Author:

Keywords:

microfluidics, magnetic particles

Abstract:

Segmented flow or droplet microfluidics has been successfully used in many applications such as chemical reactions, bio-assays and the production of micro-and nanoparticles. The asymmetric splitting of droplets in microchannels is a feature that can benefit many applications both in research and industry, such as sampling of chemical reactions or separation of cells and particles from the droplets. Current methods use passive systems to achieve the unequal split, creating an unequal backpressure in the two branches of the split with different lengths of narrow channels. These splitting junction are fixed and thus have a fixed splitting ratio. To achieve a better, dynamical control of the splitting active methods could be used: valves, membranes or optical and electronic methods. We developed a segmented flow system that can split droplets with ratios up to 20:1 and this ratio can be dynamically controlled with an additional oil flow. This microfluidic chip was fabricated in PDMS by the well-established mold and chip production methods. To avoid a trial and error approach - making and testing multiple designs - a computational fluid dynamics (CFD) model was developed and validated. The simulations were used to optimize the design of the splitting T-junction and the extra inlet as well as the flows needed to split the drops in all ratios. For future designs and concepts, we can use this model to optimize the design or simulate the results, before fabrication the actual PDMS chips. To test the splitting system for future assays, we tried to separate magnetic particles from the droplet using an external magnet. We were able to retain all particles in 10 % of the droplet, thus removing 90 % of the original volume in one step. This greatly improves the washing efficiency during an assay when comparing to literature.