Hi, I have a user who would ideally like to image at 4C on one of our confocal microscope. We can’t really invest in a new incubator but I wonder if anyone has tried to add few small buckets of dry ice inside the Zeiss large incubation chamber to cool down the space? Is that a terrible idea 
…?
Never tried it or anything similar…but please ask Zeiss before you do it, in case anything can be damaged. Also, don’t expect great lens performance at 4C.
Cooling down the entire enclosure to almost freezing sounds very risky to me. High stress on materials in the microscope and condensation on all sorts of surfaces are two things I would be worried about. I would say the safest way is using a stage incubator with refrigerant being pumped through, and combine that with an air lens (assuming the confocal microscope is an inverted configuration). Condensation on the bottom of the dish/chamber will still be an issue, though. Bioptechs has a commercial solution for such a stage incubator (Cooled FCS2), but maybe you have a workshop that can build a simple one for you.
4 degrees C is a water ice solution, not a dry ice solution.
Plastic bags or gloves with ice inside, tied off, and packed around the sample may work. We did this many years ago with a BioRad MRC 600 confocal. We had to constantly correct the focus manually, but that was before laser autofocus systems.
We also had a metal stage with channels in it to pump water. To lock proteins in Golgi and then release them we ran cold water through the tubes and then switched the tubes to a warm water bath. Focus changed dramatically, but we got the imaging to work.
Warning: Do not use when room humidity is high. Condensation on the scope is bad. Make sure also that there is no leakage. Water in scope very bad.
I am not sure if it helps, but for the petri dishes we used the instec cell insert, they have different temperature parameters options, our was able to cool down to 10C, It was with Peltier elements.
You have options, but not good ones.
- If you cool the system locally, the temperature differential between the enclosure and non-chilled parts of the system can play heck with your optics due to expansion-contraction. A very good focus control system like Nikon PFS / Leica AFC etc. will help a little.
- Condensation will fog up optical surfaces outside and inside your system. You will need an excellent dehumidifier at a minimum. If condensation forms there’s no guarantee it will go away without a trace afterwards and won’t cause electrical issues.
- LN2? OMG no. Oy. Wet ice is also a bad idea; it will quickly become water and lead to humidity and water in your system. If you want active cooling then you should attach a Peltier refrigeration device to the stage and have a thermometer feedback loop through an arduino to regulate the temp. However…
- Just move the confocal to a cold room. The scope should be rated to work at 4C, although you should talk with their service beforehand or you’ll probably void a service agreement. Going into the cold room isn’t such a big deal; it’s coming out again that will get you. You’ll have to seal all the units in plastic and let them warm very slowly…otherwise condensation will form inside and do very bad things.
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Thank you all for you terrific answers! I am glad I asked, it seems that, as I expected, my idea was pretty bad 
When I needed to cool down my sample I made this 3D printed coverslip holder that I connected to a refrigerated water-bath with external circulation system.
The whole thing has the same size that a standard slide.
I had no condensation problems.
Section:
While back, read this Application Note on Mouser, the electronics component distributor. Its for Peltier junctions from a company called Laird. They can provide a more turn-key OEM type of DIY solution, design/tech support, drawings, etc. Used some of their products for other purposes before (lasers).
https://www.mouser.com/pdfDocs/Heating-and-cooling-for-incubator-chambers-appnote.pdf
You may be able to use their “Tunnel Series” devices to simply blow cold air into existing ducts.