A high-performance flexible ammonia sensor with PANI/MXene nanocomposite and temperature compensation for smart fish freshness monitoring

Sea bream has gained widespread popularity for its succulent flesh and high nutritional value. However, inadequate control of packaging conditions during storage and transportation renders this high-protein fish particularly susceptible to spoilage. Therefore, this paper proposes a high-precision, flexible ammonia sensing system (FASS) with temperature decoupling for detecting fish freshness, so as to enhance food quality and safety. The FASS primarily comprises a flexible ammonia sensing unit, a temperature decoupling unit, back-end circuitry, and a power supply module. Utilizing processes such as magnetron sputtering and laser direct writing, the ammonia sensing unit and temperature decoupling unit were fabricated on a PET substrate and the PANI/MXene gas-sensitive materials were successfully prepared through PANI polymer modification. During gas-sensing response testing, the ammonia sensing unit exhibited a response/recovery time of 49/307 s for 10 ppm ammonia, with a sensitivity of 18.102 % ppm −1 within 2–10 ppm. With the combination of the temperature decoupling unit, a three-dimensional fitting surface was constructed for the gas response of the ammonia sensing unit, temperature, and ammonia concentration within the 0–30 °C range, achieving a goodness-of-fit of 0.99 and enabling precise ammonia concentration detection across a broad temperature and humidity range. Finally, the reliability of the FASS application was validated during fish meat storage. By integrating a Bi-LSTM model for temporal prediction of ammonia concentrations, an RMSE of merely 0.073 ppm was achieved.