Optical Tweezers

Idea: In this experiment we learn how force can be used to characterize
molecular processes in biological systems

Biophysics Lab Course, Institute of Biophysics, Ulm University


An optical trap is calibrated by measuring the escape force for polystyrene beads and its dependence on laser power.

Rotation of E.coli attached with one flagellum to a glass substrate is used for the investigation of the flagellar motor.

The torque excerted by the flagellar motor is determined in two ways:

  • The angular velocity is measured, knowing the friction of the surrounding medium.
  • The escape force for rotational motion is measured with optical tweezers.