A novel fluorescence "turn off-on" sensor based on N-doped graphene quantum dots in amino acid ionic liquid medium and its application.

The spectrum behavior of N-doped graphene quantum dots (N-GQD) in 1-hexyl-3-methylimidazolium tryptophan ionic liquid (TryIL) was studied. It was showed that TryIL could self-aggregate into water/oil micellar in aqueous solution and N-GQD was assembled on hydrophilic part of TryIL micelle to construct a novel fluorescence "turn on-off" probe (N-GQD-TryIL). the fluorescence intensity was quenched through the formation of N-GQD-TryIL-Cu(II) complex due to the strong binding ability between Cu2+ and N-GQD-TryIL. In the following fluorescence "turn-on" step, the chiral ligand exchange between levodopa (LD) and Cu(II)-N-GQD-TryIL to partly recovery the fluorescence intensity. Corresponding influencing factors and mechanisms in fluorescence "turn-off" and "turn-on" process were discussed. Thus, a sensitive and selective fluorescence "turn off" and "turn on" platform for assay Cu(II) and LD was designed. Under the optimal conditions, Cu(II) and LD exhibited good linear relationship in the range of 0.051-16.00 μg/mL and 0.55-5.00 μg/mL. The LOD of them was 0.017 μg/mL and 0.16 μg/mL respectively. This method was successfully applied to the determination of Cu(II) and LD in real samples. Moreover, N-GQD-TryIL performed application prospects in bio-imaging due to protein affinity of the hydrophilic part.