Studying Voltage Dependent Noise in Polymer and Solid State Nanopores

Abstract

Studying the noise properties of ion currents in nanopores can improve detection limits for nanopore sensors as well as give insight into behavior of transport at the nanoscale. We focused on the so-called 1/f noise that is observed in the low frequency regime of the ion current power spectra. We found that 1/f noise in single conically shaped nanopores in polymer films exhibits voltage-dependent noise properties, which are not observed for cylindrical pores. The current passing through the nanopore in the low conductance state shows equilibrium 1/f noise, similar to the noise observed in solid state nanopores. Equilibrium fluctuations are defined as the voltage independent power spectrum magnitude normalized by the current squared. The high conductance state causes the 1/f noise to increase exponentially with increased applied voltage, showing a non-equilibrium 1/f noise. Therefore we can switch between the equilibrium and non equilibrium behavior simply by adjusting the voltage. The current in the high conductance state is about 5 times higher then the current in the low conductance state but the noise at 1 Hz is over 100 times higher. Cylindrically shaped nanopores in polymer and solid-state films do not show current rectification and show equilibrium 1/f noise. We discuss these results and give a comparison of the nanopore noise in these various systems. We hypothesize that the non-equilibrium current fluctuations originate from structural fluctuations of flexible polymer pores. The hypothesis is tested by comparison of noise properties between polymer and silicon nitride pores studied at different electrolyte concentrations.