Guidelines on How to Store Biological Samples in ULT Freezers

Although many researchers use ultra-low temperature freezers also known as ULTs few know the requisite steps they can take to protect their samples.

Although many researchers use ultra-low temperature freezers also known as ULTs few know the requisite steps they can take to protect their samples. There was a situation that happened at a ULT freezer at the Harvard Brain Tissue Resource Center back in 2012. The freezer failed and as a result, a third of the largest collection of autism brain samples were damaged. The reading on the freezer was -80 0C while the temperature was the same as that of the refrigerator. If you are searching for low-temperature freezer, here are a few tips to help you safeguard your samples in the freezer.

Avoid Redundant Freezers

There is no need for searching for low-temperature freezer only to end up getting a redundant one. You have probably noticed that most labs will equip their freezers with an alarm system. However, they fail to install independent monitors to check the temperature as well as install enough backup systems. You may protect your samples by using an alarm system but the temperature can increase or reduce slightly and fail to trigger the alarm.

The best way to truly protect your samples is by installing another pair of independent monitors and connect them with the alarm system. You then have to run them through another port into the freezer. You can also use liquid nitrogen or C02 as a backup. If the freezer fails or is damaged, the backup system will release the gas into the chamber giving you enough time to relocate your samples into another functional freezer. On the same note, you have to ensure that you have another freezer set aside for emergencies.

Protection Against Freezer Burn

Freezing is complex in nature and cannot be fully understood. Different freezing temperatures result in various types of ice crystals which also form under various rates. Stable hexagonal crystals can be formed with a temperature of -800C. However, it is delicate to transition the crystals in and out of their stable condition. Generally, if you have bigger cells then it is very critical that you cool them slowly. A cooling rate of about 100C per minute in a stable temperature environment is recommended even if the cells are permeable and more tolerant.

The best way to protect your samples against freezing as a result of more solute concentration and formation of ice-crystals is by adding a cryoprotective layer using glycerol or other additives. The cryoprotective layer will enhance the dehydration of the cells before intracellular freezing and glycerol is a better option.

Customise the Conditions to Suit the Cell Type

There are specific factors that you need to consider before you prepare the cells for cryopreservation. Some of these conditions include the cell type, its viability, its physiological state and other conditions necessary for growth. Plant cells should be harvested at the late-log phase then use the two-step cooling process to preserve them. First store the cells at -300C for quite some time then freeze at -800C.

You also need to consider if the cells are grown under aerated or nonaerated conditions. For instance, certain microbial cells especially yeast and bacteria will be highly resistant to the negative effects of cooling and freezing if they grew in aerated conditions compared to the nonaerated ones. In addition, you need to ensure that there is no germination taking place before freezing fungal spores. It is also important to confirm viability and determine recovery through cell counting before and after freezing a culture. This enables you to determine the success rate of your method. The bigger the number of cells previously present, the higher the recovery.

Establish Strict Storage Protocols

You need to organise your lab actively by establishing strict protocols, especially for -8000C. make sure that your staff members get access to the freezer once they catalogue their samples in one central location. Also, ensure that t the is backup for the cataloged samples. 

Always ensure that all samples are labeled properly before they are stored. Don’t use a blue permanent marker as they usually fade off after sometime when placed in the freezer. Writing directly on the samples preserved by ethanol is not also recommended as the writing on polypropylene tubes may wear off eventually rendering the writings illegible. Some stickers can also fall off after spending some time in the ULTs. You should, therefore, test several types before you commit your resources to bulk purchases.To conclude, you should always be on the lookout for the signs of high-energy consumption. Excess condensation, loud sound from the freezer, overheating rooms and water leaks are some of the signs that your freezer may be in trouble. Remember that the lower your temperatures the higher your energy consumption rate. You may need to store your samples at -700C compared to the usual -800C as it is only done out of habit.