LAUSR

Ionic current measurements through solid state nanopores consistently show a power spectral density that scales as 1/f^α at low frequency f , with an exponent α ∼ 0.5 - 1.5, but strikingly, the physical origin of this behavior remains elusive. Here we perform simulations of particles reversibly adsorbing at the surface of a nanopore, and show that the fluctuations in the number of adsorbed particles exhibit low-frequency pink noise. We furthermore propose theoretical modeling for the time-dependent adsorption of particles on the nanopore surface for various geometries, which predicts a frequency spectrum in very good agreement with the simulation results. Altogether, our results highlight that the low-frequency noise takes its origin in the reversible adsorption of ions at the pore surface combined with the long-lasting excursions of the ions in the reservoirs. The scaling regime of the power spectrum extends down to a cut-off frequency which is far smaller than simple diffusion estimates. Using realistic values for the pore dimensions and the adsorption-desorption kinetics, this predicts the observation of pink-noise for frequencies down to the hertz for a typical solid-state nanopore, in good agreement with experiments.