Design of a Single-Layer Microchannel for Continuous Sheathless Single-Stream Particle Inertial Focusing

Abstract

High-throughput, high-precision single-stream focusing of microparticles has a potentially wide range of applications in biochemical analysis and clinical diagnosis. In this work, we develop a sheathless three-dimensional (3D) particle-focusing method in a single-layer microchannel. This novel microchannel consists of periodic high-aspect-ratio curved channels and straight channels. The proposed method takes advantage of both the curved channels, which induce Dean flow to promote particle migration, and straight channels, which suppress the remaining stirring effects of Dean flow to stabilize the achieved particle focusing. The 3D particle focusing is demonstrated experimentally, and the mechanism is analyzed theoretically. The effects of flow rate, particle size, and cycle number on the focusing performance were also investigated. The experimental results demonstrate that polystyrene particles with diameters of 5-20 μm can be focused into a 3D single file within seven channel cycles, with the focusing accuracy up to 98.5% and focusing rate up to 98.97%. The focusing throughput could reach up to ∼10 counts/min. Furthermore, its applicability to biological cells is also demonstrated by 3D focusing of HeLa and melanoma cells and bovine blood cells in the proposed microchannel. The proposed sheathless passive focusing scheme, featuring a simple channel structure, small footprint (9 mm × 1.2 mm), compact layout, and uncomplicated fabrication procedure, holds great promise as an efficient 3D focusing unit for the development of next-generation on-chip flow cytometry.

Inertial focusing with sub-micron resolution for separation of bacteria

“…It is label-free (the separation of particles is based on size and geometry), its throughput is very high compared to most other approaches and it is less prone to clogging since particles do not contact the walls of the channel. This technique has been used for manipulation of biological samples, such as label-free separation of erythrocytes and leukocytes from a blood sample, 1 acquisition of circulating tumour cells 2,3 or cell synchronization. 4 For smaller particles, like prokaryotic cells, less work has been done since the forces causing the migration are strongly related to the size of the particles.…”

New advances in microfluidic flow cytometry

“…Recently, inertial focusing has gained increasing attention in microfluidics , since its implementation does not need the sheath flows and other external forces. Inertial focusing can be implemented in a variety of structures such as the low‐aspect‐ratio straight channel interspersed with a series of constrictions (Fig. A), the low‐aspect‐ratio channel bifurcated into high‐aspect‐ratio channels with different hydrodynamic resistances (Fig.…”

“…(D) Schematic diagram of a 3D focusing structure of periodically interconnected straight channels and curved channels. (Reprinted and reproduced from , with the permission of ACS Publishing. )…”

Inertial microfluidics: Recent advances

“…Thanks to the ability of efficient and flexible cell manipulation in complex biofluids, microfluidics has been widely utilized for sample pretreatments, such as focusing [8,9], concentration [10,11], separation [12,13], and purification [14,15], of cells according to their unique biophysical properties (e.g., size, shape, deformability, density, dielectric property, and surface biomarker). These pretreatment steps are important for downstream disease diagnosis and biomedical research.…”