A fluorescence optics has been developed to measure the rotation dynamics of individual flagellar motor at high spatial and temporal resolution, in the hope to visualize discrete steps in the rotation. An electrophysiological device is also being developed to measure the proton or ion current of sub-picoampere. These devices are being used to assay and characterize the function of the motors from various mutants. A relatively large fluctuation in the angular speed has now become visible.

A 40 nm fluorescent bead is attached to the straight hook of the flagellar motor without the long filament. The optics with a pyramid mirror divides the photons from the bead into four, and the detector with four photomultipliers measures the light intensities at every 0.2 msec to determine the position of the bead moving along a circle with a diameter of about 30 nm. The accuracy of the bead positioning is 2 nm, which corresponds to about 2π/100 in the accuracy of the angular position. At 200 Hz rotation, the angular velocity and its change can now be measured every 2π/15, and some data show unexpectedly large and rapid fluctuations of the rotation speed.