Highly Selective Ammonia Detection in NiO‐Functionalized Graphene Micropatterns for Beef Quality Monitoring

Abstract Graphene has emerged as one of the most promising materials for next‐generation gas sensor platforms due to its high flexibility, transparency, and hydrophobicity. However, graphene shows inherent low selectivity in gas sensing. This has led to extensive development of noble‐metal decoration on graphene to modulate its surface chemistry for enhanced selectivity. While noble metals such as Pt, Pd, and Au have widely been employed to functionalize graphene surface, non‐noble metal decoration of graphene has remained underexplored. Here, an unprecedented room‐temperature self‐activated graphene gas sensor functionalized by NiO nanoparticles and its application to wearable devices monitoring ammonia gas in daily life are demonstrated. NiO‐functionalized graphene micropatterns show ultra‐high selectivity to ammonia with a low detection limit of 2.547 ppt. Density functional theory (DFT) calculations reveal that the strong attraction between NiO and NH₃ induced by charge depletion and the vertex region of NiO accelerate the adsorption of NH₃ molecules. Furthermore, a wearable graphene device demonstrates the capability to detect ammonia emissions from beef, triggering an alarm call when a specific threshold is exceeded. This work proposes the functionalization of graphene with transition metal oxides, extending beyond the conventional noble metal decoration, and the potential utilization of the graphene for wearable devices.