High-Dimension Ionic Memory in Oscillating Ion Current Signals

Nanopores provide controlled nanoconfinement that can be utilized to induce localized chemical reactions. Here we present a nanopore exhibiting memory in the frequency of ion current oscillations induced by the dynamic formation and removal of nanoprecipitates within the pore volume. We find that the onset and characteristics of these current oscillations depend on the direction of the voltage scan, with memory effects evidenced in the frequency of switching between high and low conductance states, and the probability of the pore to be in the open state. We have also emulated conductive synaptic switching behavior by applying voltage pulses, demonstrating the prospect of these nanopores for neuromorphic computing applications. A hypothesis is presented stating that the memory effects arise from the delayed formation and clearing of nanoprecipitates due to a spatial-temporal asymmetry, as well as from long term variations in the effective surface charge. We propose a model where precipitate formation is limited by the cation arrival rate. Our delayed logistic expression successfully recreates steady state and oscillatory features in the transmembrane current. Nanopores with memory encoded in the frequency of ion current oscillations emulate how the brain stores memory and open up a possibility for high-dimensional ionic memory for iontronics.