Continuous blood cell separation by hydrophoretic filtration

We propose a new hydrophoretic method for continuous blood cell separation using a microfluidic device composed of slanted obstacles and filtration obstacles. The slanted obstacles have a larger height and gap than the particles in order to focus them to a sidewall by hydrophoresis. In the successive structure, the height and gap of the filtration obstacles with a filtration pore are set between the diameters of small and large particles, which defines the critical separation diameter. Accordingly, the particles smaller than the criterion freely pass through the gap and keep their focused position. In contrast, the particles larger than the criterion collide against the filtration obstacle and move into the filtration pore. The microfluidic device was characterized with polystyrene beads with a minimum diameter difference of 7.3%. We completely separated polystyrene microbeads of 9 and 12 microm diameter with a separation resolution of approximately 6.2. This resolution is increased by 6.4-fold compared with our previous separation method based on hydrophoresis (S. Choi and J.-K. Park, Lab Chip, 2007, 7, 890, ref. 1). In the isolation of white blood cells (WBCs) from red blood cells (RBCs), the microfluidic device isolated WBCs with 210-fold enrichment within a short filtration time of approximately 0.3 s. These results show that the device can be useful for the binary separation of a wide range of biological particles by size. The hydrophoretic filtration as a sample preparation unit offers potential for a power-free cell sorter to be integrated into disposable lab-on-a-chip devices.