Two-dimensional concentration of microparticles using bulk acousto-microfluidics

Abstract

In this Letter, we report two-dimensional focusing of microparticles in a glass capillary whose cross section is square outside and round inside using bulk acousto-microfluidics. An imaging system allowing measurements of three-dimensional microparticle acoustophoresis is designed to simultaneously present the two-dimensional focusing processes from combinations of vertical and lateral views in a same frame. The underlying mechanisms of microparticle acoustophoresis in the glass capillary device are explained by a full-device numerical model, which solves the coupling of ultrasonic transducer, glass, and fluid layers of the experimental device. We show here that decent two-dimensional microparticle focusing can be achieved when acoustic pressure nodal lines are generated on cross sections of the fluid channel from the excitation of a single ultrasonic transducer. Based on the developed understanding, we further demonstrate here robust two-dimensional focusing of microparticles by creating an acoustic pressure node point at the channel center from excitations of two orthogonally placed ultrasonic transducers.