Eur. Phys. J. Special Topics 227, 2413–2424 (2019)
https://doi.org/10.1140/epjst/e2019-800026-y

Regular Article

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

¹ Department of Physics, Harvard University, Cambridge, MA 02138, USA
² Department of Physics, Hamilton College, Clinton, NY 13323, USA
³ Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
⁴ Faculty of Medicine, University of Oslo, 0318 Oslo, Norway
⁵ Faculty of Mathematics and Natural Sciences, University of Oslo, 0315 Oslo, Norway
⁶ Department of Chemistry and Chemical Engineering, Chalmers University of Technology, 412 96 Göteborg, Sweden

^a e-mail: vnm@seas.harvard.edu

Received: 1 March 2018
Received in final form: 14 June 2018
Published online: 28 March 2019

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.