Intracellular Monitoring of Luminescent Ag₂S Nanoparticles in Fibroblasts

Interaction between nanoparticles (NPs) and cells is a key concern in nanotechnology‐based biomedical applications. This study investigates cytocompatible silver sulfide (Ag2S) quantum dots (QDs), which emit strongly in the second near‐infrared (NIR II) region, for their potential in image‐guided therapies. Since cellular microenvironments contain acidic pH, hydrogen peroxide (H2O2), and reactive oxygen species (ROS), which can affect luminescence, Ag2S NPs (AS NPs) coated with three ligands: DTDTPA (dithiolated diethylene triamine pentaacetic acid), 11MUA (11 mercaptoundecanoic acid), and PEG (polyethylene glycol) were studied in fibroblast cells over 9 days. Long term photoluminescence (PL) tracking showed distinct behavior. AS DTDTPA and AS 11MUA exhibited increasing uptake but decreasing PL, while AS PEG showed both enhanced PL and uptake over time. No significant changes in NP size or structure explained the PL differences. Exposure to H2O2 revealed that AS DTDTPA and AS 11MUA lost PL due to oxidation or shell detachment, reducing surface passivation. In contrast, AS PEG showed intensified PL, possibly from removal of metallic silver and increased PL lifetime. These results highlight time dependent PL changes in cellular and oxidative environments. DTDTPA and PEG coatings may act as ROS scavenger and promoter, respectively, while enabling NIR II imaging and offering insights into NP design for stable optical tracking and therapeutic use.