One-step and green strategy for exfoliation and stabilization of graphene by phosphate pillar[6]arene and its application for fluorescence sensing of paraquat

Abstract

A one-step, safe, and green approach is reported for the synthesis of 2D graphene nanosheet in water phase exfoliated by the water-soluble phosphate pillar[6]arene (PP6). Compared with the conventional method that the graphite is firstly oxidized, exfoliated to graphene oxide and then reduced to graphene sheets, the present proposed method is directly exfoliated from graphite by one-step process without using any strong oxidizing agents, such as H2SO4 or KMnO4. More importantly, the graphene obtained by this environmentally friendly method possesses excellent crystalline structure. Besides, the prepared graphene could be stabilized through π-π stacking interaction between graphene and the hydrophobic segments of benzene rings in PP6, and PP6 functionalized graphene (PP6@graphene) simultaneously combines the fluorescence quenching property of graphene and molecular recognition capability of PP6. Therefore, we construct a competitive fluorescence assay based on the molecular recognition interaction between PP6@graphene and acridine orange (AO) for determination of paraquat (PQ), a nonselective herbicide with high toxicity to humans. The fluorescence of AO is completely quenched by fluorescence resonance energy transfer (FRET) interaction between AO and PP6@graphene, and the quenched fluorescence recovers upon the successive addition of PQ, because the inclusion capability of PP6 towards PQ is stronger than that of AO. Linear response ranges of 0.2–2 μM and 2–18 μM are obtained for determination of PQ and the detection limit is 0.06 μM (S/N = 3). The constructed sensing platform is also used to detect PQ in three water samples with satisfying results, which indicates that the competitive host-guest supermolecular recognition method has potential application in practical environmental risk assessment of PQ.