Fig.3 . Particle focusing behavior at different Re. 1 µm (green) and 7 µm (in red) particles imaged at five regions of the spiral channel at a total flow rate of 1 mL/min (Sample flow rate: 50 µL/min). (A) Near the inlet (region 1), both sized particles are positioned at the outer wall of the channel. The 7 µm particles remain focused at the outer wall in all regions 1-5 while 1 µm particles migrate toward the inner wall (region 4) and can be separated (region 5). Scale bar : 100 µm. (B) Normalized fluorescent cross-section intensity distributions across the channel width at the outlet (region 4). At low Re (Re=5), both 1 and 7µm particles are not focused. At higher flow rates (Re = 25 – 32), the 1 µm particles migrate toward the inner wall, while the 7 µm beads stay focused at the outer wall.