techniques. [5,6] This technology can serve as an efficient tool for an application such as biosensing, [7][8][9] electrophysiological recording, [10] and drug delivery. [11][12][13] Organic electronic ion pumps (OEIPs) are a primary example of organic bioelectronics combining electronic and ionic properties of organic electronics materials [14][15][16] to enable release, via electronic addressing, of ionic-biochemical signals for biological applications. OEIPs operate as an "iontronic" resistors [17][18][19] and can be used to electrophoretically deliver charged species through a cation or anion exchange membrane (AEM), resulting in high spatiotemporal delivery resolution and high dosage precision (one electron per delivered monovalent ion). [14] In recent years, these electrophoretic delivery devices have been used to trigger cell signaling in vitro, [1,20] to control epileptiform activity in brain slice models, [21][22][23] to effect sensory function in vivo, [19] to suppress pain sensation in awake animals, [17] and to modulate plant physiology. [24,25] OEIP devices based on glass capillary fibers offer several design advantages for use in freestanding or implantable geometries. OEIPs fiber capillaries, in contrast to planar OEIPs devices, provide less water uptake inside the channel providing a large ion-transport cross-section with high ionic conductivity, which allows transport of relatively large ions such as drugs and neurotransmitters. [26,27] These devices can furthermore be more easily implanted or located in proximity to targeted cells, tissues, or organs.In the present work, we demonstrate OEIPs based on glass capillary fibers that are filled with a polyelectrolyte (polycationic AEM). The AEM is characterized by a high concentration of fixed positive charges that allows for the selective transport of negative ions while blocking coions from drifting in the opposite direction. Nonfixed mobile ions with the same charge with the fixed charges of ion exchange membrane are referred to as coions while ions with opposite charge are referred to as counterions. The permselectivity, according to Donnan exclusion, holds if the ionic concentrations in the adjacent electrolytes are considerably lower than the fixed charge concentration of the AEM. [28] The potential gradient, and associated current through the OEIPs fiber capillaries, is established by applying a potential difference between electrodes (Ag/AgCl) applied in the source and target solutions. [27] The polarizable electrodes in this An organic electronic ion pump (OEIP) delivers ions and drugs from a source, through a charge selective membrane, to a target upon an electric bias. Miniaturization of this technology is crucial and will provide several advantages, ranging from better spatiotemporal control of delivery to reduced invasiveness for implanted OEIPs. To miniaturize OEIPs, new configurations have been developed based on glass capillary fibers filled with an anion exchange membrane (AEM). Fiber capillary OEIPs can be easily implanted in proximi...
