Scientists have discovered a new way to control tiny solid particles inside liquid droplets—by using sound.
This breakthrough could lead to new tools for medical testing, drug development, and even small-scale physics experiments.
The research, led by Chuyi Chen from North Carolina State University, focuses on how ultrasound waves can be used to spin liquid droplets and concentrate the particles inside them.
By placing a droplet on a special surface that vibrates with high-frequency ultrasound, the liquid begins to spin in place.
This spinning motion pushes the particles suspended in the droplet to spiral inward, forming a concentrated cluster right in the center.
“It’s like creating a tiny whirlpool inside the droplet,” said Chen, who is an assistant professor of mechanical and aerospace engineering.
“The sound waves make the fluid inside the droplet spin in a circle, and that motion causes the solid particles to move in a corkscrew pattern, collecting at a single spot.”
This new method allows researchers to gather particles in liquid without needing filters or chemicals.
That could be especially useful in biomedical applications, where scientists often need to detect tiny amounts of material inside cells or fluids. Concentrating those materials could make it much easier for sensors to pick up the signal they’re looking for.
Until now, the physics behind this swirling effect wasn’t fully understood. But in their new paper published in Science Advances, Chen and his team explain the forces at work in detail.
Knowing how the spinning works—and what factors affect it—means scientists can now design systems that use it more precisely.
The study shows that changing the droplet’s surface tension, size, or the strength of the ultrasound waves can all influence how the particles move. That gives researchers multiple ways to fine-tune the effect, depending on what they need.
Besides helping in medicine and drug testing, the technique also opens the door to new kinds of physics research. The spinning droplets behave a bit like miniature tornadoes, making it possible to study how particles move in rotating systems—without needing large or expensive equipment.
“This gives us a simple, low-cost way to explore some really interesting physics,” Chen said. “It’s compact and easy to observe, and it could be useful across many scientific fields.”
This innovative method of spinning droplets and controlling particles could lead to the development of new lab tools, offering scientists a precise, efficient, and fascinating way to work with fluids on a tiny scale.
