Sorting cells by their density
Fig 2
A simulation of paths followed by four different types of particles in a microchannel containing fluid with a uniform density (A; 1.05 g/mL) and in a microchannel containing three zones with different fluid densities (B; 1.05, 1.07, and 1.09 g/mL), obtained using our custom software density_sorter.py (S1 and S2 Files).
In both cases, marker color connotes particle density (1.080 g/mL for red; 1.060 g/mL for green), and marker size connotes particle size (40 μm diameter for the larger marker; 20 μm diameter for the smaller marker). The particles all start at the same location at the top of the channel, and the position of each particle is calculated using Eqs 1 and 2 at 5 second intervals. Each fluid has a flow rate of 1.2 μL/min, for a combined flow rate of 3.6 μL/min. In a fluid of uniform density (A), the particles sink at different speeds but they all end up collecting on the bottom of the channel. However, in a continuously-flowing density gradient (B), both sizes of green (1.060 g/mL) particles sink until they reach the interface between the top two fluids, and both sizes of red (1.080 g/mL) particles sink until they reach the interface between the bottom two fluids. The particles then exit the channel in different locations and are thereby sorted according to their density alone (not their size).