Transcript Poster Nathan and Nilesh_v3

Polystyrene Coating of Microfluidic Devices
to Reduce Hydrophobic Absorption
Nathan A. Unterman, RET Fellows 2010, Glenbrook North High School
Nilesh Kavthekar, IMSA Fellow 2010
RET Mentor: Dr. David T. Eddington
NSF-RET Program
Motivation
Consequences
Hypothesis
PDMS
is an inexpensive
andiseasily
Polydimethylsiloxane
(PDMS)
an
inexpensive
and moldable
material used for
formed material
for biofluidic
micro-fluidic
This material
is
experiments.experiments.
Its hydrophobicity
allows
preferred
due its transparency
and gas
for the absorption
of hormones,
permeability.
Its
hydrophobicity
and
structure
pheromones, and similar substances,
allows for the absorption of enzymes,
thus inhibiting controlled use of
pheromones, and other hydrophobic testing
hydrophobic
materials.
sub-stances, thus
preventing controlled use of
Inexpensive and simple thin film
coating of PDMS is necessary to create
a barrier to prevent absorption of
hydrophobic molecules in device
channels for biological and other
applications.
The process for spin coating PDMS
microfluidic channels with polystyrene
(PS) solution can be optimized to
minimize the absorption of small
hydrophobic molecules.
Device Characteristics
Results (Continued)
these materials1.
Device Design and
Fabrication
Images at Different Stages of
Measurement
Using lithography techniques, a
Y-channel master was fabricated with
SU8 photoresist.
(Same sample in all pictures)
1 mm
1 mm
1 mm
Master on Silicon
With this master, testing devices were
made using PDMS.
Pre-filled
Dye Filled
Flushed
Results
Master with PDMS
Inlet and outlet holes were bored in the
cured PDMS. Employing
plasma treatment, the
PDMS was attached to a
glass slide.
Normalized Change in Mean Intensity %
PDMS test device
60
50
40
30
Conclusions
20
10
0
1600
2800
4000
Spin Speed (RPM)
The normalized mean intensity was
 Intensity
Intensity
calculated by
x100%.
Intensity
Post  soak
Polystyrene (PS) was chosen as the
channel coating material.
Coating (PS)
PDMS
Control
0.05% Conc
0.5% Conc
5% Conc
Mean Intensity vs. Spin Speed
Pr e  soak
Filled
This normalized the change in intensity
for each device to itself.
Side View
Different concentrations and spin rates
were chosen based on work done by
Hall et al2.
Testing Matrix for Spin Coating Polystyrene
RPM
2800
4000
Polystyrene
Concentration
0.05%
0.50%
5%
Control
60
50
40
30
20
1600 RPM
10
2800 RPM
0
0
0.05
0.5
Concentration of Polystyrene in Toluene Solution (%)
Future Work
5
Change in Intensity vs. Spin Speed
Intensities were measured as follows:
•Pre-fill
•Rhodamine B dye fill (soak for one
hour)
•De-ionized water flush (flush, one hour
soak, flush).
The intensity measurements were
normalized and plotted.
•The 0.05% and 0.5% concentrations of
PS did not minimize hydrophobic
absorption when compared to the control
devices.
•Spin rate does not significantly affect
hydrophobic absorption.
•The least penetrable concentration was
the 5% PS in toluene.
•The 5% solution created coatings that
made noticeable changes in the channel
geometry of the devices.
4000 RPM
There was no significant difference
among experimental groups of different
spin speeds with the same PS
concentration.
Normalized Change in Mean Intensity (%)
1600
Normalized Change in Mean Intensity (%)
Change in Intensity vs. PS Concentration
Top View
Potential errors included:
•The formation of bubbles in channels
that would cause variation of mean
intensity.
•Variation of coatings in devices,
including cracking and deformations in
the imaged areas possibly due to
handling.
•Non-uniform coating due to
evaporation of solvent before
completion of spin cycle.
60
50
40
30
0.05%
0.5%
5%
20
10
0
0
1000
2000
3000
4000
Spin Speed (Rotations Per Minute)
There were significant differences
among experimental groups with
different PS concentrations and the same
spin speed.
•Testing coating capabilities with
different channel geometries.
•Optimize with more precision in the
0.5% to 5% range.
•Consider other materials than PS that
will coat PDMS.
•Utilize other coating techniques such as
vapor deposition, flushing/evaporation,
atomizer spray, etc.
•Testing humidity, temperature, and
pressure variations when coating the PS.
References
1Toepke,
Michael, and David Beebe, Lab Chip, 2006, 6, pp.
1484-1486.
2Hall, David, Patrick Underhill, and John Torkelson, Polymer
Acknowledgements
NSF Grant EEC-0743068
Dr. David J. Beebe, Dr. Eric Hagedorn for answering questions in their work.
Dr. Andreas Linninger, Director of the RET-IMSA summer internship program.
Engineering and Science, Volume 38 Number 12, pp 2039-2045.
August 2010