A sensitive gold nanoflower-based lateral flow assay coupled with gold staining technique for the detection of SARS-CoV-2 antigen

An enhanced lateral flow assay (LFA) is presented for rapid and highly sensitive detection of acute respiratory syndrome coronavirus-2 (SARS-CoV-2) antigens with gold nanoflowers (Au NFs) as signaling markers and gold enhancement to amplify the signal intensities. First, the effect of the morphology of gold nanomaterials on the sensitivity of LFA detection was investigated. The results showed that Au NFs prepared by the seed growth method showed a 5-fold higher detection sensitivity than gold nanoparticles (Au NPs) of the same particle size, which may benefit from the higher extinction coefficient and larger specific surface area of Au NFs. Under the optimized experimental conditions, the Au NFs-based LFA exhibited a detection limit (LOD) of 25 pg mL⁻¹ for N protein using 135 nm Au NFs as the signaling probes. The signal was further amplified by using a gold enhancement strategy, and the LOD for the detection of N protein achieved was 5 pg mL⁻¹. The established LFA also exhibited good repeatability and stability and showed applicability in the diagnosis of SARS-CoV-2 infection.