Particle inertial focusing and its mechanism in a serpentine microchannel

Particle inertial focusing in a curved channel promises a big potential for lab-on-a-chip applications. This focusing concept is usually based on the balance of inertial lift force and the drag of secondary flow. This paper proposes a new focusing concept independent of inertial lift force, relying solely on secondary flow drag and particle centrifugal force. Firstly, a focusing mechanism in a serpentine channel is introduced, and some design considerations are described in order to make the proposed focusing concept valid. Then, numerical modelling based on the proposed focusing mechanism is conducted, and the numerical results agree well with the experimental ones, which verify the rationality of proposed mechanism. Thirdly, the effects of flow condition and particle size on the focusing performance are studied. The effect of particle centrifugal force on particle focusing in a serpentine microchannel is carefully evaluated. Finally, the speed of focussed particles at the outlet is measured by a micro-PIV, which further certifies the focusing positions of particles within the cross section. Our study provides insights into the role of centrifugal force on inertial focusing. This paper demonstrates for the first time that a single focusing streak can be achieved in a symmetric serpentine channel. The simple serpentine microchannel can easily be implemented in a single-layer microfluidic device. No sheath flow or external force field is needed allowing a simple operation in a more complex lab-on-a-chip system.