Voltage-Gated Hydrophobic Nanopores

ABSTRACT Hydrophobicity is a fundamental property that is responsible for numerous physical and biophysical aspects of molecular interactions in water. Peculiar behavior is expected for water in the vicinity of hydrophobic structures, such as nanopores. Indeed, hydrophobic nanopores can be found in two distinct states, dry and wet, even though the latter is thermodynamically unstable. Transitions between these two states are kinetically hindered in long pores but can be much faster in shorter pores. As it is demonstrated for the first time in this paper, these transitions can be induced by applying a voltage across a membrane with a single hydrophobic nanopore. Such voltage-induced gating in single nanopores can be realized in a reversible manner through electrowetting of inner walls of the nanopores. The resulting I –V curves of such arti ficial hydrophobic nanopores mimic biological voltage-gated channels.

pH Valve Based on Hydrophobicity Switching

ABSTRACT  pH switchable valves were constructed using nanoporous membranes, the surface of which was modified by mixtures of aminopropyl trimethoxy silane and butyl trimethoxy silane. The modified membranes are dry at neutral and basic conditions because of their hydrophobicity but open to flux of aqueous solutions at slightly acidic pH because of protonation of amino groups. The resulting high contrast between the open and the closed states and a high flux in the open state because of large pore size make the approach attractive in applications where pH switching is employed, for example, in drug delivery applications.

Water Confinement in Hydrophobic Nanopores. Pressure-induced Wetting and Drying

ABSTRACT  Wetting and drying of hydrophobic pores with diameters lower than 0.2 micrometers by aqueous solutions at different hydrostatic pressures is investigated by measuring the ionic conductance variation through the nanopores. The critical pressure for water intrusion into the nanopores increases with lowering the pore diameter and the surface tension of the hydrophobic modification, in agreement with the Laplace equation. Nevertheless, restoring the pressure to the atmospheric one does not result in spontaneous pore dewetting unless bubbles are left inside the pores. Such bubbles can appear at the regions of narrowing cross section and/or varying quality of the hydrophobic modification and thus can be engineered to control water expulsion.

 

For a further, more complete list of Dr. Smirnov’s publications visit: http://web.nmsu.edu/~snsm/group/publications