Microrobots from Toposelective Nanoparticle Attachment

TL;DR

This paper presents a versatile, scalable method for fabricating photocatalytic microrobots from common nanoparticles and microparticles, enabling asymmetric functionalization and active motion for potential applications in targeted delivery and microscale mixing.

Contribution

A novel protocol for attaching photocatalytic nanoparticles onto microparticles using a multi-functional polymer and Pickering-wax emulsification, allowing large-scale production of active microrobots.

Findings

Microrobots exhibit orientation-dependent 3D motion under UV light.

The method enables asymmetric functionalization of microparticles.

The platform connects photocatalyst libraries with active matter research.

Abstract

Microrobots hold promise for applications ranging from targeted delivery to enhanced mixing at the microscale. However, current fabrication techniques suffer from limited throughput and material selection. Here, we demonstrate a versatile route enabling the synthesis of microrobots from off-the-shelf micro- and nano-particles. Our protocol hinges on the toposelective attachment of photocatalytic nanoparticles onto microparticles, exploiting a multi-functional polymer and a Pickering-wax emulsification step, to yield large quantities of photo-responsive active Janus particles. The polymer presents both silane and nitrocatechol groups, binding silica microspheres to a range of metal oxide nanoparticles. The Pickering-wax emulsions protect part of the microspheres' surface, enabling asymmetric functionalization, as required for self-propulsion. The resulting photocatalytic microrobots display a characteristic orientation-dependent 3D active motion upon UV illumination, different to that conventionally described in the literature. By connecting the extensive library of heterogeneous nanoparticle photocatalysts with the nascent field of active matter, this versatile material platform lays the groundwork towards designer microrobots, which can swim by catalysing a broad range of chemical reactions with potential for future applications.