Manipulating high-throughput microparticle aggregation in capillary via elastic-acoustics orbital angular momentum transfer

Vortex acoustic fields are an emerging particle manipulation technique that gathers particles at a central zero-pressure point. Acoustic fields carrying orbital angular momentum (OAM) are reflected by hard boundaries, limiting their application within capillaries for aggregation of bioparticles in the cell analysis and biomolecule purification. We report a design for generating standing wave vortex acoustic fields within a capillary and investigate its effects on particle aggregation. The design uses a spiral phase helical tube placed outside the capillary to transfer elastic OAM to the fluid inside. Simulation results show that the first-order acoustic field is identical to the first-order Bessel beam and exhibits single vortex second-order acoustic streaming. In a background flow of 1×10−5 L/s, polystyrene particles with a diameter of 2 μm aggregated along a radial trajectory under the combined action of radial acoustic radiation force and tangential Stokes drag force. This method offers an efficient solution for the manipulation and detection of biological particles.