Rectification of ion current in nanopipettes by external substrates.

Area of Science:

• Nanotechnology
• Electrochemistry
• Computational Physics

Background:

• Nanopipettes are crucial tools for manipulating ions at the nanoscale.
• Understanding ion transport dynamics is key to optimizing nanopipette applications.
• Electrostatic interactions play a significant role in confined ionic systems.

Purpose of the Study:

• To investigate ion distribution and current-voltage (i-V) response in nanopipettes.
• To explore the influence of probe-to-substrate distance (Dps) on ion transport.
• To elucidate the effects of substrate charge on ion current rectification (ICR) and permselectivity.

Main Methods:

• Finite-element method (FEM) simulations were employed.
• Simulations analyzed ion distribution and i-V characteristics.
• Parametric studies varied Dps, substrate charge polarity, and charge density (σ).

Main Results:

• Electrostatic interactions dominate ion transport when Dps is near the Debye length (∼10 nm).
• Substrate charge reversibly enhances or reduces ICR and permselectivity.
• A neutral substrate can surprisingly reduce and reverse ICR for a charged nanopipette.

Conclusions:

• Nanopipette current is regulated by ion enrichment/depletion within the pipette, affecting conductivity.
• Substrate charge and Dps are critical parameters for controlling nanopipette ion transport.
• Simulated results explain ICR modulation via ion depletion effects at varying potentials.