Picric acid (PA) detection at parts per trillion (ppt) levels is achieved by a conjugated polyelectrolyte (PMI) in 100% aqueous media and on a solid platform using paper strips and chitosan (CS) films. The unprecedented selectivity is accomplished via combination of ground state charge transfer and resonance energy transfer (RET) facilitated by favorable electrostatic interactions.

The fabrication of a two terminal sensor device based on a histidine substituted perylene diimide (PDI-HIS) thin film for the sensitive detection and quantification of ammonia (NH₃) vapors by monitoring the changes in its current intensity is reported at room temperature under ambient conditions. The thin film morphological variations of the drop cast PDI-HIS films before and after exposure to NH₃ vapors are characterized by FESEM and TEM confirming the diffusion/adsorption of the NH₃ vapors. The solution cast PDI-HIS thin film gas sensor device exhibited rapid, highly sensitive and selective vapor phase response towards NH₃ with a detection limit as low as 0.56 ppm which is much lower than the maximum permissible limit set for NH₃ (25 ppm) for prolonged exposure. Furthermore, control sensing experiments performed using alkyl substituted PDI (PDI-n-octyl) demonstrated that the presence of histidine groups at the imide position of PDI-HIS drastically affects the solid-state aggregation mode as well as redox potential that ultimately enhances the sensing response of the device. The key performance parameters of the device such as sensitivity, response/recovery time, selectivity, recyclability, stability and detection limit demonstrated the protocol as simple, reliable, cost-effective and most efficient in performing NH₃ detection under very realistic conditions.