Microfluidics and Nanofluidics vol:18 issue:2 pages:293-303
Droplet-based segmented flow microfluidic systems have proven their potential for high throughput detection and quantification of analytes. However, the required sample preparations are often performed off-chip, as on-chip methods are lacking. Microparticles are especially suited for the extraction and purification of target molecules from a sample and are successfully used in other microfluidic systems and in laboratory-scale methods. The current magnetic separation methods in segmented flow microfluidics are limited in their function to purify, as only a limited part of the original droplet volume can be removed from the particles. In this paper, we report the implementation of a selective DNA extraction assay with microparticles in a segmented flow microfluidic system. The combination of magnetic separation with asymmetric droplet splitting allows the removal of 90 % or even 95 % of the original sample volume in a single separation step. It is shown that the hybridization and capture efficiency of the particles are identical for off-chip and on-chip methods. Next, the effect of the particle separation efficiency on the extraction efficiency is tested for different splitting regimes. When up to 90 % of the droplet volume is removed, nearly all particles are correctly separated and the non-separated particle fraction remains below 5 %. Only if 95 % of the original volume is removed, the unseparated fraction becomes significant (>10 %). Finally, the impact of separation at a higher splitting ratio for the repeated washing of the particles is discussed. With this novel system, more complex and relevant bioassays can be implemented completely in a droplet-based segmented flow context.