Diego Baresch
Institut de Mécanique et d’Ingénierie (I2M), Univ. Bordeaux

“Gradient force acoustical traps: a new tool to probe soft and biological matter”

The controlled manipulation of matter using the radiation pressure of light is well established as a powerful tool in the physical and biological sciences: “optical tweezers” use a single laser beam to trap and manipulate individual particles with precisely controlled forces. The piconewton force range and nanonometer spatial resolution make optical tweezers ideally suited to probe biomolecular interactions, colloidal systems, organelles, and even living cells. Despite the wide applicability of optical tweezers in biological and soft matter physics, the challenge remains on probing bulk soft materials such as cell colonies or biological tissue, which require much larger stresses to be significantly deformed.
Using the radiation pressure of sound, rather than light, we have recently developed single-beam acoustical tweezers, which can trap elastic particles as large as 400 microns with forces up to the micronewton range, reducing the beam intensity by 5 orders of magnitude compared to their optical counterpart. The main characteristics of this technique open prospects to investigate mechanisms where large deformations and stresses are required, involving turbid or opaque-to-light media or requiring the gentle manipulation of fragile objects. I will present the basic physical mechanisms underpinning acoustical tweezers and their recent application to manipulate individual microbubbles involved in various biomedical applications of ultrasound.