Potentiometric Studies on Ion-Transport Selectivity in Charged Gold Nanotubes

Area of Science:

• Nanofluidics
• Electrochemistry
• Materials Science

Background:

• Nanotubes with fixed negative charges ideally reject anions, transporting only cations.
• The critical salt concentration (C_crit) for ideal cation permselectivity is crucial for nanofluidic device optimization.
• The double-layer overlap model (DLOM) predicts C_crit is independent of cation type, a prediction yet to be fully tested in gold nanotubes.

Purpose of the Study:

• Investigate the effect of different salt cations on C_crit in 10 nm diameter gold nanotubes.
• Determine if the DLOM accurately predicts C_crit across various cations for gold nanotubes.
• Understand why DLOM fails for polymeric nanopores but may hold for gold nanotubes.

Main Methods:

• Potentiometric studies were conducted on a 10 nm diameter gold nanotube membrane.
• The critical salt concentration (C_crit) was measured for different salt cations.
• Experimental results were compared against predictions from the double-layer overlap model (DLOM).

Main Results:

• C_crit was found to be the same for all salt cations studied, within experimental error.
• Experimental C_crit values for gold nanotubes matched the predictions of the DLOM.
• The chemical nature of the fixed negative charges in the membrane explains the differing applicability of DLOM between gold nanotubes and polymeric nanopores.

Conclusions:

• The DLOM accurately predicts C_crit for gold nanotubes, independent of the cation.
• Chemical differences in membrane charge composition are key to the differing performance of DLOM in gold nanotubes versus polymeric nanopores.
• This study validates the DLOM for cation permselectivity in gold nanotubes, highlighting the importance of material chemistry.