Coordinatively Self-Assembled Luminescent Gold Nanoparticles: Fluorescence Turn-On System for High-Efficiency Passive Tumor Imaging

A fluorescence turn-on system for highly efficient and prolonged tumor imaging has been established by a Co2+-induced coordination self-assembly strategy, in which luminescent glutathione (GSH)-modified gold nanoparticles (LGAuNPs) are assembled into LGAuNPs assemblies (LGAuNPs-Co) through a coordination bond between an unoccupied orbit of Co2+ and lone pair electrons of GSH on the surface of LGAuNPs. The LGAuNPs-Co is sensitive to microenvironment pH, and its quenched luminescence will be turned on in tumor tissues (acidic microenvironment), which behaves as a fluorescence turn-on system for passive tumor imaging. The fluorescence turn-on system combines advantages of the enhanced permeability and retention (EPR) effect of NPs and pH-induced fluorescence turn-on property at the tumor site, which results in a larger fluorescence intensity (FI) difference between normal and tumor tissues as compared with that of luminescent Au NPs (LAuNPs, only with the EPR effect) (similar to 12-fold). Such a large FI difference results in that LGAuNPs-Co has rapid (similar to 1.6 h), persistent (similar to 24 h p.i.), and highly efficient tumor targeting capability in comparison with LGAuNPs. Moreover, the LGAuNPs-Co also has much longer tumor retention, faster renal clearance, and lower reticuloendothelial system (RES) uptake than LGAuNPs. Therefore, the fluorescence turn-on system is very promising for cancer diagnosis and therapy.