The polarization reverse of diode-like conical nanopore under pH gradient

Abstract

In the past decade, with the improvement of nanofabrication technology, silica nanopores and nanochannels have been widely used in the fields of ion pumps, energy conversion, ion channels, metal ion detection, and biosensors. Although both potential and pH gradient can significantly change the performance of ion current rectification in nanoscale, the potential mechanism is still not fully understood. In this study, the ion current rectification, surface charge distribution and ion selectivity of silica nanopore under different background salt concentration and pH gradient were discussed by an analytical model, which takes into account the effects of electroosmotic flow, multiple ionic species, and the acid base neutralization. The results show that the polarity of nanopore rectifier can be changed by changing the acidity and alkalinity at both ends of the nanopore. For the first time, we find that the rectification polarity of silica conical nanopore exhibits different performances under high and low electric field intensity. One case in this study shows the rectification ratio curve of the nanopore will have a maximum or minimum value and the extreme point is near the zero of the ion current. With the increase of the concentration of background salt solution, the voltage at the zero point of ion current approaches the zero point, and then the maximum or minimum point moves to the left. The extreme point offset and polarity reversal phenomena may have potential application value in nanopore-based sensing devices.