Inorganic　nanoprobes　have　attracted　increasing　attention　in　the　biomedical　field　due　to　their　versatile　functionalities　and　excellent　optical　properties.　However,　conventional　nanoprobes　have　a　relatively　low　retention　time　in　the　tumor　and　are　mostly　applied　in　the　first　near-infrared　window　(NIR-I,　650-950　nm),　limiting　their　applications　in　accurate　and　deep　tissue　imaging.　Herein,　we　develop　a　Janus　nanoprobe,　which　can　undergo　tumor　microenvironment　(TME)-induced　aggregation,　hence,　promoting　tumor　retention　time　and　providing　photoacoustic　(PA)　imaging　in　the　second　NIR　(NIR-II,　950-1700　nm)　window,　and　enhancing　photodynamic　therapy　(PDT)　effect.　Ternary　Janus　nanoprobe　is　composed　of　gold　nanorod　(AuNR)　coated　with　manganese　dioxide　(MnO2)　and　photosensitizer　pyropheophorbide-a　(Ppa)　on　two　ends　of　AuNR,　respectively,　named　as　MnO2-AuNR-Ppa.　In　the　tumor,　MnO2　could　be　etched　by　glutathione　(GSH)　to　release　Mn2+,　which　is　coordinated　with　multiple　Ppa　molecules　to　induce　in　situ　aggregation　of　AuNRs.　The　aggregation　of　AuNR　effectively　improves　the　NIR-II　photoacoustic　signal　in　vivo.　Moreover,　the　increased　retention　time　of　nanoprobes　and　GSH　reduction　in　the　tumor　greatly　improve　the　PDT　effect.　We　believe　that　this　work　will　inspire　further　research　on　specific　in　situ　aggregation　of　inorganic　nanoparticles.　©　2022　American　Chemical　Society.