Derivatization of Plastic Microfluidic Devices with

Polyelectrolyte Multilayers

Susan L. R. Barker, Michael J. Tarlov, Micheal Branham, Jay Xu,

William MacCrehan, Michael Gaitan, Laurie E. Locascio

Overview

• Fabrication of plastic microdevices

• Characterization of surface chemistry

• Derivatization with polyelectrolyte multilayers– EOF mobility– Separations and selectivity– Control of flow direction

Silicon Template Imprinting

Silicon TemplateSEM of silicon template

Raised siliconused to imprint channels

Si

Plastic

Imprinted Plastic SEM of imprinted channel

01020304050607080

0 500 1000 1500 2000 2500 3000

Pressure (psi)

Dept

h (%

of i

mag

e he

ight

)

0

2

4

6

8

10

12

14

16

18

20

0 5 10 15 20

Time (Minutes)

Dep

th (

m)

Room Temperature Imprinting

plastic

press

template

press

Al block

Al block

Xu, J.; Locascio, L. E.; Lee, C. S.

Anal. Chem. 2000, 72, 1930-1933.

Plastic Substrate

PDMS Lid

EOF Comparison

Substrate EOF MobilitySingle Material Device

EOF Mobility Hybrid Devices

Silica 5.0 x 10-4 * --

PETG 4.3 x 10-4 § 4.1 x 10-4

PC -- 3.0 x 10-4

PS 1.8 x 10-4 § 2.5 x 10-4

PDMS 1.8 x 10-4 n --

PMMA 2.5 x 10-4 § 1.4 x 10-4

*Huang, X.; Gordon, M.; Zare, R.N. Anal. Chem. 1988, 60, 1837.

§Locascio, L., Perso, C., Lee, C. J. Chrom., A 1999, 857, 275-284.

Imprinted channel treated with carboxylate-reactive dye

Brightfield Image Fluorescence Image

Chemical Mapping

• Microchannel floor is uncharged• Microchannel walls have high charge• EOF originates from wall

Polyelectrolyte Multilayers

• Facile construction

• Reproducible surface chemistry

• Control of EOF mobility

• Control of flow direction

- - - - - - - - - -

- - - - - - - - - -Plastic Substrate

PEM

Polyelectrolytes

SO3-Na+

n •HCl CH2NH2

CH2CH n

Polystyrene sulfonatePoly(allylamine hydrochloride)

• 15 min. treatment of channel with 1 M NaOH at 50-60°C• 20 min. treatment with polycation, pH 9, 0.5M NaCl• 20 min. treatment with polyanion, pH 9, 0.5M NaCl• Alternating 5 min. treatments with positive and negative

polyelectrolytes to create desired total number of layersChen, W.; McCarthy, T. J. Macromolecules 1997, 30, 78-86

XPS of PEM Treated Polystyrene

385390395400405410

Binding Energy (eV)

Re

lati

ve C

ou

nts

1 M NaOH

1 M NaOH, PAH

1 M NaOH, PAH, PSS

Native PS

155160165170Binding Energy (eV)

Rela

tive

Cou

nts

1 M NaOH

1 M NaOH, PAH

1 M NaOH, PAH, PSS

Native PS

Nitrogen 1s Sulfur 2p

EOF Mobility in PEM Treated PETG

-4.0E-04 -2.0E-04 0.0E+00 2.0E-04 4.0E-04 6.0E-04

EOF Mobility (cm2/V s)

Native Plastic

1 M NaOH

3 Layer PEM

14 Layer PEM

13 Layer PEM

4 Layer PEM

Comparison of EOF Mobility in PEM Treated PETG and PS

-6.0E-04 -3.0E-04 0.0E+00 3.0E-04 6.0E-04

EOF Mobility (cm2/V s)

PS

PETG

Native Plastic

13 Layer PEM

14 Layer PEM

225

250

275

300

325

0 200 400 600 800 1000 1200

Time (s)

PM

T V

olt

age

(m

V)

15 s injections 10 s

injections 5 s injections

0 100 200 300 400 500 600

Time (s)

Re

lati

ve

Vo

lta

ge

A. Separations after continuous channel use

B. Separations after PEM regeneration

PEM coated channels produce reproducible results

The PEM coating can be regenerated by application of the final electrolyte layer

Avidin PEMs

PEMs only

Native plastic

PEMs Incorporating Chemical SelectivityReactions with fluorescein-labeled biotin

Control of Electroosmotic Flow Direction

Solution Flow+ -

Solution Flow+ -+ + ++++++ ++ +++++ + + +

+++ ++ + + ++++ + + +++++

+

+

++

++

+

+

Flow Imaging

Advantage of this approach is that there is no distortion of the plug caused by the sample “injection” process

Used to measure the effect of substrate material and microchannel geometry on sample dispersion

Paul, P. H.; Garguilo, M. G.; Rakestraw, D. J. Anal. Chem. 1998, 70, 2459-2467

Two sides of channel have opposite charge

+++

++

+ +

+ +

Parallel, Opposite Flow

PAH

H2OT-device in single plastic material

• Whole device first coated with PAH then PSS (negative charge)

• Device then treated with H2O or PAH on opposite sides of same channel

Cross Sectional View

Solution Flow +- +++ ++++++++ ++ +++++Flow Imaging

A plug of fluorescent dye is uncaged in the microchannel

Electro-osmosis moves the dye in opposite directions

Conclusions• Variations in plastic surface chemistry

occur due to differences in polymer composition and as a result of fabrication methods.

• Polyelectrolyte multilayers are effective for plastic derivatization and result in – tunable EOF mobilities– reproducible separations and assays– control of flow direction

Acknowledgements

Dr. David Ross

Maria I. Aquino

Dr. James Hickman

Heather Canavan