Sedimentation pinched-flow fractionation for size- and density-based particle sorting in microchannels

A simple and efficient device for density-based particle sorting is in high demand for the purification of specific cells, bacterium, or environmental particles for medical, biochemical, and industrial applications. Here we present microfluidic systems to achieve size- and density-based particle separation by adopting the sedimentation effect for a size-based particle sorting technique utilizing microscale hydrodynamics, called pinched-flow fractionation (PFF). Two schemes are presented: (a) the particle inertia scheme, which utilizes the inertial force of particle movement induced by the momentum change in the curved microchannel, and (b) the device rotation scheme, in which rotation of the microdevice exerts centrifugal force on the flowing particles. In the experiments, we successfully demonstrated continuous sorting of microparticles according to size and density by using these two schemes, and showed that the observed particle movements were in good agreement with the theoretical estimations. The presented schemes could potentially become one of the functional components for integrated bioanalysis systems that can manipulate/separate small amount of precious biological samples.