“A DNA sample is usually stored at low temperature, between 4ºC to -80ºC temperature depending on the requirement. Here is the guide for the collection, storage, Handling and transportation of a DNA sample.”
Did you know?
- The oldest DNA sample we have is 7,00,000 years old. In 2013, a team of scientists extracted DNA from 7,00,000 years old horse fossils.
- In the same year, another team of researchers extracted and sequenced the DNA from 4,00,000 years old Neanderthal fossils.
- 4,000 to 40,000 years old DNA from a woolly mammoth found in Siberia and the Arctic.
- The ancient human DNA that we have is 7,000 to 8,000 years old.
DNA (Deoxyribose Nucleic acid) holds crucial information regarding one’s health and condition. It is, thus, used for genetic analysis and disease diagnosis. Good quality DNA is used in DNA profiles, DNA fingerprinting, HLA typing, ancestry testing, disease screening and diagnosis, etc.
DNA sample collection to testing is a long process, roughly taking a week to test. In addition, DNA is highly prone to contamination and degradation so sample collection, handling, storage and transportation play an important role here.
In this article, I will solve all your questions regarding DNA samples and storage.
How to collect a DNA sample?
A DNA sample can be collected from any biological tissue having DNA as its genetic material. Any prokaryotic cells (bacteria or viruses) or eukaryotic cells (animal, plants, fungi or algae) can be used for DNA sample collection.
For DNA testing, common samples for DNA collection are blood, buccal swab, saliva, hair follicle, semen, solid tissue or any biological fluid. DNA samples can be collected using various DNA isolation methods.
A few important and popular DNA isolation techniques are listed here:
- DNA isolation from Blood.
- Phenol: Chloroform: Isoamyl alcohol DNA Extraction.
- Proteinase K DNA extraction protocol.
After DNA sample collection (by any technique listed here), it is important to store and handle it correctly.
How to store a DNA sample?
DNA is susceptible to external stimuli like– temperature, chemicals, heat, radiation, or pH change. It can easily be degraded if adequate conditions are not maintained. So, good laboratory practices are required to maintain our DNA in its original and intact form.
Ideally, the DNA sample is stored at a low temperature between 4ºC to -80ºC, in an 8.0pH buffer and sterile (contamination-free) environment. Although, depending on the requirement, DNA can be stored at various temperatures. Important conditions are listed here.
- Low Temperature: ideally -80ºC or lower.
Every DNA sample should be stored at a lower temperature. We have discussed this point in the next section.
- Sterile container.
A DNA sample should be stored in a clear, sterile and molecular biology-grade plastic container.
- Minimal freezing and thawing.
Repeated freeze and thawing degrade DNA substantially, research suggests and thus, avoid multiple and repeated freeze-thawing.
- Minimal sunlight exposure.
Sunlight contains harmful radiations that can degrade DNA. For example, UV light degrades DNA directly. Avoid direct DNA sample exposure to sunlight or UV rays.
- No chemical or nuclease exposure.
Chemicals, for example—Alkylating agents, reactive oxygen species, peroxidase, reactive nitrogen species, etc can affect the stability of DNA. In addition, nuclease contamination destroys the DNA by catalytic action.
- Separate from other chemicals and solutions.
It is advisable to store a DNA sample separately from other hazardous chemicals and nucleases.
- Proper labeling and documentation.
Proper labeling and documentation play a vital role in long-term DNA storage. Every sample should be stored with a proper label, and crucial information (batch name, quality, quantity, date and ID) on the container.
- In different aliquots.
As we said, store DNA in aliquots so that it remains stable and untouched for years.
- Adequate buffering conditions.
As aforementioned, DNA is pH sensitive and thus, it should be stored in a buffer solution with 8.0pH. Ideally, it can be stored in a TE (Tris-EDTA) buffer. However, for short-term storage, it can also be stored in nuclease-free water.
Temperature for DNA Sample Storage:
Temperature plays a crucial role in DNA sample storage and transportation. As the temperature increases, the stability of the DNA sample decreases. As aforesaid, it’s crucial to know the stability of DNA at different temperatures.
20 to 25ºC can be considered as room temperature at which DNA remains the least stable. Thus, this temperature range is used for short-term DNA storage. DNA can remain stable for a few hours to a few days (not more than a week) without degradation at room temperature.
4 to 8ºC Temperature:
A DNA sample can be stored at 4 to 8ºC temperature for a few days to a few weeks. Maximum, we can store DNA at this temperature for a month, but still, it degrades.
This temperature is the best zone to store a DNA sample, particularly, for labs or research centers. At -20ºC temperature, DNA can be stored for a few years without degradation. However, to improve the storing capacity, preservatives or DNA stabilizers and strict buffer conditions are required.
If you are working in a lab, for small-scale research in college, store DNA at -20ºC without worry. Your sample will remain intact for 2 to 3 years, at least. It saves your cost.
For long-term DNA storage, the sample can be stored at an extremely low temperature in liquid nitrogen. At -80ºC temperature, it can remain stable for hundreds of years without degradation.
To improve the storing efficiency avoid freeze-thawing the sample at this temperature. Use proper buffering conditions and avoid sunlight exposure. Ancient DNA samples and some important and precious DNA samples are ideally stored at -80ºC temperature in liquid nitrogen.
Important Tips for DNA Storage:
- Never handle any DNA sample without gloves.
- For long-term storage, never dissolve DNA in water, use TE buffer.
- DNA can also be stored in the precipitation form as well.
- Never dissolve DNA in tap water. Use nuclease-free and molecular-grade water only.
- Do not use re-used containers for sample collection. It may contaminate a DNA sample.
- Never store DNA samples with microbes or microbial cultures. It may contaminate the sample in the long run.
- Never heat the DNA sample for thawing. It degrades or denatures the DNA badly. Thaw at room temperature, only.
- Check the quality and quantity, periodically or before use.
How to Handle a DNA Sample?
DNA sample handling is also an essential procedure for a geneticist and we should have to learn to handle it. Sample handling, which means how to process it, plays a crucial role to minimize DNA degradation & loss, and the risk of contamination.
Here I am listing important tips for DNA sample handling.
Wear sterile– gloves, face mask, lab coat and head cap before handling a DNA sample.
Clean the area with alcohol before opening the cap of a container having DNA. You can use a safety cabinet or laminar airflow to handle a DNA sample.
It is also important to minimize the sample exposure time. Organize all the utilities prior to handling the sample to save time and avoid unnecessary interruption.
If possible, process or handle the sample on ice or at a 4ºC temperature. At lower temperatures, chances of nuclease action are minimal.
It’s also important to note that all the plastic and glass utilities used in the process are sterile and pre-autoclaved.
DNA is a sensitive sample. Handle it gently. Physical pressure or rough handling can fragment the DNA. Do gently pipetting and avoid vigorous pipetting. Prevent sample foaming, shearing, agitation and excessive mixing.
Last, but not least, it’s crucial to manage biological waste disposal. Discard waste according to the standard laboratory procedure. Keep in mind that the waste disposal area should not be located very nearer to the DNA sample processing area.
How to Transport a DNA Sample?
Now, coming to the last segment of this article, if we need to send a DNA sample outside our laboratory, what precautions do we have to take?
The DNA sample should be transported in a proper cold chain. The sample should be collected in a sterile tube, labeled and documented properly, sealed with parafilm and placed in an icebox at a temperature between 4 to 8ºC.
These are the ideal conditions for DNA sample transportation.
For budding geneticists or expert scientists, it’s pivotal to know DNA sample storage, handling and transportation. DNA is an important and rare sample and thus, care must be taken while dealing with it.
A person should at least have basic training in molecular genetics or know these points before using any DNA sample. I hope you like this article. Please share it and comment if you have any questions.