Current fluctuations in nanopores reveal the polymer-wall adsorption potential

TL;DR

This study shows how ionic current noise in nanopores can reveal details about polymer adsorption, with noise characteristics depending on polymer length and salt concentration, and uses simulations to understand the underlying processes.

Contribution

It introduces a novel method to analyze polymer-wall interactions in nanopores through noise spectral analysis and validates it with simulations.

Findings

Noise spectral density changes with polymer adsorption

Polymer movement on/off surface generates characteristic noise

Simulation results match experimental data

Abstract

Modification of surface properties by polymer adsorption is a widely used technique to tune interactions in molecular experiments such as nanopore sensing. Here, we investigate how the ionic current noise through solid-state nanopores reflects the adsorption of short, neutral polymers to the pore surface. The power spectral density of the noise shows a characteristic change upon adsorption of polymer, the magnitude of which is strongly dependent on both polymer length and salt concentration. In particular, for short polymers at low salt concentrations no change is observed, despite verification of comparable adsorption in these systems using quartz crystal microbalance measurements. We propose that the characteristic noise is generated by the movement of polymers on and off the surface and perform simulations to assess the feasibility of this model. Excellent agreement with experimental data is obtained using physically motivated simulation parameters, providing deep insight into the shape of the adsorption potential and underlying processes. This paves the way towards using noise spectral analysis for in situ characterisation of functionalised nanopores.