Oligonucleotides are relatively stable molecules. However, to avoid degradation and loss, it is essential to store oligonucleotides under the right conditions.
Handling, stability, and storage of oligonucleotides
DNA oligonucleotides free of DNAse are relatively stable in deionized water. However, in an aqueous solution, slow acid-catalyzed depurination can occur. Because of its chemical structure, RNA is less stable than DNA. Exposure of RNA to small amounts of RNases will impact the stability of RNA oligonucleotides.
Since RNases are prevalent in many standard laboratory conditions, use RNAse free water and buffers for RNA storage and handling. RNA is most stable when stored as an ethanol precipitate at -80°C.
Long term storage
For long term storage, the temperature is most important. Hence, it is best to store oligonucleotides in solid form or a solution frozen at -20°C or -80°C.
For storage at four (4) °C, resuspend oligonucleotides in TE buffer. Oligonucleotides resuspended in the correct buffer are more stable at room temperature than dried oligonucleotides.
In general, store oligonucleotides in the dark and avoid exposure to UV light.
Store oligonucleotides modified with photolabile group frozen in the dark at -20°C, or lower and avoid light exposure.
Store RNA oligonucleotides as ethanol precipitate at -80°C.
Short term storage
Oligonucleotides stored at 37 °C or 98.6°F are stable up to 6 weeks when kept dry, resuspended in water or TE buffer.
Oligonucleotides stored in water at room temperature are usually stable for up to 6 weeks.
Divide oligonucleotide solutions after receiving into aliquots and store in several tubes or vials in the freezer at -20°C.
If possible, select aliquot volumes between 50 to 250 μl and label them carefully.
Freeze-dried or lyophilized oligonucleotides
Liquid nitrogen or a similar approach allows the freezing of oligonucleotides in aqueous solutions. A high vacuum lyophilizer freeze-dries the samples. This process removes water by sublimation and results in a fluffy white powder. However, because of the water-loving nature (hydrophilicity) of nucleic acids, a freeze-dried solid oligonucleotide can contain approximately 40% of water by weight. Therefore, quantitation of the amount of oligonucleotide present needs to be done after dissolving in water by measuring the absorbance.
Freeze-drying allows storing oligonucleotides for long periods.
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