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.

芯片上的荧光激活细胞分选（FACS）需要光学鉴定细胞的类型，然后从进入的流线中选择性地置换该颗粒，可用的置换选择的数量决定了所获得的不同分类结果的数量。表面声波（SAW）提供了一种有效的产生声场的方法，该声场能够对悬浮的粒子和细胞施加力。SAW耦合到微流体通道中包含的流体中。单个声表面波源会引起行波，将行进的粒子推向传播方向，而一对声源会产生驻波，将粒子移动到压力节点。通过脉冲SAW场，两种方法都已用于置换选定的粒子，通过将粒子推向沿传播方向最远的通道壁或将它们移动到最近的压力节点。但是，这项工作表明，通过连续的源对可以获取多个结果，每个源对在空间上相互偏移，结果是级联操作，在此演示中，产生了四个可能的结果。