A simple estimation method of photosynthetic condition based on pH measurement using ISFET sensor

We have constructed a simple estimation method of the dependence to photosynthetic rate of the light intensity using semiconductor pH sensor. As the rearing environment is important for effective growth of plants, simple measurement method of the photosynthetic rate is desired. Plants in photosynthesis absorb carbon dioxide (CO₂) and release carbohydrates and oxygen. As CO₂ is readily soluble in water and decrease pH, the pH of water reflects the degree of photosynthesis of water plants. To quantify the small changes of pH, we applied an automated pH measurement system consisting of ion-sensitive field effect transistor (ISFET) sensor we developed earlier. The pH measured in a test tank (0.35 L) containing a small quantity (2 g) of water plant Egeria densa rose by 0.15 (100), 0.5 (500), 1.0 (1000), and 1.7 (2000) (Differential pH (Lux)) after 5 hours light irradiation.