Recent Announcements
New paper in Small
Gun Ho Lee, Jong Bin Kim, Tae Min Choi, Jung Min Lee, and Shin-Hyun Kim*, "Structural Coloration with Nonclose-Packed Array of Bidisperse Colloidal Particles", Small, accepted for publication (2018).  |
Our paper is featured as inside cover 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, 14, 1802520 (2018).  |
New Article in Chem. Mater.
Osmotic-Stress-Mediated Control of Membrane Permeability of Polymeric Microcapsules by Sangmin Lee, Tae Yong Lee, Dong Jae Kim, Bomi Kim, and Shin-Hyun Kim Microcapsules with regular pore size can provide size-selective permeation, which is promising for immunoisolation of cells, protection of enzymes or catalysts, and development of capsule-type sensors. However, conventional approaches have limited biocompatibility or poor dispersion stability of encapsulants. Here, we suggest a simple yet pragmatic method to produce semipermeable microcapsules using osmotic stress. With a capillary microfluidic device, monodisperse microcapsules with ultra-thin polymer membranes are prepared by double-emulsion templating. The microcapsules are subjected to a hypotonic condition, by which water is pumped in, imposing a tensile stress on the membrane. The osmotic stress initiates cracks at weak spots. As cracks propagate, the pressure gradually reduces as ions diffuse through them, finally resulting in a finite width of cracks. The final width can be controlled from 5 to 10 nm using an initial osmotic pressure of 230 to 690 kPa, enabling fine adjustment of the cut-off threshold of permeation. This osmotic-pressure-mediated control is highly compatible with delicate biological molecules and colloidal dispersions as no etching chemicals are required to form pores. Taking advantage of this method, we demonstrate a capsule-type molecular sensor based on surface-enhanced Raman scattering that obviates pretreatment of samples because the membrane allows the entrance of small target molecules while blocking the large adhesive proteins.  |
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.  |
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