Controlling the size and adhesion of DNA droplets using surface-active DNA molecules

TL;DR

This study demonstrates how surface-active DNA molecules can be used to control the size and adhesion properties of biomolecular liquid droplets, with potential applications in biosensing and biomaterials.

Contribution

We show that long DNA molecules act as surfactants on DNA nanostar droplets, enabling control over droplet size and adhesion properties through surfactant concentration.

Findings

Surfactant DNA enriches at droplet interfaces, forming a sparse brush-like layer.

Increasing surfactant concentration reduces droplet size to sub-micron scale.

DNA surfactant prevents droplet adhesion to solid surfaces.

Abstract

Liquid droplets of biomolecules serve as organizers of the cellular interior and are of interest in biosensing and biomaterials applications. Here, we investigate means to tune the interfacial properties of a model biomolecular liquid consisting of multi-armed DNA 'nanostar' particles. We find that long DNA molecules that have binding affinity for the nanostars are preferentially enriched on the interface of nanostar droplets, thus acting as surfactants. Fluorescent measurements indicate that, in certain conditions, the interfacial density of the surfactant is around 20 per square micron, indicative of a sparse brush-like structure of the long, polymeric DNA. Increasing surfactant concentration leads to decreased droplet size, down to the sub-micron scale, consistent with arrest of droplet coalescence by the disjoining pressure created by the brush-like surfactant layer. Added DNA surfactant also keeps droplets from adhering to both hydrophobic and hydrophilic solid surfaces, apparently due to this same disjoining effect of the surfactant layer. We thus demonstrate control of the size and adhesive properties of droplets of a biomolecular liquid, with implications for basic biophysical understanding of such droplets, as well as for their applied use.