Fluorescence turn-off sensing of TNT by polyethylenimine capped carbon quantum dots

•Polyethylenimine capped carbon quantum dots (PEI-C-dots) sensor developed for TNT.•Fluorescence quenching via donor–acceptor interaction enabled TNT sensing.•The quantum yield of the PEI-C-dots was 54% and LOD for TNT as low as 93 μg/L.•Similar nitramine explosives, common ions, and camouflage materials did not interfere.•Interferent picric acid was removed on a basic anion exchanger before determination.