Acoustic Tweezers Can Position Tiny Objects

Manipulating tiny objects like single cells or nanosized beads often requires relatively large, unwieldy equipment. Engineers have now developed a system that converts sound into a dime-sized tweezer, small enough to fabricate on a chip using standard chip manufacturing techniques.

Acoustic tweezers can manipulate live cells without damaging or killing them. They can also position many tiny objects simultaneously and place them equidistant from each other in either parallel lines or on a grid. The grid configuration is probably the most useful for biological applications, such as placing skin cells on a grid to grow new skin.

The new technique works using standing surface acoustic waves. If two sound sources are placed opposite each other and each emits the same wavelength of sound, there will be a location where the opposing sounds cancel each other. This location can be considered a trough. Because sound waves have pressure, they can push very small objects, so a cell or nanoparticle will move with the sound wave until it reaches the trough. The particle or cell will then stop and "fall" into the trough.

If the sound comes from two parallel sound sources facing each other, the troughs form a line or series of lines. If the sound sources are at right angles to each other (shown in yellow, above), the troughs form an evenly spaced set of rows and columns like a checkerboard. In this case, too, the cells (shown in red) are pushed until they reach the location where the sound is no longer moving.

In a recent issue of Lab on a Chip, the Penn State researchers noted that the patterning performance is independent of the particle's electrical, magnetic and optical properties.

Because of the versatility, miniaturization, power consumption and technical simplicity of acoustic tweezers, the researchers expect the technique to become a powerful tool for many applications such as tissue engineering, cell studies, and drug development.

- A'ndrea Elyse Messer, Penn State

Image credit: Tony Jun Huang, Jinjie Shi, Penn State