Group 2 Y2 project---The mobility of bacteria in microfluidics structure: The fabrication of PDMS

We started our first project practice work on Jan 30th, 2012, Monday, this week. Thanks to the great help from Dr. Andrew Libberton, we recieved a valuable video of the microfabrication of PDMS by a research group in MIT. This provides us a basis on how to make the PDMS, which is the fundamental experiment required appliance as the part of microfluidics.

The video link: http://www.jove.com/video/203/chemotactic-response-of-marine-micro-organisms-to-micro-scale-nutrient-layers

Here is the video notes dictation records.

Stage 1:
Clean the wafer with specifically required solvents.
Use the shining side to code.
Dry the wafer with Nitrogen.
Bake, 130°C, 5-10 mins
Prepare two hot plates, 65°C and 95°C at the same time.

Stage 2:
Spin-coating the wafer:
Pouring the photoresist, low and no bubbles.
Let the photoresist stay on the wafer for 1 min before spin.
Spin time: total: 55 secs; 0-500 rpm, 5 secs; spin extra 10 secs; 500-3000 rpm, 7secs; spin extra 30 secs.
Place the wafer after spining on hot plates: 65°C, 5 mins; then 95°C, 20 mins.
Cooling down: 65°C 2-3 mins; room temperature, 5 mins or more.

Stage 3:
UV lights expose:
Exposed part: harder.
Unexposed part: wash away.
Mask used for exposition: the side with ink on it is adhere to the wafer.
Safty! Wearing Glasses!
Then expose the wafer.
Finally, put the wafer exposed on hot plates: 65°C 5mins, 95°C 20 mins (the time on hot plates varies from numbers of parameters involved.

Stage 4:
Develop:
Before the further operation, the photoresist on wafer was needed to be removed first.
Place the specific solvent (PMMA) into a beaker, then put the wafer in.
Fresh solvent to wash the extra photoresist on wafer, then, another solvent again.
At last, use the hydrogen to dry the wafer.
Stage 5:
PDMS:
Mix PDMS powder and curing agent (liquid) with ration 10:1;
Large amount of bubbles should be generated while mixing.
Fix the wafer with tape
Use the compressor to clean the dust on wafer.
Pour the PDMS on wafer.
Put the mixed PDMS and wafer in vacuum container to debubbled.
Finally, when there is no bubble, put them into the oven; 65 °C, 12hrs.

Stage 6:
Get the PDMS:
Use a knife to peel off the PDMS, and take them out. Knife should be careful with little pressure. The first cut stops when the knife hit the wafer.
Punch the holes, for inlet and outle.
Tap the channel to remove the dust.
Bond the PDMS to a glass slide for experiment.

On Monday afternoon, we went to the Bioelectronics lab in University of Liverpool to fabricate the PDMS in practise. We are not actual touch the equipment or wafer or solvents, because most of them are dangerous, and are required of operations by highly qualified experimenters. However, it is still fantastic to take part into this.

Photos of lab work were attached in blog.

First time to the Bioelectronics Lab