Experimental test of Sinai's model in DNA unzipping

TL;DR

This study experimentally tests Sinai's model using DNA unzipping, measuring force correlations and scaling behaviors to validate theoretical predictions of disordered elastic systems.

Contribution

It provides the first single-molecule experimental validation of the functional RG predictions for disordered elastic systems in equilibrium.

Findings

Force-force correlator matches theoretical predictions

Roughness exponent measured as 1.34±0.06, consistent with 4/3

Universal scaling properties observed during unzipping

Abstract

The experimental measurement of correlation functions and critical exponents in disordered systems is key to testing renormalization group (RG) predictions. We mechanically unzip single DNA hairpins with optical tweezers, an experimental realization of the diffusive motion of a particle in a one-dimensional random force field, known as the Sinai model. We measure the unzipping forces $F_w$ as a function of the trap position $w$ in equilibrium and calculate the force-force correlator $\Delta_m(w)$, its amplitude, and correlation length, finding agreement with theoretical predictions. We study the universal scaling properties since the effective trap stiffness $m^2$ decreases upon unzipping. Fluctuations of the position of the base pair at the unzipping junction $u$ scales as $u \sim m^{-\zeta}$, with a roughness exponent $ \zeta=1.34\pm0.06$, in agreement with the analytical prediction $\zeta = \frac{4}{3}$. Our study provides a single-molecule test of the functional RG approach for disordered elastic systems in equilibrium.