A Multi-level Microchannel Integrated Microfluidic Device for Extraction and Separation of Microparticles

Abstract

Microfluidic devices facilitate the separation of microparticles, blood samples, and even microorganisms by miniaturizing the centrifugal, magnetic, hydrodynamic, electrokinetic, or dielectrophoretic mechanisms on a chip. Most microfluidic devices are fabricated using standard photolithography technology so that they are limited to a single, uniform microchannel depth. However, multi-level microchannels (MLMs) can significantly enhance the separation performance and efficiency. In this work, a simple method is described for fabricating MLMs by combining a polydimethylsiloxane (PDMS) grey-scale photomask (PGSP) and standard photolithography technology. The PGSP adjusts the total amount of UV absorption in photoresist via a wide range of dye concentrations, which in turn adjusts the degree of cross-linking of the photoresist. This enables the fabrication of a multi-depth photoresist master for microfluidic PDMS replica devices. Using the device, it was demonstrated that an MLM-integrated microfluidic device can filter and accumulate both polystyrene microparticles (5.4 μm, 9.2 μm, and 12.0 μm in diameter) and yeast cells in a Korea traditional rice wine (Makgeolli) by size. It was also demonstrated that a pneumatic pressure controller makes it possible to sequentially extract the separated microparticles and yeast cells from the device. In addition, another microfluidic separation device utilizing chemotaxis of microorganisms was developed to extract motile microorganisms (e.g. Escherichia coli) from immotile ones (e.g. yeast). For this, the concentration gradient across the microchannel was well produced along the microchannel and motile E. coli cells were successfully separated from immotile yeast cells. Because the PGSP-based soft-lithography technology provides a simple but powerful fabrication method for MLMs, it is believed that the fabrication method can be widely used for micro total analysis systems that benefit from MLMs. Furthermore, both the microfluidic separation devices that can actively modulate filter gaps and extract motile from immotile microorganisms using chemotaxis could be utilized for biotechnological applications such as the filtration, concentration, and extraction of mammalian cells and microorganisms.