Although　newly-developed　black　phosphorus　quantum　dots　(BPQDs)　with　unique　photocatalytic　properties　have　attracted　much　attention　for　biomedical　applications,　especially　phototherapy,　the　environmental　instability　and　weak　photocatalytic　activity　of　BPQDs　remains　a　considerable　challenge　preventing　their　clinical　application.　Herein,　we　have　designed　new　Janus　nanoparticles　(J-MOPs)　based　on　BPQDs　and　tetrahydroxyanthraquinone　(THQ)-Cu　metal-organic　particles　(MOPs)　to　simultaneously　improve　the　environmental　stability　and　photocatalytic　activity　for　the　PDT　treatment　of　cancers.　The　J-MOPs　were　simply　assembled　from　BPQDs　and　THQ　via　Cu-mediated　P-Cu-THQ　＂host-metal-guest＂　coordination　effects.　The　encapsulation　of　BPQDs　inside　J-MOPs　and　P-Cu　bonds　effectively　isolated　BPQDs　from　water-air　and　occupied　the　P　lone-pair　electrons,　respectively,　to　improve　the　stability　of　BPQDs.　Furthermore,　the　dramatic　electron-hole　separation　and　migration　abilities　of　J-MOPs　increased　the　reactivity　toward　O　2　,　which　enhanced　singlet　oxygen　(　1　O　2　)　generation　against　cancers　compared　with　BPQDs　alone　when　exposed　to　670　nm　laser　irradiation.　Intriguingly,　tumor　acid-triggered　J-MOPs　degradation　resulted　in　the　release　of　Cu　2+　ions　that　further　served　as　a　Fenton-like　agent　to　generate　OH　from　H　2　O　2　,　which　enhanced　the　antitumor　effects　of　the　J-MOPs.　Therefore,　we　have　highlighted　the　potential　of　J-MOPs　as　a　photocatalyst　for　photodynamic　cancer　therapy.　©　2019　the　Partner　Organisations.