Researchers from the University of Birmingham, U.K., have developed a highly sensitive testing method for COVID-19 that can be deployed at entertainment venues, airport arrival terminals, and in remote settings where clinical testing laboratories are not available, according to a news release from the university.
The scientists used a three-way comparison study to confirm that the exponential amplification reaction (EXPAR) method is just as sensitive, but faster, than both PCR and LAMP. The Birmingham COVID-19 test, called RTF-EXPAR, gives a sample-to-signal time of under 10 minutes, even for low viral levels where current lateral flow tests are less effective.
Both PCR and LAMP tests detect viral RNA, which can be present in extremely low levels in swabs taken from the mouth and nose. These tests use a two-step process that involves first converting to RNA to DNA (a process called reverse transcription) and then ‘amplifying’ the material many times over so it can be detected in the sample.
At University of Birmingham, the assay team designed a new RNA-to-DNA conversion step that avoids reverse transcription, making it reverse transcription-free (RTF). In addition, their amplification step to generate the read-out signal uses EXPAR, an alternative DNA amplification process to PCR and LAMP.
The study revealed that the RTF-EXPAR method converts under 10 strands of RNA into billions of copies of DNA in under 10 minutes, using a one-pot assay that is compatible with more basic, benchtop equipment than that used with current testing methods.
RTF-EXPAR also demonstrated improvements over both PCR and LAMP-based assays on time to signal detection. At low concentrations of RNA (7.25 copies/µL), the time to signal detection was 42.67 minutes for PCR, 11.25 minutes for LAMP, and 8.75 minutes for EXPAR. At high (1450 copies/µL) concentrations of viral RNA, the time to signal detection was 34.00 minutes for PCR, 11.25 minutes for LAMP, and 3.08 minutes for EXPAR.