Surface tensiometry of phase separated protein and polymer droplets by the sessile drop method

TL;DR

This paper adapts the sessile drop method to measure surface tension of phase-separated protein and polymer droplets using minimal sample volumes, enabling physical characterization of scarce biological samples.

Contribution

It demonstrates the feasibility of scaling down the classic sessile drop method for small biological samples and links droplet shape analysis with sedimentation velocity measurements.

Findings

Effective measurement of surface tension with small sample volumes.

Use of sedimentation velocity to determine density differences.

Provision of MATLAB tool for shape analysis.

Abstract

Phase separated macromolecules play essential roles in many biological and synthetic systems. Physical characterization of these systems can be challenging because of limited sample volumes, particularly for phase-separated proteins. Here, we demonstrate that a classic method for measuring the surface tension of liquid droplets, based on the analysis of the shape of a sessile droplet, can be effectively scaled down for this application. The connection between droplet shape and surface tension relies on the density difference between the droplet and its surroundings. This can be determined with small sample volumes in the same setup by measuring the droplet sedimentation velocity. An interactive MATLAB script for extracting the capillary length from a droplet image is included in the ESI.