Capillary tweezers for manipulating colloidal particles

Optical tweezers became ubiquitous tools because they can manipulate individual colloidal particles and measure piconewton-scale forces. Despite their widespread adoption, there is still a need for other tweezers that can operate at different force magnitudes and on different materials. In this talk, I will introduce a new kind of tweezer called a “capillary tweezer” that uses lateral capillary interactions to trap and manipulate individual colloidal particles. A capillary tweezer relies on the repulsive force exerted on a denser-than-water object that floats at a fluid-fluid interface in a channel with hydrophilic walls. This repulsive capillary interaction traps the particle in the center of the channel. Changing the shape of the channel changes the shape of the interface and thus moves the particle. We can place capillary tweezers on a microscope and image the motion of the particle. I will discuss measurements of the forces that act on the colloids.