Intrinsic Stepwise Translocation of Stretched ssDNA in Graphene Nanopores

We investigate by means of molecular dynamics simulations stretch-induced stepwise translocation of single-stranded DNA (ssDNA) through graphene nanopores. The intrinsic stepwise DNA motion, found to be largely independent of size and shape of the graphene nanopore, is brought about through alternating conformational changes between spontaneous adhesion of DNA bases to the rim of the graphene nanopore and unbinding due to mechanical force or electric field. The adhesion reduces the DNA bases' vertical conformational fluctuations, facilitating base detection and recognition. A graphene membrane shaped as a quantum point contact permits, by means of transverse electronic conductance measurement, detection of the stepwise translocation of the DNA as predicted through quantum mechanical Green's function-based transport calculations. The measurement scheme described opens a route to enhance the signal-to-noise ratio not only by slowing down DNA translocation to provide sufficient time for base recognition but also by stabilizing single DNA bases and, thereby, reducing thermal noise.