Flow-rate-insensitive deterministic particle sorting using a combination of travelling and standing surface acoustic waves
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Manipulation of cells by acoustic forces in a continuous flow offers a means to sort on the basis of physical properties in a contactless, label-free and biocompatible manner. Many acoustic sorting systems rely on either standing waves or travelling waves alone and require specific exposure times to the acoustic field, fine-tuned by manipulating the bulk flow rate. In this work, we demonstrate a flow-rate-insensitive device for continuous particle sorting by employing a pressure field that utilises both travelling and standing acoustic wave components, whose non-uniform spatial distribution arises from the attenuation of a leaky surface acoustic wave. We show that in parts of the pressure field in which the travelling wave component dominates, particles migrate across multiple wavelengths. In doing so, they drift into areas of standing wave dominance, whereby particles are confined within their respective nodal positions. It is demonstrated that this final confinement location is dependent on the particle size and independent of the force field exposure time and thus the flow rate, permitting the continuous separation of 5.1-, 6.1- and 7.0-µm particles. Omitting the need to precisely control the bulk flow rate potentially enables sorting in systems in which flow is not driven by external pumps.
KeywordsParticle sorting Microfluidics Lab on a chip Acoustofluidics Surface acoustic wave (SAW) Standing wave Travelling waves Acoustic radiation force
We gratefully acknowledge support received from the Australian Research Council, Grant No. DP160101263. This work was performed in part at the Melbourne Centre for Nanofabrication (MCN) in the Victorian Node of the Australian National Fabrication Facility (ANFF). This research was undertaken with the assistance of resources from the National Computational Infrastructure (NCI), which is supported by the Australian Government.
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