Electrokinetic Janus micromotors moving on topographically flat chemical patterns

TL;DR

This paper demonstrates microscale ionic transport phenomena using electrokinetic Janus micromotors on flat charged surfaces, revealing insights into electrostatic interactions and potential applications in lab-on-chip systems.

Contribution

It introduces a novel microscale system mimicking ionic channels with Janus micromotors moving over complex charge patterns without topographical features.

Findings

Electrokinetic Janus micromotors exhibit selective guidance and flow focusing.

Long-range electrostatic interactions influence particle behavior and interface crossing.

System mimics nanoscale ionic transport processes at microscale.

Abstract

Ionic and molecular selectivity is considered unique for the nanoscale and not realizable in microfluidics. This is due to the scale-matching problem -- a difficulty to match the dimensions of ions and electrostatic potential screening lengths with the micron-sized confinements. Here, we demonstrate a microscale realization of the ionic transport processes closely resembling those specific to ionic channels or in nanofluidic junctions, including selectivity, guidance through complex geometries and flow focusing. As a model system, we explore electrokinetic spherical Janus micromotors moving over charged surfaces with a complex spatial charge distribution and without any topographical wall. We discuss peculiarities of the long-range electrostatic interaction on the behavior of the system including interface crossing and reflection of positively charged particles from negatively charged interfaces. These results are crucial for understanding the electrokinetic transport of biochemical species under confinement, have the potential to increase the precision of lab-on-chip-based assays, as well as broadening use cases and control strategies of nano-/micromachinery.