Miniaturized Ionic Polarization Diodes for Neurotransmitter Release at Synaptic Speeds

Current neural interfaces rely on electrical stimulation pulses to affect neural tissue. The development of a chemical delivery technology, which can stimulate neural tissue with the body's own set of signaling molecules, would provide a new level of sophistication in neural interfaces. Such technology should ideally provide highly local chemical delivery points that operate at synaptic speed, something that is yet to be accomplished. Here, the development of a miniaturized ionic polarization diode that exhibits many of the desirable properties for a chemical neural interface technology is reported. The ionic diode shows proper diode rectification and the current switches from off to on in 50 mu s at physiologically relevant electrolyte concentrations. A device model is developed to explain the characteristics of the ionic diode in more detail. In combination with experimental data, the model predicts that the ionic polarization diode has a delivery delay of 5 ms to reach physiologically relevant neurotransmitter concentrations at subcellular spatial resolution. The model further predicts that delays of <1 ms can be reached by further miniaturization of the diode geometry. Altogether, the results show that ionic polarization diodes are a promising building block for the next generation of chemical neural interfaces.