Silver sulfide (Ag2S) has gained widespread attention in second near-infrared (950-1700 nm, NIR-II) window imaging because of its high fluorescence quantum yield and low toxicity. However, its "always on" fluorescence shows inapplicability for targeted molecule-activated biomedical applications. Herein, we first developed a novel silver/silver sulfide Janus nanoparticle (Ag/Ag2S JNP) for specific activatable fluorescence imaging in the NIR-II window. Inner-particle electron compensation from Ag to Ag2S upon laser irradiation endowed JNPs an "off" state of fluorescence, whereas the oxidization of Ag incubated with H2O2, decreasing the electron-transfer effect and illuminating the NIR-II fluorescence of the Ag2S part. In contrast, the absorption of Ag/Ag2S JNPs slightly decreased in an H2O2-dependent manner, showing an activated photoacoustic imaging mechanism. The Ag/Ag2S JNPs were used for noninvasive location and diagnosis of diseases in vivo, such as for liver injury and cancer, with high sensitivity and accuracy.
Keywords: Janus nanoparticles; NIR-II; disease diagnosis; fluorescence imaging; photoacoustic imaging.