Polyaniline films were deposited potentiostatically (0.9 in a the stainless steel substrate conventional three electrode cell, with as the working electrode, a saturated KCl calomel reference solution was 0.1 M aniline/aqueous 1 M H2SO4. Film thickness was varied by deposition time, in the range 200-2400 s. Fingerprint visualization was carried out potentiodynamically rate, v 0.02 V s in monomerfree (-0.2 0.9; scan aqueous 1 M H2SOv Single images were extracted from a video Supporting Information) acquired using a H. (see the video in the resolution, with a Pentax Optio M40 digital camera or, for higher Thomas, G. L Reynoldson, T. E.J Phys. D Appl. Plays. 1975, 8,724-229.