Current fluctuations in nanopores reveal the polymer-wall adsorption potential

Modification of surface properties by polymer adsorption is a widely used technique to tune interactions in molecular experiments such as nanopore sensing. Here, we explore passive adsorption of neutral polymers to the surface of glass nanopores by studying the fluctuations in the ionic current. We find a characteristic change in the spectral density of current fluctuations upon the introduction of polyethylene glycol (PEG) to the pore, however, this noise increase depends sensitively on both salt concentration and polymer length. By systematically varying these two parameters and combining our experimental results with Monte Carlo simulations we confirm the source of the noise as transient polymer adsorption. Furthermore, we use this analysis to infer details of the adsorption potential, yielding significant insight into surface interactions within the pore. This paves the way to in-situ characterisation of functionalised nanopores, and highlights the detailed and fundamental insight that noise analysis provides into molecular adsorption phenomena.