S-vacancy-engineered SbSI nanorods for heating-free NH₃ sensing under ambient and refrigerated conditions

Monitoring spoilage-related gases is important for the quality evaluation and safety assurance of fresh food. Ammonia (NH₃), a representative volatile marker released during food deterioration, can be generated not only during ambient storage and retail display but also under refrigerated transportation and distribution. However, developing chemiresistive NH₃ sensors that operate without external heating while maintaining effective sensing performance across these conditions remains challenging. Herein, vacancy-engineered SbSI nanorods were developed as NH₃ sensing materials. The vacancy-rich SSI-TAA sensor delivered a response of 172% toward 10 ppm NH₃ at room temperature, which was approximately 4.9 times higher than that of vacancy-free SbSI. Moreover, the response increased to 368% at 5 °C, indicating effective sensing performance at low temperature. Theoretical calculations reveal that sulfur vacancies enhance NH₃ adsorption on SbSI in the room-temperature paraelectric state, with stronger NH₃ adsorption in the low-temperature ferroelectric state, supporting the experimentally observed sensing enhancement under ambient and refrigerated conditions. This work demonstrates that vacancy engineering is an effective strategy for improving NH₃ sensing in SbSI and highlights the potential of SbSI-based sensors for freshness evaluation and spoilage monitoring of fresh food.