de Malsche, Wim

Eijkel, Jan

Olthuis, Wouter

Tiflidis, Christina

English

This work presents a fast and reproducible particle focusing technique by AC-actuation perpendicular to pressure-driven flow. We attribute the effect amongst others to the AC electroosmotic flow generated in the system.</p

University of Twente Research Information

Continuous Flow Particle Focusing by AC-ActuationChristina Tiflidis1,2*, Eiko Westerbeek1,2, Wouter Olthuis2, Jan Eijkel2, Wim De Malsche11Department of Chemical Engineering, Vrije Universiteit Brussel (VUB), Pleinlaan 2, 1050 Brussels, Belgium2BIOS Lab-on-a-Chip Group, MESA+ Institute for Nanotechnology, MIRA Institute for Biomedical Technology and Technical Medicine, Max Planck Center for Complex Fluid Dynamics, University of Twente Enschede 7500AE, the Netherlands*Christina.Tiflidis@vub.be• Fabrication of completely transparent microfluidic devices with ITOembedded electrodes.• Creation of AC-EOF perpendicular to pressure-driven flow.• Particle focusing was found and characterized by microscopicobservation.• Varying parameters:1) Frequency2) Amplitude3) Axial flow velocity4) Zeta potentialABSTRACTThis work presents a fast and reproducible particle focusing technique byAC-actuation perpendicular to pressure-driven flow. We attribute theeffect amongst others to the AC electroosmotic flow generated in thesystem.INTRODUCTIONEXPERIMENTALWe use a unique chip design which is completely transparent, with indiumtin oxide (ITO) electrodes forming the top and bottom of the channel forAC actuation.Figure 1: Schematic illustration of the setup.ACChip DimensionsWidth: 40 μmDepth: 20 μmLength: 12 mm   Focusing experiments with 2 types of 0.5 μm diameter PS particles0.0025% w/v suspensions in unbuffered KNO3 solution (0.1 mM, pH 6.2):• Non-modified (ζ-potential -47.5 mV)• PVA-coated (ζ-potential -22 mV)RESULTS & DISCUSSION • Focusing occurred in a time span of 0.17 s (1 V) to 1.5 s (0.25 V) without axialflow and 0.07 s (1 V) to 0.09 s (0.25 V) at max. axial flow velocity (62.5 mm/s).• The bead focusing velocity was found to scale with applied voltage as V1.5.• For the PVA-coated particles, the focusing velocity increased faster with flowvelocity than for non-modified PS particles.ACKNOWLEDGMENTSThis work has been supporting by the European Research Councilthrough the Starting ERC Grant EVODIS 2020. The author wantsto thank J.G. Bomer, H. Le The, V. Papadimitriou andJ.T. Loessberg-Zahl for their support.REFERENCES[1] Y. W. Kim et al., Lab Chip, 2009, 9, 1043-1045.[2] N. G. Green et al., Physical Review, 2002, E66, 026305[3] N. Islam et al., Microfluid Nanofluid, 2007, 3:369-375[4] M. Talebi et al., Presented Eurosensors 2017 Conference, Paris• The focusing phenomenon, focusing speed and the dependence onaxial flow velocity are surprising.• Is the particle focusing caused by AC-EOF as a stagnation point in thecenter line, is it a dielectrophoretic effect or combination of both? Thiswill be further investigated by a newly developed 3D-PIV technique.• We think this particle focusing device has great potential for versatile,generic and rapid (bio)particle focusing.CONCLUSIONSSIMULATIONSSinusoidal AC-potentials0.25 to 1 V peak-peak& 1 kHz frequency Applied by a function generator Focusing depends on:• Axial flow velocity• Particle size / ζ-potential / concentration• Frequency / potential amplitudeNo theory for focusing yet, only AC-EOF explained1) Focusing at low axial velocity 1.56 mm/sSeries of overlaid framesFigure 3: Average electro-osmotic flow over a full cycle, the color map shows the magnitude of the flow and the arrow field the direction. Figure 2: Schematic illustration of the electroosmotic-flow during half a cycle, in the second half of the cycle the direction of the field changes as well as the sign of the charge on the electrodes. Therefore the direction of the flows stays the same. Inset: SEM-Image2) Focusing at high axial velocity of 62.5 mm/sSeries of overlaid framesVisualrecordingFluorescenceintensity profilesacross channelwith & withoutAC-actuationFluorescenceintensity profileswith & withoutAC-actuationVisualrecordingView publication stats

Continuous flow particle focusing by AC-actuation

https://doi.org/10.13140/RG.2.2.22147.55848

Continuous flow particle focusing by AC-actuation

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