The assay time is considerably reduced from about an hour to few minutes by the newly reported RTF-EXPAR method which uses reverse transcriptase-free (RTF) approach for conversion of RNA into DNA followed by EXPAR (Exponential Amplification Reaction) for amplification at single temperature.
Controlling the rate of COVID-19 spread requires an accurate and a faster virus testing strategy. RT-PCR (reverse transcriptase polymerase chain reaction), the most accurate testing method being currently employed is a two-step test that takes around 60 minutes per sample.
The researchers from the University of Birmingham have reported a novel method for detection of SARS-CoV-2. This could enable much faster testing and is sufficiently sensitive.
The viral RNA detection by RT-PCR (reverse transcriptase polymerase chain reaction) involves conversion of viral RNA to complementary DNA (cDNA) followed by amplification of cDNA by a quantitative PCR (qPCR). The cDNA is then detected using a fluorescent dye. This takes up to an hour.
The assay time is considerably reduced from about an hour to few minutes by the newly reported RTF-EXPAR method which uses reverse transcriptase-free (RTF) approach for conversion of RNA into DNA followed by EXPAR (Exponential Amplification Reaction) for amplification at single temperature. The amplification taking place at a single temperature is the key to speed, because it avoids lengthy heating and cooling steps of RT-PCR. Further, the section of DNA being amplified is smaller compared RT-PCR. Hence, EXPAR generates up to 108 strands of DNA product in few minutes. The duplex formation is monitored, as in RT-PCR method using fluorescent dye, SYBR Green.
Interestingly, the new method can be modified to detect several other infectious diseases caused by RNA viruses, for example Ebola, RSV, etc.
Source(s):
Carter et al (2020). Sub-5-minute Detection of SARS-CoV-2 RNA using a Reverse Transcriptase-Free Exponential Amplification Reaction, RTF-EXPAR. Preprint. Published at medRxiv Posted January 04, 2021. DOI: https://doi.org/10.1101/2020.12.31.20248236
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