Phototaxis of synthetic microswimmers in optical landscapes

TL;DR

This study demonstrates that synthetic microswimmers can exhibit phototaxis by sensing light gradients through diffusiophoretic torques, enabling directed motion in complex light landscapes, with potential applications in dynamic environments.

Contribution

The paper shows that synthetic photo-activated particles can perform phototaxis via diffusiophoretic torques, extending biological phototaxis concepts to engineered microswimmers.

Findings

Particles exhibit strong orientational response to light gradients.

Phototactic behavior persists even in periodic asymmetric landscapes.

Experimental results agree with minimal numerical models.

Abstract

Many microorganisms, with phytoplankton and zooplankton as prominent examples, display phototactic behaviour, that is, the ability to perform directed motion within a light gradient. Here we experimentally demonstrate that sensing of light gradients can also be achieved in a system of synthetic photo-activated microparticles being exposed to an inhomogeneous laser field. We observe a strong orientational response of the particles because of diffusiophoretic torques, which in combination with an intensity-dependent particle motility eventually leads to phototaxis. Since the aligning torques saturate at high gradients, a strongly rectified particle motion is found even in periodic asymmetric intensity landscapes. Our results are in excellent agreement with numerical simulations of a minimal model and should similarly apply to other particle propulsion mechanisms. Because light fields can be easily adjusted in space and time, this also allows to extend our approach to dynamical environments.