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.

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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

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Nano-Materials Company Engineers Tetrapod Quantum Dots to Improve Diagnostic Accuracy of Biomedical Assays and Devices


201306047919620SAN MARCOS, Texas, Nov. 7, 2013 /PRNewswire/ — Quantum Materials Corp. announced today that it has provided Tetrapod Quantum Dots (TQD) to an advanced medical device manufacturer to optimize performance of an “engineered spectrum” quantum dot-enabled light source to better provide useful data to researchers and practitioners that has not been easily discernible until now.

David Doderer, Vice President of R&D, explained, “We are fulfilling specific requests for  tetrapod quantum dots, in this case,  to create tailored light for investigation of tissue.  Differences between healthy and suspect tissue often can be better identified if the available fluorophores’ color combination is engineered for either true representation of color, or emphasized in the visible spectrum depending on the tissue type. I think our bespoke tetrapod quantum dots provide the depth of data necessary to highlight subtle differences that researchers and healthcare professionals need to efficiently understand disease and devise effective treatments.”

To achieve efficient healthcare in an increasingly demanding marketplace, the ability to get actionable information is crucial. Medical diagnostic assays currently count in the multi-millions per year and per country, and differences in tissues types at the cellular level are critically important for accuracy in results.  Conventional organic dyes and other types of fluorophores are currently used for luminescence in assays by researchers, but they have limitations sometimes preventing clear distinctions in reading the data. Broad data sets can tend to obscure patterns that might become clear by removing these uncertainties.

Tetrapod quantum dots address this issue well for biochemical detection and biomedical device application by providing a broad array of colors, which translates to increased number of pieces in the data set, and also precise tune-ability and stability for high contrast and distinctive identification certainty.  For biochemical detection, most typically in a rapid assay that provides a breadth of data in a single test kit, Quantum Materials has begun conversations with biotech researchers and companies needing narrow color emissions to provide clear identification when identifying particular targets by attaching to the desired organism or cell type when specifically functionalized.

As part of this effort, the Company is developing a suitable TQD film for medical devices while maintaining consistency in both uniformity and scalability. The Company believes this technology, one of several under review, could also successfully translate into Tetrapod Quantum Dot film applications such as general light applications, electronic displays and quantum dot solar cells.

 

 

 

 

Quantum Materials Corp. manufactures Tetrapod Quantum Dots for use in medical, display, solar energy and lighting applications through patent pending continuous-flow production process.  Quantum dot semiconductors enable a new level of engineered performance in a wide array of established consumer and industrial products. QMC’s volume manufacturing methods enable consistent QD quality and scalable cost reductions to drive innovative discovery to commercial success.

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This press release contains forward-looking statements that involve risks and uncertainties concerning business, products, and financial results. Actual results may differ materially from the results predicted. More information about potential risk factors that could affect our business, products, and financial results are included in our annual report and in reports subsequently filed with the Securities and Exchange Commission (“SEC”). All documents are available through the SEC’s EDGAR System at http://www.sec.gov/ or www.QMCdots.com. We hereby disclaim any obligation to publicly update the information provided above, including forward-looking statements, to reflect subsequent events or circumstances.

Mass producing pocket labs


mix-id328072.jpg(Nanowerk News) There is certainly no shortage of  lab-on-a-chip (LOC) devices, but in most cases manufacturers have not yet found  a cost-effective way to mass produce them. Scientists are now developing a  platform for series production of these pocket laboratories.
Ask anyone to imagine what a chemical analysis laboratory looks  like, and most will picture the following scene: a large room filled with  electrical equipment, extractor hoods and chemical substances, in which  white-robed researchers are busy unlocking the secrets behind all sorts of  scientific processes. But there are also laboratories of a very different kind,  for instance labs-on-a-chip (LOCs). These “pocket labs” are able to  automatically perform a complete analysis of even the tiniest liquid samples,  integrating all the required functions onto a chip that’s just a few centimeters  long. Experts all over the world have developed many powerful LOC devices in  recent years, but very few pocket labs have made it onto the market.
Scientists at the Fraunhofer Institute for Production Technology  IPT in Aachen want to find out why so many LOCs are not a commercial success.  They are working with colleagues from polyscale GmbH & Co. KG, an IPT  spin-off, and ten other industrial partners from Germany, Finland, Spain, the  United Kingdom, France and Italy on ways to make LOCs marketable. Their ML²  project is funded by the EU’s Seventh Framework Programme (FP7), which is  providing a total of 7.69 million euros in funding through fall 2016.
“One of the main reasons LOCs don’t make it to market is that  the technologies used to fabricate them are often not transferrable to  industrial-scale production,” says Christoph Baum, group manager at the IPT.  What’s more, it is far from easy to integrate electrical functions into pocket  labs, and of the approaches taken to date, none has yet proved suitable for mass  production.
Microfluidic negative for structuring films
Microfluidic negative for structuring films. (© Fraunhofer IPT)
Platform for series production
The ML² project aims to completely revise the way pocket labs  are made so they are more suited to series production. “Our objective is to  create a design and production platform that will enable us to manufacture all  the components we need,” says Baum. This includes producing the tiny channel  structures within which liquids flow and react with each other, and coating the  surfaces so that bioactive substances can bond with them. Then there are optical  components, and electrical circuits for heating the channels, for example. The  experts apply each of these components to individual films that are then  assembled to form the complete “laboratory”. The films are connected to one  another via vertical channels machined through the individual layers using a  laser.
The first step the researchers have taken is to adapt and modify  the manufacturing process for each layer to suit mass-production requirements.  When it comes to creating the channel structures, the team has moved away from  the usual injection molding or wet chemical processing techniques in favor of  roll-to-roll processing. This involves transferring the negative imprint of the  channels onto a roller to create an embossing cylinder that then imprints a  pattern of depressions on a continuous roll of film. The electrical circuits are  printed onto film with an inkjet printer using special ink that contains copper  or silver nanoparticles.
Each manufacturing stage is fine-tuned by the researchers in the  process of producing a number of demonstrator LOCs – for instance a pregnancy  test with a digital display. These tests are currently produced in low-wage  countries, but with increased automation set to slash manufacturing costs by up  to 50 percent in future, production would once again be commercially viable in a  high-wage country such as Germany. The team aims to have all the demonstrators  built and the individual manufacturing processes optimized by 2014. Then it will  be a case of fitting the various steps in the manufacturing process together,  making sure they match up, and implementing the entire sequence on an industrial  scale.
Source: Fraunhofer-Gesellschaft

Read more: http://www.nanowerk.com/news2/newsid=32868.php#ixzz2iaAobyHm

Graphene Mass Production, Roll to Roll


Nano Particles for Steel 324x182Graphene, the lightest and thinnest compound known to man at one atom thick, has several amazing and unique properties that make it a very interesting candidate for many futuristic applications. However, its use is presently limited due to a bottleneck in its synthesis and mass production, which are still at an infant stage and expensive.

The project, which is being funded with 10.5 million euros over four years, aims to develop the first roll-based chemical vapour deposition (CVD) machine for the mass production of few-layer graphene for transparent electrodes for LED and display applications, and adapts the process conditions of a wafer-scale carbon nanotube growth system to provide a low-cost batch process for graphene growth on silicon. The project focuses on applications such as transparent electrodes for OLEDs and GaN LEDs, optical switches, plasmonic waveguides, VLSI interconnects, and RF NEMs.

Due to its high carrier mobility,  long ballistic mean free path, a high frequency photoconductivity, and a large thermal conductivity, graphene is being considered as a component in  next-generation electronic, optoelectronics and microsystems. Production of graphene is possible by four main methods, and prototype devices based on graphene (eg. field effect transistors, photo-transistors and detectors, and transparent electrodes for touch screens,) have been demonstrated with very promising results. GRAFOL aims to turn an emerging technology, the on-substrate synthesis of graphene, into a large-scale production technology available to industry as shown conceptually in the figure.

 

The project aims to develop the first roll-based chemical vapour deposition (CVD) machine for the mass production of few-layer graphene for transparent electrodes for LED and display applications, and

(Photo : GRAFOL) The project aims to develop the first roll-based chemical vapour deposition (CVD) machine for the mass production of few-layer graphene for transparent electrodes for LED and display applications, and adapts the process conditions of a wafer-scale carbon nanotube growth system to provide a low-cost batch process for graphene growth on silicon.

It is important to realize that the advancement of microelectronics today is not only due to the shrinking of device dimensions, which nano-materials allow, but also to the enlargement of wafer size (the unit of measure for production).  The increase of wafer diameter from 50mm in 1970’s to 300mm in early 2000’s, corresponding to a  36 fold increase in area, has made it much more cost effective to manufacture  microelectronics, quite simply because more chips are made simultaneously. It is quoted by  semiconductor companies, that for graphene to be seriously considered for microelectronics, it must be  on at least the 300mm wafer scale, on Si and attain a life cycle production cost (taking into  account source materials, running costs, equipment depreciation) of $1 per square inch of  deposited area on a substrate. Such a competitive cost can only be achieved if the area of graphene  deposited is increased per run, that is, scaling the production to at  least a 300mm wafer scale (another wafer size transition to 450mm is expected towards the end of this decade).

Taking it one step further, for certain applications such as transparent electrodes graphene should be produced in even larger scale than that required for microelectronics. This  truly large-scale production of graphene would become possible with a successful development of roll-based technology.

Despite its attractive properties, graphene will not yet be used in mainstream electronic applications due to two technological obstacles, namely (1) mass production and (2) device integration. Device integration deals with aspects such as physical integration and process integration (material compatibility, thermal budget). Mass production must use the route of chemical vapour deposition (CVD) onto metal surfaces. To tackle mass production, equipment must be developed which addresses economical manufacturing (yield, throughput, equipment reliability and maintainability) as well as quality assurance (process qualification, material consistency /standard characteristics, monitoring). These obstacles are dealt with in this project.

The value-added / high tech applications developed here have been carefully selected to require graphene on surfaces, and to be those which truly benefit from not only the high specifications but also cost effective production of graphene when deposited on the wafer-scale or by a roll-based method.

GRAFOL  started in October 2011, and will run for 4 years. The coordinator is  the University of Cambridge, led by professor John Robertson. Professor  Robertson leads a team of 14 partners, consisting of both academic  research labs as well as businesses like ours. The project benefits from  expertise of the likes of Aixtron (one of the world’s largest  manufacturers of CVD machines, based in Aachen, Germany), Philips, Thales, and Intel. Financing  comes from the European Union’s FP7 research framework, under the  research theme “Nanosciences, nanotechnologies, materials  and new production technologies”, which focuses on projects with a  strong industrial impact. — Graphenea

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Continuous Flow Synthesis Method for Fluorescent Quantum Dots


NANOSPHERESQuantum dots have potential applications in fields as diverse as medicine, photovoltaics, and quantum computing. The Center for Applied Nanotechnology (CAN) in Hamburg are making great strides in making high quality quantum dots available for research and large-scale production.

Quantum dots are nano-scale particles of semiconductor material, which are so small that quantum effects start to directly affect the particles’ electrical, optical and magnetic properties. This has many interesting implications on a larger scale – for example, fluorescent quantum dots can be designed which emit different colors depending only on their size.

The properties of quantum dots have been investigated in labs to a fairly high degree, so current research is focusing on very challenging applications, or on bringing the technology into the commercial realm.

This rapid development puts greater and greater demands on the quality of the nanoparticles – a challenge which CAN is rising to with a continuous-flow production method for their CANdots® product range. Daniel Ness from CAN explains the benefits of this technique:

“Some of our nanoparticle products, including the new Series A nanoparticles with visible-range fluorescence, use our continuous-flow synthetic method. This replaces more conventional batch synthesis, and greatly improves the reproducibility of the product, as well as being much easier to scale to higher production volumes.

“The process is also less dependent on highly trained technicians, as the parameters are easier to control. We are now working on adapting this process for our other CANdots® products, and we have a patent pending on the process itself.”

 

CAN’s new product, Series A Plus, are fluorescent quantum dots made of CdSe, with applications in LEDs and solid state lighting, single particle spectroscopy and as markers for biological imaging. They were launched at the 2013 NSTI Nanotech Expo in Washington.

Daniel Ness, CAN

The CANdots® range covers many more types of quantum dots and nanocrystals, including Series C NIR/IR emitters based on PbS, and Series X rare-earth doped quantum dots with distinctive emission features ideal for tagging and security labelling.

CAN was founded in 2005 as a spin-out from the University of Hamburg, focused on the transfer of their expertise in the production of nanomaterials from research into industry. The center is working with an array of companies and universities to design and develop new nanotechnology products.

CAN are currently seeking industrial partners to work on scale-up of their continuous flow nanoparticle production process, particularly for applications in photovoltaics, LEDs, and life sciences.

                Date Added: May 30, 2013                                 | Updated: Aug 19, 2013