Functionalized graphene oxide materials for the fluorometric sensing of various analytes: a mini review

Among diverse nanomaterials, graphene oxide (GO) and reduced graphene oxide (rGO)-based nanomaterials have encountered generous attention because of their ubiquitous advantages such as photo-stability, nontoxicity, water-solubility, bio-compatibility, eco-friendliness, and cost-effectiveness. Unfortunately, the inadequacy of functional groups in graphene-based nanomaterials seriously obstructs the complexing ability with regard to analytes in the field of fluorescent chemosensors. Therefore, graphene oxide and reduced graphene oxide-based materials were functionalized/modified using organic fluorophores, organic acids, polymers, organic dyes, inorganic nanoparticles, macrocyclic compounds, rotaxanes, DNA, metal oxides, chemodosimeter molecules, etc. They find extensive applications in the field of fluorescence sensing as chemosensors, wherein they either perform as fluorophores or quenchers. The functionalization is typically supported by covalent and noncovalent interactions including electrostatic forces, π–π interaction, and hydrogen bonding to furnish effective photophysical properties for fluorescent chemosensor applications. In this mini review, we critically discuss the sensitive and selective recognition of biologically and environmentally important metal ions, anions, neutral molecules, and small biological scaffolds via divergent signalling phenomena such as photoinduced electron transfer (PET), fluorescence resonance energy transfer (FRET), intramolecular charge transfer (ICT), energy transfer (ET), excited state intramolecular proton transfer (ESIPT), aggregation induced emission (AIE), and displacement approach. Most of the discussed functionalized graphene oxide materials show high sensitivity toward various analytes compared to other potential fluorescent chemosensors.