SARS-CoV-2 Identification Using Colorimetric Loop-Mediated Isothermal Amplification

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has caused worldwide losses from all points of view. Although there are efficient vaccines against this virus, rapid detection remains essential for controlling its spread. The gold standard for the COVID-19 diagnostic is the use of quantitative real time polymerase chain reaction (RT-qPCR) from naso-/oro-pharyngeal swabs and, alternatively, saliva specimens. A faster alternative to the RT-qPCR method, the colorimetric reverse transcription loop-mediated isothermal amplification (cLAMP) has a good sensitivity and specificity and has been proposed as an efficient screening method. In this study, we analyzed several sets of LAMP primers for COVID-19 testing using purified RNA samples and raw saliva samples, and tested several reaction conditions. Our results showed that the sensitivity of cLAMP reactions on raw saliva samples can be significantly augmented by the addition of guanidine hydrochloride to levels, which allow its use for COVID-19 screening.