High-resolution particle separation by inertial focusing in high aspect ratio curved microfluidics

Javier Cruz,Klas Hjort

doi:10.1038/s41598-021-93177-w

Abstract

The ability to focus, separate and concentrate specific targets in a fluid is essential for the analysis of complex samples such as biological fluids, where a myriad of different particles may be present. Inertial focusing is a very promising technology for such tasks, and specially a recently presented variant, inertial focusing in High Aspect Ratio Curved systems (HARC systems), where the systems are easily engineered and focus the targets together in a stable position over a wide range of particle sizes and flow rates. However, although convenient for laser interrogation and concentration, by focusing all particles together, HARC systems lose an essential feature of inertial focusing: the possibility of particle separation by size. Within this work, we report that HARC systems not only do have the capacity to separate particles but can do so with extremely high resolution, which we demonstrate for particles with a size difference down to 80 nm. In addition to the concept for particle separation, a model considering the main flow, the secondary flow and a simplified expression for the lift force in HARC microchannels was developed and proven accurate for the prediction of the performance of the systems. The concept was also demonstrated experimentally with three different sub-micron particles (0.79, 0.92 and 1.0 µm in diameter) in silicon-glass microchannels, where the resolution in the separation could be modulated by the radius of the channel. With the capacity to focus sub-micron particles and to separate them with high resolution, we believe that inertial focusing in HARC systems is a technology with the potential to facilitate the analysis of complex fluid samples containing bioparticles like bacteria, viruses or eukaryotic organelles.

Highlights

Introduction to High Aspect Ratio Curved (HARC) systemsA brief summary about inertial focusing in HARC systems is included in the following paragraphs to ease the understanding of the proposed mechanism for particle separation
We reported that inertial focusing in High Aspect Ratio Curved (HARC) systems overcomes this limitation by providing a single focus position, common for a large range of particle sizes and practically invariant with the flow r ate[24,25] (Fig. 1A)
We extend the use of HARC systems to enable particle separation

Summary

Introduction

Introduction to HARC systemsA brief summary about inertial focusing in HARC systems is included in the following paragraphs to ease the understanding of the proposed mechanism for particle separation. In the particular case of the HARC systems, where the microchannel geometry is defined by the channel width (W), the height (H), the aspect ratio ( AR = H/W > 1 ) and the radius of curvature (R), FL opposes the vortexes by the inner wall, and its horizontal component acts as a barrier (referred to as the Lift Barrier, BL) (Fig. 1A). Given a sufficient channel length, all particles that were initially distributed over the cross section reach this focus position (Fig. 1A). This length, expressed as the number of loops of the microchannel (NL), can be estimated by Eq (1)24: 20(AR)[2]

Methods

Results

Conclusion