  Critical Casimir forces emerge between objects, such as colloidal particles,
whenever their surfaces spatially confine the fluctuations of the order
parameter of a critical liquid used as a solvent. These forces act at short but
microscopically large distances between these objects, reaching often hundreds
of nanometers. Keeping colloids at such distances is a major experimental
challenge, which can be addressed by the means of optical tweezers. Here, we
review how optical tweezers have been successfully used to quantitatively study
critical Casimir forces acting on particles in suspensions. As we will see, the
use of optical tweezers to experimentally study critical Casimir forces can
play a crucial role in developing nano-technologies, representing an innovative
way to realize self-assembled devices at the nano- and microscale.
