Tag Archives: TUM

Graphene and an artificial retina

A graphene-based artificial retina project has managed to intermingle the European Union’s two major FET (Future and Emerging Technologies) funding projects, 1B Euros each to be disbursed over 10 years, the Graphene Flagship and the Human Brain Project. From an Aug. 7, 2014 Technische Universitaet Muenchen (TUM) news release (also on EurekAlert),

Because of its unusual properties, graphene holds great potential for applications, especially in the field of medical technology. A team of researchers led by Dr. Jose A. Garrido at the Walter Schottky Institut of the TUM is taking advantage of these properties. In collaboration with partners from the Institut de la Vision of the Université Pierre et Marie Curie in Paris and the French company Pixium Vision, the physicists are developing key components of an artificial retina made of graphene.

Retina implants can serve as optical prostheses for blind people whose optical nerves are still intact. The implants convert incident light into electrical impulses that are transmitted to the brain via the optical nerve. There, the information is transformed into images. Although various approaches for implants exist today, the devices are often rejected by the body and the signals transmitted to the brain are generally not optimal.

Already funded by the Human Brain Project as part of the Neurobotics effort, Garrido and his colleagues will now also receive funding from the Graphene Flagship. As of July 2014, the Graphene Flagship has added 86 new partners including TUM according to the news release.

Here’s an image of an ‘invisible’ graphene sensor (a precursor to developing an artificial retina),

Graphene electronics can be prepared on flexible substrates. Only the gold metal leads are visible in the transparent graphene sensor. (Photo: Natalia Hutanu / TUM)

Graphene electronics can be prepared on flexible substrates. Only the gold metal leads are visible in the transparent graphene sensor. (Photo: Natalia Hutanu / TUM)

Artificial retinas were first featured on this blog in an Aug. 18, 2011 posting about video game Deus Ex: Human Revolution which features a human character with artificial sight. The post includes links to a video of a scientist describing an artificial retina trial with 30 people and an Israeli start-up company, ‘Nano Retina’, along with information about ‘Eyeborg’, a Canadian filmmaker who on losing an eye in an accident had a camera implanted in the previously occupied eye socket.

More recently, a Feb. 15, 2013 posting featured news about the US Food and Drug Administration’s decision to allow sale of the first commercial artificial retinas in the US in the context of news about a neuroprosthetic implant in a rat which allowed it to see in the infrared range, normally an impossible feat.

An entire chemistry lab (nanofactory) in a droplet

I love the blue in this image, which illustrates the thousand-droplets test, research suggesting the possibility of a nanofactory or laboratory within a droplet ,

Droplets with a diameter of only a few micrometers act as the reaction vessels for a complex oscillating reaction - Photo: Maximilian Weitz / TUM

Droplets with a diameter of only a few micrometers act as the reaction vessels for a complex oscillating reaction – Photo: Maximilian Weitz / TUM

A Feb. 19, 2014 news item on Azonano reveals more,

An almost infinite number of complex and interlinked reactions take place in a biological cell. In order to be able to better investigate these networks, scientists led by Professor Friedrich Simmel, Chair of Systems Biophysics and Nano Biophysics at the Technische Universitaet Muenchen (TUM) try to replicate them with the necessary components in a kind of artificial cell.

This is also motivated by the thought of one day using such single-cell systems for example as “nanofactories” for the production of complex organic substances or biomaterials.

All such experiments have so far predominantly worked with very simple reactions, however. NIM Professor Friedrich Simmel and his team have now for the first time managed to let a more complex biochemical reaction take place in tiny droplets of only a few micrometers in size. Together with co-authors from the University of California Riverside and the California Institute of Technology in Pasadena, USA, the scientists are presenting their findings in the current edition of Nature Chemistry.

The Feb. 18, 2014 TUM press release, which originated the news item, details the experiements,

Shaking once – investigating thousands of times

The experiment is conducted by putting an aqueous reaction solution into oil and shaking the mixture vigorously. The result is an emulsion consisting of thousands of droplets. Employing only a tiny amount of material, the scientists have thus found a cost-efficient and quick way of setting up an extremely large number of experiments simultaneously.

As a test system, the researchers chose a so-called biochemical oscillator. This involves several reactions with DNA and RNA, which take place repetitively one after the other. Their rhythm becomes visible because in one step two DNA strands bind to each other in such a way that a fluorescent dye shines. This regular blinking is then recorded with special cameras.

Small droplets – huge differences

In the first instance, Friedrich Simmel and his colleagues intended to investigate the principal behavior of a complex reaction system if scaled down to the size of a cell. In addition, they specifically wondered if all droplet systems displayed an identical behavior and what factors would cause possible differences.

Their experiments showed that the oscillations in the individual droplets differed strongly, that is to say, much stronger than might have been expected from a simple statistical model. It was above all evident that small drops display stronger variations than large ones. “It is indeed surprising that we could witness a similar variability and individuality in a comparatively simple chemical system as is known from biological cells”, explains Friedrich Simmel the results.

Thus, it is currently not possible to realize systems which are absolutely identical. This de facto means that researchers have to either search for ways to correct these variations or factor them in from the start. On the other hand, the numerous slightly differing systems could also be used specifically to pick out the one desired, optimally running set-up from thousands of systems.

Investigating complex biosynthetic systems in artificial cells opens up many other questions, as well. In a next step, Friedrich Simmel plans to address the underlying theoretical models: “The highly parallel recording of the emulsion droplets enabled us to acquire plenty of interesting data. Our goal is to use these data to review and improve the theoretical models of biochemical reaction networks at small molecule numbers.”

Here’s link to and a citation for the paper,

Diversity in the dynamical behaviour of a compartmentalized programmable biochemical oscillator by Maximilian Weitz, Jongmin Kim, Korbinian Kapsner, Erik Winfree, Elisa Franco, & Friedrich C. Simmel. Nature Chemistry (2014) doi:10.1038/nchem.1869 Published online 16 February 2014

This paper is behind a paywall.

Carbon nanotubes one way: gas and other flexible sensors

A Sept. 24, 2013 Technische Universitaet Muenchen (TUM) press release (also on EurekAlert) promises that flexible sensors are on the horizon,

Carbon nanotube-based gas sensors created at TUM offer a unique combination of characteristics that can’t be matched by any of the alternative technologies. They rapidly detect and continuously respond to extremely small changes in the concentrations of gases including ammonia, carbon dioxide, and nitrogen oxide. They operate at room temperature and consume very little power. Furthermore, as the TUM researchers report in their latest papers, such devices can be fabricated on flexible backing materials through large-area, low-cost processes.

Thus it becomes realistic to envision plastic food wrap that incorporates flexible, disposable gas sensors, providing a more meaningful indicator of food freshness than the sell-by date. Measuring carbon dioxide, for example, can help predict the shelf life of meat. “Smart packaging” – assuming consumers find it acceptable and the devices’ non-toxic nature can be demonstrated – could enhance food safety and might also vastly reduce the amount of food that is wasted. Used in a different setting, the same sort of gas sensor could make it less expensive and more practical to monitor indoor air quality in real time.

Dexter Johnson in a Sept. 26, 2013 posting on Nanoclast (an IEEE [Institute of Electrical and Electronics Engineers] blog) warns (Note: Links have been removed),

While this sounds great, the obstacle preventing this from becoming a reality has always been cost. Thin-film sensory packaging may make sense for a high-cost item, but for an inexpensive grocery store product, it’s hard to justify an additional cost that may be as much as the product itself. I made this point nearly a decade ago in report I authored titled, “The Future of Nanotechnology in Printing and Packaging”.

This doesn’t even take into account the often biased opinion people have about nanotechnology in relation to food.

Dexter recommends the researchers focus their commercialization efforts on robotic skins and other high ticket applications.

In reading the description of how the researchers created these flexible sensors, Dexter’s concerns are brought int high relief,

The most basic building block for this technology is a single cylindrical molecule, a rolled-up sheet of carbon atoms that are linked in a honeycomb pattern. This so-called carbon nanotube could be likened to an unimaginably long garden hose: a hollow tube just a nanometer or so in diameter but perhaps millions of times as long as it is wide. Individual carbon nanotubes exhibit amazing and useful properties, but in this case the researchers are more interested in what can be done with them en masse.

Laid down in thin films, randomly oriented carbon nanotubes form conductive networks that can serve as electrodes; patterned and layered films can function as sensors or transistors. “In fact,” Prof. Lugli [Prof. Paolo Lugli, director of TUM’s Nanoelectronics Institute] explains, “the electrical resistivity of such films can be modulated by either an applied voltage (to provide a transistor action) or by the adsorption of gas molecules, which in turn is a signature of the gas concentration for sensor applications.” And as a basis for gas sensors in particular, carbon nanotubes combine advantages (and avoid shortcomings) of more established materials, such as polymer-based organic electronics and solid-state metal-oxide semiconductors. What has been lacking until now is a reliable, reproducible, low-cost fabrication method.

Spray deposition, supplemented if necessary by transfer printing, meets that need. An aqueous solution of carbon nanotubes looks like a bottle of black ink and can be handled in similar ways. Thus devices can be sprayed – from a computer-controlled robotic nozzle – onto virtually any kind of substrate, including large-area sheets of flexible plastic. There is no need for expensive clean-room facilities.

“To us it was important to develop an easily scalable technology platform for manufacturing large-area printed and flexible electronics based on organic semiconductors and nanomaterials,” Abdellah says. “To that end, spray deposition forms the core of our processing technology.”

Remaining technical challenges arise largely from application-specific requirements, such as the need for gas sensors to be selective as well as sensitive.

Here are citations for and links to three of the researchers’ papers,

Fabrication of carbon nanotube thin films on flexible substrates by spray deposition and transfer printing. Ahmed Abdelhalim, Alaa Abdellah, Giuseppe Scarpa, Paolo Lugli. Carbon, Vol. 61, September 2013, 72-79. DOI: 10.1016/j.carbon.2013.04.069

Flexible carbon nanotube-based gas sensors fabricated by large-scale spray deposition.
Alaa Abdellah, Zubair Ahmad, Philipp Köhler, Florin Loghin, Alexander Weise, Giuseppe Scarpa, Paolo Lugli. IEEE Sensors Journal, Vol. 13 Issue 10, October 2013, 4014-4021. DOI: 10.1109/JSEN.2013.2265775

Scalable spray deposition process for high performance carbon nanotube gas sensors. Alaa Abdellah, Ahmed Abdelhalim, Markus Horn, Giuseppe Scarpa, and Paolo Lugli. IEEE Transactions on Nanotechnology 12, 174-181, 2013. DOI: 10.1109/TNANO.2013.2238248

All three papers are behind paywalls.

In one of those coincidences that take place from time to time, I wrote about an upcoming event taking place in the Guardian’s London offices, a panel discussion on nanotechnology and food,in a Sept.  26, 2013 posting.

Breakthroughs with self-assembling DNA-based nanoscaled structures

With all the talk about self-assembling DNA nanotechnology, it’s possible to misunderstand the stage of development this endeavour occupies as the title, Reality check for DNA Nanotechnology, for a Dec. 13, 2012 news release on EurekAlert suggests,

… This emerging technology employs DNA as a programmable building material for self-assembled, nanometer-scale structures. Many practical applications have been envisioned, and researchers recently demonstrated a synthetic membrane channel made from DNA. Until now, however, design processes were hobbled by a lack of structural feedback. Assembly was slow and often of poor quality.

In fact, the news release is touting two breakthroughs,

Now researchers led by Prof. Hendrik Dietz of the Technische Universitaet Muenchen (TUM) have removed these obstacles.

One barrier holding the field back was an unproven assumption. Researchers were able to design a wide variety of discrete objects and specify exactly how DNA strands should zip together and fold into the desired shapes. They could show that the resulting nanostructures closely matched the designs. Still lacking, though, was the validation of the assumed subnanometer-scale precise positional control. This has been confirmed for the first time through analysis of a test object designed specifically for the purpose. A technical breakthrough based on advances in fundamental understanding, this demonstration has provided a crucial reality check for DNA nanotechnology.

In a separate set of experiments, the researchers discovered that the time it takes to make a batch of complex DNA-based objects can be cut from a week to a matter of minutes, and that the yield can be nearly 100%. They showed for the first time that at a constant temperature, hundreds of DNA strands can fold cooperatively to form an object — correctly, as designed — within minutes. Surprisingly, they say, the process is similar to protein folding, despite significant chemical and structural differences. “Seeing this combination of rapid folding and high yield,” Dietz says, “we have a stronger sense than ever that DNA nanotechnology could lead to a new kind of manufacturing, with a commercial, even industrial future.” And there are immediate benefits, he adds: “Now we don’t have to wait a week for feedback on an experimental design, and multi-step assembly processes have suddenly become so much more practical.”

Dexter Johnson comments in his Dec. 18, 2012 posting (which includes an embedded video) on the Nanoclast blog (located on the Institute of Electrical and Electronics Engineers [IEEE] website),

The field of atomically precise manufacturing—or molecular manufacturing—has taken a big step towards realizing its promise with this latest research.  We may still be a long way from realizing the “nanotech rapture”  but certainly knowing that the objects built meet their design specifications and can be produced in minutes rather than weeks has to be recognized as a significant development.

Three papers have been published on these breakthroughs, here are the citations,

Xiao-chen Bai, Thomas G. Martin, Sjors H. W. Scheres, Hendrik Dietz. Cryo-EM structure of a 3D DNA-origami object. Proceedings of the National Academy of Sciences of the USA, Dec. 4, 2012, 109 (49) 20012-20017; on-line in PNAS Early Edition, Nov. 19, 2012. DOI: 10.1073/pnas.1215713109

Jean-Philippe J. Sobczak, Thomas G. Martin, Thomas Gerling, Hendrik Dietz. Rapid folding of DNA into nanoscale shapes at constant temperature. Science, vol. 338, issue 6113, pp. 1458-1461. DOI: 10.1126/science.1229919

See also: Martin Langecker, Vera Arnaut, Thomas G. Martin, Jonathan List, Stephan Renner, Michael Mayer, Hendrik Dietz, and Friedrich C. Simmel. Synthetic lipid membrane channels formed by designed DNA nanostructures. Science, vol. 338, issue 6109, pp. 932-936. DOI: 10.1126/science.1225624