Au-Ag Core-shell Nanoparticles for Simultaneous Bacterial Imaging and Synergistic Antibacterial Activity

Abstract Au@Ag nanoparticles (NPs) were recently found to display giant two-photon photoluminescence (2PPL) enhancement with an enhancement factor up to 815 fold upon aggregate formation. Based on this finding, two-photon imaging of bacteria by Au@Ag NPs under near-infrared (NIR) femtosecond laser pulses was demonstrated in this study as positively charged Au@Ag NPs can form aggregates on the negatively charged bacterial surface, yielding strong 2PPL emission. The aggregation-enhanced 2PPL of Au@Ag NPs stemmed from higher two-photon excitation efficiency, implying strong two-photon photothermal effects. Au@Ag NPs showed strong antibacterial activity (minimum inhibition concentration as low as 7.5 pM against S. aureus ) and negligible toxicity to human dermal fibroblasts. Their bactericidal activity was further enhanced under NIR irradiation due to strong two-photon photothermal effects. Au@Ag NPs effectively removed 85% of the notorious bacterial biofilm within 4 minutes under NIR irradiation. These Au@Ag NPs can potentially be used as imaging and antibacterial agents.