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.　©