Continuous 3D particle focusing in a microchannel with curved and symmetric sharp corner structures

A new microchannel that enables continuous three-dimensional (3D) particle focusing with a single sheath flow is reported. The 3D particle focusing is based on the combination of the microfluidic drifting effect induced by a curved microchannel and the momentum-change-induced inertial effect induced by a series of repeated symmetric sharp corner structures on both side walls of the microchannel. The microfluidic drifting effect induces particle focusing in the vertical direction (z direction) while the momentum-change-induced inertial effect induces particle focusing in the horizontal direction (on the x-y plane). Eventually, particles are three-dimensionally focused at the center of the microchannel. The 3D particle focusing behavior in the present microchannel was demonstrated by the experiment using 7.32 mu m particles at a sample flow rate of 66.7 mu L min(-1) and a sheath flow rate of 400 mu L min(-1). Force analysis and computational fluid dynamics (CFD) simulation confirmed particles of different sizes (from 5 to 15 mu m) could also be three-dimensionally focused in the present microchannel over a wide range of flow rates. In comparison with other 3D passive focusing techniques, this microchannel built in a single layer only requires a single sheath flow, and hence avoids complex flow control. With its simple structure and operation, this device can potentially be used in 3D particle focusing processes in many lab-on-a chip applications, such as micro flow cytometer.