Acoustic particle trapping in a microfluidic device using frequency modulated signal

Recently, several biological cell manipulation techniques using electrostatic, magnetic, optical, and acoustic forces have been developed to precisely control various cell motions within such devices. In our previous research, a 30 MHz lithium niobate single element transducer was fabricated to experimentally demonstrate the feasibility of acoustic trapping, where a droplet could be held stationary in two-dimensional trap. In order to control streaming particles in a fluid in a microfluidic device, it is necessary to generate trapping forces greater than the drag force arising from the surrounding fluid flow. In this paper, a 24 MHz PZT4 transducer was built to immobilize 60 ∼ 70 µm droplets flowing in a polydimethylsiloxane (PDMS) microfluidic device. The experimental results showed that the current device may serve as an acoustic switch to direct particle motions in cell sorting devices.