Universal Casimir attraction between filaments at the cell scale

TL;DR

This paper demonstrates a universal, long-range Casimir attraction between dielectric filaments in biological environments, which could influence filament bundle cohesion in cells.

Contribution

It derives a universal Casimir free energy for parallel dielectric cylinders in salted water, relevant for biological filaments, independent of their dielectric properties.

Findings

Casimir interaction is long-ranged and not screened by salt.

The free energy is a universal function of geometry.

The attraction exceeds thermal energy at biologically relevant scales.

Abstract

The electromagnetic Casimir interaction between dielectric objects immersed in salted water includes a universal contribution that is not screened by the solvent and therefore long-ranged. Here, we study the geometry of two parallel dielectric cylinders. We derive the Casimir free energy by using the scattering method. We show that its magnitude largely exceeds the thermal energy scale for a large parameter range. This includes length scales relevant for actin filaments and microtubules in cells. We show that the Casimir free energy is a universal function of the geometry, independent of the dielectric response functions of the cylinders, at all distances of biological interest. While multiple interactions exist between filaments in cells, this universal attractive interaction should have an important role in the cohesion of bundles of parallel filaments.