Stretching of Tethered DNA in Nanoslits.

External forces and confinement are two fundamental and complementary approaches for biopolymer stretching. By employing micro- and nanofluidics, we study the force-extension dynamics by simultaneously applying external forces and confinement to single-DNA molecules. In particular, we apply external electric fields to stretch single DNA molecules that are attached to microspheres anchored at a nanoslit entrance. Using this method, we measure the force-extension relation of tethered DNA and describe this relation with modified wormlike chain models. This allowed experimental validations of several theoretical predictions, including the increase in the global persistence length of confined DNA with increasing degree of confinement and the "confined Pincus" regime in slit confinement.