Particle collection using vibrating bubbles

In this study, we present a microfluidics channel capable of collecting and focusing particles by the use of a vibrating air/water interface. The device contains a sidewall cylindrical void that traps air to create a microbubble surface, a modified version of the commonly used lateral cavity acoustic transducer (LCAT). By employing a relatively narrow rectangular channel (50 μm wide), we show that particles can be trapped and released into a narrow region. The collection process is described through an analysis of the transient state of the vortex. Additionally, it is found that the focusing efficiency, i.e. the width of focusing region, depends on the particles diameter and the excitation amplitude. 6.60 μm particles can easily be made to form a single line along the channel wall opposite the bubble under suitable conditions. For 2.01 μm particles, the focussing can be to a region of one third of the channel width. The focusing width grows with decreasing excitation amplitude, down to a certain voltage beyond which the vortices are too weak to induce any streaming.