Self-Assembled Ultra-thin Silica Layers for On-Chip Chromatography
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1191-OO06-06
Self-Assembled Ultra-thin Silica Layers for On-Chip Chromatography
Sun Choi*,1, Inkyu Park2 and Albert P. Pisano1 1
Berkeley Sensor and Actuator Center (BSAC), University of California at Berkeley, Berkeley,
California 94720, USA 2
Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology
(KAIST), 335 Gwahangno, Yuseong-gu, Daejon 305-701, South Korea
ABSTRACT We propose a novel method for self-assembled packing of silica microsphere in microchannel which can be potentially used for on-chip chromatography. Solvent-evaporation based 2D crystallization technique [1] can enable mono-dispersed micro-particles to be self-assembled by capillary attractive forces. We apply this technique to assemble dense packing of silica microsphere and form ultra thin layers (2~3 layers) within open microchannel. Open microchannel has been constructed by conventional photolithography of SU8 photoresist. A small droplet (Volume: 0.1μL) of silica suspension (Diameter: 3µm, Solvent: DI Water, Concentration: 1.25wt%) has been placed in the defined inlet of micro channel. Capillary force within the open SU8 microchannel induces the flow of silica suspension in the channel. The packing of microsphere starts from the outlet side of the channel, where the thickness of solvent drastically decreases due to sudden increase of cross-sectional area of channel, and this packing propagates to the inlet side of the channel until solvent evaporates completely. As a result, a dense packing of silica microspheres are successfully assembled and a thin layer of silica microspheres are formed within open micro-channel.
INTRODUCTION Chromatography has been one of the most widely used techniques for the analysis and separation of the mixtures of biochemical compounds in research laboratories and industrial factories. Numerous chromatography techniques such as High-Performance Liquid Chromatography (HPLC), Thin Layer Chromatography (TLC) use absorbents (ex: silica, alumina, cellulose) as stationary phase material [2]. Effective loading of absorbents in those techniques has been a huge challenge since it requires additional implementation of highpressure pump system (for HPLC) or limits selective coating of absorbents on supporting plate (for TLC). In order for chromatography to be efficiently integrated with micro-fluidic Lab-on-achip devices, novel techniques for easy and simple packing of absorbents within micro channels should be developed. We have demonstrated an ultra-fast microfluidic approach to self-assemble silica micro-particles in three-dimension by taking advantage of simple photolithography and
capillary action of micro particles-dispersed suspensions. Silica and silica gel microspheres have been successfully assembled within micro-open channel by using this approach. THEORY Medium-evaporation based two dimensional crystallization technique [1] was applied to assemble mono-dispersed micro-particles of suspension in a micro-open channel which was fabricated by UV-photolithography. A small droplet
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