Self‐Assembled Ag₂S‐QD Vesicles for In Situ Responsive NIR‐II Fluorescence Imaging‐Guided Photothermal Cancer Therapy

Abstract Bioimaging guided photothermal therapy possesses great promise for lesion diagnosis and effective treatment. However, distinguishing lesion from normal tissues for precise cancer therapy remains a great challenge. Herein, a stimulation‐responsive assembled Ag₂S vesicle (Ag₂S Ve) is proposed by self‐assembly of Ag₂S quantum dots (QDs) coated with pH‐sensitive copolymer thiolated polystyrene‐co‐poly(4‐vinylpyridine). The Ag₂S Ve shows significant absorption enhancement in the near‐infrared (NIR) region and strong fluorescence inhibition in the second near infrared (NIR‐II) region. Triggered by the acidic environment, the release of Ag₂S QDs promptly mediates the quenched NIR‐II fluorescence from “off” to “on.” In vivo studies reveal that the theranostic Ag₂S Ve can be specifically activated in acidic tumor tissues, whereas it exhibits nonfunctional in normal tissues. Larger sizes endow vesicles a higher tumor accumulation efficiency and controllable disassembly shows illuminating characteristics toward lesion tissues, which provides an innovative therapeutic strategy for activated NIR‐II fluorescence imaging guided cancer therapy.