Separation of particles with bacterial size range using the control of sheath flow ratio in spiral microfluidic channel

Abstract A method of concentrating and separating small particles with a specific size in a microfluidic system can be applied to obtain high-purity biological samples, such as viruses, bacteria, and cells. This paper presents the highly efficient separation method of bacteria-sized particles using Dean flow and inertial force in a curved spiral microfluidic channel. By adjusting the flow rate ratio of particle solution to sheath flow at the inlet, the stream line of small particles circulating in the transverse direction with Dean flow becomes more distinct from large particle stream line focused at specific equilibrium position by inertial force. Therefore, submicron-sized particles can be separated from larger particles with high efficiency. In addition, the effects of the number of small particle circulations with Dean flow on the extraction efficiency have been studied. The fluidic channel has been tested for the separation of fluorescent particles with diameters of 0.81 μm, 2.29 μm, and 4.70 μm. The channel design and flow control were optimized so that 0.81-μm particles circulated in the channel along with Dean flow, while 2.29-μm and 4.70-μm particles were concentrated at separate equilibrium points by the inertial force. The extraction yields of 0.81-μm, 2.29-μm, and 4.70-μm particles were measured to be 98.42%, 97.69%, and 99.17%, respectively. Moreover, separation of bacteria from 2.29-μm and 4.70-μm particles has been demonstrated with 98.01% extraction yield.