Flexible Pico-Liter Acoustic Droplet Ejection Based on High-Frequency Ultrasound Transducer.

Acoustic droplet ejection (ADE) uses the acoustic energy produced by a focused ultrasound beam to provide a non-contact, highly precise, automatic, and cost-effective liquid transfer method for life science applications. The reported minimum precision of the current acoustic liquid transfer technology is 1 nL. Since precision improvement always brings valuable results in biological research, it is highly necessary to develop pico-liter precision liquid transfer technology. In this work, we developed a 40 MHz ultrahigh-frequency focused ultrasound transducer with a large aperture of 7 × 7 mm2 and a wide bandwidth of 76.4%. The designed transducer can successfully eject pico-liter droplets, and the droplet ejection accuracy ranges from 28 pL to 439 pL. The effects of the acoustic parameters, including excitation amplitude, pulse width, and frequency, on the size of the ejected droplet were studied. A wide range of ejected droplet sizes could be obtained by adjusting the acoustic parameters, thereby making liquid transfer flexible. The flexible pico-liter liquid transfer based on the wide-bandwidth, high-frequency ultrasound transducer is easier to achieve automatically, and thus it has broad prospects in biological research and industrial applications.