Live-tracking of beef freshness by sub-ppb level ammonia detection using WS₂/rGO nanoflakes incorporating edge site-enriched acidic sulfur

Highly accurate, easily accessible room temperature wireless gas-sensing technology can be utilized to monitor food freshness in real time to prevent food fraud and spoiled food consumption, thus safeguarding humans from diseases. In this work, we coupled a high-sensitivity ammonia gas sensor with interface transmitter/gateway Bluetooth technology to produce a wireless communication system for live tracking beef freshness. Herein, we propose a chemiresistive gas sensor containing hydrothermally produced sulfur-rich WS₂/rGO hierarchical nanoflakes for gas sensing at RT. The as-developed nanohybrid was subjected to various physicochemical techniques, including XRD analysis, HR-SEM, FE-TEM, FTIR spectroscopy, Raman spectroscopy, and XPS. The sensitivity of the sulfur-rich WS₂/rGO nanohybrid towards NH₃ was twice as high as that of pristine sulfur-rich WS₂ with an LOD of 0.5 ppb and a response of 7.5% at RT. The NH₃-sensing mechanism was attributed to a negative charge donated by NH₃ on the positively charged sulfur-rich WS₂/rGO composite, which enabled it to interact with certain functional groups (SO₃H, -OH, and H₂O) and enhanced the resistance of the material. In addition, the composite had a 3.7-fold greater response to NH₃ than other VOCs and great stability after 25 cycles. Moreover, the practical application potential was also evaluated for beef freshness monitoring. This technology can be expanded to rapidly tune gas-sensing active materials via nanoengineering for various applications in wireless gas sensors, such as air-quality, automobile-exhaust, food-deterioration, and gas-leak monitoring.