Microfluidics: Cost Effective Approach and Comparison
M. Davis1, A. Mohammad2, A. Aprelev1, C. Brown1, F. Ferrone1
1 Department of Physics & Astronomy, Drexel University
2 Department of Chemistry, Drexel University
> Motivation
> Processing Microfluidic Devices
> Construction of a Plasma chamber
> Quality Control- Channel Uniformity
Sickle cell disease is an autosomal recessive disease that is a disorder of the blood, cause by an inherited abnormal hemoglobin. It
is currently estimated as the most common genetic disorder and
affects millions of people worlds wide. While there are improvements being made in health care, there is still no cure for sickle
cell disease. This is at least in part because of no proper metric to base a painful episodes known as a vaso-occlusive crisis.(1)
Diluted blood sample imaged inside of
a micro-channel.
> Microfluidics
Manipulation of a system is mandatory for a researcher to study
it. Since the group is interested in sickle cell disease, the scale of
interest would be that of a single blood cell exiting the capillaries
through the venules. This means that we are looking at cross section diameters most appropriately measured in µm and volumes
less than a µL.
Strength of a bond depends on many factors. The two parameters
that can be controlled directly by us are exposure time and power.
In order to determine the optimal conditions for bonding we want
a low contact angle, no visible film, and for a large area to bond immediately after contact is made. The conclusions for our system are
represented in the table below.
Component
Clean Room (Class 100 6x6’)
Spin Coater
Lithography Station
Plasma Chamber
Total
Standard Our Cost
$55,000
NA
$7,000
$300
$16,000† $100‡
$12,000
$150*
$90,000
$550
†Includes mask aligner, Xe lamp and lithography mask.
‡Only includes a UV led and lithography mask.
The operational cost of providing oxygen to both systems does not
include itself here. Often the approach is to add an oxygen tank to
the system. However, since our lab already had access to an oxygen
concentrator it is used instead.
> Basic Fabrication Theory
Time(s) Power(W) Contact Angle(deg±5o )
0
N/A
111
5
700
7
10
700
39
15
700
58
20
700
103
5
500
5
10
500
57
15
500
59
20
500
86
(*) Sometimes developed on the surface.
Film Adhesion(~%)
No
N/A
No
50
No*
60
Yes
5
Yes
0
No
60
No
40
No*
15
Yes
0
> Quality Control- Assessing the Spin Coat
Thickness is another factor which can lead to a poor template. By
shinning a spectrum of light onto the surface interference fringes
are observed and the thickness can be measured. Measuring several points across the wafer yields the construction of a topographical representation of the photoresist.
The first image shows a chip’s surface after it has peeled but before
bonding. The red arrow indicates where the area was zoomed in
for the second and third image. The second and third show varying degrees of contrast. Roughness was determined by calculating displacement from a center line. The average displacement was
2.4±1.0 µm.
> Conclusion & Future Work
We have demonstrated the ability to fabricate microfluidic devices
using non-standard techniques. Our alternative production aides
in research by alleviating the high cost of a lab as well as the down
time between idea and fabrication. While loosing some efficiency
during the production phase we have still effectively fabricate quality channels.
The next step of the lab will be characterization of red blood cells.
Transmission spectra, elastic moduli, velocity fields and blockages
can be monitored in real time as whole blood flows inside the channels. Yielding a better understanding of events that lead to occlusivity.
> References
Microfluidics is the study of fabrication and implementation of devices that use controlled flow to perform basic laboratory processes.
With the advancements of processing, more groups have studied biological systems with one of these devices.(2)
However, they are not made easily, nor cheaply, due to the requirement of a clean room stocked with precision equipment. This
makes them undesirable due to the enormous price tag associated
with these facilities. In order to have a proper lab capable of regularly producing a large commitment must be taken on by the research group. Special considerations for lab space must be accommodated as well as appropriation of funds, not only for initial costs
but also the upkeep and specialized maintenance associated with
each piece of equipment.
While there are shared facilities on campus, the convenience of a
fabrication facility near our other lab allows for optimal training of
new students, and time sharing between fabrication and other experimental activity.
Overall cleanliness is a significant factor during this period. Although great care is taken to preserve the surface, after spin coating
there are on average 12 defects per 75mm diammeter wafer from
non-uniformity and dust. While this is not ideal, only about 5% of
the wafers end up unusable from this.
(1) National Heart, Lung, and Blood Institute. Sickle cell anemia:
who is at risk? Bethesda, MD: US Department of Health and Human Services, National Institutes of Health, National Heart, Lung,
and Blood Institute; 2009.
(2) Microfluidic Devices For Cellomics: A general overview of the
field, H. Andersson, A. van den Berg, Lab-on-Chips for Cellomics
1-22, Kluwer Academic Publishers, 2004.