Coarse-grained simulation of polymer translocation through an artificial nanopore

The translocation of a macromolecule through a nanometer-sized pore is an interesting process with important applications in the development of biosensors for single-molecule analysis and in drug delivery and gene therapy. We have carried out a molecular dynamics simulation study of electrophoretic translocation of a generic charged polymer through an artificial nanopore as a first step to explore the feasibility of semiconductor-based nanopore devices for ultra-fast sequencing of biological macromolecules. The polymer is represented by a simple bead-spring model designed to yield an appropriate coarse-grained description of a generic linear hydrophilic polymer in solution. A detailed analysis of single translocation event is presented to assess whether the passage of individual ions through the pore can be detected by measuring variations in electrostatic potential during polymer translocation. We find that it is possible to identify single events corresponding to the passage of individual counterions and the polymer chain as a whole, through the pore. However, discrimination of individual ions on the polymer chain based on variations in electrostatic potential is problematic. Several distinct stages in the translocation process are identified, characterized by changes in polymer conformation and by variations in the magnitude and direction of the internal electric field induced by the fluctuating charge distribution. The dependence of the condensed fraction of counterions on Bjerrum length leads to significant changes in polymer conformation, which profoundly affect the dynamics of electrophoresis and translocation.