Fig. 3.

Dynamic switching of handedness and direction of propulsion. a, b Microscope images showing reversals of handedness and direction of helical trajectories when cycling the electric field on and off for particles of radius 1.2 µm and φ = 5°. The applied field strength is 250 V cm⁻¹ at 10 kHz, and field-off interval is 5 s for a and 10 s for b. The scale bars in a and b are 5 µm. c Experimentally determined probability for reversing the handedness of helical trajectories as a function of the field-off interval duration, Δt. Along the dashed line, the particle is equally likely to adopt helical motions of either handedness. The numbers in the plot represent the particle radius (in µm) used in determining the probabilities P(Δt) of corresponding color. d Increase in characteristic field-off interval for equiprobability of inverting helix chirality with increasing particle radius. Here, the points represent experimentally determined data and the solid line corresponds to the theoretically calculated diffusion time. The y-error bars in d refer to the standard deviation of probability values for multiple experiments and x-error bars refer to the polydispersity of the particle size