Nanometer scale resolution, multi-channel separation of spherical particles in a rocking ratchet with increasing barrier heights

TL;DR

This paper introduces a nanofluidic device that uses a ratchet-shaped electrostatic potential to achieve nanometer-scale separation of spherical particles, with theoretical and experimental validation of its high resolution.

Contribution

The study presents a novel nanoparticle separation device based on a nanofluidic rocking Brownian motor with increasing barrier heights, demonstrating high-resolution separation capabilities.

Findings

Separation resolution of approximately 2 nm predicted and experimentally supported.

Device effectively separates spherical gold particles of 80 nm and 100 nm diameters.

The separation mechanism is governed by the energy landscape under forward tilt of the ratchet.

Abstract

We present a nanoparticle size-separation device based on a nanofluidic rocking Brownian motor. It features a ratchet-shaped electrostatic particle potential with increasing barrier heights along the particle transport direction. The sharp drop of the particle current with barrier height is exploited to separate a particle suspension into multiple sub-populations. By solving the Fokker--Planck equation, we show that the physics of the separation mechanism is governed by the energy landscape under forward tilt of the ratchet. For a given device geometry and sorting duration, the applied force is thus the only tunable parameter to increase the separation resolution. For the experimental conditions of 3.5 V applied voltage and 20 s sorting, we predict a separation resolution of $\sim 2$ nm, supported by experimental data for separating spherical gold particles of nominal 80 and 100 nm diameters.