Manipulation of Nanodroplets via a Nonuniform Focused Acoustic Vortex

Techniques for the manipulation of nanodroplets are central to many miniaturized systems in chemical and biological research and applications. In this study, we demonstrate that the dispersed nanodroplets composed of perfluorocarbon can be manipulated to form a micron-sized elliptical aggregation via a nonuniform focused acoustic vortex, and the aggregation location can be further flexibly regulated. In addition, it is unveiled theoretically and experimentally that the fundamental mechanism for the elliptical aggregation is the nonuniform distribution of the pressure, which makes the acoustic radiation forces acting on the dispersed nanodroplets converge at a certain point. Moreover, the required acoustic droplet vaporization threshold for the nanodroplets is significantly lowered, while the generated microbubbles remain similar in size after aggregation. The findings of this study provide an alternative field of opportunities for targeted drug delivery and imaging using nanodroplet emulsions.