Highly selective QCM sensor based on functionalized hierarchical hollow TiO2 nanospheres for detecting ppb-level 3-hydroxy-2-butanone biomarker at room temperature

Listeria monocytogenes (LM) is a dangerous foodborne pathogen for humans. One emerging and validated method of indirectly assessing LM in food is detecting 3-hydroxy-2-butanone (3H2B) gas. In this study, the synthesis of 3-(2-aminoethylamino) propyltrimethoxysilane (AAPTMS) functionalized hierarchical hollow TiO2 nanospheres was achieved via precise controlling of solvothermal reaction temperature and post-grafting route. The sensors based on as-prepared materials exhibited excellent sensitivity (480 Hz@50 ppm), low detection limit (100 ppb), and outstanding selectivity. Moreover, the evaluation of LM with high sensitivity and specificity was achieved using the sensors. Such stable three-dimensional spheres, whose distinctive hierarchical and hollow nanostructure simultaneously improved both sensitivity and response/recovery speed dramatically, were spontaneously assembled by nanosheets. Meanwhile, the moderate loadings of AAPTMS significantly improved the selectivity of sensors. Then, the gas-sensing mechanism was explored by utilizing thermodynamic investigation, Gaussian 16 software, and in situ diffuse reflectance infrared transform spectroscopy, illustrating the weak chemisorption between the -NH- group and 3H2B molecules. These portable sensors are promising for real-time assessment of LM at room temperature, which will make a magnificent contribution to food safety.