Magnetic-Gold Plasmonic Blackbodies for Photothermal Immunochromatographic Detection and Inactivation of <i>Salmonella typhimurium</i>

Foodborne pathogens present significant public health risks, demanding sensitive on-site detection and effective antibacterial strategies. To address this, we synthesized magnetic-gold plasmonic blackbody (MNP@GPB) nanocomposites by coating a gold/polydopamine hybrid layer onto magnetic nanoparticles (MNPs) via in situ redox polymerization. The resulting MNP@GPBs exhibited excellent colloidal stability, broadband absorption, rapid magnetic responsiveness, and efficient photothermal conversion. Leveraging these properties, we engineered multifunctional probes for magnetic enrichment, colorimetric and photothermal signal generation, and antibacterial action in immunochromatographic assays (ICAs) for sensitive detection and simultaneous inactivation of <i>Salmonella typhimurium</i>. The limits of detection for MNP@GPB-ICA in the colorimetric and photothermal formats were 1.4 × 10³ and 3.4 × 10² CFU/mL, respectively, representing approximately 8-fold and 32-fold improvements in sensitivity over gold nanoparticle-based-ICA. Notably, near-complete inactivation of residual <i>S. typhimurium</i> on the test line was achieved after near-infrared irradiation, substantially reducing the risk of secondary contamination from discarded strips. MNP@GPBs thus represent a transformative platform unifying diagnostic signaling with antibacterial functionality for food safety monitoring.