Polyacrylic acid can be grafted onto polytetrafluoroethylene (PTFE) once the latter has been reduced locally by an electrode. Two reduction treatments are performed either by direct contact of an electrode or by scanning electrochemical microscopy (SECM) leading to disc shaped reduced zones of, respectively, similar to 1 mm and similar to 100 mum diameter. Deactivation of reduced PTFE zones by air or oxidant exposure yields unsaturations on the polymeric surface that are prone to graft copolymerization. The grafted polymer, polyacrylic acid, is a cation exchanger that can complex to a fluorescent and reducible cation such as toluidine blue. Desorption of the cation from the polymeric film is characterized using UV-visible, fluorescence spectroscopies and also SECM. The latter technique is used to study the desorption kinetics, which is interpreted by a model taking into account the slow diffusion of the cation inside the membrane. The mean thickness of the film, which is initially similar to 100 mn is about the same after one year of air exposure, which emphasizes the stability of the film with time. (C) 2004 Elsevier Ltd. All rights reserved.