Use a sealing mat to prevent evaporation of 96-well plates stored above freezing

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Use a sealing mat to prevent evaporation of 96-well plates stored above freezing

Article created: Feb 4, 2008
Article by: Jeremiah Faith

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I can't stand waiting for my primers to thaw when I run a PCR. So when I know I'll be running the same PCR reaction frequently, I leave a 10 uM working stock of my primers at 4C, particularly for 96-well primer plates (they thaw very slowly). However, the first time a used up an entire 96-well primer plate, I noticed that the edges of the plate (i.e. rows A and H; columns 1 and 12) ran out quite a bit faster than the remaining wells. At the time, I'd been told to use aluminum foil plate seals for my primers. But it was clear that the aluminum seal wasn't sufficient to prevent evaporation of my primers.

A sealing mat will lower evaporation

After digging around biosupply websites, I noticed some companies that sold 96-well plates also sold silicon sealing mats for them; the sealing mats looked like the same material IDT used to seal the full concentration primer plates they sent me. The sealing mats were a little pricey, but they did the trick. I can now leave my primer plates in the fridge for long periods of time (a few months) and have little to no evaporation.

Tips to help you seal the mat

It is very important to purchase the sealing mat that matches your plate. I have some wide-well, expanded volume 96-well plates and some standard well – each needs a different size mat. Also, these mats seal extremely tight, especially at the beginning; it can actually hurt your thumbs a little to seal a plate for the first time.

I find it is easier to seal the plate the first time while it's empty (i.e. before you fill it with your solution). Because you have to apply a large amount of pressure to seal the mat, if you slip with a plate that is already full of liquid, you'll have liquid everywhere (and a ruined plate). Once you seal the plate and remove the sealing for the first time, it becomes much easier to seal with the same mat each subsequent time. Some companies also sell a (very expensive) machine to seal the plate for you.

Start from the top of the plate (row A) and work your way down one row at a time. If you try to seal the whole plate by just pushing down all over and not going a row at a time, it can be quite difficult to seal. When you want to remove the seal, pull slowly and diagonally from one corner towards the opposite corner. I find this diagonal mat removal is much gentler and less likely to spill than pulling from right-to-left or top-to-bottom.

96-well plates and their matching sealing mats

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Below are the part numbers for the plates and matching sealing mats that I frequently use in the lab. The expanded volume plate is more difficult to seal than the plate with standard well sizes.

Supplier	Part Number	Description
Corning	3357	standard volume, V bottom, sterile, polypropylene 96-well plates
Corning	3080	storage sealing mats for 3357
Corning	3344	expanded volume, V bottom, sterile, polypropylene 96-well plates
Corning	3346	storage sealing mats for 3344
Corning	3081	expensive machine for sealing plates (I've never tried it)