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

Abstract

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.