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Novel Strategies to Transform a Commercially Available Iboga Alkaloid to Post-Iboga Alkaloids
(PhD candidate HyeonggeunLim, Professor Sunkyu Han, PhD candidate Sikwang Seong)
KAIST chemists have synthesized seven different iboga and post-iboga natural products from commercially available catharanthine by mirroring nature’s biosynthetic post-modification of the iboga skeleton. They devised a novel strategy to biosynthesize the natural products via a series of selective and efficient oxidation and rearrangement reactions. This will serve as a stepping stone for developing therapeutic medications against cancer and narcotics addiction.
The research team, led by Professor Sunkyu Han, conceptualized and coined the term “Post-Iboga” alkaloids to describe the natural products that are biosynthetically derived from iboga-type alkaloids, which are composed of rearranged indole and/or isoquinuclidine backbones.
Iboga alkaloids have attracted significant attention from the scientific community due to their intriguing polycyclic structures and potential therapeutic uses against drug addictions. Nature has evolved to add architectural repertoires to this family of secondary metabolites by diversifying the iboga frameworks.
Notable examples are the FDA-approved anticancer drugs vinblastine and vincristine, both derived by the oxidative dimerization of catharanthine and vindoline subunits. Admittedly, synthetic foci toward the biosynthetic iboga-derivatives have historically been on these aforementioned dimeric natural products.
Recent natural product isolation studies on Tabernaemontana corymbosa and Ervatamia officinalis species have resulted in discoveries of various secondary metabolites that are biosynthetically derived from iboga alkaloids. These recent outbursts of iboga-derived natural product isolation reports have kindled interests toward these family of natural products.
The research team utilized (+)-catharanthine, the starting material for the industrial production of the anticancer drug Navelbine®. Well-orchestrated oxidations at the C19 position and the indole moiety of the catharanthine derivative, followed by differential rearrangements under acidic conditions, provided synthetic samples of voatinggine and tabertinggine respectively.
On the other hand, opportune oxidations at the C19 position and the alpha position of the tertiary amine moiety of the catharantine derivative, followed by a transhemiaminalization, produced the first synthetic sample of chippiine/dippinine-type natural product, dippinine B.
It is important to note that the chippiine and dippinine-type alkaloids have been targeted among synthetic chemists for over 30 years but had not succumbed to synthesis prior to this report.
Professor Han believes that their study will serve as a blueprint for further explorations of the synthesis, biosynthesis, and pharmacology of this emerging family of natural products. This study was published in Chem on November 15, 2018 (DOI: 10.1016/j.chempr.2018.10.009).
2018.11.16 View 4891 -
New Anisotropic Conductive Film for Ultra-Fine Pitch Assembly Applications
(Professor Paik(right) and PhD Candidate Yoon)
Higher resolution display electronic devices increasingly needs ultra-fine pitch assemblies. On that account, display driver interconnection technology has become a major challenge for upscaling display electronics.
Researchers have moved to one step closer to realizing ultra-fine resolution for displays with a novel thermoplastic anchoring polymer layer structure. This new structure can significantly improve the ultra-fine pitch interconnection by effectively suppressing the movement of conductive particles. This film is expected to be applied to various mobile devices, large-sized OLED panels, and VR, among others.
A research team under Professor Kyung-Wook Paik in the Department of Materials developed an anchoring polymer layer structure that can effectively suppress the movement of conductive particles during the bonding process of the anisotropic conductive films (ACFs). The new structure will significantly improve the conductive particle capture rate, addressing electrical short problems in the ultra-fine pitch assembly process.
During the ultra-fine pitch bonding process, the conductive particles of conventional ACFs agglomerate between bumps and cause electrical short circuits. To overcome the electrical shortage problem caused by the free movement of conductive particles, higher tensile strength anchoring polymer layers incorporated with conductive particles were introduced into the ACFs to effectively prevent conductive particle movement.
The team used nylon to produce a single layer film with well-distributed and incorporated conductive particles. The higher tensile strength of nylon completely suppressed the movement of conductive particles, raising the capture rate of conductive particles from 33% of the conventional ACFs to 90%. The nylon films showed no short circuit problem during the Chip on Glass assembly. Even more, they obtained excellent electrical conductivity, high reliability, and low cost ACFs during the ultra-fine pitch applications.
Professor Paik believes this new type of ACFs can further be applied not only to VR, 4K and 8K UHD display products, but also to large-size OLED panels and mobile devices.
His team completed a prototype of the film supported by the ‘H&S High-Tech,’ a domestic company and the ‘Innopolis Foundation.’ The study, whose first author is PhD candidate Dal-Jin Yoon, is described in the October issue of IEEE TCPMT.
Figure 1: Schematic process of APL structure fabrication.
Figure 2: Proto-type production of APL ACFs.
2018.11.13 View 5652 -
OUIC Presents the Six Most Promising Techs Transferrable to Local SMEs
KAIST will showcase the six most promising technologies for small and medium enterprises (SMEs) on November 14 in the Academic Cultural Complex. To strengthen the competitive edge of local SMEs in Daejeon, the Office of University-Industry made a survey of their technological needs and came up with the six most promising technologies. Developers will introduce their technologies during the session.Besides the introduction of the promising technologies, the session will also provide a program named University to Business (U2B) to match up technologies according to the SMEs’ needs. SMEs who wish to engage in technology transfers can receive counseling and other support programs during the session.First, Professor Seok-Hyung Bae from the Department of Industrial Design will present a technology for controlling cooperation robots. Professor Bae inserted flexible materials between the controllers to allow robots to use both hands stably and operate more accurately and swiftly. It can be applied to automatic robots, industrial robots, and service robots.Professor Hyun Myung from the Department of Civil & Environmental Engineering will demonstrate a robot navigation system in a dynamic indoor and outdoor environment, which can be applied to robotics in logistics, smart factories, and autonomous vehicles. Providing robust simultaneous localization and mapping systems, this technology shows high-performing navigation with low-cost sensors.Meanwhile, Professor Siyoung Choi from the Department of Chemical and Biomolecular Engineering will introduce a technology for forming stable adhesive emulsions. An emulsion is a stable mixture of water and oil. Conventionally, a small amount of surfactant is added to stabilize an emulsion. Here, Professor Choi developed a stable emulsion system without using any chemical substances. This technology can be applied to various fields, including the cosmetics, pharmaceutical, semiconductor, and painting industries. The session will also present smart IoTs platform technology developed by Professor Jinhong Yang from the KAIST Institute for IT Convergence. His technology minimizes errors occurring when multiple IoT devices are connected simultaneously. Professor Yong Keun Park from the Department of Physics will introduce a technology for measuring glycated hemoglobin by using the optical properties of red blood cells. This technology can be applied to make low-cost, small-sized measuring equipment. It can also be used for vitro diagnoses including diabetes, cardiovascular disorders, tumors, kidney disease, and infectious diseases. Professor Yong Man Ro from the School of Electrical Engineering will show technology for biometric access control. Conventional technologies for face recognition fall behind other biometrics. Professor Ro and his team developed a facial dynamics interpreting network which allows very accurate facial recognition by interpreting the relationships between facial local dynamics and estimating facial traits. This technology can be applied to security and communication in finance, computers, and information system.KAIST President Sung-Chul Shin said, “KAIST will continue to support SMEs to have stronger competitiveness in the market. Through technology transfer, we will drive innovation in technological commercialization where a university’s research and development creates economic value.”
2018.11.13 View 7449 -
Faster and More Powerful Aqueous Hybrid Capacitor
(Professor Jeung Ku Kang from the Graduate School of EEWS)
A KAIST research team made it one step closer to realizing safe energy storage with high energy density, high power density, and a longer cycle life. This hybrid storage alternative shows power density 100 times faster than conventional batteries, allowing it to be charged within a few seconds. Hence, it is suitable for small portable electronic devices.
Conventional electrochemical energy storage systems, including lithium-ion batteries (LIBs), have a high voltage range and energy density, but are subject to safety issues raised by flammable organic electrolytes, which are used to ensure the beneficial properties. Additionally, they suffer from slow electrochemical reaction rates, which lead to a poor charging rate and low power density with a capacity that fades quickly, resulting in a short cycle life.
On the other hand, capacitors based on aqueous electrolytes are receiving a great deal of attention because they are considered to be safe and environmentally friendly alternatives. However, aqueous electrolytes lag behind energy storage systems based on organic electrolytes in terms of energy density due to their limited voltage range and low capacitance.
Hence, developing aqueous energy storage with high energy density and a long cycle life in addition to the high power density that enables fast charging is the most challenging task for advancing next-generation electrochemical energy storage devices.
Here, Professor Jeung Ku Kang from the Graduate School of Energy, Environment, Water and Sustainability and his team developed an aqueous hybrid capacitor (AHC) that boasts high energy density, high power, and excellent cycle stability by synthesizing two types of porous metal oxide nanoclusters on graphene to create positive and negative electrodes for AHCs.
The porous metal oxide nanoparticles are composed of nanoclusters as small as two to three nanometers and have mesopores that are smaller than five nanometers. In these porous structures, ions can be rapidly transferred to the material surfaces and a large number of ions can be stored inside the metal oxide particles very quickly due to their small particle size and large surface area.
The team applied porous manganese oxide on graphene for positive electrodes and porous iron oxide on graphene for negative electrodes to design an aqueous hybrid capacitor that can operate at an extended voltage range of 2V.
Professor Kang said, “This newly developed AHC with high capacity and power density driven from porous metal oxide electrodes will contribute to commercializing a new type of energy storage system. This technology allows ultra-fast charging within several seconds, making it suitable as a power source for mobile devices or electric vehicles where solar energy is directly stored as electricity.”
This research, co-led by Professor Hyung Mo Jeong from Kangwon National University, was published in Advanced Functional Materials on August 15, 2018.
Figure 1. Image that shows properties of porous metal oxide nanoparticles formed on graphene in the aqueous hybrid capacitor
2018.11.09 View 6629 -
Global Lounge Opens for Language and Cultural Exchange
KAIST celebrated the opening of its new Global Lounge on November 8. KAIST’s president, administrative executives, representatives of Korean and international student associations, and many other students attended the ceremony.
The Global Lounge, located on the fourth floor of the Academic Cultural Complex, was opened for students to share language and culture in a warm and pleasant environment. The Global Lounge will serve as a comfortable and open space. Students around the world can build networks by interacting with one another and freely sharing their ideas.
The lounge offers travel guidebooks and magazines for those who wish to learn more about countries around the world. It also boasts a room for seminars and a tearoom. The seminar room will be used for multipurpose space; while activities such as meditation, tea classes, and etiquette lessons will take place in the tearoom. One of the major highlights of the global lounge is that it exhibits cultural artifacts donated by embassies in Korea.
At the opening ceremony, President Sung-Chul Shin expressed the importance of communication and interaction among students by saying, “You can better embrace challenges and come up with creative ideas when you are interacting with others. I hope this Global Lounge serves as a multi-functional space for raising cultural awareness.”
2018.11.08 View 2362 -
Team KAT Wins the Autonomous Car Challenge
(Team KAT receiving the Presidential Award)
A KAIST team won the 2018 International Autonomous Car Challenge for University Students held in Daegu on November 2.
Professor Seung-Hyun Kong from the ChoChunShik Graduate School of Green Transportation and his team participated in this contest with the team named KAT (KAIST Autonomous Technologies). The team received the Presidential Award with a fifty million won cash prize and an opportunity for a field trip abroad.
The competition was conducted on actual roads with Connected Autonomous Vehicles (CAV), which incorporate autonomous driving technologies and vehicle-to-everything (V2X) communication system.
In this contest, the autonomous vehicles were given a mission to pick up passengers or parcels. Through the V2X communication, the contest gave current location of the passengers or parcels, their destination, and service profitability according to distance and level of service difficulty.
The participating vehicles had to be equipped very accurate and robust navigation system since they had to drive on narrow roads as well as go through tunnels where GPS was not available. Moreover, they had to use camera-based recognition technology that was invulnerable to backlight as the contest was in the late afternoon.
The contest scored the mission in the following way: the vehicles get points if they pick up passengers and safely drop them off at their destination; on the other hand, points are deducted when they violate lanes or traffic lights. It will be a major black mark if a participant sitting in the driver’s seat needs to get involved in driving due to a technical issue.
Youngbo Shim of KAT said, “We believe that we got major points for technical superiority in autonomous driving and our algorithm for passenger selection.”
This contest, hosted by Ministry of Trade, Industry and Energy, was the first international competition for autonomous driving on actual roads. A total of nine teams participated in the final contest, four domestic teams and five teams allied with overseas universities such as Tsinghua University, Waseda University, and Nanyang Technological University.
Professor Kong said, “There is still a long way to go for fully autonomous vehicles that drive flexibly under congested traffic conditions. However, we will continue to our research in order to achieve high-quality autonomous driving technology.”
(Team KAT getting ready for the challenge)
2018.11.06 View 9331 -
Controlling Crystal Size of Organic Semiconductors
A KAIST research team led by Professor Steve Park from the Department of Materials Science and Engineering
Recently, solution-processable organic semiconductors are being highlighted for their potential application in printed electronics, becoming a feasible technique to fabricate large-area flexible thin film at a low cost. The field-effect mobility of small-molecule organic semiconductors is dependent on the crystallinity, crystal orientation, and crystal size. A variety of solution-based coating techniques, such as ink-jet printing, dip-coating, and solution shearing have been developed to control the crystallinity and crystal orientation, but a method for developing techniques to increase the crystal size of organic semiconductors is still needed.
To overcome this issue, the research team developed an inorganic polymer micropillar-based solution shearing system to increase the crystal size of an organic semiconductor with pillar size. Using this technique, the crystallization process of organic semiconductors can be controlled precisely, and therefore large-area organic semiconductor thin film with controlled crystallinity can be fabricated.
A variety of solution-based coating techniques cannot control the fluid-flow of solutions appropriately, so the solvent evaporates randomly onto the substrate, which has difficulty in the fabrication of organic semiconductor thin film with a large crystal size.
The research team integrated inorganic polymer microstructures into the solution shearing blade to solve this issue. The inorganic polymer can easily be microstructured via conventional molding techniques, has high mechanical durability, and organic solvent resistance. Using the inorganic polymer-based microstructure blade, the research team controlled the size of small molecule organic semiconductors by tuning the shape and dimensions of the microstructure. The microstructures in the blade induce the sharp curvature regions in the meniscus line that formed between the shearing blade and the substrate, and therefore nucleation and crystal growth can be regulated. Hence, the research team fabricated organic semiconductor thin-film with large crystals, which increases the field-effect mobility.
The research team also demonstrated a solution shearing process on a curved surface by using a flexible inorganic polymer-based shearing blade, which expands the applicability of solution shearing.
Professor Park said, “Our new solution shearing system can control the crystallization process precisely during solvent evaporation.” He added, “This technique adds another key parameter that can be utilized to tune the property of thin films and opens up a wide variety of new applications.
The results of this work entitled “Inorganic Polymer Micropillar-Based Solution Shearing of Large-Area Organic Semiconductor Thin Films with Pillar-Size-Dependent Crystal Size” was published in the July 2018 issue of Advanced Materials as a cover article.
2018.10.30 View 5266 -
Professor Baik Awarded Sangsan Young Mathematician Prize
(Professor Hyungryul Baik)
Professor Hyungryul Baik from the Department of Mathematical Sciences was honored as the recipient of the 2018 Sangsan Prize for Young Mathematicians by the Korean Mathematical Society (KMS).
The Sangsan Prize recognizes young mathematicians who finished their degree within the previous five years and have begun an outstanding research career. Professor Baik was recognized for his studies in the fields of low-dimensional topology, geophysical mathematics, and geometric theory. In particular, his Ph.D. dissertation presented a new criterion that completely identifies the hyperbolic surface group, making an inference about the nature of the hyperbolic manifold group.
Recently, Professor Baik co-published a paper entitled Spaces of Invariant Circular Orders of Groups with Professor Eric Samperton at the University of California Santa Barbara in the renowned academic journal Groups, Geometry, and Dynamics in 2018.
Professor Baik earned his BS at KAIST and finished his MS and Ph.D. in mathematics in 2014 at Cornell University. He joined KAIST as a faculty member last year.
2018.10.30 View 5239 -
KAIST Thanks Supporters for Building KAIST of Today
KAIST hosted its first Fundraising Gala on October 26, 2018. It was organized to demonstrate deep gratitude to those who have made contributions to KAIST, making it possible to progress every year.
The KAIST Development Foundation (KDF) endeavored to make a meaningful and inclusive event by collecting archives that show the history of donations while sending invitatio ns to all the members of KAIST, including donors and potential donors as well as professors and student representatives.
Approximately 200 distinguished guests attended the gala, including major donors, Chairperson of KDF Soo Young Lee and Chairman Beang Ho Kim, Former Minister of Science Dr. Geun Mo Jung, Former Minister of Science and Technology Woo Sik Kim, and KAIST alumni including the first Korean astronaut So-Yeon Yi.
(Student cheer leading club, ELKA)
At the gala, KAIST shared its 47 years of funding and an expenditure summary with major performances achieved from the year it was founded. According to the summary, KAIST has received more than 323.1 billion won since 1971. The total number of donors was 12,906 while the number of contribution reached 77,710.
Among the total funding (323.1 billion won), corporate gifts made up 43.1% of the total and individual gifts stood at 39.1%, showing that KAIST has received and is receiving support evenly from companies and individuals.
Taking a close look at the major donors, there is an interesting fact about KAIST’s fundraising culture. There has been continuous support from individuals who did not have any personal or academic ties with KAIST before donating. However, they have made large gifts to KAIST so that the best students in the fields of science and technology can be fostered for the sake of national development. The major donors included Young Han Kim (1999), Moon Soul Chung (2001), Byiung Joon Park (2007), Keun Chul Ryu (2008), Beong Ho Kim (2009), Chun Shik Cho and E won Oh (2010), Soo Young Lee (2012), Tae-won Chey (2014), Jeong Ja Cho (2015), and Chang Kun Sohn (2017).
Especially, M. S. Chung, B. H. Kim, C. S. Cho and S. Y. Lee made additional mega-gifts to KAIST, showing continuous support for KAIST’s development.
Nevertheless, the KAIST fundraising culture could not be created with major donors only. Among the total number of donors (12,906), alumni showed the strong engagement standing at 40.4% while parents and students were at 26.1% and 12.7% respectively. The contribution numbers follow the order of alumni (34.8%), parents (20.3%), staff (20%), professors (13.3%), and students (5.7%). These statistics imply that individual’s constant donations play a significant part in the fundraising culture of KAIST.
Additionally, engagement continues to rise every year, and it reached 12,039 gifts in 2017, which increased 5.7 times over ten years.
(from left: Executive Director of KDF Young-gul Kim KAIST President Sung-Chul Shin)
These valuable gifts are the vital fuel for KAIST’s progress. As of 2018, KAIST has spent 205.8 billion won: 81.9 billion won for construction and facilities operation, 79.7 billion won for academics and research, 39 billion won for academic management, and 5.2 billion won for scholarships.
The construction and facilities operation fund aided the evolution of physical infrastructure. KAIST endowed the ChungMoonSoul Building for promoting convergence between information and biotechnology, the Yang Bun Soon Building for bio and brain engineering studies, and the Chunghi & Byiung Jun Park KI Building for multi and interdisciplinary research. Their generous gifts built the foundation for KAIST taking off towards becoming a global leading university.
Meanwhile, the academic and research funds provided opportunities to professors and students to carry out creative research and academic missions. The academic management fund helped open new departments (i.e. The Cho Chun Shik Graduate School of Green Transportation and the Moon Soul Graduate School of Future Strategy) and their programs, for which their names came from the major donors.
(The first Korean astronaut So-Yeon Yi)
At the gala, special events were held for two exclusive moments that contributed to promoting and making a better image for KAIST to the public. One was the 10th anniversary of the space exploration of the first Korean astronaut Dr. Yi. The other was the 20th anniversary of the TV drama series, called ‘KAIST’ which was aired from 1999 to 2000. The writer and main casting crew members joined the event. They said that it was their first time to gather in one place after the show last aired and this event would be memorable for them as well.
President Sung-Chul Shin said, “These gifts play the role of seed money that helps KAIST obtain competence in a global scenario. I hope people have more interest in supporting KAIST through this event.”
1 Total Amount of Gift
2 Total Donors
3 Expenditure Number of Contribution
4 Expenditure
2018.10.29 View 6655 -
KAIST Launches Woorisae II
Professor Sejin Kwon from the Department of Aerospace Engineering and his team succeeded in launching a science rocket, named ‘Woorisae II’ at Saemanguem reclamation. This rocket was developed in collaboration with the Satellite Technology Research Lab (SaRTec).
The test-firing was conducted at 10:43 am on Sunday October 28, 2018 (35°N 42’ 06” 126°E 33’ 36”, Radius of 0.6NM). This launch was the follow-up to the previous launch that was cancelled due to not gaining approval for using the airspace.
Professor Kwon’s team put a great deal of effort into securing the land for the rocket launch. As a result, they got approval from the Saemangeum Development and Investment Agency for the land and the Ministry of Land, Infrastructure and Transport for the use of the airspace. The Republic of Korea Air Force and United States Air Force also approved the use of the airspace for the launch of the science rocket for research purposes.
Woorisae II is 2.2 meters long with a diameter of 20cm, and weighs 13kg without a payload. The rocket is powered by a hybrid rocket with hydrogen peroxide oxidizer producing 100 kg of force. The Woorisae II sounding rocket was designed to burn for five seconds and then continue inertial flight for 20 seconds. The target altitude of Woorisae II was set at 3,300 feet to comply with the airspace approval.
The team developed the core components, including a hybrid rocket propulsion system, flight computer and parachute recovery system, as well as a ground control station. The flight data was transmitted to the ground station and recorded to onboard computer memory.
When a malfunction occurs during the flight, Woorisae II was designed to terminate the power flight for safety by shutting the propellant valve and deploying the recovery parachute. All the rocket subsystems and components were developed and supplied by domestic startup companies such as INOCOM and NARA SPACE TEHCNOLOGY.
Generally, sounding rockets reach an altitude beyond 30km and are widely used for testing rocket engines and reentry materials as well as for conducting microgravity experiments. Instruments for atmospheric science can also be installed to measure fine dust and high altitude atmosphere. Besides these science and technology purposes, most advanced spacefaring countries have sounding rocket programs to train and educate young people in the field of space science.
Professor Kwon said, “We will plan to launch upgraded rockets on November 4 and December 6 because we already received approval from the related agencies for using this land and airspace. Based on the experiment, we are planning to develop a cost-efficient small launch vehicle that is capable of delivering a cube satellite into Earth’s orbit.”
(Photos of preparing the rocket launch)
2018.10.29 View 8100 -
Lens-free OLEDs with Efficiency comparable to that of Inorganic LEDs
(from left: Professor Seunghyup Yoo and PhD candidate Jinouk Song)
The use of organic light-emitting diodes (OLEDs) has extended to various applications, but their efficiency is still lagging behind inorganic light-emitting diodes. In this research, a KAIST team provided a systematic way to yield OLEDs with an external quantum efficiency (EQE) greater than 50% with an external scattering medium.
Having properties suitable for thin and flexible devices, OLEDs are popular light sources for displays, such as mobile devices and high quality TVs. In recent years, numerous efforts have been made to apply OLEDs in lighting as well as light sources for vehicles.
For such applications, high efficiency is of the upmost importance for the successful deployment of light sources. Thanks to continuous research and the development of OLEDs, their efficiency is steadily on the rise, and a level equivalent to inorganic LEDs has been demonstrated in some reports.
However, these highly efficient OLEDs were often achieved with a macroscopic lens or complex internal nanostructures, which undermines the key advantages of OLEDs as an affordable planar light sources and tends to hinder their stable operation, thus putting a limitation to their commercialization.
Among various methods proven effective for OLED light extraction, a team led by Professor Seunghyup Yoo at the School of Electrical Engineering focused on the external scattering-based approach, as it can maintain planar geometry and compatibility with flexibility. It is also able to be fabricated on a large scale at a low cost and causes no interference with electrical properties of OLEDs.
Conventionally, research on enhancing OLED light extraction using light scattering has been conducted empirically in many cases. This time, the team developed comprehensive and analytical methodology to theoretically predict structures that maximize efficiency.
Considering OLEDs with the external scattering layers as a whole rather than two separate entities, the researchers combined the mathematical description of the scattering phenomena with the optical model for light emission within an OLED to rapidly predict the characteristics of many devices with various structures. Based on this approach, the team theoretically predicted the optimal combination of scattering layers and OLED architectures that can lead to the maximum efficiency.
Following this theoretical prediction, the team experimentally produced the optimal light scattering film and incorporated it to OLEDs with orange emitters having a high degree of horizontal dipole orientation. As a result, the team successfully realized OLEDs exhibiting EQE of 56% and power efficiency of 221 lm/W. This is one of the highest efficiencies ever realized for an OLED unit device without the help of a macroscopic lens or internal light extraction structures.
Professor Yoo said, “There are various technologies developed for improving OLED light extraction efficiency; nevertheless, most of them have not reached a level of practical use. This research mainly provides a systematic way to attain an EQE of 50% or higher in OLEDs while keeping in mind the constraints for commercialization. The approach shown here can readily be applied to lighting devices or sensors of wearable devices.”.
This research, co-led by Professor Jang-Joo Kim from Seoul National University and Professor Yun-Hi Kim from Gyeongsang National University, was published in Nature Communications on August 10, 2018. (J. Song et al. Nature Communications, 9, 3207. DOI: 10.1038/s41467-018-05671-x)
Figure 1.Photographs of OLEDs with SiO₂ -embedded scattering layers according to scatterance
2018.10.26 View 7468 -
A Molecular Sensor for In-Situ Analysis of Complex Biological Fluids
A KAIST research group presented a molecular sensor with a microbead format for the rapid in-situ detection of harmful molecules in biological fluids or foods in a collaboration with a Korea Institute of Materials Science (KIMS) research group. As the sensor is designed to selectively concentrate charged small molecules and amplify the Raman signal, no time-consuming pretreatment of samples is required.
Raman spectra are commonly known as molecular fingerprints. However, their low intensity has restricted their use in molecular detection, especially for low concentrations. Raman signals can be dramatically amplified by locating the molecules on the surface of metal nanostructures where the electromagnetic field is strongly localized. However, it is still challenging to use Raman signals for the detection of small molecules dissolved in complex biological fluids. Adhesive proteins irreversibly adsorb on the metal surface, which prevents the access of small target molecules onto the metal surface. Therefore, it was a prerequisite to purify the samples before analysis. However, it takes a long time and is expensive.
A joint team from Professor Shin-Hyun Kim’s group in KAIST and Dr. Dong-Ho Kim’s group in KIMS has addressed the issue by encapsulating agglomerates of gold nanoparticles using a hydrogel. The hydrogel has three-dimensional network structures so that molecules smaller than the mesh are selectively permeable. Therefore, the hydrogel can exclude relatively large proteins, while allowing the infusion of small molecules. Therefore, the surface of gold nanoparticles remains intact against proteins, which accommodates small molecules. In particular, the charged hydrogel enables the concentration of oppositely-charged small molecules. That is, the purification is autonomously done by the materials, removing the need for time-consuming pretreatment. As a result, the Raman signal of small molecules can be selectively amplified in the absence of adhesive proteins.
Using the molecular sensors, the research team demonstrated the direct detection of fipronil sulfone dissolved in an egg without sample pretreatment. Recently, insecticide-contaminated eggs have spread in Europe, South Korea, and other countries, threatening health and causing social chaos. Fipronil is one of the most commonly used insecticides for veterinary medicine to combat fleas. The fipronil is absorbed through the chicken skin, from which a metabolite, fipronil sulfone, accumulates in the eggs. As the fipronil sulfone carries partial negative charges, it can be concentrated using positively-charged microgels while excluding adhesive proteins in eggs, such as ovalbumin, ovoglobulin, and ovomucoid. Therefore, the Raman spectrum of fipronil sulfone can be directly measured. The limit of direct detection of fipronil sulfone dissolved in an egg was measured at 0.05 ppm.
Professor Kim said, “The molecular sensors can be used not only for the direct detection of harmful molecules in foods but also for residual drugs or biomarkers in blood or urine.” Dr. Dong-Ho Kim said, “It will be possible to save time and cost as no sample treatment is required.”
This research was led by graduate student Dong Jae Kim and an article entitled “SERS-Active Charged Microgels for Size- and Charge-Selective Molecular Analysis of Complex Biological Samples” was published on October 4, 2018 in Small and featured on the inside cover of the journal.
Figure 1. Schematic illustrating the concentration of charged small molecules and the exclusion of large adhesive proteins using a charged hydrogel microbead containing an agglomerate of gold nanoparticles. The Raman signal of the small molecules is selectively amplified by the agglomerate.
Figure 2. Confocal laser scanning microscope images showing the concentration of oppositely charged molecules, where negatively-charged microgels are denoted by red circles and positively-charged microgels are denoted by blue circles. Green fluorescence originates from negatively-charged dye molecules and red fluorescence originates from positively-charged dye molecules.
Figure 3. Raman spectra measured from fipronil sulfone-spiked eggs, where the concentrations of fipronil sulfone are denoted; 0 ppm indicates no fipronil sulfone in the egg. The characteristic peaks of fipronil sulfone are denoted by the dotted lines.
2018.10.23 View 5817