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Microfluidics how-to part I: making chips

There are three main steps in the making of a microfluidic chip:

• Designing the chip
• Making a mould
• Moulding PDMS chips.

Unfortunately, none of this is easy. Designing chips is a subtle task, but for many applications one can re-use an existing design. Therefore, we do not cover chip design. Moulds are also usually made using expensive equipment found only in clean rooms. If you have a clean room, somebody there will be able to train you. If you do not, you can try to experiment with making moulds out of laser machined metal, but it will probably be easier, cheaper, and more efficient to order them, for example from the Stanford Foundry.

Moulding is the most common task: it must be done over and over again, as the chips are usually single use chips. Again, this is simple if your lab is equipped for PDMS moulding. If your lab is not, bear in mind that buying the equipment and learning its operation is a major investment. So, again, unless a friendly lab in your neighbourhood is equipped, we would recommend ordering the chips, and just building the control setup.

Overall, a lot of expensive equipment is needed to make the moulds and chips. If your lab or school is not equipped for chip making, it will be much easier and cheaper to order the chips (or just moulds) from the Stanford Foundry: http://www.stanford.edu/group/foundry/index.html. The MITOMI chips were designed by Sebastian during his stay with the Quake lab, and have been already been made there. Therefore, it should not be a problem to get MITOMI chips from them.

Making a mould

The complete protocol for the clean room fabrication of the mold can be found here. SU8 wafer fabrication(a.k.a. "Dress as an astronaut day"):

PDMS chip fabrication

Making PDMS chips requires specialised equipment, specifically a vacuum chamber for degassing, a spin-coater, a hole punch, an 80° C oven, and a microscope to align the layers. Buying the equipment and learning its operation is a major investment, so, again, unless a friendly lab in your neighbourhood is equipped, we would recommend ordering the chips.

If your lab is equipped, you should have no problem replicating our protocol for MITOMI chip fabrication:

1 Place molds into a TMCS vapor chamber for at least 20min

2a) Control layer mixture

2b) Mix for 1 minute, degas for 2 minutes (standard protocol)

2c) Pour onto control layer mold and place mold in vacuum chamber for at least 20min

3a) Flow layer mixture

3b) Mix for 1 minute and degas for 2 minutes (standard protocol)

3c) Spin coat onto flow layer

4 Remove control layer mold from vacuum chamber, making sure no bubbles are left on the surface (remove with a toothpick if you see some )

5 Place the control and flow layer in a 80C convection oven and incubate for 30 minutes (timing is critical here!)

6a) Remover wafers both layers from the oven, cut out control layer

6b) Punch holes

6c) Align control to the flow layer

7 Put aligned device back into 80C oven and incubate for at least 90 minutes (and here you can increase the backing time)

8a) Remove devices from oven

8b) Cut them out

8c) Punch flow layer holes and cut the edges through the flow layer

Before use the chip should be aligned to the epoxy-treated glass slide. There can be DNA, bacteria or other substances spotted on it (in case of MITOMI device we spot different variants of the tetO sequence in this project).