Free Energy of a Polymer in Slit-like Confinement from the Odijk Regime to the Bulk

We directly measure the free energy of confinement for semiflexible polymers from the nanoscale to bulk regimes in slit-like confinement. We use convex lens-induced confinement (CLiC) microscopy of DNA to directly count molecules at equilibrium in a single chamber of smoothly increasing height. Our data, acquired across a continuum of confinement regimes, provide a bridge with which to connect scaling theories established for qualitatively different regimes. We present new experimental data and simulations that connect the Odijk theory describing sub-persistence-length confinement, the interpolation model by Chen and Sullivan extending Odijk to moderate confinement, and the Casassa theory describing the transition from moderate confinement to bulk. Further, this work establishes a robust, quantitative platform for understanding and manipulating biopolymers at the nanoscale, with key applications and insights toward emerging genomic analysis tools.