Taesung Kim

Ulsan National Institute of Science and Technology, Ulsan, Ulsan, South Korea

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Publications (32)147.25 Total impact

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    ABSTRACT: Multiple copies of a cadC homolog encoding a heavy metal-responsive transcription factor were found in the genome of a bacterium isolated from ocean sediment, and the heavy metal responses of the encoded proteins were characterized using a fluorescence reporter assay. Each CadC regulator exhibited distinct specificity in response to heavy metal ions, indicating their potential use as modular heavy metal biosensors. Next, we constructed CadC-controlled T7 RNA transcription systems for intracellular signal amplification, i.e., higher sensitivity. Flow cytometry revealed that cadmium and lead ions could be recognized specifically by CadC-T7 biosensors, which could be combined with a microfluidic platform to generate heavy metal biosensor devices with increased sensitivity. Our results demonstrate the successful development of synthetic CadC-T7 genetic circuitry for use in improved heavy metal biosensor microfluidic devices. http://dx.doi.org/10.1016/j.bios.2015.12.101
    No preview · Article · May 2016 · Biosensors & Bioelectronics
  • Jongwan Lee · Minseok Kim · Jungyul Park · Taesung Kim

    No preview · Article · Jan 2016 · Lab on a Chip
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    Full-text · Dataset · Dec 2015
  • Minseok Kim · Dong-Joo Kim · Dogyeong Ha · Taesung Kim
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    ABSTRACT: Cracks are frequently observed in daily life, but they are rarely welcome and are considered as a material failure mode. Interestingly, cracks cause critical problems in various micro/nanofabrication processes such as colloidal assembly, thin film deposition, and even standard photolithography because they are hard to avoid or control. However, increasing attention has been given recently to control and use cracks as a facile, low-cost strategy for producing highly ordered nanopatterns. Specifically, cracking is the breakage of molecular bonds and occurs simultaneously over a large area, enabling fabrication of nanoscale patterns at both high resolution and high throughput, which are difficult to obtain simultaneously using conventional nanofabrication techniques. In this review, we discuss various cracking-assisted nanofabrication techniques, referred to as crack lithography, and summarize the fabrication principles, procedures, and characteristics of the crack patterns such as their position, direction, and dimensions. First, we categorize crack lithography techniques into three technical development levels according to the directional freedom of the crack patterns: randomly oriented, unidirectional, or multidirectional. Then, we describe a wide range of novel practical devices fabricated by crack lithography, including bioassay platforms, nanofluidic devices, nanowire sensors, and even biomimetic mechanosensors.
    No preview · Article · Dec 2015 · Nanoscale
  • Qitao Zhou · Taesung Kim
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    ABSTRACT: The development of lab-on-a-chip (LoC) systems has allowed for the successful combination of many detection methods with these systems. Surface-enhanced Raman spectroscopy (SERS) has the potential for use in rapid trace-level biological and environmental analysis because of its high sensitivity, rapid response, and fingerprint effect. With the development of nanotechnology, various active SERS substrates have been fabricated. By combining well-designed microchannels and SERS substrates, more effective and convenient SERS detecting systems have been realized. Furthermore, novel functions that were conventionally deemed impossible for normal SERS substrates have been achieved.
    No preview · Article · Dec 2015 · Sensors and Actuators B Chemical
  • Minseok Kim · Taesung Kim
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    ABSTRACT: Recent advances in controlling cracking phenomena established a novel unconventional fabrication technique to generate mixed-scale patterns/structures with resolution and accuracy comparable to conventional nanofabrication techniques. Here, we adapt our previous cracking-assisted nanofabrication technique (called 'crack-photolithography'), relying on only the standard photolithography to develop micro-/nanofluidic devices with greatly reduced time and cost. The crack-photolithography makes it possible not only to simultaneously produce micropatterns and nanopatterns with various dimensions but also to replicate both of the mixed-scale patterns in a high-throughput manner. Therefore, a microfluidic channel network can easily be fabricated with a nanochannel array that can function as a nanoporous membrane wherever necessary, which basically plays a key role in diffusion-allowed but convection-suppressed microfluidic devices. In addition, the nanochannel array can manipulate the transport of small molecules by adjusting its dimension and/or number at will, so that nanochannel-array-integrated micro-/nanofluidic devices prove even more robust and accurate in diffusion control than conventional membrane-integrated microfluidic devices. As an application of such micro-/nanofluidic devices, we employed synthetic bacterial cells and found that their genetic induction and expression are dominated by extracellular diffusive microenvironments that were completely engineered using the nanochannel array. Therefore, the crack-photolithography could provide innovative fabrication techniques for unprecedented micro-nanofluidic devices that show substantial potential for a wide range of biological and chemical applications.
    No preview · Article · Jul 2015 · Analytical Chemistry
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    ABSTRACT: A microbial biosensor is an analytical device with a biologically integrated transducer that generates a measurable signal indicating the analyte concentration. This method is ideally suited for the analysis of extracellular chemicals and the environment, and for metabolic sensory-regulation. Although microbial biosensors show promise for application in various detection fields, some limitations still remain such as poor selectivity, low sensitivity, and impractical portability. To overcome such limitations, microbial biosensors have been integrated with many recently developed micro/nanotechnologies and applied to a wide range of detection purposes. This review article discusses micro/nanotechnologies that have been integrated with microbial biosensors and summarizes recent advances and the applications achieved through such novel integration. Future perspectives on the combination of micro/nanotechnologies and microbial biosensors will be discussed, and the necessary developments and improvements will be strategically deliberated.
    Full-text · Article · May 2015 · Frontiers in Bioengineering and Biotechnology
  • Minseok Kim · Dogyeong Ha · Taesung Kim
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    ABSTRACT: Cracks are observed in many environments, including walls, dried wood and even the Earth's crust, and are often thought of as an unavoidable, unwanted phenomenon. Recent research advances have demonstrated the the ability to use cracks to produce various micro and nanoscale patterns. However, patterns are usually limited by the chosen substrate material and the applied tensile stresses. Here we describe an innovative cracking-assisted nanofabrication technique that relies only on a standard photolithography process. This novel technique produces well-controlled nanopatterns in any desired shape and in a variety of geometric dimensions, over large areas and with a high throughput. In addition, we show that mixed-scale patterns fabricated using the 'crack-photolithography' technique can be used as master moulds for replicating numerous nanofluidic devices via soft lithography, which to the best of our knowledge is a technique that has not been reported in previous studies on materials' mechanical failure, including cracking.
    No preview · Article · Feb 2015 · Nature Communications
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    ABSTRACT: Reporter-gene-based microbial biosensors have high potential for detecting small molecules, including heavy metal ions (HMIs), in a sensitive and selective manner by involving low costs. However, the sensitivity and dynamic range of the sensing mechanism are largely limited by the conventional culture environment that relies on the batch-type addition of the small molecules in nutrients and the subsequent genetic induction of sensing microbes. Here, we describe a high-throughput, chemostat-like microfluidic platform that can continuously supply both nutrients and inducers (HMIs) using microfabricated ratchet structures and a mixing microchannel network. We found that the microfluidic platform not only allowed microbial biosensors to be highly concentrated in a detection microchamber array but also enabled them to continuously grow and control synthetic genetic circuits in response to heavy metals. We also demonstrated that the combination of the platform and microbial biosensors enhanced the sensitivity for detecting divalent lead and cadmium ions by approximately three orders of magnitude relative to conventional batch-type methods. Because the platform is portable and only requires small sample volumes and fluorescent detection, the chemostat-like microfluidic platform in conjunction with microbial biosensors could be widely utilized to facilitate the specific and sensitive detection of molecular analytes on a chip. Copyright © 2014 Elsevier B.V. All rights reserved.
    No preview · Article · Oct 2014 · Biosensors & Bioelectronics
  • Minseok Kim · Taesung Kim
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    ABSTRACT: We present a novel biomolecule sensing method that enables sensitive and selective detection of target analytes as well as simultaneous separation of non-target analytes by utilizing microtubules (MTs) as a molecular carrier and a nanoporous hydrogel membrane (NHM) as a size-based sieve on a microfluidic chip. We functionalized MTs with aptamers, using a streptavidin and biotin linkage, to provide numerous binding sites for specific target analytes. Target analytes captured by the functionalized MTs from a mixture of complex analytes were transported by electrophoresis (EP) and then sieved by the NHM while non-target analytes passed through the NHM because of the size difference between the analytes and nanopores. Subsequently, the concentration and separation of only target analytes was achieved in a continuous and simultaneous manner because of more rapid transportation of MTs by electric fields. In this study, we demonstrated that our method can be used to detect target analytes at femtomolar levels and enrich the initial concentration by 10(5)-10(6)-fold within 10 min in terms of fluorescent signals. We also demonstrated that the method is approximately 10-100 times more sensitive than conventional nanobead-based detection methods in the light of fluorescent signals. For unlabeled target analytes in a real sample, the method can provide a means to obtain well purified and concentrated target analytes in the form of pellets for off-chip detection and analysis. Thus, we believe that using aptamer-functionalized MTs in conjunction with an NHM in the presence of electric fields can be widely utilized to facilitate the detection, concentration, and separation of specific biomolecule analytes on a chip.
    No preview · Article · Oct 2014 · Sensors and Actuators B Chemical
  • Mingjie Jia · Taesung Kim
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    ABSTRACT: Microfluidic devices utilize ion concentration polarization (ICP) phenomena for a variety of applications, but a comprehensive understanding on the generation of ICP is still necessary. Recently, the emergence of a novel single channel ICP (SC-ICP) device has stimulated further research on the mechanism of ICP generation, so that we developed a 2-D model of an SC-ICP device that integrates a nanoporous membrane on the bottom surface of the channel, allowing bulk flow over the membrane. We solved a set of coupled governing equations with appropriate boundary conditions to explore ICP numerically. As a result, we not only showed that the simulation results held a strong qualitative agreement with experimental results, but also found the distribution of ion concentrations in the SC-ICP device that has never been reported in previous studies. We confirmed again that the electrophoretic mobility (EPM) of counter-ions in the membrane is the most dominant factor determining the generation and strength of ICP, whereas the charge density of the membrane was dominant to the ICP strength only when a high EPM value was assumed. From the viewpoint of practical applications, an SC-ICP device with a long membrane under low buffer strength showed enhanced performance in the pre-concentration of charged molecules. Therefore, we believe that the simulation results could not only provide sharp insight into ICP phenomena but also predict and optimize the performance of SC-ICP devices in various microfluidic applications.
    No preview · Article · Sep 2014 · Analytical Chemistry
  • Dogyeong Ha · Ji Won Lim · Taesung Kim
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    ABSTRACT: Screening methods are highly demanded for selecting and extracting desired strains that hold particular features out of mutant libraries. Conventional screening methods using a plate reader require intensive labor and time and multiple processes [1]. For example, traditional colony based screening methods have a limitation in the control of spacing distances between colonies [2]. The screening through-put seems to be still low and unable to deal with the total number of mutant cells in engineered libraries. In addition, it appears to be hard to make a high quality of colonies at the single cell level. In this work, we report an inkjet printing technology that can make it easy to control the number of live cells to inject and produce diverse patterns repeatedly for the high throughput screening [3]. The inkjet printing technology enables not only the massive production of microcolonies at the single cell level but also co-culture of multiple types of strains simultaneously. We demonstrate that the technique possesses high reproducibility with high speed and positioning accuracy and the quality of the colony array is very good, showing a high potential for high throughput screening of engineered bacterial strains. We investigate spacing distances between fatty acid producing cells and detecting cells. By measuring and analyzing fluorescent signals from the detecting cells, it would be possible to screen the most productive, fatty acid producing cells. In short, we demonstrate that the printing parameters such as initial seeding number of cells, types of cells (plasmid and strain), and spacing distances are important for forming a uniform-sized colony array. We also demonstrate that the inkjet printing technology can be practically used for high throughput screening of bacterial cells and apply the technology to screening 4000 fatty acid producing mutants.
    No preview · Conference Paper · Sep 2014
  • Mingjie Jia · Taesung Kim
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    ABSTRACT: Many microfluidic devices have been utilizing ion concentration polarization (ICP) phenomena by using a permselective, nanoporous membrane with electric fields for a variety of pre-concentration applications. However, numerical analyses on the ICP phenomena have not drawn sufficient attention, although they are an intriguing and interdisciplinary research area. In this work, we propose a 2-D model and present numerical simulation results on the ICP, which were obtained by solving three coupled governing equations: Nernst-Planck, Navier-Stokes, and Poisson. With improved boundary conditions and assumptions, we demonstrated that the simulation results are not only consistent with other experimental results but also make it possible to thoroughly understand the ICP phenomena. In addition, we demonstrated that the pre-concentration of analytes can be simulated and quantified in terms of concentration enhancement factors (CEFs) that were related to many factors, such as ionic concentration distribution, electric fields, and flow fields including vortex flows across the membrane. Furthermore, we demonstrated that a high electrophoretic mobility (EPM) of counter-ions in the membrane plays the most important role in producing accurate simulation results while the effect of the charge density of the membrane is relatively insignificant. Hence, it is believed that the model and simulation results would provide good guidelines to better develop microfluidic pre-concentration devices based on the ICP phenomena.
    No preview · Article · Jul 2014 · Analytical Chemistry
  • Minseok Kim · Mingjie Jia · Youngmi Kim · Taesung Kim
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    ABSTRACT: We report a microfluidic device that can rapidly and accurately generate various concentration gradients in a controllable manner for the chemotaxis study of motile bacterial cells by integrating hydrogel into polydimethylsiloxane (PDMS) microchannels. We performed numerical simulations for both the PDMS-sealed hydrogel hybrid device and a representative conventional hydrogel-based device to theoretically compare their characteristics. In addition, we experimentally demonstrated that the PDMS-sealed hydrogel device not only produces various linear and nonlinear concentration gradients without flow-induced shear stresses on motile bacterial cells but also exhibits remarkable advantages over conventional hydrogel-based devices. For example, the PDMS-sealed hydrogel device can be used for fast and accurate generation of various concentration gradients, prevents dehydration of hydrogel and evaporation of solutions, directs diffusion of chemicals such as chemoattractants, exhibits long-term durability, and is easy to handle. Because the hydrogel used is biocompatible and arbitrary concentration profiles can be easily designed and produced on a chip, we believe that not only the PDMS-sealed hydrogel fabrication method but also the versatile concentration gradient generation device can be used for various studies on interaction between chemicals and cells including bacterial chemotaxis assays.
    No preview · Article · Apr 2014 · Microfluidics and Nanofluidics
  • Yoonkwang Nam · Minseok Kim · Taesung Kim
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    ABSTRACT: Most microfluidic devices are fabricated by using standard photolithography technology so that they are typically limited to a single, uniform microchannel depth. In this work, we employ a polydimethylsiloxane (PDMS) gray-scale photomask (PGSP) developed in our previous work for fabricating multi-level microchannels (MLMs) that hold a high potential for enhancing the separation performance and efficiency of microparticles. Since the PGSP provides a series of multiple, uniform and precise filter gaps in a microchannel, we describe an MLM-integrated microfluidic device that not only filters but also accumulates microparticles by size such as polystyrene beads and yeast cells. In addition, we integrate a pneumatic pressure controller that manually manipulates the filter gaps to enable sequential extraction of the separated, accumulated microparticles from the device for additional post-analysis. Since the PGSP-based soft-lithography technology provides a simple but powerful fabrication method for MLMs, we believe that both the fabrication method and the separation and extraction device can be widely used for micro total analysis systems that benefit from MLMs.
    No preview · Article · Jan 2014 · Sensors and Actuators B Chemical
  • Yoonkwang Nam · Minseok Kim · Taesung Kim
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    ABSTRACT: Most polymer-replica-based microfluidic devices are mainly fabricated by using standard soft-lithography technology so that multi-level masters (MLMs) require multiple spin-coatings, mask alignments, exposures, developments, and bakings. In this paper, we describe a simple method for fabricating MLMs for planar microfluidic channels with multi-level barriers (MLBs). A single photomask is necessary for standard photolithography technology to create a polydimethylsiloxane grey-scale photomask (PGSP), which adjusts the total amount of UV absorption in a negative-tone photoresist via a wide range of dye concentrations. Since the PGSP in turn adjusts the degree of cross-linking of the photoresist, this method enables the fabrication of MLMs for an MLB-integrated microfluidic device. Since the PGSP-based soft-lithography technology provides a simple but powerful fabrication method for MLBs in a microfluidic device, we believe that the fabrication method can be widely used for micro total analysis systems that benefit from MLBs. We demonstrate an MLB-integrated microfluidic device that can separate microparticles.
    No preview · Article · Sep 2013 · Journal of Micromechanics and Microengineering
  • Minseok Kim · Taesung Kim
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    ABSTRACT: The integration of nanoporous membranes into microfluidic devices allows a wide range of analytical and biochemical applications such as stable concentration gradient generation, sample pre-concentration, and ion and biomolecule filtration in a controllable manner. However, further applications of nanoporous membranes in microfluidic devices require rapid and controllable fabrication methods of various nanoporous precursor materials; currently, few such methods exist. Here, we describe simple and robust methods that can be used for microfabricating four different precursor materials as leakage-tight membranes in a microfluidic channel network. The methods consist of a common integration process and individual solidification processes such as solvent evaporation, UV-curing, and temperature treatment. We demonstrate that the fabricated membranes can be used for electrokinetic, nanofluidic pre-concentration of bio-samples such as proteins, cells, and microspheres on either the anodic or cathodic side of the membranes. In addition, we not only characterize the physicochemical properties of the membranes such as conductance of membrane-integrated microchannels, relative permselectivity, and pre-concentration ability, but also compare fabrication availability, membrane robustness, surface charge density tunability and biocompatibility with buffer solutions. The methods are versatile for many nanoporous precursor materials and easy to control the location and dimension of the membranes. Hence, the methods developed and the characterized properties of the membranes tested in this work could be widely employed for further applications of nanoporous membranes in microfluidic systems.
    No preview · Article · Aug 2013 · The Analyst
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    ABSTRACT: We present a light-switchable gene expression system for both inducible and switchable control of gene expression at a single cell level in Escherichia coli using a previously constructed light-sensing system. The λ cI repressor gene with an LVA degradation tag was expressed under the control of the ompC promoter on the chromosome. The green fluorescent protein (GFP) gene fused to a λ repressor-repressible promoter was used as a reporter. This light-switchable system allows rapid and reversible induction or repression of expression of the target gene at any desired time. This system also ensures homogenous expression across the entire cell population. We also report the design of a miniaturized photobioreactor to be used in combination with the light-switchable gene expression system. The miniaturized photobioreactor helps to reduce unintended induction of the light receptor due to environmental disturbances and allows precise control over the duration of induction. This system would be a good tool for switchable, homogenous, strong, and highly regulatable expression of target genes over a wide range of induction times. Hence, it could be applied to study gene function, optimize metabolic pathways, and control biological systems both spatially and temporally.
    Preview · Article · Jan 2013 · PLoS ONE
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    ABSTRACT: This paper describes a system to study how small physical perturbations can affect bacterial community behavior in unexpected ways through modulation of diffusion and convective transport of chemical communication molecules and resources. A culture environment that mimics the chemically open characteristic of natural bacterial habitats but with user-defined spatio-temporal control of bacteria microcolonies is realized through use of an aqueous two phase system (ATPS). The ATPS is formulated with non-toxic dextran (DEX) and poly(ethylene glycol) (PEG) dissolved in cell culture media. DEX-phase droplets formed within a bulk PEG-phase stably confine the bacteria within it while small molecules diffuse relatively freely. Bacteria-containing DEX droplets can also be magnetically relocated, without loss of its bacterial content, when DEX-conjugated magnetic particles are included. We found that decreasing the distance between quorum-sensing (QS)-coupled microcolonies increased green fluorescent protein (GFP) expression due to increased inter-colony chemical communication but with upper limits. Periodic relocation of the chemical signal receiver colony, however, increased GFP expression beyond these typical bounds predicted by quorum sensing concepts alone by maintaining inter-colony chemical communication while also relieving the colony of short-range resource depletion effects. Computer simulations suggest that such increased productive output in response to periodic non-lethal physical pertubations is a common feature of chemically-activated interactive cell systems where there is also a short-range inhibitory effect. In addition to providing insights on the effect of bacteria relocation, the magnetic ATPS droplet manipulation capability should be broadly useful for bioanalyses applications where selective partitioning at the microscale in fully aqueous conditions are needed.
    Full-text · Article · Jan 2013 · Journal of the American Chemical Society
  • Minseok Kim · Mingjie Jia · Taesung Kim
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    ABSTRACT: We describe a novel and simple mechanism for inducing ion concentration polarization (ICP) using a surface-patterned perm-selective nanoporous film like Nafion in single, open microchannels. Such a surface-patterned Nafion film can rapidly transport only cations from the anodic side to the cathodic side through the nanopore clusters so that it is possible to generate an ICP phenomenon near the Nafion film. In this work, we characterize transport phenomena and distributions of ion concentration under various electric fields near the Nafion film and show that single-channel based ICP (SC-ICP) is affected by Nafion film thicknesses, strengths of applied electric fields, and ionic strengths of buffer solutions. We also emphasize that SC-ICP devices have several advantages over previous dual-channel ICP (DC-ICP) devices: easy and simple fabrication processes, inherently leak-tight, simple experimental setup requiring only one pair of electrodes, stable and robust ICP induced rapidly, and low electrical resistances helping to avoid Joule heating, and membrane perm-selectivity breakdown but allowing as high bulk flow as an open, plain microchannel. As an example of applications, we demonstrate that SC-ICP devices not only have high potential in pre-concentrating proteins in massively parallel microchannels but also enable the concentration and lysis of bacterial cells simultaneously and continuously on a chip; therefore, proteins within the cells are extracted, separated from the concentrated cells and then pre-concentrated at a different location that is closer to the Nafion film. Hence, we believe that the SC-ICP devices have higher possibilities of being easily integrated with traditional microfluidic systems for analytical and biotechnological applications.
    No preview · Article · Jan 2013 · The Analyst