Abstract
Monitoring environmental conditions inside greenhouses is essential to optimize crop growth, improve water-use efficiency, and reduce resource consumption. Among these parameters, relative humidity (RH) strongly influences plant transpiration, stomatal regulation, and disease development. However, conventional sensors typically measure bulk environmental conditions and often fail to capture microclimatic variations near plant surfaces. In this work, we present a flexible paper-based impedimetric humidity sensor fabricated by dispense printing poly(3,4-ethylenedioxythiophene) polystyrene sulfonate interdigitated electrodes on a cellulose substrate. The sensor response was first characterized under controlled climate chamber conditions to evaluate its frequency-dependent impedance behavior, hysteresis under humidity cycling, and temperature cross-sensitivity, while mechanical robustness under bending deformation was also assessed. Subsequently, the device was deployed in the environment and attached to the abaxial leaf surface of tomato leaves to monitor the dynamics of local humidity. Measurements performed over four consecutive day–night cycles showed that the printed sensors reliably tracked environmental RH variations and exhibited good agreement with a commercial reference sensor. When positioned directly on the leaves, the sensors captured localized humidity dynamics influenced by plant transpiration and leaf microclimate effects. Additional humidity–temperature cross-sensitivity measurements confirmed that humidity remained the dominant parameter governing the sensor response within the investigated temperature range. These results demonstrate the potential of cost-effective, biodegradable printed sensors for in situ monitoring of plant microenvironments, providing a promising approach for scalable sensing platforms in precision agriculture and smart greenhouse management.