Impact of surface chemistry on the adhesion of an energetic small molecule to a conducting polymer surface

The modification of the surface chemistry of a film is a key strategy to enhance the binding of molecules of interest in various sensing and detection applications. For example, the adhesion of explosive residues to a swab is critical for the detection of trace explosives in air transportation environments, and it can be enhanced by increasing the affinity of the swab to target molecules through favored chemical interactions. Here, the surface chemistries of polypyrrole (PPy) films were systematically tuned through the electropolymerization of thin layers of N-substituted pyrrole monomers to evaluate their interactions with a model explosive compound, trinitrotoluene (TNT). The surface groups examined included carboxylic acid, methyl, and amino-phenyl groups, in order to address a wide range of chemical functionalities. The interaction between the functionalized PPy films with TNT was compared with the interactions between TNT and commercial swabbing materials in a vapor deposition process. The amount of TNT deposited from the vapor phase on each of the different films was quantified by the ultraviolet-visible (UV-vis) light absorbance of the Meisenheimer complex formed from the interaction of TNT with a basic solution. The PPy films with surface functionalities that allowed for hydrogen bonding displayed the highest deposition of TNT, while Teflon-coated commercial materials had the lowest interaction with TNT. Thus, this work provides insight into the surface groups of interest for the enhanced collection of trace explosives as well as the critical design criteria for the next generation of swabbing materials.