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In this paper, we propose a serial dilution microfluidic chip which is able to generate logarithmic or linear step-wise concentrations. These concentrations were generated via adjustments in the flow rate of two converging fluids at the channel junctions of the ladder network. The desired dilution ratios are almost independent of the flow rate or diffusion length of molecules, as the dilution device is influenced only by the ratio of volumetric flow rates. Given a set of necessary dilution ratios, whether linear or logarithmic, a serial dilution chip can be constructed via the modification of a microfluidic resistance network. The design principle was suggested and both the logarithmic and linear dilution chips were fabricated in order to verify their performance in accordance with the fluorescence intensity. The diluted concentrations of a fluorescein solution in the microfluidic device evidenced relatively high linearity, and the cytotoxicity test of MCF-7 breast cancer cells via the logarithmic dilution chip was generally consistent with the results generated with manual dilution.

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A novel fabrication technique was developed to fabricate round microchannels and applied to a micro mixer having a barrier structure using surface tension of PDMS. When the solidified PDMS layer (channel layer) contacts the liquid PDMS film (meniscus layer), a meniscus is formed around the sidewall in the microchannel due to surface tension. The external load pressure and contact area of the channel layer were adjusted to form various cross-sectional shapes such as a U shape, ellipse, semi-circle and circle. Since the width of the channel also determines the depth formed by the difference in capillary height, a multi-depth channel can be fabricated using a one-step process. It was applied to a dual-depth serpentine mixer, eliminating the aligned bonding of conventional soft lithography. The 3D-structure mixer enhanced mixing performance in the range of Re > 10 compared with a 2D-structure. It could fully mix phenolphthalein and sodium hydroxide when the Reynolds number was 80. The suggested fabrication method could be very useful in various microfluidic devices that need round corners and multi-depth channels.