Acoustofluidic Particle Trapping in a Structured Microchannel Using Lateral Transducer Modes

By using lateral extensional modes of piezoelectric plate transducers for the actuation of a microfluidic chip containing a structured microchannel, we achieved 2-D single-node acoustofluidic particle trapping inside a circular cavity as well as 2-D multinode trapping in straight channels. In order to manipulate the particles in two lateral dimensions, we used two separate PZT transducers attached to the bottom of the microfluidic chip, where each is responsible for generating a standing acoustic wave in a specific direction inside the microfluidic structures of the chip. We demonstrate the trapping of polymer microspheres and trapping of human embryonic kidney cells with a performance that can compete with current bulk acoustic methods that typically employ transducer thickness modes. The acoustic energy density of the involved acoustic fields reaches several hundred (430) joules per cubic meter, leading to trapping times of tenths of a second (150 ms) and nanonewton trapping forces (0.42–1.7 nN). The relatively low, submegahertz resonance frequency of the utilized lateral transducer mode in the cavity trapping results in a large, millimeter long wavelength of the acoustic wave inside the fluid, which enables the collection of comparably large volumina of multiple tens of nanoliter containing several thousands of particles or cells. Consequently, with the large volumes involved, it appears feasible to trap bigger objects, such as multicellular organisms or organoids with approximately 1 mm in size.