The Synergistic Effect of UV Light and Humidity-Enabled Swift and Sensitive Fruit Ripeness Monitoring Based on Bi ₂ Se ₃ Nanosheet-Decorated ZnO Nanorods

Ethylene (C₂H₄) serves as a gaseous biomarker of fruit ripeness during the stages of growth and storage, thus necessitating swift and sensitive detection to assess the evolution of maturity and flavor for target fruits. However, C₂H₄ vapor is difficult to discern due to its nonpolar inertness and robust molecular structure at room temperature (RT). To this end, a new chemiresistive sensor based on bismuth selenide (Bi₂Se₃) decorated with zinc oxide (ZnO) nanorods was prepared in this work. Contrary to the high sensor resistance and lack of signal toward C₂H₄ under dark environments at RT, UV illumination endowed the composite film sensor with low resistance and a noticeable signal. Furthermore, the recovery speed was intriguingly reduced from 10 min to less than 2 min when water vapor was simultaneously introduced. In particular, the optimal 1.0-Bi₂Se₃/ZnO sensor delivered a response of 38.7% and a response/recovery time of 27/87 s toward 5 ppm of C₂H₄. Also, the long-term stability was remarkably improved with respect to the pure ZnO counterpart. In addition, excellent linearity across the concentration range from 1 to 20 ppm, good repeatability, and high selectivity over C₂H₄ were displayed. The effective on-site freshness detection of bananas via the as-prepared 1.0-Bi₂Se₃/ZnO sensor, by combining electrical signal and visual information demonstrated a huge application potential for fruit ripening monitoring under the synergistic effect of UV illumination and humidity at RT, well catering to the demanding requirements of low power consumption and high miniaturization in the field of future smart sensors.