Plastic electronics made easy

QDOTS imagesCAKXSY1K 8(Nanowerk News)  Scientists have discovered a way to  better exploit a process that could revolutionise the way that electronic  products are made.
The scientists from Imperial College London say improving the  industrial process, which is called crystallisation, could revolutionise the way  we produce electronic products, leading to advances across a whole range of  fields; including reducing the cost and improving the design of plastic solar  cells.
The process of making many well-known products from plastics  involves controlling the way that microscopic crystals are formed within the  material. By controlling the way that these crystals are grown engineers can  determine the properties they want such as transparency and toughness.  Controlling the growth of these crystals involves engineers adding small amounts  of chemical additives to plastic formulations. This approach is used in making  food boxes and other transparent plastic containers, but up until now it has not  been used in the electronics industry.
The team from Imperial have now demonstrated that these  additives can also be used to improve how an advanced type of flexible circuitry  called plastic electronics is made.
The team found that when the additives were included in the  formulation of plastic electronic circuitry they could be printed more reliably  and over larger areas, which would reduce fabrication costs in the industry.
The team reported their findings this month in the journal  Nature Materials (“Microstructure formation in molecular and polymer  semiconductors assisted by nucleation agents”).
Dr Natalie Stingelin, the leader of the study from  the Department of Materials and Centre of Plastic Electronics at Imperial, says:
“Essentially, we have demonstrated a simple way to gain control  over how crystals grow in electrically conducting ‘plastic’ semiconductors. Not  only will this help industry fabricate plastic electronic devices like solar  cells and sensors more efficiently. I believe it will also help scientists  experimenting in other areas, such as protein crystallisation, an important part  of the drug development process.”
Dr Stingelin and research associate Neil Treat looked at two  additives, sold under the names IrgaclearÒ XT 386 and MilladÒ 3988, which are  commonly used in industry. These chemicals are, for example, some of the  ingredients used to improve the transparency of plastic drinking bottles. The  researchers experimented with adding tiny amounts of these chemicals to the  formulas of several different electrically conducting plastics, which are used  in technologies such as security key cards, solar cells and displays.
The researchers found the additives gave them precise control  over where crystals would form, meaning they could also control which parts of  the printed material would conduct electricity. In addition, the  crystallisations happened faster than normal. Usually plastic electronics are  exposed to high temperatures to speed up the crystallisation process, but this  can degrade the materials. This heat treatment treatment is no longer necessary  if the additives are used.
Another industrially important advantage of using small amounts  of the additives was that the crystallisation process happened more uniformly  throughout the plastics, giving a consistent distribution of crystals.  The team  say this could enable circuits in plastic electronics to be produced quickly and  easily with roll-to-roll printing procedures similar to those used in the  newspaper industry. This has been very challenging to achieve previously.
Dr Treat says: “Our work clearly shows that these additives are  really good at controlling how materials crystallise. We have shown that printed  electronics can be fabricated more reliably using this strategy. But what’s  particularly exciting about all this is that the additives showed fantastic  performance in many different types of conducting plastics. So I’m excited about  the possibilities that this strategy could have in a wide range of materials.”
Dr Stingelin and Dr Treat collaborated with scientists from the  University of California Santa Barbara, and the National Renewable Energy  Laboratory in Golden, US, and the Swiss Federal Institute of Technology on this  study. The team are planning to continue working together to see if subtle  chemical changes to the additives improve their effects – and design new  additives.
They will be working with the new Engineering and Physical  Sciences Research Council (EPSRC)-funded Centre for Innovative Manufacturing in  Large Area Electronics in order to drive the industrial exploitation of their  process. The £5.6 million of funding for this centre, to be led by researchers  from Cambridge University, was announced earlier this year. They are also  exploring collaborations with printing companies with a view to further  developing their circuit printing technique.
Controlling crystals
Here are some of the technologies that could benefit from Drs  Treat and Stingelin’s research:
Improving drugs
Most drugs work by blocking or activating proteins in our  bodies. To develop better drugs, scientists must understand what these proteins  look like. The work carried out by the Imperial team could enable researchers in  the future to develop more accurate models of proteins, by converting them into  a crystalline form.
More efficient solar technology
Solar cells are made from a solid mixture of electrically  conducting crystalline chemicals. Currently these cells only convert about 10%  of the Sun’s energy into electricity. Dr Treat and Stingelin’s additives may  provide a way of improving crystal growth in solar cells, which could improve  the amount of energy they convert.
New flexible electronics
Flexible semiconductor films can be made by methods such as  inkjet printing. Using additives that control how inkjet-printed droplets of  semiconductors crystallise will mean they crystallise in evenly distributed  patterns that conduct electricity efficiently. This means industry can produce  these printed electronics more easily and cheaply.
Source: By Joshua Howgego, Imperial College London

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Why the Shape of Nanoparticles Matters

QDOTS imagesCAKXSY1K 8(Nanowerk News) Conventional treatments for diseases  such as cancer can carry harmful side effects—and the primary reason is that  such treatments are not targeted specifically to the cells of the body where  they’re needed. What if drugs for cancer, cardiovascular disease, and other  diseases can be targeted specifically and only to cells that need the medicine,  and leave normal tissues untouched?  
A new study involving Sanford-Burnham’s Erkki Ruoslahti, M.D.,  Ph.D., contributing to work by Samir Mitragotri, Ph.D., at the University of  California, Santa Barbara, found that the shape of nanoparticles can enhance  drug targeting. The study, published in Proceedings of the National Academy  of Sciences (“Using shape effects to target antibody-coated  nanoparticles to lung and brain endothelium”), found that rod-shaped  nanoparticles—or nanorods—as opposed to spherical nanoparticles, appear to  adhere more effectively to the surface of endothelial cells that line the inside  of blood vessels.
“While nanoparticle shape has been shown to impact cellular  uptake, the latest study shows that specific tissues can be targeted by  controlling the shape of nanoparticles. Keeping the material, volume, and the  targeting antibody the same, a simple change in the shape of the nanoparticle  enhances its ability to target specific tissues,” said Mitragotri.
“The elongated particles are more effective,” added Ruoslahti.  “Presumably the reason is that if you have a spherical particle and it has  binding sites on it, the curvature of the sphere allows only so many of those  binding sites to interact with membrane receptors on the surface of a cell.”
In contrast, the elongated nanorods have a larger surface area  that is in contact with the surface of the endothelial cells. More of the  antibodies that coat the nanorod can therefore bind receptors on the surface of  endothelial cells, and that leads to more effective cell adhesion and more  effective drug delivery.
Testing targeted nanoparticles
Mitragotri’s lab tested the efficacy of  rod-shaped nanoparticles in synthesized networks of channels called “synthetic  microvascular networks,” or SMNs, that mimic conditions inside blood vessels.  The nanoparticles were also tested in vivo in animal models, and separately in  mathematical models.
The researchers also found that nanorods targeted to lung tissue  in mice accumulated at a rate that was two-fold over nanospheres engineered with  the same targeting antibody. Also, enhanced targeting of nanorods was seen in  endothelial cells in the brain, which has historically been a challenging organ  to target with drugs.
Nanoparticles already used in some cancer drugs
Nanoparticles have been studied as vessels to carry drugs  through the body. Once they are engineered with antibodies that bind to specific  receptors on the surface of targeted cells, these nanoparticles also can, in  principle, become highly specific to the disease they are designed to treat.
Ruoslahti, a pioneer in the field of cell adhesion—how cells  bind to their surroundings—has developed small chain molecules called peptides  that can be used to target drugs to tumors and atherosclerotic plaques.
Promising results
“Greater specific attachment exhibited by rod-shaped particles  offers several advantages in the field of drug delivery, particularly in the  delivery of drugs such as chemotherapeutics, which are highly toxic and  necessitate the use of targeted approaches,” the authors wrote in their paper.
The studies demonstrate that nanorods with a high aspect ratio  attach more effectively to targeted cells compared with spherical nanoparticles.  The findings hold promise for the development of novel targeted therapies with  fewer harmful side effects.
Source: Sanford-Burnham Medical Research Institute 

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Nano-rod solar cell generates hydrogen

QDOTS imagesCAKXSY1K 8A new type of solar collector that uses gold nano-rods could convert sunlight into energy without many of the problems associated with traditional photovoltaic solar cells.

24 February 2013 Will Parker


The developers of the new technique, from the University of California – Santa Barbara, say it is “the first radically new and potentially workable alternative to semiconductor-based photovoltaic devices to be developed in the past 70 years.” They provide details of the new solar hydrogen generator in the journal Nature Nanotechnology.

In conventional photovoltaic cells, sunlight hits the surface of semiconductor material, one side of which is electron-rich, while the other side is not. The photon excites the electrons, causing them to leave their positions, and create positively-charged “holes.” The result is a current of charged particles – electricity.

In the new technique, it is not semiconductor materials that provide the electrons and venue for the conversion of solar energy, but a “forest” of gold nano-rods operating in water. Specifically, gold nano-rods capped with a layer of crystalline titanium dioxide and platinum, and a cobalt-based oxidation catalyst deposited on the lower portion of the array.

“When nanostructures, such as nano-rods, of certain metals are exposed to visible light, the conduction electrons of the metal can be caused to oscillate collectively, absorbing a great deal of the light,” explained Martin Moskovits (pictured front center), a professor of chemistry at UCSB. “This excitation is called a surface plasmon.”

As the “hot” electrons in these plasmonic waves are excited by light particles, some travel up the nano-rod, through a filter layer of crystalline titanium dioxide, and are captured by platinum particles. This causes the reaction that splits hydrogen ions from the bond that forms water. Meanwhile, the holes left behind by the excited electrons head toward the cobalt-based catalyst on the lower part of the rod to form oxygen.

The researchers say that hydrogen production was clearly observable after about two hours. Importantly, the nano-rods were not subject to the photo-corrosion that often causes traditional semiconductor materials to fail and Moskovits says the device operated with no hint of failure for “many weeks.”

Though still in its infancy, the research promises a more robust method of converting sunlight into energy. “Despite the recentness of the discovery, we have already attained ‘respectable’ efficiencies. More importantly, we can imagine achievable strategies for improving the efficiencies radically,” Moskovits said.


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Source: University of California – Santa Barbara