Lysine-Assisted Oxygen-Vacancy Engineering of In2O3/TiO2 Nanotube Heterostructures for Room-Temperature Triethylamine Sensing

Triethylamine (TEA), a representative volatile amine generated during seafood spoilage, is an important indicator for freshness evaluation and food-safety monitoring. However, most chemiresistive TEA sensors still rely on elevated operating temperatures, which limits their practical use in on-site analysis. Here, a room-temperature TEA sensing strategy is reported based on lysine-assisted defect engineering of an In2O3/TiO2 heterostructure grown on TiO2 nanotube arrays. By introducing lysine during the growth of an indium metal-organic framework precursor, the thermal conversion behavior of the precursor is modified, facilitating the formation of oxygen-vacancy (OV)-rich In2O3 while preserving the nanotube architecture. The resulting OV-In2O3/TiO2 heterostructure combines defect-activated surface chemistry with heterointerface-induced band bending and depletion-layer modulation, thereby promoting TEA adsorption/activation and accelerating interfacial charge transfer at room temperature. The resulting sensor shows a response of 2.23 toward 10 ppm TEA, fast response/recovery times of 27/50 s, and a detection limit of 37 ppb, together with good selectivity, reproducibility, and stability. A flexible TiO2NTs/Ti-based device further enables real-time monitoring of turbot spoilage, demonstrating its potential for nondestructive seafood freshness evaluation.