We introduce 10,12-Pentacosadiynoic acid conjugated with pyridine-2-aldoxime (pralidoxime, PAM) as a positively charged amphiphilic molecule capable of forming a polymer with polydiacetylene (PDA-PAM) via 1,4-addition photopolymerization of self-assembled PAM-modified monomers. Colloidally stabilized vesicles formed by PDA-PAM and unmodified pentacosadiynoic acid via electrostatic interactions in a basic aqueous medium exhibit a colorimetric transition in the presence of malathion. The malathion detection limit, through color change observed by the naked eye, is in the mM range (liquid suspension) or at nmol/cm(2) levels (solid membrane); the response to exposure to malathion was rapid, within seconds. Density functional theory (DFT) calculations on the PDA-PAM system before and after binding with the target molecule (malathion) demonstrate that the large blue absorption shift of 0.42 eV observed in the malathion-bound configuration of the polymer is due to the dissociation of the positive charge center on the pralidoxime functional group from the negative charge center on the carboxylic terminus. (C) 2018 Elsevier Inc. All rights reserved.