Structural evolution of Cu3(HHTP)2 during acidic oxidative polymerization for enhanced PANI-based ammonia sensing

Structural evolution of Cu 3 (HHTP) 2 under polymerization is revealed. • Cu 3 (HHTP) 2 -derived species and PANI synergistically enhance NH 3 sensing. • The sensor achieves a wide NH 3 detection range of 0.5–500 ppm. • The sensor exhibits reliable sensing under high humidity and bending. • The sensor realizes real-time monitoring of seafood spoilage. Ammonia (NH 3 ) is a key volatile indicator of seafood spoilage, and developing sensitive NH 3 sensors that operate stably in complex environments is highly desirable. Conductive polymers such as polyaniline (PANI) have attracted attention for room-temperature sensing, but their limited adsorption capability and environmental stability still restrict practical applications. In this work, a flexible NH 3 sensor was developed by integrating PANI with Cu 3 (HHTP) 2 through in situ oxidative polymerization. During the acidic polymerization process, Cu 3 (HHTP) 2 undergoes structural evolution, generating Cu-containing and HHTP-derived components that remain associated with the PANI matrix. The optimized PACU20 sensor exhibits a wide detection range of 0.5–500 ppm NH 3 , a high response value of 14.5 toward 100 ppm NH 3 , and rapid response/recovery times of 37/56 s. Furthermore, the sensor maintains stable sensing performance under high humidity conditions and repeated bending cycles, indicating its robustness under practical storage and flexible operating environments. The enhanced sensing behavior might be attributed to the synergistic interaction between PANI and Cu 3 (HHTP) 2 -derived components, which regulate the local chemical environment of PANI and enhance NH 3 -induced charge variation. Practically, the sensor was applied to monitor ammonia evolution during fish and shrimp spoilage, demonstrating its potential for seafood freshness evaluation.