A team of researchers from the Universities of Bath, Bristol and Dundee has discovered for the first time that ultrasonic waves can be used to grab several microparticles at a time, effectively creating a pair of invisible ‘ultrasonic hands’ that can move tiny objects, such as cells, under a microscope.
Using tiny plastic spheres the size of biological cells, they found that objects could be moved along independent paths and then carefully brought together. These capabilities provide new tools to study cells which could help biologists or medics perform a variety of delicate tasks such as sorting or assembling cells into patterns for tissue engineering, stem cell work and regenerative medicine.
An electronically controlled acoustic tweezer was used to demonstrate two acoustic manipulation phenomena: superposition of Bessel functions to allow independent manipulation of multiple particles and the use of higher-order Bessel functions to trap particles in larger regions than is possible with first-order traps. The acoustic tweezers consist of a circular 64-element ultrasonic array operating at 2.35 MHz which generates ultrasonic pressure fields in a millimeter-scale fluid-filled chamber. The manipulation capabilities were demonstrated experimentally with 45 and 90-μm-diameter polystyrene spheres. These capabilities bring the dexterity of acoustic tweezers substantially closer to that of optical tweezers.