Real-time in-situ monitoring of environmental stress in aquatic plants by dissolved oxygen-quenched fluorescence/materials movement-induced beam deflection

We report a novel optical detection system that allows for real-time in-situ monitoring of environmental stress such as heavy metal stress in aquatic plants by making use of the dissolved oxygen-quenched fluorescence and material movements-induced beam deflection. A blue semiconductor diode-laser was used as the light source of both the probe beam and excitation light for fluorescence. The laser light was focused to a vicinity of the plant/water interface in a culture dish by an objective lens. Deflection of the probe beam was detected by a position sensor, and fluorescence from the vicinity was monitored by a PMT.  A Ru-complex (Tris (2, 2'-bipyridyl) ruthenium (II) chloride) was used as a fluorescent probe, and Egeria densa Planch was used as a model aquatic plant. The results show that the optical detection system can monitor DO and the material movements at a vicinity of the aquatic plants not only much more sensitively, but also much more closely to real time than analytical methods that monitor concentration changes at a bulk solution. The method was successfully used for monitoring of heavy metal stress in aquatic plants.