The cell-free genomic DNA (gDNA) concentration in serum ranges from 1500 to\n7500 copies/mL within 2 h after phlebotomy (6â??24 times the concentration observed in plasma).\nHere, we aimed to evaluate the gDNA size distribution in serum with time after coagulation and\nto test if crude serum can be directly used as a source of gDNA for qPCR. Next, we investigated if\nsingle nucleotide polymorphisms (SNPs) could be genotyped directly from the crude serum isolated\nfrom capillary blood using a hand-powered paper centrifuge. All tested PCR targets (65, 100, 202 and\n688 base pairs) could be successfully amplified from DNA extracted from serum, irrespective of\ntheir amplicon size. The observed qPCR quantitation cycles suggested that the genomic DNA yield\nincreased in serum with incubation at room temperature. Additionally, only 65 and 101 base pair\nqPCR targets could be amplified from crude serum soon after the coagulation. Incubation for 4 days at\nroom temperature was necessary for the amplification of PCR targets of 202 base pairs. The 688 base\npair qPCR target could not be amplified from serum directly. Lastly, serum was successfully separated\nfrom capillary blood using the proposed paper centrifuge and the genotypes were assigned by testing\nthe crude serum using allele-specific qPCR, producing small amplicon sizes in complete agreement\nwith the genotypes assigned by testing the DNA extracted from whole blood. The serum can be used\ndirectly as the template in qPCR for SNP genotyping, especially if small amplicon sizes are applied.\nThis shortcut in the SNP genotyping process could further molecular point-of-care diagnostics due to\nelimination of the DNA extraction step.
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