Active colloidal particles in emulsion droplets: A model system for the cytoplasm

TL;DR

This study creates an artificial cell system with active and passive particles in emulsion droplets, demonstrating enhanced diffusion of active particles and exploring the potential to mimic cellular cytoplasm activity.

Contribution

The paper introduces a model system with active Janus particles in emulsion droplets to mimic cytoplasmic activity, highlighting initial steps and challenges in replicating cellular dynamics.

Findings

Active particles exhibit enhanced diffusion within droplets.

Passive tracers show minimal coupling with active particles.

Correcting for droplet motion is essential for accurate tracking.

Abstract

In living cells, molecular motors create activity that enhances the diffusion of particles throughout the cytoplasm, and not just ones attached to the motors. We demonstrate initial steps toward creating artificial cells that mimic this phenomenon. Our system consists of active, Pt-coated Janus particles and passive tracers confined to emulsion droplets. We track the motion of both the active particles and passive tracers in a hydrogen peroxide solution, which serves as the fuel to drive the motion. We first show that correcting for bulk translational and rotational motion of the droplets induced by bubble formation is necessary to accurately track the particles. After drift correction, we find that the active particles show enhanced diffusion in the interior of the droplets and are not captured by the droplet interface. At the particle and hydrogen peroxide concentrations we use, we observe little coupling between the active and passive particles. We discuss the possible reasons for lack of coupling and describe ways to improve the system to more effectively mimic cytoplasmic activity.