Paper-Based Impedimetric Sensor for on-Plant Humidity and Transpiration Monitoring

To minimize electronic waste, flexible and printed electronics (i.e., sensors) on disposable or biodegradable substrates are becoming increasingly popular. In this work, we demonstrate the fabrication, by exclusive means of dispense printing, of an impedimetric relative humidity (RH) sensor with poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) based interdigitated electrodes (IDEs) directly printed on a paper cellulose-based substrate. The sensor response to humidity was evaluated first in a climatic chamber, showing a sensitivity of
$1.89^{\circ} / 30-60 {\%}$
RH and
$1.55^{\circ} / 60-90 {\%}$
RH at 500 Hz and 100 kHz, respectively. After that, the sensor response to leaf transpiration was subsequently assessed directly on the leaf of a tomato plant. Our findings show that the eco-friendly sensor can be successfully used to monitor the RH near the microclimate of the plant, as well as to follow the leaf transpiration process during the day and night shifts.