Design of nanocrystalline nickel oxide for detection of triethylamine and fish spoilage monitoring.

Fish and seafood freshness can be monitored through volatile organic compounds (VOCs) released during spoilage, especially volatile nitrogenous compounds (VNCs) such as triethylamine (TEA). Consuming spoiled seafood can lead to serious health issues such as food poisoning, gastrointestinal problems, and intoxication, emphasising the importance of accurate real-time monitoring techniques. P-type semiconducting metal oxides (SMO x ), particularly pristine binary materials, are attractive candidates for gas sensing due to their low cost and ease of synthesis. In this work, we demonstrated that the crystallite and particle sizes of nickel(ii) oxide (NiO) nanoparticles strongly affect TEA sensing performance. NiO nanoparticles annealed at 500 °C (NiO-500) showed the best sensor response (233.7 ± 9.3%) to 100 ppm TEA at 300 °C under dry air, with excellent repeatability and long-term stability. The sensor achieved experimental and theoretical detection limits of 1 ppm and 125 ppb, respectively. The NiO-500 sensor was subsequently used to monitor the spoilage of Nile tilapia under room-temperature and refrigerated storage conditions. At room temperature, VOC emissions were detected after 22 h, primarily from VNCs such as trimethylamine (TMA), indicating rapid spoilage. In contrast, refrigerated samples showed only very low VNC emissions after 6 days of storage. These findings highlight the potential of pristine SMO x -based gas sensors as simple, low-cost, and viable alternatives for monitoring the freshness of fish and seafood.