Synergistic Gas Sensing and Superhydrophobic Composites Enabled Real-Time Detection of Milk Spoilage

Real-time monitoring of milk spoilage is crucial for ensuring food safety and minimizing waste; however, it remains challenging due to the lack of sensitive and robust detection technologies operable in humid environments. While metal oxide sensors are promising for volatile sensing, their performance is often compromised by poor room-temperature activity and liquid interference. Herein, we design a superhydrophobic SnO₂/montmorillonite (MMT)@wax composite that overcomes these limitations by synergistically combining enhanced gas sensing and exceptional liquid resistance. MMT shows an intrinsic affinity to ammonia through ion-mediated adsorption within its interlayer galleries. Formation of a heterojunction between MMT and SnO₂ further amplifies the ammonia response. A wax-based superhydrophobic coating not only effectively shields the sensing material from liquid environments but also preserves high sensitivity, fast response/recovery, remarkable reversibility, and long-term stability. During accelerated spoilage testing of milk at 30 °C, the composite sensor reliably detects ammonia vapors from the fourth day onward, as validated by gas chromatography and correlated with synchronous pH changes indicative of quality deterioration. The capability of continuous monitoring throughout the spoilage process is demonstrated. This work offers a scalable and field-ready platform for real-time quality assessment of liquid foods, bridging material innovation with practical sensing applications.