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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 - PowerPoint PPT Presentation
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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