Optical trapping is a technique that has facilitated much of the progress made in the study of the biophysics of molecular motors at the level of single molecules. A 3-D optical trap can be used to push single motors around, via “handles” such as micron-sized polystyrene spheres. It can also be used to measure the position of such handles with nanometre resolution. To this end we developed an optical trap with back-focal plane detection and fast programmable feedback. A helium-neon laser (632 nm) is used for position detection and a solid-state fibre laser (1064 nm, 3W CW) forms the trap. Acousto-optic deflectors (AODs) controlled by a digital signal processing board are used to achieve programmable feedback loops with flexible control options and speeds up to 8 kHz.
The system is designed for studies of two rotary molecular motors: the bacterial flagellar motor and the F1Fo-ATPase. The flagellar motor of bacteria is ~50nm in diameter. It is located in the cell membrane and enables the cell to swim by coupling ion-flow across the membrane through the MotA and MotB stator proteins to rotation of the FliF, FliG, FliM and FliN rotor proteins. The motor can rotate in both clockwise and counter-clockwise directions. Recently sub-steps in rotation have been observed. Rotation of the motor drives a helical filament via a universally-jointed hook, providing a propulsive force for bacterial cells to swim. The bacterial flagellar motor is extremely efficient and powerful, and can drive the filament to rotate at speeds of up to 1700 Hz.

*Kolokvij Hrvatskog biofizičkog društva