Non-motile objects are used to probe intrinsic properties of their environment and enable us to study fundamental aspects of their motion. In nature, however, organisms are not passive but exploit non-equilibrium phenomena to produce active motion.  

In this research project, optical tweezers have been used to study the motion of microspheres and nanospheres inside the harmonic potential of a focused laser beam. Immersed inside a critical binary mixture the absorption of light on the particles' surface induces a gradient that provides the necessary asymmetry to generate active motion. We have observed in both cases on the microscale and nanoscale that the particle leaves its equilibrium position in the center of the beam and performs orbital rotations around it instead.

Although our micro- and nanoengine have to be distinguished by their exact propulsion mechanism (see Figure below), they both provide fundamental insights into the non-equilibrium of biomimetic systems.