Microfluidic device for sheathless particle focusing and separation using a viscoelastic fluid

• We report a new two stage microfluidic device for particle separation.
• Use of a viscoelastic fluid enhanced the separation efficiency.
• Tunability of separable particle size was achieved by varying the flow property.
• Our device shows potential of clinical application.

Continuous sheathless particle separation with high efficiency is essential for various applications such as biochemical analyses and clinical diagnosis. Here, a novel microfluidic device for highly efficient, sheathless particle separation using an elasticity-dominant non-Newtonian fluid is proposed. Our device consists of two stages: sheathless three-dimensional focusing (1 st stage) and separation (2nd stage). It is designed based on the principle of a viscoelasticity-induced particle lateral migration, which promises precise separation of particles in a microfluidic device. Particles of 5- and 10-μm diameters were all focused at the centerline of a circular channel at the 1st stage and successfully separated at the 2nd stage with an efficiency of ∼99.9% using size-based lateral migration of particles induced by the viscoelasticity of the medium. We also demonstrated the capability of our device for separation of blood cells into multiple fractions. The tunability of separable particle size could be achieved by changing the viscoelastic property of the medium and flow rate.