Light-induced micro and nano machines

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.
Top: Microengine driven by the asymmetric absorption of light on its surface. Bottom: Nanoengine driven by light absorption on an asymmetric shape. Left: SEM images of the particles. Middle: Examples of Trajectories. Right. Simulations of their motion.


Non-equilibrium properties of an active nanoparticle in a harmonic potential.

Falko Schmidt, Hana Šípová-Jungová, Mikael Käll, Alois Würger, Giovanni Volpe

Nature Communications, vol. 12(1), 2021 Feb 26, pp. 1902-1902

Microscopic Engine Powered by Critical Demixing.

Falko Schmidt, Alessandro Magazzù, Agnese Callegari, Luca Biancofiore, Frank Cichos, Giovanni Volpe

Physical Review Letters, vol. 120(6), 2018 Jan 9