Preparation of Ag-enhanced PANI/SnO2 ammonia sensor and its application in beef freshness detection

In this study, a high-performance ammonia (NH 3 ) gas sensor based on silver nanoparticles (AgNPs)-modified polyaniline (PANI)/tin dioxide (SnO 2 ) composite (Ag/PANI/SnO 2 ) was fabricated via a hydrothermal method. Gas-sensing performance evaluations revealed that incorporating PANI reduced both the response and recovery times of SnO 2 to NH 3 at room temperature. This phenomenon is attributed to the p-n heterojunction formed at the PANI/SnO 2 interface, which enhances charge carrier separation and mobility, thereby facilitating rapid modulation of the depletion layer width and the potential barrier height. Additionally, the integration of AgNPs significantly amplified the sensor's response to NH 3 , owing to the provision of additional oxygen free radicals (O 2 - (ads) ) that promote adsorption and reaction with NH 3 molecules. Compared to pristine SnO 2 , the Ag/PANI/SnO 2 composite exhibited a remarkable reduction in response time from 15.72 s to 1.18 s and in recovery time from 3.75 s to 1.23 s for 1000 ppm NH 3 . The response value increased by 382.07 times from 13.5 to 5158, representing a significant enhancement over pristine SnO 2 . Moreover, experiments showed that Ag/PANI/SnO 2 can be used to detect beef freshness based on monitoring the concentration of NH 3 generated from the reaction between microorganisms and amino acids on the beef surface during spoilage, thereby expanding the application scope of NH 3 sensors.