Highly sensitive and flexible ammonia sensor based on PEDOT:PSS doped with Lewis acid for wireless food monitoring

Ammonia serves as a crucial indicator of food spoilage, but current sensors lack sufficient sensitivity, stability, selectivity, and automation for practical on-site and real-time monitoring. A highly sensitive and flexible ammonia sensor based on PEDOT:PSS doped with Lewis acid (FeCl3 solution) for wireless food monitoring is proposed in this study to solve the above limitations. The intercalation effect caused by the diffusion of Fe3+ and hydrolyzed H+ in the film coordinating with SO3− groups present in PSS chains leads to an increased distance between adjacent PEDOT-rich domains. It enhances ammonia sensitivity by providing additional ionic carriers and carrier transport paths within the PEDOT:PSS molecule. The results demonstrated a significant enhancement in the sensitivity of PEDOT:PSS sensor doped with FeCl3, exhibiting a response value of about 25 % at 25℃ for 1 ppm NH3, with an impressive detection limit of 0.23 ppm and quantification limit of 0.78 ppm (1–400 ppm). Moreover, it showcases acceptable repeatability both at 1 ppm (RSD = 4.30 %) and 100 ppm ammonia (RSD = 3.61 %), along with the notable selectivity and long-term stability. XPS, Raman analysis, and the density function theory (DFT) calculations further elucidated the sensing mechanism of the sensor towards ammonia. Additionally, a portable wireless detection device was designed, which was equipped with the Bluetooth communication and the micro-controller system to detect the decay process of fresh shrimp, realizing wirelessly real-time monitoring of food freshness through a smart phone. It's worth noting that the innovative sensing technology holds great promise for food quality monitoring.