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Photonic crystals allow the fabrication of miniaturized spectrometers
By Courtesy of Nanowerk
Photonic crystals allow the fabrication of miniaturized spectrometers
(Nanowerk Spotlight) Spectrometers are used in materials analysis by measuring the absorption of light by a surface or chemical substance. These instruments measure properties of light over a specific portion of the electromagnetic spectrum. In conventional spectrometers, a diffraction grating splits the light source into several beams with different propagation directions according to the wavelength of the light. Thus, to achieve sufficient spatial separation for intensity measurements at a small slit, a long light path – i.e., a large instrument – is required.
However, for lab-on-a-chip or microTAS (total analysis system) applications, the spectrometer must be integrated into a sub-centimeter scale device to produce a stand-alone platform. To achieve this, researchers at the Korea Advanced Institute of Science and Technology (KAIST) propose a new paradigm in which the spectrometer is based on an array of photonic crystals with different bandgaps.
"Because photonic crystals refelct light of different wavelengths selectively depending on their bandgaps, we can generate reflected light spanning the entire wavelength range for analysis at different spatial positions using patterned photonic crystals," Seung-Man Yang, Director of the National Creative Research Initiative Center for Intergrated Optofluidic Systems and Professor of the Department of Chemical & Biomolecular Engineering at KAIST, tells Nanowerk. "Therefore, when the light source impinges on the patterned photonic crytals, we can construct the spectrum using the reflection intensity profile from the constituent photonic crystals."
Photonic crystals – also known as photonic band gap material – are similar to semiconductors, only that the electrons are replaced by photons (i.e. light). By creating periodic structures out of materials with contrast in their dielectric constants, it becomes possible to guide the flow of light through the photonic crystals in a way similar to how electrons are directed through doped regions of semiconductors. The photonic band gap (that forbids propagation of a certain frequency range of light) gives rise to distinct optical phenomena and enables one to control light with amazing facility and produce effects that are impossible with conventional optics.
To demonstrate this new concept based on patterned photonic crystals, Yang and his group used non-close-packed colloidal crystals of silica particles dispersed in photocurable resin. Due to the repulsive interparticle potential, monodisperse silica particles spontaneously crystallize into non-close-packed face-centered cubic (fcc) structures at volume fractions above 0.1. Therefore, the particle volume fraction determines both the lattice constant and the bandgap position.
a) Optical image of an ETPTA film containing porous photonic crystal stripe patterns with 20 different bandgaps. b) Reflectance spectra from the 20 strips. c) Optical microscope image of the middle region with the parallel stripe pattern (denoted as white-dotted box in a). d) Cross-sectional SEM images of first, sixth, eleventh and seventeenth strips. The scale bars in a, c and d are 1 cm, 2mm and 2 µm, respectively. (reprinted with permission from Wiley-VCH Verlag)
Reporting their findings in a recent issue of Advanced Materials ("Integration of Colloidal Photonic Crystals toward Miniaturized Spectrometers"), the KAIST team has demonstrated the integration of colloidal photonic crystals with 20 different bandgaps into freestanding films (prepared by soft lithography), and their application as a spectrometer.
Yang explains that the team was able to precisely control the photonic bandgap by varying the particle size and volume fration.
"The prepared colloidal composite structures showed high physical rigidity and chemical resistivity" he says. "The composite structure is suitable for spectroscopic use due to the small full widths at half maximum (FWHMs) of the reflectance spectra, which mean that there is little overlap of the reflectance spectra of neighboring photonic crystal strips."
"On the other hand" says Yang, "porous photonic crystals showed large FWHMs and high reflectivities, which should prove useful in many practical photonic applications that require high optical performance and physical rigidity as well as simple and inexpensive preparation."
In addition to fabricating miniaturized spectrometers, which can for instance be integrated into small lab-on-a-chip devices, these integrated photonic crystals can be potentially used for tunable band reflection mirrors, optical switches, and tunable lasing cavities. Moreover, patterned photonic crystals with RGB colors are well-suited for use in reflection-mode microdisplay devices.
Yang points out that, although the spectrometric resolution can be reduced by employing the smaller bandgap interval and photonic bandwidth, there is a limitation. "Now, we are studying photonic crystals with continuous modulation of bandgap position. We expect that the photonic crystals can reduce the resolution to 0.01 nm."
By Michael Berger. Copyright 2010 Nanowerk
2010.03.17 View 13053 -
Opening Ceremony Held on February 3, 2010 for Intellectual Property Training Center
KAIST Opened Training Center for Young Entrepreneurs
Commissioner Jung-Sik Koh of Korean Intellectual Property Office (KIPO) and KAIST faculty members including Soon-Hong Jang, Vice President of Operations and Kwang-Hyung Lee, Dean of Academic Affairs Office, joined an opening ceremony held on February 3rd, 2010 to launch a training center for the next generation entrepreneurs who will lead the intellectual property (IP) industry in Korea.
The training center was built in cooperation with KIPO to educate and support young entrepreneurs and prepare them to become tomorrow’s IP business leaders like Bill Gates of Microsoft and Google’s founders, Larry Page and Sergey Brin.
Going through a vigorous selection process, a total of 101 students (51 for intermediate and 50 for advanced level) were chosen last December for an orientation program that will begin February 3rd and continue through February 5th. In addition to the training center at KAIST, KIPO supported to launch another training center at the Pohang University of Science and Technology (POSTECH), which has been up and running since January 27th, 2010.
2010.02.04 View 12526 -
Prof. Lee"s Team Succeeds in Producing Plastics Without Use of Fossil Fuels
A team of scientists led by Prof. Sang-Yup Lee of the Department of Biological Sciences at KAIST have succeeded in producing the polymers used for everyday plastics through bioengineering, rather than through the use of fossil fuel based chemicals, the university authorities said on Tuesday (Nov. 24).
This groundbreaking research, which may now allow for the production of environmentally conscious plastics, has been published in two papers in the journal Biotechnology and Bioengineering.
Polymers are molecules found in everyday life in the form of plastics and rubbers. The team consisted of scientists from KAIST and Korean chemical company LG Chem focused their research on polylactic acid (PLA), a bio-based polymer which holds the key to producing plastics through natural and renewable resources.
"The polyesters and other polymers we use everyday are mostly derived from fossil oils made through the refinery or chemical process," said Lee. "The idea of producing polymers from renewable biomass has attracted much attention due to the increasing concerns of environmental problems and the limited nature of fossil resources. PLA is considered a good alternative to petroleum based plastics as it is both biodegradable and has a low toxicity to humans."
Until now PLA has been produced in a two-step fermentation and chemical process of polymerization, which is both complex and expensive. Now, through the use of a metabolically engineered strain of E.coli, the team has developed a one-stage process which produces polylactic acid and its copolymers through direct fermentation. This makes the renewable production of PLA and lactate-containing copolymers cheaper and more commercially viable.
"By developing a strategy which combines metabolic engineering and enzyme engineering, we"ve developed an efficient bio-based one-step production process for PLA and its copolymers," said Lee. "This means that a developed E. coli strain is now capable of efficiently producing unnatural polymers, through a one-step fermentation process,"
This combined approach of systems-level metabolic engineering and enzyme engineering now allows for the production of polymer and polyester based products through direct microbial fermentation of renewable resources.
"Global warming and other environmental problems are urging us to develop sustainable processes based on renewable resources," concluded Lee. "This new strategy should be generally useful for developing other engineered organisms capable of producing various unnatural polymers by direct fermentation from renewable resources".
2009.11.30 View 13892 -
Prof. Sang-Yup Lee Founding Member of Board of Editors of mBop
Prof. Sang-Yup Lee of the Department of Chemical and Biomolecular Engineering at KAIST has been appointed as one of the founding board of editors of the mBio which will be launched next year, the university reported on Friday (Nov. 20).
mBio is the American Society for Microbiology"s first all-online, open access journal which will be launched in next May. According to the mBio website, the journal"s scope "will reflect the enormity of the microbial world, a highly interconnected biosphere where microbes interact with living and non-living matter to produce outcomes that range from symbiosis to pathogenesis, energy acquisition and conversion, climate change, geologic change, food and drug production, and even animal behavioral change."
Prof. Lee, LG Chem Chair Professor, is currently the Dean of the College of Life Science and Bioengineering and director of the Center for Systems and Synthetic Biotechnology. He received his B.S. in Chemical Engineering from Seoul National Univeristy in Korea and his M.S. and Ph.D. in Chemical Engineering from Northwestern University.
As of September 2009, he has published 298 journal papers and has more than 440 patents either registered or applied. Also, he has published 47 books/book chapters, "Systems Biology and Biotechnology of Escherichia Coli" being the latest.
His research interests are systems biology and biotechnology, industrial biotechnology, metabolic engineering, synthetic biology and nanobiotechnology. In particular, he has pioneered systems metabolic engineering, which integrates systems biology with metabolic engineering, for the development of micropoganisms possessing superior properties for industrial applications.
2009.11.20 View 11614 -
Prof. Lee"s Team Pioneers Biotechnological Production of Chemical Using Renewable Materials
A research team led by Prof. Sang-Yup Lee of the Bio and Brain Engineering Department at KAIST has succeeded in engineering the bacterium E. coli to produce the industrial chemical putrescine, university authorities said on Monday (Aug. 31).
Putrescine, a four carbon chain diamine, is an important platform chemical with a wide range of applications for the pharmaceutical, agrochemical and chemical industries. It is currently used to synthesize nylon-4,6, a widely used engineering plastic.
The research result, published in the Biotechnology and Bioengineering journal, proviDrdes a renewable alternative to the traditional process using fossil fuels.
Currently the production of putrescine on an industrial scale relies on chemical synthesis, which requires non-renewable petrochemicals and expensive catalyst systems. This process is highly toxic and flammable with potentially severe repercussions for both the environment and human health.
"For the first time we have developed a metabolically engineered E. coli strain that efficiently produces putrescine," said Professor Lee. "The development of a bio-refinery for chemicals and materials is very important in a world where dependency on fossil fuels is an increasing concern."
The team developed a strain of E.coli capable of producing putrescine through metabolic engineering. This is where a cell"s metabolic and regulatory networks are enhanced in order to increase production of a needed material.
First the team weakened or deleted competing metabolic pathways within the E. coli strain before deleting pathways which cause putrescine degradation. They also amplified the crucial enzyme Spec C, which converts the chemical ornithine into putrescine. Finally the putrescine exporter, which allows excretion of intracellularly made putrescine, was engineered while a global regulator was engineered to further increase the concentration of putrescine. The final result of this process was an engineered E.coli strain which produced 24.2 g of putrescine per litre.
However, as it was believed that putrescine is toxic to microorganisms the team had to study putrescine tolerance in E.coli before it could be engineered to overproduce the chemical to the levels needed for industrial production.
The results revealed that E. coli can tolerate at least 0.5 M of putrescine, which is tenfold higher than the usual concentration in the cell. This level of tolerance was an important surprise as it means that E. coli can be engineered to overproduce putrescine to industrially competitive levels.
"The previously expected toxicity of putrescine may explain why its microbial production has been overlooked," said Lee. "Now a metabolically engineered E. coli strain has been developed which is capable of efficiently producing putrescine using renewable methods to an industrial level. This metabolic engineering framework should be useful for developing metabolically engineered microorganisms for the efficient production of other chemicals from renewable resources," he added.
2009.09.01 View 12908 -
KAIST College of Life Sciences and Bioengineering Signs MOU with Harvard
KAIST’s College of Life Sciences and Bioengineering recently signed a memorandum of understanding (MOU) with Harvard University’s Center for Brain Science on July 20, which will allow for joint research and exchange in researchers between the two institutions.
Headed by Director Kenneth Blum, Harvard’s Center for Brain Science leads the world in brain-related research. The new MOU will allow for research cooperation, exchanges of professors, researchers, and students, joint usage of infrastructure and research materials, and finally, sharing of research assignments.
The Dean of the College of Life Sciences and Bioengineering Sang Yup Lee, who concerted efforts to form the MOU said, “This agreement will bring together two of the world’s leading brain-related research teams, and I hope that combining their expertise will bring great advances in brain science and engineering.
KAIST’s College of Life Science and Bioengineering, which is known for its creative interdisciplinary research, is producing exemplary research results in the field of brain science from its Biological Sciences and Bio and Brain Engineering departments.
In addition to cooperation with Harvard, KAIST has also formed partnerships with Emory University, Japan’s RIKEN Brain Institute, and Germany’s Max Planck Institute. Not only does it have a worldwide network pertaining to brain research, but KAIST has also engaged in cooperative research with prominent domestic institutions such as, Asan Medical Center, the Korea Research Institute of Bioscience and Biotechnology, the Korea Research Institute of Standards and Science, and the SK Corporation. Through these connections, KAIST has managed to lead in mutually cooperative brain interdisciplinary research.
2009.08.10 View 14583
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KAIST Professor Sang-Yup Lee Chair of International Metabolic Engineering Conference Due Next Year
KAIST distinguished professor Sang-Yup Lee was named to chair the 17th Metabolic Engineering Conference which will convene on Jeju Island, Korea, next year, under the theme of "Metabolic Engineering for Green Growth." It was decided at the 16th Biochemical Engineering Conference held in Burlington, Vermont, on July 5-9.
Metabolic Engineering Conference in 2010 will not only involve presentations and discussions about metabolic engineering, but will inaugurate the “World Council on Industrial Biotechnology,” which will bring together global corporations and the world’s experts in industrial biochemical engineering, according to sources at KAIST.
A KAIST official commented, “The fact that the Metabolic Engineering Conference is to be held here [in Korea] proves that Korea is being acknowledged as a key player in this field.”
As the world faces the depletion of fossil fuels and environmental pollution, nations are showing increasing interest in industrial biochemical alternatives, such as microscopic organisms or new chemicals, to solve their problems. In addition, efficient production of biochemical materials and bio-fuels using microbes is deemed vital for the future.
“The Korean government has become a model to other countries thanks to its leadership in carrying out the ‘Green Growth’ policy,” Professor Sang-Yup Lee said. He stated that KAIST is recognized for its research in advanced biochemical material and fuel production methods.
“Green Growth,” a concept first developed by ESCAP, the UN agency working for social and economic cooperation in Asia and the Pacific, aims to achieve sustainable economic growth without destroying the environment.
Ref. Department of Biochemical Engineering, Metabolic and BioMolecular Engineering Lab, KAIST
2009.07.17 View 12579 -
KAIST Research Team Unveils Method to Fabricate Photonic Janus Balls
A research team led by Prof. Seung-Man Yang of the Department of Chemical and Biomolecular Engineering has found a method to fabricate photonic Janus balls with isotropic structural colors.
The finding draws attention since the newly-fabricated photonic balls may prove useful pigments for the realization of e-paper or flexible electronic displays.
The breakthrough was published in the Nov. 3 edition of the science journal "Advanced Materials." The Nov. 6 issue of "Nature" also featured it as one of the research highlights under the title of "Future Pixels."
Prof. Yang"s research team found that tiny marbles, black on one side and colored on the other, can be made by "curing" suspensions of silica particles with an ultraviolet lamp. When an electric field is applied, the marbles line up so that the black sides all face upwards, which suggests they may prove useful pigments for flexible electronic displays.
The researchers suspended a flow of carbon-black particles mixed with silica and a transparent or colored silica flow in a resin that polymerizes under ultraviolet light. They then passed the mixture through a tiny see-through tube. The light solidified the silica and resin as balls with differently colored regions, each about 200 micrometers in diameter.
Over the last decades, the development of industrial platforms to artificially fabricate structural color pigments has been a pressing issue in the research areas of materials science and optics. Prof. Yang, who is also the director of the National Creative Research Initiative Center for Integrated Optofluidic Systems, has led the researches focused on fabrication of functional nano-materials through the process of assembling nano-building blocks into designed patterns.
The "complementary hybridization of optical and fluidic devices for integrated optofluidic systems" research was supported by a grant from the Creative Research Initiative Program of the Ministry of Education, Science & Technology.
2008.11.12 View 12989 -
Prof. Sang-Yup Lee Receives Merck Award for Metabolic Engineering
Prof. Sang-Yup Lee of KAIST"s Department of Chemical and Biomolecular Engineering has been chosen as the winner of the 2008 Merck Award for Metabol;ic Engineering established by the world"s leading pharmaceutical and chemical company Merck, KAIST officials said Tuesday, Sept. 16.
The Distinguished Professor of KAIST and LG Chem Chair Professor will receive the award on Sept. 18 during the 7th Metabolic Engineering convention now underway at Puerto Vallarta, Mexico. Prof. Lee will give a commemorative lecture, titled "Systems Metabolic Engineering for Chemicals," at the biannual academic conference. Prof. Lee is the fourth to win the coveted award which is given to the world"s top expert in metabolic engineering with outstanding achievements in the field.
Prof. Lee, 44, who graduated from Seoul National University and earned his master"s and doctoral degrees in chemical engineering from Northwestern University of the United States, is now the dean of the College of Life Science and Bioengineering, KAIST. Since 1994, he has served as the head of the Metabolic and Biomolecular Engineering National Research Laboratory, director of the BioProcess Engineering Center, Director of the Bioinformatics Research Center and Co-Director of the Institute for the BioCentury in KAIST.
Prof. Lee said he was receiving the Merck award "as a representative of KAIST graduates, students and researchers" who have worked with him at the Metabolic Engineering Lab. He added he was happy to see the outcome of bioengineering development projects supported by the Ministry of Education, Science and Technology over the past years was now being recognized by the world"s leading scientific society with the Merck Award.
Metabolic engineering, the art of optimizing genetic and regulatory processes within cells to increase the cell"s production of a certain substance, develops technologies that hold the key to the resolution of the world"s energy, food and environmental problems. The indispensible technology in bioengineering can be applied to the production of biomass to obtain alternative fuel.
Prof. Lee has actively participated in publishing such academic periodicals as Biotechnology Journal (as chief editor), Biotechnology and Bioengineering (deputy editor) and Metabolic Engineering (a member of the editorial committee).
2008.09.17 View 14460 -
Prof. Lee Appointed to Advisory Board of the U.S. Joint BioEnergy Institute
Prof. Sang-Yup Lee of the Department of Chemical and Biomolecular Engineering, KAIST, has been appointed as a member of the scientific advisory board of the Joint BioEnergy Institute under the wing of the U.S. Department of Energy, university authorities said on Monday (Aug. 4).
The Joint BioEnergy Institute (JBEI) is a scientific partnership in the San Francisco Bay area, California, led by Lawrence Berkeley National Laboratory (Berkeley Lab). Its partner organizations include the Sandia National Laboratories, the University of California in Berkeley, UC Davis, the Carnegie Institution for Science and the Lawrence Livermore National Laboratory.
JBEI
2008.08.07 View 11655 -
Storing Stably Hydrogen Atoms in Icy Materials Discovered
KAIST, Aug. 8, 2008 -- A KAIST research team led by Prof. Huen Lee of the Department of Chemical & Biomolecular Engineering has discovered that icy organic hydrates, which contain small cages that can trap guest molecules, can be used to create and trap hydrogen atoms at higher temperatures.
The properties and reactions of single hydrogen atoms are of great scientific interest because of their inherent quantum mechanical behavior; experimentally, they can be generated and stabilized at very low temperatures (4 K) by high-energy irradiation of solid molecular hydrogen.
The finding was reported in the journal of American Chemical Society and featured in the "Editor"s Choice" in the July 11 issue of Science as a recent research highlight.
Hydrogen is a clean and sustainable form of energy that can be used in mobile and stationary applications. Hydrogen has the potential to solve several major challenges today: depletion of fossil fuels, poor air quality, and green house gas emissions.
However, the trapping of hydrogen atoms in crystalline solid matrix has never been attempted mainly because of experimental difficulties in identifying the generated hydrogen atoms with either spectroscopic or microscopic technique.
"To overcome the barriers and limitations of the existing storage approaches, we have continuously attempted to find the new hydrogen storage media such as icy powders and other related inclusion compounds," said Prof. Lee
The discovery follows the breakthrough concept Prof. Lee"s research team proposed in Nature in 2005 to use pure ice to capture and store hydrogen molecules. At moderate temperature and pressure conditions small guest molecules are entrapped in pure ice powders to form the mixed icy hydrate materials.
"Stable existence of single hydrogen molecule/radical in icy crystalline matrices may offer significant advantages in exploring hydrogen as a quantum medium because icy hydrogen hydrates can be formed at milder conditions when compared with pure solid hydrogen, which requires the ultra low temperature of 4.2 K," said Prof. Lee.
The novel design and synthesis of ionic and radicalized icy hydrates are expected to open a new field for inclusion chemistry and ice-based science and technology. Specifically, the fact that hydrogen atoms can be stably stored in icy materials might provide versatile and practical applications to energy devices including fuel cells, ice-induced reactions, and novel energy storage process, according to the KAIST professor.
2008.08.07 View 12664 -
KAIST Professors Article Featured as Cover Thesis of Biotechnology Journal
An article authored by a research team of Prof. Sang-yup Lee at the Department of Chemical and Biomolecular Engineering and Dr. Jin-Hwan Park at the KAIST Institute for the BioCentury has been featured as the cover thesis of the August 2008 issue of Trends in Biotechnology.
The paper, titled "General strategy for strain improvement by means of systems metabolic engineering," focuses on the application of systems biology for the development of strains and illustrates future prospects. Trends in Biotechnology, published by Cell Press, is one of the most prestigious review journals in the field.
Jin-Hwan Park, the primary author of the research thesis, said that the KAIST team"s research work was expected to provide substantial help to researchers involved in biotechnology industry.
The strategy has been established on the basis of the experiences gained in the actual microbial production process using the systems biology methods which his research team has recently worked on, Prof. Park said.
2008.07.24 View 13850