Voltage-Gating of Ions and Water in Hydrophobic Nanopores

Abstract

The behavior of water in nanopores is very different from bulk water and strongly depends on the chemical characteristics of the pore walls. If the pore walls are lined with hydrophobic groups the density of water was predicted to be significantly lower than in the bulk and if a pore is sufficiently narrow, the water can even evaporate stopping any transport through the membrane. We provided an experimental evidence for the nano-induced water evaporation and condensation by chemically modifying polymer nanopores with decylamines. Hydrophobic properties of the pore walls were confirmed by contact angle measurements of a polymer film subjected to the same modification as the nanopores. The hydrophobic pores are closed for water and ionic transport unless a sufficiently high transmembrane potential is applied. The off state of the pore corresponds to the pore filled with water vapor. The pores conduct ion current only if the water undergoes condensation. The switching between open and closed was found fully reversible over many up to 20 cycles. For the intermediate voltages the pore would fluctuate between two conducting states. We also found that hydrophobic interactions tune rectifying properties of the pores. Understanding hydrophobic properties in nano-confinement is important in the light of recent findings of the role of hydrophobic interactions in the function of voltage-gated channels. Application of hydrophobic-gating in building drug-delivery systems was investigated with multi-pore membranes.