Sometimes we tend to forget that all our efforts to build an all-encompassing library of DNA Barcodes generate very valuable byproducts. Probably one equally important legacy is the huge number of DNA extracts and in many cases the associated tissue samples that stored in various places and hopefully available to future generations.
Tissue samples today are either preserved in formalin, at temperatures between - 80 and - 90 C, or in liquid nitrogen, at about 193 C. The formalin method works well for preserving the carcass of a specimen, but certainly not for any material that is intended for further molecular work. No doubt, freezing at very low temperatures is the number one choice but the energy costs are often prohibitive and for years researchers are trying to find alternatives. There are some industry products out there that bind DNA and allow for storage at room temperature but quite a few of them are either not suitable for long term storage (as in museum tissue collection) or they haven't been tested accordingly. The latter is no surprise at it is admittedly difficult to simulate storage over decades.
Some Norwegian researchers have been looking at the salt cod industry for a potential tissue sample drying technology that could save money without sacrificing tissue quality. In their new paper they describe how took samples from the lungs, heart, liver and kidneys from lab animals and froze these rapidly in liquid nitrogen. The frozen material was dried at + 5 and - 10 C in a heat pump drier at atmospheric pressure, which is a variation of the method used in the fisheries industry to dry salt cod. Drying things at low temperatures allows water to sublimate.
The type of heat pump used was originally developed in the 1970s, during the oil crisis. It was initially developed as a fuel-efficient way to dry fish, but it has since become an industry standard. Naturally, the heat pumps have changed some since then, but the principle is the same.
The colleagues determined the quality of RNA, which is usually even more unstable than DNA. They measured the quality of the extracted RNA by using spectrophotometric analysis immediately after freezing, and again after five months. This was done by examining the fragmentation of the molecules. The different types of samples were also tested using optical and electron microscopes, to see how well tissue and cell structures were preserved.
Preliminary results show that drying at temperatures of about 0 degrees is best for preserving RNA, with about the same amount of decomposition of molecules in samples that were dried compared to samples that were stored conventionally. This was true for all five types of tissue that were tested. Cell structures were mostly preserved, although some fine details in the cells seemed to have been affected by this method.
Overall very promising:
...the technology seems promising for research biobanking, with its main advantages being low cost, high energy efficiency, and relative independence on an advanced technical infrastructure. Further study will be needed in order to clarify the possibilities and limits, and further refinement and optimization will be needed in order to unleash the full potential of the methodology.
The commercial prospect of a drying technique capable of producing high-quality material suitable for long-term storage seems bright in view of the rapidly growing market of research biobanking.