Polydiacetylene/Zn2+/ZnO nanocomposites for colorimetric detection of cationic surfactants: Effects of ZnO ratios, solvents, and stimuli structures

Polydiacetylenes (PDAs) are smart materials that have been utilized as colorimetric sensors of various stimuli. Fine-tuning the sensitivity of PDAs often requires structural modification of their side chains and/or headgroups, involving complicated synthesizing and time-consuming purifying processes. This contribution presents a simple approach for controlling the sensitivity of PDA/Zn2+/ZnO nanocomposites to cationic surfactants. We have found that the detection of cationic surfactants in different concentration regions can be achieved by varying the ZnO ratios and the alkyl chain lengths of PDAs. The nanocomposites with higher ZnO ratios or longer alkyl side chains exhibit the color transition at higher concentrations of cationic surfactants. The nanocomposites can also detect the cationic surfactants in different organic solvents and buffer solutions. Moreover, the sensors can be used to differentiate the structures of cationic surfactants. The cationic surfactants with shorter alkyl chains result in the color transition at higher concentrations. The number of alkyl chains and headgroups in cationic surfactants also affects the color-transition behaviors. Our results extend the utilization of PDA materials with tunable sensitivity for sensing the cationic surfactants in various media.