Spatially Confined/Ligand-Directed Ultrabright NIR-AIE Nanoprobe for In Vitro Rapid Detection and In Situ Imaging of Bacterial Septic Arthritis

Bacterial infection is a major threat to joint surgery and can lead to amputation or death. However, advanced tools for early, rapid, and accurate identification of joint-infecting bacterial species remain limited. Here, we report a universal strategy for fabricating ultrabright near-infrared (NIR) AIEgen fluorescent probes (PPANPs) that enable lateral flow assay (LFA)-based rapid bacterial identification in joint fluid before surgery, as well as in situ imaging diagnosis and photothermal antibacterial intervention in the joint cavity. Structurally, PPANPs display a core–shell–shell architecture, in which aggregated NIR AIEgens form the fluorescent core, NIR lead sulfide (OA-PbS) forms the inner shell, and poly(maleic anhydride-alt-1-octadecene) (PMAO) forms the outer shell. This spatially confined design combines physical confinement, ligand-mediated molecular organization, and cooperative luminescence within the PbS–AIE hybrid nanoassembly, promoting compact and ordered AIE packing and thereby enhancing NIR fluorescence intensity, quantum yield, and photothermal performance compared with conventional embedding methods. s a diagnostic platform, PPANP-labeled LFA achieves 100% sensitivity for Staphylococcus aureus ( S. aureus ) identification within 10 min, outperforming standard plate culture (>96 h). Moreover, PPANPs enable rapid in situ imaging of S. aureus infection in mouse joints within 30 min and exhibit potent photothermal antibacterial activity in vitro under low-power-density laser irradiation.