What is Digital PCR?
What is PCR?PCR (polymerase chain reaction) tests are a fast, highly accurate way to diagnose certain infectious diseases and genetic changes. The tests work by finding the DNA or RNA of a pathogen (disease-causing organism) or abnormal cells in a sample.
Principle of the PCR
PCR makes it possible to obtain, by in vitro replication, multiple copies of a DNA fragment from an extract. Matrix DNA can be genomic DNA as well as complementary DNA obtained by RT-PCR from a messenger RNA extract (poly-A RNA), or even mitochondrial DNA. It is a technique for obtaining large amounts of a specific DNA sequence from a DNA sample. This amplification is based on the replication of a double-stranded DNA template. It is broken down into three phases: a denaturation phase, a hybridization phase with primers, and an elongation phase. The products of each synthesis step serve as a template for the following steps, thus exponential amplification is achieved
Digital PCR
In contrast to qPCR, the digital PCR (dPCR) uses an alternative method that is not dependent upon the determination of the amplification cycle that the reporter dye signal exceeds a threshold. Instead, prior to amplification, the samples to be subjected to dPCR are divided into thousands of independent PCR reactions and are scored as either positive or negative for amplification of the viral sequence of interest. The positive wells are counted and converted to a target concentration in the original sample. This binary assignment of each reaction greatly minimizes the dependence of measurement on parameters such as the efficiency of the assay and the calibration of the instrument. Therefore, dPCR is the absolute quantification methodology with the greatest potential for quantification of low-load viral nucleic acids.
In the diagnostic routine, it is very common to obtain positive qPCR results obtained at the detection limit of this methodology, which may generate uncertainty of the result. dPCR is a complementary methodology that works beyond the limit of detection of qPCR, since it is based on the Poisson distribution. Consequently, this methodology has a significant impact on research as well as on diagnostic applications.
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