Self assembled assembled monolayers of amine- and carboxylic acid terminated thiols have been chemisorbed on gold electrodes deposited on flexible polyethylene terephthalate substrates. These devices, being flexible, low cost, and highly resistant could find application in several fields such as the design of implantable biomedical devices and disposable light-weight sensors. Four different molecules have been investigated, namely cysteamine, 12-mercaptododecanoic acid, aminothiophenol, and 3-mercaptopropionic acid, each bearing either an amino or a carboxylic terminal group and different chain lengths. These molecules have been chosen since the SAM they can form could find application as such or constitute the basis for a further modification step. The modified surfaces have been characterized by electrochemical techniques and the surface pK(a) values of the terminal groups have been estimated by impedance titration. (C) 2012 Elsevier Ltd. All rights reserved.