Dynamic translocation of ligand-complexed DNA through solid-state nanopores with optical tweezers.

We investigated the threading and controlled translocation of individual lambda-DNA (λ-DNA) molecules through solid-state nanopores with piconewton force sensitivity, millisecond time resolution and picoampere ionic current sensitivity with a set-up combining quantitative 3D optical tweezers (OT) with electrophysiology. With our virtually interference-free OT set-up the binding of RecA and single peroxiredoxin protein molecules to λ-DNA was quantitatively investigated during dynamic translocation experiments where effective forces and respective ionic currents of the threaded DNA molecule through the nanopore were measured during inward and outward sliding. Membrane voltage-dependent experiments of reversible single protein/DNA translocation scans yield hysteresis-free, asymmetric single-molecule fingerprints in the measured force and conductance signals that can be attributed to the interplay of optical trap and electrostatic nanopore potentials. These experiments allow an exact localization of the bound protein along the DNA strand and open fascinating applications for label-free detection of DNA-binding ligands, where structural and positional binding phenomena can be investigated at a single-molecule level.