Recycling of Polymerase Chain Reaction (PCR) Kits.

Polymerase chain reaction (PCR) kits have been used as common diagnosing tools during the outbreak of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, with daily worldwide usage in the millions. It is well known that at the beginning of the pandemic, there was a shortage of PCR kits. So far, the ecosystem of a PCR kit is linear use; that is, kits are produced, used once, and disposed of as biolab waste. Here, we show that to mitigate the risk of future shortages, it is possible to envision recyclable PCR kits based on a more sustainable use of nucleic acid resources. A PCR kit is mainly composed of primers, nucleotides, and enzymes. In the case of a positive test, the free nucleotides are polymerized onto the primers to form longer DNA strands. Our approach depolymerizes such strands, keeping the primers and regenerating the nucleotides, i.e., returning the nucleic acid materials to the original state. The polymerized long DNA strands are hydrolyzed into nucleotide monophosphates that are then phosphorylated into triphosphates using a method that is developed from a recent publication. We used oligonucleotides with a 3'-terminal phosphorothioate (PS) backbone modification as nonhydrolyzable PCR primers, which are able to undergo the recycling process unchanged. The nuclease resistance of oligonucleotides with a ribose sugar modification was also evaluated, which showed worse recycling efficiency than PS-modified oligonucleotides. We successfully recycled both PCR primers and nucleotide monomers (∼75% yield). We demonstrate that the method allows for the direct reuse of PCR kits. We also show that the recycled primers can be isolated and then added to endpoint or quantitative PCR. This recycling approach provides a new path for circularly reusing nucleic acid materials in PCR kits.