Ag_2–3xBi_xS Quantum Dots as Single-Component Theranostic Agents for Second Near-Infrared Fluorescence Imaging-Guided Photothermal Therapy

Silver sulfide (Ag2S) nanomaterials are being researched increasingly because of their multifunctional potential in the second near-infrared (NIR-II) region (1000–1500 nm). Here, we report Ag2–3xBixS quantum dots (Ag2–3xBixS QDs) as single-component theranostic nanomaterials for NIR-II fluorescence imaging and synchronous photothermal therapy. Bismuth doping in Ag2S QDs leads to a fluorescence red shift to the NIR-II region and simultaneously enhances the photothermal conversion efficiency to 58.9%, which can be ascribed to the altered band gap introduced by bismuth doping. This Ag2S-based NIR-II theranostic agent can be synthesized in a controlled manner by an albumin biomineralization method under mild conditions. The encapsulation of the biomacromolecular albumin endowed Ag2–3xBixS QDs with greatly strengthened biocompatibility and stability. The survival rate of cancer cells was only 13% after irradiation with an 808 nm laser at a density of 1.2 W cm–2 for 10 min. Meanwhile, in vivo experiments have confirmed the desirable NIR-II fluorescence imaging capability of Ag2–3xBixS QDs. Thus, this study provides a highly efficient single-component theranostic agent with great promise for application in the field of precision theranostics.