Particle concentration via acoustically driven microcentrifugation: microPIV flow visualization and numerical modelling studies

Abstract

Through confocal-like microparticle image velocimetry experiments, we reconstruct, for the first time, the three-dimensional flow field structure of the azimuthal fluid recirculation in a sessile drop induced by asymmetric surface acoustic wave radiation, which, in previous two-dimensional planar studies, has been shown to be a powerful mechanism for driving inertial microcentrifugation for micromixing and particle concentration. Supported through finite element simulations, these insights into the three-dimensional flow field provide valuable information on the mechanisms by which particles suspended in the flow collect in a stack at a central position on the substrate at the bottom of the drop once they are convected by the fluid to the bottom region via a helical spiral-like trajectory around the drop periphery. Once close to the substrate, the inward radial velocity then forces the particles into this central stagnation point where they are trapped by sedimentary forces, provided the convective force is insufficient to redisperse them along with the fluid up a central column and into the bulk of the drop.

Microscale acoustofluidics: Microfluidics driven via acoustics and ultrasonics

“…8. Combined with separate work in concentration (Li et al, 2007a;Shilton et al, 2008;Raghavan et al, 2010) as described in Sec. IV.C.1, a method was made possible for rapidly concentrating dust and surface contaminants to a small location, microcentrifugation, perhaps over a sensor.…”

“…Much of what might be predicted by ANSYS in these problems should therefore be carefully interpreted. However, because the software is user friendly, it is convenient as a guide to understand complex flow phenomena driven by SAW, as in Raghavan et al (2010), for example. Using a more sophisticated approach incorporating compressibility, viscous effects, and a model of the Stokesian fluid boundary layer, found that, in channels physically machined into the LN substrate using exciplex lasers, fluid could be driven to flow in a recirculating fashion along the entire length of the channel if its width was less than one wavelength within the fluid at the SAW excitation frequency.…”

“…They also demonstrated the separation of red blood cells from plasma in blood samples with starting concentrations of up to 100% whole blood. Because the flow field is especially complex, Raghavan et al (2010) used microparticle image velocimetry and a simplified finite element analysis approach (using ANSYS) to study the flow field generated by the arrangement described by Li et al (2007a), and found that the flow rotation occurs about a tilted axis, the tilt appearing because of the induced acoustic streaming in the bulk (as fast streaming) at the Rayleigh angle. Shilton et al (2008) extended the work of Li et al (2007a) by exploring other IDT configurations on 128YX LN to determine whether the concentration speed could be improved, from simple straight electrodes to focusing electrodes with either a circular or elliptical focus.…”

Rare‐Cell Enrichment by a Rapid, Label‐Free, Ultrasonic Isopycnic Technique for Medical Diagnostics

“…Asymmetric actuation of the drop on the surface of the piezoelectric substrate with the SAW (Figure 1 a) causes a circular rotational motion, inducing secondary flows (Figure 2 a) in a manner similar to Batchelor flows [12][13][14][15] (see Note 2 in the Supporting Information). Here we have used a slanted finger interdigitated electrode (SFIDT; Figure 1 a) to create a narrow path of propagation, providing the asymmetry in the propagation of the waves.…”

Enhancement of biosensing performance in a droplet-based bioreactor by in situ microstreaming

“…However, some technical solutions were proposed to yield a simplified microstreaming. Yeo et al presented a centrifugation system based on SAW that produces the rotation of the liquid in a droplet in a reproducible way by playing on the configuration of the transducers and reflectors, 12 and presented a comprehensive experimental study of the three-dimensional ͑3D͒ flow that causes particle concentration in SAW-stirred droplets, 13 revealing the presence of an azimuthal secondary flow in addition to the main vortexlike circular flow present in acoustically stirred droplets. The efficiency of SAW stirring in microdroplets to favorably cope with mass transport issues was finally shown by Galopin et al, 14 but the effect of the stirring on the analyte/biosensor interaction was not studied.…”