He turned to nickel, because it is a fantastic conductor. To make a flexible, but still highly conductive metal electrode, Choi came up with the idea of electroplating nickel onto polyester fabric. The process is simple, and the nickel-coated textile retains the mechanical properties of the fabric. The electrodes had a very low electrical resistance, about 0.35 ohms per square, comparable to that of a pure nickel metal foil.

The other critical component is the polymer used to bind the anode and cathode materials onto the electrodes in the battery. If this binder material fails, the battery will peel apart and stop functioning. Choi found that polyurethane had the right mechanical properties. To complete the battery, Choi’s group used conventional lithium-ion battery materials for the anodes and cathodes.

Choi’s group put the polyester-based batteries through their paces. Other groups have demonstrated bending and flexing of batteries, but the KAIST team thought the real test of mechanical durability would be to fold the device with firm creases. They powered an array of light-emitting diodes with the battery and folded it repeatedly. After 10,000 folding and unfolding cycles, the textile battery still worked. Batteries built with aluminum foil electrodes broke after three cycles and stopped working altogether after 100 cycles.

The KAIST group showed that their textile batteries can be sewn into a sweatshirt and a watchband. They also integrated the batteries with flexible solar cells so the batteries could recharge without needing to be removed from the clothing. “It’s quite comfortable to wear,” Choi says, adding that the battery is sealed so people could wash the fabric with the battery still attached.

“I’m really impressed,” says Yi Cui, a battery researcher at Stanford University. The KAIST group has successfully put their batteries through much harsher mechanical tests than others have been able to, he says.

The next step, Cui says, is to use battery materials that can store more energy to further improve the performance. So far, the KAIST team has used lithium iron phosphate for the cathode and lithium titanium oxide for the anode. Cui says that using a carbon anode material in the textile battery would increase the battery’s voltage, which determines how much power the device can deliver and how fast it can recharge. The voltage of the textile battery is about 2.5 V, and Choi says it should be about 3.8 V for practical applications.

Indeed, Choi’s group is experimenting with other materials, in collaboration with an unnamed South Korean battery maker that is interested in scaling up production of the wearable batteries.

Chemical & Engineering News
ISSN 0009-2347
Copyright © 2013 American Chemical Society

Tetrapod Quantum Dots Light the Way to Stronger Polymers


Berkeley Lab Researchers Use Fluorescent Tetrapod Quantum Dots to Measure the Mechanical Strength of Polymer Fibers

qdot-images-3.jpgFluorescent tetrapod nanocrystals could light the way to the future design of stronger polymer nanocomposites. A team of researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) has developed an advanced opto-mechanical sensing technique based on tetrapod quantum dots that allows precise measurement of the tensile  strength of polymer fibers with minimal impact on the fiber’s mechanical properties.

In a study led by Paul Alivisatos, Berkeley Lab director and the Larry and Diane Bock Professor of Nanotechnology at the University of California (UC) Berkeley, the research team incorporated into polymer fibers a population of tetrapod quantum dots (tQDs) consisting of a cadmium-selenide (CdSe) core and four cadmium sulfide (CdS) arms. The tQDs were incorporated into the polymer fibers via electrospinning, among today’s leading techniques for processing polymers, in which a large electric field is applied to droplets of polymer solution to create micro- and nano-sized fibers. This is the first known application of electrospinning to tQDs.

 

Fluorescent tetrapod quantum dots or tQDs (brown) serve as stress probes that allow precise measurement of polymer fiber tensile strength with minimal impact on mechanical properties. Inserts show relaxed tQDs (upper) and stressed tQDs (lower).

“The electrospinning process allowed us to put an enormous amount of tQDs, up to 20-percent by weight, into the fibers with minimal effects on the polymer’s bulk mechanical properties,” Alivisatos says. “The tQDs are capable of fluorescently monitoring not only simple uniaxial stress, but stress relaxation and behavior under cyclic varying loads. Furthermore, the tQDs are elastic and recoverable, and undergo no permanent change in sensing ability even upon many cycles of loading to failure.”

Alivisatos is the corresponding author of a paper describing this research in the journal NANO Letters titledTetrapod Nanocrystals as Fluorescent Stress Probes of Electrospun Nanocomposites.” Coauthors were Shilpa Raja, Andrew Olson, Kari Thorkelsson, Andrew Luong, Lillian Hsueh, Guoqing Chang, Bernd Gludovatz, Liwei Lin, Ting Xu and Robert Ritchie.

From left, Andrew Olson, Shilpa Raja and Andrew Luong are members of Paul Alivisatos's research group who used electrospinning to incorporate tetrapod quantum dot stress probes into polymer fibers. (Photo by Roy Kaltschmidt)

From left, Andrew Olson, Shilpa Raja and Andrew Luong are members of Paul Alivisatos’s research group who used electrospinning to incorporate tetrapod quantum dot stress probes into polymer fibers. (Photo by Roy Kaltschmidt)

Polymer nanocomposites are polymers that contain fillers of nanoparticles dispersed throughout the polymer matrix. Exhibiting a wide range of enhanced mechanical properties, these materials have great potential for a broad range of biomedical and material applications. However, rational design has been hampered by a lack of detailed understanding of how they respond to stress at the micro- and nanoscale.

“Understanding the interface between the polymer and the nanofiller and how stresses are transferred across that barrier are critical in reproducibly synthesizing composites,” Alivisatos says. “All of the established techniques for providing this information have drawbacks, including altering the molecular-level composition and structure of the polymer and potentially weakening mechanical properties such as toughness. It has therefore been of considerable interest to develop optical luminescent stress-sensing nanoparticles and  find a way to embed them inside polymer fibers with minimal impact on the mechanical properties that are being sensed.”

The Berkeley Lab researchers met this challenge by combining semiconductor tQDs of CdSe/CdS, which were developed in an earlier study by Alivisatos and his research group, with electrospinning. The CdSe/CdS tQDs are exceptionally well-suited as nanoscale stress sensors because an applied stress will bend the arms of the tetrapods, causing a shift in the color of their fluorescence. The large electric field used in electrospinning results in a uniform dispersal of tQD aggregates throughout the polymer matrix, thereby minimizing the formation of stress concentrations that would act to degrade the mechanical properties of the polymer. Electrospinning also provided a much stronger bond between the polymer fibers and the tQDs than a previous diffusion-based technique for using tQDs as stress probes that was reported two years ago by Alivisatos and his group. Much higher concentrations of tQDs could also be a achieved with electrospinning rather than diffusion.

When stress was applied to the polymer nanocomposites, elastic and plastic regions of deformation were easily observed as a shift in the fluorescence of the tQDs even at low particle concentrations. As particle concentrations were increased, a  greater fluorescence shift per unit strain was observed. The tQDs acted as non-perturbing probes that tests proved were not adversely affecting the mechanical properties of the polymer fibers in any significant way.

“We performed mechanical tests using a traditional tensile testing machine with all of our types of polymer fibers,” says Shilpa Raja, a lead author of the Nano Letters paper along with Andrew Olson, both members of Alivisatos’ research group. “While the tQDs undoubtedly change the composition of the fiber – it is no longer pure polylactic acid but instead a composite – we found that the mechanical properties of the composite and crystallinity of the polymer phase show minimal change.”

The research team believes their tQD probes should prove valuable for a variety of biological, imaging and materials engineering applications.

“A big advantage in the development of new polymer nanocomposites would be to use tQDs to monitor stress build-ups prior to material failure to see how the material was failing before it actually broke apart,” says co-lead author Olson. “The tQDs could also help in the development of new smart materials by providing insight into why a composite either never exhibited a desired nanoparticle property or stopped exhibiting it during deformation from normal usage.”

For biological applications, the tQD is responsive to forces on the nanoNewton scale, which is the amount of force exerted by living cells as they move around within the body. A prime example of this is metastasizing cancer cells that move through the surrounding extracellular matrix. Other cells that exert force include the fibroblasts that help repair wounds, and cardiomyocytes, the muscle cells in the heart that beat.

“All of these types of cells are known to exert nanoNewton forces, but it is very difficult to measure them,” Raja says.

“We’ve done preliminary studies in which we have shown that cardiomyocytes on top of a layer of tQDs can be induced to beat and the tQD layer will show fluorescent shifts in places where the cells are beating. This could be extended to a more biologically-relevant environment in order to study the effects of chemicals and drugs on the metastasis of cancer cells.”

Another exciting potential application is the use of tQDs to make smart polymer nanocomposites that can sense when they have cracks or are about to fracture and can strengthen themselves in response.

“With our technique we are combining two fields that are usually separate and have never been combined on the nanoscale, optical sensing and polymer nanocomposite mechanical tunability,” Raja says. “As the tetrapods are incredibly strong, orders of magnitude stronger than typical polymers, ultimately they can make for stronger interfaces that can self-report impending fracture.”

This research was primarily supported by the DOE Office of Science.

#  #  #

Lawrence Berkeley National Laboratory addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit www.lbl.gov.

DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit the Office of Science website at science.energy.gov/.

 

Additional Information

For more about the research of Paul Alivisatos go here

Origami Form and Nanotechnology combine to advance batteries


Nanotubes images(Nanowerk News) A combination of nanotechnology and the  traditional art of paper folding, known as origami, could be a key to a  significant step toward improved battery technologies.
Arizona State University engineers have constructed a  lithium-ion battery using paper coated with carbon nanotubes that provide  electrical conductivity.
Using an origami-folding pattern similar to how maps are folded,  they folded the paper into a stack of 25 layers, producing a compact, flexible  battery that provides significant energy density – or the amount of energy  stored in a given system or space per unit of volume of mass.
foldable battery
The  above image illustrates the architecture of a foldable lithium-ion battery ASU  engineers have constructed using paper coated with carbon nanotubes. They began  with a porous, lint-free paper towel, coated it with polyvinylidene difluoride  to improve adhesion of carbon nanotubes and then immersed the paper into a  solution of carbon nanotubes. Powders of lithium titanate oxide and lithium  cobalt oxide – standard lithium battery electrodes – are sandwiched between two  sheets of the paper. Thin foils of copper and aluminum are placed above and  below the sheets of paper to complete the battery.
Their research paper in the journal Nano Letters (“Folding Paper-Based Lithium-Ion Batteries for  Higher Areal Energy Densities”) has drawn attention from websites that focus  on news of technological breakthroughs.
The researchers have also developed a new process to incorporate  a polymer binder onto the carbon nanotube-coated paper. The polymer binder  improves adhesion of the structure’s active materials.
The achievements open up possibilities of using the origami  technique to create new forms of paper-based energy storage devices, including  batteries, light-emitting diodes, circuits and transistors, says Candace Chan,  who led the research team.
Chan is an assistant professor of materials science and  engineering in the School for Engineering of Matter, Energy and Transport, one  of ASU’s Ira A. Fulton Schools of Engineering.
Fellow ASU engineering faculty members, associate professor  Hanqing Jiang and assistant professor Hongyu Yu, have played leading roles in  the work.
We have also covered this work in our Nanowerk Spotlight series  here: Nanotechnology  researchers fabricate foldable Li-ion batteries.
Source: Arizona State University

Read more: http://www.nanowerk.com/news2/newsid=32871.php#ixzz2ia63F79I

Inexpensive, Flexible Solar Cells: Rice & Penn State Collaborate


QDOTS imagesCAKXSY1K 8(Phys.org) —Work by a team of chemical engineers at Penn State and Rice University may lead to a new class of inexpensive organic solar cells.
chemicalengi

Work by a research team at Penn State and Rice University could lead to the development of flexible solar cells. The engineers’ technique centers on control of the nanostructure and morphology to create organic solar cells made of block polymers. Credit: Curtis Chan

Most solar cells today are inorganic and made of . The problem with these, Gomez explained, is that inorganic solar cells tend to be expensive, rigid and relatively inefficient when it comes to converting sunlight into electricity.

But offer an intriguing alternative that’s flexible and potentially less expensive.

Not many organic solar cells currently exist. He said, “There are a bunch of prototypes floating around. You see them in places like in solar-powered laptop bags and on the top of some bus depots.”

The problem is that the bulk of organic solar cells employ fullerene acceptors—a carbon-based molecule that’s extremely difficult to scale up for mass production.

Gomez’s approach skips the fullerene acceptor altogether and seeks to combine

The idea of utilizing molecular self-assembly for solar cells isn’t new, but Gomez said, “It’s not been well executed.”

He continued, “It’s like trying to mix oil and water.” The issue is that weak and disorder at junctions of different organic materials limited the performance and stability of previous organic solar cells.

But by controlling the and morphology, the team essentially redesigned the molecules to link together in a better way.

The engineers were able to control the donor-acceptor  through microphase-separated conjugated block copolymers.

“We have not only demonstrated control of the microstructure, but also control of the interface responsible for the initial steps in charge photogeneration in a way never achieved before,” Gomez said.

The result, which was detailed in a recent issue of the American Chemical Society‘s Nano Letters journal, is an organic solar cell made of that’s three percent efficient.

The team included Penn State chemical engineering graduate student Changhe Guo; undergraduate student Matt Witman; Rafael Verduzco, the Louis Owen Assistant Professor of Chemical and Biomolecular Engineering at Rice University; Joseph Strzalka, research scientist at Argonne National Laboratory; and research scientists Cheng Wang and Alexander Hexemer of Lawrence Berkeley National Laboratory.

Though the team’s prototype is not as efficient as some solar cells that are commercially available, Gomez explained the work shows flexible organic solar cells are indeed possible.

“Our cells right now don’t capture a lot of light. We need to look back and redesign the molecule. We think we can do better than 3 percent,” he said.

Read more at: http://phys.org/news/2013-08-chemical-inexpensive-flexible-solar-cells.html#jCpmolecules in a solution.

Tetrapod Quantum Dots Light the Way


QDOTS imagesCAKXSY1K 8Fluorescent tetrapod nanocrystals could light the way to the future design of stronger polymer nanocomposites. A team of researchers with the U.S. Dept. of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) has developed an advanced optomechanical sensing technique based on tetrapod quantum dots that allows precise measurement of the tensile strength of polymer fibers with minimal impact on the fiber’s mechanical properties.

In a study led by Paul Alivisatos, Berkeley Lab Dir. and the Larry and Diane Bock Prof. of Nanotechnology at the Univ. of California (UC) Berkeley, the research team incorporated into polymer fibers a population of tetrapod quantum dots (tQDs) consisting of a cadmium-selenide (CdSe) core and four cadmium-sulfide (CdS) arms. The tQDs were incorporated into the polymer fibers via electrospinning, among today’s leading techniques for processing polymers, in which a large electric field is applied to droplets of polymer solution to create micro- and nano-sized fibers. This is the first known application of electrospinning to tQDs.

Alivisatostetrapodx500

 

 

 

 

 

 

 

 

 

Fluorescent tetrapod quantum dots or tQDs (brown) serve as stress probes that allow precise measurement of polymer fiber tensile strength with minimal impact on mechanical properties. Inserts show relaxed tQDs  (upper) and stressed (lower).

Image:  LBN Laboratory.

“The electrospinning process allowed us to put an enormous amount of tQDs, up to 20% by weight, into the fibers with minimal effects on the polymer’s bulk mechanical properties,” Alivisatos says. “The tQDs are capable of fluorescently monitoring not only simple uniaxial stress, but stress relaxation and behavior under cyclic varying loads. Furthermore, the tQDs are elastic and recoverable, and undergo no permanent change in sensing ability even upon many cycles of loading to failure.”

Alivisatos is the corresponding author of a paper describing this research in NANO Letters. Co-authors were Shilpa Raja, Andrew Olson, Kari Thorkelsson, Andrew Luong, Lillian Hsueh, Guoqing Chang, Bernd Gludovatz, Liwei Lin, Ting Xu and Robert Ritchie.

Polymer nanocomposites are polymers that contain fillers of nanoparticles dispersed throughout the polymer matrix. Exhibiting a wide range of enhanced mechanical properties, these materials have great potential for a broad range of biomedical and material applications. However, rational design has been hampered by a lack of detailed understanding of how they respond to stress at the micro- and nanoscale.

“Understanding the interface between the polymer and the nanofiller and how stresses are transferred across that barrier are critical in reproducibly synthesizing composites,” Alivisatos says. “All of the established techniques for providing this information have drawbacks, including altering the molecular-level composition and structure of the polymer and potentially weakening mechanical properties such as toughness. It has therefore been of considerable interest to develop optical luminescent stress-sensing nanoparticles and find a way to embed them inside polymer fibers with minimal impact on the mechanical properties that are being sensed.”

The Berkeley Lab researchers met this challenge by combining semiconductor tQDs of CdSe/CdS, which were developed in an earlier study by Alivisatos and his research group, with electrospinning. The CdSe/CdS tQDs are exceptionally well-suited as nanoscale stress sensors because an applied stress will bend the arms of the tetrapods, causing a shift in the color of their fluorescence. The large electric field used in electrospinning results in a uniform dispersal of tQD aggregates throughout the polymer matrix, thereby minimizing the formation of stress concentrations that would act to degrade the mechanical properties of the polymer. Electrospinning also provided a much stronger bond between the polymer fibers and the tQDs than a previous diffusion-based technique for using tQDs as stress probes that was reported two years ago by Alivisatos and his group. Much higher concentrations of tQDs could also be achieved with electrospinning rather than diffusion.

When stress was applied to the polymer nanocomposites, elastic and plastic regions of deformation were easily observed as a shift in the fluorescence of the tQDs even at low particle concentrations. As particle concentrations were increased, a greater fluorescence shift per unit strain was observed. The tQDs acted as non-perturbing probes that tests proved were not adversely affecting the mechanical properties of the polymer fibers in any significant way.

“We performed mechanical tests using a traditional tensile testing machine with all of our types of polymer fibers,” says Shilpa Raja, a lead author of the Nano Letters paper along with Andrew Olson, both members of Alivisatos’ research group. “While the tQDs undoubtedly change the composition of the fiber—it is no longer pure polylactic acid but instead a composite—we found that the mechanical properties of the composite and crystallinity of the polymer phase show minimal change.”

The research team believes their tQD probes should prove valuable for a variety of biological, imaging and materials engineering applications.

“A big advantage in the development of new polymer nanocomposites would be to use tQDs to monitor stress build-ups prior to material failure to see how the material was failing before it actually broke apart,” says co-lead author Olson. “The tQDs could also help in the development of new smart materials by providing insight into why a composite either never exhibited a desired nanoparticle property or stopped exhibiting it during deformation from normal usage.”

For biological applications, the tQD is responsive to forces on the nanoNewton scale, which is the amount of force exerted by living cells as they move around within the body. A prime example of this is metastasizing cancer cells that move through the surrounding extracellular matrix. Other cells that exert force include the fibroblasts that help repair wounds, and cardiomyocytes, the muscle cells in the heart that beat.

“All of these types of cells are known to exert nanoNewton forces, but it is very difficult to measure them,” Raja says.

“We’ve done preliminary studies in which we have shown that cardiomyocytes on top of a layer of tQDs can be induced to beat and the tQD layer will show fluorescent shifts in places where the cells are beating. This could be extended to a more biologically-relevant environment in order to study the effects of chemicals and drugs on the metastasis of cancer cells.”

Another exciting potential application is the use of tQDs to make smart polymer nanocomposites that can sense when they have cracks or are about to fracture and can strengthen themselves in response.

“With our technique we are combining two fields that are usually separate and have never been combined on the nanoscale, optical sensing and polymer nanocomposite mechanical tunability,” Raja says. “As the tetrapods are incredibly strong, orders of magnitude stronger than typical polymers, ultimately they can make for stronger interfaces that can self-report impending fracture.”

Source: Lawrence Berkeley National Laboratory

A nanotechnology holy grail in label-free cancer marker detection: Single molecules


QDOTS imagesCAKXSY1K 8(Nanowerk News) Just months after setting a record for  detecting the smallest single virus in solution, researchers at the Polytechnic  Institute of New York University (NYU-Poly) have announced a new breakthrough:  They used a nano-enhanced version of their patented microcavity biosensor to  detect a single cancer marker protein, which is one-sixth the size of the  smallest virus, and even smaller molecules below the mass of all known markers.  This achievement shatters the previous record, setting a new benchmark for the  most sensitive limit of detection, and may significantly advance early disease  diagnostics.  Unlike current technology, which attaches a fluorescent molecule,  or label, to the antigen to allow it to be seen, the new process detects the  antigen without an interfering label.
Stephen Arnold, university professor of applied  physics and member of the Othmer-Jacobs Department of Chemical and Biomolecular  Engineering, published details of the achievement in Nano Letters (“Label-Free Detection of Single Protein Using a  Nanoplasmonic-Photonic Hybrid Microcavity”), a publication of the American  Chemical Society.
nanoshell
The  detection of single thyroid cancer marker (Thyroglobulin, Tg) and bovine serum  albumin (BSA) proteins with masses of only 1 ag and 0.11 ag (66 kDa),  respectively.
In 2012, Arnold and his team were able to detect in solution the  smallest known RNA virus, MS2, with a mass of 6 attograms. Now, with  experimental work by postdoctoral fellow Venkata Dantham and former student  David Keng, two proteins have been detected: a human cancer marker protein  called Thyroglobulin, with a mass of just 1 attogram, and the bovine form of a  common plasma protein, serum albumin, with a far smaller mass of 0.11 attogram.  “An attogram is a millionth of a millionth of a millionth of a gram,” said  Arnold, “and we believe that our new limit of detection may be smaller than 0.01  attogram.”
This latest milestone builds on a technique pioneered by Arnold  and collaborators from NYU-Poly and Fordham University.  In 2012, the  researchers set the first sizing record by treating a novel biosensor with  plasmonic gold nano-receptors, enhancing the electric field of the sensor and  allowing even the smallest shifts in resonant frequency to be detected. Their  plan was to design a medical diagnostic device capable of identifying a single  virus particle in a point-of-care setting, without the use of special assay  preparations.
At the time, the notion of detecting a single  protein—phenomenally smaller than a virus—was set forth as the ultimate goal.
Proteins run the body,” explained Arnold. “When the immune  system encounters virus, it pumps out huge quantities of antibody proteins, and  all cancers generate protein markers. A test capable of detecting a single  protein would be the most sensitive diagnostic test imaginable.”
To the surprise of the researchers, examination of their  nanoreceptor under a transmission electron microscope revealed that its gold  shell surface was covered with random bumps roughly the size of a protein.  Computer mapping and simulations created by Stephen Holler, once Arnold’s  student and now assistant professor of physics at Fordham University, showed  that these irregularities generate their own highly reactive local sensitivity  field extending out several nanometers, amplifying the capabilities of the  sensor far beyond original predictions. “A virus is far too large to be aided in  detection by this field,” Arnold said. “Proteins are just a few nanometers  across—exactly the right size to register in this space.”
The implications of single protein detection are significant and  may lay the foundation for improved medical therapeutics.  Among other advances,  Arnold and his colleagues posit that the ability to follow a signal in real  time—to actually witness the detection of a single disease marker protein and  track its movement—may yield new understanding of how proteins attach to  antibodies.
Arnold named the novel method of label-free detection  “whispering gallery-mode biosensing” because light waves in the system reminded  him of the way that voices bounce around the whispering gallery under the dome  of St. Paul’s Cathedral in London. A laser sends light through a glass fiber to  a detector. When a microsphere is placed against the fiber, certain wavelengths  of light detour into the sphere and bounce around inside, creating a dip in the  light that the detector receives. When a molecule like a cancer marker clings to  a gold nanoshell attached to the microsphere, the microsphere’s resonant  frequency shifts by a measureable amount.
The research has been supported by a grant from the National  Science Foundation (NSF). This summer, Arnold will begin the next stage of  expanding the capacity for these biosensors. The NSF has awarded a new $200,000  grant to him in collaboration with University of Michigan professor Xudong Fan.  The grant will support the construction of a multiplexed array of plasmonically  enhanced resonators, which should allow a variety of protein to be identified in  blood serum within minutes.
Source: Polytechnic Institute of New York  University

Read more: http://www.nanowerk.com/news2/newsid=31508.php#ixzz2aO4P2QPW

Improved colloidal quantum dots to make solar cells more efficient


QDOTS imagesCAKXSY1K 8A new technique developed by University of Toronto Engineering Professor Ted Sargent and his research group could lead to significantly more efficient solar cells.

 

In a paper published in the journal Nano Letters, the group describes a new technique to improve efficiency in what are called colloidal quantum dot photovoltaics. It’s a technology that already promises inexpensive and more efficient solar cell technology.

QuantumDotCell

A Quantum Cell

But researchers say such devices could be even more effective if they could better harness the infrared portion of the sun’s spectrum, which is responsible for half of the sun’s power that reaches the Earth.

The solution has an unwieldy name: spectrally tuned, solution-processed plasmonic nanoparticles. These particles, researchers say, provide unprecedented control over light’s propagation and absorption.

The new technique developed by Sargent’s group shows a possible 35% increase in the technology’s efficiency in the near-infrared spectral region, says co-author Susanna Thon (pictured left). Overall, this could translate to an 11% solar power conversion efficiency increase, she says, making quantum dot photovoltaics even more attractive as an alternative to current solar cell technologies.

“There are two advantages to colloidal quantum dots,” Thon says. “First, they’re much cheaper, so they reduce the cost of electricity generation measured in cost per watt of power. But the main advantage is that by simply changing the size of the quantum dot, you can change its light-absorption spectrum.

“Changing the size is very easy, and this size-tunability is a property shared by plasmonic materials: by changing the size of the plasmonic particles, we were able to overlap the absorption and scattering spectra of these two key classes of nanomaterials.”

Sargent’s group achieved the increased efficiency by embedding gold nanoshells directly into the quantum dot absorber film. Gold is not usually thought of as an economical material but researchers say lower-cost metals can be used to implement the same concept proved by Thon and her co-workers.

The current research provides a proof of principle, says Thon.

“People have tried to do similar work but the problem has always been that the metal they use also absorbs some light and doesn’t contribute to the photocurrent—so it’s just lost light.”

More work needs to be done, she adds.

“We want to achieve more optimization, and we’re also interested in looking at cheaper metals to build a better cell. We’d also like to better target where photons are absorbed in the cell—this is important photovoltaics because you want to absorb as many photons as you can as close to the charge collecting electrode as you possibly can.”

The research is also important because it shows the potential of tuning nanomaterial properties to achieve a certain goal, says Paul Weiss, Director of the California NanoSystems Institute at the University of California, Los Angeles (UCLA).

“This work is a great example of fulfilling the promise of nanoscience and nanotechnology,” Weiss says. “By developing the means to tune the properties of nanomaterials, Sargent and his co-workers have been able to make significant improvements in an important device function, namely capturing a broader range of the solar spectrum more effectively.”

Jointly-tuned plasmonic-excitonic photovoltaics using nanoshells

Source: University of Toronto

U of Toronto breakthrough promises more efficient solar cells


QDOTS imagesCAKXSY1K 8TORONTO, ON – A new technique developed by University of Toronto Engineering Professor Ted Sargent and his research group could lead to significantly more efficient solar cells, according to a recent paper published in the journal Nano Letters.

The paper, “Jointly-tuned plasmonic-excitonic photovoltaics using nanoshells,” describes a new technique to improve efficiency in colloidal quantum dot photovoltaics, a technology which already promises inexpensive, more efficient solar cell technology. Quantum dot photovoltaics offers the potential for low-cost, large-area solar power – however these devices are not yet highly efficient in the infrared portion of the sun’s spectrum, which is responsible for half of the sun’s power that reaches the Earth.

The solution? Spectrally tuned, solution-processed plasmonic nanoparticles. These particles, the researchers say, provide unprecedented control over light’s propagation and absorption.

The new technique developed by Sargent’s group shows a possible 35 per cent increase in the technology’s efficiency in the near-infrared spectral region, says co-author Dr. Susanna Thon. Overall, this could translate to an 11 per cent solar power conversion efficiency increase, she says, making quantum dot photovoltaics even more attractive as an alternative to current solar cell technologies.

“There are two advantages to colloidal quantum dots,” Thon says. “First, they’re much cheaper, so they reduce the cost of electricity generation measured in cost per watt of power. But the main advantage is that by simply changing the size of the quantum dot, you can change its light-absorption spectrum. Changing the size is very easy, and this size-tunability is a property shared by plasmonic materials: by changing the size of the plasmonic particles, we were able to overlap the absorption and scattering spectra of these two key classes of nanomaterials.”

Sargent’s group achieved the increased efficiency by embedding gold nanoshells directly into the quantum dot absorber film. Though gold is not usually thought of as an economical material, other, lower-cost metals can be used to implement the same concept proved by Thon and her co-workers.

She says the current research provides a proof of principle. “People have tried to do similar work but the problem has always been that the metal they use also absorbs some light and doesn’t contribute to the photocurrent – so it’s just lost light.”

More work needs to be done, she adds. “We want to achieve more optimization, and we’re also interested in looking at cheaper metals to build a better cell. We’d also like to better target where photons are absorbed in the cell – this is important photovoltaics because you want to absorb as many photons as you can as close to the charge collecting electrode as you possibly can.”

The research is also important because it shows the potential of tuning nanomaterial properties to achieve a certain goal, says Paul Weiss, Director of the California NanoSystems Institute.

“This work is a great example of fulfilling the promise of nanoscience and nanotechnology,” Weiss says. “By developing the means to tune the properties of nanomaterials, Sargent and his co-workers have been able to make significant improvements in an important device function, namely capturing a broader range of the solar spectrum more effectively.”

Nanoparticles Split Water, Power Fuel Cell


QDOTS imagesCAKXSY1K 8Si Nanoparticles Split Water, Power Fuel Cell

by Tim Palucka

Materials Research Society | Published: 29 January 2013

Generating electricity in the field to power a laptop or night vision goggles could someday be just as simple as adding water to a cartridge containing silicon nanoparticles and a base. Researchers at the University at Buffalo (SUNY) have demonstrated that nanoparticles of Si in a basic solution can split water to release hydrogen and power a portable fuel cell to produce electricity. The ability to split water on-demand without adding heat, light, or electricity to the system could be a significant advance in fuel cell technology.

TEM 10 nm SI - Hydrogen“The reaction rate with these very small 10-nm Si particles is so much faster than with the relatively large 100 nm Si particles,” says Mark Swihart, whose team published their results in a recent issue of ACS Nano Letters. “Because of this fast reaction rate and the fact that there’s no delay between when you add water and when the reaction starts, it makes the technology at least practical in terms of being able to power a device instantaneously.”

 

While there was some scant evidence in the scientific literature that Si could perform this feat of splitting water to release hydrogen, it was largely ignored because the reaction rate was so slow as to be uninteresting. Using Al, Zn, or metal hydrides for this purpose looked so much more promising that Si fell by the wayside.

But Swihart and his group have been working with Si nanoparticles for more than a decade, mostly in the realm of quantum dot research. In doing so, they frequently had to use a base such as hydrazine for etching, and they noticed that hydrogen was released when aqueous hydrazine reacted with Si. Investigation showed that the hydrogen came not from decomposition of hydrazine, but from the oxidation of Si to release hydrogen from water.

Further investigation of the reaction using Si particles of different sizes, focusing on 10-nm and 100-nm-diameter particles with aqueous KOH, showed a particle size dependent liberation of hydrogen from water. But the factor of 150 increase in the reaction rate for the 10-nm-diameter particles compared to the 100-nm-particles was well in excess of the factor of 6 difference in their specific surface area. Thus, the increase in rate is much greater than expected based on increased surface area alone.

Swihart believes the difference is caused by geometry, not surface area. The 111 lattice planes etch much more slowly than other planes of Si, so crystals terminated entirely by 111 planes react slowly.  “The 10 nm particles etch isotropically—they just get smaller and go away,” he says. There’s no time for faceting to occur in this case. But the 100 nm particles undergo anisotropic etching. The faster-reacting 100 and 110 planes etch away first, leaving a particle with slower-reacting 111 planes behind in what he describes as a “hollow nano-balloon structure.” “With the bigger particles,” Swihart says, “eventually the unreactive 111 surfaces are the ones that end up being left,” thus slowing the reaction rate.

As a proof-of-concept, the research team tested a small fuel cell with a 20 stack polymer electrolyte membrane, comparing the fuel cell’s power output when fed hydrogen from the Si nanoparticle reaction versus hydrogen from a gas cylinder. Stoichiometrically, two moles of H2 should be generated for one mole of Si. In the tests, the fuel cell powered by H2 generated by reaction with Si produced more current and voltage than when the fuel cell was fed a stoichiometric amount of H2 from a gas cylinder. The difference is due to additional hydrogen, beyond the stoichiometric reaction amount, that terminates the Si surfaces after fabrication of the nanoparticles.

While there is much more work to be done, Swihart believes that if this technology is ever to become practical as a portable electricity generator, the KOH (or other base) would have to be mixed in with the Si in a cartridge, so you would not have to carry around a bottle of KOH solution. Such a device would come with the instructions “just add water.” For a soldier in the field needing to power night vision goggles, water from a nearby stream could be all he needs.

 

Read the abstract in ACS Nano Letters  here.