Dual-mode lateral flow Immunochromatographic assay with Nanobody-functionalized hollow copper sulfide nanoprobe for Salmonella Typhimurium detection in food.

To overcome the limited sensitivity and matrix tolerance of traditional lateral flow immunoassays (LFIA), we developed a nanobody-based colorimetric-photothermal dual-mode LFIA for detecting Salmonella Typhimurium. Hollow copper sulfide (HCuS) nanoparticles served as dual-signal reporters, leveraging a light-cavity effect to achieve a 49.26% photothermal conversion efficiency. To maximize target capture, biotinylated nanobodies were directionally immobilized onto HCuS via a streptavidin-biotin system, effectively preserving antigen-binding activity. Under optimized conditions, this platform enabled reliable quantitative evaluation with a naked-eye screening limit of 1 × 103 CFU mL-1. The assay achieved quantitative detection limits of 129 CFU mL-1 (colorimetric) and 103 CFU mL-1 (photothermal), alongside a linear range of 103-107 CFU mL-1. Validation in spiked milk and juice samples yielded satisfactory recoveries ranging from 88.44% to 112.37%, with low relative standard deviations (<8.77%). Ultimately, this rationally designed immunoprobe provides a robust, rapid, and matrix-tolerant tool for on-site food safety monitoring.