Figure 3.

(a) Schematic of magnetic dipolar colloidal helices in the presence of a rotating magnetic field. The opposite enantiomers (red and green) possess a magnetic dipole moment (blue arrow) that aligns and thus rotates with the applied rotating magnetic field. The helices will align such that their drag is reduced, and hence they propel in opposite directions. (b) Tracks of right- (red) and left-handed (green) particles in a magnetic field of 20 G, rotating at a frequency of 20 Hz, over a time interval of 20 s. Scale bar is 20 μm. (c) Relative intensity change with time of the scattering intensity across the width of a 5 mm cuvette filled with a suspension of right- or left-handed colloids in a rotating magnetic field of a strength of 50 G and a frequency of 40 Hz. The colloid concentrations are on the order of 10^–14 M. In the lower left corner are representative images of a cuvette containing left-handed enantiomer after 0- and 10-min field application. There is a clear decrease in intensity at the right of the cuvette as the helices swim to the left.