Welcome to BiNEL - The Kwon Research Group @ SNU

 Programmable magnetic microacturator on Nature Materials, 2011. 10 [read]

Polymeric microcomponents are widely used in microelectromechanical systems (MEMS) and lab-on-a-chip devices, but they suffer from the lack of complex motion, effective addressability and precise shape control1,2. To address these needs, we fabricated polymeric nanocomposite microactuators driven by programmable heterogeneous magnetic anisotropy. Spatially modulated photopatterning3 was applied in a shapeindependent manner to microactuator components by successive confinement of self-assembled magnetic nanoparticles in a fixed polymer matrix. By freely programming the rotational axis of each component, we demonstrate that the polymeric microactuators can undergo predesigned, complex two- and three-dimensional motion

Inside Cover articles on small, 2011. 8 [read]

In this communication, we report an optofl uidic synthesis method for generating magnetochromatic microspheres with dynamically controlled size and color. By combining microfluidic droplet generation with magnetic self-assembly and photopolymerization, we synthesize monodisperse magnetochromatic microspheres having a tailored size and photonic stop-band. By virtue of real-time amplitude modulation of the external magnetic fi eld, we can actively control the nanoscale interparticle spacing of the superparamagnetic CNCs within individual magnetochromatic microspheres during the polymerization. Active in situ control of the interparticle spacing allows for heterogeneous color distribution in a single synthesis environment without a loss of throughput. To our knowledge, this is the fi rst microsphere synthesis approach to yield heterogeneous chromatic microspheres in a onestep process that allows for real-time color variation during fabrication. Furthermore, we demonstrate the generation of structural color pattern using patterned magnets. Reversible structural color tuning techniques utilizing superparamagnetic CNCs have recently been demonstrated, but no method has both instantaneous color tuning and reversible patterning capabilities. Our structural color patterning process using magnetochromatic microspheres and patterned magnets is simple, fast, and reversible, making inexpensive structural color patterning applications feasible

Cover page on Nature Materials 2010. 8 [read] 

News&Views in Nature Materials 2010. 8 [read]

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Encoded particles have a demonstrated value for multiplexed high-throughput bioassays such as drug discovery and clinical diagnostics. In diverse samples, the ability to use a large number of distinct identification codes on assay particles is important to increase throughput. Proper handling schemes are also needed to readout these codes on free-floating probe microparticles. Here we create vivid, free-floating structural colour particles with multi-axis rotational control using a colour-tunable magnetic material and a new printing method. Our colour-barcoded magnetic microparticles offer a coding capacity easily into the billions with distinct magnetic handling capabilities including active positioning for code readouts and active stirring for improved reaction kinetics in microscale environments5. A DNA hybridization assay is done using the colour-barcoded magnetic microparticles to demonstrate multiplexing capabilities.

Structural Color Printing on Nature Photonics 2009. 9 [read]

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Many creatures in nature, such as butterflies and peacocks, display unique brilliant colours, known as ‘structural colours’, which result from the interaction of light with periodic nanostructures on their surfaces. Mimicking such nanostructures found in nature, however, requires state-of-the-art nanofabrication techniques that are slow, expensive and not scalable. In this article, we demonstrate high-resolution patterning of multiple structural colours within seconds, based on successive tuning and fixing of colour using a single material along with a maskless lithography system. We have invented a material called ‘M-Ink’, the colour of which is tunable by magnetically changing the periodicity of the nanostructure and fixable by photochemically immobilizing those structures in a polymer network. We also demonstrate a flexible photonic crystal for the realization of structural colour printing. The simple, controllable and scalable structural colour printing scheme presented may have a significant impact on colour production for general consumer goods. 

Inside Cover and Hot articles on Lab on a Chip 2009. 7 [read]

We demonstrate the microfluidic sorting of directionally oriented (anisotropic) microstructures by their orientational state in solution using the concept of railed microfluidics. After being injected into a microfluidic channel, the microstructures rotate and flip in various directions. In order to sort microstructures in an organized way, we designed the microstructures and the microchannel to allow for orientation-based control of microstructure movement. In order to sort microstructures based on their rotation, we used a wedge shaped fin on the microstructures and a Y-shaped railed microfluidic channel. For sorting flipped particles, we use a double-railed microfluidic channel that has grooves on both its top and bottom surfaces. By integrating the two sorting methods we demonstrated high throughput, autonomous sorting into four different orientational states: unrotated–unflipped, rotated–unflipped, unrotated–flipped, and rotated–flipped. Here we not only demonstrate orientational assembly of directionally dependent microstructures, but also present design considerations for future work

Front Cover and Hot articles on Lab on a Chip 2009. 6 [read]

3D fabrication of hybrid microstructures is demonstrated using optofluidic maskless lithography and a membrane-controlled height-tunable microfluidic channel. The method allows for high-throughput synthesis of hybrid 3D microstructures and in situ biomaterial patterning.

Cover page on Nature Materials 2008. 7 [read]

Research Highlights in Nature 2008. 6. 26 [read]

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A technique for the self-assembly of polymeric microstructures, which works by using a guiding 'rail' mechanism, is reported online this week in Nature Materials. The method could be used for manufacturing two-dimensional patterns of living cells for tissue engineering and manipulating silicon devices for microchip packaging.
On the micrometre scale, conventional assembly techniques such as robotics are often not applicable, and can result in errors in the final product. Sunghoon Kwon and colleagues devised a way to guide the assembly of microstructures within microfluidic channels, and make complex structures composed of more than 50 individual ones. All the microstructures used at the start of the process are incorporated in the product and different shapes can also be guided to specific locations, allowing the construction of two-dimensional representations of, for example, the Eiffel Tower, a Greek temple and a computer keyboard.
The method works by introducing a groove or 'rail' into the top surface of the channels and a complementary shape in the polymeric microstructure. In contrast to other fluidic assembly routes, the structures are guided along the rail rather than moving in the exact direction of fluid flow in the channel.