Where do we store samples before release?

The Biobank itself

Our HTA licence requires the HBRC to be secure. This means that access to the biobank is heavily restricted – only essential staff are permitted to enter or leave without needing the help of a member of essential staff. In fact, you can’t even get into the building without special access.

Fresh samples

We store fresh tissue at 4°C for a few minutes up to overnight – anything longer, and it's not fresh! For bodily fluids like blood and urine, we usually store samples at 4°C for a few minutes up to overnight, but if special tubes are used, we can store them at room temperature for up to a week or so.

Frozen samples

We can store frozen samples at 3 different temperatures. Mostly, we store them in special freezers at -80°C – that's as cold as the Antarctic! This ensures that samples can be kept for a long time without their makeup changing significantly.

Sometimes, scientists want our samples to remain “viable” – that is, to stay in a condition which allows them to be grown in a laboratory. To do this, we store them in “liquid nitrogen” (more correctly termed, “under vapour phase of liquid nitrogen” – i.e. in the air just above a pool of liquid nitrogen in a tank). This ensures that samples remain at around -190°C – so cold that all chemical activity pauses.

The reason that we don’t store samples in liquid nitrogen itself is to guarantee that material or chemicals from one sample don't accidentally contaminate other samples (which would be bad for the science, and might also offend donors). There is also an important safety reason – if liquid nitrogen were to get trapped inside a sample tube, when the tube was retrieved from storage, any trapped liquid nitrogen would immediately start warming up, and it would expand into a gas of volume 700 times larger than it was when liquid. If that happened, and the gas couldn’t escape quickly enough, the sample tube would explode!

Very occasionally, scientists ask us to store samples at -20°C (roughly the same temperature as your home freezer on its coldest setting). This doesn’t keep samples as stable in the long term, so it's only done by special request.

We have eleven -80°C freezers in use, two empty ones for backup, two -20°C freezers, and a liquid nitrogen tank. Our building is on an emergency generator supply, so even in a power-cut, our freezers can keep going. Our liquid nitrogen tank is topped up automatically every day to counter the effects of natural evaporation, and we have agreements in place to store our samples elsewhere in case of emergency.

Histology (“fixed” or “FFPE”) samples

Most of our histology samples come from leftovers in the NHS archives. However, we do sometimes make our own in the same way that the NHS does. Histology samples can be stored at room temperature.

To allow such storage, samples are first “fixed” in formalin – the internal structure of their cells is hardened and linked in such a way that it won’t degrade.We could (and are sometimes asked to) leave samples in fixative, but long-term storage like this can affect the how samples behave when embedded in wax later – so we prefer to fix samples for only 48 hours.

We then extract the water from the samples using increasing amounts of alcohol, before we replace the alcohol itself with a solvent called Xylene. (By the way, the alcohol is not the sort that you can drink!)

We replace the Xylene with paraffin wax – hence the term “FFPE” (formalin-fixed, paraffin-embedded). Finally we take our FFPE samples and nestle them in a square block of the same type of wax ("blocking up").

Samples can be stored in this state for decades. From time to time, we will cut very thin “sections” from FFPE blocks (usually 3-4 millionths of a metre thick) and put them onto glass slides for staining by the scientists.

Staining may be:

• Chemically-based – such as the classic pink-and-purple of pathology “H&Es” (haematoxylin and eosin)“Immunohistochemistry” – fluorescent markers attached to antibodies latch onto the proteins of interest in a sample
• “Digital Spatial Profiling” – very advanced techniques which can look at tens of thousands of different markers in each sample

We leave anything that isn't basic chemical staining to scientists and other facilities – HBRC's expertise is in biobanking!

How do we know that -80°C is -80°C?

In the same way that our HTA licence requires us to keep our biobank secure, it also requires us to prove that we are keeping our samples at the correct temperature – not just for -80°C storage, but for liquid nitrogen, -20°C, 4°C, or at “room temperature” (widely defined as 15-30°C).To do this, we have thermometers in every freezer, every fridge, every room, as well as in the liquid nitrogen tank.

Our thermometers are securely linked to a monitoring system which records (forever!) each temperature, every minute, of every day, of every year. Not only that, but if any temperature goes above or below certain limits, the system will alert us. We can then look at what's happening from wherever we are, using special software, and decide whether it's just a temporary blip (e.g. because someone opened a freezer door) or something which needs attention (e.g. because a freezer is coming to the end of its life).