Acoustic tweezers find their biomedical niche

Acoustic tweezers and optical tweezers operate on the same physics principle: since waves carry momentum, they can be used to manipulate objects in space. Acoustic tweezers use sound waves, rather than light waves, which allow them to trap and maneuver larger objects. Bruce W. Drinkwater describes the advantages of acoustic tweezers and future directions for the field.

In biomedical research, objects of study range in scale from the size of DNA to the size of organisms. Optical tweezers can manipulate objects up to the approximate size of organelles or small cells, but to trap larger cells or clumps of cells, a longer wavelength is needed. The amount of energy needed to get an optical laser to that wavelength is often enough to opticute a sample—to destroy it with light.

The need to control larger samples in smaller experiments has driven biomedical interest in applications for acoustic tweezers, which are generally able to manipulate cells and larger objects such as microorganisms. They show particular potential for lab-on-a-chip devices, which can perform laboratory techniques such as drug development and diagnostic tests on a microscale. These devices manipulate organoids, or clumps of cells that create a more realistic micro-environment for biomedical research than a petri dish. Organoids are too big to be manipulated by optical tweezers.

“As the interest has grown, there’s been this great diversity of devices that have started to emerge,” Drinkwater said. “And recently, it’s 3D devices that seem to be coming to the fore.”

Future acoustic tweezers may not only be three-dimensional, but may operate at gigahertz frequencies, which would allow them to compete with optical tweezers at smaller wavelengths.

Source: “A perspective on acoustical tweezers - devices, forces and biomedical applications,” by Bruce W. Drinkwater, Applied Physics Letters (2020). The article can be accessed at https://doi.org/10.1063/5.0028443 .