Electro-osmotic flow in nanoconfinement: Solid-state and protein nanopores

Area of Science:

• Physics
• Biophysics
• Physical Chemistry

Background:

• Electro-osmotic flow (EOF) drives fluid motion in nanopores under electric fields.
• Its precise role in single-molecule electrophoresis through nanopores remains unclear due to complex hydrodynamic and electrostatic interactions.
• Understanding EOF is crucial for controlling analyte translocation velocity.

Purpose of the Study:

• To investigate the fundamental role of electro-osmotic flow in analyte translocation through various nanopores.
• To analyze how pore geometry, surface charge, and applied electric fields influence EOF and translocation dynamics.
• To elucidate the relationship between pore characteristics and EOF behavior in single-molecule analysis.

Main Methods:

• Utilized the Poisson-Nernst-Planck and Navier-Stokes (PNP-NS) coupled equations.
• Modeled cylindrical solid-state nanopores and three protein nanopores (α-hemolysin, MspA, CsgG).
• Simulated fluid velocity profiles as a function of pore properties and electric field strength.

Main Results:

• Apparent charges of protein nanopores differ from their net charge; inner surface charge correlates with apparent charge.
• Fluid velocity exhibits non-monotonic dependence on applied voltage.
• Each protein nanopore displays unique EOF and velocity-voltage relationships, not solely determined by net charge.
• Point mutations can significantly alter EOF direction and magnitude.

Conclusions:

• EOF is a critical factor in macromolecule transport through nanopores, with complex dependencies on pore characteristics.
• Nanopore design, including charge distribution and geometry, can be tuned to control EOF and analyte translocation speed.
• This computational analysis provides insights for designing advanced nanopore systems for molecular analysis and separation.