1. The Microfluidics Project Analytical Chemistry Divsion
Control and Modulation of Biochemical Reactions in Plastic Microfluid Devices
Laurie Locascio
The Microfluidics Project
Analytical Chemistry Divsion
NIST

2. Overview Fabrication of plastic microdevices Imprinting Laser ablation
Biochemical separations in plastic microfluidic devices
Characterization of surface chemistry
Changing the surface of plastic devices

3. Imprinting: 1000-8000 lbs ROOM TEMPERATURE OR HEATED PROCESS
Imprinting Plastic
Plastic Si
SEM of silicon template
3” Silicon Template
Raised 3-D inverse
of microfluid channel
Imprinting: lbs ROOM TEMPERATURE OR HEATED PROCESS
Imprinted Plastic
Martynova, L., Locascio, L.E. et.al. Anal. Chem. 1997, 69,

4. Biochemical Assays in Plastic Microfluid Systems
Morphine Immunoassay
Channel: High charge, fast EOF
Isoelectric Focusing of Proteins
Channel: Low charge, low EOF + -
pH4
pH10
Detector
Morphine-3-glucuronide/
morphine Mab
Morphine Mab
Device
Acrylic
25 mmchannel
1 cm arm
400 V/cm
High surface adsorption leads to sample loss and peak broadening

5. Isoelectric Focusing (IEF)
Fill channel with ampholyte solution and protein sample - +
Establish pH gradient and focus protein
pH=4
pH=10
pH 4
pH 6
Peaks 10 times broader than in capillary
Some residual charge/adsorption causing peak broadening
Channel: Low surface charge, lower EOF

6. Surface Charge Density/Distribution
Surface Interactions in Protein Separation
Surface Charge Density/Distribution
Higher charge = high EOF
Greater protein adsorption with high charge density, low buffer strength
Peak dispersion caused by uneven charge distribution - +
EOF
EOF Mobility = Flow velocity/Field Strength
Surface Roughness
High surface roughness induces protein precipitation and aggregation

7. Chemical Mapping of Plastic Surfaces
Labeling of charged groups with specific fluorescent probes
Carboxylate and amine groups identified
Carboxylate groups labeled with EDAC (ethyldimethylaminopropyl carbodiimide hydrochloride)/fluorescein
Results measured by fluorescence microscopy

8. Measuring Surface Charge in Imprinted Channels
Room Temperature Imprinting
Hot Imprinting
Brightfield
Image
Fluorescence
Image
Microchannel floor is uncharged in room T imprints
Wall charge varies with imprinting protocol

9. Surface Morphology: PMMA Channels
Hot Imprinted Channel
Laser Ablated Channel

10. Sample Dispersion in Plastic Microchannels
Note:
PDMS highly variable
Sample Width (mm)
Distance (mm)

11. Why Surface Modification?
Reduce device variability
Improve measurement reproducibility
Reduce peak broadening
Improve detection limits

12. Polyelectrolyte Multilayers
Alternating layers of positively and negatively charged polyelectrolytes held by electrostatic interaction
Plastic Substrate
PEM
Facile construction
Reproducible surface chemistry
Control of EOF mobility
Change surface charge to prevent adsorption

13. Polyelectrolytes 15 min treatment of channel with 1 M NaOH at 50-60°C
Poly(allylamine hydrochloride)
Polystyrene sulfonate
•HCl
CH2NH2
CH2CH n
SO3-Na+ n
15 min treatment of channel with 1 M NaOH at 50-60°C
20 min treatment with polycation followed by polyanion
Alternating 5 min treatments with polycation and polyanion solutions for desired number of layers
Chen, W.; McCarthy, T. J. Macromolecules 1997, 30, 78-86

14. EOF Mobility in PEM Treated PETG

15. EOF Mobility in PEM Treated Plastics

16. Surface Regeneration with PEMS
Peaks broad but reproducible
Surface regenerable with application of final layer

17. Controlling Flow with PEMS
PAH
H2O
T-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
Two sides of channel have opposite charge
Cross Sectional View +

18. - + Split Flow Imaging Fluorescent dye uncaged in microchannel
Electroosmosis moves the
dye in opposite directions
Solution Flow + -

19. Particle Distribution in Split Flow

20. Acknowledgements NIST University of Maryland Dr. Susan Barker
Dr. David Ross
Dr. Emanuel Waddell
Dr. Tim Johnson
Dr. Michael Gaitan
Dr. Michael Tarlov
Maria I. Aquino
Jay Xu
Dr. Cheng Lee

21. Conclusions
Protein separations dependent on charge distribution and density
Surface charge density can be modified by fabrication protocol
Surface charge and charge density can be altered in a reproducible manner by PEMS

22. Flow Imaging
To measure the effect of substrate material and microchannel geometry on sample dispersion
No distortion of the plug caused by the sample “injection” process
Paul, P. H. et.al.Anal. Chem. 1998, 70,

23. Flow Profile: Electroosmotic Pumping
PMMA
PDMS
Quartz tubing

24. Measuring Surface Charge in PMMA Ablated Channels
Microchannels laser ablated under nitrogen with varying ablation power
15 mJ
25 mJ
40 mJ

25. Microchannel Laser Ablation
Eximer Laser
(Kr, Fl, Neon balance)
248 nm
Focussing Optics
Process Gas
Vacuum
Channel
Programmable stage
vacuum chuck

26. Altering Ablation Conditions to Affect Surface Charge
PETG ablated in air
PETG ablated under O2
Surface charge density varies with process gas