Freeze Drying and PCR

The current coronavirus disease COVID-19 outbreak caused by severe acute respiratory syndrome SARS-CoV-2 is a public health emergency of international concern. Timely diagnosis and management are essential for disease control. Polymerase chain reaction (PCR) is an accurate and sensitive molecular technique and is considered the “gold standard” for the diagnosis of COVID-19.

What exactly does the Polymerase Chain Reaction do? Polymerase is a protein that makes copies of DNA, and cells use polymerase to copy DNA when they divide. Chain reaction describes how PCR is an exponential reaction. Each time polymerase makes a copy, the number of copies doubles. If you start with 2 identical DNA sequences and then copy them, you make 4 sequences. Copy those to make 8, then 16, then 32, and so on. After 35 rounds of making copies, PCR produces around 34 billion pieces of the target DNA.

Illustration showing how the polymerase chain reaction (PCR) produces lots of copies of DNA

PCR Reagents

Producing PCR reagents in a controlled environment helps to prevent the introduction of contaminants. In liquid form these diagnostic reagents may be light or oxygen sensitive, have short shelf lives at room temperature, may require low storage temperatures to retain their activity and can be more prone to exposure of contaminants. Stability is also an issue, with the standard method of preservation being storage at ≤20⁰C following the addition of glycerol or a similar cryo-protectant which can be expensive in the long term.

To maintain bioactivity, PCR reagents must be transported and stored at a low temperature. This presents challenges to already overburdened transport logistics networks and cold storage space at diagnosis and hospital laboratories. Freeze-drying is a process mainly used for stabilizing of heat-labile biological drug substances contained in aqueous solutions. Because water drives many destabilization pathways, removing most of the water can prolong the shelf-life of the product. Because freeze-dried reagents typically contain all of the necessary components for testing (at appropriate concentrations), errors associated with improper handling of wet reagents can also be reduced. This reduces preparation time and, thus, testing throughput.

Freeze drying PCR components can increase product life time from just a few hours/days in liquid form to several months/years in the dried format. Achieving a successful freeze dried product reduces cold chain storage requirements and product wastage (due to product expiry), therefore improving the environmental sustainability of the product. This has clear advantages: reducing the importance and criticality of forecasting product demand, storage facility requirements, transport logistics and associated costs of these.

Freeze-thawing and assembly of multiple PCR reagents creates the potential for pipetting errors, batch-to-batch inconsistency and poor result reproducibility by virtue of their labor-intensive nature. Using pre-formulated freeze dried reagents that contain all the components needed for PCR offers simplicity and minimizes hands-on time; essential for improved laboratory throughput and time-sensitive results.

By minimizing the number of reagent handling steps needed in reaction set-up, sample handling and pipetting steps are reduced, lowering the risk of sample degradation, cross-contamination and critically, human error.