Single-beam Acoustic Tweezers for Cell Biology: Molecular to in vivo level

Acoustic tweezers have attracted attention in various fields of cell biology, including in vitro single-cell and intercellular mechanics. Compared with other tweezing technologies such as optical and magnetic tweezers, acoustic tweezers possess stronger forces and are safer for use in biological systems. However, due to the limited spatial resolution, or limited size of target objects, acoustic tweezers have primarily been used to manipulate cells in vitro. To extend the advantages of acoustic tweezers to other levels (e.g., molecular and in vivo levels), researchers have recently developed various types of acoustic tweezers such as single-beam acoustic tweezers (SBATs), surface acoustic wave tweezers, and acoustic-streaming tweezers. Among these, SBATs utilize a single-focused beam, making the transducer and system simple, noninvasive, and capable of producing strong forces compared with other types of tweezers. Depending on the acoustic beam pattern, SBATs can be classified into Rayleigh regime, Mie regime, and acoustic vortex with different trapping dynamics and application levels. In this review, we provide an overview of the principles and configuration of each type of SBAT, their applications ranging from molecular to in vivo studies, and their limitations and prospects. Thus, this review demonstrates the significance and potential of SBAT technology in biophysics and biomedical engineering.