Separation of suspended particles by arrays of obstacles in microfluidic devices

TL;DR

This paper investigates how arrays of obstacles in microfluidic devices can be used to separate suspended particles, such as DNA molecules, by analyzing particle transport using the Fokker-Planck equation and simulations.

Contribution

It provides a theoretical analysis of particle separation mechanisms in obstacle arrays, highlighting the role of driving forces and asymmetry for effective separation.

Findings

Separation requires a non-zero normal component of the driving force.

Vector separation depends on force differences, not diffusion coefficients.

Monte-Carlo simulations agree with Fokker-Planck solutions.

Abstract

The stochastic transport of suspended particles through a periodic pattern of obstacles in microfluidic devices is investigated by means of the Fokker-Planck equation. Asymmetric arrays of obstacles have been shown to induce the continuous separation of DNA molecules of different length. The analysis presented here of the asymptotic distribution of particles in a unit cell of these systems shows that separation is only possible in the presence of a driving force with a non-vanishing normal component at the surface of the solid obstacles. In addition, vector separation, in which different species move, in average, in different directions within the device, is driven by differences on the force acting on the various particles and not by differences in the diffusion coefficient. Monte-Carlo simulations performed for different particles and force fields agree with the numerical solutions of the Fokker-Planck equation in the periodic system.