Microparticle concentration and separation inside a droplet using phononic-crystal scattered standing surface acoustic waves

Abstract

Rapid particle and biocell concentration and separation are important for the development of miniaturized physical, biological, and chemical systems. In this study, the scattering of standing surface acoustic waves (SSAWs) in an acoustofluidic phononic crystal (PnC) device is used to actuate spatial concentration and separation of suspended microparticles with two different sizes in a sessile droplet. The simulation design of the device and manipulation mechanisms of the two distinct particles are presented and discussed. A surface acoustic wave (SAW) acoustofluidic device with a nickel pillar-type PnC electroplated on a piezoelectric substrate, 128°YX LiNbO3, is designed and fabricated. A 30-MHz SSAW field is scattered within the directional phononic bandgap of the PnC to generate simultaneously acoustic radiation force and acoustic streaming flow to concentrate and separate 2- and 20-μm polystyrene microparticles. Experiments are conducted to verify the device functions on concentrating and separating microparticles. The results also suggest the possibilities of regarding phononic crystals as an effective element to tailor the SAW field for building other innovative acoustofluidic devices to achieve novel concentration, separation, and acoustic manipulation of biocells and biomolecules in discrete microfluidic systems.