The ability to generate and precisely control microscale fluid jets is pivotal for advancements in biomedicine, from diagnostics to targeted delivery. However, existing jet generation technologies are constrained by structural complexities, low efficiency, and limited control, hindering their application in high-throughput microfluidic systems. Here, we introduce a paradigm shift by demonstrating that pulsed excitation of a 2 GHz bulk acoustic wave (BAW) resonator can generate ultrafast, orifice-free, and highly directional microjets within a microfluidic chamber. Crucially, we show for the first time that the dimensions and velocity of these acoustic jets can be dynamically and precisely tuned by simply varying the input power and pulse width of the acoustic excitation, enabling theoretical jet rates exceeding 200,000 per second. Leveraging this unique capability, we constructed a fluorescence-activated cell sorter that utilizes these on-demand microjets to actively deflect target cells into a collection channel with high speed and accuracy. This pulsed acoustic streaming (PAS) sorter achieves a throughput of 1662 cells/s with >97% purity while maintaining cell viability. We further demonstrated its biomedical utility by successfully sorting murine M1 and M2 macrophages with a recovery purity exceeding 98% for the M2 phenotype. Our work establishes pulsed acoustic microjets as a robust, efficient, and highly controllable mechanism for high-throughput cellular manipulation, opening new avenues in cell analysis, diagnostics, and therapeutic delivery.
Guan et al. (Fri,) studied this question.