Video-Based Force Detection In Optical Tweezers To Measure Dna Translocation Through Si-Nx And Lipid-Coated Nanopores

To quantify minute forces with sub-pN precision on single molecules translocating through nanopores we developed real-time video-based 3D force detection for an optical tweezers system.With this setup, we investigate the threading force on a single dsDNA molecule inside silicon-nitride nanopores, as well as lipid-coated solid-state nanopores.We observe a strong dependence of the threading force on the nanopore size that can be related to the magnitude of the electro osmotic flow (EOF) inside the nanopore, which opposes the electrophoretic force.We show that the EOF can be additionally reduced by coating the nanopore wall with an electrically-neutral lipid bilayer, resulting in an 85% increase in threading force.Our experimental findings can be described by a quantitative theoretical model that incorporates a hydrodynamic slip effect by introducing a finite slip length of 0.5 nm at the dsDNA surface.