Targeted Flow-Free Proton Delivery to Arabidopsis Seedlings Using a Capillary-Based Organic Electronic Ion Pump (cOEIP).

The capillary-based Organic Electronic Ion Pump (cOEIP) is an emerging bioelectronic delivery tool that enables precise and electronically controlled delivery of charged biomolecules to biological targets without inducing bulk fluid flow. Traditional treatment methods often induce mechanical disturbances or secondary signaling that obscure the direct physiological effects of the delivered compounds. In contrast, the iontronic devices enable precise, flow-free ionic delivery, allowing the isolation of responses specifically attributable to the applied biomolecule. Here, we present a detailed protocol for integrating the cOEIP with live confocal imaging of Arabidopsis thaliana roots, enabling spatiotemporally resolved studies of root physiology under controlled ionic delivery. As a model application, we demonstrate the localized delivery of protons (H⁺) to the root microenvironment, providing a framework for investigating pH-dependent signaling processes. The protocol includes step-by-step instructions for device assembly, preparation, calibration, and experimental setup, accompanied by representative images illustrating the mounting and operational procedures. Importantly, this approach can be adapted for the delivery of a wide range of charged biomolecules, expanding the toolkit for dynamic in vivo studies of plant-environment interactions.