Fig. 2: Breathing mode of voltage-gated nanopores.
a Ionic current trace under the transmembrane voltage of −1.1 V applied to a 100 nm nanopore in a 30-nm-thick SiNx membrane with MnCl2 (cis)/PBS (trans) solution arrangement. The precipitated phosphate layer sealed the pore, suppressing Iion to below 100 pA. At the same time, conductive pulses emerged stochastically, suggestive of repeated opening and closure of small pores. b Magnified view of the conductive Iion spikes, characterized by the height Ip and width td representing the size and the lifetime of the small pores, respectively. On the other hand, the time interval Δt characterizes the frequency of the pore creation. a–c denote the three stages of the pore evolution. c Scatter plots of Ip as a function of td. d Breathing mode of the voltage-gated nanopore comprising the three processes from (a–c). When the precipitate completely seals the nanopore, the ionic current becomes silent (a). During this stage, the transmembrane voltage is ineffective in causing the precipitation since it generates no ion flux. Meanwhile, the dissolution reaction at the acidic MnCl2 solution side proceeds to gradually narrow the nanoprecipitate layer. As a result, a small pore is pierced at a certain moment, causing the rapid rise in Iion (b). Simultaneously, the focused electric field starts to feed the reactant ions into the pore for the precipitation, leading to the closure of the pore (c). These three stages of chemical reactions occur autonomously to repeatedly form and close small pores, which is observed as the firing of Iion spikes. e Logarithmic Δt histogram indicating the pore piercing frequency of ~10 Hz.
