Non-destructive Mid-IR Spectroscopy with Quantum Cascade Laser Can Detect Ethylene Gas Dynamics of Apple Cultivar 'Fuji' in Real Time

Many plants, including fruits and vegetables, release biogenic gases containing various volatile organic compounds such as ethylene (CH), which is a gaseous phytohormone. Non-destructive and in-situ gas sampling technology to detect trace CH released from plants in real time would be attractive for visualising the ageing, ripening, and defence reactions of plants. In this study, we developed a CH detection system with a detection limit of 0.8 ppb (3σ) using laser absorption spectroscopy. The CH detection system consists of a mid-infrared quantum cascade laser oscillated at 10.5 µm, a multi-pass gas cell, a mid-IR photodetector, and a gas sampling system. Using non-destructive and in-situ gas sampling, while maintaining the internal pressure of the multi-pass gas cell at low pressure, the change in trace CH concentration released from apples (Malus domestica Borkh.) can be observed in real time. We succeeded in observing CH concentration changes with a time resolution of 1 s, while changing the atmospheric gas and surface temperature of apples from the 'Fuji' cultivar. This technique allows the visualisation of detailed CH dynamics in plant environmental response, which may be promising for further progress in plant physiology, agriculture, and food science.