Sheathless focusing of microbeads and blood cells based on hydrophoresis

This paper presents a microfluidic device for sheathless focusing of microbeads and blood cells based on a hydrophoretic platform comprising a V-shaped obstacle array (VOA). The VOA generates lateral pressure gradients that induce helical recirculations. Following the focusing flow particles passing through the VOA are focused in the center of the channel. In the device, the focusing pattern can be modulated by varying the gap height of the VOA. To achieve complete focusing within 4.4% coefficient of variation, the relative size differences between the gap and the particle were 3 and 4 microm for 10 and 15 microm beads, respectively. Red blood cells were used to study the hydrophoretic focusing pattern of biconcave, disk-shaped particles.