Team:EPF-Lausanne/Tools/Microfluidics/HowTo1

From 2011.igem.org

(Difference between revisions)
 
(41 intermediate revisions not shown)
Line 1: Line 1:
-
{{:Team:EPF-Lausanne/Templates/MicrofluidicsHeader|title=Microfluidics how-to part I: making chips}}
+
{{:Team:EPF-Lausanne/Templates/MicrofluidicsHeader|title=Microfluidics How-To Part I: Making Chips}}
There are three main steps in the making of a microfluidic chip:
There are three main steps in the making of a microfluidic chip:
Line 7: Line 7:
* Moulding PDMS chips.
* 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.
+
Designing chips is a subtle task, but for many applications one can re-use an existing design. Moulds are also usually made using expensive equipment found in clean rooms.
-
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 on fabrication, based on our [https://2011.igem.org/Team:EPF-Lausanne/Protocols/Master_microfabrication_for_PDMS_replica_molding protocols]. If you do not, you can try to experiment with making moulds out of laser machined metal, but it will probably be easier to order them. Stanford offers a [http://www.stanford.edu/group/foundry/index.html foundry service].
-
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.
+
Moulding is the most common task: it must be done over and over again, as the chips are usually single use. Again, this requires specific equipment not usually found in a bio lab. So unless a friendly lab in your neighbourhood is equipped, you'll probably have to order the chips.
-
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==
-
==Making a mould==
+
Our moulds are made by photolithography: a layer of AZ or SU-8 resist is spin-coated onto a silicon wafer, then exposed, developed,  
-
to write here: AZ, SU8, steps of fabrication, may be choose some of pictures and not display all
+
and etched, to only a positive image of the channels in resist. The mould is thus a plane of silicon, with features made in photoresist. To provide the mould walls, we place the wafer in an aluminium-foil-lined petri dish.
-
SU8 wafer fabrication(a.k.a. "Dress as an astronaut day"):
+
The complete protocol for the clean room fabrication of the mold can be found [[Team:EPF-Lausanne/Protocols/Master_microfabrication_for_PDMS_replica_molding|here]]. Many pictures of the fabrication process in our clean rooms are in our [https://picasaweb.google.com/114670117111403230486/CleanRoomMouldFabrication?authuser=0&feat=directlink picasa gallery]
-
<html>
+
[[File:EPFL-AZ-Robot.JPG|thumb|left|AZ photolithography robot.]]
-
<embed type="application/x-shockwave-flash" src="https://picasaweb.google.com/s/c/bin/slideshow.swf" width="600" height="400" flashvars="host=picasaweb.google.com&captions=1&noautoplay=1&hl=en_US&feat=flashalbum&RGB=0x000000&feed=https%3A%2F%2Fpicasaweb.google.com%2Fdata%2Ffeed%2Fapi%2Fuser%2F114670117111403230486%2Falbumid%2F5654374714730282977%3Falt%3Drss%26kind%3Dphoto%26hl%3Den_US" pluginspage="http://www.macromedia.com/go/getflashplayer"></embed>
+
[[File:EPFL-Mask-Aligner.JPG|thumb|left|Changing masks on the mask aligner.]]
-
</html>
+
[[File:EPFL-Wetbench.JPG|thumb|left|Wet bench for SU8 development.]]
-
== PDMS chip fabrication ==
+
==PDMS==
-
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.
+
PDMS or poly(dimethylsiloxane), informally known as ''silicone'', is a cross-linkable elastomer. In layman's terms, it is a transparent rubber-like material.
-
If your lab is equipped, you should have no problem replicating our [[Team:EPF-Lausanne/Protocols/PDMS_two_layer_device_fabrication|protocol]] for MITOMI chip fabrication:
+
[[File:EPFL-PDMS-chips.JPG|thumb|right|250px|PDMS chips: the four rectangular transparent blocs]]
-
<html>
+
It is used for the fabrication of microfluidic chips for many reasons:
-
<embed type="application/x-shockwave-flash" src="https://picasaweb.google.com/s/c/bin/slideshow.swf" width="600" height="400" flashvars="host=picasaweb.google.com&hl=en_US&feat=flashalbum&RGB=0x000000&feed=https%3A%2F%2Fpicasaweb.google.com%2Fdata%2Ffeed%2Fapi%2Fuser%2F114670117111403230486%2Falbumid%2F5654596587940840561%3Falt%3Drss%26kind%3Dphoto%26hl%3Den_US" pluginspage="http://www.macromedia.com/go/getflashplayer"></embed>
+
-
</html>
+
-
<p> 1    Place molds into a TMCS vapor chamber for at least 20min</p>
+
* Being flexible, it is easy to cast, and conforms to imperfect surfaces.
-
<p> 2a)  Control layer mixture</p>
+
* It accurately reproduces micro-scale patterns.
-
<p> 2b)  Mix for 1 minute, degas for 2 minutes (standard protocol)</p>
+
* It is transparent down to UV light, allowing easy optical microscope observation and enabling fluorescence techniques of UV-range absorption.
-
<p> 2c)  Pour onto control layer mold and place mold in vacuum chamber for at least 20min</p>
+
* It is non-toxic, allowing on-chip cell culture.
-
<p> 3a)  Flow layer mixture </p>
+
* It can seal reversibly or irreversibly to itself or glass, allowing the fabrication of multi-layer devices, and strong bonding to glass slides.
-
<p> 3b)  Mix for 1 minute and degas for 2 minutes (standard protocol)</p>
+
* Its surface chemistry can be controlled.
-
<p> 3c)  Spin coat onto flow layer</p>
+
* It is oxygen permeable, allowing air to diffuse out of the channels through the chip when the channels are filled.
-
<p> 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 )</p>
+
-
<p> 5    Place the control and flow layer in a 80C convection oven and incubate for 30 minutes (timing is critical here!)</p>
+
-
<p> 6a)  Remover wafers both layers from the oven, cut out control layer </p>
+
-
<p> 6b)  Punch holes </p>
+
-
<p> 6c)  Align control to the flow layer</p>
+
-
<p> 7    Put aligned device back into 80C oven and incubate for at least 90 minutes (and here you can increase the backing time)</p>
+
-
<p> 8a)  Remove devices from oven</p>
+
-
<p> 8b)  Cut them out </p>
+
-
<p> 8c)  Punch flow layer holes and cut the edges through the flow layer</p>
+
 +
For more information on PDMS chip fabrication: Mcdonald, J.C. et al. Fabrication of microfluidic systems in poly (dimethylsiloxane). Electrophoresis 21, 27–40(2000).
-
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). 
+
== Making the Chips ==
 +
MITOMI chips are two layer devices. A thick upper layer is imprinted with the flow channels (those that will contain reagents) and a thin bottom layer is imprinted with the control channels (used to actuate on-chip valves). The role of each layer is explained further in [[Team:EPF-Lausanne/Tools/Microfluidics/HowTo2|Part II]].
 +
 +
Casting PDMS involves mixing a precursor and a curing agent (sold as the Sylgard 184 kit by Dow Corning), degassing, pouring into the mould (or spin-coating onto the wafer for the thin layers), and partial curing at 80°C. After curing, holes are punched through the flow layer, to allow plugging in of external tubing (again, see part II). The two layers are then superposed and aligned by hand, so that the valves from the control layer overlap the correct channels on the flow layer.
 +
 +
After alignment, curing is finalised. This fully solidifies the chip and ensures a strong bond between the two layers. After curing, holes are punched through to the flow layer. For most chips, the last step is to bond them them to a glass microscope slide, following a plasma surface treatment if strong bonding is required. In the case of the MITOMI chips, they are instead aligned onto a spotted array from a DNA library. At this point, the chip is ready to use.
 +
 +
The specifics of each step are explained in our [[Team:EPF-Lausanne/Protocols/PDMS_two_layer_device_fabrication|protocol]] for MITOMI chip fabrication. The process is illustrated on our [https://picasaweb.google.com/114670117111403230486/ChipFab_steps?authuser=0&feat=directlink Picasa gallery]. More pictures of chip fabrication are also available [https://picasaweb.google.com/114670117111403230486/ChipFabMITOMI?authuser=0&feat=directlink here].
 +
 +
[[File:EPFL-Pouring.JPG|thumb|left|Pouring PDMS. Note the vacuum chamber for degassing.]]
 +
[[File:EPFL-Cutout.JPG|thumb|left|Cutting out the chip after curing.]]
 +
[[File:EPFL-Align.JPG|thumb|left|The two layers have to be aligned by hand.]]
{{:Team:EPF-Lausanne/Templates/Footer}}
{{:Team:EPF-Lausanne/Templates/Footer}}

Latest revision as of 03:27, 22 September 2011