Ultra-flexible PINE arrays for month-long, continuous intracellular ion flux monitoring in plants with nanomolar accuracy

High-precision in vivo monitoring of ion fluxes is essential yet challenging for the study of plant electrophysiology, including growth regulation, signal transduction and stress responses. Existing methods for probing ion dynamics are limited by low sensitivity, high invasiveness that interferes physiological processes, and the inability to accurately resolve intracellular ion homeostasis with sufficient spatial and temporal resolution. Here, we introduce plant intracellular nanoelectrode (PINE) arrays manufactured on 1-m-thick polymer substrates, which enable ultrasensitive and selective measurement of ionic current via scalable nanofabrication techniques. The fabricated PINE arrays possess dimensions smaller than those of typical plant cells and possess reduced mechanical stiffness, facilitating minimally invasive integration with living plant cells. This subcellular-scale plant-electronic interface allows for reliable, selective intracellular detection of K+ flux with a detection limit as low as [~]10-8 M. We demonstrate continuous, stable monitoring in tomato stem cells over six weeks, accurately capturing dynamic potassium fluctuations throughout all key growth stages. The proposed approach supports long-term, real-time tracking of ion-specific intracellular dynamics without disrupting plant cellular structures or altering endogenous ion concentrations. By providing unprecedented access to intracellular ion homeostasis and signaling networks, PINE represents a powerful platform for advancing precision agriculture and enabling future digital plant engineering.