Fig. 3: Salt dependence of in-pore chemistry.
a Ionic current traces with different salts in cis. MgCl2 can seal the nanopore only partially (orange), due to the relatively faster dissolution reaction than precipitation. On the other hand, AlCl3 synthesizes insoluble precipitates to seal the pore, keeping the ionic current in a silent mode (skyblue). Intermediate dynamic reaction balance is achieved with MnCl2 (red) and CaCl2 (green), exhibiting breathing mode via the chemically-driven spontaneous pore piercing. b, c Ip versus td scatter plots for MnCl2 (a) and CaCl2 (b) added to cis. Data clustered at above 5 nA in the case of CaCl2 indicates the larger pores created than those in MnCl2, manifesting the distinct in-pore chemistry with Mn2+ and Ca2+. d Ip–Vb scatter plots in the mixture of CaCl2 (1 M) and MnCl2 (1 M). e Ionic current showing three giant Iion spikes. f A close-up view of a giant spike, revealing a specific pattern in the ionic current changes. The Iion range is limited to a maximum of 12 nA to highlight fine features immediately preceding the spike. Only a portion of the giant spike is shown, whereas its actual amplitude exceeds 50 nA, as depicted in (e). This burst mode of Iion spiking comprises four stages. It begins with a silent state for ~0.2 s, followed by small spike firing for ~1.5 s. Subsequently, larger spikes are fired. Soon after, it caused a giant spike. These processes continue to fire giant spikes at a certain period. g Underlying mechanism of the burst mode. It begins with synthesis of the thick precipitate layer completely sealing the nanopore to cause the silent Iion feature (a). Meanwhile, the layer is thinned gradually via dissolution (b), initiating the small pore piercing to fire the relatively weak Iion spikes (c). As the precipitate layer is thinned further, the small pores tend to be created at higher rates, leading to coalescence into large pores (d). Eventually, the layer is partially ruptured to generate a giant spike (e). What follows is the in-pore precipitation to repair the precipitate layer (a). The series of reaction processes takes place to cause the repeated bursts of the ionic current traces with CaCl2.
