Bidirectional particle transport and size selective sorting of Brownian particles in a flashing spatially periodic energy landscape

TL;DR

This paper presents an experimental and theoretical study of a magnetic landscape that enables size-dependent, bidirectional transport and sorting of paramagnetic colloids without microfluidic channels, controlled remotely by magnetic fields.

Contribution

It introduces a novel size-sensitive transport scheme using a modulated magnetic landscape, allowing simultaneous bidirectional movement and sorting of particles based on size.

Findings

Particles of different sizes move in opposite directions due to distinct energy landscapes.

The technique enables remote, adjustable control of particle speed and trajectory.

The method does not require microfluidic channels, simplifying particle sorting processes.

Abstract

We demonstrate a size sensitive experimental scheme which enables bidirectional transport and fractionation of paramagnetic colloids in a fluid medium. It is shown that two types of magnetic colloidal particles with different sizes can be simultaneously transported in opposite directions, when deposited above a stripe-patterned ferrite garnet film subjected to a square-wave magnetic modulation. Due to their different sizes, the particles are located at distinct elevations above the surface, and they experience two different energy landscapes, generated by the modulated magnetic substrate. By combining theoretical arguments and numerical simulations, we reveal such energy landscapes, which fully explain the bidirectional transport mechanism. The proposed technique does not require pre-imposed channel geometries such as in conventional microfluidics or lab-on-a-chip systems, and permits remote control over the particle motion, speed and trajectory, by using relatively low intense magnetic fields.