An optical tweezers study of nanosecond duration DNA conformations through DNA-surface binding distance measurements

Optical tweezers have been widely used to study DNA properties including time dependent changes in conformation; however, such studies have emphasized direct fluorescent observation of the conformations of dyed DNA molecules. In this work we explore DNA conformations that allow undyed DNA to link to spatially separated surfaces. In one set of experiments, we used optical tweezers to hold a polystyrene bead at a fixed distance from the sample capillary wall and measured the probability of the binding as a function of the separation between the polystyrene bead and the capillary, where the beads were fully confined in liquid. In a separate magnetic crystal experiment, we used magnetic forces to control the separation between magnetic beads in a hexagonal lattice at an air-water interface and measured the probability of linking to beads in the crystal. In both types of experiments peak binding occurs at a surface separation several times longer than the radius of gyration of the DNA. These experiments provide fundamental information on elusive, but significant DNA conformations, as well as technologically useful information on the probability of the DNA binding that will link two surfaces.