Foliar Graphene Sensor for Monitoring Intracellular and Extracellular Leaf Hydration Dynamics

Understanding plant water status and cellular hydration is fundamental to plant physiology, drought resilience, and precision agriculture. Yet current approaches infer hydration indirectly from soil moisture, microenvironmental conditions, or bulk tissue measurements, leaving the cellular water dynamics that govern physiological function largely inaccessible. In particular, no sensing platform enables in vivo differentiation between extracellular and intracellular water status in living leaves. Here, we present a foliar graphene sensor (FGS), a transparent, ultralight, breathable, and conformal atomic sensor. Unlike invasive metal electrodes that may damage tissue and hydrogel electrodes that can dehydrate over time, this foliar sensor enables non-invasive, continuous and multi-week quantitative monitoring of extracellular and intracellular water content in living plant leaves without disturbing physiological activity. By directly measuring the bioelectrical impedance spectrum of leaf tissue and incorporating the leaf as part of the sensing circuit, the device captures intrinsic plant hydration dynamics in real time. The sensing approach is broadly applicable across plant types and operational under natural outdoor conditions. In vivo measurements reveal that plants preferentially maintain intracellular water during dehydration–rehydration cycles, providing the first direct evidence of this physiological hierarchy in intact plants.