Blunt-end driven re-entrant ordering in quasi two-dimensional dispersions of spherical DNA brushes

TL;DR

This study explores how blunt-end interactions in DNA-coated colloids influence their assembly, revealing non-monotonic behaviors driven by osmotic pressure, short-range attractions, and electrostatic repulsions, with tunable assembly via salinity and other parameters.

Contribution

It demonstrates that blunt-end stacking interactions in DNA brushes can be used to control colloidal assembly and re-entrant ordering, expanding understanding of DNA-mediated colloidal interactions.

Findings

Non-monotonic particle shrinking observed with increasing density.

Aggregation and re-entrant ordering driven by short-range attractions.

Attractions can be tuned by salinity and other parameters.

Abstract

We investigate the effects of crowding on the conformations and assembly of confined, highly charged, and thick polyelectrolyte brushes in the osmotic regime. Particle tracking experiments on increasingly dense suspensions of colloids coated with ultra-long double stranded DNA (dsDNA) fragments reveal non-monotonic particle shrinking, aggregation and re-entrant ordering. Theory and simulations show that shrinking is induced by the osmotic pressure exerted by the counterions absorbed in neighbor brushes, while aggregation and re-entrant ordering are the effect of a short-range attraction competing with the electrostatic repulsion. Blunt-end interactions between dsDNA fragments of neighboring brushes are responsible for the attraction and can be tuned by inducing free-end backfolding through the addition of monovalent salt. Our results show that base stacking is a mode parallel to hybridization to steer colloidal assembly, in which attractions can be fine-tuned through salinity and, potentially, grafting density and temperature.