Multiple outcome particle manipulation using cascaded surface acoustic waves (CSAW)

On-chip fluorescent activates cell sorting (FACS) requires the optical identification of a cell's type followed by the selective displacement of that particle from the incoming streamline, the number of displacement choices available dictate the number of different sort outcomes which are obtained. Surface acoustic waves (SAW) offer an effective way of generating a sound field which is capable of exerting forces on suspended particles and cells. The SAW couples into the fluid contained within a microfluidic channel. A single SAW source can cause a travelling wave which pushes particles in the direction of propagation, whilst a pair of sources can give rise to a standing wave which moves particles to pressure nodes. By pulsing the SAW field on, both approaches have been used to displace selected particles, either by pushing particles to the channel wall furthest along the propagation direction or moving them to the nearest pressure node. However, this work shows that multiple outcomes can be obtained by successive source pairs, each spatially offset from each other, the result is a cascaded manipulation yielding, in this demonstration, four possible outcomes.

Automated summary

Surface acoustic waves (SAW) can generate a sound field in a microfluidic channel to exert forces on suspended particles and cells, enabling selective displacement. Different outcomes can be achieved by using a single SAW source or a pair of sources at different spatial positions to manipulate the particles.