Recent Announcements
New communication in Adv. Mater.
Tae Min Choi, Kwanghwi Je, Jin-Gyu Park, Gun Ho Lee, and Shin-Hyun Kim, "Photonic Capsule Sensors with Built-in Colloidal Crystallites", Advanced Materials, accepted for publication (2018).  |
New paper in Small
Dong Jae Kim, Sung-Gyu Park, Dong-Ho Kim, and Shin-Hyun Kim, "SERS-Active Charged Microgels for Size- and Charge-Selective Molecular Analysis of Complex Biological Samples", Small, accepted for publication (2018). (Co-corresponding author) SERS-active charged microgels are microfluidically designed by embedding agglomerates of gold nanoparticles in a matrix. The microgels concentrate oppositely-charged small molecules while excluding large proteins. As nanogaps among gold nanoparticles serve as hot spots for SERS, Raman signal of charged molecules is dramatically enhanced without interruption of protein. Therefore, the microgels enable direct molecular analysis of complex biological samples.  |
New Article in Science Advances
Sang Seok Lee, Jong Bin Kim, Yun Ho Kim, and Shin-Hyun Kim, "Wavelength-tunable and shape-reconfigurable photonic capsule resonators containing cholesteric liquid crystals", Science Advances, published online (2018). (Corresponding author) [pdf] Cholesteric liquid crystals (CLCs) have a photonic bandgap due to the periodic change of refractive index along their helical axes. The CLCs containing optical gain have served as band-edge lasing resonators. In particular, CLCs in a granular format provide omnidirectional lasing, which are promising as a point light source. However, there is no platform that simultaneously achieves high stability in air and wavelength tunability. We encapsulate CLCs with double shells to design a capsule-type laser resonator. The fluidic CLCs are fully enclosed by an aqueous inner shell that promotes the planar alignment of LC molecules along the interface. The outer shell made of silicone elastomer protects the CLC core and the inner shell from the surroundings. Therefore, the helical axes of the CLCs are radially oriented within the capsules, which provide a stable omnidirectional lasing in the air. At the same time, the fluidic CLCs enable the fine-tuning of lasing wavelength with temperature. The capsules retain their double-shell structure during the dynamic deformation. Therefore, the CLCs in the core maintain the planar alignment along the deformed interface, and a lasing direction can be varied from omnidirectional to bi- or multidirectional, depending on the shape of deformed capsules.  |
New Article in Chemistry of Materials
Gun Ho Lee, Tae Yoon Jeon, Jong Bin Kim, Byungjin Lee, Chang-Soo Lee, Su Yeon Lee, and Shin-Hyun Kim, "Multicompartment Photonic Microcylinders toward Structural Color Inks", Chemistry of Materials, Accepted for publication (2018). (Co-corresponding author) Structural coloration is promising as an alternative to chemical coloration because it has characteristics of their high color brightness, no fading, and low toxicity. Here, we report a pragmatic micromolding technique to create functional photonic microcylinders which are useful as structural color pigments. Photocurable dispersions of silica particles with interparticle repulsion are molded to spontaneously form regular arrays in confined volumes, which are instantly stabilized by photopolymerization. The resulting photonic microcylinders, released from the mold, exhibit pronounced structural colors from the entire visible range. In addition, multiple compartments can be integrated into single microcylinders through volatile-solvent-mediated sequential molding. As each compartment can be independently rendered to be structurally-colored, transparent, or magneto-responsive, the multicompartment microcylinders show advanced functionalities, such as color-brightness tunability and switchable color properties. These photonic microcylinders will serve as structural color pigments in a wide range of aesthetic coatings and authentication tags.  |
New Article in ACS AM&I
Chan Ho Park, Sang Min Lee, Ghasidit Pornnoppadol, Yoon Sung Nam, Shin-Hyun Kim, and Bumjoon J. Kim, "Microcapsules Containing pH-Responsive, Fluorescent Polymer-Integrated MoS2: Effective Platform for in-situ pH Sensing and Photothermal Heating", ACS Applied Materials & Interfaces, Accepted for publication (2018). (Co-corresponding author, Park and Lee contributed equally)  We report the design of a novel microcapsule platform for in-situ pH sensing and photothermal heating, involving the encapsulation of pH-responsive polymer-coated MoS2 nanosheets (NSs) in microcapsules with an aqueous core and a semipermeable polymeric shell. The MoS2 NSs were functionalized with pH-responsive polymers having fluorescent groups at the distal end to provide pH-sensitive Förster resonance energy transfer (FRET) effect. The pH-responsive polymers were carefully designed to produce a dramatic change in polymer conformation, which translated to a change in FRET efficiency near pH 7.0 in response to subtle pH changes, enabling the detection of cancer cells. The pH-sensitive MoS2 NSs were microfluidically encapsulated within semipermeable membranes to yield microcapsules with uniform size and composition. The microcapsules retained the MoS2 NSs without leakage, while allowing the diffusion of small ions and water through the membrane. At the same time, the membranes excluded adhesive proteins and lipids in the surrounding media, protecting the encapsulated MoS2 NSs from deactivation and enabling in-situ pH monitoring. Moreover, the encapsulated MoS2 NSs showed high-performance photothermal heating, rendering the dual-functional microcapsules highly suitable for cancer diagnosis and treatment. |
New paper in Adv. Funct. Mater.
HanGyeol Lee, Tae Yoon Jeon, Su Yeon Lee, Seung Yeol Lee, and Shin-Hyun Kim, "Designing Multicolor Micropatterns of Inverse Opals with Photonic Bandgap and Surface Plasmon Resonance", Advanced Functional Materials, Accepted for publication (2018). (Corresponding author) Structural coloration provides unique features over chemical coloration, such as non-fading, color tunability, and high color brightness, rendering it useful in various optical applications. To develop the structural colors, two different mechanisms of coloration—photonic bandgap (PBG) and surface plasmon resonance (SPR)—have been separately utilized. In this work, we suggest a new method to create structurally-colored micropatterns by regioselectively employing SPR in a single film of inverse opal with PBG. The inverse opals are prepared by thermal embedding of opal into a negative photoresist and its subsequent removal. The inverse opals have a hexagonal array of open pores on the surface which serves as a template to make SPR-active nanostructures through a directional deposition of gold; perforated gold film and an array of curved gold disks are formed. With a shadow mask lithographically prepared, the gold is regioselectively deposited on the surface of the inverse opal, which results in two distinct regions of gold-free inverse opal with PBG and gold nanostructure with SPR. As PBG and SPR develop their own structural colors respectively, the resultant micropatterns exhibit pronounced dual colors. More importantly, the micropatterns show the distinguished optical response for evaporation of volatile liquids that occupy the pores.  |
New Article in Lab Chip
Hui-Sung Moon,* Kwanghwi Je, Jae-Woong Min, Donghyun Park, Kyung-Yeon Han, Seungho Shin, Woong-Yang Park, Chang Eun Yoo* and Shin-Hyun Kim,* "Inertial-Ordering-Assisted Droplet Microfluidic for High-Throughput Single-Cell RNA-Sequencing", Lab on a Chip, Accepted for publication (2018). (Moon & Je contributed equally, Co-corresponding author) [pdf] Single-cell RNA-seq reveals the cellular heterogeneity inherent in the population of cells, which is very important in many clinical and research applications. Recent advances in droplet microfluidics have achieved the automatic isolation, lysis, and labeling of single cells in droplet compartments without complex instrumentation. However, barcoding errors occurring in the cell encapsulation process because of the multi-beads-in-droplet and insufficient throughput because of the low concentration of beads for avoiding multi-beads-in-a-droplet remain important challenges for precise and efficient expression profiling of single cell. In this study, we developed a new droplet-based microfluidic platform that significantly improved throughput while reducing barcoding error through deterministic encapsulation of inertially ordered beads. Highly concentrated beads containing oligonucleotide barcodes were spontaneously ordered in a spiral channel by an inertial effect, which was in turn encapsulated in droplets one-by-one, while cells were simultaneously encapsulated in the droplets. The deterministic encapsulation of beads resulted in a high fraction of single-bead-in-a-droplet and rare multi-beads-in-a-droplet although the bead concentration increased to 1000 μL-1, which diminished barcoding error and enabled accurate high-throughput barcoding. We successfully validated our device with single-cell RNA-seq. In addition, we found that multi-beads-in-a-droplet, generated using a normal drop-seq device with a high concentration of beads, underestimated transcript numbers and overestimated cell numbers. This accurate high-throughput platform can expand the capability and practicality of Drop-Seq in single-cell analysis.  |
New paper in Adv. Mater. Technol.
Sangmin Lee, Tae Yong Lee, and Shin-Hyun Kim, "Microfluidic Production of Capsules-in-Capsules for Programmed Release of Multiple Ingredients", Advanced Materials Technologies, Accepted for publication (2018). (Corresponding author) Capsules with thin shells have a high loading capacity and are thus well-suited containers for reagents that must be stored in confined volumes. Capsules contained in larger capsules, so-called double capsules, allow the encapsulation of distinct reagents within small, defined, well-separated volumes. Therefore, they offer possibilities to initiate reactions in confined volumes and to release distinct bioactives sequentially while minimizing the risk for cross contaminations. Here, we present a new microfluidic capillary device that enables the assembly of water-oil-water-oil-water (W/O/W/O/W) quadruple-emulsion drops whose oil layers are ultra-thin. These quadruple emulsions can be converted into double capsules with thin membranes through either evaporation-induced consolidation of biodegradable polymers or photopolymerization of monomers. We demonstrate that the membrane composition of the inner and outer capsules can be independently selected to enable programmed release of distinct encapsulants. For example, we employ biodegradable polymers with two different degradation rates as the membrane materials that enable sequential release of two different encapsulants. In addition, the release of the encapsulants can be triggered by external stimuli such as osmotic pressure. This new class of double capsules provides new opportunities for drug delivery and screening assays that require sequential release of multiple water-soluble ingredients.  |
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