Cascade flow diagram.
3 spiral rectangular channels (500, 300 and 200 μm high) are cascaded to fractionate a mix of particles with a wide range size as described in Table S5. Each spiral presents a similar design, scaled down to focus different particle sizes (~100 μm for the 500 μm high spiral, ~50 μm for the 300 μm high spiral and ~30 μm for the 200 μm high spiral). The initial sample volume (500 mL) is injected through the 500 μm high spiral (blue arrow) and split equally into two outlets. The focused outlet contains focused particles while smaller particles are homogeneously distributed in the two outlets. The focused outlet is continuously re-injected at the inlet of the spiral until the desired volume is reached (~50 mL in this case). A 50 mL sample is collected from the unfocused outlet for measurements, the remainder of which is then injected through the 300 μm high spiral and recirculated in a similar manner until the volume at the focused outlet reaches ~50 mL. The same process is repeated with the 200 μm high spiral (final volume at the focused outlet ~50 mL). The flow rates were 22, 12 and 7 mL/min respectively.