Noise properties of rectifying and non-rectifying nanopores

Achieving a full understanding of the noise in resistive pulse sensing experiments is central to the development of this important single molecule technique. Here, we present a comprehensive study of the noise properties of conical glass nanopores as components in an ionic circuit by studying the power spectral density of the system in salt solutions at a range of concentrations. We begin by investigating the ionic current rectification of the pores, showing that it is only observed above a critical Dukhin number in agreement with theoretical predictions. We then investigate the noise properties of the pores and demonstrate that the fluctuations in the ionic current at no applied potential difference can be well modelled over four decades of frequency as thermal fluctuations over a complex impedance. Finally, we show that-when an ionic current flows-1/fnoise dominates the power spectrum below ∼100 Hz. Fluctuations in the surface current govern the low-frequency 1/fnoise, with the asymmetric shape of the pore leading the magnitude to scale with∣I3∣, faster than predicted by Hooge's empirical relation.