Acoustic Tweezers for Trapping Late-Stage Zebrafish Embryos

This paper reports our recent design of an immersive acoustic tweezers capable of trapping and holding large and heavy particles such as micro-particles up to 1 mm in diameter, as well as zebrafish embryos at their 24 - 36 hours post fertilization, by developing a 3-dimensional energy well in the bulk of liquid medium. The acoustic tweezer is built on a 2.03 mm thick lead zirconate titanate (PZT) substrate and operated at its thickness mode, with 18 symmetric beamforming sectors (pie shaped when viewed from top) arranged for 3 focal lengths (17.0, 18.5 and 20 mm). For a single focal length, the six beamforming sectors (with air-cavity-reflectors for eliminating out-of-phase wave interference) work together as a sectored Fresnel lens. The acoustic waves aiming at different focal lengths interfere with each other such that they produce a Bessel beam zone (with negative axial radiation force) along the center line perpendicular to the transducer surface, which works as the energy well for trapping and holding particles. The tweezers using 1.17 MHz ultrasound shows strong trapping capability and large trapping zone, and is capable of trapping and holding late-stage zebrafish embryos (0.7 - 1mm in diameter and 1.3 - 1.5 mg in weight). The fabricated acoustic tweezers has been shown to trap 24hours-post-fertilization zebrafish embryos when it is placed either horizontally or vertically.