Solid-electrolyte-gated ZnO chemiresistors: iontronic conditioning for enhanced ethylene sensing and fruit-ripening monitoring

Abstract

Ethylene monitoring is important for post-harvest handling of climacteric fruits, but oxide chemiresistors often require elevated operating temperatures. Here, a solid-electrolyte-gated ZnO chemiresistor was developed by integrating a doctor-bladed ZnO film with a lithium-ion conducting glass–ceramic (LICGC) substrate. The ZnO layer retained the wurtzite phase, and electrochemical measurements of the ZnO/LICGC/Au stack showed bias-induced interfacial charging suitable for ionic/electrochemical conditioning. The pristine device gave reproducible responses to 20–50 ppm ethylene at 250 °C. After applying a 1.5 V bias across LICGC for 10 min, the response increased over 50–250 °C, with measurable 20 ppm ethylene sensing at 50 °C. At 50 °C, the conditioned device showed a 16% response to 20 ppm ethylene, whereas water vapor at 95% relative humidity and representative fruit-relevant volatile interferents tested at nominal 20 ppm produced only 0–1.0% response. The response to 20 ppm ethylene remained within 14.5–15.0% during a 10-day storage test. LICGC-gated ZnO transistor measurements showed gate-current hysteresis and persistent conductance modulation, supporting Li⁺-assisted interfacial modulation of the ZnO depletion layer. Together, the sensing, electrochemical and transistor results show that LICGC-enabled iontronic conditioning can extend ZnO ethylene sensing toward lower operating temperature by pre-setting the oxide interfacial/electronic baseline. © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2026.