Dual-mode and multiplex lateral flow immunoassay: A powerful technique for simultaneous screening of respiratory...

Respiratory viral infectious usually exhibit similar clinical symptoms, making a great challenge for their accurate diagnostic in early stages. Herein, we developed a dual-mode and multiplex lateral flow immunoassay (LFIA), in which near-infrared (NIR)-responsive Janus Au_shell-Fe₃O₄ nanoparticles (NPs) were synthesized as new reporters for highly sensitive colorimetric/photothermal detection of H3N2 influenza and SARS-CoV-2 viruses in a single assay. The Janus Au_shell-Fe₃O₄ well combined the NIR responsiveness and high molar absorption coefficient of Au_shell and magnetic properties of Fe₃O₄. In the detection, two test (T) lines were arranged on the strip, which could capture corresponding virus antigen-Au_shell-Fe₃O₄ complexes, forming color bands. Hence, according to the position of color bands and their photothermal signals, the type and amount of virus could be quickly determined. The naked-eye limits of detection (LODs) for H3N2 and SARS-CoV-2 were both 50 ng/mL. The photothermal quantitative ranges were from 10 to 10⁶ pg/mL with LODs of 2 pg/mL (H3N2) and 7 pg/mL (SARS-CoV-2), which were nearly 10000 times lower than naked-eye detection. Moreover, this multiplex LFIA showed good specificity and anti-interference ability, which was applied to complex samples with satisfactory results. Thus, this Au_shell-Fe₃O₄ LFIA showed great application potential in rapid virus screening and early detection.