Fluorescence　biosensors　that　enable　highly　sensitive　detection　of　glutathione　(GSH)　are　in　great　demand　for　various　biological　investigations　and　early　disease　diagnoses.　Here,　we　report　a　turn-on　fluorescence　nanoplatform　based　on　fluorescent　semiconducting　polymer　nanoparticle@MnO2　nanosheets　(P-dot@MnO2)　nanocomposites　for　rapid　homogeneous　determination　of　GSH.　The　near-infrared　(NIR)　fluorescent　P-dots　were　prepared　by　doping　NIR　dyes　into　polymer　matrix　and　then　encompassed　by　MnO2,　which　resulted　in　a　remarkable　fluorescence　quenching.　Owing　to　the　selective　decomposition　of　MnO2　by　GSH,　the　fluorescence　recovery　was　achieved　in　the　presence　of　GSH.　On　the　basis　of　the　target-induced　turn-on　fluorescence　response,　the　developed　nanoplatform　can　readily　detect　GSH　with　a　high　sensitivity　up　to　0.26 μM,　as　well　as　a　superior　specificity.　Furthermore,　it　was　successfully　applied　in　monitoring　the　intracellular　GSH　in　living　cells,　revealing　its　great　potential　in　biomedical　applications.　[Figure　not　available:　see　fulltext.]　©　2020,　Springer-Verlag　GmbH　Germany,　part　of　Springer　Nature.