Helical polyaniline (PANI) nanofibers were facilely synthesized via a direct electrochemical method without using any template in the presence of (1S)-(+)-camphor-10-sulfonic acid (D-CSA) or (1R)-(-)-camphor-10-sulfonic acid (L-CSA) as the dopant. The helical morphologies of the PANI nanofibers prepared from potentiostatic deposition were confirmed with SEM and TEM. The helical PANI nanofibers induced by D-CSA and L-CSA exhibited mirror-imaged circular dichroism spectra in the UV-vis range, indicating the stereochemical selectivity of the electrochemical polymerization. The colors and optical activities of these nanofibers can be maintained on an indium-tin oxide (ITO) coated electrode with a dedoping/redoping treatment. The optical activities of the helical PANI nanofibers reversibly varied with different oxidized forms, which were easily controlled by the different potentials applied to the nanofibers. (C) 2009 Elsevier Ltd. All rights reserved.