Development of a Wearable Sensor-PAM for Continuous Monitoring of Photosynthetic Dynamics

Continuous monitoring of photosynthetic performance is essential for understanding plant responses to fluctuating environments and has important applications in plant physiology, field phenotyping, and digital agriculture. However, conventional pulse-amplitude modulation (PAM) fluorometers are primarily designed for point measurements and are not suitable for long-term monitoring while attached to intact leaves. Here, we developed Sensor-PAM, a wearable chlorophyll fluorescence measurement system capable of continuously monitoring photosynthetic dynamics from the abaxial side of a leaf. The system combines a commercially available color sensor with blue LEDs in a compact, low-cost optical design to perform PAM measurements. Chlorophyll fluorescence measured from the abaxial leaf surface showed a strong correlation with conventional adaxial measurements and accurately reflected changes in photosynthetic performance induced by chilling and high-light stress. Measurements obtained using Sensor-PAM also showed good agreement with those from a commercial PAM fluorometer across diverse plant species. Furthermore, the wearable system enabled continuous monitoring of the effective quantum yield of photosystem II [Y(II)] from the same position on the same strawberry leaf for three days under both greenhouse and outdoor conditions, successfully capturing photosynthetic responses to changing irradiance and temperature in real time. These findings establish Sensor-PAM as a wearable platform for continuous chlorophyll fluorescence monitoring, extending conventional PAM fluorometry from point-based measurements to long-term monitoring of photosynthetic dynamics under natural environmental conditions.