Factors influencing the capillary separation of leukocytes from whole blood in a plastic-based microfluidic chip

This study describes some of the influencing factors, such as capillary action, static electricity and magnetic force, on the ability to separate living leukocytes from a single droplet of blood (<1 μl) in a plastic-based microfluidic chip.The chip was constructed from two substrate materials sandwiched together to form a micron-order gap (40 μm) with an upper hydrophilic (glass) surface and a lower hydrophobic (acrylic resin) surface. A blood sample flowed into the gap between the two substrates driven by the difference in surface tension between the two materials. Leukocytes adhered to the lower hydrophobic surface, whereas red corpuscles flowed toward the exit of the microfluidic device (this phenomenon is referred to as micro-flow). The separation rate of the red corpuscles was 91 ± 9% in a unit area of 0.1 mm2.Furthermore, we analyzed the change in the numbers of living leukocytes that could be collected after separation in the chip under different conditions. When SiO2 and iron composite particles, 10 μm in size, were added to the blood sample, leukocytes formed colonies containing two or three cells. The colonies could be moved freely on the x–y plane using a Nd magnet. When the upper board was charged by static electricity, the colonies adhered to the underneath of the upper board. Five or more colonies, as well as 10 or more individual leukocytes, were able to collect in a 0.1 mm2 area of the chip after micro-flow operation. Thus, the separation efficiency of a living cell colony containing Fe particles in a capillary chip is markedly influenced by magnetic and electrostatic forces.