research
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Nuclease-Resistant Hybrid Nanoflowers
An eco-friendly method to synthesize DNA-copper nanoflowers with high load efficiencies, low cytotoxicity, and strong resistance against nucleases has been developed by Professor Hyun Gyu Park in the Department of Chemical and Biomolecular Engineering and his collaborators.
The research team successfully formed a flower-shaped nanostructure in an eco-friendly condition by using interactions between copper ions and DNA containing amide and amine groups. The resulting nanoflowers exhibit high DNA loading capacities in addition to low cytotoxicity.
Flower-shaped nanocrystals called nanoflowers have gained attention for their distinct features of high surface roughness and high surface area to volume ratios. The nanoflowers have been used in many areas including catalysis, electronics, and analytical chemistry.
Of late, research breakthroughs were made in the generation of hybrid inorganic-organic nanoflowers containing various enzymes as organic components. The hybridization with inorganic materials greatly enhanced enzymatic activity, stability, and durability compared to the corresponding free enzymes.
Generally, the formation of protein nanocrystals requires high heat treatment so it has limitations for achieving the high loading capacities of intact DNA.
The research team addressed the issue, focusing on the fact that nucleic acids with well-defined structures and selective recognition properties also contain amide and amine groups in their nucleobases. They proved that flower-like structures could be formed by using nucleic acids as a synthetic template, which paved the way to synthesize the hybrid nanoflowers containing DNA as an organic component in an eco-friendly condition.
The team also confirmed that this synthetic method can be universally applied to any DNA sequences containing amide and amine groups. They said their approach is quite unique considering that the majority of previous works focused on the utilization of DNA as a linker to assemble the nanomaterials. They said the method has several advantageous features. First, the ‘green’ synthetic procedure doesn’t involve any toxic chemicals, and shows low cytotoxicity and strong resistance against nucleases. Second, the obtained nanoflowers exhibit exceptionally high DNA loading capacities.
Above all, such superior features of hybrid nanoflowers enabled the sensitive detection of various molecules including phenol, hydrogen peroxide, and glucose. DNA-copper nanoflowers showed even higher peroxidase activity than those of protein-copper nanoflowers, which may be due to the larger surface area of the flower- shaped structures, creating a greater chance for applying them in the field of sensing of detection of hydrogen peroxide.
The research team expects that their research will create diverse applications in many areas including biosensors and will be further applied into therapeutic applications.
Professor Park said, “The inorganic component in the hybrid nanoflowers not only exhibits low cytotoxicity, but also protects the encapsulated DNA from being cleaved by endonuclease enzymes. Using this feature, the nanostructure will be applied into developing gene therapeutic carriers.”
This research was co-led by Professor Moon Il Kim at Gachon University and KAIST graduate Ki Soo Park, currently a professor at Konkuk University, is the first author. The research was featured as the front cover article of the Journal of Materials Chemistry B on March 28, Issue 12, published by the Royal Society of Chemistry.
The research was funded by the Mid-Career Researcher Support Program of the National Research Foundation of Korea and the Global Frontier Project of the Ministry of Science, ICT & Future Planning.
(Figure: (A) Schematic illustration of the formation of nuclease-resistant DNA–inorganic nanoflowers. (B) SEM images showing time-dependent growth of DNA-nanoflowers. The concentration of A-rich ssDNA (Table S1, ESI†) was 0.25 mM.)
2017.04.14 View 8285 -
Improving Traffic Safety with a Crowdsourced Traffic Violation Reporting App
KAIST researchers revealed that crowdsourced traffic violation reporting with smartphone-based continuous video capturing can dramatically change the current practice of policing activities on the road and will significantly improve traffic safety.
Professor Uichin Lee of the Department of Industrial and Systems Engineering and the Graduate School of Knowledge Service Engineering at KAIST and his research team designed and evaluated Mobile Roadwatch, a mobile app that helps citizen record traffic violation with their smartphones and report the recorded videos to the police.
This app supports continuous video recording just like onboard vehicle dashboard cameras. Mobile Roadwatch allows drivers to safely capture traffic violations by simply touching a smartphone screen while driving. The captured videos are automatically tagged with contextual information such as location and time. This information will be used as important evidence for the police to ticket the violators. All of the captured videos can be conveniently reviewed, allowing users to decide which events to report to the police.
The team conducted a two-week field study to understand how drivers use Mobile Roadwatch. They found that the drivers tended to capture all traffic risks regardless of the level of their involvement and the seriousness of the traffic risks. However, when it came to actual reporting, they tended to report only serious traffic violations, which could have led to car accidents, such as traffic signal violations and illegal U-turns. After receiving feedback about their reports from the police, drivers typically felt very good about their contributions to traffic safety.
At the same time, some drivers felt pleased to know that the offenders received tickets since they thought these offenders deserved to be ticketed. While participating in the Mobile Roadwatch campaign, drivers reported that they tried to drive as safely as possible and abide by traffic laws. This was because they wanted to be as fair as possible so that they could capture others’ violations without feeling guilty. They were also afraid that other drivers might capture their violations.
Professor Lee said, “Our study participants answered that Mobile Roadwatch served as a very useful tool for reporting traffic violations, and they were highly satisfied with its features. Beyond simple reporting, our tool can be extended to support online communities, which help people actively discuss various local safety issues and work with the police and local authorities to solve these safety issues.”
Korea and India were the early adaptors supporting video-based reporting of traffic violations to the police. In recent years, the number of reports has dramatically increased. For example, Korea’s ‘Looking for a Witness’ (released in April 2015) received more than half million reported violations as of November 2016. In the US, authorities started tapping into smartphone recordings by releasing video-based reporting apps such as ICE Blackbox and Mobile Justice. Professor Lee said that the existing services cannot be used while driving, because none of the existing services support continuous video recording and safe event capturing behind the wheel.
Professor Lee’s team has been incorporating advanced computer vision techniques into Mobile Roadwatch for automatically capturing traffic violations and safety risks, including potholes and obstacles. The researchers will present their results in May at the ACM CHI Conference on Human Factors in Computing Systems (CHI 2017) in Denver, CO, USA. Their research was supported by the KAIST-KUSTAR fund.
(Caption: A driver is trying to capture an event by touching a screen. The Mobile Radwatch supports continuous video recording and safe event captureing behind the wheel.)
2017.04.10 View 9778 -
Crowdsourcing-Based Global Indoor Positioning System
Research team of Professor Dong-Soo Han of the School of Computing Intelligent Service Lab at KAIST developed a system for providing global indoor localization using Wi-Fi signals. The technology uses numerous smartphones to collect fingerprints of location data and label them automatically, significantly reducing the cost of constructing an indoor localization system while maintaining high accuracy.
The method can be used in any building in the world, provided the floor plan is available and there are Wi-Fi fingerprints to collect. To accurately collect and label the location information of the Wi-Fi fingerprints, the research team analyzed indoor space utilization. This led to technology that classified indoor spaces into places used for stationary tasks (resting spaces) and spaces used to reach said places (transient spaces), and utilized separate algorithms to optimally and automatically collect location labelling data.
Years ago, the team implemented a way to automatically label resting space locations from signals collected in various contexts such as homes, shops, and offices via the users’ home or office address information. The latest method allows for the automatic labelling of transient space locations such as hallways, lobbies, and stairs using unsupervised learning, without any additional location information. Testing in KAIST’s N5 building and the 7th floor of N1 building manifested the technology is capable of accuracy up to three or four meters given enough training data. The accuracy level is comparable to technology using manually-labeled location information.
Google, Microsoft, and other multinational corporations collected tens of thousands of floor plans for their indoor localization projects. Indoor radio map construction was also attempted by the firms but proved more difficult. As a result, existing indoor localization services were often plagued by inaccuracies. In Korea, COEX, Lotte World Tower, and other landmarks provide comparatively accurate indoor localization, but most buildings suffer from the lack of radio maps, preventing indoor localization services.
Professor Han said, “This technology allows the easy deployment of highly accurate indoor localization systems in any building in the world. In the near future, most indoor spaces will be able to provide localization services, just like outdoor spaces.” He further added that smartphone-collected Wi-Fi fingerprints have been unutilized and often discarded, but now they should be treated as invaluable resources, which create a new big data field of Wi-Fi fingerprints. This new indoor navigation technology is likely to be valuable to Google, Apple, or other global firms providing indoor positioning services globally. The technology will also be valuable for helping domestic firms provide positioning services.
Professor Han added that “the new global indoor localization system deployment technology will be added to KAILOS, KAIST’s indoor localization system.” KAILOS was released in 2014 as KAIST’s open platform for indoor localization service, allowing anyone in the world to add floor plans to KAILOS, and collect the building’s Wi-Fi fingerprints for a universal indoor localization service. As localization accuracy improves in indoor environments, despite the absence of GPS signals, applications such as location-based SNS, location-based IoT, and location-based O2O are expected to take off, leading to various improvements in convenience and safety. Integrated indoor-outdoor navigation services are also visible on the horizon, fusing vehicular navigation technology with indoor navigation.
Professor Han’s research was published in IEEE Transactions on Mobile Computing (TMC) in November in 2016.
For more, please visit http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7349230http://ieeexplore.ieee.org/document/7805133/
2017.04.06 View 8644 -
Improving Silver Nanowires for FTCEs with Flash Light Interactions
Flexible transparent conducting electrodes (FTCEs) are an essential element of flexible optoelectronics for next-generation wearable displays, augmented reality (AR), and the Internet of Things (IoTs). Silver nanowires (Ag NWs) have received a great deal of attention as future FTCEs due to their great flexibility, material stability, and large-scale productivity. Despite these advantages, Ag NWs have drawbacks such as high wire-to-wire contact resistance and poor adhesion to substrates, resulting in severe power consumption and the delamination of FTCEs.
A research team led by Professor Keon Jae Lee of the Materials Science and Engineering Department at KAIST and Dr. Hong-Jin Park from BSP Inc., has developed high-performance Ag NWs (sheet resistance ~ 5 Ω/sq, transmittance 90 % at λ = 550 nm) with strong adhesion on plastic (interfacial energy of 30.7 J∙m-2) using flash light-material interactions.
The broad ultraviolet (UV) spectrum of a flash light enables the localized heating at the junctions of nanowires (NWs), which results in the fast and complete welding of Ag NWs. Consequently, the Ag NWs demonstrate six times higher conductivity than that of the pristine NWs. In addition, the near-infrared (NIR) of the flash lamp melted the interface between the Ag NWs and a polyethylene terephthalate (PET) substrate, dramatically enhancing the adhesion force of the Ag NWs to the PET by 310 %.
Professor Lee said, “Light interaction with nanomaterials is an important field for future flexible electronics since it can overcome thermal limit of plastics, and we are currently expanding our research into light-inorganic interactions.”
Meanwhile, BSP Inc., a laser manufacturing company and a collaborator of this work, has launched new flash lamp equipment for flexible applications based on the Professor Lee’s research.
The results of this work entitled “Flash-Induced Self-Limited Plasmonic Welding of Ag NW Network for Transparent Flexible Energy Harvester (DOI: 10.1002/adma.201603473)” were published in the February 2, 2017 issue of Advanced Materials as the cover article.
Professor Lee also contributed an invited review in the same journal of the April 3, 2017 online issue, “Laser-Material Interactions for Flexible Applications (DOI:10.1002/adma.201606586),” overviewing the recent advances in light interactions with flexible nanomaterials.
References
[1] Advanced Materials, February 2, 2017, Flash-Induced Self-Limited Plasmonic Welding of Ag NW network for Transparent Flexible Energy Harvester http://onlinelibrary.wiley.com/doi/10.1002/adma.201603473/epdf
[2] Advanced Materials, April 3, 2017, Laser-Material Interactions for Flexible Applications
http://onlinelibrary.wiley.com/doi/10.1002/adma.201606586/abstract
For further inquiries on research:
keonlee@kaist.ac.kr (Keon Jae Lee), hjpark@bsptech.co.kr (Hong-Jin Park)
Picture 1: Artistic Rendtition of Light Interaction with Nanomaterials
(This image shows flash-induced plasmonic interactions with nanowires to improve silver nanowires (Ag NWs).)
Picture 2: Ag NW/PET Film
(This picture shows the Ag NWs on a polyethylene terephthalate (PET) film after the flash-induced plasmonic thermal process.)
2017.04.05 View 9520 -
Expanding the Genetic Code of Mus Musculus
Professor Hee-Sung Park of the Department of Chemistry, who garnered attention for his novel strategy of installing authentic post-translational modifications into recombinant proteins, expanded his research portfolio to another level. Professor Park’s team was the first to report the generation of a mouse strain with an expanded genetic code, allowing site-specific incorporation of unnatural amino acids.
Professor Park published the research on the new chemical biology method for achieving selective chemical modifications in proteins in Science last September. The research team, this time in collaboration with Professor Chan Bae Park of the Department of Physiology at the Ajou University School of Medicine, demonstrated temporal and spatial control of protein acetylation in various organs of the transgenic mouse using a recombinant green fluorescent protein as a model protein. This research was published in the online edition of Nature Communications on February 21.
This approach enables the rapid onset of position-specific acetylation of a target protein at any developmental stage, facilitating temporal and spatial control of protein acetylation in various organs of the transgenic mouse. Such temporal and spatial control of protein acetylation will be of prime importance for investigating many essential biological processes and human diseases at the tissue and organism level.
Almost all human proteins, the products of about 25,000 genes, are known to undergo various post-translational modifications during and after synthesis. Post-translation modifications regulate the function of cellular proteins, playing a key role in many essential processes such as delivering signals and body growth. However, the unusual protein modifications, aroused from genetic and/or environmental factors, trigger severe diseases including cancer, dementia, and diabetes.
The team inserted transgenes into the mouse genome to allocate the site-specific addition of unnatural amino acids. The researchers inserted a modified version of lysine into the house mice, which allowed for the control of the acetylation. They used recombinant green fluorescent proteins from transgenic house mice as models for control of the acetylation.
The team was also able to regulate the acetylation of specific temporal and spatial frames in the mice, restraining the abnormality in proteins to certain organs such as the liver and kidneys. The research team said the strategy will provide a powerful tool for systematic in vivo study of cellular proteins in the most commonly used mammalian model organisms for human physiology and disease. Professor Park said, “This method can be easily extended to generate a wide range of custom-made transgenic mouse strains for further investigating diverse proteins of interest.” He added, “This method can be further extended to generate a wide range of custom-made transgenic mouse strains, opening a new paradigm for investigating anti-cancer and cerebral disease treatments.
This work was supported by grants from KAIST Systems Healthcare and the Medicinal Bioconvergence Research Center and the Intelligent Synthetic Biology Center of the Global Frontier Project funded by the Ministry of Science, ICT & Future Planning and the Ministry of Food and Drug Safety.
(Figure:Temporal and spatial control of in vivo protein acetylation)
(a) Temporal expression of acetylated GFPuv in the AcK-GFPamber mouse. The expression of GFPuv in skeletal muscle, liver, and lung tissues was detected only in the AcK-injected mouse. Scale bar, 200 µm. (b) Western blotting of anti-FLAG-immunoprecipitated proteins from tissues of the AcK-GFPamber mouse. Acetylated GFPuv was produced after AcK injection. (c) Spatial expression of acetylated GFPuv in the AcK-GFPamber mouse. Acetylated GFPuv was observed only in skeletal muscle when AcK was directly delivered to the tissues. Sacle bar, 200 µm.
2017.03.27 View 8441 -
First Mutations in Human Life Discovered
The earliest mutations of human life have been observed by research team led by the Wellcome Trust Sanger Institute and their collaborators. Analyzing genomes from adult cells, the scientists could look back in time to reveal how each embryo developed.
Research team of the Sanger Institute including Professor Young Seok Ju of the Graduate School of Medical Science and Engineering at KAIST published an article of “Somatic Mutations Reveal Asymmetric Cellular Dynamics in the Early Human Embryo” in Nature on March 22.
The study shows that from the two-cell stage of the human embryo, one of these cells becomes more dominant than the other and leads to a higher proportion of the adult body.
A longstanding question for researchers has been what happens in the very early human development as this has proved impossible to study directly. Now, researchers have analyzed the whole genome sequences of blood samples (collected from 279 individuals with breast cancer) and discovered 163 mutations that occurred very early in the embryonic development of those people.
Once identified, the researchers used mutations from the first, second and third divisions of the fertilized egg to calculate which proportion of adult cells resulted from each of the first two cells in the embryo. They found that these first two cells contribute differently to the whole body. One cell gives rise to about 70 percent of the adult body tissues, whereas the other cell has a more minor contribution, leading to about 30percent of the tissues. This skewed contribution continues for some cells in the second and third generation too.
Originally pinpointed in normal blood cells from cancer patients, the researchers then looked for these mutations in cancer samples that had been surgically removed from the patients during treatment. Unlike normal tissues composed of multiple somatic cell clones, a cancer develops from one mutant cell. Therefore, each proposed embryonic mutation should either be present in all of the cancer cells in a tumor, or none of them. This proved to be the case, and by using these cancer samples, the researchers were able to validate that the mutations had originated during early development.
Dr. Young Seok Ju, first author from the Wellcome Trust Sanger Institute and KAIST, said: "This is the first time that anyone has seen where mutations arise in the very early human development. It is like finding a needle in a haystack. There are just a handful of these mutations, compared with millions of inherited genetic variations, and finding them allowed us to track what happened during embryogenesis."
Dr. Inigo Martincorena, from the Sanger Institute, said: "Having identified the mutations, we were able to use statistical analysis to better understand cell dynamics during embryo development. We determined the relative contribution of the first embryonic cells to the adult blood cell pool and found one dominant cell - that led to 70 percent of the blood cells - and one minor cell. We also sequenced normal lymph and breast cells, and the results suggested that the dominant cell also contributes to these other tissues at a similar level. This opens an unprecedented window into the earliest stages of human development."
During this study, the researchers were also able to measure the rate of mutation in early human development for the first time, up to three generations of cell division. Previous researchers had estimated one mutation per cell division, but this study measured three mutations for each cell doubling, in every daughter cell.
Mutations during the development of the embryo occur by two processes - known as mutational signatures 1 and 5. These mutations are fairly randomly distributed through the genome, and the vast majority of them will not affect the developing embryo. However, a mutation that occurs in an important gene can lead to disease such as developmental disorders.
Professor Sir Mike Stratton, lead author on the paper and Director of the Sanger Institute, said: "This is a significant step forward in widening the range of biological insights that can be extracted using genome sequences and mutations. Essentially, the mutations are archaeological traces of embryonic development left in our adult tissues, so if we can find and interpret them, we can understand human embryology better. This is just one early insight into human development, with hopefully many more to come in the future."
(Figure 1. Detection of somatic mutations acquired in early human embryogenesis )
(Figure 2. Unequal contributions of early embryonic cells to adult somatic tissues )
2017.03.23 View 7195 -
Furniture That Learns to Move by Itself
A novel strategy for displacing large objects by attaching relatively small vibration sources. After learning how several random bursts of vibration affect an object's pose, an optimization algorithm discovers the optimal sequence of vibration patterns required to (slowly but surely) move the object to a specified position. Displacements of large objects induced by vibration are a common occurrence, but generally result in unpredictable motion. Think, for instance, of an unbalanced front-loading washing machine. For controlled movement, wheels or legs are usually preferred.
Professor Daniel Saakes of the Department of Industrial Design and his team explored a strategy for moving everyday objects by harvesting external vibration rather than using a mechanical system with wheels. This principle may be useful for displacing large objects in situations where attaching wheels or complete lifting is impossible – assuming the speed of the process is not a concern.
His team designed vibration modules that can be easily attached to furniture and objects, and this could be a welcomed creation for people with limited mobility, including the elderly. Embedding these vibration modules as part of mass-produced objects may provide a low-cost way to make almost any object mobile.
Vibration as a principle for directed locomotion has been previously applied in micro-robots. For instance, the three-legged Kilobots move thanks to centrifugal forces alternatively generated by a pair of vibrations on two of its legs. The unbalanced weight transforms the robot into a ratchet and the resulting motion is deterministic with respect to the input vibration. To the best of our knowledge, we are the first to add vibratory actuators to deterministically steer large objects regardless of their structural properties.
The perturbation resulting from a particular pattern of vibration depends on a myriad of parameters, including but not limited to the microscopic properties of the contact surfaces. The key challenge is to empirically discover and select the sequence of vibration patterns to bring the object to the target pose.
Their approach is as follows. In the first step we systematically explore the object’s response by manipulating the amplitudes of the motors. This generates a pool of available moves (translations and rotations). We then calculate from this pool the most efficient way (either in terms of length or number of moves) to go from pose A to pose B using optimization strategies, such as genetic algorithms. The learning process may be repeated from time to time to account for changes in the mechanical response, at least for the patterns of vibration that contribute more to the change.
Prototype modules are made with eccentric rotating motors (type 345-002 Precision Microdrive) with a nominal force of 115g, which proved sufficient to shake (and eventually locomote) four-legged IKEA chairs and small furniture such as tables and stools. The motors are powered by NiMH batteries and communicate wirelessly with a low-cost ESP8266 WiFi module. The team designed modules that are externally attached using straps as well as motors embedded in furniture.
To study the general method, the team employed an overhead camera to track the chair and generate the pool of available moves. The team demonstrated that the system discovered pivot-like gaits and others. However, as one can imagine, using a pre-computed sequence to move to a target pose does not end up providing perfect matches. This is because the contact properties vary with location. Although this can be considered a secondary disturbance, it may in certain cases be mandatory to recompute the matrix of moves every now and then. The chair could, for instance, move into a wet area, over plastic carpet, etc.
The principle and application in furniture is called “ratchair” as a portmanteau combining “Ratchet” and “Chair”. Ratchair was demonstrated at the 2016 ACM Siggraph Emerging Technologies and won the DC-EXPO award jointly organized by the Japanese Ministry of Economy, Trade and Industry (METI) and the Digital Content Association of Japan (DCAJ). At the DCEXPO Exhibition, Fall 2016, the work was one of 20 Innovative Technologies and the only non-Japanese contribution.
*This article is from the KAIST Breakthroughs, research newsletter from the College of Engineering.
For more stories of the KAIST Breakthroughs, please visit http://breakthroughs.kaist.ac.kr
http://mid.kaist.ac.kr/projects/ratchair/
http://s2016.siggraph.org/content/emerging-technologies
https://www.dcexpo.jp/ko/15184
Figure 1. The vibration modules embedded and attached to furniture.
Figure 2. A close-up of the vibration module.
Figure 3. A close-up of the embedded modules.
Figure 4. A close-up of the vibration motor.
2017.03.23 View 8710 -
A Transport Technology for Nanowires Thermally Treated at 700 Celsius Degrees
Professor Jun-Bo Yoon and his research team of the Department of Electrical Engineering at KAIST developed a technology for transporting thermally treated nanowires to a flexible substrate and created a high performance device for collecting flexible energy by using the new technology.
Mr. Min-Ho Seo, a Ph.D. candidate, participated in this study as the first author. The results were published online on January 30th in ACS Nano, an international journal in the field of nanoscience and engineering. (“Versatile Transfer of an Ultralong and Seamless Nanowire Array Crystallized at High Temperature for Use in High-performance Flexible Devices,” DOI: 10.1021/acsnano.6b06842)
Nanowires are one of the most representative nanomaterials. They have wire structures with dimensions in nanometers. The nanowires are widely used in the scientific and engineering fields due to their prominent physical and chemical properties that depend on a one-dimensional structure, and their high applicability.
Nanowires have much higher performance if their structure has unique features such as an excellent arrangement and a longer-than-average length. Many researchers are thus actively participating in the research for making nanowires without much difficulty, analyzing them, and developing them for high performance application devices.
Scientists have recently favored a research topic on making nanowires chemically and physically on a flexible substrate and applies the nanowires to a flexible electric device such as a high performance wearable sensor.
The existing technology, however, mixed nanowires from a chemical synthesis with a solution and spread the mixture on a flexible substrate. The resultant distribution was random, and it was difficult to produce a high performance device based on the structural advantages of nanowires. In addition, the technology used a cutting edge nano-process and flexible materials, but this was not economically beneficial. The production of stable materials at a temperature of 700 Celsius degrees or higher is unattainable, a great challenge for the application.
To solve this problem, the research team developed a new nano-transfer technology that combines a silicon nano-grating board with a large surface area and a nano-sacrificial layer process. A nano-sacrificial layer exists between nanowires and a nano-grating board, which acts as the mold for the nano-transfer. The new technology allows the device undergo thermal treatment. After this, the layer disappears when the nanowires are transported to a flexible substrate.
This technology also permits the stable production of nanowires with secured properties at an extremely high temperature. In this case, the nanowires are neatly organized on a flexible substrate. The research team used the technology to manufacture barium carbonate nanowires on top of the flexible substrate. The wires secured their properties at a temperature of 700℃ or above. The team employed the collection of wearable energy to obtain much higher electrical energy than that of an energy collecting device designed based on regular barium titanate nanowires.
The researchers said that their technology is built upon a semiconductor process, known as Physical Vapor Deposition that allows various materials such as ceramics and semiconductors to be used for flexible substrates of nanowires. They expected that high performance flexible electric devices such as flexible transistors and thermoelectric elements can be produced with this method.
Mr. Seo said, “In this study, we transported nanowire materials with developed properties on a flexible substrate and showed an increase in device performance. Our technology will be fundamental to the production of various nanowires on a flexible substrate as well as the feasibility of making high performance wearable electric devices.”
This research was supported by the Leap Research Support Program of the National Research Foundation of Korea.
Fig. 1. Transcription process of new, developed nanowires (a) and a fundamental mimetic diagram of a nano-sacrificial layer (b)
Fig. 2. Transcription results from using gold (AU) nanowires. The categories of the results were (a) optical images, (b) physical signals, (c) cross-sectional images from a scanning electron microscope (SEM), and (d-f) an electric verification of whether the perfectly arranged nanowires were made on a large surface.
Fig. 3. Transcription from using barium titanate (BaTiO3) nanowires. The results were (a) optical images, (b-e) top images taken from an SEM in various locations, and (f, g) property analysis.
Fig. 4. Mimetic diagram of the energy collecting device from using a BaTiO3 nanowire substrate and an optical image of the experiment for the miniature energy collecting device attached to an index finger.
2017.03.22 View 8370 -
Highly-Efficient Photoelectrochemical CO2 Reduction
Direct CO2 conversion has continuously attracted a great deal of attention as a technology to produce fuels and chemical building blocks from renewable energy resources. Specifically, substances such as carbon feedstocks and fuels can be produced by utilizing sunlight, water, and CO2 as semiconductors and a water interface through photoelectrochemical CO2 reduction.
A KAIST research team demonstrated a novel photoelectrode structure for highly-selective and efficient photoelectrochemical CO2 reduction reactions. The research team led by Professor Jihun Oh of the Graduate School of EEWS (Energy, Environment, Water and Sustainability) presented a Si photoelectrode with a nanoporous Au thin film that is capable of reducing CO2 to CO with 90 percent selectivity in aqueous solution. The research team’s technology will provide a basic framework for designing the semiconductor photoelectrode structure necessary for photoelectrochemical conversion.
In order to achieve steady conversion of CO2, it is necessary to use a high-performance catalyst to lower overpotential. Among the metal catalysts, Au is known to be an electrocatalyst that converts CO2 to CO.
Conventionally, bare Au, as a catalyst, produces a lot of hydrogen gas due to its low CO selectivity. In addition, the high cost of Au remains a challenge in using the catalyst. Professor Oh’s research team addressed the issue by creating a nanoporous Au thin film formed by the electrochemical reduction of an anodized Au thin film.
As a result, the team could demonstrate an efficient, selective photoelectrochemical reduction reaction of CO2 to CO using electrochemically-treated Au thin films on a Si photoelectrode. The electrochemical reduction on anodized Au thin films forms a nanoporous thin layer exhibiting many grain boundaries of nanoparticles on the Au surface. This dramatically improves the selectivity of the reduction reaction with a maximum CO faradaic efficiency of over 90% at low overpotential and durability.
The research team also used an Au thin film of about 200 nanometers, 50,000 times thinner than previously reported nanostructured Au catalysts, resulting in a cost-effective catalyst. When depositing the catalyst on the semiconductor surface in the type of nanoparticles, the substrate of the thin film will be affected in the course of electrochemical reduction.
Thus, the research team designed a new Si photoelectrode with mesh-type co-catalysts that are independently wired at the front and back of the photoelectrode without influencing the photoelectrode, and made it possible for electrochemical reduction.
Due to the superior CO2 reduction reaction activity of the nanoporous Au mesh and high photovoltage from Si, the Si photoelectrode with the nanoporous Au thin film mesh shows conversion of CO2 to CO with 91% Faradaic efficiency at positive potential than CO equilibrium potential.
Professor Oh explained, “This technology will serve as a platform for diverse semiconductors and catalysts. Researchers can further improve the solar-to-CO2 conversion efficiency using this technology.
Dr. Jun Tae Song, the first author continued, “This new approach made it possible to develop a simple but very important type of electrode structure. It is the first time to achieve CO2 conversion at the potential lower than equilibrium potential. We believe that our research will contribute to efficient CO2 conversion.”
This research was published in the inside front cover of Advanced Energy Materials on February 8, 2017. The research was funded and supported by the Korea Carbon Capture & Sequestration R&D Center. Professor Sung-Yoon Chung of the EEWS also participated in this research.
(Figure: Schematic diagram of a Si photoelectrode that patterns with mesh-type nanoporous Au)
2017.03.08 View 9090 -
Semiconductor Photonic Nanocavities on Paper Substrates
Professor Yong-Hoon Cho of the Department of Physics and his team at KAIST have developed a semiconductor photonic nanocavity laser that can operate on a paper substrate.
The researchers hope that this novel method, which involves transferring nano-sized photonic crystal particles onto a paper substrate with high absorptiveness, will enable the diagnoses of various diseases by using high-tech semiconductor sensors at low cost.
The results of this research were published in the November 17th, 2016, issue of Advanced Materials.
Photonic crystals, which utilize light as a medium to provide high bandwidths, can transfer large amounts of information. Compared with their electronic counterparts, photonic crystals also consume less energy to operate.
Normally, semiconductor photonic particles require substrates, which play only a passive role in the assembly and endurance of individual, functional photonic components. These substrates, however, are bulky and environmentally hazardous as they are made up of non-biodegradable materials.
The research team overcame these two shortcomings by replacing a semiconductor substrate with standard paper. The substrate’s mass was reduced considerably, and because paper is made from trees, it degrades. Paper can be easily and cheaply acquired from our surroundings, which drastically reduces the unit cost of semiconductors.
In addition, paper possesses superior mechanical characteristics. It is flexible and can be repeatedly folded and unfolded without being torn. These are traits that have long been sought by researchers for existing flexible substrates.
The research team used a micro-sized stamp to detach photonic crystal nanobeam cavities selectively from their original substrate and transfer them onto a new paper substrate. Using this technique, the team removed nanophotonic crystals that had been patterned (using a process of selectively etching circuits onto a substrate) onto a semiconductor substrate with a high degree of integration, and realigned them as desired on a paper substrate.
The nanophotonic crystals that the team combined with paper in this research were 0.5 micrometers in width, 6 micrometers in length, and 0.3 micrometers in height—about one-hundredth of the width of a single hair (0.1 millimeter).
The team also transferred their photonic crystals onto paper with a fluid channel, which proved that it could be used as a refractive index sensor. As can be seen in current commercial pregnancy diagnosis kits, paper has high absorptiveness. Since photonic crystal particles have high sensitivity, they are highly suitable for applications such as sensors.
Professor Cho stated that “by using paper substrates, this technology can greatly contribute to the rising field of producing environmentally-friendly photonic particles” and “by combining inexpensive paper and high-performance photonic crystal sensors, we can obtain low prices as well as designing appropriate technologies with high performance.”
Dr. Sejeong Kim of the Department of Physics participated in this study as the first author, and Professor Kwanwoo Shin of Sogang University and Professor Yong-Hee Lee of KAIST also took part in this research. The research was supported by the National Research Foundation’s Mid-Career Researcher Program, and the Climate Change Research Hub of KAIST.
Figure 1. Illustration of photonic crystal lasers on paper substrates
Figure 2. Photonic crystal resonator laser and refractive index sensor operating on paper substrates
2017.03.01 View 7024 -
Quantum Dot Film Can Withstand High Temperatures and Humidity
The joint KAIST research team of Professor Byeong-Soo Bae of the Department of Materials Science and Engineering and Professor Doh Chang Lee of the Department of Chemical and Biomolecular Engineering was able to fabricate a siloxane-encapsulated quantum dot film, which exhibits stable emission intensity over one month even at high temperatures and humidity.
The results of this study were published in the Journal of the American Chemical Society (JACS) on November 29, 2016. The research article is entitled “Quantum Dot/Siloxane Composite Film Exceptionally Stable against Oxidation under Heat and Moisture.” (DOI: 10.1021/jacs.6b10681)
Quantum dots (QDs), light-emitting diodes (LEDs) for next-generation displays, are tiny particles or nanocrystals of semiconducting materials. Their emission wavelength can easily be adjusted by changing their sizes, which are just a few nanometers. A wide spectrum of their colors can also achieve ultra-high definition displays.
Due to these characteristics, QDs are coated on a film as a polymer resin in dispersed form, or they are spread on an LED light source. They are thus considered to be crucial for next generation displays.
Despite their exceptional optical properties, however, QDs are easily oxidized in a high temperature and high humidity environment, and, as a result, this greatly deteriorates their luminescence quality (quantum efficiency). Therefore, they are encapsulated in an extra thin layer to block oxygen and moisture.
QD displays in the current market have a film inserted to separate them from LEDs, which create heat. The high unit cost of this protective layer, however, increases the overall cost of displays, lowering their price competitiveness in the market.
For a solution, the research team applied the sol-gel condensation reaction of silane precursors with QDs. This technology uses the reactions of chemical substances to synthesize ceramics or glass at a low temperature.
The team applied QDs in a heat resistant siloxane polymer by employing this technology. The siloxane resin acted as a cup holding the QDs and also blocked heat and moisture. Thus, their performance can be maintained without an extra protective film.
QDs are evenly dispersed into the resin from a chemical process to fabricate a QD embedded film and retained the high quality luminescence not only at a high temperature of 85°C and in a high humidity of 85%, but also in a high acid and high base environment. Remarkably though, the luminescence actually increased in the high humidity environment.
If this technology is used, the overall price of displays will decrease by producing a stable QD film without an extra protective barrier. In the future, the QD film can be directly applied to a blue LED light source. As a result, it will be possible to develop a QD display that can reduce the amount of QDs needed and improve its performance.
Professor Bae said, “We have proposed a way to make quantum dots overcome their limitations and have wide applications as they are being developed for next-generation displays. Our technology will make significant contributions to the display industry in the country.”
He also added, “In the future, we plan to cooperate with companies both in and out of the country to improve the performance of quantum dots and concentrate on their commercialization.”
The research team is currently applying for related patents both in and out of the country. The team is also plan ning to transfer the patents to Sol Ip Technology Inc., a company founded at KAIST, to start the commercialization.
Picture 1:
Siloxane-encapsulated quantum dot (QD) films showing performance stability in boiling water
Picture 2 and 3:
So-gel condensation reaction in silane precursors between Methacryloxypropyltrimethoxysilane (MPTS) and diphenylsilanediol (DPSD). The inset shows photographs of a QD-oligosiloxane resin under room light (left) and a UV lamp (λ = 365 nm) (right).
Free radical addition reactions among carbon double bonds of methacryl functional groups and oleic acids. The inset shows photographs of a QD-silox film under room light (left) and a UV lamp (λ = 365 nm) (right).
2017.02.24 View 9465 -
Controlling Turtle Motion with Human Thought
KAIST researchers have developed a technology that can remotely control an animal’s movement with human thought.
In the 2009 blockbuster “Avatar,” a human remotely controls the body of an alien. It does so by injecting human intelligence into a remotely located, biological body. Although still in the realm of science fiction, researchers are nevertheless developing so-called ‘brain-computer interfaces’ (BCIs) following recent advances in electronics and computing. These technologies can ‘read’ and use human thought to control machines, for example, humanoid robots.
New research has demonstrated the possibility of combining a BCI with a device that transmits information from a computer to a brain, or known as a ‘computer-to-brain interface’ (CBI). The combination of these devices could be used to establish a functional link between the brains of different species. Now, researchers from the Korea Advanced Institute of Science and Technology (KAIST) have developed a human-turtle interaction system in which a signal originating from a human brain can affect where a turtle moves.
Unlike previous research that has tried to control animal movement by applying invasive methods, most notably in insects, Professors Phill-Seung Lee of the Mechanical Engineering Department and Sungho Jo of the Computing School propose a conceptual system that can guide an animal’s moving path by controlling its instinctive escape behavior. They chose a turtle because of its cognitive abilities as well as its ability to distinguish different wavelengths of light. Specifically, turtles can recognize a white light source as an open space and so move toward it. They also show specific avoidance behavior to things that might obstruct their view. Turtles also move toward and away from obstacles in their environment in a predictable manner. It was this instinctive, predictable behavior that the researchers induced using the BCI.
The entire human-turtle setup is as follows: A head-mounted display (HMD) is combined with a BCI to immerse the human user in the turtle’s environment. The human operator wears the BCI-HMD system, while the turtle has a 'cyborg system'—consisting of a camera, Wi-Fi transceiver, computer control module, and battery—all mounted on the turtle’s upper shell. Also included on the turtle’s shell is a black semi-cylinder with a slit, which forms the ‘stimulation device.’ This can be turned ±36 degrees via the BCI.
The entire process works like this: the human operator receives images from the camera mounted on the turtle. These real-time video images allow the human operator to decide where the turtle should move. The human provides thought commands that are recognized by the wearable BCI system as electroencephalography (EEG) signals. The BCI can distinguish between three mental states: left, right, and idle. The left and right commands activate the turtle’s stimulation device via Wi-Fi, turning it so that it obstructs the turtle’s view. This invokes its natural instinct to move toward light and change its direction. Finally, the human acquires updated visual feedback from the camera mounted on the shell and in this way continues to remotely navigate the turtle’s trajectory.
The research demonstrates that the animal guiding scheme via BCI can be used in a variety of environments with turtles moving indoors and outdoors on many different surfaces, like gravel and grass, and tackling a range of obstacles, such as shallow water and trees. This technology could be developed to integrate positioning systems and improved augmented and virtual reality techniques, enabling various applications, including devices for military reconnaissance and surveillance.
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Reference: “Remote Navigation of Turtle by Controlling Instinct Behavior via Human Brain-computer Interface,” Journal of Bionic Engineering, July 2016 (DOI: 10.1016/S1672-6529(16)60322-0)
Depiction of Cyborg System
A human controller influences the turtle’s escape behavior by sending left and right signals via Wi-Fi to a control system on the back of the turtle.
2017.02.21 View 13783