The use of lateral flow assays to detect nucleic acid targets has many applications including point-of-care diagnostics, environmental monitoring, and food safety. A sandwich format, similar to that in protein immunoassays, is often used to capture the target nucleic acid sequence with an immobilized complementary strand anchored to a substrate, and then to visualize this event using a complementary label nucleic acid bound to a nanoparticle label. A critical component of high-sensitivity nucleic acid detection is to utilize high-density capture surfaces for the effective capture of target nucleic acid. Multiple methods have been reported, including the use of streptavidin-based protein anchors that can be adsorbed to the lateral flow substrate and that can utilize the high-affinity streptavidin-biotin linkage to bind biotinylated nucleic acid capture sequences for subsequent target nucleic acid binding. However, these protein anchors have not been systematically characterized for use in the context of nucleic acid detection. In this work, we characterize several protein-based anchors on nitrocellulose for (i) capturing the robustness of the attachment of the protein anchor, (ii) capturing nucleic acid density, and (iii) targeting nucleic acid capture. Further, we demonstrate the signal gains in target nucleic acid hybridization made by increasing the density of capture nucleic acid on a nitrocellulose substrate using multiple applications of protein loading onto nitrocellulose. Finally, we use our high-density capture surfaces to demonstrate high-sensitivity nucleic acid detection in a lateral flow assay (in the context of a SARS-CoV-2 sequence), achieving a LOD of approximately 0.2 nM.
Keywords: high-density capture; lateral flow assay; nitrocellulose substrate; nucleic acid detection; protein anchor; streptavidin–biotin linkage.