Fig 1. Photograph (A) and cross-section illustration (B) of a 3D-printed density sorter chip.

Fluids with three different densities (1.070, 1.085, and 1.110 g/mL) are pumped into the inlets; under laminar flow conditions these fluids form a micron-scale density gradient flowing along the horizontal channel. If a mixture of blood cells is included in the top fluid, the flowing white blood cells (average density ρ = 1.080 g/mL) quickly sink to the interface between the 1.070 and 1.085 g/mL fluids where they are neutrally buoyant, and the flowing red blood cells (average density ρ = 1.110 g/mL) sink to the interface between the 1.085 and 1.110 g/mL fluids. When the channel splits, the white blood cells flow out of the top outlet and the red blood cells flow out of the bottom outlet.