In-situ biological ozone detection by measuring electrochemical impedances of plant tissues

This work demonstrates biological detection of a low concentration of O3 by measuring electrochemical impedances of tissues in tobacco and tomato plants located indoor and outdoor. The lower range of generated ozone in the O3-air mix is about 30 ug/m3 over the atmospheric level, which allows phytosensors to be considered as biodetectors of environmental pollutants. The ozone stress affects stomatal regulation that in turn influences the hydrodynamics of fluid transport system in plants. Sensors utilize electrochemical impedance spectroscopy (EIS) to measure ionic fluid content at several positions on the plant stem and calculate a variation of fluid distribution in control and experimental cases indoors. Outdoor setup uses the same methodology and sensors but different analysis due to uncontrolled nature of ozone pollution and the overlap of various stressors. The measurement results indicate a qualitative and quantitative reaction of hydrodynamic system to changes in O3 concentration in the upper part of stem with a delay of 10-20 minutes between the onset of exposure and biological response. The probability of false-negative responses from a single plant is about 0.15 +/-0.06. Pooling data from at least three plants allows for 92% confidence in detecting excess O3. Measurements on days with low and high ozone levels of 80 ug/m3 to 130 ug/m3 result in a 2.33-fold difference in sensor values and thus demonstrate biological detection of high O3 also outdoors. Statistically significant data include 948 sensor-plant attempts during 51 days with 9 plants and about 10E7 samples collected in automated experiments. Long-term measurements have demonstrated the high reliability of electrochemical sensors, especially in harsh outdoor conditions with rain, heat and UV/IR radiations. The described approach has applications in environmental monitoring, biological pollution detection and biosensing.