Unveiling Potassium\nand Sodium Ion Dynamics in Living\nPlants with an <i>In-Planta</i> Potentiometric Microneedle\nSensor

Potassium and sodium ions (K<sup>+</sup> and Na<sup>+</sup>) play\ncrucial roles in influencing plant growth and health status. Unfortunately,\ncurrent strategies to determine the concentrations of such ions are\ndestructive for the plants because it is necessary to collect/extract\nthe sap for further analysis and produce either scattered or delayed\nresults. Here, we introduce a new potentiometric dual microneedle\nsensor for nondestructive, real-time, and continuous monitoring of\nK<sup>+</sup> and Na<sup>+</sup> concentrations in living plants.\nThe developed sensors show a response time <5 s, close-to-Nernstian\nslope (∼55 mV dec<sup>–1</sup>), resiliency to five\ninsertions on the stem, good repeatability (max. %RSD = 0.3%) and\nreversibility (max. %RSD = 3%), appropriate continuous operation for\n24 h, and linear range of responses that cover expected plant physiological\nlevels (5–50 mM for Na<sup>+</sup> and 50–120 mM for\nK<sup>+</sup>). Moreover, the accuracy was successfully investigated\nby comparing the results provided by the microneedle sensors to those\nobtained by a standard reference method (e.g., ion chromatography).\nFinally, we demonstrate that the developed analytical device is capable\nof tracking K<sup>+</sup> and Na<sup>+</sup> transportation from the\nhydroponic solution to the stem within 5–10 min. This research\nwill contribute to establishing a new generation of analytical platforms\nfor smart agriculture offering real-time information.