Issue 7, 2019

Inertial focusing with sub-micron resolution for separation of bacteria

Abstract

In this paper, we study inertial focusing in curved channels and demonstrate the alignment of particles with diameters between 0.5 and 2.0 μm, a range of biological relevance since it comprises a multitude of bacteria and organelles of eukaryotic cells. The devices offer very sensitive control over the equilibrium positions and allow two modes of operation. In the first, particles having a large variation in size are focused and concentrated together. In the second, the distribution spreads in a range of sizes achieving separation with sub-micron resolution. These systems were validated with three bacteria species (Escherichia coli, Salmonella typhimurium and Klebsiella pneumoniae) showing good alignment while maintaining the viability in all cases. The experiments also revealed that the particles follow a helicoidal trajectory to reach the equilibrium positions, similar to the fluid streamlines simulated in COMSOL, implying that these positions occupy different heights in the cross section. When the equilibrium positions move to the inner wall as the flow rate increases, they are at a similar distance from the centre than in straight channels (∼0.6R), but when the equilibrium positions move to the outer wall as the flow rate increases, they are closer to the centre and the particles pass close to the inner wall to elevate their position before reaching them. These observations were used along with COMSOL simulations to explain the mechanism behind the local force balance and the migration of particles, which we believe contributes to further understanding of the phenomenon. Hopefully, this will make designing more intuitive and reduce the high pressure demands, enabling manipulation of particles much smaller than a micrometer.

Graphical abstract: Inertial focusing with sub-micron resolution for separation of bacteria

Supplementary files

Article information

Article type
Paper
Submitted
24 1 2019
Accepted
15 2 2019
First published
19 2 2019
This article is Open Access
Creative Commons BY-NC license

Lab Chip, 2019,19, 1257-1266

Inertial focusing with sub-micron resolution for separation of bacteria

J. Cruz, T. Graells, M. Walldén and K. Hjort, Lab Chip, 2019, 19, 1257 DOI: 10.1039/C9LC00080A

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