To use DNA in any forensic application, the nucleic acids must be accurate. If not, someone’s freedom, even life, could be in danger. The U.S. FBI’s Combined DNA Index System (CODIS) provides an idea of how valuable DNA is to modern law enforcement agencies. With someone’s guilt or innocence at stake, DNA samples must be handled properly and stored safely. Chemical degradation can turn a forensic sample into DNA debris. Keeping a sample cold, sometimes really cold, can keep the DNA useful for months, even years.
To keep samples super cold, some researchers use an ultra-low temperature freezer, known among scientists as a ULT. As a rule of thumb, a ULT can keep samples at −80° Celsius, but some even go a few degrees lower.
A variety of sources endorse storing DNA at low temperatures. For example, an article on News-Medical.net noted that DNA “storage at −20 °C and −80 °C can prevent degradation for months or years.”
On ResearchGate, questions regarding When storing genomic DNA for quantitative PCR it is important to remember that as long as your storing the DNA at a pH of 8.0 (ie: in non-DEPC treated nuclease-free TE, pH 8.0) it should be safe for a long time (years) at −20C or −80C. Also, ensure that the tubes are sealed tightly so that sublimation of the buffer is limited. Consider using wrapping the tops with parafilm.
How long can you store the cDNA in −80°C without any loss in stability? DNA can be stored for many years at −80°C, with even longer storage for purified DNA.
Of course, it’s not just the temperature that must be considered when assessing proper DNA storage, DNA must also be stored in the right labware. A routine mistake in DNA storage protocol is failing to use DNase-free microtubes. Which can lead to diminished DNA quality. Some scientists store DNA in water, and one report shows that even cold temperature is not enough to save those nucleic acids for long. DNA should be stored in the proper liquid when cooled, like ethanol.
In using a ULT for any application, keep energy use in mind. Make sure to select an energy-efficient ULT, such as NuAire's Blizzard HC VIP NU-99338J -86°C Ultralow Freezer (ULT). As NuAire explains: “HC in Blizzard HC stands for Hydrocarbon. Hydrocarbon refrigerants are non-toxic and non-ozone depleting making it the most environmentally friendly refrigerant in a ULT. Hydrocarbon refrigerants reduce your total cost of ownership by reducing energy consumption up to 60% when compared to existing HFC refrigerant technology.”
In many cases, a ULT can also be set at −70°C, and keep samples just as safe. Moreover, that temperature change can translate into significant reductions in a ULT’s energy use. In a forensic application, scientists must be sure to validate any DNA-storage methods. If the process includes storage in a ULT, the equipment must be reliable at keeping the temperature at the desired setting and keeping all samples at that temperature. Only then can a DNA sample stand up in court when needed.