Microsphere capture and perfusion in microchannels using flexural plate wave structures

A standing acoustic field excited by an ultrasonic flexural plate wave (FPW) device is shown to trap microspheres and cells suspended in a pressure-driven flowing liquid. Capture is achieved by counteracting the viscous drag forces on a particle with acoustic radiation pressure. The suitability of this technique for biochemical analysis is demonstrated with two experiments: (1) acoustically trapped streptavidin-coated 1 μm microspheres conjugated to fluorescent 200 nm biotinylated microspheres; and (2) perfusion of the membrane permeant fluorescein diacetate across acoustically trapped cells. Biochemical interaction was monitored with a fluorescence microscope. Efforts to integrate acoustic traps with on-chip FPW microfluidic pumps are also described.