LN2 Removal

This is a new feature called "What is that?" where I will show a photo of something from the lab and then discuss what it is, what it does, and why scientists use it.  Every lab that I've ever worked in, I gave tons of tours - to my family, to other scientists, to kids and to the public!  Seeing what a real lab looks like and understanding how things work is one of the ways I use to demystify science and scientists. Think of this new series as a virtual lab tour with me as your tour guide!  I hope at some point soon to turn this feature into a short video series...but until then, enjoy learning about what "that" is!

So what are these? These are liquid nitrogen freezers.

Let's start by talking about freezers in general. What temperature is your freezer at home? Well it needs to be cold enough to freeze things. The freezing temperature of water is 32° Fahrenheit (F) or 0° Celsius (C), so you want your freezer to at least be able to freeze water, but you also want it to preserve your food.  Part of preservation is preventing bacteria from growing since bacteria could potentially cause food poisoning when you thaw and eat 

the food (especially if it isn't cooked first).  The colder the temperature, the less likely the bacteria is to be able to grow.  Also, the colder the freezer is, the less likely it is that enzymes (proteins that perform chemical reactions in cells) are active and breaking down the food's nutrients. So the ideal freezing temperature for food is 0°F or -18°C.

In the lab, we have -20°C freezers that store reagents and look a lot like the upright freezer that my mom has in her basement to store extra food (and chill martini glasses). We also have -80°C freezers, also called ultra low freezers referring to the "ultra low" temperature.  These are better at storing proteins at a temperature that is cold enough to inactivate them. These ultra low freezers are also good for storing RNA.  RNA has a natural enemy, a protein called RNase, which is essentially a high-powered chomping Packman after the Pac-Dots dots that make up the RNA. At really cold temperatures, this RNase Packman is inactive and can't work, keeping the RNA sample safe.

As a bit of a segue, my 4-year-old nephew calls me on Facetime a few times a month and always asks me to "show him some science." One of the first things I showed him was our "Biospecimen Cryostorage" where we store the samples from our biobank, and which is what is pictured above. This room has three Liquid Nitrogen Freezers, and these are even colder that the ultra-low freezers. With liquid nitrogen (abbreviated to LN2) in the base, the whole tank is cooled to below -275°F or -170°C. If you feel like you've heard of liquid nitrogen before, you probably have. This is the liquid that is used at Science Centers to freeze roses and then smash them into a million pieces.  If you've seen any cooking show in the past 5 years, you've probably seen a chef use liquid nitrogen and pour it into a mix of cream and sugar to make a fast ice cream. However, in science we use liquid nitrogen as a way to quickly freeze and preserve living cells and tissue - a process overall known as cryopreservation.

Liquid nitrogen diagram

To better understand the photo and to really understand "what this is", I have labeled areas above.  Each of the two tanks pictured can hold up to 40,000 individual samples.  These samples could be blood samples, tissue samples, samples of cells, etc.  In our case, these samples are stored in 2 ml (milliliter) tubes in plastics boxes in racks inside each freezer. Each box can hold 96 samples and each rack (see photo below) can hold 13 boxes (over 1200 samples). The freezers are automatically filled by tanks filled with liquid nitrogen sitting right next to each freezer.  Each freezer isn't completely filled with liquid nitrogen for a few reasons. First, it would be really expensive but more importantly, it isn't necessary. The temperature of liquid nitrogen is -190°C but the vapor keeps the tank colder than -170°C, which is still good enough to keep all of the proteins in these cells completely inactive.

Samples are removed from these tanks on a regular basis and distributed to researchers.  You can see an image on the left of a rack of boxes being removed. It is important when selecting individual samples that they are not allowed to warm up and thaw.  This thawing can activate proteins that break down the samples or causes ice crystals when re-thawing that affect the integrity of a tissue sample or the viability of frozen cells, for example.

What is that?

Liquid nitrogen freezers and a filler tank

What does it do?

Keeps biospecimens or other samples at really low temperatures

Why do scientists use them?

To keep samples well preserved and viable so that they work better for their experiments.

Dr. Cathy Seiler is the Program Manager for the tissue biorepository at St. Joseph's Hospital and Barrow Neurological Institute. She has her BA in Biochemistry and Molecular Biology from Boston University and PhD in the Biological Sciences from Cold Spring Harbor Laboratory. Her research and teaching focuses on genetics, cancer, and personalized medicine. Find her on Facebook at www.facebook.com/thingsitellmymom

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