During the summer of 2010, I worked for Professor Salthouse of the UMass Biomedical Electronics Laboratory (BEL) I researched microfluidic device production and its application to on-chip CMOS imaging of cells.

Abstract for Poster Presentation at the End of the Summer

Inexpensive Integrated Lab-on-a-Chip Diagnostic Device

Lab-on- a-chip (LOC) technology allows for rapid detection of cells, proteins or nucleic acids and could provide for detection without the use of a clinical laboratory, expensive instrumentation or specialized personnel.  Although microfluidic LOC devices can integrate laboratory functions including simple detection on a chip, they are difficult to create.  To date, the manufacture of microfluidic devices requires the use of a clean room and skilled technicians. Experimentation with a variety of unique methods to lower production cost was completed to develop an effective and inexpensive LOC.  The fluidic channels can be created using a PDMS casting of a printed transparency or printed circuit board.  The detection of cells can be accomplished using a common web cam and imaging algorithms.  Prototype devices were produced that allow the visualization of cells within the channels and manipulation of video footage showed that individual cell detection is possible.  Development of a unique miniature syringe pump allows for controlled metering of cell culture material.  Further work will focus on an integrated device that can manipulate and detect targeted cells and microorganisms for use in clinical diagnostics, food production, and environmental testing.  Future development may allow for on-chip PCR-based target amplification.

A microfluidics device filled with blue dye that was made for photographs to be used in publication.

(PDMS devices are very difficult to photograph because of their translucence and reflectivity)

During the summer I worked on developing a protocol for rapidly creating inexpensive microfluidics quickly; this could lead to the use of microfluidics in High School laboratories or in inexpensive devices.  The time from idea to production is little more than 2 hours for a custom microfluidic device.

The mold for the device was created using printed circuit board etching.  Copper clad circuit boards can be purchased in discrete "weights" of copper.  Each weight corresponds to a thickness that will determine the ceiling height of the microfluidic device to be cast from it.

Toner is used as the resist for the etching procedure.  It is seen in the above pictures before treatment with toner reactive foil.

Accuracy using the PulsarProFX Toner Transfer Paper has been achieved to 0.1mm traces spaced at as little as 0.1mm apart.

Toner reactive foil is used to fill any imperceivable gaps in the toner resist layer itself.  TRF need only be used when the accuracy of the final product is critical (for use with molds vs use as a simple electrical conductor)

Viewing the traces under a stereoscope.  The width of the above traces is 0.1mm.  I have not been able to reliably etch traces this thin (my current limit is 0.15mm).

Stephen McKinley, UMass Biomedical Electronics Laboratory
Materials Needed
a. Sylgard 184 PDMS kit
b. Glass microscope slides
c. Blunt 20 gauge needles
d. Comfort Point .33x12.7 Insulin Syringes
e. Cole Parmer #30 PTFE Thin Wall tubing
f. Imaging Device
g. Syringe Pump
h. Hot Plate (90 C)
i. Glossy acrylic spray
j. 0.32” FR4 copper clad board (1/2oz = 15µm; 1oz=30µm; 2oz=60µm)
k. Laminator (supplied by PulsarProFX)
l. Toner Transfer Paper
m. Toner Printer
n. Scale

Safety

PDMS is inert and harmless, however it is very messy. Lay paper towels around the working
area and wear gloves to avoid a mess.

Creation of the Master
1. Prepare the artwork desired for the device at full scale and in reverse (mirror image)
2. Print the artwork onto the shiny whitish side of PulsarProFX Toner Transfer Paper (TTP)
using a toner-based printer
3. Clean the .032” copper clad board with steel wool and acetone (or methanol) if needed
4. Affix one edge of the TTP to the board art-side down using a piece of scotch tape along
its edge
5. Place the taped edge of the copper clad into the laminator and allow it to pass through
on highest heat
Reverse the board’s orientation and pass it through once more
6. Immediately immerse the board into a bath of warm water (70 C)
7. Lift off the TTP and allow board to dry
8. Etch the board in Ammonium Persulfate (150g per liter) for 30min – 1hour at 65 C or until all unwanted copper has been removed from the board
9. Section the board into appropriate sized pieces

10. spray coat the boards liberally with glossy acrylic spray allow to dry
11. Degas the acrylic coating by placing the board on the hot plate (70 C) for 10 minutes

Preparing the PDMS
12. Combine PDMS to hardener in a 10:1 (w/w) ratio, stir gently until mixed
13. Pour PDMS mixture over each master to achieve desired thickness
14. Degas the PDMS in a vacuum chamber (if available)
15. Place the uncured PDMS device onto the hot plate for 25 minutes (70 C)
16. Remove from hot plate and release the PDMS from its mold using a scalpel
17. Place the device on a glass slide and create input/output ports using a 20 gauge needle
Preparing the slide
18. Combine PDMS to hardener in a 5:1 (w/w) ratio, stir gently until thoroughly mixed
19. Apply 4 drops of PDMS spread across the surface of a slide
20. Sandwich the PDMS with another slide and squeeze until the PDMS is evenly distributed
21. Gently shear the two slides apart and place them on the hot plate (70 C) for 10 minutes
22. Place the device onto the slide while avoiding trapping air bubbles between the two
surfaces
23. Place the device onto the hot plate (90 C) and cure 25 minutes with about 7500Pa
of pressure applied to the top of the device (200 grams on top of a device measuring
20mmx10mm)
Imaging Cells
24. Insert the tip of an insulin needle into a length of PTFE tubing
25. Insert the other end of the tubing into the microfluidic device
26. Load the syringe with cell culture or dye
27. Apply pressure using the syringe pump
28. View cells or dye as they pass through the microfluidic device