Self-Assembled Ultra-thin Silica Layers for On-Chip Chromatography

Abstract

We propose a novel method for self-assembled packing of silica microsphere in micro-channel which can be potentially used for on-chip chromatography. 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 [1]. Effective loading of absorbents in those techniques has been a huge challenge since it requires additional implementation of high-pressure 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-a-chip devices, novel techniques for easy and simple packing of absorbents within micro channels should be developed.

Solvent-evaporation based 2-D crystallization technique [2] 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 micro-channel 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.

We will present the characterization of silica packing with regard to various process parameters and also will include theoretical interpretation of this packing technique in more detail. We will also present our future approach to integrate our technique on-chip chromatography applications.