Observed minimum focusing sizes in relation to the spiral channel height and particle size (blue diamonds) compared against predictions (red squares) established by the hydraulic diameter relationship (a/Dh > 0.0715).
Error bars of +/− 10% result from the bead size distributions used for these experiments (cf. beads characteristics in Table S4) with the data shown being based on the mean particle size reported by the manufacturer. The location of single particles is imaged using a high speed camera (cf. Fig. S5) or by visual observation for the larger particles (>75 μm) as presented in the video in SI. Particles are “observed to focus” when they align close to the inner wall of the spiral with 100% of particles going into the focused outlet based on 100 recorded images (number of particles detected for each case>200).