Tag Archives: Helmholtz-Zentrum Dresden-Rossendorf

Neurotransistor for brainlike (neuromorphic) computing

According to researchers at Helmholtz-Zentrum Dresden-Rossendorf and the rest of the international team collaborating on the work, it’s time to look more closely at plasticity in the neuronal membrane,.

From the abstract for their paper, Intrinsic plasticity of silicon nanowire neurotransistors for dynamic memory and learning functions by Eunhye Baek, Nikhil Ranjan Das, Carlo Vittorio Cannistraci, Taiuk Rim, Gilbert Santiago Cañón Bermúdez, Khrystyna Nych, Hyeonsu Cho, Kihyun Kim, Chang-Ki Baek, Denys Makarov, Ronald Tetzlaff, Leon Chua, Larysa Baraban & Gianaurelio Cuniberti. Nature Electronics volume 3, pages 398–408 (2020) DOI: https://doi.org/10.1038/s41928-020-0412-1 Published online: 25 May 2020 Issue Date: July 2020

Neuromorphic architectures merge learning and memory functions within a single unit cell and in a neuron-like fashion. Research in the field has been mainly focused on the plasticity of artificial synapses. However, the intrinsic plasticity of the neuronal membrane is also important in the implementation of neuromorphic information processing. Here we report a neurotransistor made from a silicon nanowire transistor coated by an ion-doped sol–gel silicate film that can emulate the intrinsic plasticity of the neuronal membrane.

Caption: Neurotransistors: from silicon chips to neuromorphic architecture. Credit: TU Dresden / E. Baek Courtesy: Helmholtz-Zentrum Dresden-Rossendorf

A July 14, 2020 news item on Nanowerk announced the research (Note: A link has been removed),

Especially activities in the field of artificial intelligence, like teaching robots to walk or precise automatic image recognition, demand ever more powerful, yet at the same time more economical computer chips. While the optimization of conventional microelectronics is slowly reaching its physical limits, nature offers us a blueprint how information can be processed and stored quickly and efficiently: our own brain.

For the very first time, scientists at TU Dresden and the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) have now successfully imitated the functioning of brain neurons using semiconductor materials. They have published their research results in the journal Nature Electronics (“Intrinsic plasticity of silicon nanowire neurotransistors for dynamic memory and learning functions”).

A July 14, 2020 Helmholtz-Zentrum Dresden-Rossendorf press release (also on EurekAlert), which originated the news items delves further into the research,

Today, enhancing the performance of microelectronics is usually achieved by reducing component size, especially of the individual transistors on the silicon computer chips. “But that can’t go on indefinitely – we need new approaches”, Larysa Baraban asserts. The physicist, who has been working at HZDR since the beginning of the year, is one of the three primary authors of the international study, which involved a total of six institutes. One approach is based on the brain, combining data processing with data storage in an artificial neuron.

“Our group has extensive experience with biological and chemical electronic sensors,” Baraban continues. “So, we simulated the properties of neurons using the principles of biosensors and modified a classical field-effect transistor to create an artificial neurotransistor.” The advantage of such an architecture lies in the simultaneous storage and processing of information in a single component. In conventional transistor technology, they are separated, which slows processing time and hence ultimately also limits performance.

Silicon wafer + polymer = chip capable of learning

Modeling computers on the human brain is no new idea. Scientists made attempts to hook up nerve cells to electronics in Petri dishes decades ago. “But a wet computer chip that has to be fed all the time is of no use to anybody,” says Gianaurelio Cuniberti from TU Dresden. The Professor for Materials Science and Nanotechnology is one of the three brains behind the neurotransistor alongside Ronald Tetzlaff, Professor of Fundamentals of Electrical Engineering in Dresden, and Leon Chua [emphasis mine] from the University of California at Berkeley, who had already postulated similar components in the early 1970s.

Now, Cuniberti, Baraban and their team have been able to implement it: “We apply a viscous substance – called solgel – to a conventional silicon wafer with circuits. This polymer hardens and becomes a porous ceramic,” the materials science professor explains. “Ions move between the holes. They are heavier than electrons and slower to return to their position after excitation. This delay, called hysteresis, is what causes the storage effect.” As Cuniberti explains, this is a decisive factor in the functioning of the transistor. “The more an individual transistor is excited, the sooner it will open and let the current flow. This strengthens the connection. The system is learning.”

Cuniberti and his team are not focused on conventional issues, though. “Computers based on our chip would be less precise and tend to estimate mathematical computations rather than calculating them down to the last decimal,” the scientist explains. “But they would be more intelligent. For example, a robot with such processors would learn to walk or grasp; it would possess an optical system and learn to recognize connections. And all this without having to develop any software.” But these are not the only advantages of neuromorphic computers. Thanks to their plasticity, which is similar to that of the human brain, they can adapt to changing tasks during operation and, thus, solve problems for which they were not originally programmed.

I highlighted Dr. Leon Chua’s name as he was one of the first to conceptualize the notion of a memristor (memory resistor), which is what the press release seems to be referencing with the mention of artificial synapses. Dr. Chua very kindly answered a few questions for me about his work which I published in an April 13, 2010 posting (scroll down about 40% of the way).

‘Llam’ me lend you some antibodies—antibody particles extracted from camels and llamas

Sometimes the urge for wordplay overwhelms me as it did this morning (June 12, 2014) when I saw llamas mentioned in a news item. For anyone unfamiliar with how Canadian English (and I can safely include American English here but am not sure about any other Englishes) is spoken, we leave out consonants in some phrases. For example, ‘let me’ becomes ‘lemme’, which when you’re playing with ‘llama,’ becomes ‘llam’me. As for the verb ‘lend’, I used it for its alliterative quality and used more accurate verb ‘extracted’ later in the headline.

Getting on to the antibodies and the camels and llamas, here’s more from a June 12, 2014 news item on Nanowerk (Note: A link has been removed),

The use of nanoparticles in cancer research is considered as a promising approach in detecting and fighting tumour cells. The method has, however, often failed because the human immune system recognizes the particles as foreign objects and rejects them before they can fulfil their function. Researchers at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and at University College Dublin [UCD[ in Ireland have, along with other partners, developed nanoparticles that not only bypass the body’s defence system, but also find their way to the diseased cells (“Diagnostic nanoparticle targeting of the EGF-receptor in complex biological conditions using single-domain antibodies”). This procedure uses fragments from a particular type of antibody that only occurs in camels and llamas. The small particles were even successful under conditions which are very similar to the situation within potential patients’ bodies.

A June 12, 2014 HZDR press release, which originated the news item, supplies a quote from one of the researchers where he explains the problems he and his colleagues were attempting to address,

Describing the current state of research, Dr. Kristof Zarschler of the Helmholtz Virtual Institute NanoTracking at the HZDR explains, “At the moment we must overcome three challenges. First, we need to produce the smallest possible nanoparticles. We then need to modify their surface in a way that the proteins in the human bodies do not envelop them, which would thus render them ineffective. In order to ensure, that the particles do their job, we must also somehow program them to find the diseased cells.” Therefore, the Dresden [HZDR is in Dresden] and Dublin researchers combined expertise to develop nanoparticles made of silicon dioxide with fragments of camel antibodies.

The press release and Zarschler go on to explain the advantages of camel and llama antibodies,

In contrast to conventional antibodies, which consist of two light and two heavy protein chains, those taken from camels and llamas are less complex and are made up of only two heavy chains. “Due to this simplified structure, they are easier to produce than normal antibodies,” explains Zarschler. “We also only need one particular fragment – the portion of the molecule that binds to certain cancer cells – which makes the production of much smaller nanoparticles possible.” By modifying the surface of the nanoparticle, it also gets more difficult for the immune system to recognize the foreign material, which allows the nanoparticles to actually reach their target.

The ultra-small particles should then detect the so-called epidermal growth factor receptor (EGFR) in the human body. In various types of tumours, this molecule is overexpressed and/or exists in a mutated form, which allows the cells to grow and multiply uncontrollably. The Dresden researchers could demonstrate in experiments that nanoparticles that have been combined with the camel antibody fragments can more firmly bind to the cancer cells. “The EGFR is a virtual lock to which our antibody fits like a key,” explains Zarschler.

Most exciting are the experiments the researchers performed with human blood (from the press release),

They even obtained the same results in experiments involving human blood serum – a biologically relevant environment the scientists point out: “This means that we carried out the tests under conditions that are very similar to the reality of the human body,” explains Dr. Holger Stephan, who leads the project. “The problem with many current studies is that artificial conditions are chosen where no disruptive factors exist. While this provides good results, it is ultimately useless because the nanoparticles fail finally in experiments conducted under more complex conditions. In our case, we could at least reduce this error source.”

There are no immediate plans for clinical trials according to the press release,

However, more time is required before the nanoparticles can be utilized in diagnosing human tumours. “The successful tests have brought us one step further,” explains Stephan. “The road, however, to its clinical use is long.” The next aim is to reduce the size of the nanoparticles, which are now approximately fifty nanometres in diameter, to less than ten nanometres. “That would be optimal,” according to Zarschler. “Then they would only remain in the human body for a short period – just long enough to detect the tumour.”

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

Diagnostic nanoparticle targeting of the EGF-receptor in complex biological conditions using single-domain antibodies by K. Zarschler, K. Prapainop, E. Mahon, L. Rocks,  M. Bramini, P. M. Kelly, H. Stephan, and K. A. Dawson. Nanoscale, 2014,6, 6046-6056 DOI: 10.1039/C4NR00595C
First published online 16 Apr 2014

This paper is in an open access journal.

The researchers have provided an illustration of the new antibody particles,

 Title Bild Nanopartikel Copyright 	CBNI, UCD

Title Bild Nanopartikel
With help of proteins, nanoparticles can be produced, which bind specifically to cancer cells, thus making it possible to detect tumours. Copyright CBNI, UCD

Luminous bacteria sense pharmaceuticals and metals in wastewater

Scientists at the Helmholtz Association of German Research Centres have conceptualized a technique using luminescent bacterial proteins for sensing pharmaceuticals and metals in waste water. From the Helmholtz Association of German Research Centres June 12, 2013 press release,

While residual medications don’t belong in the water, trace metals from industrial process waters handled by the recycling industry are, in contrast, valuable resources. Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) have developed a simple color sensor principle which facilitates the easy detection of both materials as well as many other substances. This is the concept: If the analyzed sample shines red, then the water is ‘clean;’ if its color turns green, however, then it contains the substances the scientists wish to detect. The researchers recently published their concept in the scientific journal Sensors and Actuators B: Chemical (DOI: 10.1016/j.snb.2013.05.051).

Here’s the concept, from the press release,

The sensor principle is based on a red and a green fluorescent dye. If a substance to be detected is present in a water sample, then the sensor shines green; a red color, however, indicates that the substance is not present. What is the reason for the color difference? “The color molecules are located on a nanostructured surface consisting of bacterial proteins. The dyes are so close to one another that energy is transferred from the green to the red dye if these dyes are irradiated with light at a specific wavelength, for example, the light emitted by a laser. Then the sample shines red. This energy transfer, though, only occurs if the water sample is ‘clean.’ If, however, any foreign substances such as, for example, the pharmaceuticals or pollutants to be detected accumulate between the color molecules at specific binding sites, then the transfer is interrupted and only the green dyes shine,” explains Ulrike Weinert. Her doctoral dissertation revolves around the binding of color molecules on nano surfaces.

The network project (“AptaSens”) was subsidized by the Federal Ministry of Education and Research (BMBF). Nanostructured surfaces are an important part of the project. They are extracted from the envelope proteins of bacteria which are cultivated by the researchers in a lab. “The proteins form regular lattice structures at the nano level. They are ideally suited to evenly arrange functional groups and other molecules,” notes Weinert.

Another essential component of the sensor principle are the binding sites on the nano surface of the substances which are to be detected. That’s why so-called aptamers are used. These aptamers are short, single-stranded DNA oligonucleotides; the DNA segments can be designed in such a way that they are capable of specifically binding the most diverse substances such as the pharmaceuticals or the pollutants mentioned above. Dr. Beate Strehlitz from the Leipzig-based Helmholtz Centre for Environmental Research (UFZ) has specialized in this field. Within the scope of the AptaSens project, her team developed such a receptor for the antibiotic kanamycin which is used, for example, for the treatment of such bacterial infections of the eye as conjunctivitis, or in veterinary medicine.

The next step will be testing, from the press release,

What remains to be done now is to combine the kanamycin receptor with the dyes to test the color sensor principle with a sample substance. “From there, it’s just a small step to the development of a complete color sensor,” notes Katrin Pollmann [Dr. Katrin Pollmann, Team Leader Biotechnology at the HZDR {Holtzman Centres}]. For this, the researchers need to integrate the individual components – which include bacterial proteins, dyes, and aptamers – into a sensor chip. They have actually conducted a number of experiments with suitable substrates such as, for example, glass or silicon dioxide. “The sensor chip could be as small as a thumbnail. It could be wetted on site with the water sample to be analyzed. This would also include a laser light source which activates the chip as well as a detector that measures the change in color,” adds Pollmann. The scientists are now applying for a follow-up project.

I’d love to get a little more information about which metals (gold nanoparticles? silver nanoparticles? zinc oxide nanoparticles? etc.) could be detected in the water. If the information is in the research team’s published paper, that is available only behind a paywall.  H/T to Nanowerk (June 12, 2013 news item) for alerting me to this research work.

Here’s a citation (the link was provided earlier in this post),

U. Weinert, K. Pollmann, J. Raff. “Fluorescence Resonance Energy Transfer by S-layer coupled fluorescence dyes”, in Sensors and Actuators B: Chemical (2013), DOI: 10.1016/j.snb.2013.05.051

For anyone who’s interested in more information about aptamers, there’s my Oct. 25, 2011 posting which featured an interview with Dr. Maria DeRosa about her work with them.