▎ 摘　　要

Novel nanocomposites of (2,2,6,6-tetramethylpiperidin-1-yl) oxyl (TEMPO) derivatized zinc phthalocyanine (TEMPO-ZnPc) with graphene quantum dots (GQDs) or S/N co-doped graphene quantum dots (SNGQDs) were synthesized. The fluorescence of both GQDs and SNGQDs was quenched ("turned OFF'') upon non-covalent coordination with TEMPO-ZnPc. However, the emission of GQDs (or SNGQDs) was restored ("turned ON'') in the presence of ascorbic acid (AA) due to the selective and specific interaction of TEMPO-ZnPc with AA. Among the tested biomolecules and ions, only AA induced the restoration of the quenched GQDs fluorescence emission resulting in the "Off-On'' mode of the GQDs. The `` turn ON'' fluorescence signal was modulated by different concentrations of AA and the limits of detection were in the nanomolar range of 0.2 nM and 0.8 nM for SNGQDs-TEMPO-ZnPc and GQDs-TEMPO-ZnPc, respectively. The quenching mechanism was elucidated based on Forster resonance energy transfer (FRET) in which the GQDs acted as the energy donor.