Quantification of Particle Separation in Electrokinetically Driven

Flow through a Bifurcating MicrochannelElaine Mau, Jeffrey Zahn, Rutgers University

IntroductionTo separate various particles or cells within a

sample for diagnostic assay, a bifurcating

microchannel utilizes varying flow ratios within the

daughter channels to direct particles into a certain

channel (Figure 1).

Figure 1: Bifurcation Law using Pressure Driven Flows a) Greater pressure difference

and higher shear force causes particle to move towards higher flow branch b) Position

of centroid with respect to the critical stream line determines where the particle

flows.

The purpose of this work is to study the

properties of using electrokinetic flows to create

the different flow ratios.

Objectives� To design a means of generating electrokinetic

flow in a reproducible way

� To demonstrate the effect of voltage/flow ratio

on particle recovery counts

� To analyze the differences, if any, between

electrokinetic and pressure driven flows.

� To determine the how to apply electrokinetic

flow for particle separation using data recorded

MethodsFabrication of Device

� Standard Soft Lithography Techniques

� PDMS/Glass

� Beads used:

� 15 µm Polystyrene Divinylbenzene

(PS-DVB), green fluorescence

� 1 µm, PS-DVB, green fluorescence

� 1 µm, Melamine, red fluorescence

Well techniques

� Poked holes using needle end

� Needle as well, convenient

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Method 1: Needle

� Drilled and poked holes

� Used various ports and fittings

� Epoxy

� PDMS

Method 2: Ports and Fittings

Figure 2: Early methods for creating wells (a) Needle (b) Ports and Fitting.

� Biopsy punch for wells in PDMS

� Oxygen Plasma Treated

� Polycarbonate lid with wells, easy

access for electrodes

� Aluminum base with viewing window

� Grease between lid and base, vigorous

tapping

Method 3: Housing

Figure 3: Housing (a) ProEngineering model (b) Actual Device

Polycarbonate Lid

Figure 4: To test the affect of Magnalube-G PTFE grease on lid, the lid was

placed on the table with and without grease.

Experimental Set-up

a) b)

Figure 5: To create the high and low flow rates using electrokinetic flow,

different voltages were applied at the end of each reservoir, such as the figure

above.

Figure 6: System used for experiment a) Schematic b) Actual.

a)

b)

Results� General Problems

� Settling of Beads

� Head pressure and back flow

� Some clogging issues

� No bubble trapped in channels

� Method 1: Syringe

� Bubble Formation

� Method 2: Ports and Fittings

� Inconvenient for electrodes

� Affected by bubble formation

� No reproducibility

� Method 3: Housing

� Convenient for electrodes

� Difficult reproducibility

� Lid’s hydrophobicity (Figure 8)

� Electrophoretic effect seen (Figure 9)

Figure 7: Bubble formation at tip of the needle.

Figure 9: When electrokinetic flow worked, beads traveled in the opposite direction as

expected. (a) 1 µm beads polystyrene beads traveled from negative to positive terminal.

Most 15 µm beads followed the direction of flow for small particles; a few went the other

direction (b) 1 µm melamine beads were seen to travel from negative to positive terminal

and vise versa.

a) b)

a) b)

Figure 8: Results of test for polycarbonate lid. (a) Without grease, water would spread on

the table; however, when assembled, there was some leaking and electrokinetic flow did

not occur. (b) With grease, hydrophobic effect was observed. When assembled, vigorous

tapping occasionally allowed connection between water from the lid and and that from

the well.

a) b)

Conclusions

Acknowledgments

I would like to acknowledge Dr. Zahn’s graduate

students, Larry Sasso and Alex Fok.

I would like to thank Rutgers University and Aresty

Research Center for providing funding for this

research.

� First two methods are difficult to implement and

produce results that are not reproducible

� The holder, although easier to assemble, is

difficult to get working because of the lid’s

properties.