Nucleic acid lateral flow assay with recombinase polymerase amplification: Solutions for highly sensitive detection of RNA virus.

We propose nucleic acid lateral flow assay (LFA) coupled with reverse transcription recombinase polymerase amplification (RT-RPA) resulting from step-by-step multiparametric adjustments to both RT-RPA reactions and LFA interactions. The assay was realized for RNA virus detection using the example of potato virus X (PVX), a dangerous phytopathogen. The assay stages were adjusted for sensitive detection. (1) DNA target was designed and verified. A fragment (146 bp) of coat protein gene (gp5) and biotin-/fluorescein-labeled forward/reverse primers were chosen to produce target amplicons. (2) In a test strip, the construction advantage of the realization of the highest affinity interaction (biotin-streptavidin in our research) through gold nanoparticle conjugate (streptavidin immobilized on the GNP surface) was demonstrated. (3) RPA with reverse transcription was adjusted including primer concentration, order of components' mixing, and reaction temperature. Due to the adjustments, the assay was able to detect 0.14 ng PVX per g potato leaves at 30 min. The PVX assay was 260 times more sensitive than conventional lateral flow assay based on antibodies and demonstrated the same sensitivity as PCR detection. The proposed adjustments are applicable for ultrasensitive and rapid detection of various RNA viruses.