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Optoelectronics A new candidate for ultra-thin optoelectronics: DNA-peptide By RPaul Buckley esearchers at Tel Aviv University (TAU) claim to have developed a molecular backbone of super-slim, bendable digital displays that uses a novel DNA-peptide structure to produce thin, transparent, and flexible screens. The research, which has been published in Nature Nanotechnology, was conducted by Prof. Ehud Gazit and doctoral student Or Berger of the Department of Molecular Microbiology and Biotechnology at TAU’s George S. Wise Faculty of Life Sciences, in collaboration with Dr. Yuval Ebenstein and Prof. Fernando Patolsky of the School of Chemistry at TAU’s Faculty of Exact Sciences, harnesses bionanotechnology to emit a full range of colors in one pliable pixel layer - as opposed to the several rigid layers that constitute today’s screens. “Our material is light, organic, and environmentally friendly,” said Prof. Gazit. “It is flexible, and a single layer emits the same range of light that requires several layers today. By using only one layer, you can minimize production costs dramatically, which will lead to lower prices for consumers as well.” The researchers tested different combinations of peptides: short protein fragments, embedded with DNA elements which facilitate the self-assembly of a novel molecular architecture. Peptides and DNA are two of the most basic building blocks of life. Each cell of every life form is composed of such building blocks. In the field of bionanotechnology, scientists utilize these building blocks to develop novel technologies with properties not available for inorganic materials such as plastic and metal. “Our lab has been working on peptide nanotechnology for over a decade, but DNA nanotechnology is a distinct and fascinating field as well. When I started my doctoral studies, I wanted to try and converge the two approaches,” said Berger. “In this study, we focused on PNA - peptide nucleic acid, a synthetic hybrid molecule of peptides and DNA. We designed and synthesized different PNA sequences, and tried to build nano-metric architectures with them.” Using methods such as electron microscopy and X-ray crystallography, the researchers discovered that three of the molecules they synthesized could self-assemble, in a few minutes, into ordered structures. The structures resembled the natural double-helix form of DNA, but also exhibited peptide characteristics. This resulted in a unique molecular arrangement that reflects the duality of the new material. “Once we discovered the DNA-like organization, we tested the ability of the structures to bind to DNA-specific fluorescent dyes,” said Berger. “To our surprise, the control sample, with no added dye, emitted the same fluorescence as the variable. This proved that the organic structure is itself naturally fluorescent.” The structures were found to emit light in every color, as opposed to other fluorescent materials that shine only in one specific color. Moreover, light emission was observed also in response to electric voltage - which make it a perfect candidate for opto-electronic devices like display screens. Ag nanodiscs to boost MoS’s LED performance 2RBy Paul Buckley esearchers at Northwestern University’s McCormick School of Engineering have fabricated a series of silver nanodiscs which when arranged on top of a sheet of molybdenum disulfide (MoS2) are able to boost the light emission performance of the monolayer thick material. With enhanced light emission properties, MoS2 could make a good candidate for light emitting diode technologies. Monolayer MoS2’s ultra-thin structure is strong, lightweight, and flexible, which makes the material a good candidate for many applications, such as high-performance, flexible electronics. Such a thin semiconducting material, however, has little interaction with light, limiting the material’s use in light emitting and absorbing applications. “The problem with these materials is that they are just one monolayer thick,” said Koray Aydin, assistant professor of electrical engineering and computer science at the McCormick School of Engineering. “So the amount of material that is available for light emission or light absorption is very limited. In order to use these materials for practical photonic and optoelectric applications, we needed to increase their interactions with light.” Aydin and his team tackled this problem by combining nanotechnology, materials science, and plasmonics, the study of the interactions between light and metal. The team discovered that the nanodiscs enhanced light emission and determined the specific diameter of the most successful disc, which is 130 nanometers. “We have known that these plasmonic nanostructures have the ability to attract and trap light in a small volume,” said Serkan Butun, a postdoctoral researcher in Aydin’s lab. “Now we’ve shown that placing silver nanodiscs over the material results in twelve times more light emission.” The use of the nanostructures - as opposed to using a continuous film to cover the MoS2 - allows the material to retain its flexible nature and natural mechanical properties. The team’s next step is to use the same strategy for increasing the material’s light absorption abilities to create a better material for solar cells and photodetectors. “This is a huge step, but it is not the end of the story,” Aydin said. “There might be ways to enhance light emission even further. But, so far, we have successfully shown that it’s indeed possible to increase light emission from a very thin material.” Supported by Northwestern’s Materials Research Science and Engineering Center and the Institute for Sustainability and Energy at Northwestern, the research is described in the March 2015 online issue of NanoLetters. 24 Electronic Engineering Times Europe April 2015 www.electronics-eetimes.com


EETE APR 2015
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