Extraction-free colorimetric RT-LAMP for SARS-CoV-2 RNA detection from saliva

AimTo develop a rapid and easy diagnostic assay for detection of SARS-CoV-2 RNA presented in saliva samples. MethodThe color-based RT-LAMP was used to detect nucleocapsid (N) gene of SARS-CoV-2 without RNA extraction from saliva. ResultsRNA spiked saliva can be used directly for cDNA synthesis after heat inactivation of the saliva and diluted 2-fold with either water or PBS. For both PCR and LAMP, 20% of saliva did not have obvious effect on the reaction. Saliva did not interfere with RT-LAMP when the volume of saliva was less than 20% of the total volume. The sensitivity of the RT-LAMP reached to 1.034x10-5 ng/{micro}l (475 copies/l). The RT-LAMP assay was validated by testing 20 RNA spiked saliva samples. The assay specificity was similar to that of data without saliva. ConclusionsThe RT-LAMP colorimetric assay can be used as a screening method with the advantages of being rapid, easy to use than the qRT-PCR.