Real-time in-situ Simultaneous Monitoring of Dissolved Oxygen and Materials Movements at a Vicinity of Micrometers from an Aquatic Plant by Combining Deflection of a Probe Beam and Fluorescence Quenching.

It is desirable to be able to monitor the intake or release of the components at different organs of aquatic plants in real time and in-situ. Here, we report a novel optical detection system that allows for real-time in-situ simultaneous monitoring of the dissolved oxygen and material movements at a vicinity of micrometers from the aquatic plant surface. A blue semiconductor diode-laser was used as the light source of both the probe beam and excitation light for fluorescence. The laser light reflected by a dichroic mirror was focused to a vicinity of the plant/water interface in a culture dish by an objective lens. The distance between the focused laser beam and the plant surface was adjusted by an X-Y-Z micro-stage. Deflection of the probe beam was detected by a position sensor, and fluorescence from the vicinity was monitored by a PMT. A commercial fluorescent DO sensor, which simultaneously monitored temperature, was immersed into the culture dish at about 1 cm away from the aquatic plants. A white-light LED was used to illuminate the aquatic plants in the dish in photosynthesis process. 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 DO-quenched fluorescence and material movement-induced deflection signals are compared at different distances from the aquatic plant surface. 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.