A nanogap-enhanced SERS nanotag–based lateral flow assay for ultrasensitive and simultaneous monitoring of SARS-CoV-2 S and NP antigens

A lateral flow assay (LFA) strip based on dual 5,5′-dithiobis-(2-nitrobenzoic acid) (DTNB)–encoded satellite Fe₃O₄@Au (Mag@Au) SERS tags with nanogap is reported for ultrasensitive and simultaneous diagnosis of two SARS-CoV-2 functional proteins. Composed of Fe₃O₄ core, satellite gold shell with nanogaps, and double-layer DTNB, the Mag@Au nanoparticles with an average size of 238 nm were designed as multifunctional tags to efficiently enrich the target SARS-CoV-2 protein from complex samples, significantly enhancing the SERS signal of the LFA strip and provide quantitative SERS detection of analyte on test lines. The developed dual DTNB-encoded satellite Mag@Au-based LFA allowed simultaneous quantification of spike (S) protein and nucleocapsid (NP) protein with detection limits of 23 pg mL⁻¹ and 2 pg mL⁻¹, respectively, lower than commercial ELISA kits and reported SERS-LFA detection system–based Au NPs and Fe₃O₄@3 nm Au MNPs. This magnetic SERS-LFA also showed high performance of multi-variant strain detection and further distinguished clinical samples of Omicron variant infection, demonstrating the potential of in situ detection of respiratory virus diseases. Graphical Abstract: [Figure not available: see fulltext.]