Graphene quantum dots wrapped square-plate-like MnO₂ nanocomposite as a fluorescent turn-on sensor for glutathione

Benefiting from their excellent optical absorption and electron transfer properties, manganese dioxide nanomaterials have been widely applied for fluorescence-based nanosensors. In this work, graphene quantum dots (GQDs) wrapped square-plate-like MnO₂ nanocomposite was synthesized from potassium permanganate via an in situ redox procedure under ultrasonication with poly(allylamine hydrochloride) (PAH) being involved. Through an effective fluorescence resonance energy transfer (FRET) process and inner filter effect (IFE) between GQDs and MnO₂, the fluorescence of GQDs was quenched. Furthermore, the introduction of glutathione (GSH) decomposed MnO₂ and caused fluorescence recovery of GQDs. Therefore, a MnO₂ mediated nanosensor was established for fluorescent turn-on sensing of GSH. A satisfactory linear range was found to be 0.07-70 μM and the detection limit was as low as 48 nM. Besides, the fluorescent recognition of cancer cells using GQDs-MnO₂ nanocomposite was achieved because of the obviously higher GSH content in cancer microenvironment than normal cells. This nanosensor was constructed directly in GQDs solution in the presence of PAH without the complicated modifications or connections, making it a facile and novel nanosensor for GSH.