Dual‐Functional Plasmonic‐Fluorescent Nanocomposites for Synergistic Antimicrobial Activity and High‐Resolution Bioimaging

We report a dual‐functional plasmonic–fluorescent nanocomposite (PFN) engineered through Zn 2+ ‐directed assembly of 8‐hydroxyquinoline‐5‐sulfonic acid (HQS)‐stabilized silver nanoparticles (Ag NPs) with a luminescent zinc quinolate complex (ZQC), integrating antimicrobial activity with high‐resolution bioimaging within a single platform. Zn 2+ coordination between quinolate N/O donor sites and surface sulfonate groups drives the formation of a structurally robust hybrid nanostructure with synergistic plasmon–fluorophore interactions. The resulting PFNs exhibit intense green emission (530 nm), high photoluminescence quantum yield (30%), an extended fluorescence lifetime (6.4 ns), exceptional photostability, and long‐term optical stability exceeding 30 days. PFNs show broad‐spectrum bactericidal activity against Staphylococcus aureus (MIC 50 = 0.029 ± 0.002 µg mL −1 ) and Pseudomonas aeruginosa (MIC 50 = 0.020 ± 0.001 µg mL −1 ), with values lower than those of individual Ag NPs or ZQC, confirming synergistic enhancement. Mechanistic studies reveal a multifactorial antibacterial pathway involving electrostatic membrane adhesion, Zn 2+ ‐assisted surface perturbation, and ROS‐mediated oxidative stress, which is supported by live/dead staining and FESEM analysis. PFNs exhibit high cytocompatibility (∼85%–90% cell viability in HEK and HeLa cells) and selective tumor cell uptake, enabling bright confocal imaging superior to that of ZQC alone. Collectively, PFNs provide a scalable theranostic nanoplatform integrating fluorescence imaging, plasmon‐modulated emission, and antimicrobial functionality for advanced biomedical applications.