Ammonia and amine responsive conjugated materials for reusable colorimetric sensing

Ammonia and primary amines play indispensable roles in nature, agriculture, biology, and the chemical industry. Beyond their critical functions, they also serve as vital indicators in various applications, such as monitoring food spoilage, air pollution, and certain chronic diseases. Therefore, the development of novel materials for precise, simultaneous, and rapid detection of ammonia and amines is at the forefront of current research. In this study, we synthesized a series of π-conjugated materials containing cyclic maleic anhydride (MA) moieties, which provide reactive sites for ammonia/amine interaction, enabling colorimetric sensing. The materials were synthesized via green chemistry approaches without the use of metal catalysts or hazardous solvents. We investigated the colorimetric response of these materials toward ammonia and primary amines using optical spectroscopy and demonstrated their practical applicability by fabricating paper-based colorimetric assays. Notably, the color change induced by ammonia exposure was reversible upon treatment with acid, indicating the reusability of the sensor. This work presents a new class of sustainably synthesized materials as an alternative to conventional methods, offering a reusable sensing platform for colorimetric ammonia/amine detection.