Fig. 1 . Schematic overview of the bacteria separation method. Particles of two different sizes are shown at different positions (regions 1,2,3 and 4) of a spiral channel. At region 1 (closer to inlet), both particle sizes are pre-positioned at the outer wall by the viscoelastic sheath buffer. As the Dean vortices develop (region 2-4), the smaller particles (green) are dragged with vortices and migrate toward the inner wall while the larger particles (red) remain focused at the outer wall. The larger particles remain focused throughout the channel length due to a balance between the three dominant forces (FL, FE and FD)