Calibration-free, high-sensitivity CO2 sensor based on cavity ringdown spectroscopy for real-time seed respiration monitoring.

A real-time, calibration-free, and high-sensitively CO2 sensor based on cavity ringdown spectroscopy (CRDS) has been developed, incorporating a Fabry-Pérot (F-P) cavity with a finesse of 6500 and an STM32-controlled ringdown acquisition scheme. The sensor enables CO2 concentration measurements at the ppb level. Allan variance analysis indicates a minimum detectable sensitivity of 1.452 × 10-9 cm-1 at an integration time of 452 s, corresponding to the minimum detectable gas concentration of 400 ppb, which demonstrates the sensor's long-term stability. In addition, using this sensor, the effects of different soaking durations on rice seed respiration were investigated. The results indicate that the sensor can effectively monitor and differentiate the respiration intensity and rate of seeds under varying soaking times, allowing real-time observation of seed respiration status.