Force spectroscopy of polymer desorption: theory and molecular dynamics simulations

Abstract

Forced detachment of a single polymer chain, strongly adsorbed on a solid substrate, is investigated by two complementary methods: a coarse-grained analytical dynamical model, based on the Onsager stochastic equation, and Molecular Dynamics (MD) simulations with a Langevin thermostat. The suggested approach makes it possible to go beyond the limitations of the conventional Bell-Evans model. We observe a series of characteristic force spikes when the pulling force is measured against the cantilever displacement during detachment at constant velocity vc (displacement control mode) and find that the average magnitude of this force increases as vc increases. The probability distributions of the pulling force and the end-monomer distance from the surface at the moment of the final detachment are investigated for different adsorption energies ε and pulling velocities vc. Our extensive MD simulations validate and support the main theoretical findings. Moreover, the simulations reveal a novel behavior: for a strong-friction and massive cantilever the force spike pattern is smeared out at large vc. As a challenging task for experimental bio-polymer sequencing in future we suggest the fabrication of a stiff, super-light, nanometer-sized AFM probe.

Anomalous critical slowdown at a first order phase transition in single polymer chains

“…where the variances σ 2 1 (Z) and σ 2 2 (Z) are evaluated at the most probable valuen according to Eqs. (6,7). From C(t) we can calculate the average relaxation time [33], τ = ∞ 0 dt C(t), giving…”

A wormlike chain model of forced desorption of a polymer adsorbed on an attractive wall

“…Recently Paturej et al [22] study the desorption of a polymer adsorbed on an attractive wall by pulling with an external force at one end of the polymer. They have used the FJC model to describe the polymer.…”

Theoretical Approaches for Understanding the Interplay Between Stress and Chemical Reactivity

“…Force-extension isotherms were obtained in the simulations and showed that regions exist in which the molecule is mechanically unstable, which leads to unfolding and results in transitions between high-F and low-F regimes. The development of these mechanically unstable regions and the transitions between force regimes were found to be related to fluctuations in F, which in turn are related to the stiffness of the harmonic potential used to apply F. Additional simulations by Vilgis and coworkers have modeled F-induced polymer chain scission using similar models [74][75][76][77].…”